Thermoacoustic cooler

Cooling and freezing are important processes in industry. Especially in the food industry (product quality) and in the chemical industry (separations) large amounts of energy are used to lower the temperature of the product streams.

We have made an inventory of the present cold requirements in the Dutch industry and existing installations have been characterised with respect to energy use and economy. These data have been compared to the targeted performance of new innovative cooling concepts. Based on this study the most important application area of a thermoacoustic cooling machine, from an energy saving point of view, is cooling at a temperature level of -100?C. At this temperature level methane is removed from the product stream after a naphtha cracker. Multi-stage compression coolers are used at this moment, each using a different working medium depending on the temperature level. Thermoacoustic cooling has the big advantage that only one machine can achieve the required temperature lift. The system has no moving parts and uses a environmentally friendly working medium (helium). The energy saving potential in the Netherlands amounts to 1,5-2,5 PJ per year.

A powerful acoustic wave is necessary to drive the thermoacoustic cooler. This wave can, for example, be generated from a thermoacoustic engine or with an electrically driven linear motor. This last option is tested at ECN. The picture below shows a test installation in which a linear motor, producing about 250 acoustic power, is used to drive a thermoacoustic cooler.

The research is directed to the acoustic and thermal optimisation of the cooler. The objective is to generate a temperature level of -100?C with a one-step cooler and reach an efficiency that is higher that today?s multi-stage compression coolers.

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