Magnet cooldown thermal switch apparatus
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing cryogen-free MRI magnets require several days to cooldown due to the weaker cooling power of the second stage of the cold head, leading to prolonged magnet cooldown times.
Innovation Solution
A thermal switch is introduced between the first and second stages of the cold head, allowing a thermal connection during initial cooldown stages when temperatures are above a threshold, and disconnecting when temperatures drop below this threshold, optimizing cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the second stage of the cold head is used to cool down the cold mass, then the cold mass reaches the target temperature of ~4K, but the cooldown process takes many days due to the weaker cooling power
Solution Approach 1:
The thermal switch enables preliminary cooling action by the first stage (with higher cooling power of ~40W) before the second stage completes its cooling. During early cooldown when temperature is above the threshold, the first stage pre-cools the cold mass through the closed thermal switch, preparing the system for faster final cooling without extending the overall cooldown time
Solution Approach 2:
The thermal switch changes its thermal conductance parameter based on temperature. Above the threshold temperature, it provides high thermal conductance to allow the first stage to cool the cold mass. Below the threshold, it transitions to low thermal conductance to isolate the first stage, preventing it from limiting the second stage's cooling performance at lower temperatures
2Power
If the first stage is thermally connected to the second stage during early cooldown, then the cooling power is increased, but thermal isolation is lost when lower temperatures are required
Solution Approach 1:
The thermal switch dynamically adjusts the thermal connection between the first and second stages based on operating conditions. The switch transitions from a closed state (high thermal conductance) during early cooldown to an open state (low thermal conductance) when the temperature drops below the threshold, enabling the system to adapt its thermal configuration for optimal performance at different temperature ranges
Solution Approach 2:
The thermal switch utilizes differential thermal expansion or contraction of materials with different thermal expansion coefficients. As the temperature changes, the differential expansion causes the thermal switch to transition between closed and open states, passively controlling the thermal connection without requiring external actuation
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 thermal switch significantly reduces the total cooldown time of the MRI magnet by utilizing the higher cooling capacity of the first stage during initial cooldown and isolating it during later stages to achieve lower temperatures.
Implementation Method 1
This disconnection may be achieved through passive means, such as differential thermal expansion between cooling contacts and a support structure made from a different material
Implementation Method 2
The first stage of the cold head, with a power of ~40 W cools down the thermal shield to ~45K
Implementation Method 3
The second stage of the cold head, with a power of ~1 W cools down the cold mass to ~4K
Implementation Method 4
The thermal switch provides a thermal connection between the first and second stage of the cold head
Data Source
AI summary
A thermal switch for thermally shorting the first and second stage of a cold head during early stages of cooldown of an MRI magnet for reducing the total cooldown time is disclosed. The thermal switch provides a thermal connection between the first and second stage of the cold head, and so the thermal shield and the cold mass are cooled down with the higher power of the first stage of the cold head while the overall temperature is greater than a threshold temperature. When the temperature drops below the threshold, the thermal connection becomes disconnected and then the cold mass is connected thermally only to the second stage, and the first stage remains connected to the thermal shield but isolated from the cold mass. This disconnection may be achieved passively, such as differential thermal contraction between cooling contacts and a support structure made from a different material.