Numerical Study of Heat Transfer and Entropy Generation of Nanofluids Buoyant-Thermocapillary Convection around a Gas Bubble

Abstract

Buoyant-thermocapillary convection is an important heat transfer mechanism in nucleate boiling and nanofluids has been used as heat transfer medium extensively, so it is necessary to study the heat enhancement mechanism of nanofluids buoyant-thermocapillary convection around gas bubble. The present paper first reports the flow, heat transfer and entropy generation characteristics of nanofluids buoyant-thermocapillary convection around a gas bubble in a cavity, and the effects of nanoparticles volume fraction and size on buoyant-thermocapillary convection are discussed. The results show that, as nanoparticles volume fraction increases from 0 to 0.05, the convective intensity and entropy generation of buoyant-thermocapillary convection decreases gradually, and the average Nusselt number of bottom wall first increases and then decreases. As nanoparticles volume fraction is 0.02 the average Nusselt number is the largest and increased by 3.1% relative to that of pure fluid. As nanoparticles diameter increases from 20 nm to 80 nm, the temperature and flow fields indicate as the same structure, but the entropy generation increases gradually. The average Nusselt number of bottom wall increases slightly with nanoparticles diameter increasing, particularly, the average Nusselt number for nanoparticles diameter (dp) 80 nm is increased by 2.28% relative to that of dp = 20 nm.