This document describes a conjugate heat transfer analysis of an electronics cooling system using OpenFOAM. It outlines the objectives to develop a CFD model for CHT analysis and validate it with experiments. The methodology section describes the governing equations solved for fluid and solid regions as well as the interface coupling. A simple circuit board cooling case is modeled and tested. Additionally, a server cooling case is proposed with details on geometry, meshing, boundary conditions and results showing temperature distributions.

1. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Conjugate Heat Transfer for Electronic Cooling
using OpenFOAM
Avinash Valiba Gorde(CMS-1310)
Internal Guide
Dr. Sukratu Barve
Dr. Mihir Arjunwadkar
Centre for Modelling and Simulation
External Guide
Dr. Vikas Kumar
Mr. Mohan Labade
Centre for Development of Advanced Computing Pune,INDIA
June 20, 2015

2. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Outline
1 Need of Project
2 Objectives
3 Methodology
4 CHT Case in OpenFOAM
5 Server Case
6 Preprocessing
7 Results
8 Conclusion
9 Future Scope
10 References

3. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Need of Project
Considering following aspect,
A very limited conjugate heat transfer case studies have been
analyzed using OpenFOAM.

4. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Objectives
To develop a CFD model for conjugate heat transfer analysis
of an electronics cooling system
Validation of CFD model with experimental results

5. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Methodology
Conjugate Heat Transfer
In CHT computational domain is divided into fluid and solid
regions. The NaviereStokes equations and the energy equation in
the fluid regions are solved first. Then the heat transfer equation
in the solid regions is solved.
Figure : Conjugate Heat Transfer

6. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Steady state heat transfer
Steady state conditions the temperature within the system does
not change with time.
Steady State Equation for Solid
− · (κ T) = Sh (1)
Unsteady state heat transfer
Unsteady state conditions the temperature within the system
changes with time.
Unsteady State Equation for Solid
ρCp
∂T
∂t
= · (κ T) + Sh (2)

7. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Solver
chtMutiRegionSimpleFoam Solver
It is steady state solver for conjugate heat transfer. It is
combination of heatConductionFoam and buoyantFoam for
conjugate heat transfer
Governing Equation Used by OpenFoam
chtMultiregionSimpleFoam Solver
Continuity Equation
∂ρ
∂t
+
−→
· (ρ−→u ) = 0 (3)

8. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Momentum Equation
The sum of all forces acting on a body is equal to the rate of
change of momentum of it
1) Body forces = gravitational, centrifugal
2)Surface forces acting on the surface of the body e.g. pressure or
viscous forces
∂ (ρu)
∂t
+ · (ρuu) = − p + · τ − ρg (4)
Energy Equation
∂(ρE)
∂t
+ · (ρuE) = · (α e) − · [u (p − ρgr)] + Sh (5)
α =
µCp
κ is the thermal diffusivity.
Sh is the thermal source term.
e is the specific internal energy.
E is the specific total energy of the gas defined as:
E = e + u2
2

9. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Equation in solid region
∂ (ρh)
∂t
= · (α h) + Sh (6)
α =
µCp
κ is the thermal diffusivity.
Sh is the heat source term.
h is the sensilbe enthalpy.

10. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Coupling at the solid-fluid interface
Tw =
ks
δxs
Ts
kf
δxf
+ ks
δxs
+ (1 − k) Tf +
Tref
δxf
=
kf
δxf
Tf + ks
δxs
Ts
kf
δxf
+ ks
δxs
(7)
Tf and Ts are the temperatures of the fluid and solid regions
kf and ks are the heat conductivities of the fluid and solid
Tref is a reference temperature
δxf and δxs are the distances between the cell centers
Figure : Interface Temp

11. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
CHT Case in OpenFOAM
Geometry For Simple Circuit Board Cooling
Figure : Simple cht case

12. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Meshing For Simple Circuit Board Cooling
Figure : Simple cht case

13. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Implementation of Heat Source
Heat source
In src/fvOptions/lnInclude
const dimensionSet ds =
rho.dimensions()*fld.dimensions()/dimTime*dimVolume;
ds = ρ * h/time * volume
ds = kg/m3 * J/(kg * S) * m3
ds = W (watt)
tmp <fvMatrix<Type > >tmtx(new fvMatrix < Type >(fld, ds));
h (200 0);

14. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Boundary Conditions
Solid Region
Initial Temperature=300K.
Wall is zeroGradient.
Heat Source 200 Watt (4 IC’s).
Interface between solid(IC), fluid(AIR) Mixed B.C.
Fluid Region
Velocity v=0.3m/s.
p = atmospheric.
Initial Temperature (T) = 299K.
Inlet=fixed Value Outlet=inletOutlet for Velocity &
Temperature.
Walls maintained at symmetry, zeroGradient.
Interfaces between solid and fluid = Mixed B.C.

15. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Temperature contour at mid plane
Figure : Temperature variation in solid along xaxis

16. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
300
320
340
360
380
400
420
0 0.2 0.4 0.6 0.8 1 1.2 1.4
TemperatureinKelvin
Distance along X-axis
'100_watt.csv' u 8:2
'200_watt.csv' u 8:2
Figure : Temperature Distribution

17. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Server Case

18. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Server Case
Geometry of Server
This is Intel Server Board S2600GZ/GL having 2 SOCKETS, 24
RAMS, PCB, 2SMPS

19. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Generalized geometry of Server
Figure : Generalized model of server

20. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Sink of Socket
High Thermal conductivity, larger surface area
Low thermal resistance
Material Aluminium, Copper
Air can be easily flow through it
Figure : Sink of Socket

21. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Meshing
For server create 3 blocks specifying coordinates of each point.
Dimensions are L=0.46m Zaxis, W=0.41m Xaxis, H=0.09m Yaxis
it is structured mesh
Figure : blockMesh for Server

22. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
topoSet
topoSet utility is use to create different domain inside the mesh
block.
Figure : blockMesh for Server

23. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Turbulance Model
RNG κ − turbulence model
Useful for rapidly strains flows, Heat and mass transfer
Low Reynold number effect
Standard κ − model for high reynolds number
Turbulent Kinetic Energy (k)
∂ (ρk)
∂t
+
∂ (ρkui )
∂xi
=
∂
∂xj
αk µeff +
∂k
∂xj
+ Gk + Gb − ρ − Ym + Sk (8)
Dissipation rate ( )
∂ (ρ )
∂t
+
∂ (ρ ui )
∂xi
=
∂
∂xj
αk µeff +
∂
∂xj
+ C1
k
(Gk + C3 Gb) − C2ρ
2
k
− R + S (9)
The coefficient updated each iteration
C
∗
1 = c1 −
η 1 − η
η0
1 + βη3
(10)
η =
k
τij τij (11)

24. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Table : Constant values for turbulence model
C1 C2 C3 Cµ η β σk σ
1.42 1.68 -0.33 0.085 4.38 0.012 0.7194 0.7194

25. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Boundary Conditions
Solid Region
Initial Temperature=299K.
Walls zeroGradient.
Heat Source :- 103 Watt (2 sockets), 4 Watt (on 1, 4, 9, 12,
13, 14, 16, 21, 24 ).
Interface between solid(SOCKETs, RAMs), fluid(AIR) Mixed
B.C.
Fluid Region
Velocity v=2.1m/s.
p = atmospheric.
Initial Temperature (T) = 299K.
Inlet=fixed Value Outlet=inletOutlet for Velocity &
Temperature.
Walls maintained at symmetry, zeroGradient.
Interfaces between solid and fluid = Mixed B.C.

26. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Solid Thermophysical Properties
Table : Solid thermophysical properties
Solid name κ(W/mK) Cp(J/kgK) rho(kg/m3) Material
SOCKET 1 & 2 124 702 2325 Silicon
SINK 1 & 2 220 903 2700 Aluminium
RAM 124 702 2325 Silicon
SMPS 1 & 2 53 450 8000 Steel
BOX 1 & 2 53 450 8000 Steel
FLAPPER 53 450 8000 Steel
BOARD 0.02 1800 1500 FR4

27. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Table : Fluid(AIR) thermophysical properties
Parameter value
Cp (J/kg K) 1000
µ 1.8e−05
Pr 0.7

28. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Results
Temperature Contours
Figure : Temperature distrubution in Server

29. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Temperature along Heat Sink
coordinates are (0.1 0.02 0.28) and (0.1 0.02 0.360)
298
300
302
304
306
308
310
312
314
316
318
320
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
TemperatureinKelvin
distace along z-axis
SinkTemp betn fins
Figure : Temp. distrubution of fin along z-direction

30. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Temperature between fin passage
coordinates are (0.06 0.02 0.332) & (0.19 0.02 0.0332)
298
300
302
304
306
308
310
312
314
316
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
Temp.inKelvin
distace along x-axis
HeatsinkTemp
Figure : Temp. distrubution of fin along x-direction

31. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Temperature Variation of RAMs & SOCKETs
coordinates are (0.095 0.0075 0) & (0.09 0.0075 0.46)
295
300
305
310
315
320
325
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Temp.inKelvin
distace along z-axis
SOCKET & RAM Temp
Figure : Temperature distribution along z-direction

32. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Comparision with experimental results
Comparision of Sockets & Rams Temperature obtained from cfd
model & experiment
Table : Comparision of Socket & Ram Temp(K)
Region OpenFOAM Result Experimental Result
SOCKET 319.838 318
RAM 301.43 303

33. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Error in Results
The % error in Sockets & Rams Temperature :
%error =
Resultexp − Resultcfd
Resultcfd
∗ 100 (12)
Sockets Temperature % error
%error =
318 − 319.838
319.838
∗ 100 = 0.57% (13)
Rams Temperature % error
%error =
303 − 301.43
301.43
∗ 100 = 0.52% (14)

34. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Conclusion
Results obtained from cfd model are good, as compared to
experimental results.
This CFD results gives three dimensional temperature
distribution in server components such as RAMs, SOCKETs,
BOARD
The % error in Sockets temperature is 0.57 % and Rams
temperature is 0.52 %

35. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Future Scope
To implement Fan boundary condition for mass flow rate
To implement micro thickness baffle for sink region

36. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
References
ANSYS.
Fluent 6.3 users guide.
www.sharcnet.ca/Software/Fluent6/html/ug/node479.htm.
Yunus A. Cengel.
Heat Transfer A Practical Approach.
McGraw-Hill, forth edition, 2003.
Yongsheng Lian Chaolei Zang.
Conjugate heat transfer analysis using simplified household refrigerator model.
Technical report, Department of Mechanical Engineering University of Lousville USA, June 2014.
Porterie B. Consalvi J.L., Pizzo Y.
Numerical analysis of heating process in upward flame spread over thick pmma slab.
Fire Safty J, V43(N5):351–362, 7/08.
John D.Anderson.
Computational Fluid Dynamics Basic with application.
Mc GrawHill, 2000.
Wilcox D.C.
Turbulence Modeling for CFD.
DCW Industries, 3 edition, 2006.
D.E.Dwyer.
Defining ventilation boundary condition for green house climate model.
Master’s thesis, Delft University of Technology, August 2014.
OpenFOAM Foundation.
Openfoam programmer guide.
www.openfoam.org.
OpenFOAM Foundation.
Openfoam user guide.
www.openfoam.org.

37. Need of Project Objectives Methodology CHT Case in OpenFOAM Server Case Preprocessing Results Conclusion Future Sco
Thank You !