challenges and limitations of thermosiphon ... · i in a natural circulation loop, advances in...
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Challenges and limitations of thermosiphon coolingthermosiphon cooling
What we learned from CMS…
Philippe BrédyPhilippe BrédyCEA Saclay
DSM/Dapnia/SACM/LCSE
Symposium for the Inauguration of the LHC Cryogenics, CERN, 31/05 & 01/06 2007
• The thermosiphon principle (example of two phase )
– Self sustained natural boiling convection– Self sustained natural boiling convection• Heating applied (Heat to be removed)
– Boiling– Weight unbalance between legs of a loop
Induced flow limited by friction– Induced flow limited by friction
Q
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Single channel Loop
• Rising heat exchangers with various geometry • A mass flow and a flow quality deduced from geometry and heat load
k h ll d h d d• An upper tank –the well-named phase separator- is needed– to recover gas and to supply supply or condensation of gas (cryocooler)– for separation of the two phases
ΔP flow (m,x,geometry)
ΔP (x, hi)
Hyp: homogenous model(x << 10%)
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Advantages vs Inconveniencesf fl N d h h• A passive creation of flow
– no pumps or regulation valves• Need a minimum height
– Pressure head to create flow
• Autonomy in case of external cryogenic failure (volume of liquid in the phase separator)
• Circuit geometry must avoid any high point or strong i l itiin the phase separator)
• Minimization of the liquid
singularities– separation of the phases– risk of vapor lockq
volume– use of the phase separator
as a back-up volume for liquid
p
• No possible external actiond p ssibl f st ti fas a back up volume for liquid
• A quasi-isothermal loop
– and a possible frustration for the operator !
- mainly function of height • Pre-cooling before starting the ThS effect
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Examples of applications on largeapplications on large superconducting magnets with LHe/GHe magn ts w th LH /GHloop at Tsat
ATLAS CS (LHC)S CS ( C)CMS (LHC)…
ALEPH (LEP)
SMS G0 (JLAB)
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PANDA, R3B (GSI)…
CLOE (CORNELL)
CMSPhase separator cryostat
• 220 tons at 4.5 K
• 174 to 500 W at 4 5 K• 174 to 500 W at 4,5 K
• 5 modules
• 86 parallel exchangersCoil cryostat • 86 parallel exchangersCoil cryostat
X 2 X 5
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CMS thermosiphonPhase separator cryostat (892 l GHe+LHe)
C i
First global calculation : x = 3,5 % ( 6,5% in SD)m = 200 g/s ( 400 g/s in SD)
Cryogenicchimney Thermosiphon loop (350 l)
TopLHe supply pipe ∅ 60.3 x 1.65 LHe/GHe return pipes ∅48.3 x 1.6
Outlet manifolds(∅ 45 x 2 5)
CB-2 CB+1CB0CB-1
(∅ 45 x 2.5)
CB+2
Heat exchangers(∅i 14)
BottomInlet manifolds(∅ 45 x 2 5)
(∅i 14)
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(∅ 45 x 2.5)
CMS R&DHeight between LHe tank
eAltitude 0
Height between outflow and liquid level
LHe tank
Upstream
(3.04)
Venturiflowmeter
Upstreamline (4.56)
Collecting manifold (∅ 0.04)
7 heatexchanger tubes (5 00 )
Experimental test loop scaling CMS
Distributing if ld (∅ 0 04)
tubes (5.00 )
Hydrostatic head 9.22(level at 50 %)
scaling CMS design
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manifold (∅ 0.04) (level at 50 %)
CMS R&D200(on experimental test
(scaling values)
120
140
160
180
/s)
(on experimental test loop ≈ 1/10 CMS)
• A strong mass transfer in comparison 60
80
100
120
Mas
s flo
w (g
Experimental andpwith heat deposit• A large margin• Homogenous model
0
20
40
0 50 100 150 200 250 300 350 400 450
Experimental and homogenous model
Homogenous model correct still above 14%• h > 1600 W.m2.K• ΔPr/Δps 1
Total deposited power Q (Watt)
0,10
0,12
0,14
lity
• ΔPr/Δps ∼ 1• ΔT height ~ 60 mK• x < 3% (CMS nominal)
0 04
0,06
0,08V
apor
Qua
l
0,00
0,02
0,04
0 50 100 150 200 250 300 350 400 450
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0 50 100 150 200 250 300 350 400 450
Total deposited power Q (Watt)
CMS R&D• Self-sustained circulation with the heat depositedSelf sustained circulation with the heat deposited
(on experimental test loop)
4.80 K
150 W
4.72 Ktotal mass flow vs different heat loads
100 W
125 W
150 W
4.64 K75 W
100 W
4.56 K
4.48 K
50 W
temperatures
4.40 K0 W
25 Wtemperatures
ti
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time
CMS on site• Self-sustained circulation with the heat depositedSelf sustained circulation with the heat deposited
(on site, at the beginning of a slow dump with dynamic heat load)
currentcurrent
mass flow
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CMS on site• Stabilisation and increase of the mass flow by heating theStabilisation and increase of the mass flow by heating the return lines
Eff t th il
T
Effect on the coil temperatures
- 0.01 K temperature decrease on coilt
Mass flow
- Increasing and stabilization of
Effect on the mass flowIncreasing and stabilization of
mass flow rate
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CMS R&D
h d b h l• Smooth sensitivity near and above the critical point
Pc
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Limitations and Extensions- Circuit geometry : - Feeding of several parallel g y
- A minimum height- Risk of high point or
singularities where gas could
g pcircuits with different heatdeposits is possible (in CMS design, in ratio of 5)singularities where gas could
be separated from the liquid- Minimization of pressure
drop (singularities)
(feeding and collecting pipes must be designed to be as isobaric)
St tin th n tu ldrop (singularities)
- A quasi-adiabatic supply line
- Starting the natural circulation is achievable before the liquid presence (between 15 and 20 K for CMS design)q pp y
- Good separation phase in the upper tank
and 20 K for CMS design)
- Heaters on the return pipesld b d li iupper tank
(what could be its minimum size?)could be used to limit instabilities due to gas/liquid separation at low velocity
(l h t l d i i )(low heat load or over-sizing)
- Flow quality could be chosen well higher than the traditional
14PhB, Symposium for the inauguration of the LHC Cryogenics, CERN, 31/05 & 01/06/2007
well higher than the traditional limit of 5 %
ConclusionConclusion
Confirmed by these tests and operation measurements, thermosiphon loop stays a
i t t i th i di t li fconvenient way to insure the indirect cooling of large equipment and must be taken into account during a design study without preconceived fearsduring a design study without preconceived fears.
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ReferencesReferences• 1. L. Benkheira, B. Baudouy, and M. Souhar, Heat transfer characteristics of two-phase He I (4.2 K) thermosiphon flow, International Journal of Heat and Mass Transfer, (2007) 50 3534-3544
2 L B kh i B B d d M S h Fl b ili i d CHF di ti f H I• 2. L. Benkheira, B. Baudouy, and M. Souhar, Flow boiling regimes and CHF prediction for He I thermosiphon loop, Proceedings of the 21th International Cryogenic Engineering Conference, to be published, Ed. G. Gistau, (2006) • 3. P. Brédy, F.-P. Juster, B. Baudouy, L. Benkheira, and M. Cazanou, Experimental and Theoretical study of a two phase helioum high circulation loop, Advances in Cryogenics Engineering 51, AIP, Ed. J. G W i d (2005) 496 503G. Weisend, (2005) 496-503• 4. L. Benkheira, M. Souhar, and B. Baudouy, Heat and mass transfer in nucleate boiling regime of He I in a natural circulation loop, Advances in Cryogenics Engineering 51, AIP, Ed. J. G. Weisend, (2005) 871-878• 5. B. Baudouy, Heat transfer near critical condition in two-phase He I thermosiphon flow at low y p pvapor quality, Advances in Cryogenic Engineering 49, AIP, Ed. S. Breon, (2003) 1107-1114• 6. B. Baudouy, Pressure drop in two-phase He I natural circulation loop at low vapor quality, International Cryogenic Engineering Conference proceedings 19, Ed. P. S. G. Gistau Baguer, (2002) 817-820• 7. B. Baudouy, Heat and mass transfer in two-phase He I thermosiphon flow, Advances in Cryogenic7. B. Baudouy, Heat and mass transfer in two phase He I thermosiphon flow, Advances in Cryogenic Engineering 47 B, AIP, Ed. S. Breon, (2001) 1514-1521
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