Vapor compression refrigeration testing on parabolic flights: Part 2 - heat exchanger performance

•Two-phase flow visualizations of evaporator inlet under normal and microgravity.•Consistent increase of condensation temperature at the onset of microgravity captured.•Mild evaporator oscillations observed through five independent measurements.•Categorization of cycle response by refrigerant-side cooling capacity changes to flight maneuvers. Propositions of vapor compression cycles for microgravity applications have a long history. In contrast, experimental efforts and implemented applications are rare in general and in recent years even less than in the 1980s and 1990s. The paper shows experimental results from a vapor compression cycle on parabolic flights. The focus lies on the effects of varying gravity forces on the condenser and evaporator. Flow visualizations clearly showed a change to an annular or slug-annular flow regime at the evaporator inlet shortly after the onset of gravity. The discharge pressure was found to consistently increase sharply by 1–3% across widely varying operating conditions. Oscillations were observed in the evaporator for some parabolas due to microgravity. Overall, the cycle response to varying gravity based on the cooling capacity can be categorized in four different groups, which appear to have a dependence on both the mass flow rate and the evaporator superheat.