Size considerations in interfacing thermoacoustic coolers with electronics

Small thermoacoustic coolers/heat pumps show much promise for heat management in microcircuits, especially since they can be miniaturized for interfacing with circuits. Usually they are operated in the resonant mode with sound pumping heat; the device dimensions are reduced when the acoustic pump frequency is raised. Results on the development of this technology will be presented for devices operating in the frequency range of 4 kHz to 25 kHz. Since the efficiency and cooling power depend on geometric factors, scaling in the miniaturization plays an important role. The cooling power varies with the total effective cross-sectional area of stack relative to sound field and hence on the cross-sectional area at stack position. We have developed and tested devices which vary in length from 4 cm down to 0.8 cm, the cross-sectional area being fixed by available acoustic drivers. An important issue is that of direct interfacing of single units with a microcircuit versus an array of smaller basic thermoacoustic units. Advantages of such arrays range from lifetime of drivers, long-term reliability of the device, to closer interfacing with chip on microcircuits. Results show that indeed the cooling power depends on the cross-sectional area of stack in a single unit. Also, the cooling power depends on level of acoustic drive; in the ultrasonic range it can be raised since the power density of such units is typically high.