In this study, a complete numerical simulation of a growing and departing bubble on a horizontal surface has been performed. A finite difference scheme is used to solve the equations governing conservation of mass, momentum, and energy in the vapor-liquid layers. The vapor-liquid interface is captured by a level set method which is modified to include the influence of phase change at the liquid-vapor interphase. The disjoining pressure effect is included in the numerical analysis to account for heat transfer through the liquid microlayer. From the numerical simulation, the location where the vapor-liquid interface contacts the wall is observed to expand and then retract as the bubble grows and departs. The effect of static contact angle and wall superheat on bubble dynamics has been quantified. The bubble growth predicted from numerical analysis has been found to compare well with the experimental data reported in the literature and that obtained in this work. Recently, Lee and Nydahl (1989) have numerically simulated Journal of Heat Transfer Copyright © 1999 by ASME AUGUST 1999, Vol. 121 / 623 Downloaded From: http://heattransfer.asmedigitalcollection.asme.org/ on 05/25/2015 Terms of Use: http://asme.org/terms Transactions of the ASME Downloaded From: http://heattransfer.asmedigitalcollection.asme.org/ on 05/25/2015 Terms of Use: http://asme.org/terms

Attempts have recently been made to numerically simulate film boiling on a horizontal surface. It has been observed from experiments and numerical simulations that during film boiling the bubbles are released alternatively at the nodes and antinodes of a Taylor wave. Near the critical state, however, hydrodynamic transition in bubble release pattern has been reported in the literature. The purpose of this work is to understand the mechanism of the transition in bubble release pattern through complete numerical simulation of the evolution of the vapor-liquid interface. The interface is captured by a level set method which is modified to include the liquid-vapor phase change effect. It is found from the numerical simulation that at low wall superheats the interface moves upwards, bubbles break off, and the interface drops down alternatively at the nodes and antinodes. However, with an increase in wall superheat, stable vapor jets are formed on both the nodes and antinodes and bubbles are released from the top of the vapor columns. The numerical results are compared with the experimental data, and visual observations reported in the literature are found to be in good agreement with the data.

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The past efforts in applying linear Taylor instability theory to the prediction of heat transfer during film boiling on a horizontal surface have suffered from the fact that empirical correlations must be used to define the shape of vapor-liquid interfaces and to determine the transport of mass and heat across these interfaces. The objective of this study is to clarify the physics of film boiling and to predict heat transfer coefficients through complete numerical simulation of the evolving interface between superposed layers of immiscible fluids. A coordinate transformation technique supplemented by a numerical grid generation method and a second-order projection method are combined to solve for the flow and temperature fields associated with an evolving interface. From the numerical simulation, the film thickness and, in turn, the heat transfer coefficient are found to vary both spatially and temporally. Increased wall superheat not only thickens the vapor film in the valley but also enlarges the vapor bulge. The effect of increased system pressure is to slow down the growth of the interface.

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A bubble merger process on a single nucleation site has been investigated by numerically solving the equations governing conservation of mass, momentum and energy in the vapor and liquid phases. The vapor-liquid interface is captured by a level set method which can easily handle breaking and merging of the interface. The level set method is modified to include the effects of phase change at the interface and contact angle at the wall. Also, the evaporative heat flux from the thin liquid film that forms underneath a growing bubble attached to the wall is incorporated in the analysis. Based on the numerical simulations, the effect of bubble merger on vapor removal rate, flow field and heat transfer has been quantified. The bubble merger pattern predicted numerically has been found to compare well with the experimental observations.