The pulse tube cooler (PTC) driven by a thermoacoustic engine can completely eliminate mechanical moving parts, and then achieves a simpler and more reliable device. A Stirling thermoacoustic heat engine has been constructed and tested. The heat engine can generate a maximal pressure ratio of 1.19, which makes it possible to drive a PTC and get good performance. Frequency is one of the key operating parameters, not only for the heat engine but also for the PTC. In order to adapt to the relatively low design frequency of the PTC, the operating frequency of the thermoacoustic heat engine was regulated by varying the length of the resonance tube. Driven by the thermoacoustic engine, a single stage double-inlet PTC obtained the lowest refrigeration temperature of 80.9K with an operating frequency of 45Hz, which is regarded as a new record for the reported thermoacoustically driven refrigerators.

A novel 4K 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 13.8K. 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 2.5K at the second stage. Cooling capacities of 508mW at 4.2K and 15W at 37.5K were achieved simultaneously. A one-compressor and one-rotary valve driving mode has been proposed to further simplify the structure of separate type PTC.

It is a new way of thinking to drive a pulse-tube refrigerator or other thermoacoustic refrigerator by using thermoacoustic engine instead of mechanical compressors so as to completely eliminate moving parts of refrigeration system for more reliable operation. Ceperley first proposed the idea of traveling-wave thermoacoustic heat engine in 1979 [1] and practically realized by Swift in 1999 [2]. Because the thermoacoustic conversion process occurs in its regenerator is reversible and velocity is in phase with pressure, traveling-wave thermoacoustic engine can produce and transmit acoustic power with higher efficiency theoretically. A large-scale multifunction thermoacoustic engine has been designed and constructed in Zhejiang University with the maximal input power of 5kW. The preliminary results show that the self-made engine has lower onset temperature, higher pressure ratio and higher efficiency, compared with those of the standing-wave thermoacoustic heat engine. With the filling nitrogen of 0.9MPa, the maximal pressure ratio reaches 1.21 and the operation frequency is 25Hz.

Generally, a compressor together with a rotary valve system generates the pressure oscillation in GM-type cryocoolers. The timing of the rotary valve, which is one of the key operating parameters for cryocoolers, determines the relationship between intake andexhaust processes. A systematic investigation of valve timing effects on cooling performance of a two-stage 4K pulse tube cooler (PTC) is reported. The experiments show that the optimization of valve timing can considerably improve the cooling performance for both stages. For the same PTC, a performance comparison for operation on different compressors with various input powers ranging from 0.5 to 6.0kW is also presented.

The cooling power and coeffcient of performance of a two-stage pulse tube cooler below 4K have been increased greatly by using the newly developed ceramic magnetic regenerative material GdAlO3 (GAP). Cooling powers of 200mW at 2.8K, 300mW at 3.13K, and 400mW aat 3.70K have been achieved with a compressor imput power of about 4.8kW. The results show that the cooling power near 3.0K incrases by 150% compared that of the same pulse tube cooler (PTC) employing only conventional HoCu2 and ErNi regenerator materials