Cryogenic cooling system with temperature-dependent thermal shunt
Solution Overview
Problem
Current two-stage cryocoolers require a significantly longer time to cool down from ambient to cryogenic temperatures due to the larger thermal resistance at the second stage, which hampers cooling efficiency and increases the time required for reaching cryogenic temperatures.
Innovation Solution
A cryogenic cooling system with a two-stage cold head that employs a thermal connection member with varying thermal resistance, utilizing carbon fibers and bimetal members to create a heat transfer path with low resistance at higher temperatures and high resistance at lower temperatures, allowing for efficient cooling by the more powerful first stage while preventing excessive heat load on the second stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a thermal connection member with constant thermal resistance is used to connect the second stage to the first stage, then heat transfer from the second stage to the first stage is maintained, but the thermal resistance at the second cryogenic temperature is too low causing excessive heat load on the second stage
Solution Approach 1:
The thermal connection member's thermal resistance dynamically changes with temperature. At higher temperatures (during initial cooling), the thermal resistance is low to enable fast heat transfer and reduce cooling time. At lower cryogenic temperatures (operational state), the thermal resistance becomes high to minimize heat load on the second stage. This dynamic adaptation resolves the contradiction between fast cooling and low operational heat load.
Solution Approach 2:
The thermal resistance parameter of the connection member is changed based on temperature conditions. The connection member is designed so that its thermal resistance varies with temperature, being lower at ambient and intermediate temperatures for rapid cooling, and higher at the second cryogenic temperature for reduced heat load during operation.
2Loss of energy
If the thermal resistance of the heat transfer path is increased at the second cryogenic temperature, then heat load on the second stage is reduced, but cooling efficiency during the cooling down process is decreased
Solution Approach 1:
The thermal connection member provides dynamically adjustable thermal resistance that adapts to the cooling process stage. During the cooling down process at higher temperatures, the thermal resistance is naturally lower, enabling efficient heat removal and maintaining high cooling productivity. When the second stage reaches its operational cryogenic temperature, the thermal resistance increases to reduce heat load, thus resolving the contradiction between cooling efficiency and heat load reduction.
Solution Approach 2:
The thermal connection member is designed with preliminary properties that favor rapid cooling at higher temperatures before the second stage reaches its final operational temperature. The low thermal resistance at elevated temperatures enables preliminary efficient heat removal, and only when cooling is nearly complete does the thermal resistance increase to protect against heat load.
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 configuration reduces the time required to cool down from ambient to cryogenic temperatures by leveraging the high thermal conductivity of carbon fibers at room temperature and the temperature-dependent properties of bimetal members to achieve a substantial reduction in cooling time, with thermal resistance at the second cryogenic temperature being significantly higher than at the first cryogenic temperature.
Implementation Method 1
a thermal resistance of the provided at least portion of the heat transfer path at the second cryogenic temperature is larger than a thermal resistance of the provided at least portion of the heat transfer path at the first cryogenic temperature
Implementation Method 2
at least one thermal connection member that is configured to provide, in at least one operational state of the cryogenic cooling system
Data Source
AI summary
A cryogenic cooling system (10) comprising a cryostat (12), a two-stage cryogenic cold head (24) and at least one thermal connection member (136; 236; 336; 436) that is configured to provide at least a portion of a heat transfer path (138; 238; 338; 438) from the second stage member (30) to the first stage member (26) of the two-stage cryogenic cold head (24). The heat transfer path (138; 238; 338; 438) is arranged outside the cold head (24). A thermal resistance of the provided at least portion of the heat transfer path (138; 238; 338; 438) at the second cryogenic temperature is larger than a thermal resistance of the provided at least portion of the heat transfer path (138; 238; 338; 438) at the first cryogenic temperature.