Mass transfer of supersaturated contaminants in cryogenic helium heat exchangers

Abstract

A new experimental technique is developed to measure the distribution of frost accumulated inside the passage of a cryogenic helium heat exchanger. The frost is accumulated by condensation of a contaminant on the passage wall during steady-flow operation of the balanced counterflow heat exchanger. The distribution is measured by flushing the accumulated contaminant into a detector at the exit of the passage. A heat source is moved from the cold to the warm end to convert the spatial distribution of the contaminant to concentration as a function of time in the exiting helium stream. When the degree of supersaturation is small, the accumulation distribution agrees reasonably well with the analytical solution without snow formation. As the supersaturation increases, a clear secondary peak in the distribution is observed, which results from the formation of snow in the free stream and its subsequent deposition as frost on the wall. Based on the results, an onset condition is developed for the formation of snow of a supersaturated contaminant in helium.