CUSTOMIZABLE GAS-GAP HEAT SWITCH

Abstract

The so‐called gas gap heat switch, in which the pressure is managed by a coupled small cryopump having no moving parts, is known to be a very reliable and simple heat switch.Mechanical design improvements can lead to optimized ON or OFF characteristics of a gas‐gap heat switch. Their ON conductance characteristics are mainly determined by the gas properties and the gap geometry. However, their operational temperature range is limited by the gas‐sorbent pair adsorption characteristics. Traditionally the gas chosen is helium, since it is the best conductive one below 100 K, and the sorbent used is activated charcoal. Such a switch is limited to be used at cold end temperatures below ∼15 K.In order to obtain a customizable device working at the whole range below 100 K, a gas gap heat switch was studied and extensively characterized. Hydrogen, Neon and Nitrogen were used as conducting gas, under different sorption conditions. A thermal model was built in order to determine the ON and OFF conductances over each entire temperature range.This work presents the operational temperature windows established for each gas, depending on the amount of gas used. The experimental results and those predicted by the model are in quite good agreement. Such windows allow the tuning of a gas gap heat switch to be used under particular circumstances.The adsorption properties of various types of activated charcoals and their consequences on the operational temperature windows are being studied in order to allow a still larger customization of such heat switches.