Week 4 - CHT Analysis on Exhaust port

Aim -

1. To perform Compound Heat Transfer analysis of exhaust model.

2. We will mimic the movement of fluid as well as the transmission of heat to a solid, or CHT Analysis on an Exhaust port.

3. Then, on the interior solid surface, we will determine the wall heat transfer coefficient and display the velocity and temperature contours where necessary.

4. We'll check to see if the HTC simulation forecasts are accurate. And specify the elements that affect the prediction's accuracy.

Introduction - 

Compound Heat Transfer -

          Compound heat transfer captures the effects of convection and conduction together in the heat trasfer process that involves flow of fluid medium through a solid component. By transferring thermal energy at their interfaces and transporting it by conduction inside solids and furthermore via convection within fluid domains, conjugate heat transfer analysis enables the modelling of heat transfer between solid and fluid domains.By simultaneously resolving all pertinent solid and flow field heat transfer processes, conjugate heat transfer analysis may properly forecast heat transfer.The combination of heat transmission in fluids and heat transfer in solids is known as conjugate heat transfer. Convection often prevails in fluids whereas conduction frequently does so in solids. Conjugate heat transfer is seen in a variety of circumstances, including thermal radiation, free and forced convection in gases and fluids, and conduction in solids.

The three principal ways that heat is transferred:

1. Conduction- When a stationary medium has a temperature differential, conduction is the mode of heat transfer.

2. Convection- When there is a temperature differential between the two, convection is the heat transfer between a surface and a flowing fluid.

3. Radiation- The emission of energy in the form of electromagnetic waves is referred to as radiation. There is net heat transfer through radiation between two surfaces of differing temperatures in the absence of a separating medium.

In the majority of applications, heat transfer in solids and heat transfer in fluids are coupled. This is due to the fact that solids are often submerged in a fluid and that fluids move around or between solid objects. The analysis of temperature fields and heat transfer is made possible by a precise description of the material characteristics, flow regimes, and geometrical configurations. Such a description can also serve as the basis for a numerical simulation that can be used to evaluate various configurations or forecast conjugate heat transfer effects, for example, in order to enhance the thermal performance of a particular application

Solving and Modelling Approach -

Following are the steps followed in Modellind and solving the analysis-

1. Modelling

2. Meshing 

3. Physics setup and Solution

4. Post Processing

Explanation -

1. Modelling -

• First of all we opened spaceclaim modelling environment in the fluent.
• Then we had to import the geometry model of the exhaust.
• Then we extracted the volume of the fluid that will be flowing through the exhaust.
• We then created a seperate component by moving solid volume and fluid volume to the new component.
• We then deleted the the empty components by right clicking on the parent geometry.
• This newly created component is named as 'Final Geometry'.
• We the setup the share topology option for parent geometry to 'share' status so that when we open Meshing environment this information is flawlessly shared.
• We then went to 'workbench' option and clicked on 'SharePrep' to facilitate the sharing of information between the two distinct environments of spaceclaim and meshing.
• Failing to do this will create inaccurate meshing in the further steps which will lead to incorrect solution.

2. Meshing -

• For meshing we went to Mesh environment in the fluent standalone system.
• Then we did create various named selections as inlet, outlet, outer wall convection.
• Then we created a baseline mesh to understand the number of elements and quality of mesh.
• Then we went on creating inflation layer at the interface between fluid and solid boundary. Inflation layer is neccesary because it creates body fitted mesh i.e. mesh elements of the same shape as the geometry of the model.
• Then we changed the element size as per our satisfation as it was based on the lelement quality i.e. Mesh--->quality---->mesh metric---->Element quality, and it was 14% so we moved on to setting up the problem.

3. Physics setup and Solution -

• We chose pressure based solver and steady state condition for solving the problem.
• Then we went on to selecting k-epsilon model of turbulance for solving the problem.
• We turned on the energy equation.
• We then proceeded to applying boundary conditions.
• For inlet we gave inlet velocity as 5 m/s and under thermal section, temperature as 700 K.
• We checked the outlet boundary condition as pressure based.
• We then for outer wall convection gave convection boundary condition with h = 20 W/(m^2 K) and free stream temperature 300 K.
• We then initialized the solution using hybrid initialization but within 10 iteration essential convergence was not reahced so we initialized it again this time with 15 iteration and convergence was achieved.
• Then we created contours for temperature at inlet, outlet and outer wall convection.
• Then we created solution animation for temperature contour, adjusted the view of animation.

Solution-

• We then gave 150 iteration to solve the problem and clicked on calculate.

5. Post Processing -

• We then moved on to post processing of the results by clicking on the Result section of the fluent standalone system.
• We activated the outer wall convection section, coloured it with variable velocity and temperature one at a time.
• Then we inserated a streamline plot.
• The wall convective heat transfer coefficient option was not readily available in the variable section so we had to go back to solution tab and export the required results and then import them back in the results section.
• We then created a plane and did the same process explained in earlier two points.

Results -

Temperature Plots -

Velocity Plots-

Wall Temperature Heat Transfer Coefficient - 

Factors on which accuracy of the results depends -

• On the workbench, we must allow share(share prep) and click share.This step is crucial because if you don't complete it, you won't see the single interface connecting them.Therefore, this specific stage takes care of constructing the interfaces, ensuring that your solid volume or block and fluid block share a single interface.
• Make certain that the share topology is configured for share. Only then will the meshing be homogenous and well connected. 
• The precise heat transfer coefficient for the outside border must be provided.Only then do we receive the complete, precise answer.
• Give the values precisely to avoid round-off errors, such as when describing inflation layers or any other quantities with decimal values.
• Since the interface is crucial for calculating heat transfer at that location, inflation layers must be created there in order to precisely capture the flow and compute the numbers.