Exhaust port
- Give a brief description of why and where a CHT analysis is used.
Conjugate heat transfer (CHT) refers to the coupling of conduction in solids with the convective and radiative heat transfer in the surrounding fluids. Accurately predicting CHT is an essential part of the design process.
Conjugate heat transfer investigation is a valuable tool to determine the surface temperatures and heat exchanging abilities of the designing gadgets. Through the investigation, engineers can optimize the thermal characteristics for their chosen product design.
Many industrial applications including electronics cooling, turbomachinery,HVAC. heat sink,boilers etc
- Analysis on Exhaust manifold : Here , 2 types of analysis are done first with the baseline mesh and second with the refined mesh (along with the infaltion layers).
Here, Steady Pressure-Based solver was used. Energy equations were used and for the viscous turbulence, the k-epsilon model was used.
In Materials, For fluid it is air and for the solid region, it is aluminium
Boundary conditions:
Velocity of the air at the inlet is 5m/s and temperature is 700k
Heat tranfer coefficient for the surface of the outer wall convectio is considered as 20 w/m^2k
Geometry
Case 1 :
Baseline setup with 138261 elements.
- Residuals
- Temperature distribution
- Velocity contour at the throat
- Streamline distribution
- Wall heat transfer coefficient
Case 2 :
Refined setup with 475338 elements (along with inflation layer)
- Residuals
- Temperature distribution
- Velocity contour at the throat
- Streamline distribution
- Wall heat transfer coefficient
Results and conclusion:
From the above 2 cases we can see that temperature at the throat is greater than the temperature at the inlet section of the pipe , this is because of the fact that the temperature is directly proportional to the kinetic energy of the fluid which in turn is a function of the velocity. so velocity at the throat section is higher due to the mass conservation , exhaust port has the 4 inlets and only one outlet which causes the flow to mix at one point before the throat section which increases the velocity from 5m/s to 36 m/s (for case 1) and from 5m/s to 40 m/s (for case 2). which in turn increases the temperature at the throat section.
it can also be concluded that when we refine the mesh we get smoother and more accurate results of velocity , temperature and the wall heat transfer coefficient as shown in the images of the two cases.
As the mesh becomes more finer velocity , temperature and the wll heat transfer coefficient increases.
Factor affecting the results :
Conformal mesh is the most important factor that can affect the results drastically, Non-conformality in the mesh may lead inability to share the date from fluid to the solid and may lead to absurd results.
In order to increase the accuracy of the results one of the most efficient way is to ad the inflation layers at the crucial areas.
Dependency of HTC:
The HTC in the analysis is predicted by adding a plane across the throat section.HTC are accurate only when a smoother heat transfer coefficient results are obtained in the CFD post analysis if the results are are not smoother as seen in the case 1 , it means the meshes are to be fined and the results must be obtained. The accuracy factor depends upon the element size the total number of cells and meshing quality by adding inflation layers with which the HTC is obtained