Concerns about the environmental impact of refrigerants used in vapour-compression heatpumps and refrigerators, have prompted the Stirling-Cycle Research Group at the University of Canterbury to investigate the feasibility of low-cost Stirling-cycle machines that use air as the refrigerant. Seal development is a key part of the research programme, and a series of experiments has been carried out in order to ascertain the suitability of a system using low-cost rubbing seals. Investigations have been based on a Stirling-cycle heat-pump using a wobble-yoke kinematic mechanism in a 4-α double-acting (Siemens) configuration. An automotive-type piston arrangement was employed, using Low Wear Rate Polymer (LWRP) seal-rings. The experiments highlighted some of the weaknesses of the 4-α double-acting configuration in terms of seal behaviour. While reasonable performance was attained, the difficulty of achieving adequate sealing during pressure reversal across the piston means that other configurations may be more suitable for Stirling-cycle heat-pump/refrigerator machines.
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