Bubble growth and departure trajectory under asymmetric temperature conditions

摘要

The sudden expansion of an evaporating mass during a phase change process like boiling causes the liquid-vapor interface to experience a reactionary force known as evaporation momentum force. Previous publications have illustrated that by creating a non-uniform liquid temperature distribution around a bubble, the resultant evaporation momentum force acting on the nucleating bubbles can be used to generate separate liquid-vapor pathways during boiling. This paper presents an analytical investigation on the distribution of evaporation momentum force experienced by a nucleating bubble, its effect on bubble growth rate and its role in determining the bubble departure trajectory. An analytical model is developed by incorporating evaporation momentum force into a widely accepted bubble growth model (Mikic et al., 1970) to determine the effect of evaporation momentum force on bubble growth rate. Furthermore, the horizontal displacement of a bubble when the liquid around the bubble is superheated in an asymmetric manner is determined. Experiments are designed to produce an asymmetric temperature condition around a nucleating bubble by creating a temperature gradient over the heater surface and the departure trajectory of the bubbles is observed using a high speed camera. The results indicate that the bubble departure trajectory is significantly altered under asymmetric temperature conditions and the analytical model developed shows good agreement with the experimental observations.