A Comprehensive Model for Single Bubble Nucleate Flow Boiling

Abstract

The single bubble dynamics and local thermal effects in a rectangular channel are investigated in this paper under subcooled nucleate flow boiling conditions. A combined effect of Marangoni and microlayer evaporation in flow boiling regimes has rarely been reported in open literature. Therefore, a comprehensive boiling model that combines the three submodels, namely, phase change model, microlayer evaporation model, and Marangoni model, is developed that accounts for smallscale physics such as evolution of superheat layer during bubble growth, microlayer evaporation, and scavenging of the superheated liquid during the bubble departure. The verification of model has been carried out through detailed flow and temperature field validation exercises of various bubble stages with recent experimental data reported in the literature. The effects of varying subcooled conditions and Reynolds number on bubble dynamics and the associated heat transfer rates have been examined. The study reveals a decreasing trend in the bubble diameter with increasing Reynolds number and degree of subcooling. It has also been observed that the bubble shape is affected by the Marangoni phenomena. Bubble shape slightly flattens during inception, gradually becomes spherical while sliding, and later elongates after liftoff. The individual contribution of microlayer heat flow (Qmicrolayer) is estimated to be around 22–40% for flow boiling conditions and it is the secondhighest heat transfer contributor after the latent heat transfer. The results obtained from the proposed model show a good match with published data and indicate the significance of microlayer in the single bubble flow boiling heat transfer.