Experimental Determination of Conditions for the Explosive Fragmentation of a Heterogeneous Water Droplet in Heating in a High-Temperature Gas Medium

An experimental study has been made of the processes of warming up, evaporation, and boiling of a heterogeneous (with a solid graphite particle) droplet of water in a flow of high-temperature (500–800 K) combustion products. The mechanism of explosive fragmentation (breakup) of the heterogeneous droplet with enhancement of vaporization on internal interfaces (during the nucleation of vapour bubbles at the graphite-particle surface) has been established. The characteristic times of heating of the heterogeneous droplet (2.5–4 mm in size) with an inclusion (in the shape of a cylindrical disk of diameter and height 2 mm) to explosive-fragmentation conditions have been determined. The times of complete evaporation of a liquid film from the inclusion during the implementation of the process of vaporization from the free exterior surface of the droplet have also been given. A significant difference of the conditions and characteristics of the investigated processes from the "graphite substrate–water droplet" system has been shown. Conditions under which the controlling share of heat to internal interfaces of the heterogeneous droplet is supplied through the liquid film or the inclusion have been determined.