Marangoni Effect in Subcooled Nucleate Pool Boiling

The lateral motion of bubbles attached to the heater surface during nucleate pool boiling of subcooled liquids is studied in the present paper. It is assumed that there exists the Marangoni convection surrounding a discrete vapor bubble due to the temperature difference acting on the interface between vapor and liquid. The mutual entrainment of adjacent bubbles in the Marangoni convection might drive bubbles toward each other during nucleate boiling of a subcooled liquid. This kind of motion promotes coalescence of adjacent bubbles. A scaling analysis on such flow is presented. The characteristic velocity of the lateral motion is obtained approximately. Furthermore, an approximate equation for estimating the observability of such motion is also presented. The predictions are consistent with the experimental observations. Moreover, it is predicted that the intensity of the Marangoni convection may be very high for fine bubbles initiated at some active cavities on the heater surface, which will result in the micro-jet at the top of the bubble. The effect would be especially important in cases where the bubble release rate is low such as boiling on horizontal down-facing surfaces and boiling in microgravity.