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CM-17 Talk Feb. 2007 -1-
The Use of Small Coolers forHydrogen and Helium
Liquefaction
Michael A. Green
Lawrence Berkeley Laboratory
CM-17 Talk Feb. 2007 -2-
Why is liquefaction with a cooler a problem?
• The heat of vaporization for hydrogen and helium is much lower than the heat that must be removed to cool the gas to the liquefaction temperature.
• For helium the heat of vaporization is 20.7 J g-1. The sensible heat from 300 K to 4 K is 1540 J g-1. A perfect helium liquefier has refrigeration to liquefaction coefficient of 20.7 J g-1.
• For hydrogen the heat of vaporization is 445 J g-1. The sensible heat from 300 K to 20 K is ~4000 J g-1. A perfect hydrogen liquefier has refrigeration to liquefaction coefficient of 445 J g-1.
• Hydrogen is easier to liquefy with a cooler than helium.
CM-17 Talk Feb. 2007 -3-
2-Stage GM Cooler with an Added J-T Loop
GM Cooler
Motor & Drive Unit
1st Stage
Displacer
2nd Stage
Displacer
Cooler
Compressor
J-T Valve
Helium Tank
JT Circuit
Compressor
1st Stage
T = 50 to 60 K
2nd Stage
T = 10 to 12 K
Vacuum Vessel
CM-17 Talk Feb. 2007 -4-
Liquefaction with a separate J-T loop.
• Refrigeration at 4 K is relatively easy even when the cooler can only produce 8 K at the 2nd-stage. Liquefaction of helium is nearly impossible. Re-condensation is not the same as liquefaction. The refrigeration to liquefaction coefficients for helium are greater 500 J g-1.
• The advent of 4 K coolers improved liquefaction with a separate J-T circuit, but to refrigeration to liquefaction coefficients are still high (~350 J g-1).
• Liquefaction of hydrogen is easier.
CM-17 Talk Feb. 2007 -5-
GM Cooler
Motor & Drive Unit
1st Stage
Displacer
2nd Stage
Displacer
T = 55 to 65 K
T = 20.5 K
to Compressor
Vacuum Vessel
H2 Pot
Condenser
GM Cooler
Motor & Drive Unit
1st Stage
Displacer
2nd Stage
Displacer
T = 30 to 40 K
T = 20.5 K
to Compressor
Vacuum Vessel
H2 Pot
Condenser
a) LH2 Liquefier without
1st Stage Heat Exchanger
b ) LH2 Liquefier with
1st Stage Heat Exchanger
2-Stage 4 K GM Cooler used as Liquefier
CM-17 Talk Feb. 2007 -6-
Liquefaction with a 4 K GM Cooler
• Liquefaction with a 4 K cooler is possible if there is a larger heat exchanger on the 2nd-stage.
• Adding a heat exchanger to to the 1st-stage greatly improves liquefaction of helium. The refrigeration to liquefaction coefficient is ~ 160 J g-1. Adding liquid nitrogen cooling improve liquefaction even more.
• In theory, a refrigeration to liquefaction coefficient of 600 J g-1 can be achieved for hydrogen.
CM-17 Talk Feb. 2007 -7-
Pulse Tube
Regenerator Tube
to Compressor
Vacuum Vessel
T = 60 K
T = 4.2 K
Rotary
Valve
Q = 20 W
Q = 0.50 W
Pulse Tube
Regenerator Tube
to Compressor
Vacuum Vessel
T = 60 K
T = 4.2 K
Rotary
Valve
Q = 20 W
Q = 0.38 W
T = 8 KQ = 1.25 W
a) Unmodified 0.5 W Cooler
b ) 0.5 W Cooler with an
Intercept beteen Stages
Additional Cooling can come off of theRegenerator and Pulse tubes of a
Cryomech Pulse Tube Cooler
CM-17 Talk Feb. 2007 -8-
One can get additional cooling from the tubes of Cryomech pulse tube coolers
• The experiment at Cryomech using a PT-405 cooler showed that additional cooling is available between stages from the regenerator tube and the pulse tube.
• Cooling between stages is not available for a typical GM cooler. Not all pulse tube coolers have cooling available between stages.
• The cooling between stages can greatly improve the liquefaction efficiency (a lower refrigeration to liquefaction coefficient).
CM-17 Talk Feb. 2007 -9-
Pulse Tube
Regenerator Tube
to Compressor
Vacuum Vessel
He Condenser
He Vessel
T = 60 K
T = 4.2 K
He Gas
Rotary
Valve
LHe out
1st Stage Pre-cooler
Tube Heat Exchanger
Circuit Diagram for the PT-410 Liquefier with Tube Heat Exchanger
CM-17 Talk Feb. 2007 -10-
Condensing Pot
1st Stage Heat Exchanger
Ballast Tank
Tube Heat Exchanger
Rotary Valve
Rotary Valve Motor
Cooler 1st-Stage
Cooler 2nd-Stage
PT-410 Liquefier with Tube Heat Exchanger
CM-17 Talk Feb. 2007 -11-
Liquefaction with the PT-410 Cooler
• The heat exchanger on the 1st-stage and the heat exchanger on the regenerator tube between the 1st and 2nd stages of a PT-410 cooler reduces the refrigeration to liquefaction coefficient of 45 J g-1 for helium. This is better than any other helium liquefier.
• Cooling from the tubes between stage permits one to operate the PT-415 cooler in the drop in mode because there is free-convection between the mounting tube and the cooler.
CM-17 Talk Feb. 2007 -12-
Cooler Ballast Tank
Valve Motor
Rotary Valve
Cryostat Top Plate
Cooler Top Plate
Seal
Cooler Tube
Cooler Ist Stage with Taper
Connects to Shields
Condenser (Area = 0.042 m )2
Pulse Tube
Regenerator Tube
He Gas
He Gas from Magnet
LHe to Magnet
Radiation Shield
Drop In PT-415 Cooler with Condenserfor the MICE Tracker Solenoids
CM-17 Talk Feb. 2007 -13-
The drop in cooler concept will be used for the PT-415 cooler for the MICE tracker solenoid.
• It is hoped that free-convection cooling between the cooler tubes and the mounting tube will reduce the heat leak down the mounting tube.
• The mounting tube wall thickness will be machined down from 0.87 mm to 0.37 mm.
• The 1st-stage tapered joint allows heat from the leads, the thermal radiation shield, and the cold mass supports to the cooler 1st stage.
CM-17 Talk Feb. 2007 -14-
Cryomech found that the liquefaction improved without the tube heat exchanger.
• Eliminating the heat exchanger from the cooler liquefier reduces the cost of the liquefier.
• Eliminating the heat exchanger from the cooler liquefier increases the efficiency of liquefaction about 30 percent. The new Cryomech liquefier has a refrigeration to liquefaction coefficient of 36 J g-1.
• Cryomech would like to build the hydrogen (helium) liquefier for the MICE absorbers.
CM-17 Talk Feb. 2007 -15-
Pulse Tubes
Regenerator Tubes
to Compressor
H2 Condenser
T = 50 to 60 K
T = 20.8 K
H2 Gas in
1st Stage Heat Exchanger
Rotary
Valve
Area = 0.06 m2
Area = 0.06 m2
Area = 0.04 m 2
Area = 0.07 m 2
25 μ m clearance to wall
2 LH to Vessel
Liquid
Collection
Area
2 Cold H Gas
.There is vacuum outside of liquefier
~1 mm clearance to wall
Foam Radiation Shield
A More Efficient Liquefier without the Tube Heat Exchanger
The areas shown are based on thePT-415 cooler.
CM-17 Talk Feb. 2007 -16-
The Proposed Cryomech Absorber Hydrogen Liquefaction System
Using the PT-415 Cooler
CM-17 Talk Feb. 2007 -17-
A Proposed Absorber Cooler Module
• Cryomech has a commercial interest in building a hydrogen liquefier.
• Cryomech proposes to use the pulse tubes and regenerator tubes and holes in the first stage to pre-cool the hydrogen being liquefied. Standard tube parts would be used for the liquefier.
• Hydrogen from the hydride bed (or bottles) must be fed into the upper part of the cooler space between the top plate and the first stage heat exchanger
• The absorber probably can be filled in 24 hours.
CM-17 Talk Feb. 2007 -18-
Cooler Ballast Tank
Valve Motor
Rotary Valve
Liquefier Top Plate
Seal
Liquefier Tube
Condenser ( Area = 0.06 m )2
Pulse Tube
Regenerator Tube
Radiation Shield
from
Absorber
Top
to
Absorber
Bottom
30 to 40 K Shield
Space between Wall & condenser = 1 mm
Space between Wall & 1st Stage = 25 μ m
1 st Stage = 0.04 Area m )2
25 mm ID
15 mm ID
25 mm ID
15 mm ID
2 = 0.06 Tube Area m
Hydrogen Gas Fill Line
= 0.07 Tube Area m2
Absober cooler Neck
An End View of a Proposed MICE AbsorberCooler Module with Hydrogen Liquefier
CM-17 Talk Feb. 2007 -20-
Purpose of the Cooler Experiment
• Measure the performance of the PT-415 cooler in the magnet configuration over a range of 2nd-stage temperatures from 2.5 K to about 22 K and 1st-stage temperatures from 30 K to 65 K.
• Confirm the that the PT-415 cooler will will work well in the drop in configuration. Measure the extra heat leak (if any) that comes from this method of mounting the cooler in this way.
• Demonstrate that the PT-415 cooler will liquefy both helium and hydrogen.
CM-17 Talk Feb. 2007 -21-
25 35 45 55 65 752
3
4
5
6
84W63W42W21W0 W3.0W2.5W
2.0W
1.5W
1.0W
0.5W
SECOND STAGE TEMPERATURE, K
FIRST STAGE TEMPERATURE, K
CRYOMECH TEST
0 W
6
5
4
3
2
SEC
ON
D S
TA
GE T
EM
PER
ATU
RE
K
Known Operating Points of the PT-415 Cooler
The measured test data is from Tom Painter of Florida State University.
CM-17 Talk Feb. 2007 -22-
Plans for the Cooler Experiment
• This experiment will measure the temperature of both stages of a PT-415 pulse tube cooler as a function of the heat load on both stages. On the first stage power with Q = 0, 20, 40, 60 and 80 W will be applied. At that same time, the second stage power will be changed in steps of Q = 0, 0.5, 1.0, 1.5, 2.0, 5, 10, 15, 20, 25, and 30 W.
• The measurements will be done both in vacuum and in a helium gas atmosphere.
• The experiment will compare the thermal resistance of the first stage taper boundary in vacuum and in helium gas
CM-17 Talk Feb. 2007 -23-
Cooler Experiment Purpose Continued
• The degree to which convection currents play a role in intercepting heat will be measured by recording the temperature on the tube between stages both in vacuum and in helium.
• With liquid helium in the tank, the T between the tank and the second stage cold head will be measured.
• Operate the cryogenic system with the cooler with helium at 3.8 K, 4.2 K and 4.6 K.
• Measure the liquefaction of helium at 4.3 K.
• Measure the liquefaction of hydrogen at 20.8 K.
CM-17 Talk Feb. 2007 -24-
Cooler Ballast Tank
Valve Motor
Rotary Valve
Cryostat Top PlateCooler Top Plate
Drop-in Seal
Cooler Enclosure Tube
Wall t = ~ 0.38 mm
Cooler Ist Stage with Taper
Pulse Tube
Regenerator Tube
He Gas
Radiation Shield
Liquid Level Gauge Tube
Safety Relief Tube
Liquefaction Tank
ID = ~ 125 mm
I Length ~ 150 mm
Wall t = ~ 1 mm
End t = ~ 6.4 mm
Volume = ~1.8 liters
40 - 60 K Shield
Vacuum Vessel
P
Q2
T
T
Q2
T
T
T
T
Q1
T
Q1
Condenser (Area = 0.042 m ) 2
Gas Fill Tube
T
Legend
T = Temperature Diode
Q1 = 80 W Heater
Q2 = 30 W Heater
Diagram of a Proposed Cooler Experiment
CM-17 Talk Feb. 2007 -25-
What is needed for the experiment?• One MICE PT-415 cooler for a magnet
• The actual magnet cooler mounting tube
• A liquefaction vessel (~1.5 liters) for He and H2
• A 1st stage thermal shield with MLI inside and outside the shield to minimize heat leak
• The experiment vacuum vessel
• Seven (or eight) diode temperature sensors T
• Two 1st Stage heaters Q (0 to 80 watts)
• Two 2nd Stage heaters Q (0 to 30 watts)
• Commercial LHe and LH2 liquid level gauges
CM-17 Talk Feb. 2007 -26-
Concluding Comments
• Hydrogen liquefaction is possible with both GM and pulse tube coolers. Liquefaction must be done correctly.
• Cryomech has proposed that the could fabricate the absorber hydrogen liquefaction module. This may be cost effective.
• A test of the PT-415 cooler is needed, even for the tracker magnet. If LBL doesn’t do the test, who will do the test?