The document summarizes a study of heat transfer from a circuit board using heat pipes. SINDA/FLUINT software was used to model the system and analyze the transient temperature evolution and effects of parametric variations. The study found that increasing the heat pipes' vaporization or condensation coefficients and heat load lowered the circuit board's hottest temperature, while increasing or decreasing the heat pipes' length increased the hottest temperature.

1. STUDY OF HEAT TRANSFER PROCESS
FROM A CIRCUIT BOARD
USING HEAT PIPES
Authors: Joaquín Capablo, Nelson Garcia-Polanco, John Doyle
nelsongarciapolanco@gmail.con / joaquincapablo@gmail.com
2nd September 2013, Imperial College, London, UK

2. INDEX
1. Project Introduction
2. Studied System with SINDA/FLUINT
3. Results
4. Parametrical Analysis
5. Conclusions
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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3. 1. INTRODUCTION
GREEN KITCHEN PROJECT: Innovative households can help reduce national energy consumption, not
only by improving their energy efficiency, but also by reducing and reusing the waste produced in
terms of heat and water. Marie Curie Action(Industry-Academia Partnerships and Pathways)
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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4. Heat Pipes applications
Efficient transport of concentrated heat
From the space to your kitchen…
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5. Heat Pipes comparison
Effective thermal conductivity of heat pipe with
that of solid copper and solid aluminum rods
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6. Heat Pipes
• Advantages:
-Very high thermal
conductivity
-Accurate temperature
control
-Accurate geometric control
Peterson (1994)
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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7. Studied system
1
2
3
4
Heat Generating Elements
Coin
Heat Spreader
Heat Flow
Heat Pipes
Air Cooled Heat Sink
Air Flow
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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8. 2. STUDIED SYSTEM WITH SINDA/FLUINT
SINDA/FLUINT® (www.crtech.com)
• Software for analysis, design, simulation, and
optimization of systems involving heat transfer and fluid
flow:
–
–
–
–
–
–
–
Aerospace
Energy
Electronics
Automotive
Aircraft
HVAC
Petrochemical industries
• NASA-standard analyzer for thermal control systems:
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9. Basic Overview of SINDA/FLUINT
• MAIN SIMULATORS:
– SINDA: Network-style (circuit analogy) thermal simulator
• Nodes : Temperature points
• Conductors : Heat Flow Routes
– FLUINT: Fluid network capabilities
• Lumps : Thermodynamic points
• Paths : Fluid Flow Passages
• Ties : Heat Flow between Solid and Fluid
Q
R
FR,A
UA
T,C
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
P,T,V
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10. Basic Overview of SINDA/FLUINT
• GRAPHICAL INTERFACE:THERMAL DESKTOP
– Geometric CAD-based style
• Surfaces and solid parts are geometrically modeled.
• Data exchange with CAD and structural software.
• Good performance for analysis requiring radiation calculations,
contact conductances, heat pipes, TEC devices…
– Specific module: FloCAD
• Fluid Flow Analyzer
• Generation of Flow Networks
• Calculation of Heat Transfer Factors
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11. Basic Overview of SINDA/FLUINT
• Thermo-Electric Analogy
V2
V1
Re Rt
T2
T2-T1= Rt*Q
T1
I
≈
V2-V1= Re*I
Q
• Energy Balance to each Node:
QConvection
QRadiation
CS*(dT/dt)=∑QS+QSL+Qext
QConduction
Qext
QS-L
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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12. Basic Overview of SINDA/FLUINT
• Mass Balance to each Lump
MRL2
MRL1
dM/dt= ∑MRL
• Energy Balance to each Lump
QS-L
QL2
QL1
(dEi/dt)=∑QL+QSL
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13. Basic Overview of SINDA/FLUINT
• Basic Flow Data
-Network Description
-Operation Sequence
-Output Procedures
Nodes, Conductors, Lumps…
Steady-State, Transient, Parametric Sweep
What? When?
-Control Parameters
-Concurrent Logic
-User Data
Error Tolerance, Units,…
Initialization, Customizing
Arrays, Spreadsheet
Pre-processing
Fortran Logic
DATA
Spreadsheet Relationships
Compiling
OUTPUTS
Post-processing
PLOTS
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14. Modeling Heat Pipes with SINDA/FLUINT
A Network-based Method to model a Heat Pipe
• Constant Conductance Heat Pipes (CCHPs):
– Used in the aerospace industry for about three decades for supporting
system-level design analysis.
• Extensions possible for modeling:
– CCHPs with Non-Condensible Gas (NCG).
– Variable Conductance Heat Pipes (VCHPs) with NCG reservoirs.
– Planar or Counter-Flow Thermo-Syphons.
• Other methods for modeling:
– Loop Thermo-Syphons (LTSs).
– Loop Heat Pipes (LHPs).
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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15. Modeling Heat Pipes with SINDA/FLUINT
Common Misconceptions when modeling a Heat Pipe
• Full two-phase thermo-hydraulic modeling is required:
– It represents a computational overkill in almost all cases
• Heat pipes can be represented by solid bars of high
thermal conductivity:
– It does not simulate a heat pipes’s length-independent resistance
– It cannot account for difference in film coefficients between
vaporization and condensation
– It does not provide information on power-length product QLeff
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16. Modeling Heat Pipes with SINDA/FLUINT
Typical System-Level Approach
• Network-style conductor fan approach:
– All walls nodes are attached directly via linear
conductances/resistances to a single vapor node.
– The wall nodes represent the liquid/vapor interface along
each axial segment of length.
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17. STUDIED SYSTEM
Heat transfer from a circuit board using heat pipes
Q1=10 W
Q2=20 W
Q3=250 W
Q4=50 W
Heat Sources Max. Power: 330 W
Coin: -3 mm thickness
-Copper
Heat Spreader: - 20 mm thickness
-Aluminum
Heat pipes: -2 Heat Pipes
-Diameter: 10 mm
-Constant conductance (CCHP)
-Negligible non-condensable gas
(NCG)
-Vaporization Coef.: 8.640 W/m2K
-Condensation Coef.: 132.640
W/m2K
Heat Sink: -4 Channels
-Aluminum
-Air flow: 0.05 m3/s
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18. Effect of geometric discretization
• Heat Pipes Grid Refinement: 10 – 320 nodes
Temperature of Element 3
vs.
Heat pipes nodes number
199,0
198,9
198,8
3
T( C)
198,7
198,6
198,5
198,4
198,3
198,2
198,1
198,0
0
50
100
150
200
250
Nodes number
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
300
350
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19. STUDIED SYSTEM
Heat transfer from a circuit board using heat pipes
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20. Results: Evolution of the temperature
• Transient analysis:
200
180
160
T( C)
140
120
100
80
60
Circuit Board hottest point:
-Element 3
40
20
0
10.000
20.000
30.000
40.000
50.000
t(s)
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21. Parametric study
• Analyzed Parameters (in steady state):
– Heat pipes exchange coefficients:
• Vaporization coefficient
• Condensation coefficient
– Heat load:
• Variation of the heat generated by the heat sources.
– Heat pipes configuration
• Variation of the length of the heat pipes
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22. Parametric study (I-II)
• Heat Pipes exchange coefficients
Vaporization Coefficient: 8.640 W/m2K
Condensation Coefficient : 132.640 W/m2K
198
196
196
T( C)
200
198
T( C)
200
194
194
192
192
190
5.000
6.000
7.000
8.000
VapCoeff (W/m2K)
9.000
10.000
190
100.000
110.000
120.000 130.000 140.000 150.000
CondCoeff (W/m2K)
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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23. Parametric study (III)
• Heat Load
Variation of the Heat Generated by the Heat Sources
200
T( C)
190
180
170
160
150
250
270
290
Heat Load (W)
310
330
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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24. Parametric study (IV)
• Heat Pipes Configuration
ΔL/L=7.5%
200,0
199,5
T( C)
199,0
198,5
198,0
197,5
197,0
0,00
0,20
0,40
0,60
0,80
Heat Pipes Length Variation
1,00
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25. Conclusions
• Temperature distribution and energy transfer
from a circuit board using heat pipes
• Transient Analysis of the studied system
• Parametric Study:
– Vaporization Coefficient
– Condensation Coefficient
– Heat Generated by the Heat Sources
– Heat Pipes Configuration
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