Nested Piston-Cylinder Cryocooler Without Transfer Line Losses
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Solution Overview
Problem
Long-life Stirling-class cryocoolers suffer from parasitic losses due to the transmission of pressure-volume power through a transfer line between compressor and expander modules, leading to reduced overall system efficiency.
Innovation Solution
A single-module cryocooler design where the compressor and displacer share a common working volume within a sealed housing, eliminating the need for a gas transfer tube and reducing the number of seals, allowing one moving part to move within another, thereby minimizing leakage and parasitic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a transfer line is used to transmit PV power between compressor and expander modules, then the cryocooler can be designed with separate modules, but parasitic losses increase and system efficiency decreases
Solution Approach 1:
The patent combines the compressor and expander modules into a single integrated unit where the compressor piston and expander piston share a common working volume. This eliminates the transfer line between modules, removing the source of parasitic losses while maintaining the functional separation of compression and expansion processes within the same chamber.
Solution Approach 2:
The design nests one piston within another by placing the expander piston inside the compressor piston's working volume. The expander piston moves within the annular space created by the compressor piston's movement, allowing both components to occupy and utilize the same three-dimensional space efficiently.
2Device complexity
If a gas transfer tube is used to connect separate modules, then module independence is maintained, but gas leakage increases and efficiency is reduced
Solution Approach 1:
The patent merges the working volumes of the compressor and expander into a single sealed chamber. This eliminates the need for gas transfer tubes and external sealing interfaces, thereby removing potential leakage paths while maintaining functional independence through the coordinated movement of two pistons within the same sealed environment.
3Adaptability or versatility
If multiple seals are used in separate module connections, then module flexibility is improved, but seal losses increase
Solution Approach 1:
The integration of compressor and expander into a single module with a common working volume reduces the number of required seals from multiple external sealing interfaces to just the necessary internal seals for piston movement. This consolidation maintains the adaptability of the design while minimizing seal-related energy losses.
4Ease of operation
If separate compressor and expander modules are used, then functional separation is achieved, but vibration mitigation becomes more difficult
Solution Approach 1:
By nesting the expander piston within the compressor piston's working volume and coordinating their movements, the patent creates a configuration where the vibration sources are closely coupled and can be more effectively balanced. The proximity of the two moving masses allows for better vibration mitigation through proper phasing and mass balancing, while still maintaining functional separation of the compression and expansion processes.
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
This design enhances efficiency by eliminating gas transfer losses, reducing seal losses, and simplifying vibration mitigation, resulting in a more compact, lighter, and thermodynamically efficient cryocooler system.
Implementation Method 1
a compressor... PV power produced by the compressor
Implementation Method 2
a Stirling displacer that actively controls the thermodynamic compression/expansion cycle
Implementation Method 3
The regenerator is a solid matrix that moves with the displacer... passage through the regenerator
Implementation Method 4
isothermal expansion... the expander... actively controls the thermodynamic compression/expansion cycle
Data Source
AI summary
A thermal-cycle cryocooler, such as a Stirling-cycle cryocooler, has a single working volume that is utilized by both the compressor and the displacer. The compressor and the displacer have respective movable parts, one of which is surrounded by the other. One of the parts may be a piston, a portion of which moves within a central bore or opening in a cylinder that is the other movable part. The piston may be a component of the compressor and the cylinder may be a component of the displacer, or vice versa. The working volume is located in part in a bore of the cylinder, between the piston and a regenerator that is coupled to the cylinder. Movements of either the piston or the cylinder can directly (i.e. without the use of a gas transfer line or flow passage) cause compression or expansion of the working gas in the working volume.