The Use of Small Coolers for
Hydrogen and Helium
Liquefaction
Michael A. Green
Lawrence Berkeley Laboratory
CM-17 Talk Feb. 2007
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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
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2-Stage GM Cooler with an Added J-T Loop
JT Circuit
Compressor
Cooler
Compressor
GM Cooler
Motor & Drive Unit
Vacuum Vessel
1st Stage
Displacer
1st Stage
T = 50 to 60 K
2nd Stage
Displacer
2nd Stage
T = 10 to 12 K
J-T Valve
Helium Tank
CM-17 Talk Feb. 2007
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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. Recondensation 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
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2-Stage 4 K GM Cooler used as Liquefier
CM-17 Talk Feb. 2007
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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
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Additional Cooling can come off of the
Regenerator and Pulse tubes of a
Cryomech Pulse Tube Cooler
to Compressor
to Compressor
Rotary
Valve
Rotary
Valve
Vacuum Vessel
Vacuum Vessel
Regenerator Tube
Regenerator Tube
T = 60 K
Q = 20 W
Pulse Tube
Q = 20 W
Q = 1.25 W
Q = 0.50 W
T = 4.2 K
T = 60 K
Q = 0.38 W
a) Unmodified 0.5 W Cooler
CM-17 Talk Feb. 2007
Pulse Tube
T=8K
T = 4.2 K
b) 0.5 W Cooler with an
Intercept beteen Stages
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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
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Circuit Diagram for the PT-410 Liquefier
with Tube Heat Exchanger
to Compressor
Rotary
Valve
He Gas
Vacuum Vessel
Regenerator Tube
T = 60 K
1st Stage Pre-cooler
Pulse Tube
Tube Heat Exchanger
T = 4.2 K
He Condenser
He Vessel
LHe out
CM-17 Talk Feb. 2007
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PT-410 Liquefier with Tube Heat Exchanger
Condensing Pot
Cooler 2nd-Stage
Tube Heat
Exchanger
Cooler 1st-Stage
1st Stage Heat
Exchanger
Rotary Valve
Rotary Valve Motor
Ballast Tank
CM-17 Talk Feb. 2007
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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
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Drop In PT-415 Cooler with Condenser
for the MICE Tracker Solenoids
Cooler Ballast Tank
Valve Motor
Rotary Valve
Cooler Top Plate
Cryostat Top Plate
Radiation Shield
Seal
Cooler Tube
Pulse Tube
Connects to Shields
Regenerator Tube
Cooler Ist Stage with Taper
He Gas
He Gas from Magnet
Condenser (Area = 0.042 m 2)
LHe to Magnet
CM-17 Talk Feb. 2007
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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
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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
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A More Efficient Liquefier without the
Tube Heat Exchanger
The areas shown are based on the
PT-415 cooler.
CM-17 Talk Feb. 2007
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The Proposed Cryomech Absorber
Hydrogen Liquefaction System
Using the PT-415 Cooler
CM-17 Talk Feb. 2007
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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
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An End View of a Proposed MICE Absorber
Cooler Module with Hydrogen Liquefier
Cooler Ballast Tank
Hydrogen Gas Fill Line
Valve Motor
Rotary Valve
Liquefier Top Plate
Seal
Radiation Shield
Pulse Tube
Liquefier Tube
1st Stage Area = 0.04 m 2 )
Tube Area = 0.07 m 2
Space between Wall & 1st Stage = 25 m
Regenerator Tube
Absober cooler Neck
Space between Wall & condenser = 1 mm
Condenser (Area = 0.06 m2 )
Tube Area = 0.06 m 2
30 to 40 K Shield
25 mm ID
25 mm ID
15 mm ID
15 mm ID
f rom
Absorber
Top
to
Absorber
Bottom
CM-17 Talk Feb. 2007
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A Proposed Cooler Experiment
Using the PT-415 Cooler
CM-17 Talk Feb. 2007
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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
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Known Operating Points of the PT-415 Cooler
SECOND STAGE TEMPERATURE, K
SECOND STAGE TEMPERATURE K
6
6
55
44
33
22
25
0 W 21W
3.0W
84W
63W
42W
2.5W
2.0W
1.5W
1.0W
0.5W
0W
CRYOMECH
TEST
35
45
55
65
75
FIRST STAGE TEMPERATURE, K
The measured test data is from Tom Painter of Florida State University.
CM-17 Talk Feb. 2007
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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
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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 DT 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
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Diagram of a Proposed Cooler Experiment
CM-17 Talk Feb. 2007
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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
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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?
CM-17 Talk Feb. 2007
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