UNSTEADY VAPORIZATION OF AN ISOLATED FUEL DROPLET IN A CONVECTIVE ENVIRONMENT WITH VARYING AMBIENT CONDITIONS

Abstract

In many practical problems, the fuel droplets vaporize and burn in a strong convective flow field with varying amb-ient conditions. These varying ambient conditions along with the unsteady heating and shrinking, of the droplet make the problem of droplet vaporization in a spray essentially un-steady. Therefore, various semi-emperical correlations which have been proposed to predict mass vaporization rate under quasi-steady conditions are not satisfactory for use in the overall modelling of spray processes. For a droplet, vapori-zing in a flow field with constant ambient conditions, the solution of the gas-phase boundary layer equations had been obtained earlier by Prakash and Sirignano [49] by-.an integral approach. However, the validity and accuracy of the integral approach has not been determined particularly near the zero shear stress point. In the present work, the results of the integral approach are compared with the two .. dimensional solution of the boundary layer equations, The study is further extended to ,predict droplet vaporization under varying ambient condi-tions. The quasi-steady two-dimensional conservation equations (uncoupled from the liquid-phase) for the axis-symmetric gas-phase boundary layer have been solved, for both the cir- culating and the non-circulating droplet, by using the Levy Manglerand Howa