| With the development of science and technology, helium refrigerators have been more and more widely used in many fields, including superconducting particle accelerators and detectors, nucleus fusion equipments, aerospace, space detectors, electronics devices, high-vacuum pumping stations, cryogenic medical apparatuses and so on.In the paper, the flow cycle and main facilities of the helium refrigerator with cooling capacity of 100W at 4.5K were theoretically studied. The results provide theoretical basis for the engineering design of the helium refrigerators. At first, this paper proposed three schemes for flow process of the 100W/4.5K refrigerator. They are different from the connection ways of turbo-expanders and throttle valve, which produce the refrigeration in the system. The power consumptions for them were numerically compared. The best scheme of the 100W/4.5K refrigeration was suggested.Secondly, the effects of main thermal parameters on the performance of the refrigerator were numerically studied, such as total mass flow M, discharge pressure of the compressor P2, inlet and outlet temperatures of two turbo-expanders T5,T6 and T18,T13, inlet parameters of the last heat exchanger P9,T9 respectively for the refrigerator mode and refrigerator/liquefier mode. The optimized thermal parameters for the refrigeration system were obtained. Under optimization, the exergy efficiency for the two modes separately is 12.3%, 20.8%. At the end, the exergy loss of all cryogenic facilities was analyzed.Finally, design and optimization of cryogenic heat exchangers were carried out. The influence of the unbalanced flow on the efficiency of heat transfer and thermodynamic performance were studied. The relation among the entropy generation rate Ne, the Ntu and the capacity rate ratio R was analyzed. The Ne decreased with Ntu increasing, and Ne goes up first and then down with R increasing. At Ntu≥6, Ropt is optimized and Ne is minimal. |
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