Cryogenic Cooling Assembly Using Heat Pipe and Gas Gap Switching
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Solution Overview
Problem
Mechanical cryo-coolers require longer cool-down times for target assemblies with high thermal mass due to the relatively small cooling power of their second stage, and existing solutions involving heat pipes or gas gap heat switches are inefficient or limited in operational range.
Innovation Solution
A cryogenic cooling system combining a mechanical refrigerator with a heat pipe and a heat switch assembly, where the heat pipe 'short-circuits' the thermal gradient across the heat switch assembly, allowing efficient cooling from room temperature to the temperature of the second cooled stage, and the heat switch assembly provides additional cooling via gas gap heat switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical refrigerators are used to cool target assemblies with high thermal mass, then the cooling system avoids using liquid cryogens, but the cool-down time becomes significantly longer
Solution Approach 1:
The cooling system is divided into two distinct stages: a first stage using a heat pipe for rapid initial cooling, and a second stage using a mechanical refrigerator for sustained low-temperature maintenance. This segmentation allows each component to optimize its function, with the heat pipe providing fast thermal response for high thermal mass objects and the mechanical refrigerator providing continuous cooling power.
Solution Approach 2:
The heat pipe acts as an intermediary thermal link between the mechanical refrigerator and the target assembly. It mediates the thermal energy transfer by condensing coolant vapor at its warmer end and evaporating it at its cooler end, providing an efficient heat transfer pathway that accelerates the cool-down process without requiring direct contact between the mechanical refrigerator and the target assembly.
2Loss of time
If liquid cryogens are used for rapid cooling, then cool-down time is reduced, but the apparatus becomes bulky, complicated and expensive
Solution Approach 1:
The invention extracts the essential cooling function from complex liquid cryogen handling systems by using a heat pipe, which passive thermal management device that eliminates the need for pumps, valves, and extensive insulation required by liquid cryogen systems. The heat pipe achieves rapid cooling through its phase-change mechanism while maintaining a simpler, more compact structure.
Solution Approach 2:
The active mechanical pumping and circulation system required for liquid cryogens is replaced with a passive heat pipe that utilizes natural phase change and capillary action for coolant circulation. This substitution eliminates complex mechanical components while achieving superior thermal performance for the cool-down phase.
3Temperature
If helium is used as a cryogen, then effective cooling to 4 kelvin is achieved, but the scarcity and cost increase
Solution Approach 1:
The invention changes the operational parameters by using a heat pipe with a working fluid that operates in the vapor-liquid phase change regime, achieving effective heat transfer without requiring large quantities of expensive cryogenic liquids. The heat pipe maintains efficient thermal conduction through phase change at temperatures relevant to the application, reducing dependency on scarce helium resources.
4Temperature
If a pre-cooling circuit with flowing cryogenic fluid is used, then the target assembly can be cooled below the second stage temperature, but the system requires physical movement of couplings that generates heat
Solution Approach 1:
The mechanical coupling and physical movement system is replaced with a heat pipe that provides a fixed, stationary thermal link between the cooling stage and the target assembly. The heat pipe's internal phase-change mechanism provides the necessary thermal connection without requiring any moving parts, thereby eliminating the heat generation associated with mechanical coupling adjustments.
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 combination significantly reduces the cool-down time of the target assembly by maintaining thermal communication with the second cooled stage while avoiding the need for moving parts that generate heat, and operates over a broader temperature range than either method alone.
Implementation Method 1
the temperature of the second cooled stage causes the coolant in the first part of the heat pipe to condense
Implementation Method 2
the temperature of the target assembly causes the coolant within the second part of the heat pipe to be gaseous
Implementation Method 3
a heat pipe having a first part coupled thermally to the second cooled stage and a second part coupled thermally to a target assembly
Implementation Method 4
a heat switch assembly comprising one or more gas gap heat switches, the heat switch assembly having a first end coupled thermally to the second cooled stage and a second end coupled thermally to the target assembly
Data Source
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AI summary
A cryogenic cooling system is provided comprising: a mechanical refrigerator, a heat pipe and a heat switch assembly. The mechanical refrigerator has a first cooled stage and a second cooled stage. The heat pipe has a first part coupled thermally to the second cooled stage and a second part coupled thermally to a target assembly. The heat pipe is adapted to contain a condensable gaseous coolant when in use. The heat switch assembly comprises one or more gas gap heat switches, a first end coupled thermally to the second cooled stage and a second end coupled thermally to the target assembly. The cryogenic cooling system is adapted to be operated in a heat pipe cooling mode in which the temperature of the second cooled stage is lower than the first cooled stage and wherein the temperature of the target assembly causes the coolant within the second part of the heat pipe to be gaseous and the temperature of the second cooled stage causes the coolant in the first part of the heat pipe to condense. The target assembly is cooled by the movement of the condensed liquid coolant from the first part of the heat pipe to the second part of the heat pipe during the heat pipe cooling mode. The cryogenic cooling system is further adapted to be operated in a gas gap cooling mode in which the temperature of the second cooled stage causes freezing of the coolant. The heat switch assembly is adapted to provide cooling from the second cooled stage to the target assembly during the gas gap cooling mode via the one or more gas gap heat switches.