Mass-Transfer Model in Subcooled Nucleate Boiling

Abstract

The mass-transfer model of subcooled boiling, conceived in 1952 by N. W. Snyder, is reviewed. Described is an experiment in which a water-vapor bubble was studied from its growth on a heated surface, through a thermal layer, and into a turbulent stream of subcooled water flowing parallel to the heated surface. The effectiveness of the turbulent subcooled stream in removing heat deposited by condensation on the surface of the bubble was determined. The results show that the thermal-energy transport associated with the mass-transfer mechanism in boiling heat transfer can be absorbed effectively at the top of the bubble. Also given are the results of a theoretical investigation in which two models of bubble dynamics were derived. The first model describes the artificial bubble produced in the experiment just noted. The second model describes the dynamics of a bubble growing on a heated surface, into a subcooled liquid, and with an evaporating thin liquid film below the bubble on the heated surface. The results show that the importance of the mass-transfer mechanism has been underestimated in the past and that this mechanism is responsible for a substantial portion, or almost all, of the heat transfer in subcooled nucleate boiling in forced convection.