Besides the supply our standard range of Cryogenic production plants and loose delivered cryogenerators we have over 40 years of experience in designing and supplying closed loop and custom build cooling systems.
A closed loop cryogenic cooling system is often a very efficient option, to be considered, for any kind of cryogenic cooling or application. When cooling an application with “bulk supply cryogen” typically this is vented. However, this vent gas still contains a lot of “cold” that is being wasted or creates a hazardous situation for the environment. By capturing this vent gas and feeding it back to a Stirling Cryogenerator were it is cooled (or re-liquefied) again, a closed loop is created which is very efficient.
All Stirling’s Cryogenerators (one and two stage) can be considered as a cold source for integration in these kind of closed loop systems. Systems with multiple coolers are possible and common. A Stirling’s SPC-1 and SPC-4 cryogenerator (cryocooler) provides cryogenic cooling power in the range of 500 – 4,000 Watt at 77K. They can be used in an operating range of 150 – 50 Kelvin. Stirling’s two stage Cryogenerators SPC-1T and SPC-4T provide cryogenic cooling power in the range of approx. 20 - 800 Watt from 15-40K.
Cryogenic Circulators and pumps
Within our sister brand CryoZone we have created a range of products to support these closed loop cooling systems:
All these closed loop cooling systems required a driving force to make the cryogen flow from the cold source towards the customer’s application. Most often this needs to be (Cryogenic) pump. CryoZone has developed a range of high efficient liquid and gas pumps, to make these closed loop systems feasible without wasting a lot of energy, which are (most of the time) integrated into our systems.
Ample engineering considerations and experience are required while designing a closed loop system as you will have to consider cold production, heat transfer, flow resistance, cost etc. Most often this is iterative process going back and forth checking the overall performance of the system based on changing parameters. The general starting point is the required cooling power at customer’s application, the allowable (required) delta T(emparature) across this application and the allowable working pressure of the coolant.
Liquid Nitrogen closed loop cooling systems
One of the most common closed loop systems use Liquid Nitrogen (LN2) depending on the application, the required cooling power and temperature. Temperature is typically in the 77-90K range but higher (pressurized) and lower (subcooled) is possible as wel. In these systems, liquid Nitrogen is used as a coolant and either pumped or gravity fed. Boil off gas or heated liquid is cooled again with Stirling Cryogenerators.
Helium gas cooling systems
In case lower temperatures (< 65K) are required or because of other considerations, (pressurized) Helium gas (He(g)) can be used as coolant. Besides its inert properties, Helium gas has the major advantage that a wide temperature range can be achieved (300 to 15 kelvin). In order to achieve proper energy /heat transfer it is preffered to have the Helium gas in the closed loop system at sufficient pressure (preferably in the 10 -20 barg range). With CryoZone's Cryogenic Gas Circulators the gas is pumped in a closed loop from the application to the Stirling cryocoolers, where the heat is removed.
Both cooling systems are very common for Stirling Cryogenics / DH Industries and we have a lot of experience in designing and supplying these systems.