Challenges and limitations of thermosiphon ... · I in a natural circulation loop, Advances in...

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

2PhB, Symposium for the inauguration of the LHC Cryogenics, CERN, 31/05 & 01/06/2007

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%)


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


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)


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


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)


(∅ 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


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


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


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


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


CMS R&D

h d b h l• Smooth sensitivity near and above the critical point

Pc


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


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.


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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