Neodymium-Ribbon-Regenerator Cooling Performance in a Two-Stage Gifford-McMahon Refrigerator
This work is part of an ongoing study into the way material configuration (i.e. flow geometry) can affect the performance of low-temperature regenerators. This work demonstrates a new regenerator configuration and fabrication technique for Gifford-McMahon (GM) refrigerators that operate at temperatures near 4.5 K. This new style regenerator promises to be less expensive, more reliable and perhaps provide better cooling power.
A regenerator was assembled from Neodymium ribbon that was approximately 0.32 cm (1/8 in.) wide and 0.025 cm (0.010 in.) thick. Neodymium was chosen because it has a relatively high volumetric heat capacity at temperatures below 10 K and it is a pure metal that can be drawn and formed with relative ease. Small ridges (approximately 0.0025 cm (0.001 in.) high) were embossed on one face of the ribbon. The ribbon was wound into coils similar to the way adhesive tape is wound into rolls. The small ridges on the ribbon provide spacing between the wound layers creating flow passages for gas. Several coils of ribbon were stacked one on top of another inside a stainless steel tube. This assembly formed the second stage regenerator. By selecting ribbon with different thickness and ridge heights the void fraction as well as the amount of heat transfer surface area of the regenerator could be controlled.
Test results are presented for two regenerators with ribbon geometry, one with a void fraction of about 20% and another with 15%. Test results include measurements of the pressure drop that occurs when gas flows through each regenerator as well as the cooling performance of a GM refrigerator while utilizing these regenerators. This data is compared to data for the more conventionally designed regenerator constructed from spherical Nd powder that has a void fraction of about 35%.
KeywordsPressure Drop Heat Exchanger Void Fraction Flow Passage Spherical Powder
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