Theoretical And Experimental Investigation On Characteristics Of Thermoacoustically Driven Pulse Tube Refrigeration

A thermoacoustically driven pulse tube refrigerator occupies outstanding advantages of simplicity, reliability, stability, longevity and so on, due to no moving components from ambient to cryogenic temperature. This absolutely new type of refrigerator attracts great interest of academic circles and industry. In order to explore the couple relation of the thermoacoustic engine and the pulse tube refrigerator, and to further decrease the cooling temperature, the present theoretical and experimental work focuses on the following sections:1. Numerical Simulation and Analysis on Thermoacoustic Engine A standing wave thermoacoustic engine has been numerically simulated with linear thermoacoustics. According to the computed results, the effects of length of water cooler, length and inner diameter of resonance tube and volume of buffer on the performance of the thermoacoustic engine have been discussed. These computation and analyses supply the guidance for the experimental optimization of the thermoacoustically driven pulse tube refrigerator.2. Numerical Simulation and Analysis on Thermoacoustic Engine Connected with RC Load The standing wave thermoacoustic engine connected with an RC (resistance and capacitance) load has been numerically simulated with linear thermoacoustics. According to the computed results, the effects of impedance of RC load, length and inner diameter of resonance tube, volume of buffer, heating power and working pressure on the performance have been analyzed. The coupling relation of the thermoacoustic engine and the RC load has been discussed.3. Experimental Investigation on Characteristics of Thermoacoustically Driven Pulse Tube Refrigeration Based on the simulation, the thermoacoustically driven pulse tube refrigerator has been experimentally optimized. The optimization focuses on the orificeand second-inlet settings of the pulse tube refrigerator, the mesh number and the amount of the screen in the water cooler, the packing ratio of the screen stack and the length of the resonance tube. With modified water cooler, screen stack and resonance tube, and with helium as working fluid, under the conditions of 2.1 MPa charging pressure, 2200 W heating power, 300° orifice and 405° second-inlet, a no-load cooling temperature as low as 88.6 K has been achieved. It is lower than the previous world record of 90 K that was reported by NIST (National Institute of Standards and Technology) and LANL (Los Alamos National Laboratory) in USA. In addition, it was found that the second-inlet may significantly affect the onset temperature of the thermoacoustically driven pulse tube refrigerator. The onset temperature can be greatly decreased with a temporary closure of the second-inlet valve before onset. This simple but effective operation is of benefit to the application of low-grade heat energy.4. Experimental Investigation on Characteristics of Two-stage Stirling-type Pulse Tube Refrigeration Based on the analysis of the arrangement of multistage pulse tube refrigerators, a thermally coupled two-stage Stirling-type pulse tube refrigerator with non-isothermal boundary arrangement has been established. Two linear compressors are employed to drive the two stages, respectively. The effects of frequency, working pressure and heat transfer characteristics of the heat bridge on the cooling performance have been experimentally investigated. With the total electric input power of 400 W, a no-load cooling temperature of 12.96 K has been attained by the optimized prototype. It is the lowest reported cooling temperature achieved by two-stage Stirling-type pulse tube refrigerators. The prototype can supply the cooling powers of 287 mW at 20 K and 985 mW at 30 K, respectively. According to the experimental data, it can be predicted that a cooling temperature below 30 K will be possible with the two-stage Stirling-type pulse tube refrigerator driven by the optimized standing wave thermoacoustic engine.