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 100K, 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.

Exploring the Potential of Metal–Organic Frameworks for Cryogenic Helium-Based Gas Gap Heat Switches via High-Throughput Computational Screening

“…The narrower the gap width, the higher the plateau value, and the greater the pressure at which the plateau is reached. Due to the restrictions of manufacturing technology, most gap widths reported in the literature are in the range of 100–300 μm. ,− From Figure , it can be seen that the heat transfer coefficients for gap widths between 100 and 300 μm remain nearly constant when the pressure exceeds 10 3 Pa. Therefore, the pressure in the ON state was taken as 1 × 10 3 Pa in this study.…”

Cryogenic flat-panel gas-gap heat switch

“…The pressure change from the on to the off-state and viceversa is usually realized in a gas-gap heat switch with a sorber material. Activated carbon with helium or hydrogen adsorption is commonly used at a heat sink temperature in the range of 6-30 K [6,7]. Above this range the adsorption characteristics of helium and hydrogen gas with activated carbon decreases and will not be able to provide the necessary pressure changes via a suitable heating-cooling cycle.…”