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.

Frequency effects on the performance of a two-stage 4K pulse tube cooler (PTC) have been extensively explored. The dependence of refrigeration temperature, cooling power and efficiency on the operating frequency of a 4K PTC are investigated and compared with those of G-M and Stirling coolers. The cooling performance can be considerably improved by frequency optimization. Cooling powers of 30W at 70K, 500mW at 4.2K (1.2Hz) and 20W at 65K, 590mW at 4.2K (1.1Hz) are obtained.

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

A bench consisting of a pulse tube refrigerator driven by a standing-wave thermoacoustic prime mover has been set up to study the relationship among stack, regenerator and working fluids. The stack of the thermoacoustic prime mover is packed with dense-mesh wire screens because of their low cost and easy manufacture. The effect of the packing factor in the stack on onset temperature, refrigeration temperature and input power is explored. The optimum packing factor of 1.15 pieces per millimeter has been found experimentally, which supplies an empirical value to satisfy a compromise for enhancing thermoacoustic effect, decreasing heat conduction and fluid-friction losses along the stack. The pulse tube cooler driven by the thermoacoustic prime mover is able to obtain refrigeration temperatures as low as 138 and 196K with helium and nitrogen, respectively. Copyright

As the thermoacoustic conversion process occurring in its regenerator is considered reversible, a traveling wave thermoacoustic engine can theoretically produce and transmit acoustic power with high effi-ciency. A large scale multifunction thermoacoustic engine has been designed, constructed and tested. Compared with the results of standing wave thermoacoustic heat engines, the experimental results show the engine has a lower onset temperature, much higher pressure ratio and higher efficiency. With the filling nitrogen of 0.9MPa, the maximal pressure ratio reached 1.21, and the operation frequency was steady at 25Hz. The single stage U type orifice pulse tube cooler driven by the engine reached 153.7K when the working pressure was 1.5MPa.

The cold end heat exchanger in a cryocooler is of highest importance for the efficient heat transfer from the applied load to the working fluid. The cooling performance of a 4K pulse tube cooler (PTC) was greatly improved by the modification of the cold end heat exchanger. With no heat loads on the first stage, cooling capacities of 760mW and 900mW at 4.2K were obtained with compressor input powers of 4.8kW and 6.0kW, respectively. The coefficients of performance (COP) at 4.2K were correspondingly improved to 1.58

Cryogen-free operation of Josephson voltage standards requires a low-noise cryocooler that provides a cooling power of 100mW or less at 4.2K, and about 1W of precooling at an intermediate temperature near 70K. Due to its intrinsic low level of mechanical vibrations a pulse tube cooler (PTC) appears to be a suitable candidate for such an application. In this work, a two-stage pulse tube cooler has been developed and optimized for cooling of a 1V or 10V Josephson voltage standard near 4K. The performance of the PTC, which is driven by a compressor with a rated input power of 1.7kW, is optimized under three different conditions. So far, a minimum temperature of 2.66K and a maximum cooling power of 202mW at 4.2K with coefficient of performance (COP) of 1.15xlO-4 have been been achieved. The performance of the crycooler is expected to fully satisfy the cooling requirement of the volatge standard. In addition, the experimental results are also compared with those obtained by driving the same cooler by use of a 6kW compressor.