Exhaust Port Challenge

• Objective :

1. To perform CHT analysis for two cases with different mesh sizes.
2. Verifying the values of heat transfer coefficient for both cases.

• Introduction :

• What is CHT Analysis ?

The analysis of heat transfer of solid and liquid domains by exchange of thermal energy at the interfaces between them. Heat transfers in solids occur by conductions while in liquids it occurs by convection. At solid-liquid interface heat transfer takes place by convection.

• Where is CHT Analysis is used ?

CHT analysis is used in simulation of heat exchangers, engine equipments, cooling of electronic equipment and general purpose heating and cooling systems.

• Why is CHT Analysis used ?

CHT analysis provides temperature distribution in solid and liquid interface. It also provides velocity and pressure distribution of the liquid inside the solid.

• Geometry :

1. Geometry creation can be done using any 3D modelling software which shows multiple ports coming from engine outlet ports and then combining them with exhaust port.
2. In this case as the geoemetry is readily available we need to import the geometry into space claim.
3. After space claim launches we need to perform volume extract to get seperate solid and liquid volume.
4. In this problem we need to enable the share topology option from tool. A red circle will be visible around edges after share topology is enbled.

Figure shows the 3D image of Exhaust Port manifold.

Figure shows the edges with red color after share share topology being enabled.

• Case Setup :

Solver type - Pressure Based steady state solver

Viscous model - K-Epsilon standard with Energy equation ON.

Material - Fluid : Air; Solid : Aluminium

Inlet BC - Velocity = 5 m/s; Temperature = 700K

Outer Wall - Thermal Conditions = Convection; Heat Transfer Coefficient = 20 W/m^2K; Free Stream Temperature = 300K.

• Case I :

Meshing -

Element size = 150 mm

Nodes = 27433

Elements = 138216

Figure shows mesh for baseline setup.

Figure shows coarse mesh generated for baseline setup.

Plots -

Figure shows plot of residuals for Case 1.

Figure shows contour of temperature for Case 1.

Temperature contour over outer surface for case 1.

Velocity streamlines from inlet to outlet in Case 1.

Velocity contours over a plane for case 1.

Pressure contours over a plane for case 1.

Temperature contours over a plane for case 1.

Wall Heat Transfer coefficient over a plane for case 1.

Wall htc zoomed in near corner for case 1.

• Case II :

Meshing -

Element size = 10 mm

Inflation layer with total thickness 5 mm.

Nodes = 169709

Elements = 478267

Figure shows the refined mesh.

Figure shows the inflation layers near the liquid surface edge.

Plots -

Plot of residuals for case 2.

Temperature Contour for case 2.

Temperature contour over outer surface for case 2.

Velocity strealines from inlet to outlet for case 2.

Velocity contours over a plane for case 2.

Pressure contours over a plane for case 2.

Temperature contours over a plane for case 2.

Wall HTC over a plane for case 2.

Wall HTC zoomed in near bent for better visualization of smooth heat transfer contour for case 2.

• Results and Conclusion :

Parameters Case 1 Case 2

Max. wall temperature(K) 601.488 602.820

Max. Velocity(m/s) 37.24 41.19

Wall HTC (W/m^2K) 99.44 224

Max. Pressure(Pa) 466.3 501.3

1. The effect of element size can be clearly observed in two cases.
2. Results are more accurate and near to exact values with finer mesh.
3. The value of wall HTC varies drastically in both cases because of inflation layers.
4. Remaining values are not that much affected because of quality of mesh. Meaning we can simulations for such quantities with baseline mesh.

• Verification of HTC

Heat transfer coefficient can be verified by using Nusselt number.

Nusselt Number is given by Nu = Re.Pr where, Re - Reynolds Number and Pr - Prandtl Number

Re increases with increase in velocity which in turn will increase Nusselt number.

also, Nu = Convective heat transfer / Conductive heat transfer = h/k/L

Meaning when velocity increases, convective heat transfer will also increase.

• Accuracy of HTC depends upon :

1. Number of elements and element size of the mesh.
2. Inflation layers.
3. Selection of right viscous model.
4. Selection of material and its properties.