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1
Hardalupas, Y., and J. H. Whitelaw. "Interaction Between Sprays From Multiple Coaxial Airblast Atomizers." Journal of Fluids Engineering 118, no. 4 (December 1, 1996): 762–71. http://dx.doi.org/10.1115/1.2835507.
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Phase Doppler measurements of size, velocity, liquid flux, and average mass fractions were obtained in sprays produced by three identical coaxial airblast atomizers, with their axes placed in a triangular arrangement at distances of two air jet diameters from each other; the arrangement simulates the spray interaction in the preburner of the space shuttle main engine with water and air respectively replacing the liquid oxygen and hydrogen of the preburner sprays. Each nozzle comprised a liquid jet with exit diameter of 2.3 mm centred in a 8.95 mm diameter air stream. Two liquid flowrates were examined, while the air flowrate was kept constant, resulting in Weber number at the exit of the nozzle around 1100, air-to-liquid momentum ratio 8.6 and 38, velocity ratio 24 and 51, mass flowrate ratio 0.35 and 0.75, liquid jet Reynolds number 10,000 and 21,000 and air jet Reynolds number around 108,000. The air flow characteristics were compared to the flow without liquid injection. Up to 10 air jet diameters from the nozzle exit, individual spray characteristics dominated and maximum Sauter mean diameters, typically around 150 μm, and liquid flux were observed on the geometrical axes of the nozzles. Spray merging was strong in the region between the nozzle axes, where the Sauter mean diameter reduced and the liquid flux and the mean and rms of the fluctuations of the axial velocity of the droplets and the air flow increased relative to the single spray. Downstream of 25 air jet diameters from the nozzle exit, the multiple sprays merged to a single spray-like flow produced by a nozzle located at the centre of the triangular region between the nozzle axes. Reduction of the liquid flowrate by 50 percent, improved atomization by 25 percent, shortened the axial distance from the nozzles where the individual spray characteristics disappeared by 30 percent and increased the air flow turbulence by 20 percent. Droplet coalescence was negligible for high liquid flowrates, but for reduced liquid flowrates coalescence became important and the Sauter mean diameter increased with the axial distance from the exit by around 15 percent. Spray merging increased the air flow turbulence and the local mass fraction distribution of the air in the region between the nozzle axes by around 50 and 40 percent respectively relative to the single sprays, resulting in a fuel rich region with increased gas flow turbulence which may influence the ignition process in the preburner of the space shuttle main engine.
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Utepov, Burxon, Tuygun Khaydarov, Nurmamat Rajabov, Gulnoza Murtazayeva, Bakhtiyor Tulaganov, and Mirzoolim Avliyakulov. "Experimental studies of frequency of rotation of smooth rotating disk with coaxial-lateral air flow." E3S Web of Conferences 365 (2023): 04018. http://dx.doi.org/10.1051/e3sconf/202336504018.
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The article presents methods for determining the main parameters of a rotating atomizer sprayer. The choice of research methodology is justified based on the general pattern of liquid atomization by rotating atomizers, taking into account the influence of the air flow on them. The main indicators affecting the sprayed drops' dispersal are the air flow rate and the rotational speed of the pneumatic disk atomizer. Therefore, the correct choice of the method for determining the rotational speed ω of a pneumatic disk atomizer makes it possible, at a constant air flow rate, to obtain the required median-mass diameter of the atomized droplets. To obtain a high-quality air-droplet flow, there must be a combination between the initial speed of the main drops discharged from the spray disk's periphery and the fan installation's air flow speed.
3
Eroglu, H., and N. Chigier. "Initial Drop Size and Velocity Distributions for Airblast Coaxial Atomizers." Journal of Fluids Engineering 113, no. 3 (September 1, 1991): 453–59. http://dx.doi.org/10.1115/1.2909517.
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Initial drop size and velocity distributions, after complete disintegration of coaxial liquid jets, were determined by phase Doppler measurements. The measured radial distributions of Sauter mean diameter (SMD) were compared with the photographs of the disintegrating liquid jet. The SMD distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The results showed that SMD increases with increasing liquid supply pressure as well as with decreasing air supply pressure. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1–2 mm) downstream of the observed break-up locations. The droplets accelerated at these regions under the influence of the air velocity. Smaller droplets were found to reach higher velocities because of their larger drag-to-momentum ratio. In general, minimum droplet mean velocities were found at the center, and the maximum velocities were near the spray boundary. Size velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.
4
Zhang, Feichi, Simon Wachter, Thorsten Zirwes, Tobias Jakobs, Nikolaos Zarzalis, Dimosthenis Trimis, Thomas Kolb, and Dieter Stapf. "Effect of nozzle upscaling on coaxial, gas-assisted atomization." Physics of Fluids 35, no. 4 (April 2023): 043302. http://dx.doi.org/10.1063/5.0141156.
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Mass flow scaling of gas-assisted coaxial atomizers from laboratory to industrial scale is of major interest for a wide field of applications. However, there is only scarce knowledge and research concerning the effect of atomizer scale-up on liquid breakup and spray characteristics. The main objective of this study is therefore to derive basic principles for liquid jet breakup using upscaled nozzles to increase the liquid mass flow rate [Formula: see text]. For that purpose, atomizers with the same geometrical setup but increased sizes have been designed and experimentally investigated for [Formula: see text], 50, 100, and 500 kg/h, while the aerodynamic Weber number Weaero and gas-to-liquid ratio GLR have been kept constant. The primary jet breakup was recorded via high-speed imaging, and the liquid core length LC and the frequency of the Kelvin–Helmholtz instability fK were extracted. Applying these results as reference data, highly resolved numerical simulations have been performed to gain a deeper understanding of the effect of mass flow scaling. In the case of keeping Weaero and GLR constant, it has been shown by both experiments and simulations that the breakup morphology, given by a pulsating liquid jet with the disintegration of fiber-type liquid fragments, remains almost unchanged with the degree of upscaling n. However, the normalized breakup length [Formula: see text] has been found to be considerably increased with increasing n. The reason has been shown to be the decreased gas flow velocity vgas at the nozzle exit with n, which leads to a decreased gas-to-liquid momentum flux ratio j and an attenuated momentum exchange between the phases. Accordingly, the calculated turbulence kinetic energy of the gas flow and the specific kinetic energy in the liquid phase decrease with n. This corresponds to a decreased fKHI with n or [Formula: see text], respectively, which has been confirmed by both experiments and simulations. The same behavior has been shown for two liquids with different viscosities and at different Weaero. The obtained results allow a first-order estimate of the liquid breakup characteristics, where the influence of nozzle upscaling can be incorporated into j and Reliq in terms of n.
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Sivakumar, D., and B. N. Raghunandan. "Hysteretic interaction of conical liquid sheets from coaxial atomizers: Influence on the spray characteristics." Physics of Fluids 10, no. 6 (June 1998): 1384–97. http://dx.doi.org/10.1063/1.869663.
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Lefebvre, A. "Discussion: “Interaction Between Sprays From Multiple Coaxial Airblast Atomizers” (Hardalupas, Y., and Whitelaw, J. H., 1996, ASME J. Fluids Eng., 118, pp. 762–771)." Journal of Fluids Engineering 118, no. 4 (December 1, 1996): 645–46. http://dx.doi.org/10.1115/1.2835489.
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Hardalupas, Y., and J. H. Whitelaw. "Characteristics of sprays produced by coaxial airblast atomizers." Journal of Propulsion and Power 10, no. 4 (July 1994): 453–60. http://dx.doi.org/10.2514/3.23795.
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Hallstrom, Anders, and Jeffrey B. Danner. "SPRAYS FROM NOZZLES AND ROTARY ATOMIZERS." Atomization and Sprays 4, no. 3 (1994): 263–73. http://dx.doi.org/10.1615/atomizspr.v4.i3.20.
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Gavaises, M., and C. Arcoumanis. "Modelling of sprays from high-pressure swirl atomizers." International Journal of Engine Research 2, no. 2 (April 2001): 95–117. http://dx.doi.org/10.1243/1468087011545370.
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Tratnig, Andreas, and Günter Brenn. "Drop size spectra in sprays from pressure-swirl atomizers." International Journal of Multiphase Flow 36, no. 5 (May 2010): 349–63. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2010.01.008.
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Eroglu, Hasan, and Norman Chigier. "WAVE CHARACTERISTICS OF LIQUID JETS FROM AIRBLAST COAXIAL ATOMIZERS." Atomization and Sprays 1, no. 4 (1991): 349–66. http://dx.doi.org/10.1615/atomizspr.v1.i4.10.
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Sankar, S. V., K. E. Maher, D. M. Robart, and W. D. Bachalo. "Rapid Characterization of Fuel Atomizers Using an Optical Patternator." Journal of Engineering for Gas Turbines and Power 121, no. 3 (July 1, 1999): 409–14. http://dx.doi.org/10.1115/1.2818488.
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Planar laser scattering (PLS) and planar laser-induced fluorescence (PLIF) techniques are currently being used for rapid characterization of fuel sprays associated with gas turbine atomizers, diesel injectors, and automotive fuel injectors. These techniques can be used for qualitative, quantitative, and rapid measurement of fuel mass, spray geometry, and Sauter mean diameters in various sprays. The spatial distribution of the fuel mass can be inferred directly from the PLIF image, and the Sauter mean diameter can be measured by simultaneously recording the PLIF and PLS images and then ratioing the two. A spray characterization system incorporating the PLS and/or PLIF techniques has been loosely termed an optical patternator, and in this study, it has been used to characterize both steady and pulsed sprays. The results obtained with the optical patternator have been directly validated using a phase Doppler particle analyzer (PDPA).
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Kumar, Abhijeet, and Srikrishna Sahu. "Liquid jet breakup unsteadiness in a coaxial air-blast atomizer." International Journal of Spray and Combustion Dynamics 10, no. 3 (March 22, 2018): 211–30. http://dx.doi.org/10.1177/1756827718760905.
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The aim of this paper is to experimentally characterize the liquid jet breakup unsteadiness in a coaxial air-blast atomizer. The current research focuses on the measurement of the fluctuations of the jet breakup length and the flapping instability of the liquid jet, which contribute to the downstream fluctuations of the spray characteristics. The optical connectivity technique was used to measure the instantaneous breakup length of the water jet. Also, time resolved shadowgraph images of the primary jet breakup process were captured by high-speed imaging to characterize the jet instabilities at different axial locations from the atomizer exit. Experiments were performed for a wide range of air-to-liquid momentum flux ratio ( M) and aerodynamic Weber number ( Weg) corresponding to membrane- and/or fiber breakup mode of the jet disintegration process. The mean jet breakup length was found to vary inversely with M through a power law relation in agreement with the literature, while the breakup length fluctuations were found to first decrease and then increase with M. In order to capture the unsteady dynamics of the jet breakup process, the proper orthogonal decomposition analysis of the optical connectivity images was performed. The jet flapping and the fluctuations of the jet breakup length were identified as the second and the third spatial proper orthogonal decomposition modes, respectively, for all operating conditions of the atomizer. The amplitude and the frequency of the instabilities were measured by temporal tracking of the liquid–air interface on the shadowgraph images. The disturbance close to the injector exit corresponds to the Kelvin–Helmholtz instability, while close to the jet breakup point the jet exhibits the flapping instability, which is characterized by lateral oscillation of the jet about the atomizer axis. The influence of the liquid jet Reynolds number and momentum flux ratio on the KH and the flapping instabilities are examined.
14
Dodge, L. G., and J. A. Biaglow. "Effect of Elevated Temperature and Pressure on Sprays From Simplex Swirl Atomizers." Journal of Engineering for Gas Turbines and Power 108, no. 1 (January 1, 1986): 209–15. http://dx.doi.org/10.1115/1.3239873.
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The effects of air temperature and air pressure on spray quality of a moderately high capacity pressure swirl atomizer (127 kg/h MPa or 23.3 lbm/h psid) spraying jet-A and No. 2 diesel fuel have been examined. Drop-size distributions, in terms of both Sauter mean diameter (SMD) and the width of the distribution as given by the Rosin-Rammler N parameter, and cone angle as measured close to the nozzle (10-mm distance) have been determined over a variety of air conditions. A new correction procedure was developed to extend diffraction-based drop-size measurements in dense sprays from maximum optical opacities of 50% to maximum opacities of 96%, equivalent to an increase in spray density of a factor of five. Drop-size measurements are reported for a temperature range of room temperature (297K) to 589K and air pressures of atmospheric (101 kPa) to 597 kPa. Cone angle data are reported for temperatures to 589K and pressures to 1318 kPa. The maximum operating temperature was limited to the occurrence of autoignition. Close to the nozzle (25 mm), limited data suggest that the SMD’s were a strong function of air density, SMD ∼ ρ−0.53, but independent of air temperature (which affects air viscosity). The width of the distribution narrowed slightly with increasing density, N ∼ ρ0.15, at 25-mm distance. Trends of SMD and N are also shown as a function of distance from the nozzle at all conditions. These trends indicate some of the evaporation characteristics of fuel sprays. Pressure drop across the nozzle had an unusually large effect on SMD with SMD ∼ (ΔP)−0.86. At 10 mm from the nozzle exit, the cone angle of the nominal 80 deg cone angle nozzle was φ = 79.8–0.918 (ρ/ρ0) where ρ is the air density at the test condition and ρ0 the density at atmospheric conditions.
15
Zheng, Zekun, and Yong Huang. "INVESTIGATION ON THE INTERACTION AMONG MULTI-SPRAYS GENERATED FROM PRESSURE-SWIRL ATOMIZERS." Atomization and Sprays 27, no. 6 (2017): 477–91. http://dx.doi.org/10.1615/atomizspr.2017018229.
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MACKRORY, ANDREW J., DALE R. TREE, and LARRY L. BAXTER. "Characteristics of black liquor sprays from gas-assisted atomizers in high-temperature environments." January 2008 7, no. 1 (February 1, 2008): 19–23. http://dx.doi.org/10.32964/tj7.1.19.
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Black liquor droplets in an entrained-flow gasifier that are too large or too small can cause problems in the chemical recovery process. It is therefore important in gasifier design to understand the nature of the atomized gas spray. We used high-speed imaging to study black liquor sprays in cold and hot environments. Significant conclusions are that: 1. the droplet size distribution width is linked to the mean droplet size as for other sprays in the literature, necessitating a gasifier design that is tolerant of the distribution width associated with the target droplet size; 2. the shape of black liquor droplets is highly non-spherical, necessitating consideration of shape in addition to mass; 3. black liquor has exceptional ability to attach to the nozzle and thereby to form larger-than-desired fragments of liquor; and 4. the furnace environment has a measurable impact on droplet formation, making cold-spray-chamber test results difficult to apply to practical in-furnace spray performance. It had previously been assumed that the furnace environment does not affect the spray.
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Nasr, G. G., R. A. Sharief, and A. J. Yule. "High Pressure Spray Cooling of a Moving Surface." Journal of Heat Transfer 128, no. 8 (June 24, 2005): 752–60. http://dx.doi.org/10.1115/1.2217747.
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A novel technique is described for investigating spray cooling of moving hot surfaces. An experimental investigation is described for vertically downwards water sprays impinging on a horizontal steel annulus of 250mm diameter with a surface temperature up to 600°C, and rotating at up to 120rpm, giving a tangential velocity of 1.35ms−1. The central homogeneous zones of sprays from full-cone atomizers are used at pressures up to 2.07MPa and the ranges of impacting spray parameters are 0.98to12.5kgm−2s−1 for mass flux, 49-230μm for volume median drop diameter, and 9.8-32.3ms−1 for impinging velocity (Yule, A. J., Sharief, R. A., and Nasr, G. G., 2000, “The Performance Characteristics of Solid Cone Spray Pressure Swirl Atomizers,” Ann. Tokyo Astron. Obs., 10(6), pp. 627–646). Time histories of the steel temperature, at positions within the annulus, are presented and analyzed to deduce the transient cooling as the instrumented section of the annulus was swept repeatedly under the spray. Discussion is provided on the physical processes occurring on the basis of the observations. Correlation equations derived to find relationships of surface heat flux with the spray and surface parameters provide further insight into these processes. The results confirm results for static surfaces, that droplet size is a relatively weak parameter, while droplet momentum flux and surface velocity are important. As the surface velocity is increased, peak heat transfer rate at the surface reduces, and its position moves downstream with respect to the spray centerline.
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Cui, Chengsong, Alwin Schulz, and Volker Uhlenwinkel. "Co-Spray Forming of Gradient Deposits from Two Sprays of Different Tool Steels Using Scanning Gas Atomizers." steel research international 84, no. 11 (July 26, 2013): 1075–84. http://dx.doi.org/10.1002/srin.201200266.
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Ghaffar, Zulkifli Abdul, Salmiah Kasolang, and Ahmad Hussein Abdul Hamid. "Characteristics of Swirl Effervescent Atomizer Spray Angle." Applied Mechanics and Materials 607 (July 2014): 108–11. http://dx.doi.org/10.4028/www.scientific.net/amm.607.108.
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In the application of sprays produced by an atomizer, spray angle is one of key performance parameters. A larger spray angle is often required in providing a better spray dispersion. Swirl effervescent atomizer is one of the existing atomizers with the capability to produce a large spray angle. The formation of spray angle from this atomizer however is hardly understood. A newly-designed swirl effervescent atomizer was developed and tested with different swirl-generating vane angle in order to understand the swirl intensity effect on the spray angle. Experiments were carried out based on a cold flow test approach using water as the working fluid and nitrogen gas as the atomizing agent. High-speed shadowgraph technique was deployed to record the resultant sprays produced. Video recordings, acquired using a high-speed video camera, were converted to a sequence of images for further analysis using an image processing software. It was found that the spray angle increases with the swirl-generating vane angle. Specifically, the spray angle shows an abrupt increase for the case of swirl-generating vane angle changing from 30° to 45° but visualizes only a gradual increase in the case of swirl-generating vane angle changing from 45° to 60°.
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Hassani, Mohammad Amin, Abbas Elkaie, and Maziar Shafaee. "Numerical investigation of the full-cone spray structure and characteristics provided by a jet-swirl atomizer." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 15 (July 1, 2019): 5788–800. http://dx.doi.org/10.1177/0954410019860320.
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Jet-swirl atomizers are one of the pressure-swirl atomizers that produce full-cone spray. Although many hollow-cone pressure-swirl sprays have been studied, characteristic investigation of pressure-swirl full-cone sprays are limited to a few experimental, analytical, and numerical works where each of them investigate some of the main spray parameters. The few existing numerical studies are limited to calculate the coefficient of discharge and spray cone angle. Current numerical study investigate a newly developed jet-swirl atomizer with pressure-swirl full-cone spray, which considers other important full-cone spray characteristics including Sauter mean diameter, D10, and spray tip penetration along with the spray structure. In this study, a full-cone spray based on a newly developed jet-swirl injector is numerically simulated and analyzed using sprayFoam solver in the OpenFOAM 4.1 software. The existing code of the solver is developed and its dictionary is modified. The C+ + Sauter mean diameter and D10 codes on the cross-sectional surface are developed and this feature is added to the sprayFoam solver. The pre-published experimental and current work numerical results were in good agreement. In the simulation process, blob sheet model is used for the spray primary breakup. Two models including Taylor analogy breakup and Reitz–Diwakar have been used for the secondary breakup of the developed jet-swirl atomizer. This work shows that the results of the Reitz–Diwakar model are close to that of the Taylor analogy breakup model. The time-varying results of Sauter mean diameter, D10, and spray tip penetration are found to be in good agreement in both models. The results show that the Reitz–Diwakar model is stabilized somewhat later than the Taylor analogy breakup model. The simulated spray structure shows that the density of droplets is higher in the spray center region and this density is gradually reduced through the radial direction. The results along the radius show that the diameter of the droplets becomes larger while moving away from the center of the spray.
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Tsai, S. C., and B. Viers. "Airblast Atomization of Viscous Newtonian Liquids Using Twin-Fluid Jet Atomizers of Various Designs." Journal of Fluids Engineering 114, no. 1 (March 1, 1992): 113–18. http://dx.doi.org/10.1115/1.2909985.
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Airblast atomization of viscous Newtonian liquids is carried out using coaxial twin-fluid jet atomizers of different nozzle sizes, slit angles, and slit cross sections for air flow. As the atomizing air swirls downstream along the liquid jet, waves form on the surface of the liquid jet. As a result, the liquid jet sheds ligaments which rapidly collapse into small drops. The atomized drop sizes can be described in terms of three dimensionless groups, namely, liquid-to-air mass ratio (M˙L/M˙A), Weber number (We), and Ohnesorge number (Z) in simple forms whose exponents and coefficients are determined by the best least square fit to the experimental results using the generalized inverse method. In addition, we found that the atomized drop sizes substantially decrease as the atomizing air pressure exceeds a threshold value which varies from less than 170 to 220 kPa depending on the nozzle size and the slit cross section.
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Seredyn, Tomasz, Adam Dziubiński, and Piotr Jaśkowski. "CFD Analysis of the Fluid Particles Distribution by Means of Aviation Technique." Transactions on Aerospace Research 2018, no. 1 (March 1, 2018): 67–97. http://dx.doi.org/10.2478/tar-2018-0006.
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Abstract The article describes a computational study, using CFD models, of droplet spray dispersal in the wake of a ‘Turbo Kruk’ airplane up to 500 m downstream. The CFD Reynolds-averaged Navier-Stokes (RANS) models use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described in the work have the potential to improve current models for aerial spraying and will help in the development of new spraying procedures. In this study, the CFD models are used to describe the phenomenon of sprays released from atomizers mounted on the plane. A parametric study of the aircraft model examines the effects of crosswind on the aircraft’s vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of the present results to AGDISP predictions is provided.
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Wilson, AGL, LA Harper, and H. Baker. "Evaluation of insecticide residues and droplet drift following aerial application to cotton in New South Wales." Australian Journal of Experimental Agriculture 26, no. 2 (1986): 237. http://dx.doi.org/10.1071/ea9860237.
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In a study to determine the extent of off target drift from aerial spraying, insecticides were applied to cotton crops in various strengths of crosswind by an aircraft fitted with rotary atomizers. Both water-based and oil-based sprays were applied, at 20 and 2 litres/ha respectively. Compared with the mean insecticide deposit across a 16-m target swath, in seven runs, the mean recoveries of insecticide 15, 165 and 3 15 m downwind from the edge of the swath were 6.8, 0.13 and 0.002% respectively. Deposition on plants was nearly twice that on the ground, but the proportional decline downwind was similar. Counts of droplets deposited on paper targets fixed to masts showed that the dispersing cloud of water-based spray contracted more rapidly than did that of the oil-based spray, probably because of greater evaporation of the former. The results indicate that a 300-m wide buffer zone between target crops and areas susceptible to contamination should be adequate under most conditions.
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Shi, H., and C. Kleinstreuer. "Simulation and Analysis of High-Speed Droplet Spray Dynamics." Journal of Fluids Engineering 129, no. 5 (October 19, 2006): 621–33. http://dx.doi.org/10.1115/1.2717621.
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An experimentally validated computer simulation model has been developed for the analysis of gas-phase and droplet characteristics of isothermal sprays generated by pressure jet atomizers. Employing a coupled Euler-Lagrange approach for the gas-droplet flow, secondary droplet breakup (based on the ETAB model), was assumed to be dominant and the k-ε model was selected for simulating the gas flow. Specifically, transient spray formation in terms of turbulent gas flow as well as droplet velocities and size distributions are provided for different back pressures. Clearly, two-way coupling of the phases is important because of the impact of significant gas entrainment, droplet momentum transfer, and turbulent dispersion. Several spray phenomena are discussed in light of low back-pressure (1atm) and high back-pressure (30atm) environments. At low back-pressure, sprays have long thin geometric features and penetrate faster and deeper than at high back-pressures because of the measurable change in air density and hence drag force. Away from the nozzle exit under relatively high back pressures, there is no distinct droplet size difference between peripheral and core regions because of the high droplet Weber numbers, leading to very small droplets which move randomly. In contrast to transient spray developments, under steady-state conditions droplets are subject to smaller drag forces due to the fully-developed gas entrainment velocities which reduce gas-liquid slip. Turbulent dispersion influences droplet trajectories significantly because of the impact of random gas-phase fluctuations.
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Sivakumar, D., and B. N. Raghunandan. "A Study on Converging Thin Annular Jets." Journal of Fluids Engineering 119, no. 4 (December 1, 1997): 923–28. http://dx.doi.org/10.1115/1.2819518.
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An interesting feature of jets from liquid-liquid coaxial swirl atomizers used in bipropellant rockets or elsewhere is that the outer jet results in a tulip shaped liquid bulb even at operating pressure levels. In this context, experiments have been performed to study the discharge and tulip characteristics of annular jets through qualitative simulation of outer jet flow conditions at which tulip bulb prevails. It is shown that the discharge coefficient increases steeply with Reynolds number, a trend which is distinct from that of circular orifices. The range of flow conditions at which tulip bulb prevails decreases with the annular gap. If a swirl component is introduced into the annular jet, it alters the discharge characteristics and the tulip range with a tendency to form multiple tulips. Variation of tulip length for different annular gaps shows a common trend when plotted against liquid flow rate. The experimental data of tulip length agree reasonably with the theoretical model reported in literature.
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Dhivyaraja, K., D. Gaddes, E. Freeman, S. Tadigadapa, and M. V. Panchagnula. "Dynamical similarity and universality of drop size and velocity spectra in sprays." Journal of Fluid Mechanics 860 (December 7, 2018): 510–43. http://dx.doi.org/10.1017/jfm.2018.893.
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Sprays are a class of multiphase flows which exhibit a wide range of drop size and velocity scales spanning several orders of magnitude. The objective of the current work is to experimentally investigate the prospect of dynamical similarity in these flows. We are also motivated to identify a choice of length and time scales which could lead towards a universal description of the drop size and velocity spectra. Towards this end, we have fabricated a cohort of geometrically similar pressure swirl atomizers using micro-electromechanical systems (MEMS) as well as additive manufacturing technology. We have characterized the dynamical characteristics of the sprays as well as the drop size and velocity spectra (in terms of probability density functions, p.d.f.s) over a wide range of Reynolds ($Re$) and Weber numbers ($We$) using high-speed imaging and phase Doppler interferometry, respectively. We show that the dimensionless Sauter mean diameter ($D_{32}$) scaled to the boundary layer thickness in the liquid sheet at the nozzle exit ($\unicode[STIX]{x1D6FF}_{o}$) exhibits self-similarity in the core region of the spray, but not in the outer zone. In addition, we show that global drop size spectra in the sprays show two distinct characteristics. The spectra from varying $Re$ and $We$ collapse onto a universal p.d.f. for drops of size $x$ where $x/\unicode[STIX]{x1D6FF}_{o}>1$. For $x/\unicode[STIX]{x1D6FF}_{o}<1$, a residual effect of $Re$ and $We$ persists in the size spectra. We explain this characteristic by the fact that the physical mechanisms that cause large drops is different from that which is responsible for the small drops. Similarly, with the liquid sheet velocity at the nozzle exit ($u_{s}$) as the choice of velocity scale, we show that drops moving with a velocity $u$ such that $u/u_{s}<1$ collapse onto a universal p.d.f., while drops with $u/u_{s}>1$ exhibit a residual effect of $Re$ and $We$. From these observations, we suggest that physically accurate models for drop size and velocity spectra should rely on piecewise descriptions of the p.d.f. rather than invoking a single mathematical form for the entire distribution. Finally, we show from a dynamical modal analysis that the conical liquid sheet flapping characteristics exhibit a sharp transition in Strouhal number ($St$) at a critical $Re$.
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Ghate, Kushal, and Thirumalachari Sundararajan. "Effects of orifice divergence on hollow cone spray at low injection pressures." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 11 (November 26, 2018): 4091–105. http://dx.doi.org/10.1177/0954410018813432.
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In this work, the effects of orifice divergence on spray characteristics have been reported. Parameters such as spray cone angle, liquid sheet thickness, coefficient of discharge, break-up length, and Sauter mean diameter are greatly affected by the half divergence angle [Formula: see text] at orifice exit. An experimental investigation is carried out in which water sprays from five atomizers having half divergence angle values of 0°, 5°, 10°, 15°, and 20° are studied at different injection pressures. Image processing techniques are used to measure spray cone angle and break-up length from spray images, whereas the sheet thickness outside the orifice exit is obtained using the scattered light from a thin Nd-YAG Laser beam. Phase Doppler interferometry is also used to obtain the Sauter mean diameter at different axial locations. A few numerical simulations based on the volume of fluid method are included to obtain physical insight of the liquid film development and air core flow inside the atomizer. It is observed that the liquid sheet thickness as well as tangential and radial components of velocity at orifice exit are modified drastically with a change in half divergence angle. As a consequence, the droplet size distribution is also altered by variation in the nozzle divergence angle. The mechanism responsible for such variations in the spray behavior is identified as the formation of an air core or air cone inside the liquid injector as a result of the swirl imparted to the liquid flow.
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Wofford, J. T., R. G. Luttrell, and D. B. Smith. "Effects of Droplet Characteristics of Permethrin Sprays Applied in Vegetable Oil and Water on Control of Heliothis Spp. in Cotton; 1984." Insecticide and Acaricide Tests 11, no. 1 (January 1, 1986): 306–7. http://dx.doi.org/10.1093/iat/11.1.306.
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Abstract A small plot field study was conducted on the Plant Science Research Farm of the Mississippi Agriculture and Forestry Experiment Station, Mississippi State, MS, to determine if insecticide carriers (vegetable oil and water) and droplet characteristics (droplet size and droplet concentration) influence control of Heliothis spp. in cotton. Four-row plots (3.87 m × 15.24 m) with 10-row buffers were planted to ‘Stoneville 825’ on 15 May and 1 Jun (2 replications required replanting) in a randomized complete block design. Vegetable oil treatments were varied by manipulating droplet size with Micro Max rotary atomizers set at 1600, 3500 and 5000 RPM and by using 3 different application rates (0.25, 0.5 and 1.0 gpa) attained by varying the ground speed. Water treatments were similarly varied by using 3 different droplet sizes, attained with TX-6, TX-4 and TX-1 hollow cone nozzles, and 3 volumetric application rates (3.0, 6.0 and 12.0 gpa) attained by varying the number of nozzles per row and the ground speed. Permethrin (Pounce 3.2 EC) was used at 0.1 lb (AI)/acre for all droplet size-carrier-volumetric application rate combinations. The controls consisted of a water-only treatment, an oil only treatment and an untreated. Treatments were applied on 15, 20 and 27 Aug. Plots were evaluated 17 Aug by randomly pulling 25 squares from plants in each plot and observing the number of squares damaged by Heliothis spp. larvae. On 25 Aug whole-plant observations were made on 5 row feet to observe Heliothis spp. damage and numbers of fruiting structures present. On 5 Oct open bolls, unopened bolls and total bolls were counted on 5 row feet in each plot. Yield data were obtained by mechanically harvesting the 2 center rows of each plot on 21 Nov.
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Hoffmann, Wesley Clint, Bradley Keith Fritz, Muhammad Farooq, Todd William Walker, Zbigniew Czaczyk, Jonathan Hornsby, and Jane Annalise Sara Bonds. "Evaluation of Aerial Spray Technologies for Adult Mosquito Control Applications." Journal of Plant Protection Research 53, no. 3 (July 1, 2013): 222–29. http://dx.doi.org/10.2478/jppr-2013-0034.
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Abstract Spray droplet size has long been recognized as an important variable that applicators of vector control sprays must be aware of to make the most effective spray applications. Researchers and applicators have several different techniques available to assess spray droplet size from spray nozzles. The objective of this study was to compare the droplet size spectrum produced by three nozzles commonly used in vector control in a high-speed wind tunnel, when characterized using three different laser-based droplet size measurement systems. Three droplet sizing systems: Malvern Spraytec laser diffraction, Sympatec HELOS laser diffraction, and TSI Phase Doppler Particle Analyzer (PDPA), were simultaneously operated, but under different operating conditions, to measure the spray droplet size-spectra for three spray nozzles. The three atomizers: a TeeJet® 8001E even flat fan nozzle, a BETE® PJ high pressure fog nozzles, and a Micronair ® AU5000 rotary atomizer were evaluated in a high speed wind tunnel at airspeeds of 53 and 62 m/s (120 and 140 mph). Based on the results of this work, only the BETE® PJ high pressure fog nozzles met the label requirements for both Fyfanon® and Anvil®. While the other nozzle might met the Dv0.5 (VMD - volume median diameter) requirement for Fyfanon®, the resulting Dv0.9 values exceeded labeled size restrictions. When applying Anvil with the BETE PJ high pressure fog nozzles, it is important to use the smaller two orifice sizes. The larger sizes tended to result in Dv0.9 values that exceeded label recommendations
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Potier, Luc, Florent Duchaine, Bénédicte Cuenot, Didier Saucereau, and Julien Pichillou. "Prediction of Wall Heat Fluxes in a Rocket Engine with Conjugate Heat Transfer Based on Large-Eddy Simulation." Entropy 24, no. 2 (February 9, 2022): 256. http://dx.doi.org/10.3390/e24020256.
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Although a lot of research and development has been done to understand and master the major physics involved in cryogenic rocket engines (combustion, feeding systems, heat transfer, stability, efficiency, etc.), the injection system and wall heat transfer remain critical issues due to complex physics, leading to atomization in the subcritical regime and the interactions of hot gases with walls. In such regimes, the fuel is usually injected through a coaxial annulus and triggers the atomization of the central liquid oxidizer jet. This type of injector is often referred to as air-assisted, or coaxial shear, injector, and has been extensively studied experimentally. Including such injection in numerical simulations requires specific models as simulating the atomization process is still out of reach in practical industrial systems. The effect of the injection model on the flame stabilization process and thus on wall heat fluxes is of critical importance when it comes to the design of wall-cooling systems. Indeed, maximizing the heat flux extracted from the chamber can lead to serious gain for the cooling and feeding systems for expander-type feeding cycles where the thermal energy absorbed by the coolant is converted into kinetic energy to drive the turbo-pumps of the feeding system. The methodology proposed in this work to numerically predict the flame topology and associated heat fluxes is based on state-of-the-art methods for turbulent reactive flow field predictions for rocket engines, including liquid injection, combustion model, and wall treatment. For this purpose, high-fidelity Large Eddy Simulation Conjugate Heat Transfer, along with a reduced kinetic mechanism for the prediction of H2/O2 chemistry, liquid injection model LOx sprays, and the use of a specific wall modeling to correctly predict heat flux for large temperature ratio between the bulk flow and the chamber walls, is used. A smooth and a longitudinally ribbed combustor configuration from JAXA are simulated. The coupling strategy ensures a rapid convergence for a limited additional cost compared to a fluid-only simulation, and the wall heat fluxes display a healthy trend compared to the experimental measurements. An increase of heat transfer coherent with the literature is observed when walls are equipped with ribs, compared to smooth walls. The heat transfer enhancement of the ribbed configuration with respect to the smooth walls is coherent with results from the literature, with an increase of around +80% of wall heat flux extracted for the same chamber diameter.
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Lapeña, José Florencio F. "Primary Care Evaluation of the Nose and Paranasal Sinuses." Philippine Journal of Otolaryngology-Head and Neck Surgery 21, no. 1-2 (November 29, 2006): 57–58. http://dx.doi.org/10.32412/pjohns.v21i1-2.847.
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Primary care evaluation of the nose and paranasal sinuses begins with inspection. The astute clinician will seldom miss the hyperemic nose and open-mouth breathing of nasal congestion, the “long-face” facies, infraorbital dark “shiners” and edema of decreased lymphatic drainage from chronic nasal obstruction, and the transverse nasal crease from repeated performance of the “allergic salute” in allergic rhinitis. Tearing may be caused by inferior obstruction of the nasolacrimal duct. Widening of the nasal bridge (Woake’s syndrome) may suggest massive nasal polyposis2. The patient with acute sinusitis may be in obvious pain and actually avoid jarring movements, and orbital complications of acute sinusitis should be apparent even to the untrained eye. A polished mirror or metal tongue depressor gently held under both nostrils can document patency of both nasal airways by observing the misting pattern even before looking inside the nose. Glatzel’s mirror test3 attempts to measure this pattern but mere observation for symmetry establishes expiratory patency. Inspiratory obstruction can be assessed by gently pulling the ipsilateral cheek laterally. If it relieves nasal obstruction (positive Cottle’s sign4), the source of obstruction is in the nasal valve area and may be surgically correctible.
Anterior rhinoscopy is best done using coaxial binocular illumination such as provided by a properly focused head mirror and bright light source. Alternately, a lumiview™ (Welch Allyn Corporation, New York, USA) or hand-held otoscope with the largest available clean ear speculum can be used. In babies and young children, gently flipping up the nasal tip with a finger facilitates viewing the nasal cavities. Adult noses are best viewed by aligning the external (downward-facing) and internal (forward-facing) nares with the aid of a nasal speculum. With the thumb on the pivot and index finger resting on the nasal tip, the prongs should be pressed by the remaining digits against the palm and spread superiorly against compliant alae rather than medially toward the septum. Insertion should be restricted to the vestibular area (alae nasi); insinuation beyond the internal nares (limen nasi) is painful, as is closing the speculum before withdrawing (pinching vibrissae). Decongestion should be performed in the presence of congested or hypertrophic turbinates and to distinguish the latter from nasal polyps (which do not shrink even with decongestion). Commercially available oxymetazoline 0.05% and 0.025% (Drixine™) or tetrahydrozoline 0.1% (Sinutab NS™) nasal solutions should be gently dropped into each nostril while the head is tilted back and nasal tip upturned. The nozzle should not touch the nose at any time. Three to five drops are instilled in one nostril after which the head is turned so that the ipsilateral ear faces down. This position (after Proetz)5 facilitates the solution spreading to the lateral wall of the nose while the patient gently sniffs in. The maneuver is then replicated for the other nostril. Three to five drops solution are then instilled in both nostrils a second time and the patient is asked to lower the forehead between the knees or to assume a knee-chest (mecca) position with forehead on the floor which facilitates spreading solution to the roof of the nose6. Adequate decongestion not only facilitates examination of the nasal cavities; it affords relief from obstruction and drainage of retained discharges. Performing the Proetz and mecca maneuvers also educates the patient in the proper way to continue decongestion at home, provided dosing duration (three to five days) and regimens (twelve hourly for oxymetazoline and eight hourly for tetrahydrozoline) are not exceeded due to the danger of rebound rhinitis. The maneuvers are also useful for nasal saline douches and instilling steroid sprays.
Palpation of the paranasal sinuses is performed by percussion or by pressing firmly but gently over the most accessible points of maximum tenderness for each sinus: the vertex (sphenoid), supero-medial roofs of the orbital sockets (frontal), nasal bones between medial canthi (ethmoid) and incisive fossa area of cheeks (maxillary). Upper jaw teeth (especially canines) may be tender when tapped gently in cases of acute maxillary sinusitis. Transillumination with a powerful light source in a darkened room may suggest the presence of fluid or masses in the frontal and maxillary sinuses. Normal air-filled frontal and maxillary sinuses should “light up” (transilluminate) with light applied over their respective palpation points. External maxillary transillumination also casts a red glow on the hard palate, and a “red streak” in the lateral recess of the oropharynx may predict sinusitis7. Better results are achieved for the maxillary sinus with transoral light against the hard palate on each side. Transillumination is positive (normal) for the maxillary sinuses when the cheeks turn red-orange, a red-orange crescent lights up the infraorbital rim, and a red-orange papillary reflex is observed on downward gaze; or when the scalloped margins and inter-sinus septum of the frontal sinuses stand out in relief against a red orange background. Opacification can be produced by fluid, masses or hypoplastic sinuses while air-fluid levels produce a combination of findings. Swelling, masses, infraorbital nerve hyposthesia and extraocular muscle motion limitations warrant urgent specialist referral.
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Joseph, A., R. Sakthikumar, and D. Sivakumar. "Experimental Characterization of Sprays in a Recessed Gas-Centered Swirl Coaxial Atomizer." Journal of Fluids Engineering 142, no. 4 (February 4, 2020). http://dx.doi.org/10.1115/1.4045986.
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Abstract The characteristics of sprays from a recessed gas-centered swirl coaxial atomizer (RGCSCA) with gas to liquid momentum flux ratio, J of the spray in the range of 2–66 are studied experimentally through the analysis of spray morphologies and droplets characteristics. The process of fully developed spray (spray free from ligaments/droplets clusters and nonspherical droplets) in the atomizer is quantified. In the RGCSCA, the distance from the atomizer exit to the fully developed spray zone decreases with increase in J. Detailed measurements of size (in the range of 6–378 μm) and velocity (in the range of 35–176 m/s) characteristics of spray droplets are carried out using phase Doppler interferometry (PDI) in the fully developed spray. The spray from the RGCSCA is comprised of two distinct spray morphologies: a central dense spray of finer droplets and an outer coarse spray. The mean drop size of the central spray exhibits a decreasing trend with the increase in J whereas that of the outer coarse spray is independent of J. The radial profiles of the mean velocities of sprays at different J are presented. For the sprays with low inertia liquid sheets, the shape of mean axial velocity profiles is Gaussian.
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Kulkarni, V., D. Sivakumar, C. Oommen, and T. J. Tharakan. "Liquid Sheet Breakup in Gas-Centered Swirl Coaxial Atomizers." Journal of Fluids Engineering 132, no. 1 (January 1, 2010). http://dx.doi.org/10.1115/1.4000737.
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The study deals with the breakup behavior of swirling liquid sheets discharging from gas-centered swirl coaxial atomizers with attention focused toward the understanding of the role of central gas jet on the liquid sheet breakup. Cold flow experiments on the liquid sheet breakup were carried out by employing custom fabricated gas-centered swirl coaxial atomizers using water and air as experimental fluids. Photographic techniques were employed to capture the flow behavior of liquid sheets at different flow conditions. Quantitative variation on the breakup length of the liquid sheet and spray width were obtained from the measurements deduced from the images of liquid sheets. The sheet breakup process is significantly influenced by the central air jet. It is observed that low inertia liquid sheets are more vulnerable to the presence of the central air jet and develop shorter breakup lengths at smaller values of the air jet Reynolds number Reg. High inertia liquid sheets ignore the presence of the central air jet at smaller values of Reg and eventually develop shorter breakup lengths at higher values of Reg. The experimental evidences suggest that the central air jet causes corrugations on the liquid sheet surface, which may be promoting the production of thick liquid ligaments from the sheet surface. The level of surface corrugations on the liquid sheet increases with increasing Reg. Qualitative analysis of experimental observations reveals that the entrainment process of air established between the inner surface of the liquid sheet and the central air jet is the primary trigger for the sheet breakup.
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"Breakup phenomena in coaxial airblast atomizers." Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences 451, no. 1941 (October 9, 1995): 189–229. http://dx.doi.org/10.1098/rspa.1995.0123.
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The breakup of a liquid jet with length-to-diameter ratio of 22 surrounded by a coaxial flow of air has been examined by a combination of high-speed photography and phase-Doppler velocimetry. The air-to-liquid momentum and kinetic energy ratios, the Reynolds number of the coaxial water and air jet flows and the exit-plane Weber number have been varied over extensive ranges and the results examined in terms of the breakup length, frequency, droplet size distributions and velocity characteristics. The photographs reveal the deterministic nature of the liquid flow at Reynolds numbers which are sufficient to guarantee turbulent flow, with the formation of a wave-like structure for a short distance followed by the formation of a liquid cluster and subsequent breakup into ligaments and droplets, with the entire process repeated in a periodic manner. Attempts are made to relate the breakup length and the frequency of the process to the air-to-liquid momentum and energy ratios, the exit Weber number and the slip velocity between the two streams at the nozzle exit. The results confirm that the ratio of the frequencies of the wave-like structures and breakup decreased with the slip velocity between the two streams and asymptotically approached a value of around one for values higher than 150 m s -1 . The photographs indicate that the droplet sizes in the sprays are due mainly to disintegration of liquid clusters produced after the initial breakup of the liquid jet and the phase Doppler measurements confirm that most of the liquid remained close to the centreline, where the mean diameter reached a maximum and the slip velocity between the droplets and the air flow was low. An atomization model based on the value of the local Weber number on the centreline of the sprays is used to explain the size characteristics of the sprays. The atomization process was affected by the air-to-liquid momentum ratio at the nozzle exit, the annular width of the coaxial atomizer, the liquid-to-air density ratio, the surface tension and the kinematic viscosity and density of the air. The rate of spread of the sprays close to the nozzle reduced with increase of the air and liquid flowrates and was affected by the initial breakup of the liquid jet and the amplitude of the wave-like structure of the liquid jet during breakup rather than by the air flow turbulence.
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Broumand, Mohsen, Murray Thomson, Sean Yun, and Zekai Hong. "Spray Characterization of a Preheated Bio-Oil Surrogate at Elevated Pressures." Journal of Engineering for Gas Turbines and Power, August 26, 2022. http://dx.doi.org/10.1115/1.4055360.
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Abstract Atomization plays an important role in the gasification or combustion of bio-oils, where the atomizer parameters need to be properly controlled to efficiently atomize a highly viscous liquid at elevated pressures with imparting the least amount of kinetic energy to the discharged droplets because of evaporation and chemical reaction constraints. With a focus on bio-oil deployments in micro gas turbines, an aqueous surrogate of a preheated bio-oil injected from a twin-fluid atomizer is used in the present study for spray size and velocity measurements at elevated pressures. The experiments were conducted in High Pressure Spray Facility of the National Research Council of Canada (NRC) using various optical diagnostics including laser sheet imaging (LSI),phase Doppler anemometry (PDA), and laser diffraction (LD). A scaling strategy was adopted to conserve the ranges of gas-to-liquid momentum flux ratio, M, at different working pressures, P. The spray cone angles are found to be insensitive to P, but they decrease with increasing M. For a constant value of M, droplet mean diameters increase and their corresponding velocities decrease with increasing P, attributed to the effect of gas-to-liquid density ratio on the primary breakup of a liquid jet in a coaxial gas stream. To predict the Sauter mean diameter of spray droplets, a correlation previously reported in the literature is modified and a novel correlation is proposed based on four dimensionless groups, namely gas Weber number and gas-to-liquid momentum flux ratio, density ratio, and viscosity ratio.
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Godavarthi, V., K. Dhivyaraja, R. I. Sujith, and M. V. Panchagnula. "Analysis and classification of droplet characteristics from atomizers using multifractal analysis." Scientific Reports 9, no. 1 (November 7, 2019). http://dx.doi.org/10.1038/s41598-019-52596-6.
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Abstract Atomizers find applications in diverse fields such as agriculture, pharmaceutics and combustion. Among the most commonly found atomizer classes of designs are pressure swirl, airblast and ultrasonic atomizers. However, it has thus far not been possible to identify the class of an atomizer from spray characteristics. We perform multifractal detrended fluctuation analysis on the droplet inter-arrival times, diameters and axial velocities of pressure swirl, airblast and ultrasonic nebulizer sprays to quantify the differences in complexity in the respective signals. We show that the width of the multifractal spectrum of the signals of droplet diameters and the inter-arrival times, measured at the edge of the spray are robust atomizer identifiers. Further, we show the presence of correlations among the droplet diameters which are otherwise considered as random or derived from a log-normal distribution. This study can be further generalized to classify fluid mechanical systems or biological sprays using an appropriately chosen single point measurement in the flow field.
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Fong, Kee Onn, Xinzhi Xue, R. Osuna-Orozco, and A. Aliseda. "Two-fluid coaxial atomization in a high-pressure environment." Journal of Fluid Mechanics 946 (August 1, 2022). http://dx.doi.org/10.1017/jfm.2022.586.
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We study the dynamics of atomization of a liquid column by a coaxial gas flow with varying gas pressures. Specifically, we analyse how the gas density increase associated with elevated gas pressures in the ambient and co-flowing gas jet influences the liquid destabilization and breakup process, as well as the resulting droplet formation and dispersion. We present new experimental results for a coaxial liquid–gas atomizer operating in a high-pressure environment, with gas–liquid momentum ratio in the range $M = 5\unicode{x2013}56$ and pressurized gas densities $\rho _g/\rho _0 = 1\unicode{x2013}5$ , where $\rho _0$ is the ambient gas density at standard conditions. High-speed shadowgraphy images are used to quantify the spatially and temporally varying liquid–gas interface in the spray near-field. Liquid core lengths, spreading angles and other spray metrics are presented, and the influence of gas density is identified from the comparison with atomization at atmospheric conditions. In the spray mid-field, phase Doppler interferometry is used in conjunction with laser Doppler velocimetry to quantify the droplet size and velocities, as well as their radial variations across the spray. Results show an increase in droplet size at elevated ambient pressures, when keeping the gas–liquid momentum ratio constant. Finally, we show that these observations are in line with predictions from the Kelvin–Helmholtz and Rayleigh–Taylor instabilities, both of which are relevant to the gas–liquid atomization process.
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Bothell, Julie K., Timothy B. Morgan, and Theodore J. Heindel. "Image-Based Feedback Control for a Coaxial Spray." Journal of Fluids Engineering 142, no. 11 (September 4, 2020). http://dx.doi.org/10.1115/1.4048131.
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Abstract Optimization of jet engine sprays has the potential to improve efficiency and reduce environmental impact. Sprays can be continually optimized in multivariate scenarios using real-time feedback control, but a method of controlling the sprays based on physical properties must first be established. In this study, a spray controller was developed to optimize the spray angle obtained from shadowgraphs, with the assumption that the largest angle is desired. The spray angle was used as an example, as it is a physically important parameter which is easily found through shadowgraph imaging. Varying ratios of swirled air to straight air, determined by the image-based feedback controller were introduced into the air portion of a coaxial airblast nozzle while keeping the total air flow rate constant. A golden section search converged on the swirled air ratio that provided the largest angle and was validated from the distribution of spray angle versus swirled air ratio. The ratio that produced a spray with the greatest angle of 25.8 ± 2 deg was found at a swirled air ratio of 0.66 ± 0.03 for a spray with a momentum ratio of 6. The successful design and implementation of this image-based feedback controller is intended to provide a foundation for developing real-time active feedback controllers for sprays.
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Escobar-Vargas, Sergio, Jorge E. Gonzalez, Drazen Fabris, Ratnesh Sharma, and Cullen Bash. "High Heat Flux With Small Scale Monodisperse Sprays." Journal of Heat Transfer 134, no. 12 (October 5, 2012). http://dx.doi.org/10.1115/1.4006486.
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This work is aimed at cooling small surfaces (1.3 mm × 2 mm and 3 mm × 5 mm) using spray from thermal ink jet (TIJ) atomizers. Particular interests in this work include obtaining heat fluxes near the critical heat flux (CHF), understanding the correlation between the heat dissipation efficiency (η) and the liquid film thickness (δ) through experimental data, and understanding the primary mode of heat transfer on spray cooling at different liquid film thickness. Current experimental results indicate that high heat fluxes (∼4 × 107 W/m2) are obtained for controlled conditions of cooling mass flow rate, higher efficiencies are achieved at smaller liquid film thickness (δ ≈ 5 μm → η ≈ 0.9), and the heat transfer by conduction through the film becomes dominant as δ decreases.
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Nakamura, Sosuke, Vince McDonell, and Scott Samuelsen. "The Effect of Liquid-Fuel Preparation on Gas Turbine Emissions." Journal of Engineering for Gas Turbines and Power 130, no. 2 (February 29, 2008). http://dx.doi.org/10.1115/1.2771564.
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The emissions of liquid-fuel fired gas turbine engines are strongly affected by the fuel preparation process that includes atomization, evaporation, and mixing. In the present paper, the effects of fuel atomization and evaporation on emissions from an industrial gas turbine engine were investigated. In the engine studied, the fuel injector consists of a coaxial plain jet airblast atomizer and a premixer which consists of a cylindrical tube with four mixing holes and swirler slits. The goal of this device is to establish a fully vaporized, homogeneous fuel/air mixture for introduction into the combustion chamber and the reaction zone. In the present study, experiments were conducted at atmospheric pressure and room temperature as well as at actual engine conditions (0.34MPa, 740K) both with and without the premixer. Measurements included visualization, droplet size, and velocity. By conducting tests with and without the premixing section, the effect of the mixing holes and swirler slit design on atomization and evaporation was isolated. The results were also compared with engine data and the relationship between premixer performance and emissions was evaluated. By comparing the results of tests over a range of pressures, the viability of two scaling methods was evaluated with the conclusion that spray angle correlates with fuel to atomizing air momentum ratio. For the injector studied, however, the conditions resulting in superior atomization and vaporization did not translate into superior emissions performance. This suggests that, while atomization and the evaporation of the fuel are important in the fuel preparation process, they are of secondary importance to the fuel/air mixing prior to, and in the early stages of the reaction in, governing emissions.
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Liang, Yifan, Lars Christian Johansen, and Mark Linne. "Characteristics of sprays produced by coaxial non-swirling and swirling air-water jets with high aerodynamic Weber numbers." Physics of Fluids, September 14, 2022. http://dx.doi.org/10.1063/5.0107480.
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This paper describes part of an experimental study on shear-based spray formation. A laminar liquid jet was ejected inside co-annular non-swirling and swirling air streams. The aerodynamic Weber numbers (We_A) and swirl numbers (S) of the flow cases ranged from 256 to 1426 and from 0 to 3.9, respectively. The aim of this paper is to investigate how S and We_A influence the breakup of a central laminar liquid jet within the fiber-type atomization regime. High-speed shadowgraphy was utilised to visualise the spray behaviour, while Phase Doppler Interferometry (PDI) was utilised to measure the droplet size and velocity distributions. It was found that as S increases, atomization is improved in a way that the droplets are blown outward from the central axis of the nozzle. However, for some specific flow cases, the median droplet diameter (D) does not appear to be related to S. Those specific flow cases are discussed in this work. For S>=0.3, upward motion of droplets located at the central axis of the nozzle was observed, which was caused by recirculating air flows. In addition, it was found that when S increases to 2.5, recirculating air flows start to penetrate to the water exit, which momentarily stops portions of the central laminar water jets from exiting. This pattern will be called turn-off behaviour in this report. In order to study the underlying mechanisms behind the turn-off behaviour, proper orthogonal decomposition (POD) was performed on the shadowgrams. It was found that the timing of turn-off initiation is random.
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Fisher, Brian T., Michael R. Weismiller, Steven G. Tuttle, and Katherine M. Hinnant. "Effects of Fluid Properties on Spray Characteristics of a Flow-Blurring Atomizer." Journal of Engineering for Gas Turbines and Power 140, no. 4 (November 7, 2017). http://dx.doi.org/10.1115/1.4038084.
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In order to understand the reasons for the apparent benefits of using a flow-blurring (FB) atomizer in a combustion system, it is necessary to first examine fundamental spray characteristics under nonreacting conditions. Previous work on FB atomizers, however, has mostly involved only water and a relatively narrow range of parameters. In this study, a phase Doppler anemometry (PDA) instrument was used to characterize FB atomizer sprays and determine the effects of varying surface tension and viscosity of the liquid. Operating at room pressure and temperature (i.e., a “cold spray”), droplet sizes and velocities were measured for water, a water/surfactant mixture (lower surface tension), a water/glycerol mixture (higher viscosity), and glycerol (much higher viscosity). For all of the tested fluids, with the exception of pure glycerol, the FB atomizer produced small droplets (below 50 μm) whose size did not vary significantly in the radial or axial direction, particularly above a characteristic distance from the atomizer exit. Results show that the spray is essentially unaffected by a 4.5× decrease in surface tension or a 7× increase in viscosity, and that Sauter mean diameter (SMD) only increased by approximately a factor of three when substituting glycerol (750× higher viscosity) for water. The results suggest that the FB atomizer can effectively atomize a wide range of liquids, making it a useful fuel-flexible atomizer for combustion applications.
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Sahoo, Santanu Kumar, Hrishikesh Gadgil, Sudarshan Kumar, and K. S. Biju Kumar. "Spatio-Temporal Analysis of a Self-Pulsating Gas-Centered Swirl Coaxial Injector with Forced Gas Jet." AIAA Journal, April 16, 2023, 1–14. http://dx.doi.org/10.2514/1.j062402.
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The objective of the present work is to examine the effects of the acoustically forced gas jet on self-pulsating sprays generated from a gas-centered swirl coaxial injector. We conduct the experiments on self-pulsating spray by forcing the gas jet over a range of forcing frequencies and amplitudes. Various image processing techniques, including proper orthogonal decomposition (POD), have been employed to characterize the spray response. Our spatial mapping of dominant frequencies from time-resolved spray width reveals that although both natural and forcing frequencies prevail in the primary breakup region, a modulation frequency (corresponding to the double of the beat frequency) outcompetes the others. The spatial influence of the forcing is also evaluated by measuring liquid mass fluctuations and drop size statistics at various downstream locations. The experiments were extended to investigate the role of various geometrical parameters, such as swirl number, recess, and length of the gas line on the spray response. The influence of the forcing was observed to prevail even in the liquid mass shedding zone with the appearance of all dominant frequencies. This may have important consequences on the thermoacoustic stability of the combustor. In any case, far downstream of the nozzle, the influence of acoustic forcing is not significant to alter the droplet statistics.
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Strasser, Wayne, and Francine Battaglia. "The Influence of Retraction on Three-Stream Injector Pulsatile Atomization for Air–Water Systems." Journal of Fluids Engineering 138, no. 11 (July 15, 2016). http://dx.doi.org/10.1115/1.4033421.
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Although coaxial airblast primary atomization has been studied for decades, relatively little attention has been given to three-stream designs; this is especially true for transonic self-pulsating injectors. Herein, the effects of nozzle geometry, grid resolution, modulation, and gas flow rate on the acoustics and spray character within an industrial scale system were investigated computationally using axisymmetric (AS) and three-dimensional (3D) models. Metrics included stream pressure pulsations, spray lift-off, spray angle, and primary droplet length scale, along with the spectral alignment among these parameters. Strong interactions existed between geometry and inner gas (IG) feed rate. Additionally, inner nozzle retraction and outer stream meeting angle were intimately coupled. Particular attention was given to develop correlations for various metrics versus retraction; one such example is that injector flow capacity was found to be linearly proportional to retraction. Higher IG flows were found to widen sprays, bringing the spray in closer to the nozzle face, and reducing droplet length scales. Substantial forced modulation of the IG at its dominant tone did not strongly affect many metrics. Incompressible 3D results were similar to some of the AS results, which affirmed the predictive power by running AS simulations as surrogates. Lastly, normalized droplet size versus normalized distance from the injector followed a strikingly similar trend as that found from prior two-fluid air-slurry calibration work.