VAPORIZATION OF MISCIBLE BINARY FUEL DROPLETS UNDER LAMINAR AND TURBULENT CONVECTIVE CONDITIONS
Résumé
Convective vaporization of single bi-component droplets under different flow conditions is investigated. Pure and mixture droplets of n-heptane and n-decane are suddenly exposed to cold or heated laminar or turbulent flows generated by a controlled flow system. A real-time image analysis procedure has been developed to determine the instantaneous vaporization rates. Distillation-type vaporization is observed for all the mixtures investigated under stagnant or cold flow conditions. It is shown that the first vaporization sequence is intrinsically non-stationary and that the quasi-steady vaporization rate of the second sequence is equal to that of pure n-decane under the same conditions. The preferential vaporization process disappears when the flow is moderately heated. However, another non-stationary process, corresponding to the heat-up of the droplet, appears. In heated convective conditions, a constant vaporization rate equal to that of the less volatile component characterizes the post-preheating period. These experimental results are discussed by using a formalism based on the comparison between the droplet vaporization rate and the liquid-phase mass diffusion rate. Preliminary experimental results are also reported on bi-component droplet vaporization in a turbulent flow, in the distillation-type vaporization regime.