Condensation heat transfer enhancement mechanism for vertical upflows by the phase separation concept at small gravity

Abstract

In the field of aerospace, minimum and seal of equipments cause the increase in the thermal loading sharply. Due to the lack of driving force, the performance of conventional condenser deteriorates greatly under the small gravity environment, which leads to reduction in the service life of equipments. In this study, a passive condenser, developed on basis of the phase separation concept, is utilized to improve the performance of the condensation heat transfer under the small gravity environment. As a result of the limitation of experiments, the mechanisms of heat transfer enhancement of the phase separation condenser tube are revealed through numerical simulation based on the volume-of-fluid (VOF) method. The following conclusions could be obtained: (1) A novel phase distribution of ‘‘gas near the tube wall and liquid in the tube core’’ is formed. The thin liquid film is indeed created after the flow pattern modulation by inserting mesh cylinder. (2) The condensation quantity for single bubble in the annular region increases about 16 times greater than that in the bare tube region in the case of Jl = 0.0574m/s and Jg = 0.0229m/s. (3) Gas volume fraction affects the parameters of liquid film thickness, bubble length and liquid bridge length. The increase in the gas volume fraction results in the decrease in the evaluation index from 21.56 to 12.82. The evaluation index is defined as the ratio of the condensation quantities per unit tube length of the annular region and the bare tube region.