CHT analysis of Graphics card

Conjucate heat transfer (CHT):

The conjugate heat transfer analysis was introduced after the computers came into wide use. Before this, the emperical 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 seperate 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 temprorary or permanent damage to the components. so it is neccessary 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 card, and hard disks.

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 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.

CHT analysis of Graphics card:

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

Analytical setup for the CHT simulation:

The analysis was performed for two types of mesh:

1) Base line mesh

2) Refined mesh

The geometry was setup in ANSYS spaceclaim. Then using share topology feature, all the components like proccessor, base, fins and enclosure were shared together to form conformal mesh. Due to this sharing feature a conformal mesh was formed between all the domains. The formation of conformal was very important to see heat transfer effects at the surface of the solid boundary. An enclosure was formed to capture effects of convection that takes place over the graphic card.

For refining the mesh, the hexagonal meshing method was used for the enclosure and for the graphics card model further mesh size was reduced. The overall mesh size was reduced to 5 mm.

The solver that was used to simulate the model was FLUENT. The pressure based equation was used and for solving turbulent equations k-epsilon model of viscosity was used. To capture the tempreature variations in the fluid and solid domains energy equations were also used. The initial boundary conditions that were used are:

Inlet:

Velocity of air: 10 m/s

Tempreature: 290K

Power used by the processor: 13W

heat generated by the processor: 203125000 W/m^3

Materials used for different components of graphics card:

Fins: Copper

Proccessor: Gold

Base: Aluminium

Geometry of each indivisual components are given below:

Baseline mesh:

Cell count: 84529

Cell size: 10.2 mm

Analysis Results:

Residual plot:

From the residuals graph we can conclude that the simulation converged around 400 iterations.

Tempreature plot:

Velocity plot:

Wall heat transfer coefficient:

Refined mesh:

Cell size:5 mm

Cell count: 484127

Residual plot:

From the above residual graph we can see that the solution is converging around 400 iteration.

Tempreature plot:

Velocity plot:

Wall heat transfer coefficient:

Conclusions:

• The maximum tempreature attained by the proccessor:

Baseline mesh: 350.8K

Refined mesh: 356.1K

• The wall Heat transfer coefficient attained by the proccessor is:

Baseline mesh: 1833 W/m^2K

Refined mesh: 645.7 W/m^2K

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