Performance measurements on a thermoacoustic refrigerator driven at high amplitudes

Since the power density in a thermoacoustic device is proportional to the square of the acoustic Mach number, there is strong motivation to design thermoacoustic refrigerators to operate at larger pressure amplitudes. Measurements are reported of a modified version of the Space Thermo-Acoustic Refrigerator (STAR), driven at peak-to-mean pressure ratios up to 6%. This pressure ratio corresponds to 30 W of cooling power-five times as large as reported for STAR in 1993. The results of these measurements are compared to a DELTAE computer model of the low-amplitude (linear) performance that matches experimental conditions on a point-by-point basis. It is found that there is a small but measurable deviation in heat pumping power from the power predicted with a linear acoustic computer model at moderate amplitudes. This deviation in heat pumping power at 6% pressure ratio is about 23%. A large disagreement in the acoustic power needed to attain a specific pressure ratio is found between measured data and DELTAE results. An overview of the instrumentation, including a measurement of exhaust heat with an absolute accuracy of 65 mW, is also presented.