Cryogenic refrigerator
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Solution Overview
Problem
Cryogenic refrigerators face reduced refrigeration performance due to high flow path resistance in the expansion space, leading to pressure drops and inefficient heat exchange, especially when refrigerant gas is supplied to the expansion space at a higher temperature than the cooling stage.
Innovation Solution
The cryogenic refrigerator design features a displacer with a clearance between the cylinder and the displacer, where the flow path resistance is lower when the displacer is at the bottom dead center than at the top dead center, optimizing the flow path area to enhance heat exchange efficiency and reduce pressure drops by varying the flow path resistance throughout the reciprocating movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flow path resistance in the expansion space is high, then the refrigerant gas flow control is improved, but the pressure drop increases and heat exchange efficiency decreases
Solution Approach 1:
The patent applies the dynamics principle by making the flow path resistance variable rather than constant. The clearance between the displacer and cylinder wall changes dynamically with displacer position, creating lower flow path resistance at bottom dead center and higher resistance at top dead center. This dynamic adjustment optimizes both refrigerant gas flow control and reduces pressure drops throughout the cycle.
Solution Approach 2:
The patent changes the flow path resistance parameter throughout the operating cycle. By varying the clearance dimension based on displacer position, the system transforms a static flow resistance into a dynamic parameter that adapts to different operational phases, improving overall system efficiency while maintaining reliable flow control.
2Use of energy by moving object
If the flow path resistance is increased to improve refrigerant gas collection, then the heat exchange efficiency improves, but the pressure drop increases
Solution Approach 1:
The dynamic variation of flow path resistance through changing clearance dimensions allows the system to optimize heat exchange efficiency during refrigerant gas collection while minimizing pressure losses. The clearance is larger when needed for low resistance flow and smaller when heat exchange efficiency is prioritized.
Solution Approach 2:
The system employs periodic action by cycling the flow path resistance through the reciprocating motion of the displacer. During different phases of the cycle, the resistance varies periodically to match the operational requirements - lower during supply phases and higher during collection phases - thereby optimizing both heat exchange and pressure management.
3Loss of energy
If the clearance between displacer and cylinder is reduced to lower flow path resistance, then the pressure drop decreases, but the heat exchange efficiency reduces
Solution Approach 1:
Rather than using a fixed small clearance, the patent employs a dynamic clearance that varies with displacer position. The clearance is larger at positions where low pressure drop is critical and smaller at positions where heat exchange efficiency is prioritized, thus resolving the contradiction between these two requirements.
Solution Approach 2:
The clearance parameter is changed dynamically throughout the cycle rather than maintained at a constant small value. This parameter transformation allows the system to achieve both low pressure drops and high heat exchange efficiency at different appropriate times during the operational cycle.
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 configuration improves refrigeration performance by increasing heat exchange efficiency and reducing pressure drops, particularly during the refrigerant gas collection process, where the flow speed is higher, leading to better cooling efficiency and reduced pressure losses.
Implementation Method 1
a Gifford-McMahon (GM) refrigerator is known. In the GM refrigerator, a displacer performs reciprocating movement in a cylinder to change a volume of an expansion space. By selectively connecting the expansion space with a discharge side or an intake side of a compressor unit in accordance with this volume change, refrigerant gas expands in the expansion space.
Implementation Method 2
a displacer performs reciprocating movement in a cylinder to change a volume of an expansion space. By selectively connecting the expansion space with a discharge side or an intake side of a compressor unit in accordance with this volume change, refrigerant gas expands in the expansion space.
Data Source
AI summary
In a cryogenic refrigerator, a displacer has an internal space in which refrigerant gas flows. A cylinder houses the displacer to enable the displacer to perform reciprocating movement and forms an expansion space of the refrigerant gas between the cylinder and a bottom surface of the displacer. The displacer supplies the refrigerant gas to the expansion space during movement inside the cylinder from a bottom dead center to a top dead center. The displacer collects the refrigerant gas from the expansion space during movement inside the cylinder from the top dead center to the bottom dead center. A flow path resistance between the displacer and the expansion space is lower when the displacer is at the bottom dead center than when the displacer is at the top dead center.