Temperature Fluctuation under Bubbles of Pool Boiling at decompression.

Abstract

Experiments on pool boiling of water were performed under decompression. Temperature fluctuation measured with 3 thermocouples which were equipped on copper block surface by plating. Rapid temperature drops in this fluctuation arise at same times. This shows the existence of evaporation of microlayer under bubbles. The evaluation of this evaporation of the microlayer and rapid temperature drops showed the existence of a new evaporation factor in obedience to the liquid surface overheating. Temperature drops have two types at decompression. One is rapid drop due to the cavity existence and the other is slow drop due to the generation in the superheated bulk liquid on the mirror surface. This rapid temperature drop have gradual drop at first stage. For verification of gradual drops, we introduced a equation concerned micro film thickness under the bubble on the basis of the viscosity and the preservation of momentum. This equation has exponential factor about microfilms. Numerical calculations showed a good agreement with the experimental data.