Gas-gap Heat Switches
Gas-gap heat switches are used for thermal management over large temperature ranges. CRC heat switches are usually filled with Helium (either He4 or He3) and are used down to a lower temperature limit of ~4K if filled with He4, or ~0.2K with He3. Other gases can be used to fill switches that operate at higher temperatures.
Heat switches may be either active or passive. A passive switch has an internal absorber and operates automatically; it turns ON and remains fully ON while the hot end temperature is greater than around 15-20K. In the ON state the thermal conductivity is large (around 100mW/K at 4K). When the hot end temperature drops below around 10K the switch will start to turn OFF though it will not be fully OFF until the hot end temperature is ~4K. When the switch is OFF it has a residual thermal conductance dictated by the material properties and dimensions of the shell.
In an active heat switch a small external gas adsorber pod is connected by a gas tube to the foot of the switch. Gas is released into the switch by electrically heating the pod under user control. The thermal conductance in ON and OFF states depend (as with the passive switch) on material properties, and also on the temperatures of the ‘hot’ and ‘cold’ ends.
Ideally a heat switch would have high on-state conductance and very low off-state conductance. In practice it is very challenging to manufacture a gas-gap heat switch that meets both criteria. The space available to accommodate the heat switch is an additional constraint. To find out whether we can provide a heat switch for your particular requirements, use our Heat Switch Questionnaire to let us know more about your intended application. We make many different designs of heat switch and will be happy to advise whether a standard or custom design will best meet your needs.
