Qiu Limin

A separate two-stage pulse tube cooler working at liquid helium temperature

A novel 4 K separate two-stage pulse tube cooler (PTC) was designed and tested. The cooler consists of two separate pulse tube coolers, in which the cold end of the first stage regenerator is thermally connected with the middle part of the second regenerator. Compared to the traditional coupled multi-stage pulse tube cooler, the mutual interference between stages can be significantly eliminated. The lowest refrigeration temperature obtained at the first stage pulse tube was 13.8 K. This is a new record for single stage PTC. With two compressors and two rotary valves driving mode, the separate two-stage PTC obtained a refrigeration temperature of 2.5 K at the second stage. Cooling capacities of 508 mW at 4.2 K and 15 W at 37.5 K were achieved simultaneously. A one-compressor and one-rotary valve driving mode has been proposed to further simplify the structure of separate type PTC.

Study on the onset temperature of a standing-wave thermoacoustic engine based on circuit network theory

Onset mechanism is one of the most fundamental issues in thermoacoustic field. However, the onset conditions and the phenomena happening in the onset process have not been well explained theoretically. In this paper, a novel model based on the circuit network analogy is proposed to predict the onset temperature of a standing-wave thermoacoustic engine. The activity and instability criteria are proposed to be the onset criteria in the model. The influences of the porosity of the heat exchanger and the stack, and the length of the resonant tube on the onset temperature are analyzed. The calculated results are in agreement with the experimental results, which indicates that the activity and instability criteria can be used to predict the onset conditions of a thermoacoustic engine.