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 -19-

A Proposed Cooler ExperimentUsing the PT-415 Cooler

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?