Week 6 - CHT Analysis on a Graphics card

Conjugate Heat Transfer Analysis on Graphics card

Parts of graphics card-fin,processor,base. Processor is the heat source and fin tray is setup to increase surface area for a faster heat transfer. The simulation is ran as follows:

Geometry- Once geometry is imported, share the topology (click on top of component branch and choose share option in topology). Workbench>share

Mesh- Mesh of 5mm is generated for this simulation. Body sizing for the fin and the base is 1 mm and for processor is 0.5mm. Along with body sizing , one should always give value to ‘max size’ in sizing under mesh , here 5mm. Global and local mesh sizing value should be co-ordinated with each other.

Setup- The simulation is performed for 3 velocities- 1,3,5m/s.

Basic- steady state solver, pressure based, absolute velocity, temperature equations taken in consideration hence choose temperature box, k-Epsilon model is chosen.

Creating materials-

Fluid-air, solid- Plastic, Silicon, Aluminium (from the solid category of materials)

Silicon thermal conductivity-148W/mK

Silicon Density-2.3292 g/cm3=2329.2kg/m3

Cp=0.7J/gC

Bakelite density-1.3g/cm3

Thermal conductivity-0.2W/mK

Cp=1.59kj/kgK

Input in cell zones

Base-Solid- Plastic material

Domain-Fluid- Air material

Fin-solid-Aluminium material

Processor-Solid-Silicon Material

Source term-1 no. constant heat source for 1watt per unit volume

Volume of processor-64mm³

Source term value(W/m³)=15625000

Boundary Values-

Inlet- Input the velocity, temp as 273K.

Reference values (from inlet):

Area- 4 walls of processor – 32e-06

Length-20mm

Hybrid Initialization Done.

Give a contour for temperature and make report for wall adjacent heat transfer coefficient.

Type of report with explanation: Wall adjacent temperature coefficient, Surface heat transfer coefficient, y plus heat transfer coefficient (inside wall fluxes option)

Choose the 4 walls of processor for these reports(not top and bottom).

Run Calculation:

Results for setup:

Velocity-1m/s

Wall-adjacent heat transfer coefficient-434.507W/m2K

Y+ transfer coefficient-244.5w/m2k

Yplus transfer coefficient:

Max temperature achieved-298K

Heat is transferred from processor to fins to atmosphere. That’s why in the middle where processor lies , fin tray seems to have higher temperature than rest of the places. This middle portion is the hotspot (where the processor lies, as it is the heat source).

Velocity-3m/s

Wall-adjacent heat transfer coefficient-434.507W/m2K

Y+ transfer coefficient-244.5w/m2k

Residual:

After 100 iterations the simulation seems to be converged.

Wall adjacent temperature:

Y plus heat transfer coefficient:

Max temperature-287K

Velocity-5m/s

Wall-adjacent heat transfer coefficient-434.507W/m2K

Y+ transfer coefficient-244.5w/m2k

Residual:

The simulation converges at nearly 100 iterations.

Wall-adjacent temperature curve

Y-plus transfer coefficient:

Max temperature achieved-289 K

Conclusion: The heat transfer coefficient is in range 400-500w/m2K and the temperature rise in the three cases is not more than 15-20 degree Celsius. The affect of velocity on temperature is nearly negligible for a range of 1-5m/s, the temperature lies between 287K-298K . As velocity increases, cooling increases and temperature rise becomes lesser.