EFFECT OF GRAVITY, WALL SUPERHEAT, AND LIQUID SUBCOOLING ON BUBBLE DYNAMICS DURING NUCLEATE BOILING

Dynamics of a vapor bubble formed on a single nucleation site has been studied in this work numerically. The effect of level of gravity, wall superheat and liquid subcooling has been studied parametrically. The numerical simulation has been carried out by solving under the condition of axisymmetry, the mass, momentum, and energy equations for the vapor and the liquid phases. In the model the contribution of micro-layer has been included and instantaneous shape of the evolving vapor-liquid interface is determined :from the analysis. It is found that effect of reduced gravity is to stretch the growth period and bubble diameter at departure. Increase in wall superheat results in reduction in the growth period with a slight increase in the bubble diameter at departure. The effect of liquid subcooling on bubble departure substantially increased. In subcooled boiling both evaporation and condensation have been shown to occur simultaneously on the vapor-liquid interface of the bubble. The predictions from the model are found to be generally in good agreement with the data obtained at earth normal gravity and in low gravity environment of KC-135 aircraft.