Gravity Dependent Condensation Pressure Drop and Heat Transfer in Ammonia Two-Phase Heat Transport Systems

摘要

Results of calculations on condensing flow in a straight condenser duct, whichinvestigated the impact of (reduced) gravity on the duct length required to achieve complete condensation, are reported. Condensers are critical components in two phase heat transport systems envisaged for future large spacecraft. In order to properly design such condensers, experimental data obtained from ground testing and reduced gravity aircraft and rocket flight testing, plus results of thermal modeling and scaling calculations are used. The result of such activities, frequently reported in the literature, is that condensation lengths required in low gravity environment exceed the corresponding lengths on Earth (in horizontal ducts) by at least one order of magnitude, while the accompanying pressure drops are almost the same. As the flow patterns are different in both situations, it was considered to be a better approach to theoretically (and later also experimentally) investigate the impact of gravity on condensation pressure drops and heat transfer for an identical flow pattern, namely annual-wavy-mist observed for vapor qualities ranging from 1 down to values below 0.1 (hence, almost the entire condensation length), both for low gravity conditions and for vertical downflow in a gravity field. The results of this approach are discussed for condensers using ammonia as the working fluid.