Numerical investigation of multi-bypass type pulse tube cryocooler

Multi-bypass has been experimental proved to be an effect configuration for pulse tube cryocooler to achieve a better cooling performance. However, at present, the understanding of its working mechanism is still ambiguous; sometimes, multi-bypass will just be viewed as a double-inlet working at a lower temperature, and sometimes, the multi-bypass configuration will be treated as a multi-stage structure. In the present work, the relations of multi-bypass and double-inlet will be numerical investigated. The numerical simulation shows that the functions of multi-bypass and double-inlet have some similarities to a certain extent, but the multi-bypass works more like a multi-stage. Compared with double-inlet, the opening of multi-bypass has a wider range for pulse tube cryocooler to achieve lower temperature. The hot end temperature has a very small effect on the cold end temperature when the opening of the multi-bypass is optimum; the effect of hot end temperature will be larger when the opening of multi-bypass deviates from its optimum value, especially when the multi-bypass opening is relative small.