A Study of the Occurrence of Microexplosion in a Single Water-in-Oil Emulsion Droplet

Abstract

This paper presents an experimental and numerical study on the occurrence of microexplosion in water-in-oil emulsion droplets. Experiments are performed for a single water/n-hexadecane emulsion droplet heated in an electric furnace. The volume fraction of water in the emulsion varies from 0.1 to 0.3 and the furnace temperature ranges from 973 to 1173 K. A mathematical model used in the numerical simulation describes the unsteady heat conduction in the emulsion droplet and the homogeneous bubble nucleation in the dispersed water droplets. Throughout the experiments, microexplosion is observed when droplet temperature is about 473 K. An increase in the furnace temperature decreases the microexplosion droplet temperature, and an increase in the water content decreases the microexplosion droplet temperature. In the numerical simulation, the strength of microexplosion when the water droplet temperature reaches the superheat limit is estimated from the homogeneous bubble nucleation rate. The strength of microexplosion peaks near the surface of an emulsion droplet. A water droplet heated to the superheat limit evaporates explosively. Furthermore, water droplets rapidly heated to the superheat limit in the higher furnace temperature evaporate explosively, so that the temperature of the droplet center is low compared with the lower furnace temperature. Although water content has no influence on the temperature of water droplets, an increased number of water droplets proportional to the water content indicates an increase in bubble nucleation. Therefore, higher water content is favorable for microexplosions, which indicates the occurrence of microexplosion at a lower droplet temperature.