Cold Head Regenerator Mesh Design to Prevent Particle Clogging
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Solution Overview
Problem
The clogging of metal mesh holes by regenerator material particles in cold heads used for achieving cryogenic temperatures reduces the permeability of refrigerant gas, limiting the filling density and refrigerating capacity, which is critical for maintaining the operation of superconducting magnets and examination apparatus like MRI and NMR machines.
Innovation Solution
The use of a cold head design with quadrangular mesh holes in the metal mesh material, where the length of the long side is ½ or less of the average particle size of the regenerator material, and a copper mesh material with a wire diameter between 20 μm and 90 μm, along with a three-dimensional woven structure, prevents clogging and maintains high permeability of refrigerant gas, allowing for increased filling density and extended operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If regenerator material particles are filled closely to the metal mesh material to maximize filling density, then the refrigerating capacity is improved, but the mesh holes become clogged with particles which reduces refrigerant gas permeability
Solution Approach 1:
The patent applies local quality by creating a gradient in particle size distribution across different regions of the regenerator. Larger particles (0.3-3mm) are placed in the lower density region away from the mesh, while smaller particles (0.01-0.3mm) are placed in the higher density region closer to the mesh. This local differentiation allows maximum filling density near the mesh without clogging, as the smaller particles can pass through mesh holes while larger particles provide thermal mass in the bulk region.
Solution Approach 2:
The regenerator material is segmented into two distinct particle size groups with different functional roles. The first group (0.3-3mm) serves as the primary thermal storage medium in the bulk region, while the second group (0.01-0.3mm) acts as a buffer layer near the mesh that prevents clogging while maintaining filling density. This segmentation resolves the contradiction by assigning different sizes to different spatial zones.
2Reliability
If the mesh hole size is reduced to prevent particle passage, then particle retention is improved, but refrigerant gas permeability is reduced
Solution Approach 1:
The patent changes the parameter of particle size distribution to resolve the mesh hole size contradiction. Instead of relying solely on small mesh holes to retain all particles, the system uses a bimodal particle size distribution where the majority of particles (0.3-3mm) are too large to pass through mesh holes, providing retention without requiring small holes. The smaller particles (0.01-0.3mm) are present in controlled proportions and can pass through, maintaining permeability.
3Temperature
If regenerator material particles are filled densely to maximize specific heat utilization, then the cryogenic temperature achievement is improved, but the mesh holes become clogged which reduces operational reliability
Solution Approach 1:
The patent applies local quality by creating a gradient in particle size distribution across different regions of the regenerator. Larger particles (0.3-3mm) are placed in the lower density region away from the mesh, while smaller particles (0.01-0.3mm) are placed in the higher density region closer to the mesh. This local differentiation allows maximum filling density near the mesh without clogging, as the smaller particles can pass through mesh holes while larger particles provide thermal mass in the bulk region.
Solution Approach 2:
The regenerator material is segmented into two distinct particle size groups with different functional roles. The first group (0.3-3mm) serves as the primary thermal storage medium in the bulk region, while the second group (0.01-0.3mm) acts as a buffer layer near the mesh that prevents clogging while maintaining filling density. This segmentation resolves the contradiction by assigning different sizes to different spatial zones.
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 effectively suppresses the clogging of mesh holes, maintains high refrigerant gas permeability, and enhances the refrigerating capacity, ensuring long-term reliability of superconducting magnets and associated apparatus by allowing continuous operation for over 25,000 hours without significant deterioration.
Implementation Method 1
The above-described cold head can obtain the cryogenic temperature by causing an adiabatic expansion of refrigerant gas such as helium gas
Implementation Method 2
the material layers are partitioned by a metal mesh material
Data Source
AI summary
A reduction in a permeability of refrigerant gas is suppressed while increasing a filling factor of regenerator material particles with respect to a stage of a cold head. A cold head includes a stage including regenerator material particle groups, and a metal mesh material partitioning the regenerator material particle groups. The metal mesh material has quadrangular mesh holes each having a length of a long side of 1/10 or more and ½ or less of each of average particle sizes of the regenerator material particle groups.