Cost-effective electrodynamic drivers with improved efficiency for thermoacoustic refrigerators

Abstract

Commercial loudspeakers were made practical for laboratory thermoacoustics by placing one in the cold end of the resonator [S. R. Murrell and G. Mozurkewich, J. Acoust. Soc. Am. 94, 1772(A) (1993)], but the efficiency of such devices suffers from the opposed directions of traveling wave/standing wave heat pumping effects and from additional thermal loads at the cold heat exchanger. Efficient designs using drivers at the higher temperature end typically require special materials and fabrication. In the proposed compliant configuration, a driver with mechanical resonance below the operating frequency (which is typical of available loudspeakers) is placed close to the ambient heat exchanger and the volume backing the driver is tuned to achieve resonance and a high electrical efficiency. Numerical results show that the current ×BL product can be as little as 25% of the required driver effort. This bypasses requirement for the expensive, high flux-density magnets needed in successful efficient designs with high effort, low-impedance drivers [Garrett et al., J. Acoust. Soc. Am. 94, 1773(A) (1993)]. Predictive models of a compliant design using a slightly modified loudspeaker and the best current supermagnet designs indicate comparable efficiencies. [Work supported by DOE.]