Design and study of the anisotropic stack/heat-exchanger refrigerator

Conventional finned heat exchangers maintain a large temperature gradient between the thermoacoustic fluid and the heat exchanger fluid to enable a large amount of heat transport. The entropy increase of heat transferal between two fluids causes irreversibility and results in the poor performance of the thermoacoustic system.; Stack geometry, on the other hand, also affects the thermoacoustic refrigerator performance. The ratio of the productive area over the dissipative area is a function of the concavity or convexity of the basic stack elements. The thermoacoustic linear theory (G. W. Swift, et al.) indicates that the pin array stack has a higher performance than other geometries.; In order to increase the overall performance of the thermoacoustic refrigerator, we designed an anisotropic stack/heat-exchanger unit (ASHE unit) to fit into the Space ThermoAcoustic Refrigerator (STAR) resonator that has a built-in copper-fin heat exchanger at the cold end. The system was driven by a high power Shipboard Electronic ThermoAcoustic Cooler (SETAC) driver. The heat exchanger, with much less temperature difference between the thermoacoustic fluid and heat exchanger fluid, was proven by our measurements to have a large heat convection coefficient. The unit eliminates the disparity of length scale between the stack and heat exchangers. The measurements have shown that the ASHE refrigerator with the copper fin heat exchanger has a coefficient of performance (COP) of 13% relative to the Carnot efficiency at a 2% pressure ratio, which increases to 16% at a 3% pressure ratio. A further analysis suggests a high 20% COP relative to the Carnot efficiency at a 3% pressure ratio when the copper-fin heat exchanger is replaced by an ASHE heat exchanger at the cold end.