Bubble growth and departure trajectory under asymmetric temperature conditions

• Effect of evaporation momentum force on bubble growth rate is determined.
• Effect of liquid temperature variation on evaporation momentum force significant.
• Lateral bubble displacement under asymmetric temperature conditions is predicted.
• Experimentally confirmed bubble displacement under asymmetric temperature conditions.

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.