Very efficient heat exchanger for cryogen free MRI magnet
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Solution Overview
Problem
The existing cooling systems for superconducting magnets, particularly in magnetic resonance (MR) scanners, face challenges due to the high cost and limited availability of liquid helium, operational complexities during temperature changes, potential health risks from helium expansion, and space constraints, which require an efficient and reliable heat exchange method.
Innovation Solution
A cryogen-free heat exchanger system utilizing a thermally conductive cylindrical container, thermally conductive tubes, and a cryogen coldhead to circulate gaseous helium in a closed loop, facilitating efficient heat transfer and re-condensation, thereby maintaining the magnet at superconducting temperatures without liquid helium and minimizing operational complexities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If liquid helium is used to cool superconducting magnets, then the magnet can be cooled to superconducting temperatures, but the system becomes dependent on expensive and limited liquid helium supply
Solution Approach 1:
The system changes the physical state parameter of helium from liquid to gaseous phase, operating the cooling system with gaseous helium circulating through heat exchangers rather than requiring liquid helium bath, thereby eliminating dependency on liquid helium supply
Solution Approach 2:
The patent replaces the liquid helium cooling mechanism with a gaseous helium circulation system that uses heat exchangers and thermal conduction, substituting the liquid-phase cooling mechanism with a gas-phase heat transfer system
2Loss of substance
If a refrigerator or heat exchanger is used to re-condense helium gas, then the coolant can be recycled, but the device complexity increases
Solution Approach 1:
The system employs passive heat exchangers that utilize natural thermal conduction and convection to re-condense helium gas without requiring active refrigeration machinery, allowing the system to self-regulate helium phase changes through thermal gradients alone
Solution Approach 2:
The patent extracts the active refrigeration component from the system, replacing it with passive heat exchange surfaces that perform the same cooling function through natural heat transfer processes, thereby simplifying the overall device architecture
3Ease of operation
If the cooling system operates from room temperature to superconducting temperatures, then the system can be started up, but operational complexities increase during temperature changes
Solution Approach 1:
The system dynamically adapts to temperature changes by utilizing phase transitions of helium and variable thermal conductivity of materials across temperature ranges, allowing automatic adjustment of cooling efficiency during start-up and operation without complex control mechanisms
4Reliability
If the magnet temperature rises during a quench, then the magnet can recover, but costly coolant is lost as it expands
Solution Approach 1:
The system maintains a closed gaseous helium environment that prevents coolant loss during quench events, as the gaseous phase can expand and contract without the volume constraints and loss risks associated with liquid helium, while the inert helium atmosphere protects the magnet during thermal transitions
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 achieves efficient cooling with no external intervention, prevents helium loss, maintains high pressure, and accommodates compact design with low flow friction, ensuring reliable operation from room temperature to superconducting conditions, and handles quench events passively.
Implementation Method 1
The cryogen coldhead is mounted to the cooling column and condenses helium gas in the cooling column into cold liquid helium
Implementation Method 2
Heat transfers from the superconducting magnet to circulating gaseous helium in a lower portion of the closed loop of thermal conductive tubing
Implementation Method 3
Heat transfers from the circulating gaseous helium in an upper portion of the close loop of thermally conductive tubing via a system heat exchanger to liquid helium
Implementation Method 4
circulates gaseous helium in a closed loop of thermally conductive tubing which circulates through a thermal siphon action
Data Source
AI summary
A heat exchanger (5) includes a thermally conductive cylindrical container (40), at least one thermally conductive tube (30), a cooling column (90), and a cryogen coldhead (100). The cooling column and coldhead condense gaseous helium to liquid helium to maintain a reservoir of liquid helium in the thermally conductive cylindrical container (40). The at least one thermally conductive tube (30) coils circumferentially around the container (40), and extends to at least one superconducting magnet coil heat exchanger (20), and back. The tube forms a selected loop which holds gaseous helium at pressure up about 104 bar (1500 PSI) or room temperature to about 0.75 bar at cryogenic temperatures.