Week 6 - CHT Analysis on a Graphics card

AIM:

To conduct a steady state conjugate heat transfer analysis on a graphics card model using ANSYS Fluent.

Theory:

In CFD, Conjugate Heat Transfer (CHT) analysis allows users to do simulation of heat transfer between solid and fluid domains. Heat transfer happens between a soild and fluid by exchanging thermal energy at the interfaces between them. Some examples are the simulation of heat exchangers and cooling of electronic equipment.

Solving approach:

Geometry:

Solver settings:

Velocity was choosen as 2m/sec.

Model Settings:
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Space 3D
Time Steady
Viscous Realizable k-epsilon turbulence model
Wall Treatment Standard Wall Functions
Heat Transfer Enabled

Material Properties:
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1. pcb -- FR4

FR4 is the most used material in manufacturing PCB.

FR4 is a standard given by the National Electrical Manufacturers Association. It is a glass-reinforced epoxy resin laminate. FR means "flame retardant" and it means that the material is compliant with the UL94V-0 standard on plastic material flammability.

Density kg/m^3 constant 1850
Cp (Specific Heat) J/(kg K) constant 1100
Thermal Conductivity W/(m K) constant 0.29

2. processor - Silicon

Density kg/m^3 constant 2000
Cp (Specific Heat) J/(kg K) constant 710
Thermal Conductivity W/(m K) constant 150

3. Fin - Aluminium

Fins must be metallic to conduct heat easily and light weight.

Density kg/m^3 constant 2719
Cp (Specific Heat) J/(kg K) constant 871
Thermal Conductivity W/(m K) constant 202.4

4. air (fluid)

Density kg/m^3 constant 1.225
Cp (Specific Heat) J/(kg K) constant 1006.43
Thermal Conductivity W/(m K) constant 0.0242
Viscosity kg/(m s) constant 1.7894e-05

Cell Zone Conditions
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processor - solid
fin - solid
base - solid
enclosure - fluid

Setup Conditions

processor

Condition Value
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Material Name processor
Specify source terms? yes
Source Terms ((energy ((constant . 156250000) (inactive . #f) (profile ))))
Frame Motion? no

Boundary Conditions
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Zones

interior-enclosure-processor-shadow 22 wall
interior-enclosure-processor 3 wall
interior-enclosure-fin-shadow 21 wall
interior-enclosure-fin 4 wall
interior-fin-processor-shadow 20 wall
interior-fin-processor 2 wall
interior-base-processor-shadow 19 wall
interior-base-processor 5 wall
interior-base-enclosure-shadow 11 wall
interior-base-enclosure 1 wall
inlet 16 velocity-inlet
outlet 17 pressure-outlet
symmetry 18 symmetry

inlet

Velocity Magnitude [m/s] 2

Equation Solved
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Flow yes
Turbulence yes
Energy yes

Pressure-Velocity Coupling

Type Coupled
Pseudo Transient yes

Power =10W

Heat generated = 10W/64mm^3

CASE 2:

Inlet velocity 3m/sec

Power 2W

CASE 3:

For first case Power was choosen as 10W and the maximum temperature on the processor was obtained as 229 degreeC. It is a high temperature for processor and is not recommended.

It is suggested to use power value as 1 or 2 watts.

Also while selecting reference values, give inlet area as area of the inlet of enclosure.