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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
KK
M
Cooling Options for Superconducting MagnetsB ath C ooling
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 oo ling: 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 oo ling: 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)
Spec
ific
Enth
alpy
(J/g
)
One-phase cooling with temperature rise from 4.5 to 4.8 Kwith 1 bar pressure drop
1.2 bar
5 bar
43 2
4 . 5 K 4 .8 K
4 .4 K ba th
H e lium P um p
C ryo s ta t
1 ba r P res sure 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 vapora tionin H ea t E xchange r
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
dTdX
qY(T)
q in W / cmT in KX in cm
2.4
3.4
2
OFHC copper
Helium II
KKPressurised 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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KKMap 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 di
ffere
nce
[m]
ElevationPoint 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]
Supe
rfici
al li
quid
vel
ocity
[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 t
empe
ratu
re [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 40Enthalpy [J/g]
Pre
ssur
e [k
Pa]
Sub-cooled liquid @ 2.2 KSaturated 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