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ItemPerformance Investigation on SITP’s 60 K High Frequency Single-Stage Coaxial Pulse Tube Cryocoolers.(Georgia Institute of Technology, 2008-05) Dang, H. Z. ; Wang, L. B. ; Wu, Y. N. ; Li, S. S. ; Yang, K. X. ; Shen, W. B.A series of 60 K high frequency single-stage coaxial pulse tube cryocoolers has been developed to provide reliable low-noise cooling at 60 K for space-borne long wave infrared focal plane arrays. The development goal and a simulation model are briefly introduced, then optimizations of the novel heat exchanger configurations, the temperature mismatch of the tubes, and the characteristics mismatch of the compressor and cold finger are described. Experiments show that our best cooler prototype has achieved 8.0% of Carnot at 60 K, and can typically provide 2 W at 60 K with 104 W of electric input power and a 300 K reject temperature. It is also shown that 2.5W of cooling capacity at 60K can be achieved when the input power is increased to 127 W. Further optimization is underway, and it is feasible that the thermodynamic performance goal can be realized in the near future.
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ItemDevelopment of SITP’s Large Capacity High Frequency Coaxial Pulse Tube Cryocoolers(Georgia Institute of Technology, 2008-05) Dang, H. Z. ; Wang, L. B. ; Wu, Y. N. ; Li, S. S. ; Yang, K. X. ; Shen, W. B. ; Fu, H.Large capacity high frequency single-stage coaxial inertance pulse tube cryocoolers have been developed and are becoming mature in SITP/CAS. The main objective of the development is to provide larger low-noise cooling powers in the range of 80-100 K for space-borne infrared detector systems. The design and performance optimization approaches are discussed, and the engineering models for them are in work. A split dual opposed piston linear compressor with a maximum swept volume of 8.2 cc is used, and the overall weight without cooler control electronics is below 7.0 kg. At present, the coolers have achieved over 12% of Carnot at 80 K, or 14% of Carnot at 100 K. The typical cooling performance of the coolers provides 5 W at 80 K or 8 W at 100 K with around 120 W of electric input power and a 313 K reject temperature. Approaches to further optimize the thermodynamic performance and detailed characterization tests are underway.
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ItemSITP’s Miniature Coaxial Pulse Tube Cryocooler(Georgia Institute of Technology, 2008-05) Dang, H. Z. ; Wang, L. B. ; Wu, Y. N.A single-stage miniature coaxial pulse tube cryocooler (PTC) has been developed in Shanghai Institute of Technical Physics, Chinese Academy of Sciences (SITP/CAS) to serve as a perfect substitute for an existing Stirling cryocooler for providing reliable low-noise cooling for an infrared detector system. The challenging work is the exacting requirement on its dimensions, which have to adapt to the given dewar. A 1.5 kg dual opposed moving magnet compressor is used to realize light weight and low contamination. A large filling pressure of 3.5 MPa and high operating frequency of up to 67 Hz are adopted to increase the energy density, which will compensate for the decrease in working gas volume due to the miniature structure. The miniature dimensions also limit the phaseshifting ability of the system when the inertance tubes act as the only phase-shifting mechanism. The simulation suggests that a second orifice would be helpful to achieve the desired phase relationship. In the practical development, the inertance tube, composed of two sections with different inner diameter and length, act as the only phase-shifter to realize a reliable system. When the cold finger diameter and length are 10 mm and 53 mm, respectively, the miniature PTC achieves 1.6 W of cooling power at 90 K with 65 W of electric input power. The no-load temperature of 64.5 K is achieved in about 7 minutes. The design approach and trade-offs are discussed, and the parametric studies and the performance characteristics are presented.
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ItemTheoretical and Experimental Investigation on the Axial Temperature Mismatch and its Optimization for Coaxial Inertance Pulse Tube Cryocoolers(Georgia Institute of Technology, 2008-05) Wang, L. B. ; Dang, H. Z. ; Wu, Y. N. ; Li, S. S. ; Yang, K. X. ; Xiong, C.In a coaxial pulse tube cryocooler, the radial thermal conduction between the pulse tube and the regenerator has a large influence on cryocooler performance. Caused by the temperature mismatch between the pulse tube and regenerator, this phenomenon needs to be carefully considered during the cryocooler design process. In this work, models with and without radial thermal conduction between the regenerator and its coaxial pulse tube have been constructed to analyze the mechanism and predict its effect on cryocooler performance. Experiments have been carried out to characterize the coaxial pulse tube axial temperature distribution under a variety of working conditions. A linear variable differential transformer (LVDT) has been used to analyze the pressure-flow phase angle in the test system. The results were then compared with the simulated results and were used to provide direction for further optimization. The simulation results show that a steady radial thermal conduction exists between the pulse tube and the regenerator, and this heat transfer can affect the fluid dynamics and thermodynamics in the system. Experiments show that the shape of the wall temperature distribution curve is a useful indicator of the cooler performance and the appropriateness of the arrangement of the pulse tube and the regenerator for achieving optimal working conditions. The simulation results are in good agreement with the experimental data, which verifies the numerical simulation modeling. To validate the theoretical and experimental studies, the configuration of a previous 2W at 60K experimental prototype PT was redesigned and optimized to get an optimal axial temperature match between the regenerator and pulse tube. The new experimental prototype achieved a COP of 2% at 60 K and 4.3% at 80 K with around 100 W of input electric power.
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ItemInvestigation on the Phase Characteristics of High Frequency Inertance Pulse Tube Cryocoolers above 50 K.(Georgia Institute of Technology, 2008-05) Li, S. S. ; Dang, H. Z. ; Wu, Y. N. ; Wang, L. B. ; Yang, K. X.Phase characteristics of an inertance pulse tube cryocooler (IPTC) mainly include the mass flows, the pressure amplitudes, and the phase shifts between them. These are decisive factors for cooler performance, and are strongly affected by variations in the inertance tube design. In this work we describe theoretical analyses and experimental studies carried out on the phase characteristics of a large capacity high frequency single-stage IPTC developed in our laboratory and operated with a variety of inertance tube geometries at 80K. The theoretical analyses focused on investigating the amplitudes and phase angles at various locations of the whole system and established the phasor relationship of the cooler by combining a phasor-type analysis and a REGEN 3.2 analysis. The COP was calculated, and the influence on compressor efficiency was analyzed based on a force balance and Ohm’s law. The experimental study stressed evaluating the phase characteristics of the cooler by making a few easy measurements of the key parameters. The measurements included the compressor piston position using LVDT (linear variable differential transformer) rods, the pressure amplitudes—in the reservoir, at outlet of compressor, and the warm end of the pulse tube — using pressure transducers, and the phase angles between them. The measured results are compared with the theoretical predictions. Both the theoretical and experimental investigations imply that the change of the inertance characteristics have a great influence on the pressure difference, cooling power, the efficiency of the cold finger, and the efficiency of the compressor. It is concluded that optimization of the inertance tube should consider both the cold finger efficiency and the compressor efficiency at the same time, in order to achieve an optimum efficiency of the overall IPTC.