INTERFACIAL HEAT-TRANSFER BETWEEN STEAM BUBBLES AND SUBCOOLED WATER IN VERTICAL UPWARD FLOW

In two-fluid modeling, accurate prediction of the interfacial transpor t of mass, momentum, and energy is required. Experiments were carried out to obtain a data base for the development of interfacial transport models, or correlations, for subcooled water-steam bubbly flow in ver tical conduits. The experimental data of interest included the interfa cial area concentration, interfacial condensation heat transfer and bu bble relative velocity. In the present investigation, bubble condensat ion in subcooled water-steam flow in a vertical annulus at low flow ra te and low pressure is investigated experimentally. A high-speed video system (up to 1000 frame/s) was used to visualize two orthogonal view s of the flow simultaneously A digital image processing technique was used to track and measure the velocity and size of the collapsing bubb les. The axial void fraction distribution was also measured by a singl e beam gamma densitometer. The results were compared with existing cor relations and a new correlation for bubble condensation Nusselt number ,vas obtained based on the present data. In the proposed correlation, the bubble condensation Nusselt number is expressed in terms of the bu bble Reynolds number, Jakob number, and void fraction. The latter term accounts for the multi-bubble effect. This correlation can predict th e present data within +/-20 percent with a correlation coefficient of 96 percent.