Conditions for Explosive Disintegration of Inhomogeneous Water Droplets on High-Temperature Heating

Abstract

Experimental investigations of the characteristic stages of the processes of heating, evaporation, and explosive disintegration of inhomogeneous water droplets (with a commensurate graphite inclusion) in a high-temperature (600–1200 K) gaseous medium are carried out. Three methods of heating droplets differing in the dominating mechanism of heat transfer are used: heating in a muffle tube furnace (thermal radiation), in a stream of heated air (radiative-convective heat transfer), and in a stream of high-temperature combustion products of a typical liquid fuel (radiative-convective heat transfer). Characteristic values of each heat flux component ate determined for the conditions of experiments, as well as their dependences on temperature. It is shown that the highest values of the radiative heat flux (determining one from the viewpoint of the origination of the effect of explosive fragmentation of droplets) correspond to the schemes of heating in a stream of combustion products and in a tubular muffle furnace. The threshold values of the gaseous media temperatures at which a stable explosive disintegration of evaporating inhomogeneous droplets is realized (Tg > 850 K for conditions of heating in a stream of heated air, Tg > 800 K for the tubular muffle furnace, and Tg > 600 K for a stream of combustion products) have been obtained experimentally. With the use of thermocouple measurements the assumption on accumulation of the energy of thermal radiation near the liquid–solid particle interface and on the resulting formation of an additional source of liquid fi lm heating has been confirmed, which leads to the overheating of the liquid and to explosive disintegration of the droplet.