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-   -   How to solve natural convection problem in fluent? (http://www.cfd-online.com/Forums/fluent/80875-how-solve-natural-convection-problem-fluent.html)

 samantasubho October 9, 2010 09:59

How to solve natural convection problem in fluent?

Friends, I am trying to solve a natural convection problem in FLUENT (natural convection from a horizontal flat plate) with prescribed wall heat flux.
For the problem I have given the boundary conditions as: left and right part of control volume: pressure inlet and top part of the control volume pressure outlet, wall prescribed heat flux.The fluid is air with Pr=0.7
After 1300 iterations also my solution is not converging. Kindly help me if possible.

 hultman October 18, 2010 07:39

I assume that it is a steady-state run, or do you mean 1300 outer iterations?

 Logan Page October 21, 2010 04:41

add an image of your mesh and BC's if u can.

 saharesobh September 3, 2012 12:06

Hello,

I am trying to solve the natural convection (mixed convection) in a Chemical vapor deposition reactor. The reactor has top and bottom plates and inlet and outlet tubes. The reactor is heated by top smaller rectangular plate embodying two heating rod. the top plate is at 250 oc and the bottom plate is at 150 oc. So because of temperature gradient, the natural convection will occurs. When I go to the boundary condition, then I go to hot plate, I see the heat flux (w/m2) and the heat generation rate (w/m3). My question is that, should I need to get the heat flux and geat generation and then put them in Fluent or the fluent get them? would you please give me some advice. I don't know why I cannot see the roll-type flow between two parallel plate?As for heat trasnfer coefficient, I don't know how can I get it? I am really confused :(.

 sicfred September 4, 2012 06:09

HI Saharesobh,

First, when you go to boundary conditions hot plate, you just need to put the temperature in the plate, if you put heat flux or heat generation rate you are changing the boundary condition of your plate; this two values are going to be calculate by fluent after you running the simulation (for example in wall fluxes).

Second, if i understood your hot plate is in the top and the cold plate is in the botton, that means that there is not natural convection, you need the heat source in the bottom (or change the direction of the gravity XD)

Quote:
 Originally Posted by saharesobh (Post 380042) Hello, I am trying to solve the natural convection (mixed convection) in a Chemical vapor deposition reactor. The reactor has top and bottom plates and inlet and outlet tubes. The reactor is heated by top smaller rectangular plate embodying two heating rod. the top plate is at 250 oc and the bottom plate is at 150 oc. So because of temperature gradient, the natural convection will occurs. When I go to the boundary condition, then I go to hot plate, I see the heat flux (w/m2) and the heat generation rate (w/m3). My question is that, should I need to get the heat flux and geat generation and then put them in Fluent or the fluent get them? would you please give me some advice. I don't know why I cannot see the roll-type flow between two parallel plate?As for heat trasnfer coefficient, I don't know how can I get it? I am really confused :(.

 saharesobh September 5, 2012 13:04

Thank you so much for your response.

You are absolutely right. You know I asked my advisor about this problem( As you said the hot wall cannot be on the top ). She said this roll-type flow is made due to the momentum and prandtl number.Because I am using HTB fluent ( Hafnium tetra Butoxide). Due to these reasons I have natural convection and roll-type flow, Is it alright if I send you my file and you look at that? I can give you my email adress if it is Ok with you. Thank you so much in advance

 sagila October 14, 2012 08:20

Hi saharesobh,

I have a tall room with a hot roof that natural convection occurs in it. The side walls are at the same temperature and the floor is adiabatic. I have problem for converging it. Could you please let me know whether you have problem with convergence for your case which is similar to my case? If yes, could you please let me know how you solved it?

Thank you in advance.

 Светлана April 17, 2014 02:07

I have same issue, I'm sure you solved it back then?

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