Measurements and Predictions of the Structure of Evaporating Sprays

Abstract

An experimental and theoretical study of turbulent evaporating sprays is described. Experiments considered round, Freon-11 sprays (Sauter mean diameters of 31 and 58 μm) produced by an air-atomizing injector directed vertically downward in still air. The following structure measurements were made: mean and fluctuating gas velocities, total concentration of Freon-11, drop size and velocity distributions, mean gas temperature, and liquid flux distributions. Three spray models were evaluated using the new measurements: (a) a locally homogeneous flow (LHF) model where interphase transport rates are assumed to be infinitely fast; (b) a deterministic separated flow (DSF) model where finite interphase transport rates are considered but drop-turbulence interactions are ignored; and (c) a stochastic separated flow (SSF) model where effects of finite interphase transport rates and drop-turbulence interactions are considered using random-walk computations for drop motion and transport. The LHF and DSF models performed poorly, since both finite interphase transport rates and drop-turbulence interactions were important for present test conditions. The SSF model gave best agreement between predictions and measurements and appears to be an encouraging approach for treating practical sprays.