Numerical simulation of a low temperature hybrid refrigerator combining GM gas expansion refrigeration with magnetic refrigeration

A hybrid refrigerator combining Gifford-McMahon (GM) gas expansion refrigeration with magnetic refrigeration, in which helium and magnetic materials regenerate each other, overcomes the low-temperature thermal saturation of regenerator materials and has been experimentally proved to reach a higher cooling power than pure GM refrigeration recently. Considering the complexity of the thermodynamics and fluid dynamics of the hybrid refrigeration, optimizations based on numerical simulation are necessary to provide useful guidance for practical design. In this paper, a transient 2D axis-symmetric model of a hybrid refrigerator is established. With this model, the effect of timing between GM refrigeration and magnetic refrigeration is studied and optimized by defining a phase angle. The corresponding cooling power and efficiency are obtained and compared with the results from pure GM refrigeration. Additionally, the operating frequency and the filling ratio of the regenerator are optimized. The results showed that the optimal phase angle is around 90°, which is close to previous experimental results, and within a certain range, the lower the temperature and frequency, the greater the advantage of hybrid refrigeration. At 4 K and 0.4 Hz, the cooling power and efficiency of hybrid refrigeration are 57% and 68% higher than GM refrigeration, respectively.