Begell House Inc.
Atomization and Sprays
AAS
1044-5110
7
3
1997
DROPLET SIZE AND AGRICULTURAL SPRAYING, PART I: ATOMIZATION, SPRAY TRANSPORT, DEPOSITION, DRIFT, AND DROPLET SIZE MEASUREMENT TECHNIQUES
235-244
10.1615/AtomizSpr.v7.i3.10
Andrew J.
Hewitt
Stewart Agricultural Research Services, Macon, Missouri, USA
A review article is presented discussing the importance of droplet size in the application of sprays for pest control and crop protection. This includes the effect of droplet size on deposition, spray transport and drift. Droplet size characterization techniques are also discussed.
ATOMIZATION CHARACTERISTICS OF AIRBLAST FUEL INJECTION INSIDE A VENTURI TUBE
245-265
10.1615/AtomizSpr.v7.i3.20
H.
Sun
Mechanical Engineering Department, Wayne State University, Detroit, Michigan, USA
T.-H.
Chue
Mechanical Engineering Department, Wayne State University, Detroit, Michigan, USA
R. R.
Tacina
NASA Lewis Research Center, Cleveland, Ohio, USA
This article describes the experimental and numerical characterization of capillary fuel injection, atomization, and dispersion of liquid fuel in a co-flowing air stream inside a single venturi tube. The experimental techniques used are all laser-based. A phase Doppler particle analyzer (PDPA) was used to characterize the atomization process, and planar laser-induced fluorescence (PLIF) was used to visualize the breakup and atomization process of the capillary fuel spray.
The PLIF experiments confirmed the domination of aerodynamic breakup mechanism in and the influence of gaseous vortical structures of various scales on the atomization process of capillary fuel spray. The PLIF images displayed a smooth liquid jet surface near the fuel tube exit, with a rough, perturbed surface developing gradually. At low relative velocities, it was observed that the initial dilational waves on the jet surface were followed by asymmetric and sinuous waves before they evolved into curling liquid ligaments and/or droplets, as the relative velocities increased.
The advantages of venturi nozzle are demonstrated in this article in terms of better atomization, more uniform fuel—air distribution, compared with straight-tube nozzles and free jets.
A modified version of KIVA-II was used to simulate the entire spray process, including breakup and atomization. It was concluded that the multidimensional spray calculation can be used as a design tool only if care is taken in the modeling of breakup and wall impingement processes.
MODELING OF MULTIPLE VAPORIZING DROPLET STREAMS IN CLOSE SPACING CONFIGURATIONS
267-294
10.1615/AtomizSpr.v7.i3.30
Jun
Xin
Department of Mechanical Engineering, The University of Illinois at Chicago, Chicago, Illinois USA
Constantine M.
Megaridis
Department of Mechanical Engineering, The University of Illinois at Chicago, Chicago, Illinois 60607, USA
A model of convective droplet evaporation dynamics is presented for droplet-array configurations that feature close spacing. Comparisons with available experimental data on single and multiple ethanol droplet streams show good agreement. Evidence is presented that evaporative cooling of ethanol micro droplets is not negligible at room temperature. It is shown that local vapor accumulation in the wake of the leading droplets plays an important role in depressing the evaporation rates of the trailing droplets. The influence of ambient blowing in a direction perpendicular to the path of droplet propagation is shown to be important for the trailing droplets in situations where the evaporative flux and the cross-stream convective flux carrying the fuel vapor away are of comparable magnitude. Model predictions for a densely arranged, ordered spray system at elevated temperature and pressure suggest that in most cases the droplets approach one another, and there exist substantial differences in evaporation characteristics between the core and the periphery of the spray. Initial droplet spacings of the order of a few droplet diameters are found to cause vapor spatial distributions which suggest that if ignition occurred, droplets would burn in groups more likely.
CHARACTERIZATION OF A SPRAY FROM AN ULTRASONICALLY MODULATED NOZZLE
295-315
10.1615/AtomizSpr.v7.i3.40
I. P.
Chung
Department of Mechanical and Aerospace Engineering, University of California, Irvine, California, USA
A.
Ganji
Berkeley Applied Science and Engineering, San Francisco, California, USA
Derek
Dunn-Rankin
Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA 92697, USA
The effects of ultrasonic modulation on liquid spray characteristics in a pressure-swirl nozzle at part load have been examined experimentally. The spray characteristics include discharge coefficient, spray appearance, spray cone angle, and spray patternation. An optical visualization technique is used to investigate the spray appearance and the spray cone angle. Spray patternation experiments are conducted both with a physical patternator and with the liquid planar laser-induced fluorescence (LPLIF) technique. The results show that the piezoelectric driver in the atomizer contains several discrete resonant frequencies. At these resonant frequencies, the ultrasonic modulation improves spray development and spray patternation, but has little effect on discharge coefficient and spray cone angle. The improvement is particularly prominent at a part-load injection pressure. Apparently, the ultrasonic modulation increases the perturbation of the liquid inside the nozzle and produces a condition for early disintegration of the liquid sheet issuing from the nozzle. Through this improved atomization, the ultrasonically modulated nozzle may improve the combustion process when engines are at part load or idle condition.
EXPERIMENTAL STUDY OF PURE AND MULTICOMPONENT FUEL DROPLET EVAPORATION IN A HEATED AIR FLOW
317-337
10.1615/AtomizSpr.v7.i3.50
G.
Chen
Department of Mechanical Engineering, The University of Illinois at Chicago, Chicago, Illinois, USA
Suresh
Aggarwal
Department of Mechanical and Industrial Engineering University of Illinois at Chicago
Thomas A.
Jackson
Air Force Aero-Propulsion Laboratory, Fuel and Lubrication Division, WRDC/POSF, Wright Patterson Air Force Base, Ohio, USA
G. L.
Switzer
Wright Patterson Air Force Base, Ohio, USA
The dynamics and vaporization of both pure and multicomponent fuel droplets in a laminar-flow field are investigated. Extensive data are obtained on the velocity and size history of a fuel droplet injected into a well-characterized hot laminar flow. Fuels considered are n-hexane, n-decane, and a bicomponent mixture of equal amounts of hexane and decane. The droplet velocity and size histories are measured by phase Doppler particle analyzer, and compared with the predictions from three different liquid-phase models, the infinite-diffusion, diffusion-limit, and thin-skin models. Predicted results generally show good agreement with measured data. For the conditions of this study, it is shown that the use of a solid-sphere, steady-state drag law adequately reproduces the measured velocity history for small to moderate droplet accelerations, provided the variable-property effects are included in the model. However, the quasi-steady drag equation is not able to capture either the large deceleration experienced by the droplet near the injection location, nor the measured inflection point, where the droplet acceleration changes sign, underscoring the importance of unsteady effects on droplet motion. The comparison of vaporization history indicates that, under relatively low-temperature conditions, the predictions of both the infinite-diffusion and the diffusion-limit models are in close agreement with experiments. However, the thin-skin model overpredicts the vaporization rate, and shows significant differences with experiments, especially for less volatile (n-decane) and multicomponent fuel droplets. The comparison also indicates that the thermophysical properties of the gas film surrounding the droplet should be calculated accurately; in particular, the effect of fuel vapor should be considered.