Cryocooler Pressure Control for Helium Superfluid Cooling
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Solution Overview
Problem
Existing cryocoolers are limited in achieving temperatures lower than 4 K, which restricts the availability of helium at superfluid transition temperatures.
Innovation Solution
A cryocooler system that includes an expander for expanding high-pressure helium and a compressor to recycle low-pressure helium, with temperature and pressure control based on a helium state diagram to maintain the helium at or below 2.17 K, ensuring the pressure is set to prevent temperature increase during adiabatic expansion, thereby enhancing cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the cryocooler operates at conventional pressures during adiabatic expansion, then the expansion process is simple, but the temperature increases instead of decreasing, preventing achievement of superfluid transition temperatures
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the pressure of helium during adiabatic expansion based on temperature conditions. When temperature is 2.17 K or lower, the pressure is controlled to be equal to or higher than the value on the curve where volumetric thermal expansion coefficient is zero. This parameter adjustment ensures temperature decrease during expansion, enabling achievement of superfluid transition temperatures while maintaining controllable device operation
Solution Approach 2:
The patent implements feedback control by detecting the temperature of helium in the expander and adjusting the pressure of low-pressure helium accordingly. The temperature detection triggers pressure adjustment to maintain the helium pressure at or above the critical value from the state diagram, ensuring the volumetric thermal expansion coefficient remains zero or positive. This feedback mechanism prevents temperature increase during expansion and enables stable operation at superfluid transition temperatures
2Temperature
If the pressure of low-pressure helium is reduced to increase cooling effect, then cooling efficiency improves, but the temperature increases during expansion due to negative volumetric thermal expansion coefficient
Solution Approach 1:
The patent resolves this contradiction by changing the pressure parameter dynamically based on temperature conditions. Instead of using fixed low pressure, the system adjusts pressure to be equal to or higher than the value on the zero volumetric thermal expansion coefficient curve when temperature is 2.17 K or lower. This ensures the helium maintains non-negative volumetric thermal expansion coefficient, preventing temperature increase during expansion while still achieving effective cooling
Solution Approach 2:
The patent applies dynamics by making the pressure control adaptive rather than static. The pressure of low-pressure helium is dynamically adjusted based on real-time temperature detection and the helium state diagram. This dynamic control allows the system to optimize cooling efficiency at each temperature stage, ensuring temperature decrease during expansion while maintaining high cooling productivity
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
The system effectively generates coldness at or below 2.17 K, enabling the helium to reach a superfluid state, improving cooling efficiency and allowing for stable operation as a cryocooler for helium-4 at a lower cost compared to helium-3.
Implementation Method 1
expanding high-pressure helium supplied from a compression device... by expanding helium... the helium inside the expander is made to expand, giving rise to coldness
Implementation Method 2
a compressor for compressing low-pressure helium, returned from the expander, to generate high-pressure helium
Implementation Method 3
The helium chilling that occurs in the expander builds up in a regenerator and meanwhile is transmitted to a cooling stage
Data Source
AI summary
In a cryocooler for developing coldness of 4 K or lower by expanding helium, an expander expands high-pressure helium. A compressor compresses low-pressure helium returned from the expander, to generate high-pressure helium, and supplies the high-pressure helium to the expander. When helium temperature in the expander is 2.17 K or lower, the pressure of the low-pressure helium is equal to or higher than pressure given by a curve, in a helium state diagram in which the horizontal axis is temperature and the vertical axis is pressure, along which helium's volumetric thermal expansion coefficient is 0.