VAPORIZATION OF MISCIBLE BINARY FUEL DROPLETS UNDER LAMINAR AND TURBULENT CONVECTIVE CONDITIONS

Convective vaporization of single bicomponent droplets under different flow conditions is investigated. Pure and mixture droplets of n-hepta ne and n-decane are suddenly exposed to cold or heated laminar or turb ulent flows generated by a controlled flow system. A real-time image a nalysis procedure has been developed to determine the instantaneous va porization rates. Distillation-type vaporization is observed for all t he mixtures investigated under stagnant or cold flow conditions. It is shown that the first vaporization sequence is intrinsically nonstatio nary and that the quasi-steady vaporization rate of the second sequenc e is equal to that of pure n-decane under the same conditions. The pre ferential vaporization process disappears when the flow is moderately heated. However, another nonstationary process, corresponding to the h eatup of the droplet, appears. In heated convective conditions, a cons tant vaporization rate equal to that of the less volatile component ch aracterizes the post-preheating period. These experimental results are discussed by using a formalism based on the comparison between the dr oplet vaporization rate and the liquid-phase mass diffusion rate. Prel iminary experimental results are also reported on bicomponent droplet vaporization in a turbulent flow, in the distillation-type vaporizatio n regime.