Microscale wall heat transfer and bubble growth in single bubble subcooled boiling of water

Abstract

A MEMS measurement technique was used to study the mechanisms of wall heat transfer and bubble growth during subcooled boiling of water in the isolated bubble region. The local wall temperature beneath a single bubble in subcooled boiling was measured at a sampling frequency of 50kHz using a MEMS sensor. The wall and liquid phase heat transfers were quantitatively evaluated by the analysis with the measured local temperature and bubble size extracted from bubble images. The microlayer evaporation provided a significant contribution to the wall heat transfer and the bubble growth, but the rewetting heat transfer during the bubble departure process was insignificant in the wall heat transfer, as with our previous results for saturated boiling. The subcooling of the bulk liquid was found not to have significant influence to the microlayer evaporation. The condensation heat transfer from vapor bubble to bulk subcooled liquid was comparable to the microlayer evaporation heat transfer, and subcooled boiling single bubbles behaved like a heat pipe on the heated wall. The bubble oscillation on the surface was observed in one case. The evaporation of the microlayer which repeatedly reformed in the oscillation process transferred a high heat flux of around 1MW/m2. Evaporation and formation characteristics of the microlayer were additionally examined.