CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

need help on natural convection

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   September 27, 2005, 15:14
Default need help on natural convection
  #1
muh
Guest
 
Posts: n/a
I've been working on "Natural Convection Between two horizontal parallel plates" for some time. but i've several problems on my project. is there anyone who can help me and who worked on such a project before. i've fixed temp. boundary condition on plates and Pressure outlet boundary condition for the side boundaries. are they true or am i wrong on this ?
  Reply With Quote

Old   September 28, 2005, 13:04
Default Re: need help on natural convection
  #2
Evan Rosenbaum
Guest
 
Posts: n/a
Two fixed temp plates and pressure outlets sounds right. You probebly need to be more specific about the problems you refer to.
  Reply With Quote

Old   September 28, 2005, 13:29
Default Re: need help on natural convection
  #3
muh
Guest
 
Posts: n/a
This project was actually done experimentally before. Now, I want to re-calculate the Nusselt number that was calculated experimentally and make a comparison. (In the experiment bottom plate was heated uniformly with a resistance and the top plate was insulated from above. After the experiment both the bottom wall temperature, top plate temperature and surrounding temperature was measured as they became stable. So I want to use these temperature values as my boundary conditions and calculate Nusselt number. But I'm not sure if I'm right or wrong to select these boundary conditions? I think I must get the same result of the experimental one. ) - From the experiment, Known data values listed below.

1) Distance between parallel plates: for example 6 mm

2) Bottom Plate: I use wall boundary condition with constant temperature. (Do I have to use shell conduction? I 've confusion on this point) Tbot = 326,5 K (Experimental data)

Top Plate : I use a wall boundary condition with constant temperature. (Do I have to use shell conduction? I 've confusion on this point) Ttop = 315,3 K (Experimental data)

Surrounding temperature : T∞ = 289,8 K (Experimental data)

QUESTIONS: Question : I use Boussinesq approximation and I don't know if I'm right or wrong ?

Question : I use Tfilm temperature for the fluid ( air ) properties ; where Tfilm=(Tbot + T&infin / 2 is it correct?

Question : I enter "Tref =Surrounding Temperature" is it correct ?

Question : I use 20*30*30 (NY*NX*NZ) grids for the numerical analysis is it enough ?

Question : Are my boundary conditions correct for this experimental apparatus?

PS: if anyone wants to help me i can send my mesh and case files to his/her private mail.i'll be glad if this could happen.

  Reply With Quote

Old   September 29, 2005, 12:29
Default Re: need help on natural convection
  #4
Evan Rosenbaum
Guest
 
Posts: n/a
There are several things you need to consider.

1. Are the experimental measurements such that you know the plates are isothermal? If there is a large gradient on the plates the results will be affected.

2. Boussinesq should be OK, as your temperature range is pretty small.

3. The film temp should be OK.

4. Make sure you also set the side boundaries to the surrounding temperature.

5. There is no way to know if your mesh is good enough ahead of time, and it depends on other factors like if you are using turbulence and, if so, which wall approach you use.

6. If the plates are not actually closed to make a closed cavity, you may need to model some portion of the surrounding air.

  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
natural convection problem with radiation jorien CFX 0 October 14, 2011 09:26
Natural Convection with heat generation krishnachandranr Main CFD Forum 0 July 28, 2009 04:22
Coupled vs Seg - Natural vs. Forced Convection Alex CD-adapco 5 December 12, 2007 05:58
natural convection at high Rayleigh mauricio FLUENT 2 February 23, 2005 20:43
Mixing By Natural Convection Processes Greg Perkins FLUENT 0 February 12, 2003 19:40


All times are GMT -4. The time now is 18:03.