Post on 15-Jan-2016
Dimensioning of CO2 cooling pipes in
detector structures
Pipe dimensioning&
Flow distribution
Detector Mechanics Forum Oxford, 20 June 2013
Bart Verlaat 1
Thermal chain in detectors
• The design of the cooling is the whole chain between heat source and heat sink
2
Heatload
Silicon C-foam Pipe wallCO2 in tube ManifoldCF-sheet
Th. p
aste
Glu
e
Glu
e
HTC
ΔP
Typical example for IBL
Thermal chain in detectors
• The design of the cooling is the whole chain between heat source and heat sink
3
Heatload
Silicon C-foam Pipe wallCO2 in tube ManifoldCF-sheet
Th. p
aste
Glu
e
Glu
e
HTC
ΔP
Load variations give gradients w.r.t the common sink => Outlet manifold!
Typical example for IBL
0 5 10 15 20 25-2
0
2
4
6
8
10
12
14
16
IBL temperature and pressure profile. MF=0.8g/s, Tsp=-40ºC, Q=101.8, xend
=0.41
Branch length (m)
Del
ta T
(`C
) &
Del
ta P
(Bar
)
1 2 3 4 56 78 9 10 11 12
Stave TFoM: 13ºC*cm2/W
Pixel maximum temperature:
-24.4ºC
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
dT Pixel Chip (ºC)
Design of cooling: From source to sink
• So the reference should not be at a pipe wall, nor at the liquid temperature as it is generally approached. – This is similar then taking a reference in the middle of the
structure.
4
Pressure drop ~20%
Heat transfer ~ 19%
Stave conductance ~61%
Loaded stave temperature: -24.4°C(0.72 W/cm2)
Unloaded stave temperature: -39°C
Atlas IBL example
Outlet Manifold = temperature reference
Inlet manifold
How to optimize the cooling as part of the whole thermal chain?
• The best thermal solution is not only related to small temperature gradients.– If so our detectors will be made of copper…– We have to find the balance between the important parameters
• Generally thermal gradients vs mass (rad. Length)
• How can we find the optimum cooling tube dimension?– Depends on the real criteria:
• Lowest mass (Radiation length)?• Smallest pipe?• Minimum amount of pipes?
– We should not only look at the pipe but also at the structure around• A smaller cooling tube is replaced by other material, when embedded.
• Where do we have to look at:– Pressure drop and heat transfer
• As part of the thermal chain
– Flow distribution• For the proper fluid conditions
5
6
First we need to understand what happens inside a cooling tube?
Heating a flow from liquid to gas
Super heated vaporSub cooled liquid 2-phase liquid / vapor
Enthalpy (J / kg)
Pres
sure
(Bar
)
Dry-out zoneTarget flow condition
Tem
pera
ture
(°C)
Low ΔT
- 30
0
30
60
90
Liquid
2- phase
Gas
I sotherm
Increasing ΔT (Dry-out)
Liquid Superheating
Understanding detector evaporator tubes
• In a 2PACL the capillary inlet temperature is a function of the outlet saturation pressure.
• The detector inlet is close to saturation.– But can be liquid due to pressure drop– Usually ambient heating is enough to
overcome sub cooled entry state– Detectors with high dP have to be designed
to cope with liquid at the inlet • FE: pre heating by electronics (CMS pixel)
• Pressure drop of the evaporator tube and outlet tube is part of the thermal resistance chain from heat source to sink!
7
2m4m
Liquid
2-phase
Heat exchanger Inlet capillaries
Outlet tubes
Manifolds
Detector staves
Outlet manifold: Pressure = fixed
Inlet manifold:
Temperature = fixed
Gas
Pre
ssu
re
Isothermal line
Enthalpy
Liquid
2-phase(Evaporation)
Temperature exchange
Outlet line dP
Detector dP
Inlet capillary dP
Inlet manifold
outlet manifold
Long branch thermal profile
2m4m
Liquid
2-phase
Heat exchanger Inlet capillaries
Outlet tubes
Manifolds
Detector staves
Outlet tubeInlet tube Evaporator tube
Offset of evaporator temperature due to outlet pressure drop
Temperature gradient inside detector due to pressure drop and heat transfer
Liquid 2-Phase
Manifold temperature = common reference of all branches
HTC
dP
Liquid entry into evaporator
Inlet: 2mm x 4m, Detector: 2mm x 4m, Outlet: 2mm x 4mHeatload on detector: 200 Watt
Flow distribution:Inlet tube reduction
9
50 W100 W
150 W
200 W
250 W
300 W
50 W100 W
150 W
200 W
250 W
300 W
1.16
g/s
1.61
g/s
1.16
g/s
3.75
g/s
1.15 bar
2.18 bar
2.52 bar
3.54 bar
Dry-out zone Dry-out zone
Figures from: DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO2 COOLING LINESBart Verlaat and Joao Noite, GL-209, 10th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids, Delft, The Netherlands 2012
2m4m
Liquid
2-phase
Heat exchanger Inlet capillaries
Outlet tubes
Manifolds
Detector staves
Inlet: 2mm x 4mStave: 2mm x 4mOutlet: 2mm x 4m
Inlet: 1mm x 4mStave: 2mm x 4mOutlet: 2mm x 4m
Pumping energy is flow x dP. Adding capillaries can save pumping power (in example 1.61*3.54/2.18*3.75=0.70 => 30% saving)
Pressure drop and dry-out calculated using CoBra
Which flow do we need when 200 Watt to a single stave is applied?
Influence of the in and outlet-lines on thermal performance
10
2m4m
Liquid
2-phase
Heat exchanger Inlet capillaries
Outlet tubes
Manifolds
Detector staves
0 2 4 6 8 10 12-1
0
1
2
3
4
5
IBL temperature and pressure profile. MF=1.61g/s, Tsp=0ºC, Q=200, xend
=0.53
Branch length (m)
Del
ta T
(`C
) & D
elta
P(B
ar)
1 2 3 4
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
0 2 4 6 8 10 12-1
0
1
2
3
4
5
IBL temperature and pressure profile. MF=3.75g/s, Tsp=0ºC, Q=200, xend
=0.22
Branch length (m)
Del
ta T
(`C
) & D
elta
P(B
ar)
1 2 3 4
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
0 2 4 6 8 10 12-1
0
1
2
3
4
5
2mmID x 5m tube temperature and pressure profile. MF=1.61g/s, Tsp=0ºC, Q=200, xend
=0.54
Branch length (m)D
elta
T (`
C) &
Del
ta P
(Bar
)
1 2 3 4
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
Figures from: DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO2 COOLING LINESBart Verlaat and Joao Noite, GL-209, 10th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids, Delft, The Netherlands 2012
Inlet: 2mm x 4mStave: 2mm x 4mOutlet: 2mm x 4m
Inlet: 1mm x 4mStave: 2mm x 4mOutlet: 2mm x 4m
Inlet: 1mm x 4mStave: 2mm x 4mOutlet: 3mm x 4m
Dealing with environmental heat pick-up
• Three important statements: – Expose return tube to ambient heating
• There is usually enough cooling power left
– Connect as much as possible the inlet to the outlet• Outlet boils first (lower P), so will take care of heat absorption
– Avoid boiling before the inlet manifold• Flow separation will feed some channels with vapor only!
11
Gas
Pre
ssu
re
Isothermal line
Enthalpy
Liquid
2-phase(Evaporation)
Pre capillary heat pickup
Inlet manifold
outlet manifold
Gas
Pre
ssu
re
Isothermal line
Enthalpy
Liquid
2-phase(Evaporation)
Manifold boiling
Outlet transfer line
outlet manifold
Outlet transfer line
Capillary dP makes manifold liquid
To keep this problem simple: Have the manifold right after the heat exchanging transfer line.
Remaining cooling power for ambient
0 5 10 15 20 25-2
0
2
4
6
8
10
12
14
16
IBL temperature and pressure profile. MF=0.8g/s, Tsp=-40ºC, Q=101.8, xend
=0.41
Branch length (m)
Del
ta T
(`C
) &
Del
ta P
(Bar
)
1 2 3 4 56 78 9 10 11 12
Stave TFoM: 13ºC*cm2/W
Pixel maximum temperature:
-24.4ºC
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
dT Pixel Chip (ºC)
IBL: A detector with very long in and outlet lines
• The IBL detector is only 800mm long, but has about 15m long in and outlets.• dT due outlet line pressure drop significantly (ca 3ºC)• Ambient heat load in same order as detector load
12
Atlas IBL example
Ambient heating
Heat exchange
Inlet Outlet
IBL
2
49
6 7
12
Ambient
Cooling tube temperature profile (HTC & ΔP)
• In detectors the aim of a cooling tube design is:– Low mass or small diameter– Low temperature gradient (hottest point wrt outlet reference)
• For efficient heat transfer: – ΔT(ΔP+HTC) and tube diameter or mass as small as possible
• To quantify the optimal diameter we can look either to the mass or tube volume involved
13
ΔT(ΔP)
ΔT(ΔP)(Reduced diameter) ΔT(HTC)
(Reduced diameter)
ΔT(HTC)
ΔT(ΔP+HTC)(Reduced diameter)
ΔT(ΔP+HTC)
Tube length
Tem
pera
ture
Fluid temperature
Tube temperature
Vtube*ΔT(ΔP+HTC))
QVolumetric heat transfer =(W/m3*K)
M*ΔT(ΔP+HTC))
QMass specific heat transfer =(W/kg*K)
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50
2
4
6
8
10
12
14
Diameter (mm)
Tem
pera
ture
Gra
dien
t (ºC
)V
olum
etric
hea
t tra
nsfe
r (W
/cm
2 K)
Volumetric heat
transfer coefficient
Optimal Diameter?
Overall temperature gradient
Heat transfer temperature gradient
Pressure drop temperature gradient
Cooling tube performance example
L=3m, Q=400W, T=-20°C
Models used: HTC and dP, Thome 2008
Comparison of fluids
• Volumetric heat transfer is also a good method to compare different fluids.– How can we put as much heat into a small as possible cooling tube??
• Interesting: Performance almost linear with fluid pressure. 15
0 1 2 3 4 5 6 7 8 9 100
0.002
0.004
0.006
0.008
0.01
0.012
0.014
Tube diameter (mm)
Vol
umet
ric h
eat
tran
sfer
con
duct
ion
(W/m
m3 K
)
Overall volumetric heat transfer conductionL=3 m, Q=400 W, T=-20 °C, VQ=0.35
CO2 (19.7 bar)
Ethane (14.2 bar)
C2F
6 (10.5 bar)
Propane (2.4 bar)
C3F
8 (2 bar)
Ammonia (1.9 bar)R134a (1.3 bar)
0 1 2 3 4 5 6 7 8 9 100
20
40
60
80
100
120
140
160
180
Tube diameter (mm)
Hea
t tr
ansf
er c
ondu
ctio
n (W
/K)
Heat transfer conductionL=3 m, Q=400 W, T=-20 °C, VQ=0.35
CO2 (19.7 bar)
Ethane (14.2 bar)
C2F
6 (10.5 bar)
Propane (2.4 bar)
C3F
8 (2 bar)
Ammonia (1.9 bar)R134a (1.3 bar)
Models used: HTC-Kandlikar and dP-Friedel
“Drawback” of smaller pipes
• In an embedded structure the smaller pipe is replaced by other material. – ‘Heavy” pipe has a lower weight, but light vapor is also replaced by
“something” • The bottleneck in most cooling structures is the glue layer around the
pipe.– Small area– Bad conductance
• Better to judge the whole thermal chain from a fixed volume
16What is now an optimal pipe diameter?
D=10mmD=10mm
Mass related results
(Same case as previous)• Calculation with IBL-like properties:
– T_tube=0.1 mm– T_glue=0.1 mm– k_tube=7.2 W/mk– k_foam=35 W/mk– k_glue=1.02 W/mk– d_glue=2400 kg/m3– d_foam=198 kg/m3– d_tube=4400; kg/m3
170 1 2 3 4 5 6 7 8 9 100
0.05
0.1
Tube diameter (mm)
Mas
s (k
g)
Mass contributionL=3 m, Q=400 W, T=-20 °C, VQ=0-0.35
mtotal
mfoam
mglue
mtube
mf luid
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
9
10
Tube diameter (mm)
Tem
pera
ture
gra
dien
t (`
C)
Temperature gradient contributionL=3 m, Q=400 W, T=-20 °C, VQ=0-0.35
dTtotal
dTfoam
dTglue
dTtube
dThtc
dTdp
0 1 2 3 4 5 6 7 8 9 100
500
1000
1500
Tube diameter (mm)
Hea
t tr
ansf
er (
W/k
g*K
)
Mass relative heat transfer (dP & HTC) L=3 m, Q=400 W, T=-20 °C, VQ=0-0.35
CO2 (19.7 bar)
Recalculating the IBL
• Selected IBL tube is 1.5mm => good choice!
• Next to do: Make similar analyses wrt radiation length
18
0 1 2 3 4 5 6 7 8 9 100
200
400
600
800
1000
Tube diameter (mm)
Hea
t tr
ansf
er (
W/k
g*K
)
Mass relative heat transfer (dP & HTC) L=0.8 m, Q=70 W, T=-40 °C, VQ=0-0.35
CO2 (10 bar)
0 1 2 3 4 5 6 7 8 9 100
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
Tube diameter (mm)
Mas
s (k
g)
Mass contributionL=0.8 m, Q=70 W, T=-40 °C, VQ=0-0.35
mtotal
mfoam
mglue
mtube
mf luid
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
9
10
Tube diameter (mm)
Tem
pera
ture
gra
dien
t (`
C)
Temperature gradient contributionL=0.8 m, Q=70 W, T=-40 °C, VQ=0-0.35
dTtotal
dTfoam
dTglue
dTtube
dThtc
dTdp
1.5mm
1.5mm
CO2 heat transfer and pressure drop modeling
• Nowadays good prediction models of CO2 are available.
• For detector analyzes we use mainly the models of J. Thome from EPFL Lausanne (Switzerland)– Cheng L, Ribatski G, Quiben J, Thome J, 2008,”New prediction methods for CO2 evaporation inside
tubes: Part I – A two-phase flow pattern map and a flow pattern based phenomenological model for two-phase flow frictional pressure drops”, International Journal of Heat and Mass Transfer, vol 51, p111-124
– Cheng L, Ribatski G, Thome J, 2008,”New prediction methods for CO2 evaporation inside tubes: Part II– An updated general flow boiling heat transfer model based on flow patterns”, International Journal of Heat and Mass Transfer, vol 51, p111-124
• Models are flow pattern based and are reasonably well predicting the flow conditions and the related heat transfer and pressure drop. Dry-out prediction is included.
• The Thome models are successfully used to predict the complex thermal behavior of particle detector cooling circuits.
• A simulation program called CoBra is under development at Nikhef/CERN-DT to analyze full detector cooling branches.
19
Experimental heat transfer data (measured at SLAC)
20
Interesting research on heat transfer is done at SLAC in a joint effort with Nikhef.M. Oriunno (SLAC) & G. Hemmink (Nikhef)
CoBra Model(CO2 BRAnch Model)
21
R1x
R2x
R3x
R5x R2y+1
R3y+1
R4x R4y+1
R1y+1
R1X+1R2X+1
R3X+!
R5X+1 R2y
R3y
R4X+1 R4y
R1y
Px+1,Hx+1,Tx+1
Px,HxTx
Py+1,Hy+1,Ty+1
Py,Hy,,Ty
T2
3
4
1
Px+1=dPx+1+Px
Hx+1=dHx+1+Hx
dH=Q1/MFQ1 is calculated in the thermal network
2
3
4
The thermal node network calculates the heat influx in the cooling pipe based on:• Applied power Q3 on node 3• Environmental heating from fixed temperature T4 on node 4• Heat exchange with another pipe section via R5 between nodes 2 and 2 of the connected
sections
CoBra example calculation
• CoBra is able to analyze complex thermal profiles of CO2 in long tubes
22
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1
0
1
2
3
4
5
6
7
2mmID x 5m tube temperature and pressure profile. MF=0.3g/s, Tsp=-30ºC, Q=90, xend
=0.99
Branch length (m)
Delta T
(`C
) &
Delta P
(Bar)
1 2 3 4
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
50
100
150
200
250
300
350
5mx1.5mmID tube (4m heated), Mass flow=0.3g/s, Q=90Watt , T=-30ºC
Dry-out
Mist
Annular
Stratified Wavy
Stratified
Bub
bly
Slu
g
Process path
Dry-out
Liqu
id
Slug
Annular
Cobra example:Node network for IBL
23
Tenvironement
R4≈ HTCair
R2 +R3 ≈ TFoM
R1 ≈ HTCCO2
TCO2
Tenvironement
TCO2 TCO2
R4 +R3 ≈ Insulation+HTCair
R5≈ Heat exchange
R1≈ HTCCO2
R2 ≈ Tube wall
Q3 ≈ Applied power
Tenvironement
TCO2
R4 +R3 ≈ HTCairR1≈ HTCCO2
R2 ≈ Tube wall
Tenvironement
TCO2
R1≈ HTCCO2
R2 ≈ Tube wall
TCO2
R1b≈ HTCCO2
R1a≈ HTCCO2
R4 +R3 ≈ Insulation+HTCair
1. Concentric line
3. Bare tube
2. Bundled lines
4. Stave
Internal heat exchange and ambient heating
24
Figure 7: CoBra calculation example of the IBL cooling tube. The branch has a 1mm inlet (1-4), a 1.5 mm cooling tube (4-8), a 2mm outlet (8-9) followed by a 3mm outlet (9-12). The dashed temperature profile is the actual sensor temperature taking into account the conductance of the support structure. The graph on the left has no internal heat exchange, the right graph takes internal heat exchange of the in and outlet tube into account.
0 5 10 15 20 25-2
0
2
4
6
8
10
12
14
16
IBL temperature and pressure profile. MF=0.8g/s, Tsp=-40ºC, Q=101.8, xend
=0.41
Branch length (m)D
elta
T (
`C)
& D
elta
P(B
ar)
1 2 3 4 56 78 9 10 11 12
Stave TFoM: 13ºC*cm2/W
Pixel maximum temperature:
-24.4ºC
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
dT Pixel Chip (ºC)
0 5 10 15 20 25-2
0
2
4
6
8
10
12
14
16
IBL temperature and pressure profile. MF=0.8g/s, Tsp=-40ºC, Q=101.8, xend
=0.5
Branch length (m)
Del
ta T
(`C
) &
Del
ta P
(Bar
)
1 2 3 4 56 78 9 10 11 12
Stave TFoM: 13ºC*cm2/W
Pixel maximum temperature:
-24.2ºC
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
dT Pixel Chip (ºC)
CapillaryNo Boiling
Boiling starts
Boiling starts
Figures from: DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO2 COOLING LINESBart Verlaat and Joao Noite, GL-209, 10th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids, Delft, The Netherlands 2012
Comparison to test results
25
Figure 8: Temperature and pressure test results of the CMS pixel upgrade cooling branch (left) and the Atlas IBL cooling branch (right). Comparison with the CoBra calculator showed that the calculator is a promising tool for predicting the temperature and pressure gradients over long length cooling branches.
0 5 10 15 20 25-1
0
1
2
3
4
5
6
7
8
9
IBL temperature and pressure profile. MF=1.1g/s, Tsp=-26.71ºC, Q=73.5, xend
=0.36
Branch length (m)D
elta
T (
`C)
& D
elta
P(B
ar)
12 3 4 56 78 9 10 1112
dT Tube wall (ºC)
dT Fluid (ºC)dP Fluid (Bar)
0 5 10 15-20
-18
-16
-14
-12
-10
-8
-6
Loop Length [m]
Tem
pera
ture
[°C
]
m = 1.48g/s | Qtotal
= 256.87W | Pin
= 26.40Bar | Tin
= -17.40°C | dP = 6.33Bar | dT = 10.86°C
0 5 10 1520
21
22
23
24
25
26
27
Pre
ssur
e [B
ar]
Exp. Wall Temperature
Theory Wall TemperatureTheory CO
2 Temperature
Theory CO2 Pressure
CMS detector (1.4mm)El
ectr
onic
s (1.
8mm
)
Inle
t tub
e (1
.8m
m)
Out
let t
ube
(1.8
mm
)Inlet tube
(1mm)
Outlet tube(3mm)O
utle
t tub
e (2
mm
)
Detector(1.5mm)
CMS-B-PIX Atlas-IBL
Figures from: DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO2 COOLING LINESBart Verlaat and Joao Noite, GL-209, 10th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids, Delft, The Netherlands 2012
Cooling development philosophy
• Whatever the model give as a result: – Don’t trust them! the
models are empirical.– Use them as a design
guideline.• Always verify in a test!
– Not only to quantify heat transfer, but as well to filter out strange behavior
26
0 2 4 6 8 10 12 14-20
-18.4
-16.8
-15.2
-13.6
-12
Length [m]
Tem
pera
ture
[°C
]
Test 1 | m = 2.94g/s | Qtotal
= 159.30W | dP = 17.77Bar | dT = 4.20°C
dTexp
=6.55°C
dPexp
=20.41bar
0 2 4 6 8 10 12 1419
23.4
27.8
32.2
36.6
41
Pre
ssur
e [B
ar]
Exp. Wall Temperature
Theory Wall Temperature
Theory CO2 Temperature
Exp. CO2 Pressure
Theory CO2 Pressure
Strange start-up behavior in the Velo
• In the Velo the CO2 does not always start boiling.
• It turned out that our bright idea of increasing the tube length wasn’t so brilliant after all.
27
18:00 18:30 19:00 19:30 20:00 20:30 21:00-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
0
4
8
12
16
20
24
28
32
36
40
44
48
52
Hea
tload
(W
)
Tem
pera
ture
(°C
), S
trok
e (m
m)
Time (hh:mm)02-Oct-2009
Pump stroke (mm) Evaporator saturation temperature (°C) Evaporator 12 begin temperature (°C) Evaporator 12 end temperature (°C) Evaporator 27 begin temperature (°C) Evaporator 27 end temperature (°C)
Tube length
At startup everything is liquid
1. The outlet starts to boil2. The good boiling heat transfer
is taking heat away from the inlet
3. As a result boiling at the inlet is suppressed.
4. Once boiling is achieved it will not go back to the liquid state
Fluid temp.
Tube wall temp.
Tem
pera
ture
Conclusions
• The common temperature boundaries of all parallel systems are:– The pressure (=saturation temperature) in the outlet manifold.– The temperature / enthalpy of the liquid in the inlet manifold.– Normally both temperatures are the same.
• Parallel channels need flow distribution by increasing the inlet pressure drop
• The in let manifold must be sub-cooled liquid.
• Overall performance of the thermal system includes:– Conductive path in detector structure– Heat transfer to the evaporative liquid– Pressure drop in evaporator and outlet tube.– Full thermal path must be considered in the design optimization
• Always verify your models with tests. 2-phase flow has sometimes strange behavior
• Avoid tube crosstalk, boiling in 1 channel can suppress boiling in the other28
Things to keep in mind when designing CO2 cooling loops: