Through years of experience Stirling Cryogenics has developed a lot of cryogenic knowledge, especially regarding handling cold and transferring this to the customers’ application.
This resulted in one of Stirling’s leading edge products: cold helium circulation pumps named CryoFans. These are created and optimized to provide a cryogenic helium flow to efficiently transport and distribute cooling power.
Stirling Cryogenics offers a range of CryoFans which, by providing a cold helium flow, thermally connect the application to a cold source. This can be a (Stirling) Cryogenerator, or a cryogenic vessel of LN2 or LHe.
The cold helium gas flow is transferred via vacuum insulated piping, allowing the cold source to be installed at an adequate distance and position from the application.
Also internally of the application the cooling power can easily be distributed over different components or a large surface.
The circulating helium gas transfers the heat generated in the application back to the cold source, which rejects this to the ambient.
Stirling Cryogenics has developed a range of standard high efficiency CryoFans.
All CryoFans have the same generic design concept. Like all centrifugal pumps, the main parts are the impeller and volute. Their dimensional shape determines the functionality and efficiency of the fan.
The impeller is driven by a high rpm electric motor providing labour to the gas. In the CryoFan design, all components are placed within a single housing with the motor installed within the pressurized gas volume. This solution does not have a rotating seal so there is no possibility of leakage.
In order to create a thermal barrier between the motor at ambient temperature and the cold impeller, the latter is mounted on a long thin stainless steel shaft. This cantilever set-up with a high-precision balanced shaft and impeller, is used to avoid the necessity of a cold bearing. This set-up ensures a Mean Time Between Maintenance of over 20.000 operating hours.
The CryoFan concept allows for easy integration into a system cryostat. Only a central bore with a flange pattern is needed. This pattern can be machined in the cryostat flange or in an ISO-K or CF blind flange. The pressure housing with pump volute is mounted inside the cryostat and the circuit lines are connected. The motor with shaft and impeller can now be mounted from the outside. This means that the complete impeller unit can be removed without breaking the vacuum of the application.
In a Closed Loop Helium Gas Cooling System, the cold helium gas is heated by the application and is then cooled by a cryocooler. This requires an efficient design resulting in a small temperature difference as well as low pressure drop.
The Stirling Cryogenerators have such integrated heat-exchanger to efficiently cool the helium gas flow.
However, most non-Stirling cryogenerator on the market are not designed to cool a flow of gas. Stirling Cryogenics has therefore designed dedicated clip-on heat exchangers for a wide variety of non-Stirling Cryogenerators ensuring a highly efficient heat flow from the pressurized gas to the cryocooler.
This results in a dT between gas and cooler of down to 1 K, ensuring maximum available cooling capacity.