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International Cryocooler Conference

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Now showing 1 - 10 of 89
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    Development of High Efficiency 4 K Two-Stage Pulse Tube Cryocooler
    (Georgia Institute of Technology, 2008-05) Xu, M. ; Takayama, H. ; Nakano, K.
    Sumitomo Heavy Industries has been continuously improving the efficiency of our 4K pulse tube cryocooler in order to make it exchangeable with our 4K GM cryocooler. In order to improve the performance, three development model pulse tube cryocoolers have been built and tested. On the latest unit, the cooling capacity of the 4K pulse tube cryocooler has been improved to be equivalent to that of the 4K GM cryocooler. A typical cooling capacity of the latest pulse tube cryocooler is 40 W at 37.0 K on the first stage and 1.0 W at 3.86 K on the second stage when the compressor is operated at 50 Hz, and 40 W at 36.8 K on the first stage and 1.0 W at 3.82 K at 60 Hz. The input power is about 6.4 kW at 50 Hz and 7.7 kW at 60 Hz at steady state with 40 W heat load on the first stage and 1.0 W on the second stage. In addition, performance in a helium atmosphere has been measured and has been improved significantly by reducing the temperature difference between regenerator and pulse tube. The experimental results are described.
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    30 W at 50 K Single-Stage Coaxial Pulse Tube Cooler with Tapered Buffer Tube
    (Georgia Institute of Technology, 2008-05) Spoor, P. S.
    The performance of large-capacity single-stage pulse-tube coolers at temperatures below 70 K is often hampered by Rayleigh streaming, or the natural boundary-layer convection that occurs in the buffer tube (‘pulse tube’). In Olson and Swift’s landmark 1997 paper1, they explained how a slight taper in the buffer tube could suppress this streaming. They also showed how the streaming could be suppressed by the proper phasing of pressure vs. flow in the buffer tube, which is enforced by the proper choice of phase-shift mechanism (i.e. length and diameter of inertance tube, etc.). This is the approach usually taken because a straight buffer tube is simpler, especially when considering a coaxial construction (where a tapered buffer tube would imply a tapered regenerator). In addition, the phasing which suppresses Rayleigh streaming coincides with efficient cycle phasing for many applications. At temperatures below 70 K, however, this is less true, and for a 50 K machine a significant benefit may be realized by decoupling the streaming suppression from the cycle phasing. At the same time, we have found that coaxial coldheads can successfully use nonconductive buffer tubes, if the material with the right thermal expansion coefficient is selected. This enables the use of a tapered buffer tube in a coax design, as the material can be thick enough to have a constant outside diameter (OD) and a tapered inside diameter (ID). This paper will discuss the results obtained on a high-capacity cooler using a tapered buffer tube and includes some measurements showing the importance of having the right taper angle.
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    Concept of a Powerful Cryogen-Free Dilution Refrigerator with Separate 1 K Stage
    (Georgia Institute of Technology, 2008-05) Uhlig, Kurt
    Helium-3,4 dilution refrigerators (DR) are the workhorses for ultralow temperature scientists. DRs can be continuously operated for unlimited periods of time, and compared to other cooling techniques offer high cooling capacities. Base temperatures are well below 10 mK for well designed DRs. Cryogen-free (CF) DRs precooled by pulse tube refrigerators (PTR) have become standard in recent years. In a typical CF-DR, the second stage of the PTR runs at temperatures between 2.5 K and 4 K. Its cooling capacity at 4 K is about of 1 W. The next cooling stage is the still of the dilution unit with a typical temperature near 0.7 K. Its cooling capacity is proportional to the He-3 flow and usually well below 20 mW. For many modern applications this is too little to cool and heatsink cold amplifiers, coax lines and electric cables. For these experiments an additional refrigeration stage at an intermediate temperature of about 1 K would be desirable. Several suggestions have been made in the past to address the task.1 In our CF-DR, we plan to implement a continuous He-4 refrigeration stage with a base temperature of ~ 1.2 K. The components of the cryostat have been tested separately, but have not been combined in our cryostat so far. The cooling capacity of a newly built 1K-stage has been measured as a function of temperature; it is about 100 mW, whereas the cooling power of the still of the DR is 17 mW. The circulation rates of the DR stage and of the new He-4 stage are about of 1 mmol/s (22 std. cm3/s) each. We present details of the planned CF-DR with 1K-stage.
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    Inertance Tube and Reservoir Modeling: Meshing, Convergence and Friction Factors for Oscillating Flow
    (Georgia Institute of Technology, 2008-05) Dodson, C. ; Razani, A. ; Roberts, T.
    Pulse tube refrigerators (PTRs) have made dramatic improvements in reliability, efficiency and usage, with the addition of the inertance tube helping to create the improvements. The combination of the inertance tube and reservoir help to create a phase shift between mass flow rate and pressure that affects the fluid dynamics in the PTR. Current models inadequately predict (in accuracy) the phase shifts in these oscillating refrigerators. Various modeling techniques have yet to address the issue of numerical solution convergence, especially with respect to the mesh size and time step size when using Computational Fluid Dynamics (CFD) models. This study aims to address the issue based on comparisons to a set of experimental results. Along with the CFD correlation, a comparison with a distributed inertance tube model based on new friction factors for oscillating flow will be reported. A comparison of isothermal to mixed surface wall boundary condition is performed.
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    Space Micro Pulse Tube Cooler
    (Georgia Institute of Technology, 2008-05) Nguyen, T. ; Petach, M. ; Michaelian, M. ; Raab, J. ; Tward, E.
    The Northrop Grumman space micro pulse tube cooler (micro) is a split configuration cooler incorporating a coaxial cold head connected via a transfer line to a vibrationally balanced back to back linear compressor. The micro compressor is scaled from the flight proven high efficiency cooler (HEC) compressor and contains non-wearing pistons suspended on flexure bearings. Designed for > 10 year operation with no performance change, the 800 gram mechanical cooler can cool sensors and optics to temperatures <50K while rejecting heat to radiators over a wide range of reject temperatures. The very small, low vibration, high frequency cooler is designed to be readily integrated into space payloads. The coaxial cold head can also be integrated with custom focal planes into an integrated detector cooler assembly (IDCA) similar to those used with the shorter lived tactical coolers. This paper reports on the performance of this cooler.
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    Self-Induced Vibration of NGAS Space Pulse Tube Coolers
    (Georgia Institute of Technology, 2008-05) Colbert, R. ; Nguyen, T. ; Raab, J. ; Tward, E.
    Space cryocoolers are often used to cool the focal planes and optics of telescopes. Since telescope and focal plane jitter can affect the clarity of the image, space cryocoolers are designed for inherent low vibration. For very sensitive applications, many cryocooler systems incorporate active vibration control in addition to passive isolation from their mounting structures. The sole moving parts in all the NGAS pulse tube coolers, whether one, two or three stage, are the moving compressor pistons and their flexure supports that are inherently balanced in a back to back configuration. To further reduce the vibration below this already very low level, all the cooler systems are provided with single axis active control on the drive axis of the compressor that contains the moving piston masses. The cryocooler control electronics takes a signal from an accelerometer mounted parallel to the drive axis and feeds it back to the compressor motor drive signals to further reduce the vibration by >40dB. In this paper we present the self-induced vibration measurements made on a number of NGAS flight coolers including the single stage HEC cooler with both linear or coaxial cold heads and a micro cooler. We also present self-induced vibration measurements for the simultaneous operation of two HEC coolers mounted to the same platform.
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    Flight Cryogenic System for the Micro-X Sounding Rocket
    (Georgia Institute of Technology, 2008-05) Wikus, P. ; Rutherford, J. M. ; Trowbridge, S. N. ; McCammon, D. ; Adams, J. S. ; Bandler, S. R. ; Das, R. ; Doriese, W. B. ; Eckart, M. E. ; Figueroa-Feliciano, E. ; Kelley, R. L. ; Kilbourne, C. A. ; Leman, S. W. ; Porter, F. S. ; Sato, K.
    The Micro-X Imaging X-ray Spectrometer is a sounding rocket payload slated for launch in 2011. An array of transition edge sensors will be used to obtain high resolution X-ray spectra of astronomical sources. An Adiabatic Demagnetization Refrigerator (ADR) forms the heart of the instrument’s cryogenic system. It consists of a Ferric Ammonium Alum (FAA) salt pill in the bore of a low current 4 T superconducting magnet. The detector array is accommodated inside a magnesium housing which is thermally connected to the FAA salt. A bath of superfluid helium functions as a heat sink for the ADR. The helium tank is suspended inside a lightweight aluminum vacuum vessel by a set of reentrant G10 thrust tubes. The cryogenic system has been designed to withstand the extreme structural loads encountered in rocket flight, while at the same time providing hold-times sufficiently long to facilitate convenient operation during the launch campaign. Due to the short duration of a sounding rocket flight, the thermal recovery time constant of the cold mass had to be kept on the order of only a few seconds. In addition, special attention has been paid to minimizing the heating of the cold stage due to the dissipation of vibration originating from the rocket motor. The assembly of the Micro-X cryogenic system has been completed, and performance tests have been carried out. The design of the Micro-X cryogenic system and the results of the performance tests are presented here-in.
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    Are P-V and T-S Diagrams Meaningful for Regenerative Cryocoolers?
    (Georgia Institute of Technology, 2008-05) Kittel, Peter
    P-V and T-S diagrams are commonly used tools to illustrate thermodynamic cycles. For recuperative cycles, it is easy to idealize a cycle so that the history of a gas element can be traced on P-V and T-S diagrams as it flows around the machine. In such cycles, dead volumes such as accumulators, reservoirs, and clearance space in piston compressors and expanders are not fundamental to the operation. However, such dead volumes do have practical purposes in controlling pressure variations in recuperative coolers. Regenerative cryocoolers also have dead volumes, which include the void volumes in heat exchangers, regenerators, and pulse tubes. Because of these volumes, gas elements do not traverse all components of the cooler. Rather, an element can remain in a single component. For the Stirling cycle, P-V and T-S diagrams can be constructed if the void volumes are ignored. However, what happens in a pulse tube cooler where the volumes of the pulse tube, inertance tube, and reservoir are fundamental to the coolers operation? P-V and T-S diagrams can still be constructed if they are reinterpreted to represent the envelope of the motion of all possible gas elements. This approach will be explored here.
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    Cryocoolers for Microsatellite Military Applications
    (Georgia Institute of Technology, 2008-05) Pettyjohn, Erin
    Space qualified cryocoolers have been extensively developed for large military and commercial satellite electro-optical (EO) infrared (IR) missions, but not so for microsatellites due to the complexity of the thermodynamics and fluid mechanics of the mechanical refrigeration system. The trend in military responsive space programs is leaning towards microsatellites that are cheaper and faster to build and launch. No longer can cryocoolers take 3-5 years to develop at a cost of millions. Therefore solutions to the cryogenic needs for microsatellites are presented through research into the thermodynamic processes. Discussions will include efficiency improvements to reduce the size, weight, and power constraints of space qualified cryocoolers, as well as current state-of-the-art cryocoolers that meet the needs of military microsatellites.
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    Progress in Joule-Thomson Microcooling at the University of Twente
    (Georgia Institute of Technology, 2008-05) Derking, J. H. ; Zalewski, D. R. ; Garcia, M. ; Holland, H. J. ; Mudaliar, A. V. ; Cao, H. S. ; Lerou, P. P. P. M. ; ter Brake, H. J. M.
    The development of miniaturized Joule-Thomson (JT) coolers has been an ongoing research topic at the University of Twente for many years. In the current research, a new run of singlestage JT microcoolers with gross cooling powers of 40 mW and 180 mW at 100 K was developed and fabricated. The temperature profiles along the counter-flow heat exchangers of both types were measured, as were their net cooling powers. Operated with nitrogen gas, the latter was measured to be 26 mW at 90 bar and 131 mW at 80 bar, for both types, respectively. Furthermore, it is shown that the influence of gravity on the performance of the microcoolers is negligible. Also, the issue of clogging caused by tiny amounts of water is further investigated. No clogging is observed when the microcooler is driven by gas cleaned with a microtorr® getter filter. However, when unpurified gas is used, clogging occurs during cool down and prevents the microcooler from cooling down below about 230 K. Furthermore, the incorporation of sorption compressors is explored to make a closed-cycle JT microcooler that delivers 50 mW at 100 K. A final design is made on the basis of a quasistatic thermodynamic analysis. The cooler will operate with methane as the working fluid, and the total input power will be around 33 W.