Pneumatic drive cryocooler
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Solution Overview
Problem
Current Gifford-McMahon cryocoolers face limitations such as parasitic magnetic fields, mechanical vibrations, direct acoustic emissions, limited tunability, and wear of seal and bushing components, which are detrimental for applications like MRI and NMR, due to motor-driven mechanisms and direct mechanical linkages.
Innovation Solution
The implementation of a pneumatically driven cryogenic refrigerator with electronic control valves and a passive force generator, such as springs or magnets, to control the displacer's motion independently of valve actuation, allowing for adjustable pressure and flow profiles, reducing vibrations and magnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motor-driven mechanisms with direct mechanical linkages are used to drive the displacer, then the displacer can be driven reliably, but parasitic magnetic fields, mechanical vibrations, and acoustic emissions are generated that are detrimental for MRI and NMR applications
Solution Approach 1:
The patent replaces motor-driven mechanical linkages with a pneumatic drive system. The displacer is driven by pressure differential forces applied to a drive piston through controlled fluid flow, eliminating motors, magnetic fields, and direct mechanical linkages that cause vibrations and acoustic emissions.
Solution Approach 2:
The patent employs pneumatic pressure control to drive the displacer. By controlling the pressure differential across the drive piston through electronic valves, the system achieves reliable displacer motion without mechanical contact or magnetic fields, solving the contradiction between reliability and harmful emissions.
2Reliability
If pneumatic drive volume is controlled by mechanically linked valves, then valve timing is synchronized with displacer position, but the structural coupling prevents independent optimization of valve timing
Solution Approach 1:
The patent replaces mechanically linked valves with electronically controlled valves. The electronic controller independently manages valve timing based on displacer position feedback, allowing precise synchronization while enabling flexible adjustment of timing parameters without structural coupling constraints.
Solution Approach 2:
The system transitions from fixed mechanical valve timing to dynamically adjustable electronic control. The valve timing can be optimized independently at different operating points through electronic control, providing adaptability while maintaining synchronization through feedback from displacer position sensors.
3Device complexity
If force imbalances on the displacer are not compensated, then the system structure remains simple, but the displacer hits the bottom or top of the cylinder causing impact vibrations
Solution Approach 1:
The patent employs feedback control where displacer position is sensed and used to control the pneumatic drive valves. This feedback mechanism detects approaching limits and adjusts pressure differential accordingly, preventing the displacer from hitting cylinder ends and eliminating impact vibrations while maintaining reasonable system complexity.
Solution Approach 2:
The system applies preliminary control actions to prevent force imbalances from causing harmful impacts. By monitoring displacer position and adjusting drive pressure before the displacer reaches extreme positions, the system proactively prevents impact vibrations rather than reacting after they occur.
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 solution reduces vibrations, magnetic material usage, and size/weight, enhancing thermodynamic efficiency and tunability, enabling precise control of the displacer's motion and refrigeration capacity, thus addressing the limitations of traditional motor-driven cryocoolers.
Implementation Method 1
pneumatic forces to cause the displacer to reciprocate within the refrigerator cylinder
Implementation Method 2
Fluid is cooled as it passes through the regenerative matrix by pressure differential
Implementation Method 3
The passive force generator may be a spring
Implementation Method 4
Fluid is cooled as it passes through the regenerative matrix
Implementation Method 5
The fluid is then expanded and further cooled at the cold end
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A Gifford-McMahon cryogenic refrigerator comprises a reciprocating displacer within a refrigeration volume. The displacer is pneumatically driven by a drive piston within a pneumatic drive volume. Pressure in the pneumatic drive volume is controlled by valving that causes the drive piston to follow a programmed displacement profile through stroke of the drive piston. The drive valving may include a proportional valve that provides continuously variable supply and exhaust of drive fluid. In a proportionally controlled feedback system, the valve into the drive volume is controlled to minimize error between a displacement signal and a programmed displacement profile. Valving to the warm end of the refrigeration volume may also be proportional. A passive force generator such as a mechanical spring or magnets may apply force to the piston in opposition to the driving force applied by the drive fluid.