2. Properties of Cryogenic Liquids
2.1 Textbooks / References
2.2 Basic Properties of Cryogenic Liquids
2.3 Density
2.4 Specific Heat and Cooling
2.5 Evaporation Heat and Enthalpy
2.6 Efficient Use1

2. Properties of Cryogenic Liquids (1/11)

2.1 Textbooks / References
References for Cryogenic Technique
We should have the reference
books for low temperatureexperiments.

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22. Properties of Cryogenic Liquids (2/11)

2.2 Basic Properties of Cryogenic Liquids
Physical Properties of Cryogenic Liquids
molecular weightBP [K] under Patm
MP [K] under Patm ,(except 3He and 4He)

3.2 (under28.9 atm)

4.2 (under150 atm)

ρ (liquid) [g/cc] at BP
ρ (gas) [g/L] at 0 OC under Patmρ (gas) [g/L] at BP
evaporation heat [J/g] at BP
critical temperature [K]critical pressure [atm]BP: boiling point, MP: melting point,
ρ: density, Patm : normal atmospheric pressure

Ref.:小林・大塚『低温技術』
32. Properties of Cryogenic Liquids (3/11)

2.3 Density
Comparison ρ [g/L] : density at boiling point (BP)4He

N2BP (K)

4.22

77.4

liquid ρL

124.8

808.4

gas ρG

16.7

4.604

ratio ρL/ρG

7.47

175.6

(ρL-ρG)/ρL

0.866

0.994

Density ratio ρL/ρG

Comparison of ρL

He (124.8)＜ N2(808.4)

The density of liquid
He is very low.

He(7.47)＜ N2(175.6)

The density ratio of He is smaller than that of N2.
A volume expansion due to vaporization of liquid He is small.

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2. Properties of Cryogenic Liquids (4/11)

2.3 Density

Amount of Available Liquid / Remaining Amount of He
Consider the case that a 100 L vessel
contains 100 L of liquid He or 100L of gas
He at 4.2 K.

liquid100ρL=12.48 (kg)When theliquid is used
forexperiments,
the gasremains.

gas

At 4.2 K, 100 L of the gas isequivalent to 13.4 L of theliquid.
equivalentliquid
100ρG=1.67 (kg)1. Even if the liquid is ideally withdrawn
from the vessel, only 86.6 L of the liquid isavailable.(=100(L)×(ρL-ρG)/ρL)(100(L)×ρG/ρL)=100*(1.67/12.48)=13.4 (L)

2. Do not release the gas inside the vessel,
even if the liquid runs out.

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2. Properties of Cryogenic Liquids (5/11)

In order to prepare forexperimental environments at
low temperature, we need toknow the specific heats of both“cryogenic liquids” and “materialsfor instruments.”
Temperature Dependence ofSpecific Heats

Specific heat (J/g･K)

2.4 Specific Heat and Coolinggas 4H2
gas 4Heliquid 3He

liquid N2

gas N2liquid 4He

teflonPyrex glass

stainless steel
manganin

APIEZON Nquartz
Araldite

Ref.:小林・大塚『低温技術』

Temperature(K)6

2. Properties of Cryogenic Liquids (6/11)

2.4 Specific Heat and Cooling

Heat Energy and Specific Heat
𝑇𝑇2

𝑄𝑄 = � 𝑐𝑐 𝑑𝑑𝑑𝑑

𝑇𝑇1
Q: heat energy, the energy removed from a material when it cools downfrom temperature T2 to T1.
c: specific heat𝜕𝜕𝜕𝜕𝜕𝜕𝑈𝑈
specific heat
𝑐𝑐𝑉𝑉 = 𝑇𝑇=𝜕𝜕𝑇𝑇 𝑉𝑉
𝜕𝜕𝑇𝑇 𝑉𝑉at constant volume𝜕𝜕𝜕𝜕𝜕𝜕𝐻𝐻specific heat
𝑐𝑐𝑝𝑝 = 𝑇𝑇=𝜕𝜕𝑇𝑇 𝑝𝑝
𝜕𝜕𝑇𝑇 𝑝𝑝at constant pressure

U: internal energy, S: entropy, H: enthalpy

By knowing “the materials and the structures of the instruments”
and “enthalpy change of cryogenic liquids,” we can estimate theamount of cryogenic liquids for the experiments.

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2. Properties of Cryogenic Liquids (7/11)

2.5 Evaporation Heat and Enthalpy
We consider two cases that these cryogenic liquids canremove heat energy from instruments.
1. Evaporation (liquid → gas)
⇒ (a) Evaporation Heat
2. Gas (low temperature) → Gas(high temperature)⇒ (b) Enthalpy Change(a) Evaporation Heat (Latent Heat of Evaporation)boiling point (K)evaporation heat (J/g)

4He4.222
20.9

N277.35
198

The evaporation heat of He is extremely small.
8

2.5 Evaporation Heat and Enthalpy(b) Enthalpy Change ΔHgas (low T) → gas(high T)⇒ How much heat energy can thesecryogenic liquids remove heat from theinstruments?

Enthalpy (cal / L)

2. Properties of Cryogenic Liquids (8/11)

evaporation
heat (N2)ΔH= required heat to warm cryogenic liquid= removed heat from the instruments

ΔHN2

ΔH of 4He in the gas phase is large (*)ΔHHe (*)

evaporation
heat (He)T (K)Ref.:小林・大塚『低温技術』

We need to use not only the“evaporation heat” but also the“enthalpy of gas” as much as
possible.
92. Properties of Cryogenic Liquids (9/11)

2.6 Efficient Use
Comparison
Required volume of cryogenic liquid for cooling 1 kg of metals
initial temperature of metals

use ofevaporationheat
use of“evaporationheat” and“enthalpy of gas”

aluminum
stainless steel
copperaluminum
stainless steel
copper

Ref.:小林・大塚『低温技術』

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2. Properties of Cryogenic Liquids (10/11)

2.6 Efficient Use

Comparison
Temperature of Cu300 KN2He

77 K
He

boiling point
of N2

4.2 K

boiling pointof He
Required amount of cryogenic liquids forcooling 1 kg of copper (Cu)
4He
4He
N2
Change of temperature

300 K →
4.2 K

77 K→
4.2 K

300 K→
77 K

Evaporation heat31.1 L2.16 L0.46 L

Evaporation heat
＋enthalpy of gas

0.79 L0.15 L0.29 LThe required amount ofcryogenic liquids
depends on the coolingprocess.

Neither “using only liquidHe” or “using onlyevaporation heat” areefficient for cooling
instruments.

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2. Properties of Cryogenic Liquids (11/11)

2.6 Efficient Use

Efficient Use of Liquid He
Example: Transfer

1. Pre-cooling by means of liquid N2
2. Efficient use of gas enthalpy[good][bad]liquidliquid

recoveryrecovery12

3.Transfer / Cryogenic Vessel
3.1 Transfer
3.2 Structure of Cryogenic Vessel
3.3 Valve handling, Connection, Port
3.4 Leave Liquid He in the Vessel
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3. Transfer / Cryogenic Vessel (1/16)

3.1 Transfer
Flow Diagram of Liquid He Transfer
heat insulationof transfer tube
vacuumvesseltransfer tube

liquid He

experiment instrument(Cryostat)Ref.「Heの汲み出し」(千葉大学) http://physics.s.chiba-u.ac.jp/cryo2/hekumidasi.html

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3. Transfer / Cryogenic Vessel (2/16)

3.1 Transfer

Filling with Liquid He
Case 1: the inside of the cryostat is higher than 4.2K
[1]
Transfer tube
[5]

gas recovery line

gas recovery linepressurization[2][4]
cryostat[3]

Ref.: 『丸善 実験物理学講座2基礎技術 II 実験環境技術』

liquid He vessel[1] Use a tube with a dry inside[2] Insert the tube slowly[3] Do not insert to the bottom[4] Insert to the bottom of the cryostat.
[5] Helium gas needs to be recovered properly.

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3. Transfer / Cryogenic Vessel (3/16)

3.1 Transfer

Case 2: Liquid He is in the cryostat.
[1][5]

Transfer tube

gas recovery line

gas recovery linepressurization[2][4]cryostat[3]

liquid He vessel[1] Use a tube with a dry inside[2] Insert the tube slowly[3] Do not insert to the bottom[4] Insert halfway (Do not insert to the bottom)[5] Helium gas needs to be collected properly
出典: 『丸善 実験物理学講座2 基礎技術 II 実験環境技術』

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3. Transfer / Cryogenic Vessel (4/16)

3.1 TransferSeveral Reasons of Transfer Failure[4]

Transfer tube

[3]

gas recovery line

cryostatgas recovery line[2]

pressurization[1]

Ref.: 『丸善 実験物理学講座』

liquid He vessel[1] The tube is too short → Connect a extension tube
[2] Gas leaks → Trouble of compression seal
[3] There is frost on the tube→ Problem with the vacuum
insulation of transfer tube
[4] High pressure of the recovery line
→ Check the valve near the recovery line.

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3. Transfer / Cryogenic Vessel (5/16)

3.2 Structure of Liquid He Vessel
Inside vesselStructure
1. Large vacuum flask
2. Rate of evaporation 1%/day
3. 800,000 to 1 million yen(100 L vessel)

A: tube entry port
B: vent
C: safety valve
D: pressure gauge

Ref. 『丸善 実験物理学講座2』18

3. Transfer / Cryogenic Vessel (6/16)

3.2 Structure of Liquid He Vessel

Vulnerable to External Shocks
Distorted vessel made ofaluminium

Vessels made of aluminum arevulnerable to external shock.

Thermal insulation is lost.

moisture condensation / frost

unrecoverable

193. Transfer / Cryogenic Vessel (7/16)

3.2 Structure of liquid He vessel

The neck of vessel is vulnerable

The internal tank is supported onlyby the inside neck.
Vulnerable to external shocks
When we carry the vessel, we shouldchoose a flat road and carry it slowly.

Handle liquid He vessel carefully.
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3. Transfer / Cryogenic Vessel (8/16)

3.3 Valve Handling, Connection, PortValve HandlingOpen and close the valve depending on the situation

Connecting
recovery line

On the way to carryplug

During the transfer
transfer tube

recovery line

close

close
open

open

close

close

ball valve (for safety)
pressure relief valve

close

close

open

balloon for pressurization

213. Transfer / Cryogenic Vessel (9/16)

3.3 Valve Handling, Connection, PortConnection to Recovery Line
Before connection

connected

pipe of recovery line
close

close

close

openopen

open

close

close

Check a plug.
Check valves.
Check tubes.
Connect to helium recovery line and open appropriate vent valves.
Never leave a dewar open to atomoshere.

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3. Transfer / cryogenic vessel (10/16)

3.3 Valve handling, Connection, Port

Connection between plastic tube and fitting

GoodBadCheck valves and connections.
Recover He gas properly.
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3. Transfer / Cryogenic Vessel (11/16)

3.3 Valve Handling, Connection, Port

Tube Entry Port for Filling and Extracting LiquidStructure

plug

nut

“retaining ring madeof metal” and “O-ringmade of rubber”

24

3. Transfer / Cryogenic Vessel (12/16)

3.3 Valve Handling, Connection, Port

Sealing Mechanism
cross-sectional view
plug

nut
retaining ringO-ring

The compressed O-ringblocks the gas flow.
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3. Transfer / Cryogenic Vessel (13/16)

3.3 Valve Handling, Connection, PortGas leakEven if the nut is tightened,
why gas leaks?

1. Wrong direction of a retaining ring
2. Misplacement of a retaining ring and a O-ring
3. Problem of O-ring (absence, damage, wrong size)
4. Size mismatch between transfer tube and port
Understand the structure and use it correctly26

3. Transfer / Cryogenic Vessel (14/16)

3.4 Leave Liquid He in the Vessel
Reasons why the remaining amount of liquid should not be 0

Empty of He liquid→ Temperature insideof vessel increase.
→He gas penetrates thevacuum insulation layer.
Thermal insulation does
not work.

Cold He gas does not penetrate the vacuum
insulation layer.
Warm He gas can penetrate the vacuum
insulation layer.
Warm N2 gas does not penetrate the vacuum
insulation layer.

Evacuation is required.

Note: Some vessels do not allow helium 27
topenetrate vacuum insulation.

3. Transfer / Cryogenic Vessel (15/16)

3.4 Leave Liquid He in the Vessel

What to do when a vessel is warmed
Operations by user
Evacuate the vacuum insulation layer. (a few day ~ one week)
Precooling with liquid nitrogen. (a few day ~ one week)
Extract liquid nitrogen from the vessel. (30min. ~ 60min.)→Carry to the centerOperation by the center staff

Evacuate nitrogen gas in the vessel.
Filling with liquid helium.

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3. Transfer / Cryogenic Vessel (16/16)

3.4 Leave Liquid He in the Vessel

To avoid wasting time and effort
Once liquid He vessel is emptied, it is timeconsuming and requires extra liquid He.

Leave liquid He in the vessel
Leave about 5 L of liquid He in a 100 L vessel.
If the vessel will not be used for a long period of time,
return the vessel to the center.
29