Week 6 - CHT Analysis on a Graphics card

Question:-

Perform a steady-state conjugate heat transfer analysis on a model of a graphics card. You can use appropriate materials of your choice for the simulation. Make sure to properly define the correct solid and fluid zones. Refer the video for further clarification and the model is provided below the video.

Run the simulation for best possible mesh with combination of coarse and refined mesh in different regions. Explain the reason for choosing the particular mesh settings.

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.

Aim:-

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

Objective:-

1. Simulate 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.

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 properties, 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:-

This project is divided into 2 parts based on the Mesh ( with a baseline and an upgraded mesh )

Again in Part 1, we run 3 different simulations with 3 different velocities 1m/s to 5m/s(using updraged mesh).

Flow chart :-

• Geometry preparation
• Mesh generation
• Fluent set up
• Post-processing

Geometry:-

A step file is imported into ANSYS space claim. There are different components , namely:

1) Fin base

2) Fins

3) Processor

4) Enclosure

5) Graphics Card

Then we give a total element size of 0.003 m and applying a body sizing to the processor with an element size of 0.0015. Making this our Refined mesh.

Fluent set up:-

The meshed model is loaded into ANSYS Fluent. Required physics of the model is set:

Pressure based solver is used, as the flow is non compressible flow. Steady state analysis is done.

Case 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

: gold

: copper

Cell zones

Fluid type: Air

Solid: Al, Au, Cu

Boundaries

Inlet : inlet velocity: 2m/s

: temperature = 300K

Outlet: outlet pressure = 0

Reference values

Standard

Initialization

Standard

The energy used by a processor is often transformed into thermal energy. To determine the amount of heat produced by a CPU, divide its entire volume by its power consumption.

"The power use of graphics cards today has significantly grown. The highest models require the power supply to deliver between 110 and 270 watts; in fact, a powerful graphics card operating at full capacity consumes as much power as the rest of the PC system's components put together."

Based on this information, we'll estimate that 55 watts were used (being half of the upgraded graphic card).

Heat generated = 55/64⋅10-9Wm3=859375000 Wm3.

Temperature of Graphics Card:-

Wall heat transfer coefficient:-

Residual Plot:-

Velocity Contour:-

Temperature Contour:-

Temperature of Base:-

Case 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

: gold

: copper

Cell zones

Fluid type: Air

Solid: Al, Au, Cu

Boundaries

Inlet : inlet velocity: 5m/s

: temperature = 300K

Outlet: outlet pressure = 0

Reference values

Standard

Initialization

Hybrid

Temperature of Graphic card:-

Wall heat transfer coefficient:-

Residual plot:-

Temperature Contour:-

Velocity Contour:-

Temperature of Base:-

Conclusions:-

CASE	VELOCITY(m/s)	TOTAL TEMPERATURE OF GRAPHICS CARD(K)	TOTAL HEAT TRANSFER COEFF ON GRAPHICS CARD (W/m^2K)
CASE 1	2	773	1030
CASE 2	5	583	1030

A higher Reynolds number indicates a faster velocity in that area. Due to the greatest heat transfer coefficient in that location, the biggest quantity of heat is transferred from the fluid to the solid there. Additionally, this raises the temperature of the solid there.
Mesh resolution close to walls often has the most influence on numerical findings because heat transfer coefficient is a product of the fluid's characteristics at film temperature, temperature differential, temperature coefficient, buoyance force, and other factors.
We need to take care of the program's boundary conditions and assumptions for the turbulent models. Refining the mesh is necessary in order to obtain desirable outcomes.

The CPU area is where the graphics card might experience a hotspot. In that area, the temperature reaches its peak.
The air velocity at the intake determines the maximum temperature that may be obtained. More velocity results in a lower maximum temperature.

The variation in air flow velocity has little to no effect on the wall heat transfer coefficient.

References:-

https://www.simscale.com/projects/hkonka/conjugate_heat_transfer_analysis_using_graphic_card/

https://www.researchgate.net/publication/332963034_Computational_Fluid_Dynamics_Simulation_on_the_Heat_Sink_Performance_of_a_Graphics_Processing_Unit_Thermal_Management

Thanks.