Liquid vapour phase change on a single nucleation site: Heat and mass transfer

Abstract

In this paper experimental results of heat and mass transfer variations during a single vapour bubble growth are carried out. The vapour bubble was created in a FC-72 liquid, on a downward facing heating element maintained at constant heating power. Heat flux and temperature measurements combined with image processing enable us to study the influence, on heat transfer, of the level of liquid subcooling, the heating power applied on the nucleation surface and the nucleation surface’s inclination. It was found that the phase change heat flux (i.e. the difference between the flux of evaporation and the flux of condensation) and the total heat flux (measured with fluxmeter and due to convection, conduction and phase change) decreased in the same order of magnitude when the level of subcooling was increased. When the heating power increased, the total heat flux increased whereas the phase change heat flux varied in a non-significant way. It was also found that the total heat flux depends on the nucleation surface inclination, whereas, for small angles, the phase change heat flux didn’t change. The analysis of those results lead to the conclusion that during boiling the liquid motions due to the bubble growth and departure play an important role in the heat transfer enhancement.