Modeling of the bubble dynamics and heat flux variations during lateral coalescence of bubbles in nucleate pool boiling

Abstract

A liquid-vapor phase change lattice Botlzmann method was used to simulate the dynamics of two bubbles during the lateral coalescence on solid surfaces in nucleate boiling. The evolution of bubble shapes and the departure diameter of bubbles were compared with experimental data. Comparisons show good agreement. The heat fluxes under nucleating, coalescing, growing and departing bubbles were simulated and directly related to the bubble dynamics. It was found that a typical ebullition cycle includes nucleation and growth of individual bubbles, coalescence of two bubbles, oscillation and departure of the coalesced bubble. The heat-flux variation under the bubbles has two major peaks, which are due to the coalescence of two bubbles, the departure of the coalesced bubble and nucleation of succeeding bubbles, respectively. The results showed that the heat flux peaks for nucleation and departure are slightly larger than the heat flux peaks for coalescence for the smaller and the larger separation distances, while those for coalescence are larger for the moderate separation distances. It was also found that there exists an optimal separation distance for the coalescing bubbles to achieve the best heat transfer performance, which provides very useful information to enhance pool boiling heat transfer.