Computer Simulation of Photophoretic Force on Rapidly Vaporizing Heterogeneous Droplet

Abstract

The theoretical/computational study is focused on the photophoretic (radiometric) effect caused by nonuniform absorption of anisotropic, high-temperature thermal radiation within a layered droplet. Transient values of the photophoretic force acting on the shrinking droplet are estimated by numerical integration of the momentum flux carried by vapor molecules interacting with the droplet's surface of nonuniform temperature. The corresponding stress tensor of the surrounding nonequilibrium gas is calculated by application of the results of the kinetic theory of evaporation of small droplet suspended in its own vapor. The radiant heat dissipation within the microheterogeneous, layered droplet is simulated by an application of the Monte Carlo method. Specific computations are performed for small droplets of ultrafine coal-water slurry (CWS) suspended in superheated steam and irradiated from one side to a high-temperature blackbody radiation. The conditions are simulating the situation of primary atomized CWS droplets facing the thermal radiation of a flame front during the first few msec in a gas turbine combustor.