From DAVID RIX
As one of the few researchers of Stirling cycle machines in Britain,
it was pleasing to see your article ’19th-century engine refrigerates without
CFCs’ (Technology, 1 September).
Sunpower’s cooler is one in a large number of such machines which the
company has built over a period of 25 years. Though the advantages attributed
to the free-piston design are true, lack of commercial success may be due
to the fact that manufacture requires unrealistic levels of accuracy and
performance is compromised by non-uniform piston motion and high losses
in the gas springs on which they oscillate. Stability and load matching
are also difficult.
At the University of Cambridge we have a high-temperature Stirling cycle
heat pump for use in industrial waste heat recovery. We are also developing
a couple of low-cost sub-kilowatt Stirling engines. All three units have
arisen from our advanced theoretical modelling work and development of key
components such as burners and regenerators.
David Rix University of Cambridge
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