In this paper the design of thermoacoustic refrigerators, using the linear thermoacoustic theory, is described. Due to the large number of parameters, a choice of some parameters along with dimensionless independent variables will be introduced. The design strategy described in this paper is a guide for the design and development of thermoacoustic coolers. The optimization of the different parts of the refrigerator will be discussed, and criteria will be given to obtain an optimal system. Ó

From kinetic gas theory, it is known that the Prandtl number for hard-sphere monatomic gases is 2/3. Lower values can be realized using gas mixtures of heavy and light monatomic gases. Prandtl numbers varying between 0.2 and 0.67 are obtained by using gas mixtures of helium-argon, helium-krypton, and helium-xenon. This paper presents the results of an experimental investigation into the effect of Prandtl number on the performance of a thermoacoustic refrigerator using gas mixtures. The measurements show that the performance of the refrigerator improves as the Prandtl number decreases. The lowest Prandtl number of 0.2, obtained with a mixture containing 30% xenon, leads to a coefficient of performance relative to Carnot which is 70% higher than with pure helium.

The characteristic pore dimension in the stack is an important parameter in the design of thermoacoustic refrigerators. A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported. Parallel-plate stacks with a plate spacing varying between 0.15 and 0.7 mm are manufactured and measured. The performance measurements show that a plate spacing in the stack of 0.25 mm (2.5 deltak) is optimum for the cooling power. A spacing of 0.4 mm (4 deltak) leads to the lowest temperature. The optimum spacing for the performance is about 0.3 mm (3 deltak). It is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal (3 deltak) for thermoacoustic refrigeration.

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Moving-coil loudspeakers are appropriate drivers for thermoacoustic refrigeration. They are cheap, commercially available, compact, light, and can be adapted to meet specific requirements. This paper deals with the optimization of loudspeakers for thermoacoustic refrigeration. Using an electrical model that describes the refrigerator, it is concluded that the electroacoustic efficiency can be maximized over a wider frequency range by matching the mechanical resonance frequency of the driver to the acoustic resonance frequency of the resonator. A gas-spring system is introduced as a practical tool to shift the mechanical resonance frequency of the driver. An electroacoustic efficiency of 35% is obtained when the mechanical resonance frequency of the driver and the acoustic resonance frequency are equal. Additionally, the efficiency is constant over a relatively wide frequency range. This has advantages for thermoacoustic refrigeration. During cool-down, the operating acoustic frequency decreases so that the refrigerator will keep near the optimum performance.