Conjugate Heat Transfer Analysis on a graphics card.

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

Objective:

• To perform steady-state conjugate heat transfer analysis of graphic card.
• To understand the effects of air velocity on heat transfer.
• To compare coarse and refined mesh results.

Introduction:

The conjugate heat transfer analysis was introduced after the computers came into wide use. Before this, the empirical relation of proportionality of heat flux to temperature difference with heat transfer coefficient which was the only tool in theoretical heat convection since the times of Newton. This model, based on a strictly mathematically stated problem, describes the heat transfer between a body and a fluid flowing over or inside it as a result of the interaction of two objects. The physical process and the governing equations are considered for the two separate sub-domains. Matching conditions for these solutions at the interface provide the distributions of temperature and heat flux along the body–flow interface, eliminating the need for a heat transfer coefficient. Moreover, it may be calculated using these data.

The CHT analytical method is used for various applications such as Electronic cooling, Boilers, Heat exchangers, Engine cooling systems, etc.

Cooling systems in Graphics card:

Computer cooling is required to reduced waste heat produced by the computer components to keep them within the operating limits. Exceeding the operating limits would cause temporary or permanent damage to the components. so it is necessary that the component should be in the permissible limits. Components that are susceptible to temporary malfunction or permanent failure if overheated include integrated circuits such as CPUs, chipsets, graphics cards, and hard disks.

The use of heatsinks cooled by airflow reduces the temperature rise produced by a given amount of heat. Attention to patterns of airflow can prevent the development of hotspots. Computer fans are widely used along with heatsink fans to reduce the temperature by actively exhausting hot air. There are also more exotic cooling techniques, such as liquid cooling. All modern-day processors are designed to cut out or reduce their voltage or clock speed if the internal temperature of the processor exceeds a specified limit.

In this simulation, the type of cooling system that was used is the air cooling system. The processor was assumed in the idle rendering state. So the processor power was considered for idle rendering state only.

Assumptions:

1) The airflow profile from the inlet is considered to be of uniform value, instead of a profile of different values.

2) Airflow resistance due to the cabinet's back mesh is considered to be 0.

3) The heat-producing chip is small in size compared to real-life graphic cards, so the heat generation capacity is reduced accordingly.

4) The physical constraints to the flow due to side walls are considered to be zero. (The temperature gradient along side walls is found to be negligible, so they are replaced with symmetry boundary conditions).

CHT Analysis on Graphics Card:

Simulation Procedure:

Step: 1 Geometry Preparation

Open the Spaceclaim and select Share to share properties in the model.

(Given Graphics Card) (Given Graphics card with an enclosure)

Enable Share Topology, To get the conformal mesh.

Step: 2 Meshing

In this study, there are two types of meshing such as Baseline and Refined are used. Both meshing are given in the table.

Before that, Name the Graphics card's components as follows:

Baseline Mesh:

Element Quality:

Cell count: 84529.

Step: 3 Set-up

In this model, there is a processor which is a source term because it generated heat continuously. If we consider at 64 mm3 by volume compared to generally available ones which are 300-400 mm3.But we consider only 1/5th the power they consume. A normal high-end GPU draws anywhere between 40 – 60 Watts for our case we have considered a power consumption of 13 Watts. Hence, the Energy generated with no losses comes out: 13 / 64*10-9 = 2.03125 * 10^8 W/m3.

Heat Generated Rate=2.03125 * 10^8 W/m3.

**1:

(OR)

**2

Here, We have to give Negligible Thickness

**: Giving some Thickness(For Conduction process), We can give directly while creating the mesh. Or we can try here.

**: Also, We can try **1 or While assigning boundary conditions (At Coupled Enable Shell conduction) as **2.

In this simulation, the following parameters are selected:

Type: Steady-state simulation

Solver: Pressure based

Velocity Formulation: Absolute Velocity

Energy Equation: Selected

Turbulence model: k-omega model (SST)

Cell zone conditions:

Processor: Gold (material) Source: 2.03125 * 10^8 W/m3.

Fin: Copper (material)

Base: Aluminum (material)

Inlet velocity: 1, 2 and 4 m/s

Inlet Temperature: 300 K

Initialization: Hybrid

Properties of a Materials:

Step:4 Results

For BaseLine Mesh,Air Velocity=2m/sec.

Residual Plots:

Temperature Plot:

Temperature Contours:

Step:4 Post-Processing

Wall Heat Transfer Coefficient:

Velocity Plot on the Plane:

Temperature Plot on the Plane:

Velocity Vector on the Plane:

Velocity Plot on the Plane with vector representation:

2. Refined Mesh:

In this meshing, individual body sizing method is selected and different sizing is given to individual components. The details of various sizing methods are given in the table. The edge sizing is also given to base cylinders. Inflation is not used in this because it is not properly created because of the complex model. If inflation is given to some individual components then also it is somehow improper or has a very aspect ratio. Hence, inflation is not used in this study.

Enclosure Size and Default Mesh size is the same...

Element Quality:

Cell count:448595

For Refined Mesh:

Case-1: Inlet Velocity=1m/sec:

SETUP is the Same as the Previous case, Change the only Velocity while assigning Boundary Conditions.

Results:

Residual Plots:

Temperature Plot:

Temperature Contours:

Post-Processing

Wall Heat Transfer Coefficient:

Velocity Plot on the Plane:

Temperature Plot on the Plane:

Velocity Vector on the Plane:

Velocity Plot on the Plane with vector representation:

Case-2: Inlet Velocity=2m/sec:

SETUP is the Same as the Previous case, Change the only Velocity while assigning Boundary Conditions.

Results:

Residual Plots:

Temperature Plot:

Temperature Contours:

Post-Processing

Wall Heat Transfer Coefficient:

Velocity Plot on the Plane:

Temperature Plot on the Plane:

Velocity Vector on the Plane:

Velocity Plot on the Plane with vector representation:

Case-3: Inlet Velocity=4m/sec:

SETUP is the Same as the Previous case, Change the only Velocity while assigning Boundary Conditions.

Results:

Residual Plots:

Temperature Plot:

Temperature Contours:

Post-Processing

Wall Heat Transfer Coefficient:

Velocity Plot on the Plane:

Temperature Plot on the Plane:

Velocity Vector on the Plane:

Velocity Plot on the Plane with vector representation:

Final Comparison:

**The hotspots in the potential hotspot in the graphic Card was the processor. since the processor generates heat due to power consumption. The main heat source of the graphic card is the processor.

Conclusion:

• From the values and hotspot regions, we can conclude that by increasing the velocity heat transfer coefficient value will be increased and max temp attained by the system will be decreased
• From the hotspot region, we can conclude that the electronic component is placed far from the processor to get lower heat. The heat sink is basically placed to get higher surface area and lower the temp, once we increase the fins graphic card will cool down faster.
• If the material is selected with high thermal conductivity, it will take lesser time to cool down, But the cost of high conductive material will be higher.
• Hence the temp of the graphic-card is depended on the placing of Cooler Fan, number of fans, Material, number of fins, Etc...
• The Graphics card model is very complex so that inflation cannot be provided. Hence, it must be solved by giving different body sizing to different components.
• Baseline mesh is not capable to capture good physics which will give poor results and it can not be useful as per industry standards.
• The fin material is selected in such a way that it will provide a high heat rate to the surrounding. Suppose copper is used as a fin material in this study.