Week 6 - CHT Analysis on a Graphics card

AIM:

Perform a steady-state conjugate heat transfer analysis on a model of a graphics card.

OBJECTIVE:

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

THEORY:

Conjugate Heat Transfer (CHT) Analysis:

• Conjugate Heat Transfer analysis is used for the processes that involve a variety of temperatures concerning solids and fluids, due to thermal interaction between them. A typical example would be the heating or cooling of a solid by the flow of air.
• The exchange of heat between two bodies is known as heat transfer and the rate of heat transfer is directly proportional to the temperature difference between them. Heat transfer in solids is usually occurred by conduction whereas in the case of fluids heat transfer occurs by convection. Efficiently combining heat transfers between solids and fluids is the key to design effective coolers, heaters, or heat exchangers. Forced convection is the most common way to achieve higher heat transfers. For some applications, the performance is further improved by combining convection with phase change (for example liquid water to vapor phase change).
• Heat transfers in solid and heat transfers in fluids are usually combined in the majority of the applications. This is because fluid flows around solids or between solid walls and usually solids are immersed in the fluids.
• An accurate description of parameters such as materialproperties, flow regimes, geometry configurations, selecting correct models based on the physics to be captured, heat transfer modes near the boundaries is needed for the analysis of temperature fields and heat transfer.

Practical CHT problems are used to determine:

• The maximum and minimum temperature in various parts of the system. eg: combustion chamber, gas turbines, chemical vessels, etc.
• Temperature Distribution is related to the thermal stress over a particular wall or system etc.
• Temperature Response in time-dependent applications such as heating/cooling problem (For example, In the case of cooling a particular system such as engine cooling)
• Overall heat transfer co-efficient.

SIMULATIONS AND PROCESS:

This project is based on the Mesh, we run 3 different simulations with 3 different velocities 1m/s to 5m/s.

Geometry Checkup:

• At the starting of the simulation process, the made-up geometry of the graphics card which also already includes encloser was imported into the Space Claim. The various components involved in the geometry are highlighted with the orange rectangular boundary line which includes the base (circuit board), Graphics card processor, Fins attached to the processor, and other components.
• The geometry and flow domain consists of a flat circuit board with a heat-generating electronic processor chip and some other components connected to it. Heat is conducted through the source (processor), the board mounted on it and the fins attached to the processor. A stream of air flows over the fins, processor, and board, causing simultaneous cooling of the solid components and heating of the airstream due to convection. Thermal energy is also transported due to the complex flow field.

Meshing:

• The first step into meshing should be to provide a name to each surface and component which was given as depicted in the below picture.
• Next, to refine the mesh near the graphics card circuit area, actually where the accuracy of the simulation is required, face sizing of 1.5mm was used.
• Generation of mesh over a graphics card circuit will show the following results after the use of the above element size on the faces.
• Mesh size for other regions was considered as 5mm. The overall mesh growth rate was taken as the default value which is 1.2.

SIMULATIONS:

Setup 1

Solver Type	Pressure-Based
Velocity Formulation	Absolute
Time	steady
Models	Viscous model: K-omega SST Energy model: On
Material	Fluid type: Air Solid-type: Aluminium : fr-4 : copper
Cell zones	Fluid type: Air Solid: Al, fr, Cu
Boundaries	Inlet : inlet velocity: 1m/s : temperature = 300K Outlet: outlet pressure = 0
Reference values	Standard
Initialization	Standard

Usually, the power consumed by a processor is converted into heat energy. To calculate the heat generated on the processor which is = Power consumed divided by the total volume of the processor

"The power consumption of today's graphics cards has increased a lot. The top models demand between 110 and 270 watts from the power supply; in fact, a powerful graphics card under full load requires as much power as the rest of the components of a PC system combined"

Taking this fact we will assume the power consumed to be 55 (being half of the upgraded graphic card)

Heat generated = 55/64*10⁻⁹W/m³ = 859375000 W/m³

Output:

Post Processing:

Temperature contour

Velocity contour

Setup 2

Solver Type	Pressure-Based
Velocity Formulation	Absolute
Time	steady
Models	Viscous model: K-omega SST Energy model: On
Material	Fluid type: Air Solid-type: Aluminium : fr-4 : copper
Cell zones	Fluid type: Air Solid: Al, fr, Cu
Boundaries	Inlet : inlet velocity: 3m/s : temperature = 300K Outlet: outlet pressure = 0
Reference values	Standard
Initialization	Standard

Output:

Post Processing:

Temperature contour

Velocity contour

Setup 2

Solver Type	Pressure-Based
Velocity Formulation	Absolute
Time	steady
Models	Viscous model: K-omega SST Energy model: On
Material	Fluid type: Air Solid-type: Aluminium : fr-4 : copper
Cell zones	Fluid type: Air Solid: Al, fr, Cu
Boundaries	Inlet : inlet velocity: 5m/s : temperature = 300K Outlet: outlet pressure = 0
Reference values	Standard
Initialization	Standard

Output:

Post Processing:

Temperature contour

Velocity contour

CONCLUSION:

• As the number of elements increases the accurate results of temperature distribution is obtained
• From the above table, it is fairly 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.