Cryogenic Helium Recirculation for Sub-1K Cooling
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Solution Overview
Problem
Current cryogenic apparatuses, such as Gifford-McMahon coolers, have limitations in reaching temperatures below 4 K efficiently and quickly, and often require direct contact with the cold head, which is not always convenient for specimen measurement.
Innovation Solution
A cryogenic apparatus comprising a two-stage Gifford-McMahon cooler system with a helium gas extraction flow duct and liquid helium recirculation circuit, including heat exchangers and a vessel for liquid helium, which allows for efficient cooling of specimens to below 1 K by using a helium recirculation circuit and minimizing radiant heat transfer through heat shields and baffles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a two-stage Gifford-McMahon cooler is used to reach temperatures below 4 K, then the cooling temperature is improved, but the cooling speed and continuous cooling power deteriorate
Solution Approach 1:
The system is divided into two independent cooling circuits: a two-stage Gifford-McMahon cooler for achieving low temperatures below 4 K, and a separate single-stage helium-3 evaporative cooler for providing rapid cooling and continuous cooling power. This segmentation allows each subsystem to optimize for its specific function without compromise.
Solution Approach 2:
A heat exchanger serves as an intermediary component that couples the two independent cooling circuits. The heat exchanger transfers cooling capacity from the evaporative cooler to the specimen while the two-stage cooler maintains the low temperature baseline, enabling both rapid cooling and continuous cooling power without direct mechanical connection between the different cooler types.
2Use of energy by moving object
If the specimen is placed directly in contact with the cold head of the cooler, then the cooling efficiency is improved, but the ease of operation and specimen placement flexibility deteriorate
Solution Approach 1:
The liquid helium bath acts as an intermediary cooling medium between the cold head and the specimen. Instead of requiring direct contact with the cold head, specimens are immersed in or cooled by liquid helium, which is supplied by the single-stage evaporative cooler. This provides flexible specimen placement while maintaining high cooling efficiency through the excellent thermal properties of liquid helium.
3Object-affected harmful factors
If the enclosure is evacuated to suppress heat transfer by convection, then the heat transfer from external environment is reduced, but the complexity of the apparatus increases
Solution Approach 1:
The system uses liquid helium as an inert cooling atmosphere within the enclosure. The single-stage evaporative cooler continuously supplies liquid helium that fills the enclosure, creating an inert helium atmosphere that conducts heat away from specimens more efficiently than vacuum while suppressing convective heat transfer from the external environment. This approach reduces thermal radiation issues associated with vacuum while maintaining effective heat management.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid cooling of specimens to temperatures below 1 K with continuous cooling power, reducing temperature gradients and vibration, while allowing for flexible specimen placement and minimizing radiant heat transfer.
Implementation Method 1
a first heat exchanger within the gas flow duct; wherein the apparatus also comprises a first duct to carry cold helium gas from a fluid outlet of the first thermo-mechanical cooler and through the first heat exchanger
Implementation Method 2
the apparatus also includes a second heat exchanger within the gas flow duct, the second heat exchanger being closer to the vessel to contain liquid helium than the first heat exchanger, and the second duct carries the liquid helium from the fluid outlet of the second thermo-mechanical cooler through the second heat exchanger to the vessel
Implementation Method 3
During use the enclosure would be evacuated, so heat transfer by convection is suppressed; under the circumstances radiation is a significant cause of heat transfer. The apparatus may also include a heat shield at the intermediate temperature, the heat shield being in thermal contact with the second thermo-mechanical cooler at a position having the intermediate temperature, and enclosing all the components of the cryogenic apparatus that are intended, in use, to be below that intermediate temperature.
Data Source
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AI summary
A cryogenic apparatus (10) includes an enclosure (12), a first thermo-mechanical cooler (20) and a second thermo-mechanical cooler (22) which project into the enclosure (12), at least the second thermo-mechanical cooler (22) being a two-stage cooler, and each cooler (20, 22) having a fluid inlet and a fluid outlet for each stage, and a helium gas extraction flow duct (40) which extends into the enclosure (12) and which communicates with a vessel (42) to contain liquid helium within the enclosure (12). There is a first heat exchanger (62) within the gas flow duct (40). A first duct (74) carries cold helium gas from a fluid outlet (73) of the first thermo-mechanical cooler (20) and through the first heat exchanger (62) to the fluid inlet (75) of the second stage of the second thermo-mechanical cooler (22). A second duct (77) carries liquid helium from the fluid outlet (76) of the second thermo-mechanical cooler (22) into the vessel (42) to contain liquid helium. In operation a pump (80) supplies helium gas to the first thermo-mechanical cooler (20), and withdraws helium gas from the gas flow duct (40). The apparatus (10) can provide rapid cooling, and can achieve significant cooling power at temperatures below 1 K.