Sorption characterization and actuation of a gas-gap heat switch

Abstract

Cryogenic gas-gap heat switches are rendered compact by using a sorption pump as actuating device. The sorption pump adsorbs gas when it is cooled and releases gas when it is heated. Upon desorption, the released gas lies in the gap between two blocks and increases the conduction heat transfer between them; in the reverse case – when the gas is adsorbed – the gap space between the two blocks behaves as an insulator. The temperatures at which there is sufficient desorption and adsorption of gas for actuating the ON an OFF states depend on several parameters of the gas-adsorbent system. The adsorption characteristics of helium gas on several carbon adsorbents were studied at pressures ranging from 50 Pa to 120 kPa and temperatures from 10 to 100 K. One of the carbons was successfully used in a heat switch at 6 K under different configurations in order to access different actuation characteristics. The experimental helium adsorption equilibrium data for each carbon were successfully fitted by a semi-empirical adsorption isotherm model. A thermal model of the heat switch, whose actuation can be tailored upon specifications, was developed based on the adsorption data. The thermal model was validated by reproducing the experimental data for two different configurations of a heat switch prototype.