Experimental Investigation and Analysis of Flow Condensation Heat Transfer in Microgravity-Experiments Onboard the International Space Station

This study presents the flow condensation heat transfer results of the Flow Boiling and Condensation Experiment (FBCE). The primary goal of FBCE is to obtain fundamental flow boiling and condensation heat transfer data in microgravity (mu ge) through experiments onboard the International Space Station. Experiments were performed with the Condensation Module for Heat Transfer (CM-HT), which is a tube-in-tube counterflow heat exchanger. Condensing nPFH flows through a stainless steel tube with an inner diameter of 7.24 mm and rejects heat to cooling water flowing in an annular channel (with inner and outer gap diameter of 7.94 and 12.70 mm, respectively) surrounding the tube. Experiments tested a broad range of nPFH mass velocities, G = 72.8 - 291.5 kg/m2s, inlet thermodynamic equilibrium qualities, xe,in = 0.28 - 1.19, inlet pressures, pin = 103.9 - 160.2 kPa, and water mass velocities, Gw = 129.4 - 324.7 kg/m2s. A parametric investigation shows local condensation heat transfer coefficient, h, is primarily dependent on G and local xe, which can be represented by the two-phase mixture Reynolds number, Retp. Channel averaged heat transfer coefficient in the saturated two-phase region, htp, increases with increasing G and xe,in. However, increasing inlet superheat does not affect htp, but does increase the heat transfer coefficient averaged over the entire channel, h. In the present experiments, G is sufficient to mitigate the effects of gravity, and htp in mu ge aligns with those for vertical down flow and horizontal flow in Earth gravity. Various correlations for htp were assessed, and the best performing correlation with a Mean Absolute Error (MAE) of 7.1% was that by Dorao and Fernandino, which is a function of Retp. Some correlations were shown to be overly dependent on the effect of gravity and were not applicable for the present mu ge database. A Separated Flow Model for annular condensation was employed to predict htp. The model's physical basis makes it seamlessly adaptable for mu ge, and it resulted in a MAE of 32.3%.