EXPERIMENTAL AND NUMERICAL STUDY OF BUBBLE GROWTH PROCESS WITHIN A SUPERHEATED WATER DROPLET

This paper reports an experimental and numerical study of bubble growth process within a water droplet due to depressurization. During the experiment, a distilled water droplet was suspended on a thermocouple, which was also used to measure the droplet temperature. A high-speed camera was applied to record the bubble expansion. A mathematical model was developed based on the momentum equation of bubble growth coupling with the energy conservation equation. The heat transfer due to flash evaporation was considered at the droplet surface. The mechanical nonequilibrium on the formation of bubble nucleus was also introduced. Especially, this model considered the influence of thermocouple on bubble growth. The model predictions agree well with the experimental data, demonstrating the soundness of the present model. Through the numerical calculations, the main factors affecting the bubble growth were analyzed. The results show that the main influences on bubble growth include pressure difference, surface tension, and friction resistance between the droplet and the thermocouple. The existence of thermocouple slows down the bubble growth, and its effect is controlled by the competition between the increase of liquid velocity and the reduction of contact area.