Study of Real Gas Effects on Regenerative Refrigeration in the Liquid Helium Temperature Range under Various Pressure Conditions

The influence of real gas effects on the performance of regenerator heat exchangers has been analyzed. An expression for the coefficient of performance （COP） of regenerators is derived. The existing body of research has been largely confined to pressures between 1 and 2 MPa, with a notable absence of insight into the manner in which the COP undergoes alteration and the nature of losses at pressures that are both higher and lower than this range. By extending the pressure range, the coefficient of performance （COP） and relative Carnot efficiency （rCOP） of regenerators under conditions of variable pressure are determined. The results demonstrate that when the cold end temperature is between 5 and 25 K, the rCOP displays a U-shaped variation with decreasing pressure. To illustrate, at a cold end temperature of 5 K, the rCOP values are 19.6%, 15.32%, and 97.64% at pressures of 2.5 MPa, 1.0 MPa, and 0.01 MPa, respectively, with the minimum rCOP occurring near the critical pressure of 0.228 MPa （0.19~0.23 MPa）. Above 25 K, the relative COP increases as pressure decreases. To illustrate, when the hot end temperature is fixed at 40 K, the rCOP values are 65.7%, 81.7%, and 99.4% at pressures of 2.5 MPa, 1.0 MPa, and 0.01 MPa, respectively, when the cold end temperature is 20 K. However, below 5 K and at higher pressures, the trend is reversed. Furthermore, the issues associated with low pressure are assessed, such as low power density and significant losses. At higher pressures, both theoretical calculations and regenerative energy simulations yield higher rCOP values. The rCOP obtained from calculations and simulations is larger than the experimental data, confirming that losses are more substantial in practical applications.