Exhaust Port Simulation

Conjugate Heat Transer :

• 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.
• In simple words, it is the heat transfer between solid and fuild simultaneously. There is a thermal coupling at the interfaces of two regions.
• Conjugate heat transfer is observed in many situations. For example, heat sinks are optimized to combine heat transfer by conduction in the heat sink with the convection in the surrounding fluid.

Why CHT :

• Understanding of the complex heat transfer mechanisms and the interactions between those mechanisms to improve the performance and increase the lifespan of the components to be analysed.
• Conjugate Heat Transfer analysis provides the temperature distribution in solid and fluids, and clear insight on velocity distribution and mechanism of heat transfer of fluid, like in engines.
• It is more accurate and fast to simulate the problem.
• Can be used in complex scenarios like in automotive components or in power plant components.
• Multiple number of regions can be simulated.
• All types of region combination can be simulated like solid-fluid,fluid-fluid, etc.

Where is CHT analysis done :

• Analysis of Heat transfer mechanism in turbocharger.
• HVAC systems.
• Burners, combusters, electronic devices.
• Automotive, power plants and various other applications.

Simulation Model :

Simulation precedure :

We are going to simulate the exhaust port with baseline and refined mesh.

Geometry :

1. Import the model of exhaust port.
2. Go in repair and clear the extra edges if any.
3. Then go in prepare and extract the inner volume.
4. After that select solid and fluid component move them to new componet.
5. Finally go in workbench and select shareprep and also share the topology in desing.

Mesh :

1. Open the mesh section in workbench.
2. First name the faces which are inlets, outlet, outer-wall-convection.
3. Then mesh the geometry and refine it with body sizing and inflation layers.

Setup :

1. Perform the mesh check.
2. Put on the energy equation and viscous model.
3. Set up the materials, solid and fluid one.
4. Then set up the boundary conditions like inlet velocity, outlet pressure, outer wall convection's HTC.
5. Also set up the solution method and report definitions.
6. Then initialize the problem with hybrid initialization.
7. After that set the Contours and solution animation and run the case with some iterations and observe the same.

Result :

1. Select the outer wall volume to make it visible. Also color it with the variable needed to be observed.
2. After that, insert the plane and color it with variable like Temperature and Velocity which shows the Temperature and Velocity flow on plane.
3. Edit the legend according to requirement. This completes the results and hence the entire simulation.

############################# { Baseline Mesh } #############################

In this we are going to use default mesh size without any inflation layers or body sizing

• Mesh

Nodes	Elements Size	Elements
27593	0.15 m	138428

• Temperature contour

• Velocity contour

• streamline

• Wall heat transfer coefficient

• Line contour

############################# { Refined Mesh } #############################

In this we are going to refine mesh using inflation layers snd body sizing.

• Mesh

Nodes	Elements	Element size	Body sizing ( Solid Body)	Inflation layer Total thickness
136289	490272	0.15 m	0.0075 m	0.005 m

• Inflation layer

Boundary Conditions :

Inlet velocity = 5 m/s

Outlet pressure = 0 pa

heat transfer coefficient = 20 W/m2-k

• Temperature contour

• Velocity contour

• Streamline

• Wall heat transfer coefficient

• Line contour

Verify HTC :

• Under forced convection circumstances, we can determine the heat transfer coefficient by using the Dittus-Boelter correlation. Using the Dittus-Boelter correlation the heat transfer coefficient can be calculated in the following way using two further dimensionless groups, the Reynolds number and the Prandtl number:

h = (k/D_H)*Nu

where k is the thermal conductivity of the liquid, D_H is the Hydraulic diameter, and Nu is the Nusselt Number which is determined by the following equation:

Nu = 0.023Re^0.8Prⁿ

where, n= 0.4 when fluid is being heated

n= 0.3 when fluid is being cooled

In this equation, Re is the Reynolds number which equates to:

Re = (m D_H)/(μ)

and Pr is the Prandtl number :

Pr = (C_p* μ)/k

For the Reynolds number, m is equal to the mass flow rate. For the Prandtl number, C_p is equal to heat capacity, and in both equations, μ is the viscosity of the fluid in consideration. Once we have all of these factors, we can get a decent estimation of the heat transfer.

• Also we can get the estimation from some published papers or from some experimental values.

Accuracy of HTC prediction :

Accuracy of the predictions depends on several things like,

• Accurate geometry of model. Its Mesh quality.
• Inflation layers
• Properties of material being used.
• Turbulence models.

Conclusion :

• From the above both cases output, we can say that the results are almost same but the refined mesh gives us more smoothness and accuracy. Therefore finer the mesh, more will be the accuracy.
• HTC are near doubled in the refined mesh case, also HTC plays quite important role.