Secondary Pulse Tube Coupling for Room-Temperature Phase Shifting
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Solution Overview
Problem
High-frequency pulse tube cryocoolers face challenges in achieving efficient phase shifting at low temperatures, leading to large temperature oscillations and low efficiency, particularly at 4 K, due to limitations in phase angle control and the need for low-temperature operation of expanders.
Innovation Solution
Incorporating a secondary regenerator or pulse tube at the warm end of the pulse tube system allows for a room temperature phase shifter or expander, utilizing commercially available pressure oscillators and optimizing geometry to achieve the necessary phase shift without the need for low-temperature operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a room temperature phase shifter is used in a high-frequency pulse tube cryocooler, then the efficiency is improved and the system complexity is reduced, but the phase shift capability at the cold end deteriorates due to temperature-dependent acoustic impedance
Solution Approach 1:
The pulse tube cryocooler is divided into two temperature zones: a room temperature phase shifter section and a cold end section. The room temperature phase shifter (inertance tube) is segregated from the cold end, allowing it to operate at room temperature where larger phase shifts are achievable, while the cold end maintains its required thermal conditions. This segmentation resolves the contradiction by allowing each section to operate in its optimal temperature range.
Solution Approach 2:
A thermal barrier or thermal isolation structure acts as an intermediary between the room temperature phase shifter and the cold end pulse tube. This intermediary allows acoustic energy to pass through while preventing thermal energy transfer, enabling the phase shifter to operate at room temperature without directly heating the cold end, thus maintaining phase shift capability while improving overall efficiency.
2Loss of energy
If the warm end of the pulse tube is maintained at low temperature (30 K), then the efficiency of the pulse tube component is improved, but the device complexity increases due to the need for a low-temperature expander
Solution Approach 1:
The system is segmented into a cold pulse tube section (30 K) and a warm end section (room temperature). The phase shifter and expander are placed in the warm end section, allowing them to operate at room temperature. This segmentation eliminates the need for a complex low-temperature expander while maintaining pulse tube efficiency through proper thermal zoning.
Solution Approach 2:
The expander and phase shifter functions are extracted from the cold end and relocated to the room temperature warm end of the system. This extraction allows the use of simpler, room-temperature components while the cold pulse tube section maintains its optimized thermal conditions for efficient refrigeration.
3Ease of operation
If a double inlet configuration with secondary orifice is used, then the phase shift is improved, but the lost work in the secondary orifice greatly reduces the overall efficiency
Solution Approach 1:
Instead of using a secondary orifice as an intermediary that causes pressure drop and energy loss, the invention uses a thermal barrier as an intermediary. This thermal barrier provides the necessary phase shift through thermal isolation rather than flow restriction, eliminating the wasteful pressure drop associated with secondary orifices while maintaining effective phase control.
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 enhances the efficiency of the cryocooler by enabling effective phase shifting at room temperature, reducing the size and power requirements of the expander, and improving overall system performance, particularly at high frequencies.
Implementation Method 1
a regenerator in fluid communication with the compressor, and a pulse tube defining a cold end and a warm end. The regenerator is in fluid communication with the cold end of the pulse tube
Implementation Method 2
a compressor, a regenerator in fluid communication with the compressor
Implementation Method 3
pulse tube refrigeration system comprising a compressor, a regenerator in fluid communication with the compressor
Data Source
AI summary
Pulse tube refrigeration or cooling systems are described which utilize a secondary regenerator or a secondary pulse tube. Use of such a secondary regenerator or pulse tube enables a commercially available pressure oscillator to be incorporated in the cooling system. The commercially available oscillator can be operated at room temperature or approximately so.