PRIMARY BREAKUP IN GAS/LIQUID MIXING LAYERS FOR TURBULENT LIQUIDS

Abstract

An experimental study of primary breakup of turbulent liquids in gas/liquid mixing layers is described. The experiments involved mixing layers along large round liquid jets (3.6, 6.4, and 9.5 mm diameter) injected at various velocities into still air and helium at atmospheric pressure with fully developed turbulent pipe flow at the jet exit. Liquids studied included water, glycerol (42% glycerin by mass), and n-heptane. Pulsed shadowgraph photography and holography were used to find conditions where turbulent primary breakup was initiated, as well as drop sizes and velocities after primary breakup. Drop sizes after primary breakup satisfied Simmons's universal root normal distribution with MMD/ SMD−1.2; therefore, they could be characterized solely by their SMB. Mass-weighted mean streamwise and cross-stream drop velocities after primary breakup were comparable to mean streamwise and cross-stream rms fluctuating velocities in the liquid, respectively, with effects of mean velocity distributions in the jet passage reflected by somewhat lower streamwise drop velocities near the jet exit. Drop size properties after turbulent primary breakup were identical for tests in either air or helium and could be correlated reasonably well by phenomenological anlyses considering effects of surface tension and liquid turbulence properties alone. However, limited data in the literature suggest that aerodynamic effects begin to influence drop sizes after primary breakup at ambient gas densities greater Лап those considered during the present experiments.