Joule-Thomson Dewar Cooling With Gradient-Based Flow Control
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Solution Overview
Problem
Existing cooling devices for detectors in Dewar vessels have a large time constant for temperature control, limiting temperature stability and allowing operation only slightly above the boiling temperature of the pressurized gas, with changes in cooling power directly affecting temperature.
Innovation Solution
A cooling device with a temperature-dependently adjustable final control element and two temperature sensors, one in the expansion chamber and one outside, to record a temperature gradient and adjust the flow through the expansion nozzle, operating the Joule-Thomson cooler in the liquid phase to exploit inherent temperature stability and reduce control loop time constants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the temperature sensor is disposed on the detector element in the jacket cavity of the Dewar vessel, then the detector temperature can be detected, but the achievable temperature stability is limited due to large time constant for the control loop
Solution Approach 1:
A liquid phase pressurized gas is introduced as an intermediary medium between the cooling system and the detector element. This liquid phase acts as a thermal mediator that rapidly equilibrates temperature changes, reducing the time constant of the control loop while accurately transmitting temperature information to the sensor disposed in the expansion chamber.
Solution Approach 2:
The system preliminarily establishes a liquid phase environment in the expansion chamber before temperature control operations begin. This preliminary preparation of the thermal environment enables faster response to temperature changes, reducing the control loop time constant while maintaining accurate temperature detection.
2Reliability
If actively regulated cooling devices operate above the boiling temperature of the pressurized gas, then stable operation is achieved, but the achievable low temperature is limited (approximately 5°K above boiling temperature)
Solution Approach 1:
The invention exploits the phase transition between liquid and gas phases of the pressurized gas. By maintaining a liquid phase in the expansion chamber through controlled pressure and temperature conditions, the system can operate at temperatures at or below the boiling point, utilizing the latent heat of vaporization for stable temperature regulation and achieving much lower temperatures than conventional gas-phase operation.
Solution Approach 2:
The system changes the physical state parameter of the pressurized gas from gas phase to liquid phase in the expansion chamber. This parameter change enables operation at lower temperatures while maintaining stability, as the liquid phase provides superior thermal inertia and temperature buffering compared to the gas phase.
3Reliability
If a liquid phase is used in the expansion chamber to exploit inherent temperature stability, then temperature stability is improved, but the control system complexity increases due to need for gradient measurement and adjusted control
Solution Approach 1:
The system implements a feedback control mechanism that continuously measures the temperature gradient between the expansion chamber and the detector element, and adjusts the cooling power accordingly. This feedback loop automatically compensates for the increased complexity by using the temperature gradient information to optimize cooling efficiency and maintain stability.
Solution Approach 2:
The invention replaces direct temperature measurement on the detector element with indirect measurement via temperature gradient detection in the liquid phase environment. This substitution simplifies the control system by measuring the gradient in the more stable liquid phase rather than directly on the detector, reducing measurement noise and improving control reliability.
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 achieves high temperature stability and allows operation at the boiling temperature of the pressurized gas, with temperature stability dependent on counterpressure and gas throughput, reducing the time constant of the regulation and improving overall cooling performance.
Implementation Method 1
A Joule-Thomson cooler is disposed on the rear of the detector element in the interior of the Dewar vessel. A pressurized gas or general coolant that is fed in is expanded at the expansion nozzle and as a result cools according to its Joule-Thomson thermal coefficients into a region close to its boiling temperature.
Implementation Method 2
a first temperature sensor disposed in the expansion chamber
Implementation Method 3
a second temperature sensor disposed within the Dewar vessel outside of the expansion chamber
Implementation Method 4
a temperature-dependently adjustable final control element for influencing a flow through the expansion nozzle, and a control device configured for recording a temperature gradient from sensor values of the first temperature sensor and of the second temperature sensor and for adjustment of the final control element depending on the recorded temperature gradient
Data Source
AI summary
A cooling device for cooling a detector element disposed in a jacket cavity of a Dewar vessel uses a Joule-Thomson cooler with an expansion nozzle that opens into an expansion chamber. The cooling device includes a final control element that is adjustable depending on temperature for influencing the flow through the expansion nozzle. A first temperature sensor is disposed in the expansion chamber and a second temperature sensor is disposed within the Dewar vessel outside the expansion chamber. The cooling device includes a control device that is configured for detecting a temperature gradient from sensor values of the first temperature sensor and of the second temperature sensor and for adjusting the final control element depending on the detected temperature gradient.