Experimental study on direct contact condensation of steam bubbles with non-condensable gas at high Reynolds numbers

Abstract

Direct contact condensation of steam bubbles with non-condensable gas is common in nuclear safety equipment. It was insufficient research on the direct contact condensation heat transfer model of steam bubbles with non-condensable gas at high Reynolds numbers (Re > 22000) in previous works. To study the effect of non-condensable gas on heat transfer of steam–air bubbles at high Reynolds numbers, a high-speed camera was used to capture the behavior of bubbles and used image processing and bubble reconstruction to obtain size and dynamic parameters of bubbles. The size and upward motion behavior of bubbles were analyzed. The heat transfer coefficient during the bubbles condensation experiment were calculated and experimental results were compared with correlations proposed by previous works. In order to better explain the heat transfer characteristics and predict the heat transfer coefficient of bubbles at high Reynolds numbers, a modified heat transfer correlation based on the correlation of rigid sphere was proposed which are functions of bubble Reynolds number, liquid Prandtl number, Jacob number, and dimensionless time. This correlation considers the influence of both forced convection around bubbles and variations in steam fractions on bubble condensation. Comparison of experimental data and the corresponding predicted values shows that the deviation between the experimental data and predicted values is within ± 25 % which indicates the modified correlation accurately predicts the experimental data in this paper.