The off-state conductance of a standard heat switch is approximately 37µW/K at a temperature of 4K. Heat switches are extremely delicate and cannot be used to provide mechanical support, indeed they MUST not be used in that way. For this reason we do not measure or specify the compressive and tensile strength. So far as
While it is possible to use different materials for the switch case, it can cause difficulties with the joining materials, thermal expansion and permeability to helium. These factors increase the expense of manufacture.
Activation (turning the switch ON) typically takes around 1.5 to 2.5mW of heater power, depending on the design requirements. This heat is usually dumped to the fixing point at 4K, as the transition temperature (ON/OFF) is around 15 to 20K.
Thermal conductivity in either the ON and OFF state of a heat switch is affected by temperature - the thermal conductivity of stainless steel and helium gas varies with temperature. Importantly, steel will determine the OFF-state conductivity, and helium gas the ON-state conductivity. Conductivity will also be affected by the switch's geometry. A typical standard
We make bespoke gas-gap switches as well as some standard types. The standard units are 2.5” (63.5mm) long and are usually mounted upright, but can operate in any orientation. Bespoke types vary in length depending on the application requirements. To design a bespoke switch, we need to know the customer's thermal requirements for the OFF-state