A highly efficient heat-driven thermoacoustic system for room-temperature refrigeration by using novel configuration

Heat-driven thermoacoustic refrigerator/heat pump with direct-coupling configuration is a promising cooling/ heating technology, showing great advantages of simple and compact structure. In order to resolve the acoustic power mismatch between engine subunit and refrigerator/heat pump subunit of the traditional direct-coupling thermoacoustic conversion configuration, a novel direct-coupling configuration with the implement of stepped piston (SP) is proposed for the first time in this study. Firstly, the fundamental reason that the basic directcoupling unit has a bad operating performance with an increasing heating temperature is analyzed and pointed out. Then, the comparisons on the two direct-coupling configurations (basic and with SP) are investigated in detail, including the global cooling performance and internal operating characteristics. It is found that with the increasing of heating temperature, the heat-to-acoustic conversion efficiency in engine subunit of the newly proposed configuration can be significantly improved, and consequently a much better overall coefficient of performance can be obtained than that of the basic direct-coupling configuration. The SP configuration can achieve an overall coefficient of performance (COP) of nearly 1.69, whereas the basic configuration can only achieve a COP of nearly 0.68 for a study case of heating temperature around 500 degrees C. This implies that the novel system is capable of achieving significant improved cooling performance by about 2-3 times compared with the basic direct-coupling type, mainly due to the more suitable acoustic field distribution and less exergy loss in thermoacoustic engine conversion subunit. It shows an extremely attracting prospect of the novel heat-driven thermoacoustic technology for low-carbon, high-efficiency and reliable cooling/heating technology in the utilization of various medium-to-high-grade heat sources.