Boil-Off Gas Cooling Path for Cryogen Loss Reduction
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Solution Overview
Problem
Superconducting magnet systems experience significant cryogen loss during transportation and when the refrigerator is inoperative due to heat leaks, leading to increased boil-off of cryogenic liquids, which are costly and result in reduced system availability.
Innovation Solution
A pipe is used to direct a portion of the boil-off gas from the cryogen vessel through the refrigerator interface and past the refrigerator, intercepting heat conducted into the system and reducing the heat load on the cryogenic vessel, thereby minimizing cryogen loss. This gas is then vented along with the remainder, using a recondensing refrigerator to cool the thermal shields and vessel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the refrigerator is removed from the refrigerator interface during transportation, then the heat load onto the internal parts of the system is reduced and cryogenic liquid loss is reduced, but the refrigerator must be replaced when putting the MRI system into operation which involves difficult and skilled operations
Solution Approach 1:
The refrigerator is extracted from the refrigerator interface during transportation to eliminate the heat conduction path through the refrigerator into the cryogenic vessel. This removal action directly reduces the heat load onto internal parts and minimizes cryogenic liquid loss during transport, while the refrigerator can be reinstalled at the operational site when needed
2Reliability
If the refrigerator remains connected to the refrigerator interface during transportation, then the refrigerator is in place and ready for operation, but the refrigerator provides a low thermal resistance path for ambient heat to reach the cryogenic vessel resulting in high boil-off
Solution Approach 1:
The refrigerator is temporarily extracted from the refrigerator interface during transportation to eliminate the thermal conduction path that would otherwise allow ambient heat to reach the cryogenic vessel. This extraction removes the harmful thermal pathway while maintaining the ability to reinstall the refrigerator at the operational site for normal operation
3Ease of operation
If the refrigerator is kept connected during transportation, then no replacement operations are needed, but the time available for delivery is reduced due to increased cryogen loss
Solution Approach 1:
The refrigerator is extracted during transportation to minimize cryogenic liquid loss, thereby extending the delivery time window. The extended time available for delivery allows flexibility in scheduling installation and operation without requiring the refrigerator to remain connected during transport
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 solution reduces cryogen loss by approximately 50% during transportation and inoperative periods, prolonging the system's operational time and minimizing the need for frequent refrigerator replacement.
Implementation Method 1
ambient heat is conducted along the passive refrigerator to reach the thermal shield(s) and/or the cryogen vessel
Implementation Method 2
Some of the heat conducted along the refrigerator into the system is intercepted and removed by that part of the boil-off gas
Implementation Method 3
cooling the superconductor by immersion in a low temperature cryogenic fluid such as liquid helium
Implementation Method 4
A requirement of an MRI magnet is that it produces a stable, homogeneous, magnetic field... it is common to use a superconducting magnet system which operates at very low temperature
Implementation Method 5
The vacuum jacket reduces the amount of heat leaking to the cryogenic vessel by conduction and convection
Implementation Method 6
The vacuum jacket reduces the amount of heat leaking to the cryogenic vessel by conduction and convection
Implementation Method 7
The thermal shields reduce the amount of heat leaking to the cryogenic vessel by radiation
Implementation Method 8
use a refrigerator to cool the thermal shields to a low temperature... use such a refrigerator to directly refrigerate the cryogen vessel
Implementation Method 9
the cooling power of the gas to cool the access neck of the cryogen vessel and to provide cooling to thermal shields by heat exchange with the cold exhausting gas
Data Source
AI summary
In order to minimize the loss of cryogen during transportation of superconductive magnet systems, or indeed at any time that the refrigerator is turned off, part of the boil-off gas is directed from the cryogen vessel through the refrigerator interface and past the refrigerator to cool the refrigerator. Some of the heat conducted along the refrigerator into the system is intercepted and removed by that part of the boil-off gas. The heat load onto the cryogenic vessel is thereby reduced, which in turn reduces the boil-off of cryogen from the cryogenic vessel. This part of the boil-off gas is then vented from the system along with the remainder of the boil-off gas, for example to leave the cryogenic liquid vessel via the access neck.