CONSTRUCTION AND PRELIMINARY TESTING OF PERFORATED-PLATE HEAT-EXCHANGERS FOR USE IN HELIUM-II REFRIGERATORS

Heat exchangers in cryogenic refrigerators must meet conflicting requi rements for high thermal efficiency and low frictional pressure drops. This is particularly true in helium II refrigerators where the gas st ream leaves the cold source at 15 mbar. Perforated-plate heat exchange rs are likely to offer better overall performances for that applicatio n than the widely used plate-fin heat exchangers. Through their design they combine a high thermal conductance in transverse direction with a low thermal conductance in axial direction. The present paper report s on the initial stage of development of a fabrication method using ph otochemical milling of copper plates and stainless steel spacers, and silver brazing for bonding. Comparison of preliminary test measurement s and calculations in the 80 to 300 K temperature range with flow rate s between land 5 g/s has confirmed that predictable results can be obt ained for the thermal efficiency and the pressure drop with an accurac y of a few percent.