Closed-Loop Cryogen Cooling for Superconducting MRI Magnets
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Solution Overview
Problem
Conventional cryogenic systems for superconducting magnets face issues such as stray magnetic fields, vibration transmission, temperature gradients, and significant cryogen loss due to venting of boil-off gas, requiring frequent refilling and inefficient cooling processes.
Innovation Solution
A closed-loop cryogenic system with a magnet cooling tube thermally coupled to the superconducting magnet, a re-condenser, a liquid cryogen container, and a gas tank, where liquid cryogen flows through the tube, vaporizes to remove heat, and the boil-off gas is re-condensed and stored in the gas tank, minimizing venting and maintaining the magnet at superconducting temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional cryogenic system uses a cooling coldhead mounted to the superconducting magnet, then the magnet can be cooled to superconducting temperature, but stray magnetic fields affect the coldhead motor and vibration is transmitted to the magnet
Solution Approach 1:
The coldhead is extracted from the magnet assembly and relocated to a separate location. The patent uses a coldhead mounting bracket that attaches to the vacuum vessel rather than the magnet, physically separating the vibration source from the superconducting magnet to eliminate vibration transmission and stray magnetic field interference.
2Temperature
If a large volume of liquid cryogen is used in a cryogen bath to cool the superconducting magnet, then the magnet can be cooled effectively, but significant cryogen is lost through boil-off gas venting requiring frequent refilling
Solution Approach 1:
The system implements continuous cryogen circulation through a closed-loop configuration. Liquid cryogen flows from the liquid container through the magnet cooling tube, absorbs heat, vaporizes, then the vapor is condensed back to liquid and returned to the container. This continuous cycle eliminates the need for venting and frequent refilling while maintaining effective cooling.
Solution Approach 2:
Instead of discarding the boil-off gas to the atmosphere, the system recovers it by condensing the vapor back into liquid form using the re-condenser. The recovered liquid cryogen is then returned to the liquid container, eliminating waste and reducing the need for frequent refilling operations.
3Use of energy by moving object
If refrigeration is turned off during power loss or maintenance, then energy consumption is reduced, but large amounts of boil-off gas vent to the atmosphere causing cryogen loss
Solution Approach 1:
The closed-loop system maintains continuous cryogen circulation and phase change operation even when the refrigeration compressor is off. The thermal energy stored in the liquid cryogen and the continuous phase change process provide a buffer that maintains cooling during power loss or maintenance periods without causing significant cryogen loss through venting.
4Temperature
If thermal connections are made between the coldhead and superconducting magnet, then cooling is transmitted to the magnet, but temperature gradients develop along the thermal connections
Solution Approach 1:
The coldhead is extracted from direct thermal contact with the magnet. Instead of mounting the coldhead to the magnet, the patent uses a thermal connection through the vacuum vessel wall and a coldhead mounting bracket, separating the coldhead location from the magnet position to minimize temperature gradients along the thermal path.
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 effectively maintains the superconducting magnet at its operating temperature with minimal cryogen loss, reducing the need for frequent refilling and enhancing operational stability during power outages or quench events by utilizing a closed-loop design that stores boil-off gas for extended ride-through operations.
Implementation Method 1
The heat of the superconducting magnet is removed by boiling off the liquid cryogen to gaseous cryogen
Implementation Method 2
a re-condenser to convert the gaseous cryogen back into liquid cryogen
Implementation Method 3
The heat of the superconducting magnet is removed by boiling off the liquid cryogen to gaseous cryogen
Data Source
AI summary
A cryogenic system for a superconducting magnet comprises a closed-loop cooling path. The closed-loop cooling path comprises a magnet cooling tube thermally coupled to the superconducting magnet. The magnet cooling tube comprises a cryogen flow passage. The closed-loop cooling tube further comprises a re-condenser is fluidly coupled to the magnet cooling tube through tube sections and a liquid cryogen container fluidly coupled between the magnet cooling tube and the re-condenser. At least one gas tank is fluidly coupled to the magnet cooling tube through a connection tube.