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Simulation of EGR

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Old   February 11, 2016, 11:19
Default Simulation of EGR
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Hi every one,

I'm trying to simulate an EGR (Exhaust Gas Recirculation) with Fluent but I have a lot of problems with the boundary conditions.
I found this "Step to Step" where I can see some options, but I would like to know the rest of options that he selected.
Could any one tell me where I can find a tutorial to do it or the files of this video?
https://www.youtube.com/watch?v=EXO85d2eEOw
Thanks!
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Old   February 16, 2016, 12:48
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Hi,

what is that you want to simulate? In the tutorial they are not modelling EGR, but the cooling down on the exhaust gas before they are actually recirculated into the combustion chamber. Do you want to model the cooling of the flue gas (i.e. just a heat transfer problem, with no chemistry involved) or the effect of EGR on the combustion process?
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Old   February 16, 2016, 13:24
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Thanks for your answer!
I want to simulate the heat exchange between the exhaust and coolant, to see the temperature variations throughout the model.
For that, I have all the inlet and outlet options but, for example, I need to calculate the heat transfer coefficient (h).
It's just a heat transfer problem.
One more thing. I have my EGR model but I need to fill it, because I must to define the fluid zones. I try to do it with fill option in DesignModeler but I can't do it. Do you know how I can do it?
Thanks!
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Old   February 16, 2016, 19:10
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Once you will have a complete CFD model (including conjugate heat transfer) the heat transfer coefficient will be a result of your calculations, it is not something that you have to specify beforehand.
What do you mean by saying that you have the EGR model? Do you have a geometry file and want to generate a mesh? I am not an expert of Design Modeler, but this is something that is doable with any meshing software.
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Old   February 17, 2016, 06:30
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What do you want to say with conjugate heat transfer?
When I select the wall between the two fluids, in boundary conditions, I select "convection" as Thermal Condition and I write the heat transfer coefficient. Am I doing something wrong?
Yes, I want to say that I have the EGR model but I don't know how to mesh both fluids domain. I will try it with Patran, but I'm not sure if I can get it.
Thnaks!
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Old   February 17, 2016, 06:47
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I really think you should get a good grasp of what you want to model before starting.

This is a typical conjugate heat transfer problem, i.e. you have a cold fluid -> convective heat transfer to a solid surface -> conduction through the solid -> convective heat transfer to a hot fluid. You are supposed to model the conjugate heat transfer in your model, so that you are not required to specify the heat transfer coefficient yourself (I reckon one of the main point of your simulation will be to evaluate the heat transfer coefficient, so it is pointless to specify it as user-defined parameter).

In order to simulate this problem you should include the effect of the solid pipe on the heat transfer process in the model. You can do this either by meshing the solid parts directly or using the thin wall option in fluent (check the theory guide for more information on this), in this case personally I would go with the second option, but you know your geometry better than me so it's up to you to decide what you want to do.
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Old   February 17, 2016, 07:42
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I am truly grateful for your answers.
I want to do exactly you say. Convection + conduction + convection between cold fluid, solid an hot fluid.
So, when I put boundary conditions, what kind of thermal condition must select?
In my first try, I put 1000 W/(m^2K) as heat transfer coefficient and I obtain good results, but now I think that I did it wrong.
Can I delete external wall and put it as thickness wall?
If I do it like you say, the gaps between two fluids, Should I fill them?
I have a lot of doubts... Sorry!
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Old   February 17, 2016, 10:37
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You should check the boundary conditions for coupled walls on the theory guide, everything is explained there.

As far as your mesh is concerned, go through the tutorials for Design Modeler or ICEM (or any other mesh generator) and you will be able to get it easily.
Good luck!
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Old   February 17, 2016, 12:54
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Now I'm reading the user's guide.
In my case, I want to know temperatures after the heat transfer between two fluids which are separated by walls. In the boundary conditions panel, I must to wirte the heat transfer coefficient in convection option, doesn't it?
But after calculate the solution, I can see this coefficient along the surface and it's different. I don't understand this.
Sorry for all my questions, but I'm begginer and I want to improve with Fluent.
Thanks!
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