Cryogenics & Fluids Home
M.J. DiPirro, P.J. Shirron, J.G. Tuttle, E.R. Canavan
Code 552
NASA/ Goddard Space Flight Center
Greenbelt, MD 20771
The gas gap heat switch is a simple thermal switch consisting of closely spaced parallel metal plates alternating between the hot and cold side of the switch housed in a gas impermeable, thermally isolating enclosure. Gas is sealed into the enclosure, providing the thermal path between the metal plates of the switch. The large surface area and close spacing of the parallel surfaces allows the gas conduction to provide good thermal contact when the switch is on. The switch is turned off by cooling a getter which absorbs the gas. We have developed passive gas gap heat switches that have on/off transition temperatures between 0.2 and 13 K. These passive switches feature rapid response, no need for external control, and more efficiency (no extral heat dissipation). The gas type, dosage, and getter type and surface area are determined by calculating the residual pressure such that the mean free path of the gas is as long as or longer than the separation between metal plates when the switch temperature is at its turn-off point. Important performance paramenters, as for all thermal switches, are the on conductance, the off conductance or parasitic heat flow, the temperature range of operation, and the method of switch activation. These parameters are given for the passive gas gap heat switches.
Advances in Cryogenic Engineering: Transactions of the Cryogenic Engineering Conference -CEC, Vol. 49A, ed. J. Waynert et al. pp. 436 - 442 (2004, American Institute of Physics).