| The mechanically pumped two-phase loop system(MPTL) is attracting more interest in space application resently, for its capability of heat collecting, and long-distance heat transferring for distribut heat sources with stable and uniform thermal control. To design the space thermal control system, it is difficult to achieve the real space environment in the ground test, such as complex space condition of the heat flux, vacuum and micro-gravity. Also, the tests on ground are strictly limited by the cost, the technique and the consuming of time. Moreover, some extreme tests may take risks to damage to the system, like freezing or exceeding the system's highest design temperature, and thus must be forbidden. So, it is necessary to employ numerical simulation to design the thermal control system.The paper describes the thermal analysis of the CO2 MPTL for the Tracker Thermal Control System (TTCS) of the Alpha Magneto- spectrometer-II (AMS-II). By employing the program SINDA/FLUINT, a dynamic model for space (DMS) and a dynamic model for ground test (DMG) are built for analysis the TTCS. The DMS simulates the TTCS operating in the space environment, while the DMG is used for calibration according to the ground test results. Since both of the two models are the same in function, the calibrated DMG can be used to evaluate the reliability of the DMS. With this proposal, the heat exchanger and condenser of the DMG are calibrated, with the heat leak of the condenser return line considered. Finally, the simulation result of modified DMG meets the test result. Moreover, the uncertainty of the key parameters is studied to figure out the reliability of the DMS model.Based on the work above, a study on the MPTL thermal control chararisitic is carried out with the DMS and DMG. The result shows that the TTCS MPTL performs very well to dissipate 144W collected from 192 sources to the space with a long distant (30m) transfer. During the period in orbit, the TTCS provides a stable (<3℃/orbit) and uniform (<1℃/9m) temperature boundary for the tracker hybrids.The DMS result also shows that the condenser will freeze in some extreme cold cases without extra heating power. Depended on the DMS, an optimized anti-freezing of the condenser is design. By choosing the flow direction of CO2, and the contacting position of the condenser inlet, the numerical result shows positive solution for this kind of condenser, for either reducing the anti-freezing power in the cold case or guaranteeing enough subcooling of the pump inlet in the hot case.With a boundary-simplified specific model, the self-adjusted ability of the mass flow in the two parallel condensers is studied. The result shows that the heat dissipation will be greatly improved even up to 40% in cold cases with 4g/s. It is also figured out that the improvement of this ability is related to the flow resistance in the feed and return lines of the condenser, the mass flow rate and the property of the fluid. The simulation result gives a good example for improving the design of this kind of parallel condensers.In order to discuss the relations between the loop and accumulator control, the simulation of imbalance heat load and heat load varying in evaporator are presented with the DMG. The result not only shows the evaporator temperature is still under control precisely, but also tells how the accumulator controls the loop in details. The way of the accumulator controlling the loop is also able to compare with the test result. At last, a concept of effective heat capacity, which related to the thermal control, is presented for the study of this two-phase accumulator. In a pilot study, it is found that the effective heat capacity is related to the loop state.Finally, I summarize the thermal chararisitic of the MPTL from TTCS. It is proved that this cooling system is small in size, and strong for its cooling ability and temperature control precision, capable for long-distance heat transfer for even complex boundary condition.
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