Steven R. Murrell
Ford Motor Co. Res. Lab., Maildrop 3028 SRL, P. O. Box 2053, Dearborn, MI 48121-2053
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 T[inf s] of the adjacent end of the stack, the temperature T[inf w] of the water flowing through the tubes, the change of water temperature (delta)T 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/(T[inf s]-T[inf w]), 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.