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Raffael‘s Sixtinische Madonna in der Galerie Alte Meister in Dresden

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KKCryogenic Engineering

CERN, March 8 - 12, 2004

• Temperature reduction by throttling and mixing

• Temperature reduction by work extraction

• Refrigeration cycles: Efficiency, compressors, helium, hydrogen

• Cooling of devices

KKApplications of Superconducting Magnets

• Energy technology Fusion reactor MHD generator Turboalternator Tranformer Fault current limiter Magnetic energy storage

(SMES) ResearchAcceleratorsDetectorsSpectrometersGyrotronsMobility

Levitated trainMHD ship propulsion

MedicineMagnetic tomographyRadiation treatment

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Cooling options with Helium

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M

Cooling Options for Superconducting MagnetsB ath C oo ling

B ath C oo ling

M

B ath C oo ling w ithTherm os iphon

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M M

O ne-phase w ith JT-S tream

O ne-phase w ithC ircu la tion P um p

Forced C ooling: O ne-phase

O ne-phase w ithC on tinuous R ecoo ling

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M M

O ne-phase w ith JT-S tream

O ne-phase w ithC ircu la tion P um p

Forced C ooling: O ne-phase

O ne-phase w ithC on tinuous R ecoo ling

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11

12

13

14

4,2 4,3 4,4 4,5 4,6 4,7 4,8 4,9 5Temperature (K)

Spe

cific

Ent

halp

y (J

/g)

One-phase cooling with temperature rise from 4.5 to 4.8 Kwith 1 bar pressure drop

1.2 bar

5 bar

4

3 2

4 . 5 K 4 .8 K

4 .4 K ba th

H e lium P um p

C ryos ta t

1 ba r P ressu re D rop

Pressure Drop Enthalpy rise Pump work RatioJ/g J/g

5 - 4 bar 0,98 0,74 1,34 - 3 bar 1,22 0,77 1,63 -2 bar 1,75 0,80 2,2

Forced Flow Supercritical Cooling with Pressure Drop

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M

R es idua l E vapo ra tionin H ea t E xchanger

Forced C oo ling: Two-phase w ith Low Q uality O utle t

M

W ith L iqu idR ec ircu la tion P um p

KKThe maldistribution problem with parallel

cooling channels

R 1

R 2

R 3

p

p

m

turbulent

laminar

Parallel cooling channels share the same pressure drop. If one channel

takes more coolant flow, all others get less.

One-phase turbulent flow gives a stable distribution.

One phase laminar flow is less stable, depends on orientation.

KKMulti-channel plate-fin heat exchangers

KKThe maldistribution problem with parallel

cooling channels with two-phase flow

If the flow is upwards, the flow distribution is probably stable.

If the channels are horizontal, the distribution is poor, if the

vapour content is too high.

If the flow is downward, the distribution is certainly poor:

One channel will take the liquid and the others only get vapour.

p

m

upw ards

dow nw ards

horizontalR 1

R 2

R 3

p

KKColdbox with horizontal multi-channel

heat exchangers

Flow distribution in exchangers is acceptable in the warm section, but has failed sometimes in the Joule-Thomson exchanger.

KKCritical Current Density

of Technical Superconductors

KKSuperfluid Helium Cooled Magnets

The coldest ring in the universe!

T1.9 K 2.728 K

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Phase Diagram of Helium

1

10

100

1000

10000

1 10

T [K]

P [k

Pa]

SOLID

HeII HeI

CRITICAL POINT

GAS

line

Saturated He II

Pressurized He II

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Superfluid Helium as a Magnet Coolant

• Temperature below 2.17 K• Low bulk viscosity• Very large specific heat

– 105 times that of the conductor per unit mass– 2 x 103 times that of the conductor per unit

volume• Very high thermal conductivity

– 103 times that of cryogenic-grade OFHC copper– peaking at 1.9 K– still, insufficient for long-distance heat transport

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Equivalent Thermal Conductivity of He II

0

500

1000

1500

2000

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2

T [K]

Y(T

) ±

5%

T

K T,q q Y T

dT

dX

q

Y(T)

q in W / cm

T in K

X in cm

2.4

3.4

2

OFHC copper

Helium II

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Pressurised vs. Saturated Superfluid Helium

+Mono-phase (pure liquid)+Magnet bath at atmospheric pressure

• no air inleaks• higher heat capacity to the lambda line

+Avoids bad dielectric strength of low-pressure gaseous helium

– Requires additional heat exchanger to saturated helium heat sink

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Map of LHC& General Layout of Cryogenic System

Pt 3

Pt 4

Pt 5

Pt 6

Pt 7

Pt 8

Pt 1

Pt 2

Pt 1.8

Cryoplant DistributionPresent Version

Cryogenic plant

KKTransport of Refrigeration in Large Distributed Cryogenic Systems

0

0.1

0.2

0.3

0.4

0.5

0 1 2 3 4 5Distance [km]

Tem

pera

ture

diff

eren

ce [K

] Pressurised He II Saturated LHe II He I

Tore Supra

TevatronHERA

UNKLHC

SSC (main Ring)

SSC (HEB)

LEP2 TESLA

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Simplified Geological Section of LHC Tunnel

KKElevation Difference along LHC Tunnel

P8

P6

P1

P4

P2

P7

P5

P3

-50

-30

-10

10

30

50

70

90

110

0 3334 6668 10002 13336 16670 20004 23338 26672

Distance [m]

Ele

vatio

n d

iffe

ren

ce [

m]

Elevation

Point with cryoplant(s)

Point without cryoplant

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KKPatterns in Quasi-horizontal Two-phase Flow

KKTwo-phase Flow of Saturated He II(Mandhane, Gregory & Aziz flow map)

Outlet

Inlet

0.001

0.01

0.1

1

10

0.01 0.1 1 10 100

Superficial gas velocity [m/s]

Su

per

ficia

l liq

uid

vel

oci

ty [m

/s]

Dispersed

Bubble

Slug

Stratified

Wavy

Annular

LHCheat exchanger

KKCalculated Temperature Profiles of LHC

Magnets

1.8

1.82

1.84

1.86

1.88

1.9

1.92

0 3334 6668 10002 13336 16670 20004 23338 26672Distance [m]

Mag

net

tem

pera

ture

[K

]

Nominal operationStandby operation

P1 P2 P3 P4 P5 P6 P7 P8 P1

Maximum allowed

KKHe Subcooling Boosts J-T Expansion

1

10

100

1000

0 10 20 30 40

Enthalpy [J/g]

Pre

ssu

re [

kPa

]

Sub-cooled liquid @ 2.2 K

Saturated liquid @ 4.5 K

Saturation dome

13 % of GHe produced in expansion

46 % of GHe produced in expansion

KKPrototype Subcooling Heat Exchangers

Stainless Steel Plate

PerforatedCopper Plateswith SS Spacers

SS Coiled Tubes

Mass-flow: 4.5 g/sP VLP stream: < 100 PaSub-cooling T: < 2.2 K

Courtesy of DATE

Courtesy of SNLS

Courtesy of Romabau