Daming Sun

Thermoacoustic compression based on alternating to direct gas flow conversion

We present a remarkable thermoacoustically driven compression effect based on the conversion of gas flow from an alternating state to a direct state. The alternating gas flow is generated by the thermoacousticeffect in thermoacoustic engines, whereas direct gas flow is achieved by means of the flow rectification effect of check valves. A demonstrative thermoacousticcompressor consisting of two standing-wave thermoacoustic engines, two reservoirs, and three check valves is constructed for experimental investigation. With nitrogen as a working gas and an initial pressure of 2.4 MPa in all components, a usable pressure difference of 0.4 MPa is achieved, with the average gas pumping rate reaching 2.85 Nm3/h during the first 3 s of the compression process. The simple mechanical structure and thermally driven nature of the compressor show potential in gas compression, power generation, and refrigeration applications.

Investigation on High-Power Stirling-Type Pulse Tube Coolers for Cooling HTS Motors

High-power Stirling-type pulse tube coolers (HSPTCs) driven by oil-free linear compressors are promising candidates for cooling HTS devices for the advantages of simple configuration, low noise and stable operation. Three U-shaped two-stage pulse tube coolers driven by a 10 kW linear compressor were built and studied. The effects of flow inhomogeneity on the temperature profiles along the regenerator and on the cooling capacity were investigated experimentally. By optimizing the impedance matching and operating conditions, the first cooler can reach a base temperature of 44.2 K; the second cooler reaches a base temperature of 27.1 K and provides a cooling power of 50 W at 45.6 K with 4.8 kW of power; the last cold head reaches a base temperature of 13.27 K and provides a cooling power of 18.3 W at 30 K. The present results form a foundation for building a HSPTC system capable of providing a cooling power of 80 W at 30 K.

Investigation on Gedeon Streaming in a Traveling Wave Thermoacoustic Engine

Introducing feedback path, traveling wave thermoacoustic engines realize relatively higher efficiency in thermoacoustic conversion. However, the toroidal topology allows acoustically induced streaming, which can seriously degrade performance of traveling wave thermoacoustic engines. With measurements of pressure and temperature distributions as effective approaches, four methods were applied to study the streaming in the thermoacoustic engine. The effects of Gedeon streaming on the temperature profile, the pressure ratio, and the thermoacoustic conversion efficiency of the engine were experimentally investigated. Experiments show that the performance of the engine can be remarkably improved with efficient streaming suppression. When Gedeon streaming is suppressed completely, maximal pressure ratio of 1.302 with nitrogen at 1.57 MPa as working gas and the maximal pressure difference of 0.63 MPa with working pressure at 2.54 MPa were obtained. This research is of importance for further understanding the mec...

Beating effect between a thermoacoustic source and its mechanical partner

Beating effects between a thermoacoustic source and its mechanical partner-a piston-spring oscillator are numerically predicted and experimentally observed in the free-decay process. Through analyzing the indicator diagram, periodic energy transfer characteristics between a thermoacoustic source and its mechanical partner during the beating oscillation are revealed and analyzed. The oscillation frequency is found to split into two modes intrinsically even when the resonance frequencies are initially tuned to be the same. The patterns and frequencies of the beating oscillations are sensitively affected by the characteristics of acoustic sources. The study sheds light on the underlying mechanisms of beating oscillations occurred in thermoacoustic systems with multiple resonant sub-units.

Advances in High Power Stirling-Type Pulse Tube Cooler

High power Stirling-type pulse tube coolers (HSPTCs) with oil-free linear compressors are promising solutions for cooling superconducting magnets. The cooling capacity of HSPTC ranges from 50 W to a few kilowatts below 100 K. At present the lowest refrigeration temperature of HSPTC has reached below 30 K. After a brief introduction of Stirling-type PTC, this paper reviews the newest developments in HSPTC. At the same time, the potential of HSPTC to be applied in cooling superconducting magnets is analysed. Possible future advances and prospective research emphases are also presented.