Week 6 - CHT Analysis on a Graphics card

Your Objectives:

1. Run the simulation by varying the velocity from 1m/sec to 5m/sec for at least 3 velocities and discuss the results.
2. Find out the maximum temperature and heat transfer coefficient attained by the processor.
3. Prove that the simulation has achieved convergence with appropriate images and plots.
4. Identify potential hotspots on the model.

INTRODUCTION

Conjugate Heat Transfer (CHT)

Conjugate heat transfer is defined as the heat transfer between two domains by exchange of thermal energy. For a system the thermal energy available is defined by its temperature and the movement of thermal energy is defined by its heat flux through the outer walls. Heat transfer in solids happens through conduction and walls by convection and in liquid phase through convection.

CHT provides the temperature prediction and the hotspot regions at the solid-fluid interface, and we can also predict the heat transfer accurately for example- Conduction through solids, convection through fluid, and thermal radiation. It also provides the velocity and pressure distribution of fluid moving inside the solid. We can also use CHT in design optimization for improvement for heat transfer and cooling capacity.

A video card (also called a graphics card, display card, graphics adapter, or display adapter) is an expansion card that generates a feed of output images to a display device (such as a computer monitor). Most video cards are not limited to a 6-inch simple output. Their integrated graphics processor can perform additional processing, removing this task from the central processor of the computer.

SPACECLAIM GEOMERTY

FINS

PROCESSOR

BASE

Topology is set to share such that the data could be shared between the different components of the graphics card.

Base Mesh

A basic mesh is generated using the standard values recommended by Ansys. This mesh is used to obtain an initial solution which will help us to determine the location where mesh refinement is required.

Element Order: Linear

Element size: Default

Simulation Setup

Solver: Steady

Type: Pressure Based

Turbulence Model: k-Omega (SST)

Materials: Different materials are used for each part, some of which are custom created

Materials assigned are as follows:

Base: Polystyrene

Fins: aluminum

Processor: Steel

Enclosure is filled with Air.

For Solid

Boundaries:

• Inlet:

Type: Velocity Inlet

Velocity: 3m/s

Temperature: 300 K

• Outlet:

Type: Pressure Outlet

Pressure: 0 Pa (Gauge Pressure)

Temperature: 300 K

• Symmetry: Symmetry
• Wall: Wall

Cell Zone Conditions

The processor is assumed as the only source of heat. The heat generated by the processor is calculated as: -

Graphics Card Power = 2W

Volume of the card = 8 x 8 x 1

= `64mm^3=64e^-9m^3`

Heat Generated = `P/V=2/(64e^(−9))`

= `31250000W/(m^3)`

Solution

• Method: Standard
• Number of Iterations: 500

Simulation Output

Residual

Temperature

Heat Transfer coefficient

Post Processing

Global Hotspot Region

Hotspot Around the Processor

Wall Heat Transfer Coefficient

Velocity Contour

Temperature Contour

REFINED MESH

MESH

Element Order: Linear

Element size: 0.003 m

Body Sizing (Fin) Element Size: 0.0005 m

Body Sizing (Processor) Element Size: 0.0005 m

Body Sizing (Base) Element Size: 0.003 m

Velocity: 1 m/s

Simulation Output

Residual

Temperature

Heat Transfer coefficient

Post Processing

Global Hotspot Region

Hotspot Around the Processor

Wall Heat Transfer Coefficient

Velocity Contour

Temperature Contour

Velocity: 3 m/s

Simulation Output

Residual

Temperature

Heat Transfer coefficient

Post Processing

Global Hotspot Region

Hotspot Around the Processor

Wall Heat Transfer Coefficient

Velocity Contour

Temperature Contour

Velocity: 5 m/s

Simulation Output

Residual

Temperature

Heat Transfer coefficient

Post Processing

Global Hotspot Region

Hotspot Around the Processor

Wall Heat Transfer Coefficient

Velocity Contour

Temperature Contour

RESULTS

Velocity	The temperature at Processor [k]	The temperature at Fins [k]	HTC at Fins [Wm2kWm2k]
1	364.18	359.49	149.94
3	338.78	329.43	154.98
5	328.95	321.91	161.42

CONCLUSION

As the number of elements increases the accurate results of temperature distribution is obtained

From the above table, it is notable that, the net temperature of components of graphics cards decreases with an increase in inlet velocity.

Hence it can be inferred that a higher inlet velocity results in better cooling and lower the average temperature thus keeping the components safe from damage.

Furthermore, it can be observed that the temperature of components increases as the inlet velocity decreases from 5 m/s to 1m/s, also proving that higher velocity results in better cooling.

From this we can conclude that , As Inlet velocity get increased --->Heat generated get decreased.