Conjugate Heat Transfer Analysis on a Graphics Card

Question

We are going to simulate flow over a graphics card for baseline and refined mesh with 3 different velocities 1,3 and 5 m/s.

Simulation Procedure :

Geometry :

1. Open the geometry section and import the given Graphics card geometry.
2. Then go to workbench section and select shareprep option so they share sides and faces with each other.

Mesh :

1. Open the mesh and name the boundaries like Inlet, Outlet, Symmetry.
2. Now, generate the default mesh provided.
3. By default, Fluent analyzes the hot spots and meshes them accordingly.
4. Here we have used body sizing for the processor as the default element size was not able to capture the heat generation(it showed just 4 elements on processor)
5. We have used sphere of influence for the processor meshing.

Setup :

1. Open the Setup and perform the mesh check.
2. Then set the pressure based solver and turn on the the energy equation.
3. Set the viscous model( we have used k-omega SST model).
4. Now set the materials for fluid and solid according to requirement.
5. Now from cell zones assing the solid and fluid zones(We have selected fuild for the enclosure and solid for Base, processor, fin).
6. In same cell zone section set the energy source for the processor so that the processor emits the energy.
7. Set the Boundaries like inlet velocity.(Here we have simulated the problem for 3 Velocities i.e. 1,3,5 m/s for both Baseline and Refined mesh).
8. Now set up the solution method(we have used Coupled Scheme with first order approx).
9. After that initialize it with hybrid initialization and set a plane to view the contours on it.
10. Finally set the velocity and temperature contours and run the simulation.

Results :

1. Open the Results section and create a plane to observe the velocity over entire graphics card.
2. Make specific parts visible with variables like temperature and wall HTC to observe their behavior over graphics card.
3. We will observer the temperature distribution over solid base, processor and fin.
4. We will also observe Wall HTC on solid base and fin base and note down their differences for different velocities.

Inputs :-

1] Solver - Pressure Based Steady.

2] Viscous Model - K-Omega SST.

3] Fluid(enclosure) - air.

4] Solid( Base, Processor and Fins) - Aluminium.

5] Velocity - 1,3,5 m/s.

6] Energy source - 2e7 W/m^3.

• Model

Results :

############################# { Baseline Mesh } #############################

We are going to decrease the mesh element size at processor so it increases the HTC. As default mesh element size generates only 4 elements on processor which will not increase HTC and no proper heat dissipation will occur, Also it will not properly capture energy source provided.

Mesh Element size = 1.0289e-2 m

Body Sizing = Sphere Radius - 0.004m

element size(in sphere) - 0.0003m

Total Elements - 230358

Total Nodes - 42446

• Mesh

• Element Quality

<<<<<<<<<<<<<<< [ For Velocity = 1 m/s ] >>>>>>>>>>>>>>>

• Velocity plane

• Residual

• Solid Base Temperature

• Processor Temperature

• Fins Temperature

• Outlet Temperature

• Wall Heat Transfer co-efficient at Solid Base

\

• Wall HTC at fins

<<<<<<<<<<<<<<< [ For Velocity = 3 m/s ] >>>>>>>>>>>>>>>

• Velocity plane

• Residual

• Solid Base Temperature

• Processor Temperature

• Fins Temperature

• Outlet Temperature

• Wall HTC at solid Base

• Wall HTC at Fins

<<<<<<<<<<<<<<< [ For Velocity = 5 m/s ] >>>>>>>>>>>>>>>

• Velocity Plane

• Residual

• Solid Base Temperature

• Processor Temperature

• Fins temperature

• Outlet Temperature

• Wall HTC at Solid Base

• Wall HTC at Fins

############################# { Refined Mesh } #############################

we are going to decrease the mesh element size at processor so it increases the HTC.

Mesh Element size = 1.65e-3 m/0.00165 m

Body Sizing = Sphere Radius - 0.004m

element size(in sphere) - 0.0005m

Total Elements - 498966

Total Nodes - 93810

• Mesh

• Element Quality

<<<<<<<<<<<<<<< [ For Velocity = 1 m/s ] >>>>>>>>>>>>>>>

• Velocity plane

• Residual

• Solid Base Temperature

• Processor Temperature

• Fins Temperature

• Outlet Temperature

• Wall HTC at Solid Base

• Wall HTC at Fins

<<<<<<<<<<<<<<< [ For Velocity = 3 m/s ] >>>>>>>>>>>>>>>

• Velocity Plane

• Residual

• Solid Base Temperature

• Processor Temperature

• Fins Temperature

• Outlet Temperature

• Wall HTC at Solid Base

• Wall HTC at Fins

<<<<<<<<<<<<<<< [ For Velocity = 5 m/s ] >>>>>>>>>>>>>>>

• Velocity Plane

• Residual

• Solid Base Temperature

• Processor Temperature

• Fins Temperature

• Outlet Temperature

• Wall HTC at Solid Base

• Wall HTC at Fins

Observations :

• From the above plots we can say that finer mesh gives more accurate reults.
• Also Finer mesh increases the heat transfer coefficient wich ultimately reduces processor temperature.
• Higher velocity results in greater heat dissipitation. we can check in outlet temperature plots that increased velocity values have reduced outlet temperature.
• Looking at the residual values, we can say that all simulations have converged after certain iterations.
• Also with increase in velocities, the energy equation residual drops way below than other residuals.
• The heat transfer coefficient is max at processor base.

Velocity(m/s)	1 m/s	1m/s	3 m/s	3 m/s	5 m/s	5 m/s
Mesh	Coarse	Finer	Coarse	Finer	Coarse	Finer
Max. Temperature of processor(C)	44.81	45.17	35.99	35.76	33.75	33.55
Base wall HTC[W/m^2 K]	1028.04	1036.28	1028.11	1036.34	1028.34	1036.50

• We can see that higer velocities and finer mesh both play vital role in increasing HTC.