Cryogenic Refrigerator Control via Phase Separator Heat Load Estimation
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Solution Overview
Problem
Cryogenic refrigerators used in installations with intense magnetic fields, such as tokamaks, face challenges in maintaining stable cooling during pulsed operating regimes, leading to potential shutdowns due to unbalanced thermal loads and increased helium flow, which existing solutions address but require costly and complex additional installations.
Innovation Solution
A method for regulating cryogenic refrigerators by determining and filtering the time derivative of the liquid bath height in the phase separator, adjusting the valve opening, and estimating thermal loads using a computer-implemented program to stabilize the cooling process, thereby managing unsteady thermal loads without the need for extensive additional equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the thermal load on the cryogenic refrigerator increases during pulsed operation, then the cooling power demand increases, but the refrigerator becomes unbalanced and may shut down
Solution Approach 1:
The control method performs preliminary action by predicting future thermal load values based on historical data and operational patterns. The controller estimates upcoming thermal demands during pulsed operation and adjusts helium flow rates in advance to prevent unbalancing of the refrigerator, thereby maintaining reliability during high power demand periods.
Solution Approach 2:
The invention implements feedback control by continuously monitoring actual thermal load values and comparing them with predicted values. The controller uses this feedback to dynamically adjust the helium flow rate through the heat exchangers, ensuring the refrigerator remains balanced and operational even when cooling power demand fluctuates during pulsed regimes.
2Reliability
If additional means are installed to smooth thermal load variations, then the refrigerator stability improves, but the device complexity and cost increase
Solution Approach 1:
The invention replaces complex mechanical smoothing devices with a computational control system. Instead of installing additional physical means to smooth thermal load variations, the method uses a controller that performs calculations based on measured and predicted thermal load data to dynamically adjust helium flow rates, achieving the same stability effect with simpler, more flexible electronic control.
Solution Approach 2:
The control method achieves refrigerator stability by dynamically changing operational parameters, specifically the helium flow rate through the heat exchangers. The controller adjusts this parameter in real-time based on predicted thermal load variations, eliminating the need for additional equipment while maintaining reliable operation during pulsed regimes.
3Power
If the helium flow rate is increased to meet higher thermal load, then the cooling capacity increases, but the thermal unbalancing of heat exchangers worsens
Solution Approach 1:
The invention applies dynamics by making the helium flow rate adjustable and responsive to changing conditions. The controller dynamically modifies the flow rate through heat exchangers based on predicted thermal load values, allowing the system to adapt to pulsed operation requirements while maintaining thermal balance. This dynamic control enables the system to provide increased cooling capacity during high-load periods without causing unbalancing.
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 effectively stabilizes the cooling process in cryogenic refrigerators during pulsed operating regimes, preventing shutdowns and maintaining efficient operation without the need for costly additional installations, by accurately estimating and managing thermal loads.
Implementation Method 1
These counter-current heat exchangers make it possible to gradually reduce the temperature of the helium circulating in the different circuits of these heat exchangers. Furthermore, for each heat exchanger, the pressure of the two exchange circuits of the exchanger differs, so that the 'upstream' circuit is a high pressure and hot circuit and the 'downstream' circuit is a low pressure circuit, colder.
Implementation Method 2
The first turbine 30 takes work from the outlet of the low pressure circuit of the first heat exchanger 20 and reinjects this work into the low pressure inlet of the second heat exchanger 21. The second turbine 31 takes work from the outlet of the low pressure circuit of the third heat exchanger 22 and reinjects this work into the low pressure inlet of the fourth heat exchanger 23. These turbines 30, 31 are complementary to the heat exchangers and contribute, by extracting work, to the cooling of the helium.
Implementation Method 3
The cryogenic refrigerator 1 finally includes a 50 Joule-Thomson valve, placed between the outlet of the low pressure circuit of the last heat exchanger 24 and the bath 41 of liquid helium at 4.5K under atmospheric pressure. This valve 50 makes it possible to liquefy the gaseous helium obtained at the outlet of the low pressure circuit of the last heat exchanger 24 by carrying out an expansion accompanied by a drop in the temperature of the helium.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a method for estimating a heat load imposed on a cryogenic refrigerator, to an associated computer program product, and to a method for controlling the cooling power output by said refrigerator. As the refrigerator (1, 1') includes a phase separator (40, 40') comprising a bath (41, 41') of refrigerant, the method for estimating the heat load imposed on said refrigerator includes a step in which said heat load is estimated using a program executed by a computer, said program being based on a mass balance carried out on the phase separator for expressing variations in the time drift of the height of the bath of refrigerant in the phase separator.