Helium-Circulation Cryostat for Low-Vibration Specimen Cooling
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Solution Overview
Problem
Existing cryogenic apparatuses face challenges in efficiently cooling specimens to temperatures below 10 K, particularly in achieving rapid cooling and minimizing vibration-induced disturbances, while maintaining effective heat transfer and preventing air infiltration.
Innovation Solution
A cryogenic apparatus comprising a thermo-mechanical cooler, a sample tube with dual fluid inlets and outlets, and a pump system for helium gas circulation, allowing for dynamic and static cooling modes, along with a heat shield and vibration-suppressing linkage to manage temperature and vibration effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thermo-mechanical cooler is used to cool the specimen, then the specimen temperature can be reduced to below 10 K, but vibration is generated that disturbs measurements
Solution Approach 1:
A cold helium gas circulation system acts as an intermediary cooling medium. The thermo-mechanical cooler cools helium gas, which then circulates through heat exchangers to cool the specimen indirectly, separating the vibration source from the measurement environment while maintaining thermal coupling
Solution Approach 2:
The cooling system is segmented into distinct functional zones: a vibration-isolated enclosure housing the specimen, a separate thermo-mechanical cooler unit, and interconnecting helium circulation pathways. This spatial segmentation isolates vibration while maintaining thermal connection through the helium medium
2Temperature
If liquid helium is supplied through a capillary flow impedance into an evaporation chamber, then cooling is achieved, but the system complexity increases and control becomes difficult
Solution Approach 1:
The system replaces complex mechanical capillary flow impedance control with a simpler thermodynamic approach using phase change of helium. Liquid helium evaporates in the evaporation chamber, and the resulting gas is circulated and condensed, providing passive flow control through phase transitions rather than mechanical restrictions
Solution Approach 2:
The system utilizes the phase transition between liquid and gaseous helium to achieve cooling and flow control. Liquid helium is supplied to the evaporation chamber where it evaporates, absorbing heat and cooling the specimen. The gaseous helium is then circulated and condensed back to liquid in a heat exchanger, creating a continuous passive cooling cycle without complex mechanical flow control
3Loss of energy
If the enclosure is evacuated to suppress heat transfer by convection, then heat isolation is improved, but air infiltration must be prevented during operation
Solution Approach 1:
The system maintains a controlled helium atmosphere within the enclosure rather than a complete vacuum. Helium gas is continuously circulated through the enclosure, providing both thermal isolation (since helium has low thermal conductivity at these conditions) and a protective inert atmosphere that prevents air infiltration and maintains stable operating conditions
Solution Approach 2:
The helium circulation system operates continuously, constantly refreshing the gas atmosphere in the enclosure. This continuous circulation maintains thermal isolation, prevents air infiltration by maintaining positive pressure, and removes any accumulated contaminants, ensuring reliable operation without interruption
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 specimen cooling to temperatures as low as 1.5 K with minimal vibration, utilizing helium gas circulation for efficient heat transfer and maintaining a controlled environment to prevent air infiltration, with the option for natural convection cooling for stable temperature maintenance.
Implementation Method 1
a thermo-mechanical cooler which projects into the enclosure... supply cold helium at a temperature below 10 K
Implementation Method 2
supply the cold helium into thermal contact with the thermo-mechanical cooler... thermal contact with the sample tube
Implementation Method 3
Helium flows up the annular channel which surrounds the entire length of the sample chamber thereby cooling the sample
Implementation Method 4
a pump having a pump inlet and a pump outlet, and a duct to supply helium gas from the pump outlet
Implementation Method 5
a heat shield at the intermediate temperature, the heat shield being in thermal contact with the thermo-mechanical cooler at a position having the intermediate temperature
Data Source
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AI summary
A cryogenic apparatus (10) comprises: an enclosure (12); a thermo-mechanical cooler (22) and a sample tube (20) that both project into the enclosure (12), where the sample tube (20) has a closed end; a pump (92) with a pump inlet and a pump outlet, and a duct to supply helium gas from the pump outlet to the thermo-mechanical cooler (22) to produce cold helium. The sample tube (20) has a first inlet (74) to allow a fluid into the sample tube (20), and a second inlet (83) to supply fluid to a thermal element (42) in thermal contact with the sample tube (20), and also has a first outlet (26) to withdraw fluid from within the sample tube (20), and a second outlet (28) to withdraw fluid from the thermal element (42). The apparatus also comprises a first duct including a first valve (80) to supply the cold helium to the first inlet (74) and a second duct including a second valve (82) to supply the cold helium to the second inlet (83); and either or both of the first outlet (26) and the second outlet (28) may be connected to the inlet of the pump (92). This enables a specimen to be cooled either in a static mode, relying on natural convection, or in a dynamic mode, with a forced gas flow, or using both modes at once. These different options enable an operator to achieve different cooling rates.