Optimal Design and Operation of Helium Refrigeration Systems Using the Ganni Cycle

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Abstract.A new 20 K helium refrigerator installed at NASA Johnson Space Center's Space Environment Simulation Laboratory (SESL) was successfully commissioned and tested in 2012. The refrigerator is used to create a deep space environment within SESL's Chamber A to perform ground testing of the James Webb Space Telescope (JWST). The chamber previously and currently still has helium cryo-pumping panels (CPP) and liquid nitrogen shrouds used to create low earth orbit environments. Now with the new refrigerator and new helium shrouds the chamber can create a deep space environment. The process design, system analysis, specification development, and commissioning oversight were performed by the cryogenics department at Jefferson Lab, while the contracts and system installation was performed by the ESC group at JSC. Commissioning data indicate an inverse coefficient of performance better than 70 W/W for a 18 kW load at 20 K (accounting for liquid nitrogen pre-cooling power) that remains essentially constant down to one third of this load. Even at 10 percent of the maximum capacity, the performance is better than 150 W/W at 20 K. The refrigerator exceeded all design goals and demonstrated the ability to support a wide load range from 10 kW at 15 K to 100 kW at 100 K. The refrigerator is capable of operating at any load temperature from 15 K to ambient with tight temperature stability. The new shroud (23 metric tons of aluminum) can be cooled from room temperature to 20 K in 24 hours. This paper will outline the design, project execution and commissioning results.

Section: Installation Commissioning and Testingmentioning

confidence: 99%

“…The cold box design and the control philosophy were presented in [2,5]. The cold box is equipped with two identical turbines to support a 100 kW load at 100 K, to aid the cool down and as a redundancy for improved availability of the system.…”

Section: Refrigeration System Testsmentioning

confidence: 99%

Commissioning of a 20 K helium refrigeration system for NASA-JSC Chamber-A

Homan

Redman²,

Ganni

et al. 2014

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“…The main differences are that the FRIB cryogenic system must handle a 4.5-K magnet load and a 50% larger shield load as compared to the 12 GeV cryogenic system. However, the 12 GeV cryogenic system design was based on a balanced system design, capable of efficiently adjusting to varying capacity and load characteristics using the Ganni Cycle Floating pressure process [2,3]. JLab conducted all the process studies required to evaluate if the recently designed 12 GeV cryogenic system could be adopted for the FRIB application.…”

Section: Refrigeration Process Specificationsmentioning

confidence: 99%

“…To address the cryogenic system cost issues, the FRIB management requested advice from Jefferson Lab's (JLab's) cryogenic group for options. The 12 GeV upgrade cryogenic system (JLab CHL-2), based on Ganni Cycle Floating Pressure Technology [2,3], is a balanced system design, capable of many modes of operation. With minor modifications, this cryogenic system can be easily adapted to different types of loads which have approximately the same total load exergy.…”

Section: Introductionmentioning

confidence: 99%

Application of JLab 12GeV helium refrigeration system for the FRIB accelerator at MSU

Ganni

Knudsen

Arenius

et al. 2014

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Abstract. The planned approach to have a turnkey helium refrigeration system for the MSU-FRIB accelerator system, encompassing the design, fabrication, installation and commissioning of the 4.5-K refrigerator cold box(es), cold compression system, warm compression system, gas management, oil removal and utility/ancillary systems, was found to be cost prohibitive. Following JLab's suggestion, MSU-FRIB accelerator management made a formal request to evaluate the applicability of the recently designed 12GeV JLab cryogenic system for this application. The following paper will outline the findings and the planned approach for the FRIB helium refrigeration system.

“…Presently, the process control of the cold box is changed over to the Ganni CycleFloating Pressure process philosophy [1,2]. As the Floating Pressure process is a constant pressure ratio and variable gas charge process, the compressor discharge pressure is automatically adjusted to match the required load as indicated by the return temperature from the load.…”

Section: Floating Pressure Controlmentioning

confidence: 99%

Floating Pressure Conversion of Two 3.5 Kw, 20 K, Helium Refrigerators

Homan¹,

Ganni²,

Sidi‐Yekhlef³

et al. 2010

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Two helium refrigerators, each rated for 3.5KW at 20K, are used at NASA's Johnson Space Center (JSC) in Building No. 32 to provide cryogenic-pumping within two large thermal-vacuum chambers. These refrigerators were originally commissioned in 1996. New changes to the controls of these refrigerators were recently completed. This paper describes some of the control issues that necessitated the controls change-over. It will describe the modifications and the new process control which allows the refrigerators to take advantage of the Ganni Cycle "floating pressure" control technology. The controls philosophy change-over to the floating pressure control technology was the first application on a helium gas refrigeration system. Previous implementations of the floating pressure technology have been on 4K liquefaction and refrigeration systems, which have stored liquid helium volumes that have level indications used for varying the pressure levels (charge) in the system for capacity modulation. The upgrades have greatly improved the performance, stability, and efficiency of these two refrigerators. The upgrades have also given the operators more information and details about the operational status of the main components (compressors, expanders etc.) of the refrigerators at all operating conditions (i.e. at various loads in the vacuum chambers). The performance data of the two systems, pre and post upgrading are presented.