Study on expansion methods of the DC flow for transferring the temperature-distributed refrigeration power.

The temperature-distributed refrigeration power in the regenerator is effectively transferred by extracting the inner direct-current (DC) flow from the regenerator. The transfer efficiency is improved by up to 1–2 times compared with traditional transfer methods because there is no radial thermal resistance in the regenerator during the transfer process. However, the specific heat capacity between the DC flow and the gas to be liquefied is usually mismatched due to the difference in pressure or working fluid, resulting in heat exchange loss. In this paper, we propose the expansion methods of the DC flow. The refrigeration power at the cold end of the refrigerator is increased by the expansion methods due to the liquefaction of the DC flow. Meanwhile, the distribution of specific heat capacity in the DC flow is altered, which generally enhances its availability. For the case study of 4He, the availability of the expanded DC flow is improved by around 40 % after expansion. The specific heat capacity between the DC flow and the gas to be liquefied becomes better matched, and the theoretical helium liquefaction rate is improved by approximately 25 %. In addition, the figure of merit (FOM) for liquefaction is enhanced by about 20 %, which includes the compression work of the expanded DC flow returning to the original refrigerator, form a closed cycle. This research enriches the study of the temperature-distributed regenerative refrigeration method and provides a reference for improving the transfer efficiency of the temperature-distributed refrigeration power and the liquefaction rate of cryogenic gases.