Design And Experimental Investigations On A Small-scale Traveling Wave Thermoacoustic Heat Engine

A thermoacoustic engine can be used to drive a pulse tube cooler(PTC) or a thermoacoustic refrigerator with many attractive advantages. The whole refrigeration system has no mechanical moving part. In addition, the advantages such as simplicity, reliability, low cost, great potential of using low quality heat sources and environmentally-friendly gases help thermoacoustic devices develop worldwide with great applications in the remote areas of developing countries where the electricity is insufficient while the solar power is available. Small-scale traveling wave thermoacoustic engines,also called thermoacoustic Stirling engines(TASHEs) have piority over the large ones due to their compact structure. However, there are many technical issues that are expected to be improved. For instance, the working frequency is too high with difficulty in matching PTCs; the pressure amplitude is not high enough; the onset temperature difference is often beyond the scope of low quality heat sources; unstable oscillations often come up during the operation, harmful for stable utilization of the acoustic wave stimulated in the thermocoustic core. According to these issues, investigations on small-scale traveling wave thermoacoustic engines were conducted numerically and experimentally in this thesis, aimed to improve the performances. The main work was summarized as follows:1) Based on the linear thermoacoustic theory, a specialized design code referred to as Design Environment for Low-Amplitude Thermoacoustic Energy Conversion(Delta EC) was applied to build the numerical model for a small-scale traveling wave thermoacoustic engine. The effects of working gases, strcuture diemensions of the main parts, operating paramenters on the general performance of the engine were numerically simulated and analyzed. The resonator, the resonator cavity, compliance and regenerator had the most important influence on the engine’s performance. Among the four acoustic parts, the resonator and the resonator cavity were found to have the greatest potential in improving the engine’s performance for their ease of unloading and resembling.2) According to the numerical results and analyses, a small-scale traveling wave thermoacoustic engine was designed and constructed with a resonator length of only 1m. The whole length of the device was less than 1.5m and the height was less than 0.5m. Three different working gases were used to investigate their effects on the performances of the small TASHE. More attention was paid to the resonator and its cavity to decrease the working frequency, onset temperature difference and increase the pressure amplitude. Using helium as working gas, the working frequency had reached 90Hz; the onset temperature difference had decreased to 198.2K and it kept realatively stable in the mean pressure range of 1-2.5MPa, which was beneficial for the engine to start working easily in a broad pressure range; the pressure ratio had reached 1.108 with mean pressure of 0.8MPa and heating power of 800 W. Based on the above studies, a new strcuture was proposed, expected to further decrease the working frequency while increasing the pressure amplitude in the future.3) The factors that influenced the exsistence of the spontaneous and periodic on-off phenomena were also experimentally studied. The type of working gas, the mean pressure range and heating power were the most important factors influencing the occurence of this kind of phenomena. For helium, the on-off phenomenon often occurred in the pressure range over the right branch of the onset temperature curve. Besides, the thermal energy losses were analyzed and the streaming was found to be in the clockwise direction, bringing more heat load on the second ambient heat exchanger, harmful for the engine’s performance.4) The prototype of the small-scale traveling wave thermoacoustic engine was used to drive a coaxial Stirling-type pulse tube cooler to realize a refrigeration system without the presence of moving mechanical part. With mean pressure of 2.5MPa, heating power of 800 W, helium as working gas, the cooling temperature reached 194.5K. Although the cooling temperature was not very satisfied, the experimental results demonstrated the great potential for the small TASHE to drive PTCs with better performance.