Project 1- Conjugate Heat Transfer Analysis on a graphics card.

Project Title: CHT analysis of graphic card

Objective: 1. Conjugate heat transfer analysis of graphic card.

               2.  Finding heat transfer coefficient of fins.

               3. Grid independence study of model.

Theory:

What is Conjugate Heat Transfer?

The term conjugate heat transfer (CHT) is used to describe processes, which involve variations of temperature within solids and fluids, due to thermal interaction between the solids and fluids. The exchange of thermal energy between the two physical bodies is called the study of Heat Transfer; the rate of transferred heat is directly proportional to the temperature difference between the bodies. A typical example is the heating or cooling of a solid object by the flow of air in which it is immersed and some other example includes conduction through solids, free and forced convection in the gases/fluids and thermal radiation.

Conjugate heat transfer corresponds with the combination of heat transfer in solids and heat transfer in fluids. In solids, conduction often dominates whereas, in fluids, convection usually dominates. Efficiently combining heat transfer in fluids and solids is the key to designing effective coolers, heaters, or heat exchangers. Forced convection is the most common way to achieve a high heat transfer rate. In some applications, the performances are further improved by combining convection with phase change (for example liquid water to vapour phase change).

Heat transfer in solids and heat transfer in fluids are combined in the majority of applications. This is because fluids flow around solids or between solid walls and because solids are usually immersed in a fluid.

What is the Conjugate Heat Transfer Analysis?

Computational Fluid Dynamics (CFD) and more specifically conjugate heat transfer (CHT) analysis can accurately predict heat transfer by simultaneous solving all the relevant solid and flow field heat transfer processes, for example, conduction through solids, free and forced convection in the gases/fluids and thermal radiation.

The CHT approach has an advantage over FE thermal analysis in that wall heat transfer coefficients and their local variations on surfaces are directly calculated within the model rather than based on simplified empirical calculations. The CHT approach, therefore, has benefits for those applications where heat transfer is either non-uniform or difficult to calculate empirically.

Model:

Fig 1 Model of graphic card

it consists aluminium fins copper heating source and steel base plate.

Fig 2 heating source

The dimension of heating source is 8*8*1mm material is copper selected for analysis.

Fig 3 Computational domain.

The fluid used for cooling of graphic card is air. it has an inlet, outlet, symmetry sides,

Meshing:

Base-LIne mesh

Fig 4 base-line mesh

Fig 5 Cut section of mesh

Mesh count

Fig 6 Mesh Outline

Fig 7 Mesh Quality

Improved mesh

Fig 8 Improved mesh

Fig 9 Mesh Outline

Fig 10 Mesh Quality

Mesh count

Setup:

1. Steady-state Pressure base condition is assumed in this analysis.

2. For cht analysis, k-omega SST model is considered.

3. The energy equation is turn on for temperature analysis.

3. SIMPLE second-order SCHEME is used.

4. For initialization hybrid, method is selected.

5. For mass momentum 10e-3 value considered for residuals and for energy 10e-6 value considered.

Boundary condition 

1. inlet: fix velocity value

2. Outlet: pressure outlet

3. Symmetry: Symmetry condition 

4. Heat source: 3.125e8 W/m3

Results

velocity 5m/s case is considered

1. Residuals

Fig 11 Residual plot

the solution is converged at 140 iterations

Fig 12 Temperature plot

As you see heating source has a maximum temperature due to heat generation. As airflow over the graphic card heat transfer from heat source to fins and base plate and then to the air

Fig 13 Velocity plot.

behind the card, velocity is less compared to front side.

Fig 14 temperature contour on the fin surface

FIg 15 Heat transfer coefficient contour on fin surface 

Due to high heat transfer coefficient temperature is less on front side of a fin.

Fig 16 Temperature contour in base plate

FIg 17 Heat transfer coefficient contour on a base plate surface 

Fig 18 Overall heat transfer coefficient at various speed