Zhanghua Wu

A high-performance thermoacoustic refrigerator operating in room-temperature range

The working principle of an efficient travelling-wave thermoacoustic refrigerator operating in room-tem-perature range has been analyzed and an experimental set-up has been built. The experiment showed that suppressing DC-flow streaming was very critical to efficient operation, and an elastic membrane was used to solve the problem successfully. At the most efficient operating point, the novel thermoacoustic refrigerator achieved a cooling capacity of about 80 W at −20°C, with a much higher efficiency than previously developed standing-wave thermoacoustic refrigerator.

EXPERIMENTAL DEMONSTRATION OF A NOVEL HEAT EXCHANGE LOOP USED FOR OSCILLATING FLOW SYSTEMS

This paper describes a non-resonant self-circulating heat exchanger which uses a pair of check valves to transform oscillating flow into steady flow that allows the oscillating flow systems own working gas to go through a physically remote high-temperature or cold-temperature heat source. Unlike traditional heat exchangers used in thermoacoustic systems, the length of the non-resonant self-circulating heat exchanger is not limited by the peak-to-peak displacement. In addition, it is also different from the resonant self-circulating heat exchanger that needs a specific resonant length. This invention may lead to easy design and fabrication of heat exchangers for oscillating-flow refrigeration system with large capacity. To verify this idea, we have built an experimental system by incorporating such a heat exchanger loop with a mechanical pressure wave generator. Measurements of heat transfer of the heat exchanger loop under different operating conditions including mean pressure, and operating frequency, e...

Thermoacoustic turbulent-flow model for inertance tubes used for pulse tube refrigerators

Publisher Summary This chapter develops a thermoacoustic turbulent-flow model for describing the inertance tube, by which can both incorporate turbulent-flow effect and heat transfer effect between gas and wall. An inertance tube is supposed to be another powerful shifter, which has the additional function of eliminating DC flow. For typical operating conditions, the flowing of the inertance tube is turbulent. Inertance-tube phase shifter can avoid DC-flow of the double-inlet phase shifter besides. The flow inside the inertance tube is usually turbulent, which makes linear network mode not accurately workable for describing performance of the inertance tube. In addition, relatively extensive experiments on various inertance tubes for low-capacity pulse tube refrigerators are made and only some of the experiment data are shown in this chapter. Comparisons between the simplified turbulent-flow model and the experimental data by hot-wire anemometry are made, which show a good agreement qualitatively, and also provide an acceptable accuracy quantitatively. Thus, a thermoacoustic turbulent-flow model is proposed to solve the problems, which can consider both turbulent-flow effect and heat transfer effect.

Investigation on a free piston stirling cryocooler with large cooling capacity

Cryocoolers with large cooling powers at 80 K are very promising as they could find important applications in superconducting field such as cooling cables, transformers and fault current limiters. The pulse tube cryocooler has attracted attention due to its virtue of no moving components in the cold region. However, as the cooling power increases, problems inside the thermal buffer tube, such as difficulty in obtaining good flow straightening, existence of Rayleigh streaming, the gravity effect etc., present big obstacles to achieving high thermal efficiency. On the other hand, a free piston Stirling cryocooler, though more complicated due to the existence of the displacer, could avoid these problems with the elimination of the thermal buffer tube. Meanwhile, the efficiency is better than the pulse tube cryocooler around 80 K due to its capability of recovering the acoustic work. In this article, a free piston Stirling cryocooler with about 300 W cooling power at 80 K is designed with our simulation based on thermoacoustic theory. The theoretical analysis and numeric model are given in detail. The phase shift effect of the displacer and the internal energy loss mechanism are discussed. From our calculation, a relative Carnot efficiency of about 50% at 80 K has been obtained analytically.

Design of a large-capacity multi-piston pulse tube cryocooler

ercial high temperature superconductors, two designs for a pulse tube cryocooler have been developed. In the first design, three parallel-arrayed inertance pulse tube cryocoolers are driven by one twinopposed linear compressor. It is hard for this system to obtain a relative Carnot efficiency of higher than 25%. In the other design, it includes three pulse tube cryocoolers and three linear compressors. The inertance tube and reservoir of each pulse tube cryocooler are omitted. The compression chamber of each compressor is connected in series through a pulse tube cryocooler to the expansion chamber of another compressor. With this configuration, the acoustic work coming out of the secondary water-cooled heat exchanger can be recovered and it is much easier for the pulse tube cryocooler to obtain better acoustic field, so the relative Carnot efficiency of this system could be higher than 35%. It should be one of the best candidates for the cryocooler in high temperature superconductor power grid.

A Traveling Wave Thermoacoustic Refrigerator within Room Temperature Range

Thermoacoustic refrigerators use sound waves to generate cooling. Furthermore, they use inert gases that are friendly to the environment. Their unique working mechanism and promising future have attracted many researchers. This article focuses on the design of a traveling wave thermoacoustic refrigerator that works in the civil refrigeration range, since traveling wave refrigerators have higher efficiencies than standing wave refrigerators. According to linear thermoacoustic theory, two analytical methods, the lumped-element network and transfer matrixes, are discussed for analysis of the thermoacoustic systems. Several possible modes for achieving efficient thermoacoustic refrigeration are analyzed with the simplified lumped-element network method. Then, a feasible thermoacoustic refrigeration mode is chosen and optimized with the transfer matrix method. The goal is to achieve a relatively high cooling capacity at a temperature of 250 K. The calculation results show that, with helium, the refrigerator can have a cooling power of 80 W and achieve a COP of 2.86; this corresponds to a relative Carnot efficiency of 57%. According to this, we have constructed a refrigerator. It has achieved a no-load cooling temperature of 263 K when driven by a mechanical compressor with helium, and achieved a cooling power of 80 W at 274 K when driven by a standing wave thermoacoustic engine with nitrogen at the pressure ratio of 1.09.