Porous heat exchangers for continuous flow helium cryostats

Abstract

An investigation was made into the effective application of porous heat exchangers of cylindrical shape through which fluid passes axially. On the basis of a theoretical analysis the conclusion derived was that the best thermal efficiency can be reached by the use of porous material with a large heat-exchanger surface, a high radial and low axial thermal conductivity (ie with a marked anisotropy of thermal conductivity), and a small radius of the heat exchanger operating at lower flows of cooling agent. The results of experiments carried out at helium and nitrogen temperatures are presented. These results have confirmed the high effectiveness of porous heat exchangers, even in comparison with chamber-type heat exchangers. For the temperature range from 1.5 to 300 K the heat exchangers composed of highly conductive metal nets (mesh gauge of the order of magnitude of 10 −1 mm) stacked perpendicularly to the direction of flow of the cooling fluid, appear to be the most promising ones.