Thermocapillary effect on bubble sweeping and circling during subcooled nucleate pool boiling of water over microwire

Bubble dynamics on a microscale heating source is crucial to the understanding of heat transfer mechanisms in nucleate boiling. In this investigation, the effect of thermocapillary convection, along with other contributors such as viscous force, on the bubble sweeping and circling phenomena observed in the experiment of subcooled nucleate boiling of deionized water over a micro platinum wire was investigated by numerical simulation and theoretical analysis. The simulation indicates that occurrence of sweeping is mainly due to the thermocapillary effect between the sweeping bubble and a neighboring bubble with a temperature drop caused by the bubble-top jet flow. Based on the parabolic interfacial temperature profile, a simplified dimensional analysis was conducted for the characteristic velocities and lengths along the heating wire and along the bubble interface. The theoretical analysis and the simulation show that the thermocapillary force and the viscous force play important roles in the bubble circling phenomenon. This work may be helpful for better understanding the interfacial force effects on the bubble behaviors and hence the boiling heat transfer at the microscale.