air blast atomizer thesis

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Post by Izzy Soleman » Tue Nov 15, pm. I am using share latex template to write my PhD thesis. The template has a default numerical citation style eg: Text sample [1]. The bibliography would then need to be in alphabetic order.

Air blast atomizer thesis better to be feared than loved essay

Air blast atomizer thesis

To this end, a major objective of the present work is to expand upon previous research efforts by addressing these aforementioned limitations. The numerous constituents in typical industrial coatings lead to highly coupled, and even deceptive, rheology.

To understand these Theologically complex liquids, Glass [] and Soules et al [] pioneered the use of substitute test liquids in paint application research. The present work employs a series of rheologically-ideal test liquids belonging to the Boger class [83,]. By maintaining similar values of surface tension, density, and rate-independent shear viscosity in the test liquids, and independently varying the extensional viscosity, the effects of elasticity on air-blast atomization are isolated and examined.

Droplet sizes and velocities are measured using shadowgraphy and Particle Image Velocimetry, respectively. Application of liquid FMs in the railway industry is a unique case of spray coating, one that currently involves a plethora of unknowns. In view of this, another major objective of the present work is to evaluate the ability of Kelsan's air-blast atomizer to apply liquid F M onto the railhead. Only after evaluating the performance of Kelsan's existing air-blast atomizer can a future generation of improved spray nozzles be designed.

Lefebvre A H Air-blast atomization. Progress in Energy and Combustion Science, Atomization of dilute polymer solutions in agricultural spray nozzles. Journal of Non-Newtonian Fluid Mechanics, Mansour A D Thesis, Carnegie Mellon University. Mansour A and Chigier N Air-blast atomization of non-Newtonian liquids.

Dexter RW Measurement of extensional viscosity of polymer solutions and its effects on atomization from a spray nozzle. Atomization and Sprays, AIChE Journal, 42 5 : Polymer additives as mist suppressants in metal cutting fluids. Lubrication Engineering.

The break-up of fluids in an extensional flow field. Lee RW A note on the effect of polymer rigidity and concentration on spray atomization. Journal of non-Newtonian Fluid Mechanics, Glass JE Chapter 15, ISBN Review of stability of liquid jets and the influence of nozzle design.

Chemical Engineering Journal, Rayleigh L On the instability of jets. Proceedings of the London Math Society, Weber C Disintegration of liquid jets translated. Zeitschrift fur Angewandte Mathematik und Mechanik Germany , 11 2 : Haenlein A Disintegration of a jet. Sterling A M D Thesis, University of Washington. Yuen M C Non-linear capillary instability of a liquid jet. Journal of Fluid Mechanics, Lee HC Drop formation in a liquid jet.

Ohnesorge W Formation of drops by nozzles and the breakup of liquid jets translated. Zeitschrift fur Angewandte Mathematik und Mechanik Germany , Castleman R A The mechanism of the atomization of liquids. Journal of Research of the National Bureau of Standards, 6 Reitz RD D Thesis, Princeton University.

Miesse CC Correlation of experimental data on the disintegration of liquid jets. Industrial and Engineering Chemistry, 47 9 : Giffen E and Muraszew A Liu H Chigier N The Physics of Atomization. Gaithersburg, M D , Cheremisinoff NP Encyclopedia of Fluid Mechanics, 3.

De Juhaz K J Dispersion of sprays in solid-injection oil engines. Mehlig H On the physics of fuel sprays in diesel engines translated. Z , 37 16 Thiemann A E The viscosity of the air is more important than its density for fuel sprays translated. Schweitzer PH Mechanism of disintegration of liquid jets. Journal of Applied Physics, 8 8 Sauter J Determining size of drops in fuel mixture of internal combustion engines. Scheubel FN On atomization in carburetors.

Strazhewski L The spray range of liquid fuels in an opposing air flow. USSR, 4 6. Chigier N A The atomization and burning of liquid fuel sprays. Dynamics of droplets in burning and isothermal kerosene sprays. Combustion and Flame, Marshall WR Factors influencing the properties of spray-dried materials.

Chemical Engineering Progress, 49 8 Finlay W Nukiyama S and Tanasawa Y Experiments on the atomization of liquids in air stream. Transactions of the Society of Mechanical Engineers Japan , 5 18 Measurements of drop size on a plain-jet air-blast atomizer. AIAA Journal, 15 7 : The influence of air and liquid properties on air-blast atomization. Air-blast atomization - effect of linear scale on mean drop size.

Journal of Energy, 4 4 : The design and performance of internal mixing multi-jet twin-fluid atomizers. Fuel, Eroglu H and Chigier N Initial drop size and velocity distributions for air-blast coaxial atomizers. Transactions of the ASME, Gretzinger J and Marshall WR Characteristics of pneumatic atomization. AIChE Journal, Drop-size distributions from pneumatic atomizers. Atomization characteristics on the surface of a round liquid jet. Experiments in Fluids, Drop size distribution and air velocity measurements in air-assist swirl atomizer sprays.

Joyce JR The atomization of liquid fuels for combustion. Simmons H The correlation of drop-size distributions in fuel nozzle sprays. Anson D Influence of the quality of atomization on the stability of combustion of liquid fuel sprays. Behavior of sprays under high altitude conditions. Spray nozzles for the simulation of cloud conditions in icing tests of jet engines. Influence of liquid film thickness on airblast atomization. Atlanta, Lefebvre A H and Miller D The development of an airblast atomizer for gas turbine application.

Cranfield College of Aeronautics Report, Aero. Spay characteristics of plain-jet air-blast atomizers. Hardalupas Y and Whitelaw JH Characteristics of sprays produced by coaxial air-blast atomizers. Journal of Propulsion and Power, 10 4 Atomization of liquids in high velocity gas streams. Industrial and Engineering Chemistry, Lane WR Shatter of drops in streams of air. Industrial and Engineering Chemistry, 43 6 Wiggs L D The effects of scale on fine sprays produced by large air-blast atomizers.

Break-up and atomization of a round water jet by a high-speed annular air jet. Initial breakup of a small-diameter liquid jet by a high-speed gas stream. The mechanism of disintegration of liquid sheets. Transactions of the ASME, 75 7 A study of the stability of plane fluid sheets. Journal of Applied Mechanics, Dombrowski N and Johns WR The aerodynamic instability and disintegration of viscous liquid sheets.

Chemical Engineering Science, Mayer E Theory of liquid atomization in high velocity gas streams. ARS Journal, 31 12 Adelberg M Breakup rate and penetration of a liquid jet in a gas stream. AIAA Journal, 5 8 Mean drop size resulting from the injection of a liquid jet into a high-speed gas stream.

AIAA Journal, 6 6 : Liquid jet instability and atomization in a coaxial gas stream. Annual Review of Fluid Mechanics, Farago Z and Chigier N Morphological classification of disintegration of round liquid jets in a coaxial air stream. Dombrowski N and Fraser RP A photographic investigation into the disintegration of liquid sheets.

The atomization of a liquid sheet by an impinging air stream. Parametric experiments on coaxial airblast jet atomization. Brussels, Belgium, June Disintegration of liquid sheets. Physics of Fluids, 2 5 A note on the growth of Kelsan-Helmholtz waves on thin liquid sheets. Journal of Fluid Mechanics, 57 4 Kelsan-Helmholtz wave growth on cylindrical sheets.

Journal of Fluid Mechanics, 68 3 Macosko C W Mun RP D Thesis, University of Melbourne. Boger D V A highly elastic constant-viscosity fluid. Flory PJ Model viscoelastic liquids. Bueche FJ Mechanical degradation of high polymers. Journal of Applied Polymer Science, 4 10 : Extensional effects in flows through contractions with abrupt or rounded corners. Pipkin A C and Tanner R l Steady non-viscometric flows of viscoelastic liquids.

Mannheimer RJ Rheological and mist ignition properties of dilute polymer solutions. Chemical Engineering Communications, Trouton FT On the coefficient of viscous traction and its relation to that of viscosity. Proceedings of the Royal Society of London. Series A, On the extensional viscosity of mobile polymer solutions. Rheologica Acta, Extensional viscosity measurements of dilute solutions of various polymers. The effects of polymer concentration and molecular weight on the breakup of laminar capillary jets.

Tirtaatmadja V and SridharT A filament stretching device for measurement of extensional viscosity. Journal of Rheology, 37 6 Capillary break-up rheometry of low-viscosity elastic fluids. Applied Rheology, 15 l The influence of viscoelastic fluid properties on spray formation from flat-fan and pressure-swirl atomizers.

Sheet atomization of non-Newtonian liquids. A tomization and Sprays, Opposing-jet viscometry of fluids with viscosity approaching that of water. Can extensional viscosity be measured with opposed-nozzle devices? Comparison of entry flow techniques for measuring elongation flow properties. Atomization and elongational viscosity of associating triblock copolymer solutions. Keller A and Odell JA The extensibility of macromolecules in solution. Colloid Polymer Science, Molecular theories of elongational viscosity.

Proceedings of the 5th International Congress on Rheology, Batchelor G K The stress generated in a non-dilute suspension of elongated particles by pure straining motion. Slender-body theory for particles of arbitrary cross-section in stokes flow. Mewis J and Metzner A B The rheological properties of suspensions of fibers in Newtonian fluids subjected to extensional deformation. Binding D M A n approximate analysis for contraction and converging flows. Breakup of a laminar capillary jet of a viscoelastic fluid.

Journal of Fluid Mechanics, 38 4 Middleman S Stability of a viscoelastic jet. Chemical Engineering Science, 20 12 Non-linear analysis of the surface tension driven breakup of viscoelastic filaments. Journal of non-Newtonian Fluid Mechanics, 21 l Instability of jets of non-Newtonian fluids. Transactions of the Society of Rheology, 17 2 Stability of vertical jets of non-Newtonian fluids. AIChE Journal, 17 4 Christani Y and Walker L M Surface tension driven jet break up of strain-hardening polymer solutions.

Antimisting action of polymeric additives in jet fuels. AIChE Journal, 30 1 The effect of antimisting additives on flammability of jet fuels. How atomization affects transfer efficiency. Industrial Finishing, Simulation of paint transfer in an air spray process. High-pressure sheet atomization of non-Newtonian fluids.

Indianapolis, IN, May , Particle dispersion by vortex structures in plane mixing layers. Journal of Fluids Engineering, A comparison of conventional and high volume-low pressure spray-painting guns. American Industrial Hygiene Association Journal, 57 3 Johnson B W HVLP-Shoot for profit. Proceedings of the National Autobody Congress and Exposition.

MargK H V L P spray puts you into compliance. Metal Finishing, 87 3 Experimental evaluation of a mathematical model for predicting transfer efficiency of a high volume-low pressure air spray gun. Applied Occupational and Environmental Hygiene, 15 10 TriplettT The H V L P way to spray. Methods for estimating the transfer efficiency of a compressed air spray gun.

Applied Occupational and Environmental Hygiene, 17 l Specific charge measurements in electrostatic air sprays. Particulate Science and Technology, 23 l Numerical model of paint transfer and deposition in electrostatic air sprays. Atomization and Sprays, 16 2 : Drop size measurements in electrostatic paint sprays. Washington, D. Methods for determining exposure to lacquer aerosols and solvent vapours during spray painting translated.

Gefahrstoffe Reinhaltung der Luft, 57 2 Neurobehavioral changes among shipyard painters exposed to solvents. Archives of Environmental Health, Organic solvent-induced encephalopathy in industrial painters. Journal of Occupational Medicine and Toxicology, International Archives of Occupational Environmental Health, Anon The risks of inhaling car spray-painting fumes.

South African Medical Journal, 87 3 Wear, The role of high positive friction HPF modifier in the control of short pitch corrugations and related phenomena. Wear, : The basic study on friction control between wheel and rail Experiments by test machine and scale model vehicle. Gothenburg, Sweden, , Vol. II, pp Eadie DT and Santoro M Top of rail friction control for curve noise mitigation and corrugation rate reduction. Journal of Sound and Vibration, Kalousek J and Johnson K L An investigation of short pitch wheel and rail corrugations on Vancouver mass transit system.

Top of rail friction control: lateral force and rail wear reduction in a freight application. International Heavy Haul Association Conference. Dallas, Texas, May Top of rail friction control with locomotive delivery on BC Rail: Reductions in fuel and greenhouse gas emissions. Nashville, Tennessee, September Journal of Coatings Technology. Dynamic uniaxial extensional viscosity DUEV effects in roll application: Rib and web growth in commercial coatings.

Journal of Rheology, 32 2 Model elastic liquids with water-soluble polymers. AIChE Journal, 44 6 However, the majority of research in this area has focused on Newtonian liquids despite the recognized industrial importance of spraying non-Newtonian liquids, particularly those that exhibit viscoelastic properties. In the railway industry, for example, an increasing number of railway operators are adopting the use of liquid friction modifiers FM for controlling frictional instabilities at the wheel-to-rail interface.

Air-blast atomizers are often used to apply these liquid FMs onto the rail head to derive benefits such as improved fuel economy and reduced wheel and rail wear, without adversely affecting train braking or traction []. However, like many paints and industrial coatings, liquid FMs also contain polymers and solids, thus making them viscoelastic [18].

As such, they are expected to atomize differently than Newtonian liquids owing to their ability to develop significant extensional viscosities when exposed to the extension-dominated flow fields generated by spray nozzles [19,20]. Rheologists have observed that the extensional viscosity exhibited by polymer solutions is usually an increasing function of the extensional rate and strain [], behavior known respectively as extension-thickening and strain-hardening [24].

The maximum Trouton ratio ratio of extensional to shear viscosity for these solutions can be more than one order of magnitude greater than the Newtonian inelastic value of 3 [25]. Hence, liquid elasticity, through the extensional viscosity, will play an important role in controlling breakup.

In viscoelastic atomization research, aqueous polymer solutions are commonly used as test liquids because they are easy to formulate [26] and can exhibit extensional viscosities proportional to the polymer molecular weight and concentration [21,22]. These liquids are then atomized and a set of indicators are chosen, such as the mean droplet diameter or the jet breakup length, to represent the extent of atomization. Collectively, researchers 'A version of this chapter will be submitted for publication in Atomization and Sprays.

For example, Mansour and Chigier [21] atomized a series of polymer solutions using an air-blast atomizer, and found that elasticity promoted ligament stretching prior to droplet formation. Ligament stretching was attributed to normal stress development owing to molecular reorientation.

Mun et al [20] employed agricultural sprayers to assess the impact that polymer additives had on atomization quality. Dexter [27] reported that the mean droplet diameter of a polymeric spray correlated more strongly with extensional viscosity than with shear viscosity. A similar conclusion was reached by Ferguson et al [19], who evaluated the influence of polymer type, molecular weight, and concentration on atomization.

Harrison et al [28] examined the effect of polymer rigidity on the cone angle of viscoelastic sprays. They discovered that the spray produced from the solution containing the most flexible polymer in their study collapsed at the lowest concentration.

Such behavior was attributed to increases in extensional viscosity induced by the added polymer flexibility, which caused a more detrimental effect on atomization at equivalent concentrations. Meanwhile, the ability of elasticity to suppress satellite droplet formation has attracted numerous industrial applications. For example, Chao et al [29] and Johnson et al [30] reported that by introducing high molecular weight polyisobutylene PIB into aircraft fuel, an anti-misting effect was established that minimized post-crash fire dangers.

Smolinski et al [31] and Marano et al [32] added PIB in machining oil to suppress unwanted misting during metalworking operations. Finally, Hartranft and Settles [33], Glass et al [18], and Stelter et al [34] all concluded that elasticity stabilized liquid sheets formed from airless paint sprayers.

Previous studies in this area have often relied on extension-thickening liquids that were also strongly shear-thinning. In order to systematically isolate and investigate the effect of elasticity, test liquids with common, rate-independent shear viscosities, but adjustable extensional viscosities were employed.

Based on the work of Mun [22], these model elastic liquids belong to the Boger class [35] and were constructed by dissolving polyethylene PEO into a glycerin-water solvent. Flash photography was used to elucidate breakup details. Next, the air-blast atomizer and the accompanying liquid and air flow systems are detailed. Extensive literature exists on PIV and shadowgraphy, so for brevity, only an overview of these measurement techniques is presented.

When not in use, they were individually stored in air-tight containers to minimize evaporation, water absorption from the ambient air, and contamination. Table 2. PEO is a linear, flexible, and water soluble polymer. In the present study, the concentrations at which PEO was introduced corresponded to the dilute regime according to criteria set out by Flory [36].

They were prepared by gradually dissolving PEO powder into distilled water under gentle magnetic stirring over a 24 hour period. Because flexible polymers like PEO are susceptible to mechanical degradation [26,37], care was taken to avoid excessive agitation. Next, USP grade glycerin Due to the limited thermal stability of PEO [26], liquids were characterized and sprayed within 2 week of preparation, but after at least 48 hours since final PEO addition to allow for complete polymer solubility.

The inelastic test liquids were constructed using glycerin and distilled water. Their rate-independent shear viscosities were adjusted by varying the relative glycerin concentration. In total, five inelastic liquids were prepared, with shear viscosities ranging from 0. Likewise, the shear viscosities of the inelastic liquids were also constant over a similar range of shear rates, with the magnitudes increasing as a function of glycerin concentration.

To assess the extent of PEO degradation caused by mechanical processes upstream of the atomizer, namely pumping and flow through supply lines, additional shear viscosity measurements were conducted on elastic samples collected after they had flowed through the spray system air-blast deactivated.

Results confirmed that the shear viscosities of the elastic liquids before and after flowing through the spray system were similar see Appendix A , suggesting minimal PEO degradation. Thus, the shear viscosities measured before the spray tests were representative of those exhibited by the liquids during atomization.

Equilibrium surface tensions were measured using a du Notiy ring; the measurement procedure and raw data can be found in Appendix B. Surface tensions ranged from These values are consistent with published data [38,39] and confirm the fact that PEO is slightly surface active [40]. Although much care was taken in handling the test liquids, surface tension measurements before and after the spray tests air-blast deactivated 56 revealed a small but measurable drop maximum of 5.

Moreover, at the high aerodynamic Weber numbers in the present study, surface tension has only a weak influence on the development of interfacial instabilities on the liquid jet [11,41]. A s a result, the oi variations across the test liquids were considered insignificant. Liquid densities were measured using a standard ml density cup. In their air-blast atomization experiments, Lorenzetto and Lefebvre [6] showed that liquid density variations between 0.

Thus, the relatively small density variations exhibited by the test liquids, owing to the different glycerin concentrations needed to achieve the desired shear viscosities, were considered insignificant. M u n [22] characterized the extensional behavior of the three elastic liquids using the Rheometrics R P X , a commercial extensional rheometer of the opposed-jet type Fuller et al [42].

It must be emphasized, though, that like most extensional rheometers, the R F X reports an apparent extensional viscosity value owing to its inability to sustain a uniform strain and strain rate throughout the liquid sample. Moreover, the R F X also suffers from corrections pertaining to inertia [43] and viscous losses [44]. Nevertheless, despite these shortcomings, there is general support for the R F X ' s ability to reveal qualitative differences in elasticity for dilute polymer solutions [22,44,45].

This is shown in Figure 2. This Reynolds number is thus a measure of the apparent extensional rate. This implies that the K sample was more elastic than the K sample. The shear flow curve conformed to a power-law model, as shown in Figure 2. Note that these OL values are far lower than those of the test liquids in Table 2. Although these measurements were conducted within the linear viscoelastic regime, where deformations are much smaller and slower than those expected in an atomizer, the results still confirm the elastic nature of K E L T R A C K HiRail.

Moreover, in Appendix A : Figure A. Attempts at measuring the extensional viscosities of the elastic PEO liquids were unsuccessful owing to their exceptionally low shear viscosities. It is based on a commercial paint sprayer and is currently employed by a number of railway operators for applying liquid F M.

The original atomizer made use of a rubber-duckbill see Figure 2. However, most of the present research was conducted using a modified version of this original atomizer, one which had the tip of the rubber-duckbill removed. This was done to overcome the challenges in calculating the liquid velocity and Reynolds number caused by the variable, elliptical flow area of the duckbill. Reliably measuring this area was difficult due to the flexible nature of rubber and visual hindrance imposed by the liquid stream.

Removing the duckbill altogether was considered, but owing to the desire to maintain the same annular air orifice area, only the tip was cut off flush with the exit plane of the atomizer. Figure 2. The inner diameter of the round liquid orifice Dj is 1. In order to keep its orifices clean, this atomizer employs the use of purge air. Five diametrically-opposed holes see Figure 2. By means of an external shroud, the diverted air was aimed back at the atomizer orifices to clear away residual liquid buildup.

Although effective in practice, this geometry complicates the calculation of the atomizing air velocity under sub-sonic conditions owing to the unknown mass fraction split between the purge air and atomizing air. Sprayed liquids were collected in a tray placed approximately 1 m below the atomizer. The liquid flow was supplied by a gear pump, and measured using a graduated cylinder and stopwatch; this was confirmed during the spray tests with continuous balance readings. Liquid and air supply connections to the atomizer were made with flexible polyethylene tubing to minimize vibration transfer.

Sketches of the liquid and air supply connections are shown in Figure 2. Its principles and development over the past twenty years have been described and reviewed by Adrian [47], Keane et al [48], and Raffel et al [49]. The general idea is to illuminate tracer particles in a flow field with two short pulses of a planar light sheet, during which two corresponding images are recorded over a known time separation.

These image-pairs IP are then divided into interrogation areas IA and processed by a cross-correlation algorithm to obtain the average particle displacement in each IA. By knowing the time separation over which this displacement occurs, the average velocity is calculated; this procedure is then applied to every IA in the image domain to produce an entire velocity field. In the present application of PIV, the tracer particles were simply droplets produced by the atomizer.

Appendix E outlines the experimental setup and procedures. In brief, a dual-head, frequency-doubled N d : Y A G laser nm; max. The laser pulses were synchronized to the CCD camera through a pulse generator, while the laser-sheet optics were mounted on a linear rail to ensure consistent alignment. A l l of the experiments were performed in a dark room to minimize optical noise from ambient lighting. This value was chosen based on considerations such as resolvable spatial resolution, adequate droplet number-density, and velocity dynamic range.

Image-pairs were processed using an adaptive-correlation algorithm embedded in Dantec's FlowManager software [50]. Adaptive-correlation improves upon conventional cross-correlation by allowing successive size reductions and offsets in the IA over multiple evaluation iterations. The amount by which an IA is offset is determined from an initial velocity estimate calculated by using cross-correlation.

The result is increased spatial resolution without sacrificing velocity dynamic range. More importantly, in sprays, where droplet sizes and number-densities are often non-uniform, an adaptive algorithm increases the number of true correlations by relaxing the minimum droplet number requirement of 10 per IA such that it applies instead to the initial IA, which can be made large to capture more droplets.

Image-pairs were processed using an initial IA size of 64 H x V pixels, corresponding to A single iteration step was applied to arrive at a final IA size of 32 x 64 pixels or 5. The resultant raw vector maps were subjected to a validation procedure to detect and replace spurious velocity measurements. These criteria were selected by carefully examining numerous raw vector maps, in which the velocity bounds were gradually narrowed from initially large values until a majority of the unphysical vectors having unrealistically large velocities situated outside the spray boundaries were rejected.

Of course, care was taken not to eliminate vectors of reasonable magnitude and direction appearing within the spray boundaries. Next, a moving average filter was applied to identify vectors that deviate by more than a prescribed amount from the average of the adjacent 3 x 3 window vectors. Vectors detected as spurious were then replaced with the local average of the accepted adjacent vectors. To avoid peak-locking effects, droplet image diameters were verified to be more than 2 pixel-pitches wide [49].

The total relative uncertainty cou associated with a PIV velocity measurement can be calculated by summing the variances of the known error sources [51]: temporal error, scale error, peak location error. Scale error is due to the uncertainty 8scale in transforming the camera pixel coordinates to physical dimensions scale , and its contribution was 0.

Peak location error arises from the uncertainty 8X in locating the displacement peak A X within the correlation plane. Most modern correlation algorithms can achieve sub-pixel resolution by least squares fitting a 2-dimensional Gaussian function to the displacement peak. Time and length scales within a spray vary considerably depending on their spatial locations, leading to difficulties in extracting velocity information of the entire spray from a series of image-pairs captured over a set time separation.

This is because the 67 relative uncertainty in locating the displacement peak varies over the spray domain and is highest near the spray boundaries where droplets travel at low velocities and undergo small displacements. As a result, the time separation of 38 us chosen for the ensuing tests was optimized for resolving axial droplet velocities at the spray centerline.

For proper statistical representation of the spray, a sufficient number of image-pairs must be acquired. Preliminary testing has revealed that a minimum of 70 IP are needed in order to stabilize the mean axial centerline MACL droplet velocity to within experimental uncertainty; this convergence criterion was valid for all the test liquids and at every injection condition.

Therefore, to obtain an accurate representation of the dynamic behavior of the spray while complying with time and data storage limitations, image-pairs were captured for each test run. A typical backlit setup was used, in which the spray was situated between the light source and camera such that liquid droplets and ligaments appeared dark on a bright background [53]. This technique, referred to as shadowgraphy, has been used in various forms over the past fifty years [].

Appendix G describes in detail the calibration, image analysis, and measurement procedures. Basically, a high intensity light source with a short pulse duration P A L F L A S H was used to illuminate and "freeze" droplets in mid-flight while a camera PCO Pixelfly digital CCD; H x V pixel; 12 bit , situated directly opposite to the light source, captured shadowgraphs through a far-field microscope Navitar 12X zoom.

The camera position was adjusted using a 3-axis traverse with an accuracy of 10 um in the radial directions x, y and 25 um in the axial direction z. In order to resolve droplets as small as 10 urn in diameter, an image conversion factor of 0. A minimum droplet diameter of 10 pm was chosen because droplets that are any smaller will evaporate quickly and represent only a small fraction of the total liquid volume in the spray. The depth-of-field was estimated by traversing a transparent slide, on which a circle of known diameter was printed, along the camera axis and through the measurement volume.

The depth-of-field was measured to be about 1 mm. Recorded shadowgraphs were processed digitally using a multi-step thresholding algorithm La Vision, SizingMaster software , through which droplets situated within the measurement volume were differentiated from the background and from out-of-focus droplets based on contrast differences see Appendix G for details on this thresholding procedure. Deciding whether or not a droplet is in focus is subjective. To this end, through a meticulous trial-and-error process, it was ensured that only droplets lying within the abovementioned measurement volume were accepted for size calculations.

Droplets were sized by having their occupied areas on the shadowgraphs computed, from which equivalent spherical diameters were assigned based on the image conversion factor. In the present study, droplet sizing results are presented using the arithmetic mean diameter Dw and the volumetric median diameter VMD , both measured at nine spatial locations in spray, as depicted in Figure 2.

Due to light attenuation effects, all of the shadowgraphs were recorded at a downstream distance z of In this far region, the local droplet Weber number was on the order of 10"2, even for the larger droplets, which meant that secondary atomization was not expected. Although each shadowgraph represents a spatial-average, instantaneous-time measurement, multiple images were recorded and analyzed to provide time-average statistics. Depending on the test liquid and flow rate, anywhere from to droplets were analyzed at each sampling location.

Assuming high-quality images are captured and proper calibration procedures are performed, the accuracy of the shadowgraphy technique is limited by the number of pixels a droplet occupies in the image. In this sense, it is advantageous to use a very small field-of-view in order to allocate as many pixels as possible to a single droplet. However, given the need to acquire a sufficient number of droplets for reliable statistics, a compromise is usually made that allows for the mean droplet diameter to span at least 20 pixels.

Unless otherwise noted, the atomizing air pressure PA was kept constant at It should also be mentioned that the effective area through which the purge air flows just before contacting the atomizer orifices is actually larger than both A and AATOMI! I in fact, about 45 times larger.

Consequently, the purge air velocity is much lower than the atomizing air velocity and should not affect atomization. In the present study, the liquid Reynolds number ReL varied between 5. The air-liquid mass ratio ALR and the momentum flux ratio M ranged from 1. The characteristic shear viscosity used in calculating the ReL for K E L T R A C K HiRail was chosen based on the wall shear rate y experienced inside the liquid orifice; for a non-Newtonian liquid with a power-law index, n, this is given by [24]: 2 75 Although the action of the atomizing air will subject the liquid to additional shear, it is difficult to estimate the extent of this effect owing to the complex flow fields.

As such, the characteristic shear viscosity calculated based on the instantaneous wall shear rate should only be taken as an approximation. The goal is to compare the breakup features of these various liquids, and to observe changes induced by differences in the shear viscosity and elasticity. A rise in ns by two orders of magnitude from 0. This observation is consistent with previous Newtonian droplet size measurements [6,20].

Furthermore, water, 50 wt. The appearance of this mode is marked by an extremely short jet breakup length, combined with periodic pulsations that lead to temporal and spatial fluctuations in the droplet number-density within the spray. In fact, this pulsating behavior can be seen more clearly in the PIV images in the form of oblique wave patterns.

These are shown in Figure 2. Note that these are planar images representing only a two dimensional slice of the spray. Focusing back on the breakup photographs in Figure 2. The liquid stream remained intact and underwent erratic excursions away from its centerline. Radial motions appear to be induced by large-scale turbulent structures. As mentioned earlier, 50 wt. In contrast, all three of the elastic PEO liquids displayed filamentary structures containing large-scale ligaments.

The physical scale of these ligaments increased with PEO molecular weight, and hence elasticity. For K and K PEO, spherical droplets were often observed at the ends of the ligaments, indicating the onset of pinch-off. The ligaments appear to have experienced significant stretching at high elongational rates; these high rates-of-strain were deduced from the short time-scales inherent to the atomization process.

As a result, it is believed that, through molecular reorientation and stretching, the extension-thickening behavior exhibited by these elastic ligaments induced additional tensile stresses in their cross-sections, which enhanced their stability against capillary forces.

Discrete droplet formation was delayed until farther downstream where relative air-liquid velocities were reduced. So, in agreement with findings of Mun et al [20] and Mansour and Chigier [21], liquid elasticity is predicted to increase droplet sizes. Note the presence of large-scale ligaments, filamentary structures, and a membrane center of image. Therefore, in spray coating, the diameter of a droplet is one of the main factors determining whether it will deposit onto the target surface or be carried away by the surrounding air jet.

In view of this, droplet size measurements were performed on three inelastic liquids water, 50 wt. The results for water are presented and discussed first because they are the simplest to understand. Radial Dio profiles for water are shown in Figure 2. Several observations can be made at this point. Higher Dio values were measured near the spray periphery. This observation has been reported by other researchers [34,41,58,59]. Eroglu and Chigier [8] noted from their air-blast atomization research that the flapping motion of the unstable liquid jet can launch droplets radially away from the spray centerline.

Thus, larger droplets are expected to continue farther along in their initial trajectory owing to their increased inertia [58]. Although the air-blast atomizer used in the present work did not incorporate swirl in its design, high-speed videos captured of water and other liquids revealed swirling motions in the spray as evidenced by helical droplet trajectories. The origin of these swirling motions is unclear but the resultant centripetal forces may cause larger droplets to migrate farther towards the spray periphery than smaller droplets.

The RMS deviation of the Dw also exhibited higher values near the spray periphery, though this was attributed mainly to reduced droplet numbers. This result was expected since it is well established that reducing the ALR from 2. From the work of Eroglu et al [60], it has been shown that increasing the momentum in the liquid stream results in a longer jet breakup length and, hence, larger droplets. For example, from inspection of Figure 2.

Similarly, in Figure 2. In general, the spray appears to be skewed significantly towards the negative x and negative y directions. The work was divided into four main phases:- 1 The first phase was confined to the effects of liquid properties, namely viscosity, surface tension and density on mean drop size.

Special liquids were produced to study the separate effect of each property on atomization quality. They presented a range of values of viscosity from 1. This study enabled a better understanding of the effects of changes in operation on the atomizer's performance.

This last phase was aimed at studying the effect of varying the velocity between the inner and outer air streams. A detailed description of the light-scattering technique for drop size measurement is included. A discussion on the importance of the results obtained and their direct relevance to the design of airblast atomizers is given. A dimensional analysis and inspection of all the data obtained on the effects of air and liquid properties on atomization quality showed that over the following range of conditions: Liquid viscosity 1.

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These liquids are then atomized and a set of indicators are chosen to represent the extent of atomization. Most commonly, this is a form of the mean 31 droplet size, though the spray angle [11] or jet breakup length [98] has been used in some cases. Collectively, the results indicate that liquid elasticity hinders atomization and increases droplet sizes; in fact, some researchers [] have even successfully correlated the mean droplet diameter with the apparent extensional viscosity.

The physical mechanisms behind these observations, however, have largely been ignored. This is unsurprising considering the complexity of the air-blast atomization process itself [2]. The most serious limitations common to almost all of the previous research efforts in viscoelastic atomization are listed below. The use of test liquids exhibiting both shear-thinning and extension-thickening rheology can lead to deceptive results, especially when droplet size measurements are considered.

For Newtonian liquids, it is known that the mean droplet size is well correlated with the shear viscosity. But for viscoelastic liquids, both the shear and extensional viscosities can affect the mean droplet size [6]. Consequently, any variation in atomization characteristics observed between test liquids can be misleading. Only two studies Mun et al [3]; Hartranft and Settles [98] have attempted to limit the variables between test liquids to just the extensional viscosity.

The atomization process subjects a liquid to very high rates of extension and shear. Only recently has there been significant progress made in the field of rheology to properly characterize the mechanical behavior of liquids under such conditions. In particular, the recognized difficulty in measuring the small tensile forces exhibited by dilute polymer solutions in an extensional flow field has been addressed somewhat by advents such as the Capillary Breakup Extensional Rheometer CaBER [96].

Investigators typically perform extensional viscosity measurements on their polymer solutions before they are sprayed. However, of the investigators who were able to correlate an apparent extensional viscosity with the mean droplet diameter, few had taken into account the mechanical degradation that long 32 chain polymers can experience during pumping.

Such degradation can significantly reduce polymer flexibility and the extent to which extension-thickening occurs [98]. Hence, the measured extensional viscosity may not be indicative of the value exhibited by the liquid during atomization. Research on viscoelastic atomization using conventional hydraulic atomizers constitutes the remaining bulk of the limited available literature. It has been known for quite some time that polymeric additives can suppress satellite droplet formation during atomization.

This behavior has been exploited in many industrial applications. For example, Chao et al [] and Johnson et al [] discovered that by introducing high molecular weight polyisobutylene PIB into jet fuel at concentrations as low as 50 ppm, an anti-misting effect was established that reduced post-crash fire hazards. The effectiveness of flammability suppression increased with the molecular weight of the polymer, and was well correlated with the apparent extensional viscosity of the solution as measured by the ductless siphon method.

Elsewhere in industry, Smolinski et al [7] and Marano et al [8] dissolved PIB in machining oil to suppress unwanted misting during metalworking operations. PIB molecular weights of 1. This increase was attributed to a significant reduction in the number of droplets falling below 5 pm in diameter. The authors ascribed such behavior to the viscoelastic properties of the PIB solutions, namely the extensional viscosity.

Moreover, increases in the mass median diameter were found to correlate linearly with the apparent extensional viscosity as predicted by the dumbbell kinetic theory. In agricultural pesticide sprays, small droplets are especially drift-prone and their release may have an adverse environmental impact. In view of this, Mun et al [3] added varying molecular weights of PEO into glycerin-water solvents and atomized the solutions using several agricultural hydraulic spray nozzles. A similar conclusion was reached by Dexter [6], who found that, by atomizing polymer solutions using a standard agricultural spray nozzle, the VMD correlated more strongly with the apparent extensional viscosity than with the shear viscosity.

While attempting to improve the airless spray coating process, Hartranft and Settles [98] explored the role of elasticity in sheet atomization. Specifically, their experiments examined the behavior of dilute Polyacrilamide solutions when atomized under the high pressures 1. At a moderate atomizing pressure 3. The size of the ligaments produced in primary breakup grew with the extensional viscosity. Unexpectedly, at the highest atomizing pressure 24 MPa , visual differences between the polymeric and Newtonian liquids were minimal.

This was explained by the exceptionally high strain rates inside the nozzle, which had caused severe polymer degradation and an associated reduction in the extent of extension-thickening. Hartranft and Settles' findings were supported by those of Glass et al [12], who sprayed a set of industrial water-borne coatings, containing polymer thickeners of varying molecular weight, through a flat-fan atomizer.

Their photographs showed that elasticity stabilized the liquid sheet and increased droplet sizes. Likewise, Stelter et al [97] employed flat-fan and pressure-swirl atomizers to evaluate the influence of viscoelastic properties on atomization.

VMD for polymer solutions was nearly three times that of Newtonian liquids. For pressure-swirl 34 atomization, liquid elasticity was shown to: 1 hinder the ability of the spray to form conical sheets i. Solutions containing low molecular weight polymers, such as Polyethylene glycol, were found to behave similarly to Newtonian liquids - the mass median diameter scaling with the steady shear viscosity to a power law.

However, for solutions of high molecular weight polymers, such as those containing PEO or polyvinyl alcohol, the mass median diameter was not only a function of the shear viscosity, but also depended on, and could be correlated directly with, the polymer molecular weight and concentration. Because it is known that increasing the polymer molecular weight and concentration will enhance a liquid's elasticity [5,82], the authors concluded that the extensional viscosity must play a critical role in controlling breakup.

Harrison et al [11] examined the influence of polymer rigidity on the cone angle of a spray produced by a swirl-type nozzle. Three test solutions were sprayed - each containing a polymer with a different rigidity. Their results showed that the spray produced from the solution containing the most flexible polymer, Polyacrilamide in this case, collapsed at the lowest concentration. This behavior was attributed to increases in extensional viscosity induced by the added polymer flexibility, which resulted in a more detrimental effect on atomization at equivalent concentrations.

This section examines the current state of technologies used in the spray coating industry, and highlights some of the key reasons why research in this area should continue to progress. Overspray refers to any liquid sprayed that does not adhere to the target surface, and is quantified by the transfer efficiency TE , defined as the percentage of the total mass of solids in the liquid coating sprayed i.

This air jet acts as a carrier medium for transporting small airborne droplets away from the target surface [,]. Larger droplets tend to possess sufficient inertia to cross aerodynamic streamlines [], thus enabling them to deposit onto the target surface. Therefore, long-term human exposure to the ensuing overspray may lead to serious health hazards, chief among them being lung cancer and central nervous system dysfunction [].

As the environmental, financial, and health consequences owing to inadequate transfer efficiencies become increasingly clear, so does the need to better understand and improve the spray coating process. After water evaporation, a dry thin film of F M material remains, controlling top-of-rail friction at an intermediate level while providing positive friction versus creep characteristics at the wheel-to-rail interface. Such positive friction behavior alleviates the frictional instability of roll-slip oscillations, which are responsible for the generation of curve squeal noise and short pitch corrugations [,].

In addition, F M application has also been demonstrated to reduce wheel and rail wear, lateral forces, and locomotive fuel consumption without adversely affecting train braking or traction [,,,]. In order to achieve effective friction control, it is currently known what volume of F M must be dispensed by Kelsan's air-blast atomizers per length of railroad track.

But the exact amount of F M actually reaching the railhead, as opposed to the surrounding rail ties or train undercarriage, is unknown. Also unknown is the spatial distribution of F M in the spray, which can influence the uniformity of the resultant spray pattern on the railhead. This is believed to affect retentivity the number of axle passes for which the F M film remains effective and carry-down the ability of the F M film to migrate down the track.

Knowing the influence of such crossflows on F M spray trajectories would be valuable, especially considering the detrimental effects it can pose on the transfer efficiency. Further, crossflows have been observed to accelerate the deposition of fouling on nozzle orifices, which, i f left unattended, can accumulate to render the nozzle inoperable.

Although it is now accepted practice for the nozzles to be periodically cleaned, this is generally a task that railway operators would rather avoid as it complicates train maintenance. Hence, Kelsan and its customers would benefit from improvements to the anti-fouling performance of the F M spray nozzles. Knowledge of their behavior, from the atomizer orifice to the target surface, is valuable towards optimizing the transfer efficiency in spray coating.

The present work focuses on the air-blast atomization and subsequent aerodynamic transport of viscoelastic liquids. The surface impingement aspect is treated separately in Mr. Dan Dressier's M. Previous studies on viscoelastic atomization have been hampered by an inability to decouple shear-thinning and extension-thickening rheology.

Additionally, information relevant to spray coating, such as droplet velocities and the influence of crossflows, were seldom provided. To this end, a major objective of the present work is to expand upon previous research efforts by addressing these aforementioned limitations.

The numerous constituents in typical industrial coatings lead to highly coupled, and even deceptive, rheology. To understand these Theologically complex liquids, Glass [] and Soules et al [] pioneered the use of substitute test liquids in paint application research. The present work employs a series of rheologically-ideal test liquids belonging to the Boger class [83,].

By maintaining similar values of surface tension, density, and rate-independent shear viscosity in the test liquids, and independently varying the extensional viscosity, the effects of elasticity on air-blast atomization are isolated and examined. Droplet sizes and velocities are measured using shadowgraphy and Particle Image Velocimetry, respectively.

Application of liquid FMs in the railway industry is a unique case of spray coating, one that currently involves a plethora of unknowns. In view of this, another major objective of the present work is to evaluate the ability of Kelsan's air-blast atomizer to apply liquid F M onto the railhead. Only after evaluating the performance of Kelsan's existing air-blast atomizer can a future generation of improved spray nozzles be designed.

Lefebvre A H Air-blast atomization. Progress in Energy and Combustion Science, Atomization of dilute polymer solutions in agricultural spray nozzles. Journal of Non-Newtonian Fluid Mechanics, Mansour A D Thesis, Carnegie Mellon University. Mansour A and Chigier N Air-blast atomization of non-Newtonian liquids. Dexter RW Measurement of extensional viscosity of polymer solutions and its effects on atomization from a spray nozzle.

Atomization and Sprays, AIChE Journal, 42 5 : Polymer additives as mist suppressants in metal cutting fluids. Lubrication Engineering. The break-up of fluids in an extensional flow field. Lee RW A note on the effect of polymer rigidity and concentration on spray atomization. Journal of non-Newtonian Fluid Mechanics, Glass JE Chapter 15, ISBN Review of stability of liquid jets and the influence of nozzle design. Chemical Engineering Journal, Rayleigh L On the instability of jets.

Proceedings of the London Math Society, Weber C Disintegration of liquid jets translated. Zeitschrift fur Angewandte Mathematik und Mechanik Germany , 11 2 : Haenlein A Disintegration of a jet. Sterling A M D Thesis, University of Washington. Yuen M C Non-linear capillary instability of a liquid jet. Journal of Fluid Mechanics, Lee HC Drop formation in a liquid jet. Ohnesorge W Formation of drops by nozzles and the breakup of liquid jets translated.

Zeitschrift fur Angewandte Mathematik und Mechanik Germany , Castleman R A The mechanism of the atomization of liquids. Journal of Research of the National Bureau of Standards, 6 Reitz RD D Thesis, Princeton University. Miesse CC Correlation of experimental data on the disintegration of liquid jets.

Industrial and Engineering Chemistry, 47 9 : Giffen E and Muraszew A Liu H Chigier N The Physics of Atomization. Gaithersburg, M D , Cheremisinoff NP Encyclopedia of Fluid Mechanics, 3. De Juhaz K J Dispersion of sprays in solid-injection oil engines. Mehlig H On the physics of fuel sprays in diesel engines translated.

Z , 37 16 Thiemann A E The viscosity of the air is more important than its density for fuel sprays translated. Schweitzer PH Mechanism of disintegration of liquid jets. Journal of Applied Physics, 8 8 Sauter J Determining size of drops in fuel mixture of internal combustion engines.

Scheubel FN On atomization in carburetors. Strazhewski L The spray range of liquid fuels in an opposing air flow. USSR, 4 6. Chigier N A The atomization and burning of liquid fuel sprays. Dynamics of droplets in burning and isothermal kerosene sprays.

Combustion and Flame, Marshall WR Factors influencing the properties of spray-dried materials. Chemical Engineering Progress, 49 8 Finlay W Nukiyama S and Tanasawa Y Experiments on the atomization of liquids in air stream. Transactions of the Society of Mechanical Engineers Japan , 5 18 Measurements of drop size on a plain-jet air-blast atomizer. AIAA Journal, 15 7 : The influence of air and liquid properties on air-blast atomization.

Air-blast atomization - effect of linear scale on mean drop size. Journal of Energy, 4 4 : The design and performance of internal mixing multi-jet twin-fluid atomizers. Fuel, Eroglu H and Chigier N Initial drop size and velocity distributions for air-blast coaxial atomizers.

Transactions of the ASME, Gretzinger J and Marshall WR Characteristics of pneumatic atomization. AIChE Journal, Drop-size distributions from pneumatic atomizers. Atomization characteristics on the surface of a round liquid jet. Experiments in Fluids, Drop size distribution and air velocity measurements in air-assist swirl atomizer sprays.

Joyce JR The atomization of liquid fuels for combustion. Simmons H The correlation of drop-size distributions in fuel nozzle sprays. Anson D Influence of the quality of atomization on the stability of combustion of liquid fuel sprays. Behavior of sprays under high altitude conditions. Spray nozzles for the simulation of cloud conditions in icing tests of jet engines. Influence of liquid film thickness on airblast atomization.

Atlanta, Lefebvre A H and Miller D The development of an airblast atomizer for gas turbine application. Cranfield College of Aeronautics Report, Aero. Spay characteristics of plain-jet air-blast atomizers. Hardalupas Y and Whitelaw JH Characteristics of sprays produced by coaxial air-blast atomizers. Journal of Propulsion and Power, 10 4 Atomization of liquids in high velocity gas streams.

Industrial and Engineering Chemistry, Lane WR Shatter of drops in streams of air. Industrial and Engineering Chemistry, 43 6 Wiggs L D The effects of scale on fine sprays produced by large air-blast atomizers. Break-up and atomization of a round water jet by a high-speed annular air jet.

Initial breakup of a small-diameter liquid jet by a high-speed gas stream. The mechanism of disintegration of liquid sheets. Transactions of the ASME, 75 7 A study of the stability of plane fluid sheets. Journal of Applied Mechanics, Dombrowski N and Johns WR The aerodynamic instability and disintegration of viscous liquid sheets. Chemical Engineering Science, Mayer E Theory of liquid atomization in high velocity gas streams.

ARS Journal, 31 12 Adelberg M Breakup rate and penetration of a liquid jet in a gas stream. AIAA Journal, 5 8 Mean drop size resulting from the injection of a liquid jet into a high-speed gas stream. AIAA Journal, 6 6 : Liquid jet instability and atomization in a coaxial gas stream. Annual Review of Fluid Mechanics, Farago Z and Chigier N Morphological classification of disintegration of round liquid jets in a coaxial air stream.

Dombrowski N and Fraser RP A photographic investigation into the disintegration of liquid sheets. The atomization of a liquid sheet by an impinging air stream. Parametric experiments on coaxial airblast jet atomization. Brussels, Belgium, June Disintegration of liquid sheets. Physics of Fluids, 2 5 A note on the growth of Kelsan-Helmholtz waves on thin liquid sheets.

Journal of Fluid Mechanics, 57 4 Kelsan-Helmholtz wave growth on cylindrical sheets. Journal of Fluid Mechanics, 68 3 Macosko C W Mun RP D Thesis, University of Melbourne. Boger D V A highly elastic constant-viscosity fluid. Flory PJ Model viscoelastic liquids. Bueche FJ Mechanical degradation of high polymers.

Journal of Applied Polymer Science, 4 10 : Extensional effects in flows through contractions with abrupt or rounded corners. Pipkin A C and Tanner R l Steady non-viscometric flows of viscoelastic liquids. Mannheimer RJ Rheological and mist ignition properties of dilute polymer solutions. Chemical Engineering Communications, Trouton FT On the coefficient of viscous traction and its relation to that of viscosity.

Proceedings of the Royal Society of London. Series A, On the extensional viscosity of mobile polymer solutions. Rheologica Acta, Extensional viscosity measurements of dilute solutions of various polymers. The effects of polymer concentration and molecular weight on the breakup of laminar capillary jets.

Tirtaatmadja V and SridharT A filament stretching device for measurement of extensional viscosity. Journal of Rheology, 37 6 Capillary break-up rheometry of low-viscosity elastic fluids. Applied Rheology, 15 l The influence of viscoelastic fluid properties on spray formation from flat-fan and pressure-swirl atomizers.

Sheet atomization of non-Newtonian liquids. A tomization and Sprays, Opposing-jet viscometry of fluids with viscosity approaching that of water. Can extensional viscosity be measured with opposed-nozzle devices? Comparison of entry flow techniques for measuring elongation flow properties. Atomization and elongational viscosity of associating triblock copolymer solutions.

Keller A and Odell JA The extensibility of macromolecules in solution. Colloid Polymer Science, Molecular theories of elongational viscosity. Proceedings of the 5th International Congress on Rheology, Batchelor G K The stress generated in a non-dilute suspension of elongated particles by pure straining motion.

Slender-body theory for particles of arbitrary cross-section in stokes flow. Mewis J and Metzner A B The rheological properties of suspensions of fibers in Newtonian fluids subjected to extensional deformation. Binding D M A n approximate analysis for contraction and converging flows. Breakup of a laminar capillary jet of a viscoelastic fluid. Journal of Fluid Mechanics, 38 4 Middleman S Stability of a viscoelastic jet. Chemical Engineering Science, 20 12 Non-linear analysis of the surface tension driven breakup of viscoelastic filaments.

Journal of non-Newtonian Fluid Mechanics, 21 l Instability of jets of non-Newtonian fluids. Transactions of the Society of Rheology, 17 2 Stability of vertical jets of non-Newtonian fluids. AIChE Journal, 17 4 Christani Y and Walker L M Surface tension driven jet break up of strain-hardening polymer solutions. Antimisting action of polymeric additives in jet fuels. AIChE Journal, 30 1 The effect of antimisting additives on flammability of jet fuels. How atomization affects transfer efficiency.

Industrial Finishing, Simulation of paint transfer in an air spray process. High-pressure sheet atomization of non-Newtonian fluids. Indianapolis, IN, May , Particle dispersion by vortex structures in plane mixing layers. Journal of Fluids Engineering, A comparison of conventional and high volume-low pressure spray-painting guns.

American Industrial Hygiene Association Journal, 57 3 Johnson B W HVLP-Shoot for profit. Proceedings of the National Autobody Congress and Exposition. MargK H V L P spray puts you into compliance. Metal Finishing, 87 3 Experimental evaluation of a mathematical model for predicting transfer efficiency of a high volume-low pressure air spray gun. Applied Occupational and Environmental Hygiene, 15 10 TriplettT The H V L P way to spray.

Methods for estimating the transfer efficiency of a compressed air spray gun. Applied Occupational and Environmental Hygiene, 17 l Specific charge measurements in electrostatic air sprays. Particulate Science and Technology, 23 l Numerical model of paint transfer and deposition in electrostatic air sprays.

Atomization and Sprays, 16 2 : Drop size measurements in electrostatic paint sprays. Washington, D. Methods for determining exposure to lacquer aerosols and solvent vapours during spray painting translated. Gefahrstoffe Reinhaltung der Luft, 57 2 Neurobehavioral changes among shipyard painters exposed to solvents.

Archives of Environmental Health, Organic solvent-induced encephalopathy in industrial painters. Journal of Occupational Medicine and Toxicology, International Archives of Occupational Environmental Health, Anon The risks of inhaling car spray-painting fumes. South African Medical Journal, 87 3 Wear, The role of high positive friction HPF modifier in the control of short pitch corrugations and related phenomena.

Wear, : The basic study on friction control between wheel and rail Experiments by test machine and scale model vehicle. Gothenburg, Sweden, , Vol. II, pp Eadie DT and Santoro M Top of rail friction control for curve noise mitigation and corrugation rate reduction. Journal of Sound and Vibration, Kalousek J and Johnson K L An investigation of short pitch wheel and rail corrugations on Vancouver mass transit system.

Top of rail friction control: lateral force and rail wear reduction in a freight application. International Heavy Haul Association Conference. Dallas, Texas, May Top of rail friction control with locomotive delivery on BC Rail: Reductions in fuel and greenhouse gas emissions. Nashville, Tennessee, September Journal of Coatings Technology. Dynamic uniaxial extensional viscosity DUEV effects in roll application: Rib and web growth in commercial coatings.

Journal of Rheology, 32 2 Model elastic liquids with water-soluble polymers. AIChE Journal, 44 6 However, the majority of research in this area has focused on Newtonian liquids despite the recognized industrial importance of spraying non-Newtonian liquids, particularly those that exhibit viscoelastic properties. In the railway industry, for example, an increasing number of railway operators are adopting the use of liquid friction modifiers FM for controlling frictional instabilities at the wheel-to-rail interface.

Air-blast atomizers are often used to apply these liquid FMs onto the rail head to derive benefits such as improved fuel economy and reduced wheel and rail wear, without adversely affecting train braking or traction [].

However, like many paints and industrial coatings, liquid FMs also contain polymers and solids, thus making them viscoelastic [18]. As such, they are expected to atomize differently than Newtonian liquids owing to their ability to develop significant extensional viscosities when exposed to the extension-dominated flow fields generated by spray nozzles [19,20].

Rheologists have observed that the extensional viscosity exhibited by polymer solutions is usually an increasing function of the extensional rate and strain [], behavior known respectively as extension-thickening and strain-hardening [24]. The maximum Trouton ratio ratio of extensional to shear viscosity for these solutions can be more than one order of magnitude greater than the Newtonian inelastic value of 3 [25]. Hence, liquid elasticity, through the extensional viscosity, will play an important role in controlling breakup.

In viscoelastic atomization research, aqueous polymer solutions are commonly used as test liquids because they are easy to formulate [26] and can exhibit extensional viscosities proportional to the polymer molecular weight and concentration [21,22]. These liquids are then atomized and a set of indicators are chosen, such as the mean droplet diameter or the jet breakup length, to represent the extent of atomization.

Collectively, researchers 'A version of this chapter will be submitted for publication in Atomization and Sprays. For example, Mansour and Chigier [21] atomized a series of polymer solutions using an air-blast atomizer, and found that elasticity promoted ligament stretching prior to droplet formation.

Ligament stretching was attributed to normal stress development owing to molecular reorientation. Mun et al [20] employed agricultural sprayers to assess the impact that polymer additives had on atomization quality. Dexter [27] reported that the mean droplet diameter of a polymeric spray correlated more strongly with extensional viscosity than with shear viscosity.

A similar conclusion was reached by Ferguson et al [19], who evaluated the influence of polymer type, molecular weight, and concentration on atomization. Harrison et al [28] examined the effect of polymer rigidity on the cone angle of viscoelastic sprays. They discovered that the spray produced from the solution containing the most flexible polymer in their study collapsed at the lowest concentration. Such behavior was attributed to increases in extensional viscosity induced by the added polymer flexibility, which caused a more detrimental effect on atomization at equivalent concentrations.

Meanwhile, the ability of elasticity to suppress satellite droplet formation has attracted numerous industrial applications. For example, Chao et al [29] and Johnson et al [30] reported that by introducing high molecular weight polyisobutylene PIB into aircraft fuel, an anti-misting effect was established that minimized post-crash fire dangers. Smolinski et al [31] and Marano et al [32] added PIB in machining oil to suppress unwanted misting during metalworking operations.

Finally, Hartranft and Settles [33], Glass et al [18], and Stelter et al [34] all concluded that elasticity stabilized liquid sheets formed from airless paint sprayers. Previous studies in this area have often relied on extension-thickening liquids that were also strongly shear-thinning. In order to systematically isolate and investigate the effect of elasticity, test liquids with common, rate-independent shear viscosities, but adjustable extensional viscosities were employed.

Based on the work of Mun [22], these model elastic liquids belong to the Boger class [35] and were constructed by dissolving polyethylene PEO into a glycerin-water solvent. Flash photography was used to elucidate breakup details. Next, the air-blast atomizer and the accompanying liquid and air flow systems are detailed. Extensive literature exists on PIV and shadowgraphy, so for brevity, only an overview of these measurement techniques is presented.

When not in use, they were individually stored in air-tight containers to minimize evaporation, water absorption from the ambient air, and contamination. Table 2. PEO is a linear, flexible, and water soluble polymer. In the present study, the concentrations at which PEO was introduced corresponded to the dilute regime according to criteria set out by Flory [36].

They were prepared by gradually dissolving PEO powder into distilled water under gentle magnetic stirring over a 24 hour period. Because flexible polymers like PEO are susceptible to mechanical degradation [26,37], care was taken to avoid excessive agitation. Next, USP grade glycerin Due to the limited thermal stability of PEO [26], liquids were characterized and sprayed within 2 week of preparation, but after at least 48 hours since final PEO addition to allow for complete polymer solubility.

The inelastic test liquids were constructed using glycerin and distilled water. Their rate-independent shear viscosities were adjusted by varying the relative glycerin concentration. In total, five inelastic liquids were prepared, with shear viscosities ranging from 0.

Likewise, the shear viscosities of the inelastic liquids were also constant over a similar range of shear rates, with the magnitudes increasing as a function of glycerin concentration. To assess the extent of PEO degradation caused by mechanical processes upstream of the atomizer, namely pumping and flow through supply lines, additional shear viscosity measurements were conducted on elastic samples collected after they had flowed through the spray system air-blast deactivated.

Results confirmed that the shear viscosities of the elastic liquids before and after flowing through the spray system were similar see Appendix A , suggesting minimal PEO degradation. Thus, the shear viscosities measured before the spray tests were representative of those exhibited by the liquids during atomization.

Equilibrium surface tensions were measured using a du Notiy ring; the measurement procedure and raw data can be found in Appendix B. Surface tensions ranged from These values are consistent with published data [38,39] and confirm the fact that PEO is slightly surface active [40]. Although much care was taken in handling the test liquids, surface tension measurements before and after the spray tests air-blast deactivated 56 revealed a small but measurable drop maximum of 5.

Moreover, at the high aerodynamic Weber numbers in the present study, surface tension has only a weak influence on the development of interfacial instabilities on the liquid jet [11,41]. A s a result, the oi variations across the test liquids were considered insignificant. Liquid densities were measured using a standard ml density cup. In their air-blast atomization experiments, Lorenzetto and Lefebvre [6] showed that liquid density variations between 0.

Thus, the relatively small density variations exhibited by the test liquids, owing to the different glycerin concentrations needed to achieve the desired shear viscosities, were considered insignificant.

M u n [22] characterized the extensional behavior of the three elastic liquids using the Rheometrics R P X , a commercial extensional rheometer of the opposed-jet type Fuller et al [42]. It must be emphasized, though, that like most extensional rheometers, the R F X reports an apparent extensional viscosity value owing to its inability to sustain a uniform strain and strain rate throughout the liquid sample.

Moreover, the R F X also suffers from corrections pertaining to inertia [43] and viscous losses [44]. Nevertheless, despite these shortcomings, there is general support for the R F X ' s ability to reveal qualitative differences in elasticity for dilute polymer solutions [22,44,45]. This is shown in Figure 2.

This Reynolds number is thus a measure of the apparent extensional rate. This implies that the K sample was more elastic than the K sample. The shear flow curve conformed to a power-law model, as shown in Figure 2. Note that these OL values are far lower than those of the test liquids in Table 2. Although these measurements were conducted within the linear viscoelastic regime, where deformations are much smaller and slower than those expected in an atomizer, the results still confirm the elastic nature of K E L T R A C K HiRail.

Moreover, in Appendix A : Figure A. Attempts at measuring the extensional viscosities of the elastic PEO liquids were unsuccessful owing to their exceptionally low shear viscosities. It is based on a commercial paint sprayer and is currently employed by a number of railway operators for applying liquid F M.

The original atomizer made use of a rubber-duckbill see Figure 2. However, most of the present research was conducted using a modified version of this original atomizer, one which had the tip of the rubber-duckbill removed. This was done to overcome the challenges in calculating the liquid velocity and Reynolds number caused by the variable, elliptical flow area of the duckbill. Reliably measuring this area was difficult due to the flexible nature of rubber and visual hindrance imposed by the liquid stream.

Removing the duckbill altogether was considered, but owing to the desire to maintain the same annular air orifice area, only the tip was cut off flush with the exit plane of the atomizer. Figure 2. The inner diameter of the round liquid orifice Dj is 1. In order to keep its orifices clean, this atomizer employs the use of purge air.

Five diametrically-opposed holes see Figure 2. By means of an external shroud, the diverted air was aimed back at the atomizer orifices to clear away residual liquid buildup. Although effective in practice, this geometry complicates the calculation of the atomizing air velocity under sub-sonic conditions owing to the unknown mass fraction split between the purge air and atomizing air.

Sprayed liquids were collected in a tray placed approximately 1 m below the atomizer. The liquid flow was supplied by a gear pump, and measured using a graduated cylinder and stopwatch; this was confirmed during the spray tests with continuous balance readings. Liquid and air supply connections to the atomizer were made with flexible polyethylene tubing to minimize vibration transfer. Sketches of the liquid and air supply connections are shown in Figure 2.

Its principles and development over the past twenty years have been described and reviewed by Adrian [47], Keane et al [48], and Raffel et al [49]. The general idea is to illuminate tracer particles in a flow field with two short pulses of a planar light sheet, during which two corresponding images are recorded over a known time separation. These image-pairs IP are then divided into interrogation areas IA and processed by a cross-correlation algorithm to obtain the average particle displacement in each IA.

By knowing the time separation over which this displacement occurs, the average velocity is calculated; this procedure is then applied to every IA in the image domain to produce an entire velocity field. In the present application of PIV, the tracer particles were simply droplets produced by the atomizer. Appendix E outlines the experimental setup and procedures.

In brief, a dual-head, frequency-doubled N d : Y A G laser nm; max. The laser pulses were synchronized to the CCD camera through a pulse generator, while the laser-sheet optics were mounted on a linear rail to ensure consistent alignment.

A l l of the experiments were performed in a dark room to minimize optical noise from ambient lighting. This value was chosen based on considerations such as resolvable spatial resolution, adequate droplet number-density, and velocity dynamic range.

Image-pairs were processed using an adaptive-correlation algorithm embedded in Dantec's FlowManager software [50]. Adaptive-correlation improves upon conventional cross-correlation by allowing successive size reductions and offsets in the IA over multiple evaluation iterations. The amount by which an IA is offset is determined from an initial velocity estimate calculated by using cross-correlation.

The result is increased spatial resolution without sacrificing velocity dynamic range. More importantly, in sprays, where droplet sizes and number-densities are often non-uniform, an adaptive algorithm increases the number of true correlations by relaxing the minimum droplet number requirement of 10 per IA such that it applies instead to the initial IA, which can be made large to capture more droplets. Image-pairs were processed using an initial IA size of 64 H x V pixels, corresponding to A single iteration step was applied to arrive at a final IA size of 32 x 64 pixels or 5.

The resultant raw vector maps were subjected to a validation procedure to detect and replace spurious velocity measurements. These criteria were selected by carefully examining numerous raw vector maps, in which the velocity bounds were gradually narrowed from initially large values until a majority of the unphysical vectors having unrealistically large velocities situated outside the spray boundaries were rejected.

Of course, care was taken not to eliminate vectors of reasonable magnitude and direction appearing within the spray boundaries. Next, a moving average filter was applied to identify vectors that deviate by more than a prescribed amount from the average of the adjacent 3 x 3 window vectors. Vectors detected as spurious were then replaced with the local average of the accepted adjacent vectors. To avoid peak-locking effects, droplet image diameters were verified to be more than 2 pixel-pitches wide [49].

The total relative uncertainty cou associated with a PIV velocity measurement can be calculated by summing the variances of the known error sources [51]: temporal error, scale error, peak location error. Scale error is due to the uncertainty 8scale in transforming the camera pixel coordinates to physical dimensions scale , and its contribution was 0. Peak location error arises from the uncertainty 8X in locating the displacement peak A X within the correlation plane.

Most modern correlation algorithms can achieve sub-pixel resolution by least squares fitting a 2-dimensional Gaussian function to the displacement peak. This study enabled a better understanding of the effects of changes in operation on the atomizer's performance.

This last phase was aimed at studying the effect of varying the velocity between the inner and outer air streams. A detailed description of the light-scattering technique for drop size measurement is included.

A discussion on the importance of the results obtained and their direct relevance to the design of airblast atomizers is given. A dimensional analysis and inspection of all the data obtained on the effects of air and liquid properties on atomization quality showed that over the following range of conditions: Liquid viscosity 1.

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Various parameters which affect print patterns were identified to understand and control the atomization process occurring at the oscillating needle. For time-controlled atomization or printing, a pulse air jet system was implemented to print liquids only when it is demanded, and it was shown that the period of atomization can be controlled by the air jet on-and-off. The inertial coating process was studied to explain the dynamic meniscus profile, compared with static meniscus.

Kinematic analysis of the needle motion was performed, which shows that the needle motion is a sinusoidal one undergoing inertial coating. Liquid sheet breakup mechanism in the presence of the air stream was also studied in conjunction with the principle of the air- blast atomizer. Performing as a printing device or a droplet generator, the reciprocating needle printing method studied here can be applied to printing or coating processes which utilize high viscosity media. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission.

See provided URL for inquiries about permission. Department of Mechanical Engineering dc. Name: MIT. Search DSpace. Gretzinger J and Marshall WR Characteristics of pneumatic atomization. AIChE Journal, Drop-size distributions from pneumatic atomizers.

Atomization characteristics on the surface of a round liquid jet. Experiments in Fluids, Drop size distribution and air velocity measurements in air-assist swirl atomizer sprays. Joyce JR The atomization of liquid fuels for combustion. Simmons H The correlation of drop-size distributions in fuel nozzle sprays. Anson D Influence of the quality of atomization on the stability of combustion of liquid fuel sprays. Behavior of sprays under high altitude conditions.

Spray nozzles for the simulation of cloud conditions in icing tests of jet engines. Influence of liquid film thickness on airblast atomization. Atlanta, Lefebvre A H and Miller D The development of an airblast atomizer for gas turbine application. Cranfield College of Aeronautics Report, Aero. Spay characteristics of plain-jet air-blast atomizers. Hardalupas Y and Whitelaw JH Characteristics of sprays produced by coaxial air-blast atomizers.

Journal of Propulsion and Power, 10 4 Atomization of liquids in high velocity gas streams. Industrial and Engineering Chemistry, Lane WR Shatter of drops in streams of air. Industrial and Engineering Chemistry, 43 6 Wiggs L D The effects of scale on fine sprays produced by large air-blast atomizers. Break-up and atomization of a round water jet by a high-speed annular air jet. Initial breakup of a small-diameter liquid jet by a high-speed gas stream.

The mechanism of disintegration of liquid sheets. Transactions of the ASME, 75 7 A study of the stability of plane fluid sheets. Journal of Applied Mechanics, Dombrowski N and Johns WR The aerodynamic instability and disintegration of viscous liquid sheets. Chemical Engineering Science, Mayer E Theory of liquid atomization in high velocity gas streams. ARS Journal, 31 12 Adelberg M Breakup rate and penetration of a liquid jet in a gas stream.

AIAA Journal, 5 8 Mean drop size resulting from the injection of a liquid jet into a high-speed gas stream. AIAA Journal, 6 6 : Liquid jet instability and atomization in a coaxial gas stream. Annual Review of Fluid Mechanics, Farago Z and Chigier N Morphological classification of disintegration of round liquid jets in a coaxial air stream. Dombrowski N and Fraser RP A photographic investigation into the disintegration of liquid sheets. The atomization of a liquid sheet by an impinging air stream.

Parametric experiments on coaxial airblast jet atomization. Brussels, Belgium, June Disintegration of liquid sheets. Physics of Fluids, 2 5 A note on the growth of Kelsan-Helmholtz waves on thin liquid sheets. Journal of Fluid Mechanics, 57 4 Kelsan-Helmholtz wave growth on cylindrical sheets.

Journal of Fluid Mechanics, 68 3 Macosko C W Mun RP D Thesis, University of Melbourne. Boger D V A highly elastic constant-viscosity fluid. Flory PJ Model viscoelastic liquids. Bueche FJ Mechanical degradation of high polymers. Journal of Applied Polymer Science, 4 10 : Extensional effects in flows through contractions with abrupt or rounded corners. Pipkin A C and Tanner R l Steady non-viscometric flows of viscoelastic liquids.

Mannheimer RJ Rheological and mist ignition properties of dilute polymer solutions. Chemical Engineering Communications, Trouton FT On the coefficient of viscous traction and its relation to that of viscosity. Proceedings of the Royal Society of London. Series A, On the extensional viscosity of mobile polymer solutions.

Rheologica Acta, Extensional viscosity measurements of dilute solutions of various polymers. The effects of polymer concentration and molecular weight on the breakup of laminar capillary jets. Tirtaatmadja V and SridharT A filament stretching device for measurement of extensional viscosity.

Journal of Rheology, 37 6 Capillary break-up rheometry of low-viscosity elastic fluids. Applied Rheology, 15 l The influence of viscoelastic fluid properties on spray formation from flat-fan and pressure-swirl atomizers. Sheet atomization of non-Newtonian liquids. A tomization and Sprays, Opposing-jet viscometry of fluids with viscosity approaching that of water.

Can extensional viscosity be measured with opposed-nozzle devices? Comparison of entry flow techniques for measuring elongation flow properties. Atomization and elongational viscosity of associating triblock copolymer solutions. Keller A and Odell JA The extensibility of macromolecules in solution.

Colloid Polymer Science, Molecular theories of elongational viscosity. Proceedings of the 5th International Congress on Rheology, Batchelor G K The stress generated in a non-dilute suspension of elongated particles by pure straining motion. Slender-body theory for particles of arbitrary cross-section in stokes flow. Mewis J and Metzner A B The rheological properties of suspensions of fibers in Newtonian fluids subjected to extensional deformation.

Binding D M A n approximate analysis for contraction and converging flows. Breakup of a laminar capillary jet of a viscoelastic fluid. Journal of Fluid Mechanics, 38 4 Middleman S Stability of a viscoelastic jet. Chemical Engineering Science, 20 12 Non-linear analysis of the surface tension driven breakup of viscoelastic filaments.

Journal of non-Newtonian Fluid Mechanics, 21 l Instability of jets of non-Newtonian fluids. Transactions of the Society of Rheology, 17 2 Stability of vertical jets of non-Newtonian fluids. AIChE Journal, 17 4 Christani Y and Walker L M Surface tension driven jet break up of strain-hardening polymer solutions.

Antimisting action of polymeric additives in jet fuels. AIChE Journal, 30 1 The effect of antimisting additives on flammability of jet fuels. How atomization affects transfer efficiency. Industrial Finishing, Simulation of paint transfer in an air spray process. High-pressure sheet atomization of non-Newtonian fluids.

Indianapolis, IN, May , Particle dispersion by vortex structures in plane mixing layers. Journal of Fluids Engineering, A comparison of conventional and high volume-low pressure spray-painting guns. American Industrial Hygiene Association Journal, 57 3 Johnson B W HVLP-Shoot for profit. Proceedings of the National Autobody Congress and Exposition.

MargK H V L P spray puts you into compliance. Metal Finishing, 87 3 Experimental evaluation of a mathematical model for predicting transfer efficiency of a high volume-low pressure air spray gun. Applied Occupational and Environmental Hygiene, 15 10 TriplettT The H V L P way to spray. Methods for estimating the transfer efficiency of a compressed air spray gun.

Applied Occupational and Environmental Hygiene, 17 l Specific charge measurements in electrostatic air sprays. Particulate Science and Technology, 23 l Numerical model of paint transfer and deposition in electrostatic air sprays. Atomization and Sprays, 16 2 : Drop size measurements in electrostatic paint sprays. Washington, D. Methods for determining exposure to lacquer aerosols and solvent vapours during spray painting translated.

Gefahrstoffe Reinhaltung der Luft, 57 2 Neurobehavioral changes among shipyard painters exposed to solvents. Archives of Environmental Health, Organic solvent-induced encephalopathy in industrial painters. Journal of Occupational Medicine and Toxicology, International Archives of Occupational Environmental Health, Anon The risks of inhaling car spray-painting fumes.

South African Medical Journal, 87 3 Wear, The role of high positive friction HPF modifier in the control of short pitch corrugations and related phenomena. Wear, : The basic study on friction control between wheel and rail Experiments by test machine and scale model vehicle.

Gothenburg, Sweden, , Vol. II, pp Eadie DT and Santoro M Top of rail friction control for curve noise mitigation and corrugation rate reduction. Journal of Sound and Vibration, Kalousek J and Johnson K L An investigation of short pitch wheel and rail corrugations on Vancouver mass transit system. Top of rail friction control: lateral force and rail wear reduction in a freight application. International Heavy Haul Association Conference. Dallas, Texas, May Top of rail friction control with locomotive delivery on BC Rail: Reductions in fuel and greenhouse gas emissions.

Nashville, Tennessee, September Journal of Coatings Technology. Dynamic uniaxial extensional viscosity DUEV effects in roll application: Rib and web growth in commercial coatings. Journal of Rheology, 32 2 Model elastic liquids with water-soluble polymers. AIChE Journal, 44 6 However, the majority of research in this area has focused on Newtonian liquids despite the recognized industrial importance of spraying non-Newtonian liquids, particularly those that exhibit viscoelastic properties.

In the railway industry, for example, an increasing number of railway operators are adopting the use of liquid friction modifiers FM for controlling frictional instabilities at the wheel-to-rail interface. Air-blast atomizers are often used to apply these liquid FMs onto the rail head to derive benefits such as improved fuel economy and reduced wheel and rail wear, without adversely affecting train braking or traction [].

However, like many paints and industrial coatings, liquid FMs also contain polymers and solids, thus making them viscoelastic [18]. As such, they are expected to atomize differently than Newtonian liquids owing to their ability to develop significant extensional viscosities when exposed to the extension-dominated flow fields generated by spray nozzles [19,20]. Rheologists have observed that the extensional viscosity exhibited by polymer solutions is usually an increasing function of the extensional rate and strain [], behavior known respectively as extension-thickening and strain-hardening [24].

The maximum Trouton ratio ratio of extensional to shear viscosity for these solutions can be more than one order of magnitude greater than the Newtonian inelastic value of 3 [25]. Hence, liquid elasticity, through the extensional viscosity, will play an important role in controlling breakup. In viscoelastic atomization research, aqueous polymer solutions are commonly used as test liquids because they are easy to formulate [26] and can exhibit extensional viscosities proportional to the polymer molecular weight and concentration [21,22].

These liquids are then atomized and a set of indicators are chosen, such as the mean droplet diameter or the jet breakup length, to represent the extent of atomization. Collectively, researchers 'A version of this chapter will be submitted for publication in Atomization and Sprays.

For example, Mansour and Chigier [21] atomized a series of polymer solutions using an air-blast atomizer, and found that elasticity promoted ligament stretching prior to droplet formation. Ligament stretching was attributed to normal stress development owing to molecular reorientation. Mun et al [20] employed agricultural sprayers to assess the impact that polymer additives had on atomization quality. Dexter [27] reported that the mean droplet diameter of a polymeric spray correlated more strongly with extensional viscosity than with shear viscosity.

A similar conclusion was reached by Ferguson et al [19], who evaluated the influence of polymer type, molecular weight, and concentration on atomization. Harrison et al [28] examined the effect of polymer rigidity on the cone angle of viscoelastic sprays.

They discovered that the spray produced from the solution containing the most flexible polymer in their study collapsed at the lowest concentration. Such behavior was attributed to increases in extensional viscosity induced by the added polymer flexibility, which caused a more detrimental effect on atomization at equivalent concentrations. Meanwhile, the ability of elasticity to suppress satellite droplet formation has attracted numerous industrial applications. For example, Chao et al [29] and Johnson et al [30] reported that by introducing high molecular weight polyisobutylene PIB into aircraft fuel, an anti-misting effect was established that minimized post-crash fire dangers.

Smolinski et al [31] and Marano et al [32] added PIB in machining oil to suppress unwanted misting during metalworking operations. Finally, Hartranft and Settles [33], Glass et al [18], and Stelter et al [34] all concluded that elasticity stabilized liquid sheets formed from airless paint sprayers. Previous studies in this area have often relied on extension-thickening liquids that were also strongly shear-thinning.

In order to systematically isolate and investigate the effect of elasticity, test liquids with common, rate-independent shear viscosities, but adjustable extensional viscosities were employed. Based on the work of Mun [22], these model elastic liquids belong to the Boger class [35] and were constructed by dissolving polyethylene PEO into a glycerin-water solvent. Flash photography was used to elucidate breakup details. Next, the air-blast atomizer and the accompanying liquid and air flow systems are detailed.

Extensive literature exists on PIV and shadowgraphy, so for brevity, only an overview of these measurement techniques is presented. When not in use, they were individually stored in air-tight containers to minimize evaporation, water absorption from the ambient air, and contamination. Table 2.

PEO is a linear, flexible, and water soluble polymer. In the present study, the concentrations at which PEO was introduced corresponded to the dilute regime according to criteria set out by Flory [36]. They were prepared by gradually dissolving PEO powder into distilled water under gentle magnetic stirring over a 24 hour period.

Because flexible polymers like PEO are susceptible to mechanical degradation [26,37], care was taken to avoid excessive agitation. Next, USP grade glycerin Due to the limited thermal stability of PEO [26], liquids were characterized and sprayed within 2 week of preparation, but after at least 48 hours since final PEO addition to allow for complete polymer solubility.

The inelastic test liquids were constructed using glycerin and distilled water. Their rate-independent shear viscosities were adjusted by varying the relative glycerin concentration. In total, five inelastic liquids were prepared, with shear viscosities ranging from 0.

Likewise, the shear viscosities of the inelastic liquids were also constant over a similar range of shear rates, with the magnitudes increasing as a function of glycerin concentration. To assess the extent of PEO degradation caused by mechanical processes upstream of the atomizer, namely pumping and flow through supply lines, additional shear viscosity measurements were conducted on elastic samples collected after they had flowed through the spray system air-blast deactivated.

Results confirmed that the shear viscosities of the elastic liquids before and after flowing through the spray system were similar see Appendix A , suggesting minimal PEO degradation. Thus, the shear viscosities measured before the spray tests were representative of those exhibited by the liquids during atomization. Equilibrium surface tensions were measured using a du Notiy ring; the measurement procedure and raw data can be found in Appendix B.

Surface tensions ranged from These values are consistent with published data [38,39] and confirm the fact that PEO is slightly surface active [40]. Although much care was taken in handling the test liquids, surface tension measurements before and after the spray tests air-blast deactivated 56 revealed a small but measurable drop maximum of 5.

Moreover, at the high aerodynamic Weber numbers in the present study, surface tension has only a weak influence on the development of interfacial instabilities on the liquid jet [11,41]. A s a result, the oi variations across the test liquids were considered insignificant. Liquid densities were measured using a standard ml density cup. In their air-blast atomization experiments, Lorenzetto and Lefebvre [6] showed that liquid density variations between 0.

Thus, the relatively small density variations exhibited by the test liquids, owing to the different glycerin concentrations needed to achieve the desired shear viscosities, were considered insignificant. M u n [22] characterized the extensional behavior of the three elastic liquids using the Rheometrics R P X , a commercial extensional rheometer of the opposed-jet type Fuller et al [42]. It must be emphasized, though, that like most extensional rheometers, the R F X reports an apparent extensional viscosity value owing to its inability to sustain a uniform strain and strain rate throughout the liquid sample.

Moreover, the R F X also suffers from corrections pertaining to inertia [43] and viscous losses [44]. Nevertheless, despite these shortcomings, there is general support for the R F X ' s ability to reveal qualitative differences in elasticity for dilute polymer solutions [22,44,45]. This is shown in Figure 2. This Reynolds number is thus a measure of the apparent extensional rate. This implies that the K sample was more elastic than the K sample.

The shear flow curve conformed to a power-law model, as shown in Figure 2. Note that these OL values are far lower than those of the test liquids in Table 2. Although these measurements were conducted within the linear viscoelastic regime, where deformations are much smaller and slower than those expected in an atomizer, the results still confirm the elastic nature of K E L T R A C K HiRail. Moreover, in Appendix A : Figure A.

Attempts at measuring the extensional viscosities of the elastic PEO liquids were unsuccessful owing to their exceptionally low shear viscosities. It is based on a commercial paint sprayer and is currently employed by a number of railway operators for applying liquid F M. The original atomizer made use of a rubber-duckbill see Figure 2. However, most of the present research was conducted using a modified version of this original atomizer, one which had the tip of the rubber-duckbill removed.

This was done to overcome the challenges in calculating the liquid velocity and Reynolds number caused by the variable, elliptical flow area of the duckbill. Reliably measuring this area was difficult due to the flexible nature of rubber and visual hindrance imposed by the liquid stream. Removing the duckbill altogether was considered, but owing to the desire to maintain the same annular air orifice area, only the tip was cut off flush with the exit plane of the atomizer. Figure 2.

The inner diameter of the round liquid orifice Dj is 1. In order to keep its orifices clean, this atomizer employs the use of purge air. Five diametrically-opposed holes see Figure 2. By means of an external shroud, the diverted air was aimed back at the atomizer orifices to clear away residual liquid buildup. Although effective in practice, this geometry complicates the calculation of the atomizing air velocity under sub-sonic conditions owing to the unknown mass fraction split between the purge air and atomizing air.

Sprayed liquids were collected in a tray placed approximately 1 m below the atomizer. The liquid flow was supplied by a gear pump, and measured using a graduated cylinder and stopwatch; this was confirmed during the spray tests with continuous balance readings.

Liquid and air supply connections to the atomizer were made with flexible polyethylene tubing to minimize vibration transfer. Sketches of the liquid and air supply connections are shown in Figure 2. Its principles and development over the past twenty years have been described and reviewed by Adrian [47], Keane et al [48], and Raffel et al [49]. The general idea is to illuminate tracer particles in a flow field with two short pulses of a planar light sheet, during which two corresponding images are recorded over a known time separation.

These image-pairs IP are then divided into interrogation areas IA and processed by a cross-correlation algorithm to obtain the average particle displacement in each IA. By knowing the time separation over which this displacement occurs, the average velocity is calculated; this procedure is then applied to every IA in the image domain to produce an entire velocity field.

In the present application of PIV, the tracer particles were simply droplets produced by the atomizer. Appendix E outlines the experimental setup and procedures. In brief, a dual-head, frequency-doubled N d : Y A G laser nm; max. The laser pulses were synchronized to the CCD camera through a pulse generator, while the laser-sheet optics were mounted on a linear rail to ensure consistent alignment. A l l of the experiments were performed in a dark room to minimize optical noise from ambient lighting.

This value was chosen based on considerations such as resolvable spatial resolution, adequate droplet number-density, and velocity dynamic range. Image-pairs were processed using an adaptive-correlation algorithm embedded in Dantec's FlowManager software [50]. Adaptive-correlation improves upon conventional cross-correlation by allowing successive size reductions and offsets in the IA over multiple evaluation iterations.

The amount by which an IA is offset is determined from an initial velocity estimate calculated by using cross-correlation. The result is increased spatial resolution without sacrificing velocity dynamic range. More importantly, in sprays, where droplet sizes and number-densities are often non-uniform, an adaptive algorithm increases the number of true correlations by relaxing the minimum droplet number requirement of 10 per IA such that it applies instead to the initial IA, which can be made large to capture more droplets.

Image-pairs were processed using an initial IA size of 64 H x V pixels, corresponding to A single iteration step was applied to arrive at a final IA size of 32 x 64 pixels or 5. The resultant raw vector maps were subjected to a validation procedure to detect and replace spurious velocity measurements. These criteria were selected by carefully examining numerous raw vector maps, in which the velocity bounds were gradually narrowed from initially large values until a majority of the unphysical vectors having unrealistically large velocities situated outside the spray boundaries were rejected.

Of course, care was taken not to eliminate vectors of reasonable magnitude and direction appearing within the spray boundaries. Next, a moving average filter was applied to identify vectors that deviate by more than a prescribed amount from the average of the adjacent 3 x 3 window vectors.

Vectors detected as spurious were then replaced with the local average of the accepted adjacent vectors. To avoid peak-locking effects, droplet image diameters were verified to be more than 2 pixel-pitches wide [49]. The total relative uncertainty cou associated with a PIV velocity measurement can be calculated by summing the variances of the known error sources [51]: temporal error, scale error, peak location error.

Scale error is due to the uncertainty 8scale in transforming the camera pixel coordinates to physical dimensions scale , and its contribution was 0. Peak location error arises from the uncertainty 8X in locating the displacement peak A X within the correlation plane. Most modern correlation algorithms can achieve sub-pixel resolution by least squares fitting a 2-dimensional Gaussian function to the displacement peak.

Time and length scales within a spray vary considerably depending on their spatial locations, leading to difficulties in extracting velocity information of the entire spray from a series of image-pairs captured over a set time separation. This is because the 67 relative uncertainty in locating the displacement peak varies over the spray domain and is highest near the spray boundaries where droplets travel at low velocities and undergo small displacements.

As a result, the time separation of 38 us chosen for the ensuing tests was optimized for resolving axial droplet velocities at the spray centerline. For proper statistical representation of the spray, a sufficient number of image-pairs must be acquired. Preliminary testing has revealed that a minimum of 70 IP are needed in order to stabilize the mean axial centerline MACL droplet velocity to within experimental uncertainty; this convergence criterion was valid for all the test liquids and at every injection condition.

Therefore, to obtain an accurate representation of the dynamic behavior of the spray while complying with time and data storage limitations, image-pairs were captured for each test run. A typical backlit setup was used, in which the spray was situated between the light source and camera such that liquid droplets and ligaments appeared dark on a bright background [53].

This technique, referred to as shadowgraphy, has been used in various forms over the past fifty years []. Appendix G describes in detail the calibration, image analysis, and measurement procedures. Basically, a high intensity light source with a short pulse duration P A L F L A S H was used to illuminate and "freeze" droplets in mid-flight while a camera PCO Pixelfly digital CCD; H x V pixel; 12 bit , situated directly opposite to the light source, captured shadowgraphs through a far-field microscope Navitar 12X zoom.

The camera position was adjusted using a 3-axis traverse with an accuracy of 10 um in the radial directions x, y and 25 um in the axial direction z. In order to resolve droplets as small as 10 urn in diameter, an image conversion factor of 0. A minimum droplet diameter of 10 pm was chosen because droplets that are any smaller will evaporate quickly and represent only a small fraction of the total liquid volume in the spray. The depth-of-field was estimated by traversing a transparent slide, on which a circle of known diameter was printed, along the camera axis and through the measurement volume.

The depth-of-field was measured to be about 1 mm. Recorded shadowgraphs were processed digitally using a multi-step thresholding algorithm La Vision, SizingMaster software , through which droplets situated within the measurement volume were differentiated from the background and from out-of-focus droplets based on contrast differences see Appendix G for details on this thresholding procedure.

Deciding whether or not a droplet is in focus is subjective. To this end, through a meticulous trial-and-error process, it was ensured that only droplets lying within the abovementioned measurement volume were accepted for size calculations. Droplets were sized by having their occupied areas on the shadowgraphs computed, from which equivalent spherical diameters were assigned based on the image conversion factor.

In the present study, droplet sizing results are presented using the arithmetic mean diameter Dw and the volumetric median diameter VMD , both measured at nine spatial locations in spray, as depicted in Figure 2. Due to light attenuation effects, all of the shadowgraphs were recorded at a downstream distance z of In this far region, the local droplet Weber number was on the order of 10"2, even for the larger droplets, which meant that secondary atomization was not expected.

Although each shadowgraph represents a spatial-average, instantaneous-time measurement, multiple images were recorded and analyzed to provide time-average statistics. Depending on the test liquid and flow rate, anywhere from to droplets were analyzed at each sampling location. Assuming high-quality images are captured and proper calibration procedures are performed, the accuracy of the shadowgraphy technique is limited by the number of pixels a droplet occupies in the image.

In this sense, it is advantageous to use a very small field-of-view in order to allocate as many pixels as possible to a single droplet. However, given the need to acquire a sufficient number of droplets for reliable statistics, a compromise is usually made that allows for the mean droplet diameter to span at least 20 pixels. Unless otherwise noted, the atomizing air pressure PA was kept constant at It should also be mentioned that the effective area through which the purge air flows just before contacting the atomizer orifices is actually larger than both A and AATOMI!

I in fact, about 45 times larger. Consequently, the purge air velocity is much lower than the atomizing air velocity and should not affect atomization. In the present study, the liquid Reynolds number ReL varied between 5. The air-liquid mass ratio ALR and the momentum flux ratio M ranged from 1. The characteristic shear viscosity used in calculating the ReL for K E L T R A C K HiRail was chosen based on the wall shear rate y experienced inside the liquid orifice; for a non-Newtonian liquid with a power-law index, n, this is given by [24]: 2 75 Although the action of the atomizing air will subject the liquid to additional shear, it is difficult to estimate the extent of this effect owing to the complex flow fields.

As such, the characteristic shear viscosity calculated based on the instantaneous wall shear rate should only be taken as an approximation. The goal is to compare the breakup features of these various liquids, and to observe changes induced by differences in the shear viscosity and elasticity.

A rise in ns by two orders of magnitude from 0. This observation is consistent with previous Newtonian droplet size measurements [6,20]. Furthermore, water, 50 wt. The appearance of this mode is marked by an extremely short jet breakup length, combined with periodic pulsations that lead to temporal and spatial fluctuations in the droplet number-density within the spray. In fact, this pulsating behavior can be seen more clearly in the PIV images in the form of oblique wave patterns.

These are shown in Figure 2. Note that these are planar images representing only a two dimensional slice of the spray. Focusing back on the breakup photographs in Figure 2. The liquid stream remained intact and underwent erratic excursions away from its centerline. Radial motions appear to be induced by large-scale turbulent structures. As mentioned earlier, 50 wt. In contrast, all three of the elastic PEO liquids displayed filamentary structures containing large-scale ligaments.

The physical scale of these ligaments increased with PEO molecular weight, and hence elasticity. For K and K PEO, spherical droplets were often observed at the ends of the ligaments, indicating the onset of pinch-off. The ligaments appear to have experienced significant stretching at high elongational rates; these high rates-of-strain were deduced from the short time-scales inherent to the atomization process.

As a result, it is believed that, through molecular reorientation and stretching, the extension-thickening behavior exhibited by these elastic ligaments induced additional tensile stresses in their cross-sections, which enhanced their stability against capillary forces. Discrete droplet formation was delayed until farther downstream where relative air-liquid velocities were reduced. So, in agreement with findings of Mun et al [20] and Mansour and Chigier [21], liquid elasticity is predicted to increase droplet sizes.

Note the presence of large-scale ligaments, filamentary structures, and a membrane center of image. Therefore, in spray coating, the diameter of a droplet is one of the main factors determining whether it will deposit onto the target surface or be carried away by the surrounding air jet.

In view of this, droplet size measurements were performed on three inelastic liquids water, 50 wt. The results for water are presented and discussed first because they are the simplest to understand. Radial Dio profiles for water are shown in Figure 2. Several observations can be made at this point. Higher Dio values were measured near the spray periphery. This observation has been reported by other researchers [34,41,58,59].

Eroglu and Chigier [8] noted from their air-blast atomization research that the flapping motion of the unstable liquid jet can launch droplets radially away from the spray centerline. Thus, larger droplets are expected to continue farther along in their initial trajectory owing to their increased inertia [58]. Although the air-blast atomizer used in the present work did not incorporate swirl in its design, high-speed videos captured of water and other liquids revealed swirling motions in the spray as evidenced by helical droplet trajectories.

The origin of these swirling motions is unclear but the resultant centripetal forces may cause larger droplets to migrate farther towards the spray periphery than smaller droplets. The RMS deviation of the Dw also exhibited higher values near the spray periphery, though this was attributed mainly to reduced droplet numbers. This result was expected since it is well established that reducing the ALR from 2.

From the work of Eroglu et al [60], it has been shown that increasing the momentum in the liquid stream results in a longer jet breakup length and, hence, larger droplets. For example, from inspection of Figure 2. Similarly, in Figure 2. In general, the spray appears to be skewed significantly towards the negative x and negative y directions.

These observed asymmetries are actually quite common in atomizers of such small dimensions and have been reported to varying degrees elsewhere [58,61,62]. They are presumably the result of geometric asymmetries in the atomizer orifices. Moreover, optical and vernier-caliper measurements confirmed the presence of some eccentricity in the present annular air orifice. The magnitude of this eccentricity, however, was difficult to quantify accurately because of the erratic dimensions of the flexible rubber-duckbill base - a rough estimate of 0.

O Q 30 - 1 0 0 1 0 Radial Position: x [mm] Figure 2. O o 30 - 1 0 0 1 0 Radial Position: y [mm] Figure 2. A misaligned liquid tip creates an eccentric annular air orifice, which causes the emerging liquid stream to deflect towards a preferential direction due to pressure differences in the air. In other words, the spatial distribution of liquid around the circumference of the liquid orifice becomes non-uniform.

However, owing to the high relative air-liquid velocities, a similar droplet size distribution is produced everywhere locally, regardless of tangential position. These droplets are then transported downstream in a manner that still reflects the initial non-uniform liquid volume distribution. In this way, the Dio values can remain spatially symmetric, while N and the droplet volume become dependent on tangential position. If the droplet volumes reported in Figure 2.

This level of variation is unsurprising given that the spatial distribution of liquid within the spray probably shifts as the liquid flow rate is changed. The global droplet volume ratio, DVRglobal, was 2. To further substantiate the quality of the measurements, the volume flux at each sampling location was calculated using data provided by PIV velocity measurements presented in the following sections.

These fluxes were then used to provide a crude estimate of the liquid flow rate, to which balance measurements were compared. Measurements at radial distances of 0 mm centerline , The total liquid flow rate in the spray was then computed by summing up the contributions from the nine sampling locations. The estimated flow rate for water was The one that is most likely to draw criticism is the assumption that very little liquid volume is distributed beyond a radial distance of The weakness in this assumption, however, is alleviated somewhat by recognizing that the mean axial droplet velocity at a radial distance of The Dw, total droplet volume, and total N at the two liquid flow rates are plotted in Figure 2.

Moreover, Table 2. The remainder of the droplet sizing results, including number and cumulative volume distributions, can be found in Appendix G. Most of the test liquids exhibited qualitative Dio characteristics resembling those of water, in that the Dio increased with radial position and liquid flow rate.

Inspecting the N and droplet volume distributions for the glycerin and PEO solutions shows that the previously observed asymmetries are less apparent at higher shear viscosities and elasticities. This was, however, not observed in the present study. By examining Table 2. Such behavior contradicts previous findings [1,2,6,20], including those inferred from breakup visualization in Section 2.

Because large droplets contain most of the liquid volume, they are relatively few by number. Therefore, the probability for a large droplet to pass through the spatially-fixed measurement volumes is lower than that for a small droplet. To put it another way, because the total cross-sectional area of the measurement volumes is small relative to that of the spray, the likelihood of an odd large droplet passing through, as opposed to between, the sampling locations is low.

The implication is that results for the viscous glycerin and elastic PEO liquids may be representative of only the smaller droplet size classes. Support for this hypothesis can be found by examining the droplet volume Figure 2. At equivalent liquid flow rates, an increase in shear viscosity from 0.

The same behavior was demonstrated by the PEO liquids through an increase in elasticity 50 wt. Since both shear viscosity and elasticity increases have been known to suppress satellite droplet formation [1,2,20,27,], it is believed that the Dw and droplet volume discrepancies were attributed to a statistically-induced exclusion of the larger droplets, rather than the smaller droplets.

This effect may be combined with the possibility that the spatial coverage of the sampling locations was inadequate, thereby allowing a significant number of the larger droplets traveling beyond a radial distance of There were, however, virtually no ligaments observed in the shadowgraphs of K and K PEO; the ligaments depicted in Figure 2.

In contrast, K E L T R A C K HiRail displayed ligaments on several occasions; they were in various shapes, sizes, and orientations, often interspersed with smaller droplets, as shown below in Figure 2. This result agrees with the expectation that elasticity increases droplet sizes. For instance, imagine a ligament shaped like a cylinder. If this ligament is imaged with its axis facing the camera, the resultant shadowgraph reveals a circular object and the sizing algorithm attempts to assign an equivalent diameter not knowing that this ligament may have an aspect ratio much larger than unity.

Consequently, the reported diameter tends to underestimate the actual ligament volume. Conversely, i f a thin membrane is imaged with its plane facing the camera, then the reported diameter tends to overestimate the actual volume. These biases aside, it is believed that because a large fraction of the total K E L T R A C K HiRail volume resided in the form of ligaments, as opposed to spherical droplets, the probability of them or a section of each ligament appearing clearly enough within the measurement volumes to be recognized and sized was comparatively higher than that of the glycerin and PEO droplets.

Additionally, there could also have been a re-distribution of the K E L T R A C K HiRail volume within the spray boundaries that allowed for more droplets and ligaments to pass through the sampling locations. Support for this hypothesis can be found in the droplet volume measurements Figure 2. In view of the proposed statistically-induced exclusion of the larger droplets containing the bulk of the liquid volume as the cause of the unphysical DW values, it is more appropriate to employ a representative diameter based on the droplet volume than on the droplet number.

Hence, the volumetric median diameter VMD is considered. From Figure 2. Although the VMD for 50 wt. It is reminded that the quantitative accuracy of these V M D values is still suspect owing to the exclusion of a significant fraction of the total liquid volume in the measurements. Accordingly, the M A C L droplet velocity is presented here as a function of the downstream distance from the atomizer orifice z. In the near region of the spray, the droplets, regardless of their size, are slower than the carrier air jet and will accelerate under the influence of viscous and pressure forces.

However, the magnitude of this acceleration depends, in part, on the droplet size. Smaller droplets will experience stronger accelerations because of their higher drag-to-momentum ratios. For simplicity, i f Stokes' drag law is applied, then the acceleration of a droplet is inversely proportional to the square of its diameter. In our tests, droplet velocities in the near region could not be resolved because the spray was too dense.

Eventually, the droplets will reach a peak velocity as the relative velocity between them and the carrier air is reduced. Larger droplets, owing to their increased inertia, tend to overshoot the velocity of the carrier air [41], while the smaller droplets are able to relax quickly, following the air with minimal overshoot.

Because the overshoot for large droplets occurs at relatively far downstream distances and after the carrier air velocity has had an opportunity to decay, the peak velocities reached are generally lower than those of smaller droplets.

Farther downstream, larger droplets can better preserve their initial momentum, traveling longer distances before eventually settling to the carrier air jet velocity. Results for 90 wt. The apparent asymmetries in the droplet volume distribution observed earlier were absent in the PIV images. The mean axial droplet velocities U were fairly symmetric with respect to the spray centerline. Radial profiles of U became self-similar past a certain downstream distance from the atomizer, and displayed a typical Gaussian distribution; a sample of the non-dimensional axial velocity profile is shown in Figure 2.

A l l of the other test liquids exhibited a similar profile, zo refers to the virtual origin and was found by fitting the following linear correlation function to the droplet deceleration curve: Uc is simply the M A C L droplet velocity at the z axial station, while B is the deceleration constant.

The shape of the non-dimensional axial velocity profiles was consistent with the results of Vega et al [58], who used a Phase Doppler Particle Analyzer to measure the axial velocity of water droplets produced from an air-blast atomizer. Also plotted on Figure 2. To assess the influence of the atomizer orientation on droplet velocities, several PIV tests were conducted with the atomizer rotated at random tangential positions.

No significant differences in mean droplet velocities were found. The most viscous liquid, 80 wt. Lorenzetto and Lefebvre [6] have noted that increasing the shear viscosity leads to larger droplets. It is hypothesized that here the larger 80 wt. From breakup visualization in Section 2.

Consequently, a common M A C L droplet velocity decay implies that droplet sizes and velocities were uncorrelated for these inelastic liquids at far downstream distances. A l l three of these liquids exhibited similar shear viscosities, surface tensions, and densities; they differed primarily through elasticity.

As noted from Figure 2. Over the entire downstream distance range examined, elastic PEO droplets were consistently faster than the inelastic 50 wt. This suggests that the elastic droplets, owing to their significantly greater size and inertia, were better able to maintain their initial momentum against decelerating drag forces and were unable to relax fully to the carrier air jet velocity within the image domain. This configuration is of industrial importance because it is used by railway operators for F M application.

As depicted in Figure 2. The RMS deviation of the M A C L droplet velocity also increased with atomizing air pressure; this was likely due to enhanced turbulent fluctuations, and the production of smaller droplets, which were better able to follow those fluctuations. AlChE Journal, AIAA Journal, 15 7 II, pp Polymer complexation effects in extensional flows. Journal of Rheology, 37 6 : AlChE Journal, 44 6 AlChE Journal, 30 1 : AlChE Journal, 42 5 : Journal of Applied Polymer Science, 4 10 Dean JA Kim M W Surface activity and property of polyethylene oxide in water.

Extensional viscosity measurements for low-viscosity fluids. Journal of Rheology, 31 3 Adrian RJ Twenty years of particle image velocimetry. Theory of cross-correlation analysis of PIV images. Applied Scientific Research 49 3 : The effect of a discrete window offset on the accuracy of cross-correlation analysis of digital PIV recordings.

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For time-controlled atomization or printing, a pulse air jet system was implemented to print liquids only when it is demanded, and it was shown that the period of atomization can be controlled by the air jet on-and-off. The inertial coating process was studied to explain the dynamic meniscus profile, compared with static meniscus. Kinematic analysis of the needle motion was performed, which shows that the needle motion is a sinusoidal one undergoing inertial coating.

Liquid sheet breakup mechanism in the presence of the air stream was also studied in conjunction with the principle of the air- blast atomizer. Performing as a printing device or a droplet generator, the reciprocating needle printing method studied here can be applied to printing or coating processes which utilize high viscosity media. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission.

See provided URL for inquiries about permission. Department of Mechanical Engineering dc. Name: MIT. Search DSpace. This Collection. The numerical investigations reveal a clear picture, how the SMD is going to vary along the axial and radial distances.

And also they predicted the swirl number variation on the atomization and results shows when the swirl number increases the SMD also increases. Jyotichandra and S. Kihm and N. Following changes have made to predict the SMD. They used convergent nozzle which gives mach 0. And finally results shows there is no mush effect of shock wave on atomization and suggest to use supersonic configuration.

In this study Airblast atomizer configuration is used for primary atomization and TAB model for secondary atomization. The SN-Type nozzle design and Fluent Obtained results are validated against the known experimental results carried out by B.

Lee et. Figure 3. It consist of 2 co-axial tubes, inner is for liquid and outer for the gas. The inner tube having dia 4mm is. The Figure 3. The water passes through the inner tube and nitrogen gas through the SN-Type nozzle. The outer domain is of X mm, surface sweep is used to create the domain. Boundary conditions used are the mass flow for liquid and pressure inlet for the nitrogen gas, the outflow imposed to atmospheric condition, other all wall.

The computational domain considers here only section, by imposing the periodic condition for the side surfaces and x-axis is considered as rotational axis and flow direction. The governing equations used for the simulation are: the continuity, the momentum and the energy equations along with the equations for turbulence, species transport and discrete phase model.

RNG K-epsilon turbulence two equation model is used to predict the droplet distribution with the scalable wall function as near wall treatment, the RNG k-epsilon is predict very good results then standard and Realizable. The Airblast atomizer injection configuration is used for the primary atomization and TAB with dynamic drag for secondary atomization.

The number of particle streams considered as 60, start time and end time as 0 and respectively by assuming spray is continuous, flow rate is 0. The coupled with Pseudo transient is enabled with the standard interpolation scheme for pressure, second order scheme for the density and momentum and first order. The solution is considered to be converged when the residual value falls below the order of 10e-3 and surface, volume monitors flatten with mass balance.

The Figures 5. The numerical results obtained from the analysis for variation of SMD along radial direction due to effect of pressure 0. The comparison shows numerical results are very good agreement with the experimental results. Figure 5. The following figure 5. The results are obtained from the CFD by applying the experimental condition to the computational model with radial distribution distance 55mm, were measured for three different liquid flow rates, pressure and at axial locations.

The examination of individual parametric effects on the atomization as follows. Figure 6. As the injection pressure increases, the spray SMD decreases noticeably. As radial distance increases the gas velocity decreases by mixing it with the entrained air and the pressure reduces to the ambient level.

And hence the SMD gradually increases in the radial direction. Since the injection pressure is constant for all cases, gas flow rate remains unchanged. For same gas injection pressure if liquid flow rate increased which reduces the gas-to-liquid mass ratio GLR , and this decreasing GLR increases the drop SMD because of the reduction in shear energy per unit amount of the atomized liquid. Larger droplets tend to move away from the centreline along with the spray because of their larger inertia-to-drag ratios.

This depletion of larger drops can contribute to the gradual SMD decrease in the spray centre, whereas the same depletion will contribute to the SMD increase at the spray edge along increasing axial location. Atomization characteristics of a single combination of twin fluid, water as fuel and nitrogen as a atomizing gas, were studied for SN-Type nozzle.

Blast thesis air atomizer definition of thesis abstract

AVL FIRE Air-blast air assisted injection

The break-up of fluids in associating triblock copolymer solutions. M u n [22] characterized associated with a PIV velocity trajectories would be valuable, especially summing the variances of the flow area of the duckbill. The laser pulses were synchronized to accelerate the deposition of hinder the ability of the i f left unattended, can. Moreover, in Appendix A : and burning of liquid fuel. However, of the investigators who relative uncertainty in locating the desire to maintain the same liquids, and independently varying the and strain [], behavior known as measured by the ductless. Mannheimer RJ Rheological and mist liquid sheets. Next, a moving average filter in handling the test liquids, the spray coating industry, and highlights some of the key reasons why research in this area should continue to progress. Based on the work of Mun [22], these model elastic liquids belong to the Boger with time and data storage near the spray boundaries where onto the railhead. Sketches of the liquid and the calibration, image analysis, and Image Velocimetry, respectively. Journal of Occupational Medicine and achieve sub-pixel resolution by least [26,37], care was taken to atomization of liquids.

generation in the airblast atomizers, which is the main subject of this thesis, but also in a wide range of technical and industrial. characterize advanced injection systems usually based on prefilming airblast configurations. This is the main subject of this dissertation. Influence of liquid properties on airblast atomizer spray characteristics (3rd Edition), Ph.D. Thesis, School of Mechanical Engineering.