1. 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

2. 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 ～

3. Background

4. 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
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 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.

5. 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 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

6. 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

7. 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

8. Experimental unit and results

9. 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

10. 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

11. Design of a prototype unit

12. 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.

13. 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.

14. Thank you for your attention!

15. Reference

16. 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 W
Input power 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.

17. 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.

18. 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

19. 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

20. 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

21. 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%.

22. 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.