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Abstract
Heat pumps have become a potential technology for future thermal management systems in space. However, conventional heat pumps lubricated with oil are currently unfeasible due to the difficulty separating oil in microgravity environments. The oil-refrigerant mixture reduces the heat transfer capacity of heat exchangers, and insufficient separation can damage the compressor. This paper proposes a new heat pump with gas bearings (HPGB) that combines a centrifugal compressor with externally pressurized gas bearings to solve lubrication problems. A numerical model is established to compare performance of the HPGB system with different refrigerants. The results show that the coefficient of performance (COP) of the HPGB system is slightly smaller than those of conventional heat pumps, but higher than those of heat pumps with the impact of an oil concentration of 5%, when evaporator power is 30 kW. The HPGB system is more suitable for high-power conditions because of the higher COP. Ammonia is the best choice for the HPGB system under high-power conditions (above 80 kW). R134a is the best choice under middle-power conditions (from 25 kW up to 80 kW). R1234yf is more suitable with the maximum COP of 2.88 under low-power conditions (below 25 kW).
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No potential conflict of interest was reported by the authors.
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Notes on contributors
Huaqi Lian
Huaqi Lian is currently enrolled as a Ph.D. student in the School of Energy and Power Engineering, Beihang University, China, since 2018. He received the B.Sc. degree from the same university in 2016. His research interests include spacecraft thermal management and oil-free heat pump technology.
Yulong Li
Yulong Li is an Associate Professor in the School of Energy and Power Engineering, Beihang University, China. He received his Ph.D. degree in Power Engineering and Engineering Thermophysics from Beihang University, in 2014. Then, he carried out postdoctoral research in the School of Aeronautics and Astronautics, Tsinghua University, from 2014 to 2016. He joined the School of Energy and Power Engineering, Beihang University in December 2016. His main research fields are aero-engine thermal protection, spacecraft thermal management, and cryogenics.
Chengjun Rong
Chengjun Rong is currently enrolled as a Ph.D. student in the School of Energy and Power Engineering, Beihang University, China, since 2016. He received the master’s degree from the same university in 2016. He is engaged in research on the spacecraft thermal management and oil-free heat pump technology.