取扱注意情報 Development of a valved non-lubricated linear compressor for compact 2K Gifford-McMahon cryocoolers March 8, 2016 Y. Hiratsuka, Q. Bao and M. Xu Technology Research Center Sumitomo Heavy Industries, Ltd. Thank you! My name is HIRATSUKA from Tokyo, I work for SHI. Today, I'd like to talk to you about　Development of a valved non-lubricated linear compressor for compact 2K Gifford-McMahon cryocoolers. 1

Outline Background and Design concept Experimental unit and results 取扱注意情報 Outline Background and Design concept Experimental unit and results Design of a prototype unit Summary At the beginning, I'd like to show you the contents my presentation. 　I'll talk about ～

Background

取扱注意情報 Background Recently, a new, compact Gifford-McMahon (GM) cryocooler for cooling superconducting single photon detectors (SSPD) has been developed at SHI since 2012. 570 mm http://www.nict.go.jp/press/2010/07/27-1.html　 Adoboku optical link Install SHI 0.1W4KGM Cryocooler Tokyo Skytree 1570 mm Optical link to district public office building RDK-101D Expander Mass, optical link CNA-11 Compressor unit Backup communication by optical fiber SSPD system SSPD Receiver Recently, a new compact Gifford-McMahon (GM) cryocooler for cooling superconducting single photon detectors (SSPD) has been developed at SHI since 2012. The SSPD system cannot be installed in a 19-inch rack and the miniaturization is required for practical use. The objective is to reduce the total height of the expander by 33% relative to the existing RDK-101 GM cryocooler, and to reduce the total volume of the compressor unit by 50% relative to the existing CNA-11 compressor. The SSPD system cannot be installed in a 19-inch rack and the miniaturization is required for practical use. SSPD SSPD Data center in Koganei-city Backup of important data The objective is to reduce the total height of the expander by 33% relative to the existing RDK-101 GM cryocooler, and to reduce the total volume of the compressor unit by 50% relative to the existing CNA-11 compressor.

Development of 2K GM expander 取扱注意情報 Development of 2K GM expander CNA-11B Air-cooled Compressor Electrical Supply: 100V/50Hz Power Consumption:1.2 kW @ 50Hz Lowest temperature : 35.2K/2.10K 0W/0.1W 1-stage : 1.0W at 41.1 K 2-stage : 20mW at 2.2 K RDK-101D In 2013 ~85 mm 0W/40mW 0W/20mW It was miniaturized by the addition of various improvements to RDK-101D. 4W/0W 1W/0W 2W/0W No-load This figure shows the development of 2K GM expander. we set the design temperature targets of the first and the second stages to 1 W and 20 mW of heat load at 60 K and 2.3 K, respectively. In 2014, Bao reported that the goal of cooling performance was achieved and the height of the expander cylinder was reduced by about 33% relative to the existing 0.1 W 4 K GM cryocooler, RDK-101D. Bao, Q., Engineering Conference and International Cryogenic Materials Conference in 2014, Achieved the goal of cooling performance Reduced the height of the expander cylinder by about 33% relative to the existing 0.1 W 4 K GM cryocooler, RDK-101D

Compressor development concept 取扱注意情報 Compressor development concept Photograph in compressor unit (CNA-11) Helium gas and oil flow chart　of compressor unit (CNA-11) Adsorber Oil separator オイルセパレータ Oil separator 320 Adsorber アドゾーバ Compressor capsule Heat exchanger 熱交換器 Heat exchanger These components are necessary to remove oil in helium gas because oil is used as a lubricant in the existing compressor. 450 Major design changes are indispensable because the adsorber and the oil separator have almost the same volume as the compressor capsule. Compressor capsule 圧縮機 The target of size reduction is to reduce the volume of the existing CNA-11 compressor unit by about 50%. Although optimization of the internal compositions is one of the ways to reduce the volume of the compressor unit, major design changes are indispensable because the adsorber and the oil separator have almost the same volume as the compressor capsule. Thus, it is considered that an effective way to reduce the total volume is to exclude these parts, i.e. to develop a non-lubricated compressor. An effective way to reduce the total volume is to exclude these components, i.e. to develop a non-lubricated compressor. 6

Design of an compressor capsule 取扱注意情報 Design of an compressor capsule Design target of the linear compressor for 2K GM cryocooler. Cross section of a valved non-lubricated linear compressor capsule. Item Specification First stage cooling capacity 1 W at 60 K Second stage cooling capacity 20 mW at 2.3 K Maximum electric input power 1.2 kW　AC100 V Operating frequency 60 ~ 70 Hz Inlet cooling temperature Water 30 ℃ Initial gas pressure 1.5~ 2.0MPa Mass flow rate > 0.8 g/sec Compressor efficiency > 60 % Unit volume < 35 L Discharge Suction Magnet Outer yoke Coil Flexure bearing Outlet valve Inlet valve Offset coil Piston Cooling water In 2015, a prototype capsule of a non-lubricated linear compressor for a 2K GM cryocooler was developed. This table shows the design target of the linear compressor for 2K GM cryocooler and this figure shows the cross section of a valved non-lubricated linear compressor capsule. The electric input power and the capsule volume are set to be similar to the specification of a CNA-11 compressor. To design a valved linear compressor for a 2K GM cryocooler, the electric input power and the capsule volume are set to be similar to the specification of a CNA-11 compressor. 7

Experimental unit and results

Performance of a 2K GM cryocooler with a linear compressor 取扱注意情報 Photograph of an experimental unit of the valved non-lubricated linear compressor. The cooling performance test results of 2K GM cryocooler using a commercial CNA-11 compressor and a linear compressor. Heat exchanger Helium mass flow meter Pressure gauge 2K GM cryocooler Linear compressor Item With CNA-11 Measured results Electric　input power 1.2 kW /50Hz 1) Compressor input power - 0.9 kW 2) Cooling fan and water pump 50 W 3) Expander valve motor 4) Inverter loss 180 W First stage temperature with 1 W 45 K 49 K 2nd temperature at 2.3 K 17 mW No-load 2nd temperature 2.2 K 2.17 K By reducing the leakage losses of the gap between the piston and the cylinder, the inlet and the outlet valve, the compressor efficiency has been further improved after the initial preliminary tests. A compact 2K GM expander was operated with the prototype of a non-lubricated linear compressor, and the cooling performance was measured. This figure shows photograph of an experimental unit of the valved non-lubricated linear compressor. In this table, the cooling performance test results of 2K GM cryocooler using a commercial CNA-11 compressor and a linear compressor are shown. Almost the same second stage cooling capacity has been obtained with a linear compressor as with a CNA-11 compressor. The compressor input power is 0.9 kW and the power consumption of the cooling fan, the cooling water pump and the expander valve motor is about 0.1 kW. Thus, the total electric input power of the compressor unit including the inverter loss is about 1.2 kW since the inverter efficiency is about 80%. Achieved a cooling capacity of 1 W at 49 K and 17 mW at 2.3 K with an electric input power of less than 1.2 kW

Affect of initial pressure and cooling water temperature 取扱注意情報 The second stage cooling capacity and the lowest temperature with respect to the initial gas pressure at a compressor input power of 1 kW. The second stage cooling capacity and the compressor discharge temperature with respect to the inlet cooling water temperature. This figure shows the second stage cooling capacity and the lowest temperature with respect to the initial gas pressure at a compressor input power of 1 kW. As the initial gas pressure increases, the lambda point of helium is reduced, thus the lowest temperature is decreased.The cooling capacity at 2.3K reached the maximum at initial pressure of about 1.8 MPa. This figure shows the second stage cooling capacity and the compressor discharge temperature with respect to the inlet cooling water temperature. Although as the water temperature increases the discharge temperature of the compressor increases, the influence of the inlet cooling water temperature on the cooling capacity is negligible. Compressor input power 1 kW Compressor input power 1 kW Lower no load temperature with higher initial pressure Small impact on performance by cooling water temperature

Design of a prototype unit

取扱注意情報 Prototype unit Volume of compressor unuit: 29L Volume of CAN-11: 70L L450 L360 W390 L300 W350 W198 H230 H400 H145 This photograph shown a compressor unit and the electric box. The volume of the compressor unit is 28 l, while that of the electric box is about 9 l and thus the total volume is about 37 l, which is close to the target of 35 l. The electric box runs at power 100 V. To optimize the performance of the system, PID function for temperature control by the input power of the compressor has been installed. Compared with a CNA-11 compressor unit, you can see that it is much more compact. In addition, since there is no oil, it is also possible to use by tilting the compressor unit.　At the moment, we are trying to reduce the noise and vibration of the compressor unit. Volume of electricity box: 9L Total volume of the compressor unit and the electricity box is about 38 L, which is close to the target of 35 L.

取扱注意情報 Summary An experimental unit of a valved non-lubricated linear compressor for a 2K GM cryocooler, which can be used for cooling superconducting electronic devices, has been developed. Under no-load condition, a low temperature of 2.17 K has been achieved. With 1 W and 17 mW heat load, the temperature was 49 K at the first stage and 2.3 K at the second stage with an electric input power of less than 1.2 kW. The total volume of a prototype unit can be reduced to 38 L. In the future, we plan to further improve the efficiency of the compressor, to reduce the size of the heat exchanger thus reduce the total volume of the compressor. Let me summarize the point of our presentation.

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Reference

Design of motor Analysis model of 1AirGap linear motor. Calculation results of the transition analysis of a 1AirGap linear motor. Magnet Inner yoke Outer yoke Coil Operating Frequency 50 Hz Capacitor 0.22 mF Turn number 190 turn Volt 95 Vrms Current 14.4 Arms Force 708.6 N Force constant 49.3 N/A Copper loss 140.3 W Iron loss 123.0 W Power factor 0.99 P-V work 1101.1 W Input power 1364.4 W Motor efficiency 0.81 It is possible to further improve the efficiency of the motor by reducing this air gap between the yoke and the magnet. Then, in order to reduce the number of gaps, the yoke was designed to be integrated with the magnet.

Design of flexure bearing 取扱注意情報 Design of flexure bearing Calculation results of a flexure bearing with a sub-spring using contact stress analysis. 補助ばねを採用し応力低減 It is possible to reduce stress by 5~10% when using this concept.

2K GM cryocooler with the valved linear compressor Photograph of an experimental unit of a compact 2K GM cryocooler with the valved linear compressor. Linear compressor Cool down curves of a compact 2K GM cryocooler with a linear compressor. Heat exchanger Buffer tank Pressure gauge Pressure gauge Buffer tank 2K-GM Expander With 1 W and 14 mW heat load, the temperature was 50 K at the first stage and 2.3 K at the second stage with an input power of about 1.2 kW 18

Design of an experimental unit Design target of the linear compressor for 2K GM cryocooler. Analysis model of a valved linear compressor. Item Specification First stage cooling capacity 1 W at 60 K Second stage cooling capacity 20 mW at 2.3 K Maximum electric input power 1.2 kW　AC100 V Operating frequency 60 ~ 70 Hz Inlet cooling temperature Water 30 ℃ Initial gas pressure 1.3 ~ 2.0MPa Mass flow rate > 0.8 g/sec Compressor efficiency > 60 % Unit volume < 35 L To design a valved linear compressor for a 2K GM cryocooler, the mass flow rate and the pressure ratio are set to be similar to the specification of a CNA-11 compressor. Furthermore, under these determined conditions, the movement of the compressor parts has been analysed. To reduce the pressure drop loss as much as possible, the gas charging side was installed at the piston upper end. 19

Experimental unit Cross section of an experimental unit of a valved linear compressor Discharge Outlet valve Magnet Outer yoke Inlet valve Cooling water Piston Coil Flexure bearing Offset coil Suction

Performance of compressor capsule Photograph of an experimental unit of the linear compressor. Comparison between the experimental and the calculation results of the compressor. Item Measurement Calculation Operating frequency 50 Hz High / Low pressure 2.27 / 1.09 MPa 2.25 / 0.85 MPa Discharge temperature 133.3 ℃ 125 ℃ Charge temperature 25 ℃ 28 ℃ Mass flow rate 0.89 g/sec 0.93 g/sec Piston stroke 13.1 mm 13.5 mm Input power 1.2 kW P-V work 0.86 kW 0.81 kW Ideal P-V work 0.76 kW F-X work 0.91 kW 0.99 kW Volume efficiency 0.64 0.87 Indicated efficiency 0.88 0.99 Motor efficiency 0.75 0.82 Mechanical efficiency 0.95 Compressor efficiency 0.40 0.62 The motor efficiency and the volumetric efficiency improvement is necessary. The final target is over 60%.

Affect of compressor input power 取扱注意情報 Affect of compressor input power Compressor operating frequency 70Hz This figure shows the second stage cooling capacity with respect to the compressor input power. It　is possible to increase the cooling capacity by increasing the compressor input power. Possible to increase the cooling capacity by increasing the compressor input power.