An Investigation of Certain Thermodynamic Loses in Miniature Cryocoolers

This report results from a contract tasking University of Oxford as follows: A detailed investigation of these losses was made using different gases over a range of frequencies, and the losses were estimated from the 'pdV' work done by the piston on the gas in the cylinder Having allowed for the pumping loss due to the clearance seal, the work done on the gas was evaluated, and this data was compared with expressions derived by Kornhauser and others using sliding seal compressors An important conclusion is that these expressions, derived for conventional sliding seal compressors, are valid for clearance seal machines, once the seal pumping loss has been allowed for Other conclusions that can be drawn from these results are: * For Peclet numbers in the range 10 to 1000, Kornhauser's modified version of Lee's equation gives good results and can be used in applications involving typical clearance seals * There appears to be a significant deviation from Lee's expression for all but the lightest gases (i.e, Helium and Hydrogen) where the Peclet number is above 1000. It would be of interest and value to investigate this further to discover the cause and whether there is a change in flow regime that can be defined by a type of Reynolds number. The original document contains color images.