Comparative study of heat exchangers for thermoacoustic devices

Abstract

Among the critical elements of a thermoacoustic device are its internal heat exchangers. This work quantifies the behavior of actual heat exchangers in situ in an operating thermoacoustic refrigerator. Each heat exchanger consisted of a specified arrangement of metal in contact both with oscillating gas adjacent to a thermoacoustic stack and also with water bearing tubes. Measured quantities were the temperature Ts of the adjacent end of the stack, the temperature Tw of the water flowing through the tubes, the change of water temperature δT between tube inlet and outlet, and the water flow rate. The heat-transfer rate Q was determined from the latter two quantities. The overall heat-transfer conductance G, defined by G=Q/(Ts−Tw), is determined by three quantities: the gas-to-metal temperature drop, the fin efficiency, and the metal-to-water temperature drop. Raw experimental results will be presented for several gas-side heat-exchanger geometries, including copper screen, reticulated aluminum foam, and bundled copper tubes. Where possible, comparisons will be made to simple theoretical expectations.