Testing Program for Etched Foil Regenerator Material

Abstract

Desirable characteristics of a regenerator include a small dead volume, high heat capacity, high rates of heat transfer, high thermal conductivity normal to flow, low thermal conductivity parallel to flow and low pressure drop. In theory, parallel plate regenerators should offer a better combination of these properties than regenerators of other types. Theoretical predictions have not always been confirmed in practice. To date, most parallel plate regenerators have been fabricated by rolling a strip of foil on itself, with some method of separating the layers with spacers. Possible explanations for disappointing performance include inaccurate spacing of the parallel plates leading to circulation DC flows in different parts of the regenerator. Solid foil aligned with fluid flow also conducts heat more readily than stacked screens or packed beds of regenerator materials, and thus incurs greater losses of that type. Etched foil regenerators address these problems. Layers of foil are assembled without separate spacers; instead, the flow channels are etched into the surface of the foil. Perforations in the foil interrupt thermal conduction paths and permit cross-flows of fluid between layers of foil. For the planned tests, samples of three patterns of etched foil have been assembled flat, with square cross sections, providing as uniform an etched foil structure as possible. Two samples allow flow to proceed straight through the regenerator. Those samples differ only in their porosity. A third sample, comparable in porosity to the less-porous straightthrough sample, forces flow into a zigzag path through the regenerator. The regenerators are encased in sabots of an engineering plastic through which square holes had been broached. The assembly technique employs thingauge foil shoehorns that accompany the regenerators into the sabots and are then broken off.