Low operating temperature integral thermo acoustic devices for solar cooling and waste heat recovery

Abstract

Utilizing low temperature differences from solar vacuum tube collectors or waste heat in the range 70-200 °C seems to be the most promising field of applications for thermoacoustic systems. At these reduced temperatures overall system performance is increasingly affected by the ratio between amplified (useful) power and acoustic power stored in the resonance circuitry. Well known is that this ratio can be improved by deploying multiple regenerator units (hex-reg-hex). However, in commonly used torus or coaxial bypass configurations the correct timing (real and high acoustic impedance) is hardly realized inside more than two regenerator units (soft spot). Acoustic losses in the standing wave resonator account for another fundamental limitation because of the relatively low transferred power at a given pressure amplitude. Therefore a novel acoustic geometry will be presented in which a high and near real impedance can be maintained in even more than two regenerator units and in which acoustic feedback is performed by a true traveling wave. This approach improves the overall performance of integral thermoacoustic systems. Details and experimental results of a solar driven thermoacoustic cooler and ongoing work on thermoacoustic tri-generation utilizing exhaust gas of a standard gas-engine will be presented.