and Surface Disturbance Evolution on Turbulent Liquid Jets in Gases

Splattering of droplets during liquid jet impingement on solid targets alters the efficiencies of jet impingement heat transfer processes and chemical containment safety devices, and leads to problems of aerosol formation in jet impingement cleaning processes. A study of the turbulent liquid jet impingement splattering, the evolution of the disturbances on the free surface of a turbulent liquid jet in gas and the relation between splattering and the jet surface disturbances is presented here. Experimental results on the amount of splattering for jets of water, isopropanolwater solutions, and soap-water mixtures are reported here. Jets were produced by straight tube nozzles of diameter 0.8 5.8 mm, with fully-developed turbulent pipeflow upstream of the nozzle exit. These experiments cover Weber numbers between 130 31,000, Reynolds numbers between 2700 98,000, and nozzle-to-target separations of 0.2 < z/d < 125. Splattering of up to 75% of the incoming jet liquid is observed. The results show that only the Weber number and x/d affect the fraction of jet liquid splattered. The presence of surfactants does not alter the splattering. Also a new correlation for the onset condition for splattering is presented. A laser-based optical technique is used to measure the amplitudes of surface disturbances on turbulent liquid jets in air. Measurements were made on jets of water, isopropanol-water solutions, soap-water mixtures and water with drag reducing additive, guar, between 0.2 and 50 nozzle diameters from the nozzle. Measurements show a non-exponential growth of the rms amplitude of the surface disturbances on the jet as it moves downstream. Power spectra of the surface disturbances show the broadband turbulent disturbances to be dominant over any single wavenumber Rayleigh-type instability. The measured rms amplitude of roughness on the jet surface correlates well with the fraction of impinging liquid splattered. A mathematical model of free surface turbulence is presented. The spectrum of disturbances is calculated based on the pressure spectrum of isotropic, homogeneous turbulence. Both the theoretical model and the experiments show that the highwavenumber portion of the spectrum decays as k19/3 owing to the damping effect of capillary pressure on the turbulent pressure spectrum that drives surface roughening. A mathematical model for the growth of turbulent disturbances on a free-surface liquid jet is also proposed. Thesis Supervisor: John H. Lienhard V Title: Associate Professor