CFD Online URL
[Sponsors]
Home > Forums > CFX

Defining Boundary conditions for heat transfer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 13, 2010, 10:03
Default Defining Boundary conditions for heat transfer
  #1
Member
 
Sujay
Join Date: Apr 2010
Location: Karnataka, India
Posts: 38
Rep Power: 6
sujay is on a distinguished road
The domain is nearly reactangural box with inlet pipe submerged at top and outlet at the bottom. The top (rest of inlet pipe) is like opening BC with heat radiation wherras whole bottom of reactangle is outlet. Rest four sides are wall with heat flux conditions. Kindly guide me to set these boundary conditions.

As i choose thermal enegry in heat transfer and thermal radition, four wall also shows thermal radiation model with opaque showing emmssivity and diffue fraction as 1.

I have heat flux for these wall and donot want to add the radiation here.

For opening BC, it asks opening or static temperature. What is meaning of these temperature.

Kindly guide me
Attached Images
File Type: jpg New Drawing.JPG (23.2 KB, 14 views)
sujay is offline   Reply With Quote

Old   May 13, 2010, 11:41
Default
  #2
Senior Member
 
Attesz's Avatar
 
Attesz
Join Date: Mar 2009
Posts: 352
Rep Power: 7
Attesz is an unknown quantity at this point
Only a question, Total Energy model isn't suitable in your case?
Attesz is offline   Reply With Quote

Old   May 13, 2010, 20:18
Default
  #3
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,860
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Quote:
For opening BC, it asks opening or static temperature. What is meaning of these temperature.
Opening temperature means during outflow the temperature is set by the temperature of the fluid flowing out the opening, and during inflow the temperature is set by the specified temperature (usually a total temperature).

Static temperature means the opening is always set to have the specified static temperature, regardless of the flow direction.

The temperature boundary during outflow only makes a difference for the radiation model.
ghorrocks is offline   Reply With Quote

Old   May 14, 2010, 00:53
Default
  #4
Member
 
Sujay
Join Date: Apr 2010
Location: Karnataka, India
Posts: 38
Rep Power: 6
sujay is on a distinguished road
As heat extraction is differnt from the differnt wall, domain needs to be defined with respective flux rather than total energy. So i think total energy model is not suitable.

I have no idea about the total energy model
Quote:
Originally Posted by Attesz View Post
Only a question, Total Energy model isn't suitable in your case?
sujay is offline   Reply With Quote

Old   May 14, 2010, 00:59
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,860
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Quote:
As heat extraction is differnt from the differnt wall, domain needs to be defined with respective flux rather than total energy. So i think total energy model is not suitable.
I have no idea what you are talking about. Are you saying you want to specify a heat flux at an opening? This would be very weird. The total energy model is to get CFX to solve the full compressible flow equation rather than incompressible equations so is a totally different thing.
ghorrocks is offline   Reply With Quote

Old   May 14, 2010, 03:12
Default
  #6
Member
 
Sujay
Join Date: Apr 2010
Location: Karnataka, India
Posts: 38
Rep Power: 6
sujay is on a distinguished road
  1. I want to give heat flux at the four side walls
  2. Inlet temperature at inlet
  3. radiation BC at the opening
Kindly guide me


Quote:
Originally Posted by ghorrocks View Post
I have no idea what you are talking about. Are you saying you want to specify a heat flux at an opening? This would be very weird. The total energy model is to get CFX to solve the full compressible flow equation rather than incompressible equations so is a totally different thing.
sujay is offline   Reply With Quote

Old   May 14, 2010, 05:41
Default
  #7
Senior Member
 
Attesz's Avatar
 
Attesz
Join Date: Mar 2009
Posts: 352
Rep Power: 7
Attesz is an unknown quantity at this point
I'm not so experienced in it, but if you want to calculate with radiation, you can not define it at the opening. You can set there an energy source (as flux), to take into account the effect of the radiating environment. I hope I'm not wrong...

Otherwise, if you use gas as fluid, the Total Energy model can give better results.

Regards

Last edited by Attesz; May 14, 2010 at 06:02.
Attesz is offline   Reply With Quote

Old   May 14, 2010, 09:00
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,860
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Quote:
  1. I want to give heat flux at the four side walls
Then set the side walls with a specified heat flux. Isn't that obvious?

Quote:
Inlet temperature at inlet
Then set the temperature at the inlet. Again, isn't that obvious?

Quote:
radiation BC at the opening
It is not clear what you mean. Do you mean there is a radiative heat source outside the domain which is shining into the domain and heating it up? In that case you need to define a directional radiation source at this boundary, and specify its radiative properties.

Quote:
Otherwise, if you use gas as fluid, the Total Energy model can give better results.
If buoyancy effects are not significant then incompressible flow should be fine. If the temperature range is small then the buosinessq incompressible buoyancy model is fine. Only if buoyancy effects are significant AND the temperature range is large would I consider a compressible model, that is the Total Energy model. It involves a lot more CPU time so only use it if you need to.
ghorrocks is offline   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
Impinging Jet Boundary Conditions Anindya Main CFD Forum 24 January 11, 2012 14:40
mesh file for flow over a circular cylinder Ardalan Main CFD Forum 6 April 18, 2010 00:40
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 05:05
CFX doesn't continue calculation... mactech001 CFX 6 November 15, 2009 22:25
Concentric tube heat exchanger (Air-Water) Young CFX 5 October 7, 2008 00:17


All times are GMT -4. The time now is 22:39.