Cryocooler Pressure Control for 2.17 K Superfluid Helium
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Solution Overview
Problem
Existing cryocoolers are unable to achieve temperatures lower than 4 K, which limits their ability to provide helium at its superfluid transition temperature of 2.17 K.
Innovation Solution
A cryocooler system that includes an expander for expanding high-pressure helium and a compressor to recycle low-pressure helium, with the pressure of the low-pressure helium set to a level where the volumetric thermal expansion coefficient of helium is zero in its state diagram, allowing for temperatures as low as 2.17 K to be maintained, thereby enabling the generation of coldness at or below 4 K.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cryocoolers expand helium to generate coldness, then cooling capability is provided, but the reached temperature cannot be lower than 4 K
Solution Approach 1:
The invention changes the pressure parameter of the helium gas during expansion to achieve lower temperatures. Specifically, it controls the pressure to be equal to or higher than the pressure on the α-line (where volumetric thermal expansion coefficient is zero) in the helium state diagram, enabling temperatures of 2.17 K or lower to be achieved while maintaining stable temperature control
Solution Approach 2:
The invention dynamically adjusts the pressure of the low-pressure helium based on the temperature conditions. By making the pressure control adaptive and responsive to temperature changes, the system can maintain optimal operating conditions on the α-line to achieve and sustain superfluid transition temperatures
2Temperature
If pressure of low-pressure helium is increased to achieve lower temperatures, then cooling performance improves, but system complexity increases
Solution Approach 1:
The invention implements a feedback control mechanism where the pressure of the low-pressure helium is adjusted based on temperature measurements. The system monitors temperature and adjusts pressure accordingly to maintain operation on the α-line, achieving lower temperatures through automated feedback rather than complex manual control systems
Solution Approach 2:
The system utilizes the inherent properties of helium on the α-line where the volumetric thermal expansion coefficient is zero. This self-regulating property of helium at specific pressure-temperature conditions simplifies the control system, as the helium itself provides stability when operated at the correct pressure points defined by the α-line
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 4 K, allowing for the liquefaction of helium and its transfer into a superfluid state, enhancing cooling efficiency and operational stability while maintaining low costs due to the use of helium-4.
Implementation Method 1
an expander which expands high-pressure helium
Implementation Method 2
a compressor which compresses low-pressure helium returned from the expander, generates high-pressure helium
Implementation Method 3
the pressure of the low-pressure helium is equal to or higher than a pressure of a curve in which a volumetric thermal expansion coefficient of helium is 0
Data Source
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AI summary
In a cryocooler 1 which generates a coldness having 4 [K] or lower by expanding helium, an expander 50 expands high-pressure helium. A compressor 12 compresses low-pressure helium returned from the expander 50, generates high-pressure helium, and supplies the high-pressure helium to the expander 50. When a temperature of helium in the expander 50 is 2.17 [K] or lower, the pressure of the low-pressure helium is equal to or higher than a pressure of a curve in which a volumetric thermal expansion coefficient of helium is 0 in a state diagram of helium in which a horizontal axis is temperature and a vertical axis is pressure.