Conjugate Heat Transfer Analysis of Exhaust Port using Ansys Fluent

Aim:

Conjugate Heat Transfer Analysis of Exhaust Port using Ansys Fluent

Objectives:

• To understand the conjugate heat transfer in exhaust port
• To simulate flow and heat transfer in exhaust port
• To carry out Geometry preparation, Mesh formation with good quality and selection of turbulence model by maintaining the Y+ plus value
• To understand the results of conjugate heat transfer of exhaust port

Introduction:

The Exhaust port is one of most important parts of automobile industry. In exhaust port, the fluid coming out from engine is supplied to the surrounding environment. The fluid coming out from engine has very high temperature thus when it passes through the exhaust port it will transfer heat from fluid to solid wall which is called as Conjugate Heat Transfer. Then, it will increase temperature of solid surface and transfer heat to environment. Thus, Conjugate Heat Transfer is one of most important parameters in heat transfer. Similarly, there are various other applications such as heat exchangers, Boilers, Condensers, Heaters, etc. where conjugate heat transfer plays a most important role. Hence, the conjugate heat transfer analysis of exhaust port is carried out in this study which is given below:

Simulation Procedure:

Step: 1

Open the Ansys Workbench and select the fluent

Step: 2 Geometry Preparation

In the first step, open spaceclaim and prepare geometry of model

First of all select the option of Repair and remove an extra edges of model.

Then, the select the option of volume extraction and select inside volume then name it as fluid volume.

Figure: Fluid Volume

The surrounding volume is named as solid volume which is shown below:

Figure: Solid Volume

After doing this, move this two volume into single component and select the option of delete the empty components which will delete the empty components.

Then, Select the model properties and click on share. After this select option of share in workbench which will share data at common surface which is shown below:

Figure: Share Topology

Step: 2 Meshing

In this part meshing is divided in two parts:

1. Baseline Mesh
2. Refinement Mesh

1.Baseline Mesh:

In this section mesh is generated directly which is given below:

Figure: Baseline Mesh

2. Refinement Mesh:

In this, separate body sizing is given to outer solid body. Body fitting mesh such as inflation layer on both fluid and solid side is given to capture good data. Edge sizing is given to circular edges with 36 number of divisions. The details of meshing are given in table.

Figure: Refinement Mesh

Y Plus:

In this study, Y-plus value is analyzed from 1 to 5 for k-omega model and 30 to 100 for k-epsilon model but after simulation Y plus plot will be not be in range. But, Y plus will give good results from 0.85 to 0.5. When value of Y plus less than 0.5 is used then it will show bad mesh quality which will get bad result. Y plus value of 0.8 is nearer to desired result thus it is used.

Figure: Y Plus Calculation

Length:

In this model total length will be length from inlet to outlet path from where fluid flows. But, there are four inlets thus maximum length will be considered. Hence, the length is taken as from left side inlet to outlet which shown in below figure:

Total length =749.86 + 819.99 + 6 + 710.7654

= 2286.21 mm

Table of Meshing

	Solid volume mesh size	fluid volume mesh size	Fluid-Inflation (First layer)	Solid-Inflation (First layer)	Edge sizing (No. Of divisions)	No. of Cells
Baseline Mesh	-	-	-	-	-	137687
Refinement Mesh	15 mm	100 m	0.0588 mm	5 mm	36	621669

Step: 3 Set- up

The set-up of simulation is also divided into two parts:

1. Baseline Mesh:

In this simulation, the following parameters are selected:

Type: Steady-state simulation

Solver: Pressure based

Velocity Formulation: Absolute Velocity

Energy Equation: Selected

Turbulence model: k-epsilon model (standard)

Inlet velocity: 5 m/s

Inlet Temperature: 700 k

Outer wall Conduction: 20 w/m^2 K

Wall thickness: 0 mm

Initialization: Hybrid

2. Refinement Mesh:

In this simulation, the following parameters are selected:

Type: Steady-state simulation

Solver: Pressure based

Velocity Formulation: Absolute Velocity

Energy Equation: Selected

Turbulence model: k-omega model (SST)

Inlet velocity: 5 m/s

Inlet Temperature: 700 k

Outer wall Conduction: 20 w/m^2 K

Wall thickness: 0 mm

Initialization: Standard

Step: 4 Results

In this section, the various plots including Residual change, wall heat transfer coefficient, Y plus change, Temperature plot and velocity plots are given below:

Baseline:

Wall Heat transfer coefficient = 293236.6 W/m^2 K

Figure: Residual Change

Figure: Adjacent wall heat transfer coefficient on inflation shadow

Figure: Y plus plot on fluid volume

Figure: Temperature plot on wall

Figure: Velocity streamlines

Figure: Temperature plot on plane

Figure: Velocity plot on plane

Figure: Wall heat transfer coefficient near wall

Refinement:

Wall Heat transfer Coefficient= 893.79 W/m^2 K

Figure: Residual Change

Figure: Adjacent wall heat transfer coefficient on inflation shadow

Figure: Y plus plot on fluid volume

Figure: Temperature plot on wall

Figure: Velocity streamlines

Figure: Temperature plot on plane

Figure: Velocity plot on plane

Figure: Wall heat transfer coefficient near wall

Comparisons of Results:

When the results of both cases are compared then it shows that refinement mesh gives good results. The results show that heat transfer coefficient achieved from refinement is pretty much good and Y-plus plot is also within range. The residuals are also converged. The temperature and velocity distribution achieved from refinement are also good as compared to baseline.

Temperature plots:

Velocity Plots:

Validation of Simulation Results:

The results obtained from the simulation are verified by comparing with results of research paper where same geometry and experimental set-up are used. The Second option to make experimental set-up and perform experiments then compare the results with simulation.

The accuracy of CHT heat transfer prediction depends upon following factor:

• Mesh quality and Mesh refinement
• Y-plus value and Inflation layer thickness
• Turbulence model

Conclusion:

The Conjugate heat transfer analysis is one of the most important analysis which is widely used in various applications. In this study, CHT analysis of exhaust port is carried out. The baseline and refinement mesh are used in this study. But, the refinement gives good overall result as compared to baseline. In such type of analysis, good mesh quality and refinement and correct turbulence model play an important role which give the right prediction and good results which is discussed in previous section. This also give good idea about actual applications.