Experimental investigation on interface characteristics and heat transfer during bubble condensation in narrow rectangular channel

Abstract

Direct steam contact condensation in subcooled water is widely used in various industries because of high efficiency in heat and mass transfer. A visual experimental is carried out to investigate the condensation process of single vapor bubble in narrow rectangular channel by a high-speed camera. Steam mass flux and water temperature are 0–1000 kg/(m2·s) and 57–93 °C, respectively. Four different condensation patterns are found in this study, such as chugging, ellipsoidal jetting, smooth grown bubble and rough grown bubble based on bubble behavior and surface feature. The bubble condensation period is positively correlated with initial bubble diameter. The bubble interface is smooth at low mass flow rates, while it becomes rough when the mass flow rate is high and the process of condensation is shorter. There is a bubble critical diameter during growth stage and each type of bubble will have distinctive phenomena when it reaches the critical diameter. The restriction of the narrow rectangular channel on vapor bubble is that an accelerated condensation process occurs when the bubble diameter changes from restricted to unrestricted. The factor of heat conduction is taken into account in the energy conservation equation, and the condensation heat transfer model is proposed. By deriving the energy conservation equation, a dimensionless parameter A related to the thermal conductivity of the wall and the width of flow channel is obtained. A predictive correlation for bubble diameter and a condensation Nusselt correlation are proposed, and the new correlations incorporate the dimensionless parameter A.