Cryocooler Heater-Controlled Cool-Down to Balance Stage Cooling Rates
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Solution Overview
Problem
The cool-down time of cryocoolers is prolonged due to imbalanced cooling rates between the first and second cooling stages, particularly when the first cooling stage cools faster, leading to delayed cooling of the second stage and increased working gas density in the first expansion chamber, which reduces the cooling capacity of the second stage.
Innovation Solution
A method involving a controller that applies a heat load to the first cooling stage using a heater to maintain its temperature at an intermediate target between the initial and final temperatures, balancing the cooling rates and preventing excessive cooling, thereby managing the distribution of working gas between expansion chambers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the first cooling stage cools down rapidly without control, then the cool-down speed of the first stage is improved, but the cool-down time of the second stage is prolonged due to imbalanced cooling rates
Solution Approach 1:
The heater applies a preliminary counteracting heat load to the first cooling stage to prevent excessive cooling that would cause imbalanced cooling rates. By anticipating the problem of the first stage cooling too quickly, the system applies a counter-force (heating) to maintain balanced cooling between stages, thereby reducing the overall cool-down time.
Solution Approach 2:
The system dynamically changes the temperature parameter of the first cooling stage by controlling the heater output. The controller adjusts the heat load applied to the first stage based on temperature measurements, maintaining it at an optimal intermediate temperature that balances the cooling rates of both stages and optimizes the total cool-down time.
2Temperature
If the first cooling stage is cooled too quickly, then the first stage reaches lower temperature faster, but the working gas density in the first expansion chamber increases excessively, reducing the cooling capacity of the second stage
Solution Approach 1:
The temperature sensor continuously monitors the temperature of the first cooling stage and feeds this information back to the controller. The controller uses this feedback to dynamically adjust the heater output, maintaining the first stage at an optimal temperature that prevents excessive working gas density accumulation, thereby preserving the cooling capacity of the second stage.
Solution Approach 2:
The heater acts as an intermediary device between the cooling system and the first cooling stage. It provides controlled heating to offset excessive cooling, serving as a mediator that balances the thermal processes and prevents the harmful effect of excessive working gas density that would reduce second stage cooling capacity.
3Device complexity
If no heat load is applied to control the first cooling stage temperature, then the cooling process is simpler, but the cool-down time is prolonged due to imbalanced cooling rates between stages
Solution Approach 1:
The cooling system uses its own components (heater and temperature sensor already present in the cryocooler) to self-regulate the cooling process. The controller automatically adjusts the heater based on temperature feedback, allowing the system to self-correct the imbalanced cooling rates without requiring external intervention or complex additional control mechanisms.
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 approach reduces the cool-down time by maintaining the first cooling stage at an intermediate temperature, balancing cooling rates, and ensuring efficient distribution of working gas, thus enhancing the overall cooling efficiency of the cryocooler.
Implementation Method 1
a heater thermally coupled to the first cooling stage
Implementation Method 2
a first temperature sensor that measures a first temperature of the first cooling stage
Implementation Method 3
a cold head including a first cooling stage and a second cooling stage cooled to a lower temperature than the first cooling stage
Data Source
AI summary
A cryocooler includes: a cold head including a first cooling stage and a second cooling stage cooled to a lower temperature than the first cooling stage; a heater thermally coupled to the first cooling stage; a first temperature sensor that measures a first temperature of the first cooling stage; and a controller configured to perform a cool-down operation of the cold head to cool the first cooling stage from an initial temperature to a first final target temperature and to cool the second cooling stage from the initial temperature to a second final target temperature lower than the first final target temperature, in which the controller is configured to, during the cool-down operation, acquire the first temperature from the first temperature sensor, and control the heater such that the first temperature follows an intermediate target temperature lower than the initial temperature and higher than the first final target temperature.