Exhaust Port Challenge

AIM: Conjugate heat transfer analysis of exhaust port of engine using Ansys fluent.

We can divide this project in a given methodology

• Basic of Conjugate heat transfer
• Exhaust port baseline simulation in fluent
• Mesh independent study
• Verifying HTC predictions
• learning outcome

• Conjugate heat transfer: Conjugate heat transfer process describes a process which involves a variation of temperature within solid and fluid due to the transfer of energy. Conjugate heat transfer deals with heat transfer in solids and heat transfer in the fluid. The best example is heat sink in the chip , whereby conduction combining the solids and by convection to the fluid. Typical examples of conjugate heat transfers are given below.

1. Overall heat transfer coefficient of car radiator
2. Temperature distribution of chemical vessel, gas turbine, and heat exchangers
3. Temp distribution and heat transfer coefficient from the heatsink.
4. Temp distribution with time in engine.
5. Heat loss in devices to minimize energy reducing cost.

fluid flow and temp transfer are coupled in the energy equation, That is primary reason to solve it by computational and numerical methods rather than depending on the analytical solution.

In the case of natural convection prandtl and grashof number is important , in forced convection Reynolds number is more important.

Baseline simulation of exhaust port in fluent.

• Space claim setup
• Import assembly of exhaust port in space claim.

• Extract the volume by volume extract method , as we are interested in internal flow. There will be two geometry Inside fluid and outside geometry which is solid.

• Share the topology to avoid interpretation errors.

Meshing & Boundary conditions.

• Boundary conditions are given below.
• Inlet for the air inlet
• An outlet for the outlet of air
• Outer wall for Heat transfer coefficient

• Meshing setup

Mesh type: tria

topology is shared

element size:150 mm(default)

• Fluent setup

Fluent setup is given below

• Inlet velocity 5 m/s
• Inlet temperature: 700k
• The outlet is a pressure outlet
• For outer wall convection: heat transfer coefficient 20 w/m2 .k
• Free stream temp: 300K
• Solving model: K-e realizable
• Material for solid : aluminium
• Material for fluid : air
• Initialization is hybrid and running time is 500 Iterations.

• Heat transfer coefficient at the winner wall is

• Residuals

• Temp graph at the outlet

• Change due to HTC at outer wall

• Exhaust port HTC

Max HTC at the outlet is 101.2 W/m2.K.

• Streamline contour of velocity

Temp value at outlet

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Mesh independent study

Fluent setup will be the same for mesh independent study

Mesh size: 25mm

First layer thickness:0.05mm

max layers:10

growth ratio: 1.2

• Residuals

• Overall temp contour

• Value of Y+ is maIntained within viscous sub layer

HTC at outlet

• Velocity streamline profile

.

• Temp contour

• overall HTC value

Area weighted temp value at outlet

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Case 2

Mesh size: 25mm

First layer thickness:0.2mm

max layers:5

growth ratio: 1.2

• Residuals

• Overall temp contour

• wall y+

some of the particles are in the buffer zone and some are in the viscous zone.

• overall HTC graph

average HTC value

• HTC graph at exhaust

• HTC value at corner

• Temp graph

• velocity streamline

• Area weighted temp at the outlet

• Comparison of cases and results

The experimental value of HTC is 20 w/m2.k

Video of particles travelling through outlet from inlet

• How to verify the prediction of HTC
• Basically HTC prediction is determined from experimental data. If you see the streamline velocity graphs, at the outlet, the inner radius of bend has higher velocity and temperature due to the mass conservation law.
• Due to higher velocity, there will be higher Reynolds number. Because Reynolds number is directly proportional to the velocity
• Now Reynolds number is directly propositional to nusselt number (Nu)
• Russell number is ratio of convective heat transfer to conductive heat transfer.
  
  `NU=(hl)/k`
  
  where characteristic length is fixed, and nusselt number is high, therefore the heat transfer coefficient will be high.The value of nusselt number rat outlet pipe is 102
• HTC depends on mesh refinement, inflation layer, Y+ value, experimental data, solid material, fluid properties, environmental conditions.

• Learning outcome
• From the analysis we can conclude that, by adding mesh refinement, maintaining Y+ value and adding inflation layer More accurate results are achieved.