Investigation Of Heat Pump-Cold Storage Heat Rejection System For Space Stations

Heat rejection into space grows with the enlargement of space stations. To reject the increasing heat dissipation by larger radiator surface will encounter the difficulties in system design and payout of system weight. One can also enhance the rejection of heat by raising the surface temperature of the radiator by conventional heat pumps with a penalty of heavier system weight. This thesis suggests an innovative heat pump-cold storage heat rejection system (HPCSHRS) for space station based on the characteristics of power generation of space stations. When facing the sun the heat pump works to reject heat and charge cooling for the ice storage device. When in the shadow of the earth the stored ice helps to compensate the ability of the thermal radiator to complete the rated heat rejection. This operating mode of HPCSHRS can reduce the mass associated with electrical power storage devices. To verify the feasibility and operating characteristics of HPCSHRS, systematic investigations are conducted.Firstly, steady state analysis is performed to quantify the effects of sensitive parameters on the total mass of HPCSHRS. The results show that HPCSHRS has an optimum condensing temperature and an optimum cold storage rate. Under the optimum operation, the radiator area and total system mass of HPCSHRS are 4.8% and 30.0% less than those the single-phase fluid heat rejection system respectively. Compared with the conventional heat pump heat rejection system, the radiator area of HPCSHRS is 12.0% greater than that of the heat pump system but the total system mass of HPCSHRS reduces 9.3% than that of the heat pump system.Secondly, mathematical models describing the transient thermal behavior of HPCSHRS using lumped parameter methods are developed. A transient model of single-phase fluid loop is also developed for comparison. The simulation results show that radiator area and total mass of HPCSHRS are 47.5% and 18.3% less than those of the single-phase fluid heat rejection system respectively, which demonstrates that HPCSHRS has better performance under transient operation.An experimental system is designed and set up for validating its feasibility and investigating its operation characteristics of HPCSHRS. The measured results indicate that the compressor COP is 2.14, which results in a 22.8% reduction of the radiator area, and an 7.5% increase system weight compared the single-phase fluid system. The result is close to the steady analysis and shows that HPCSHRS can indeed reduce not only radiator area but also system weight by choosing a compressor with higher COP. Compared with heat pump heat rejection system, the radiator area of HPCSHRS is increased by 23.2% and thetotal system mass of HPCSHRS is reduced by 1.6%. The experimentally obtained results also show that HPCSHRS has a preferred start-up characteristic and run stability, and can ensure the inlet water temperature of inner loop to meet thermal control requirements of the space station. The quantitative agreement between the simulation and the experiments in the inlet water temperature has verified the transient simulation model of HPCSHRS.A concentric circular pipe ice storage device is presented based on light-weighted design requirement. Charging and discharging characteristics of the device are analyzed by using heat enthalpy method, resulting in reasonable values of the structural parameter. The dynamic characteristics of charging and discharging of ice storage device is experimentally studied, showing that the theoretical and experimental results are in a good agreement. The two-phase flow and heat transfer characteristics of refrigerant in tubes of the radiator are numerically analyzed based on the optimum fin height of the radiator which is gained by numerical simulation. A system optimization model employing separated flow and distributed parameter method is also developed for assessing the influences of various design schemes on power consumption and the sizing of components by the efficient connection of the component models. Based on above investigation three different means are proposed for improving the performance of HPCSHRS.Finally, two improved thermodynamic cycle schemes, double compressor cycle and compression/ejection mixed cycle, are suggested to further reduce the power consumption by raising the compressor inlet pressure of refrigerants. The results of thermodynamic analysis show that the double compressor cycle can significantly lower power consumption of HPCSHRS by 29.4% with R22 as refrigerant. As a promising scheme, the radiator area and total system mass of the double compressor cycle of HPCSHRS are 33.0% and 9.7% less than those the single-phase fluid heat rejection system respectively. Compared with the heat pump system, radiator area increases by 7.1% but the system mass is reduces by 13.9%.