Study of Heat Transfer Process using Heat Pipes
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Transcript of Study of Heat Transfer Process using Heat Pipes
Authors: Joaquín Capablo, Nelson Garcia-Polanco, John Doyle
[email protected] / [email protected]
2nd September 2013, Imperial College, London, UK
STUDY OF HEAT TRANSFER PROCESS FROM A CIRCUIT BOARD
USING HEAT PIPES
INDEX1. Project Introduction2. Studied System with SINDA/FLUINT3. Results4. Parametrical Analysis5. Conclusions
213th UK Heat Transfer Conference, September 2-3, 2013, London – UK
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK 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)
Heat Pipes applications
413th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Efficient transport of concentrated heat
From the space to your kitchen…
Heat Pipes comparison
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Effective thermal conductivity of heat pipe with that of solid copper and solid aluminum rods
Heat Pipes
• Advantages:-Very high thermal conductivity
-Accurate temperature control
-Accurate geometric control
Peterson (1994)
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Studied system
713th UK Heat Transfer Conference, September 2-3, 2013, London – UK
1 2 3 4 Heat Generating Elements
Coin
Heat Pipes
Heat Spreader
Air Cooled Heat Sink
Heat Flow
Air Flow
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: 813th UK Heat Transfer Conference, September 2-3, 2013, London – UK
2. STUDIED SYSTEM WITH SINDA/FLUINT
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
T,C
FR,A
P,T,V
UA
R
913th UK Heat Transfer Conference, September 2-3, 2013, London – UK
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
1013th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Basic Overview of SINDA/FLUINT
• Thermo-Electric Analogy
• Energy Balance to each Node:
T2-T1= Rt*Q
CS*(dT/dt)=∑QS+QSL+Qext
QS-L
QRadiationQConvection
QConduction
Qext
T2 T1
Rt
Q
V2-V1= Re*IV2 V1
I
Re
≈
1113th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Basic Overview of SINDA/FLUINT
• Mass Balance to each Lump
• Energy Balance to each Lump
(dEi/dt)=∑QL+QSL
QS-L
QL1QL2
dM/dt= ∑MRLMRL1MRL2
1213th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Pre-processing
Fortran Logic Spreadsheet Relationships
Compiling
Post-processing
PLOTS
-Control ParametersError Tolerance, Units,…
-Output ProceduresWhat? When?
-Concurrent LogicInitialization, Customizing
-Network DescriptionNodes, Conductors, Lumps…
-User DataArrays, Spreadsheet
-Operation SequenceSteady-State, Transient, Parametric Sweep
• Basic Flow Data
DATA
OUTPUTS
1313th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Basic Overview of SINDA/FLUINT
A Network-based Method to model a Heat Pipe
14
Modeling Heat Pipes with SINDA/FLUINT
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
• 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).
Common Misconceptions when modeling a Heat Pipe
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• 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
Modeling Heat Pipes with SINDA/FLUINT
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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.
Modeling Heat Pipes with SINDA/FLUINT
Heat transfer from a circuit board using heat pipes
17
STUDIED SYSTEM
13th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Heat Sources Max. Power: 330 WCoin: -3 mm thickness
-CopperHeat Spreader: - 20 mm thickness
-AluminumHeat 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
Q1=10 W
Q2=20 W
Q3=250 W
Q4=50 W
• Heat Pipes Grid Refinement: 10 – 320 nodes
Effect of geometric discretization
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Temperature of Element 3
vs.
Heat pipes nodes number
3
198,0
198,1
198,2
198,3
198,4
198,5
198,6
198,7
198,8
198,9
199,0
0 50 100 150 200 250 300 350
T(�C
)
Nodes number
Heat transfer from a circuit board using heat pipes
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STUDIED SYSTEM
• Transient analysis:
Results: Evolution of the temperature
20
40
60
80
100
120
140
160
180
200
0 10.000 20.000 30.000 40.000 50.000
T(�C
)
t(s)
2013th UK Heat Transfer Conference, September 2-3, 2013, London – UK
Circuit Board hottest point: -Element 3
• 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
Parametric study
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• Heat Pipes exchange coefficients
Parametric study (I-II)
190
192
194
196
198
200
5.000 6.000 7.000 8.000 9.000 10.000
T(�C
)
VapCoeff (W/m2K)
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190
192
194
196
198
200
100.000 110.000 120.000 130.000 140.000 150.000
T(�C
)
CondCoeff (W/m2K)
Condensation Coefficient : 132.640 W/m2KVaporization Coefficient: 8.640 W/m2K
150
160
170
180
190
200
250 270 290 310 330
T(�C
)
Heat Load (W)
• Heat Load
Parametric study (III)
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Variation of the Heat Generated by the Heat Sources
• Heat Pipes Configuration
Parametric study (IV)
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197,0
197,5
198,0
198,5
199,0
199,5
200,0
0,00 0,20 0,40 0,60 0,80 1,00
T(�C
)
Heat Pipes Length Variation
ΔL/L=7.5%
• 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
Conclusions
2513th UK Heat Transfer Conference, September 2-3, 2013, London – UK