Liquid jets breakup processes

Wu, Ruff and Faeth12491 studied the breakup of liquid jets with holography. Their measurements showed that the liquid volume fraction on the spray centerline starts to decrease from unit atZ/<70=150 for non-turbulent flows, whereas the decrease starts at aboutZ/<70=10 for fully developed turbulent flows. Their measurements of the primary breakup also showed that the classical linear wave growth theories were not effective, plausibly due to the non-linear nature of liquid breakup processes. 

Droplet Formation in Gas Atomization. Experimental and modeling studiesl160 161 169] 318] 319] 321]- 325] have shown that gas atomization of liquid metals in spray forming and powder metallurgy processes may take place in two primary modes, i.e., liquid jet-ligament breakup and liquid film-sheet breakup. 

Current breakup models need to be extended to encompass the effects of liquid distortion, ligament and membrane formation, and stretching on the atomization process. The effects of nozzle internal flows and shear stresses due to gas viscosity on liquid breakup processes need to be ascertained. Experimental measurements and theoretical analyses are required to explore the mechanisms of breakup of liquid jets and sheets in dense (thick) spray regime. 

Prior to World War II the majority of experimental work in the field of sprays concerned itself with Diesel engine injection problems. Sauter (21C) has suggested that the efficiency of atomization is determined by its fineness and uniformity. De Juhasz (2C) has determined the effect of many different variables on the process of spraying. The more important physical factors tested include the pressure drop across the orifice, the viscosity of the liquid, and the density of the air. For the many different nozzles tested, the ratio of orifice length to diameter has little effect. To determine the effect of the density of the air into which the liquid was sprayed, the nozzles were allowed to discharge into an evacuated chamber. Under these conditions good results are still obtained, suggesting little influence of air friction on jet breakup. 

Breakup of a low-velocity liquid jet (1/velocity)0. This governs in special applications like prilling towers and is often an intermediate step in liquid breakup processes. 

Fuller, R., P.-K. Wu, K. Kirkendall, and A. Nejad. 1997. Effects of injection angle on the breakup processes of liquid jets in subsonic crossflows. AlAA Paper No. 97-2966. 

For a very viscous fluid like maple syrup, the breakup is very slow (which is why we can pour a long, thin stream of maple syriip onto pancakes without its breaking into droplets). Jet breakup is very important in such processes as spray drying, vaporization of liquid fuels in combustion, spray painting, and insecticide spraying. More on this subject can be found elsewhere [10,11,12]. 

Fig. 29.9 Primary breakup processes of round nonturbulent liquid jets in gaseous crossflow (a) We = 0, (b) We = 8, (c) We = 30, (d) We = 220. From Sallam et al. [8]. Reprinted with permission of the American Institute of Aeronautics and Astronautics...

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