Products

Closed Loop Liquid Nitrogen Cooling Systems


DH Industries has a long and strong reputation with respect to designing and supplying closed loop liquid cooling systems that utilize the efficient Stirling Cryogenics Cryogenerators as a cold source.

Although most systems use Nitrogen (LN2) as a coolant (due to its availability and/or temperature range) any cryogenic fluid can be used within the same design parameters.

In these systems cryogenic LN2 is transported to the customer’s application where the cold fluid extracts energy from the system, by heating up and/or by evaporation. The warmer fluid/vent gas is collected and, in a closed loop, fed to (a) Cryogenerator(s) where the energy is removed and the gas re-liquefied again.

These systems tend to be very efficient: Normally, in cases where an application is cooled with bulk LN2, cold vent gas going to waste. With that, a lot of effort (energy), which was required to produce and cool it, is wasted. However by collection, re-using and re-liquefying the gas the cold is saved and less energy is required to produce liquid Nitrogen again. In case the customer does not require any cooling the system will switch to stand-by mode to keep itself cold by switching the cooler on and off.

As a minimum, these systems comprise of one or more cryocoolers, a LN2 storage tank and (vacuum insulated) lines towards customers application and return lines. More often the system will have some kind of pump (to get the liquid flowing), cryogenics valves, connections and instrumentation. Within our more than 50 years of experience, we have developed the know-how and expertise to design and size these kind of set ups.

All Stirling’s Cryogenerators (one and two stage) can be considered 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 cryogenerators (cryocooler) provide 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.

Stirling Cryogenics is able to assist you with design a process set up and selecting the right equipment.

For more information on how cold is produced, see:
The Stirling Cycle

Applications

Applications and markets where closed loop LN2 cooling systems have proven to be viable solutions:

  • High temperature superconductors (Cables)
  • Magnet cooling
  • Aerospace
  • Space simulation chambers and shroud cooling
  • Instrument cooling
  • Observatories
  • Thermal shielding
  • Cryo chambers (Cryotherapy)
  • MBE cooling

Several add-ons are available for specific cases:

  • Vacuum insulated coldhead:In case the system is expected to operate below 77 Kelvin we recommend using vacuum insulated coldhead and lines. For applications above 77K perlite insulated cold heads can be used.
  • Anti-Freeze Heaters:
    In case the system will operate near the freezing point of the liquid (for instance around 65K for LN2) there is a risk of freezing the fluid. This will block the cold head and terminate the cooling process. Integrated anti-freeze heaters are available as an option, to prevent this.
  • Sub cooling:
    In case boiling of the liquid (bubble formation) is not allowed in the cooling process (for instance for HTS cables) the LN2 can be pressurized and subcooled. This way the LN2 will cool the application by heating up, without boiling. Subcoolers /pressurizers are available to achieve this mode of operation.
  • Capacity control:
    The systems will have capacity control suited for the application. This can be an on/off operation of individual cryogenerators, but additional options are available. Each cooler can (optionally) be controlled by a frequency converter in a 100-60% range. Further control is possible by adding advanced Helium pressure control
  • Pumps
    In case (LN2) pumps are required to transport the LN2, they can be supplied and integrated. Within our brand CryoZone we have developed a high efficient LN2 pump for this purpose. Also 3rd party pumps are available.
  • Tanks, buffers and connection lines:
    Depending on the mode of operations additional tanks, buffers and or connection lines might be required. Typically they will be vacuum insulated. This kind of equipment can be supplied and integrated. Different suppliers and manufacturers are possible.
  • Instrumentation, valves and safety devices:
    For proper and safe operations valves (manual or automated), instrumentation (pressure, temperature, flow) and safety devices will be required. Typically they will be vacuum insulated. This kind of equipment can be supplied and integrated. Different suppliers and manufacturers are possible.

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