CONJUGATE HEAT TRANSFER ANALYSIS OF AN EXHAUST MANIFOLD OF AN AUTOMOBILE

CONJUGATE HEAT TRANSFER IN EXHAUST PORT

INTRODUCTION :

• WHAT IS CONJUGATE HEAT TRANSFER ANALYSIS?

Conjugate heat transfer (CHT) allows the simulation of the heat transfer between solid and fluid domains by exchanging thermal energy at the interfaces between them. It requires the multi-region mesh to have a clear definition of the interfaces in the computational domain. Such a mesh can be created with the hex-dominant parametric operation in the mesh creator.

• WHY IS CONJUGATE HEAT TRANSFER USED?

CHT is majorly used because it 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 thermal analysis, in it 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.

• WHERE ARE CONJUGATE HEAT TRANSFER ANALYSIS USED?

Typical applications of this analysis type are the simulation of heat exchangers, cooling of electronic equipment, and general-purpose cooling and heating systems.

• In this CHT analysis of an exhaust port, 2 cases have been considered and their results have been studied.

CASE 1 - CHT ANALYSIS OF BASELINE MESH

• GEOMETRY

• MESHING

• MESH QUALITY (MESH METRIC)

• SCALED RESIDUALS

• TEMPERATURE CONTOUR PLOT

• VELOCITY STREAMLINES

• HEAT TRANSFER COEFFICIENT PLOT

• TEMPERATURE CUT PLANE SECTION

• VELOCITY PLOT

CASE 2 - CHT ANALYSIS OF A FINER MESH

• GEOMETRY

• MESHING

• MESH QUALITY (MESH METRIC)

• SCALED RESIDUALS

• TEMPERATURE CONTOUR PLOT

• VELOCITY STREAMLINES

• HEAT TRANSFER COEFFICIENT

• TEMPERATURE CUT PLANE SECTION

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• VELOCITY PLOT

• MESH SIZE COMPARISON

• RESULTS

It has been found that by refining the mesh quality the Average Outlet Velocity has been increased and the Average Outlet Temperature has been decreased. As can be seen from the below data.

Avg. Outlet Velocity Avg. Outlet Temp.

Baseline Mesh 22.5 m/s 675 K

Finer Mesh 25.9 m/s 668 k

• OBSERVATION

It has been observed that in the Temperature Contour plot of both cases the temperature of the exhaust port near the outlet is more than the Temperature near the inlet from where the hot fluid is entering. This is due to the high velocity (as it can be seen in the velocity cut plane above) at the outlet region which causes higher heat transfer from the fluid to solid and hence a higher temperature in this region.

• VERIFICATION

To verify the CHT analysis simulation results obtained above, the practical and experimental data should be considered in this reference.

• CONCLUSION

The CHT Analysis has been simulated for baseline mesh and a refined mesh. The more you will refine the mesh, the more accurate results will be achieved.