HEAT TRANSFER CHARACTERISTICS OF ISOLATED BUBBLE NUCLEATE BOILING OF WATER

The mechanism of isolated bubble pool nucleate boiling of water is studied by a novel approach method using the developed MEMS thermal sensor The local temperature variation beneath isolated bubble was measured using the MEMS sensor at different six wall superheats. Evaporation and dry-out of the microlayer and the rewetting of the thy-out area were obviously observed in the measured temperature variation. Wall heat transfer was numerically calculated by transient heat conduction simulation with the measured temperature as a surface boundary condition. The results showed that the microlayer evaporation transfers high heat flux of a few MW/m(2), and dominantly contributes to the heat transport from the heating wall during the bubble growth phase. The ratio of the heat transferred from the wall to the latent heat in the bubble at the departure decreased with increasing wall superheat. In other words, the contribution of the heat transfer from the superheated liquid layer surrounding the bubble becomes important with increasing wall superheat. Moreover, the microlayer thickness was calculated by integrating the local heat flux. The derived initial thickness of the microlayer was independent from the wall superheat and became thick as distance from the nucleation site increases.