Condensers are crucial components of two-phase heat transport systems envisaged for future large spacecraft. To properly design such condensers, one uses experimental data, obtained from ground testing and reduced gravity aircraft and rocket flight testing, plus results of thermal modelling and scaling calculations. A frequently reported result of such activities, is that condensation lengths required in low-gravity environment exceed the corresponding lengths on earth (in horizontal ducts) up to one order of magnitude and more, while the accompanying pressure drops are almost the same.
Since the flow patterns are different in the two situations, it is better to theoretically (and also experimentally) investigate the impact of gravity on condensation pressure drops and heat transfer for an identical flow pattern, namely annular-wavy-mist, observed along almost the entire condensation length (for vapour qualities ranging from 1 down to values below 0.1), both in low -gravity environment and in vertical downflow in a gravity field.
The paper presents in detail the results of calculations performed: the impact of gravitation on condenser pressure drop and full condensation length for two different working fluids (ammonia and R114), and various duct diameters and thermal loading conditions (the power transported, the operating and sink temperatures).