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

How to set up a differential equation for boundary

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 25, 2006, 21:37
Default How to set up a differential equation for boundary
  #1
Ray Wu
Guest
 
Posts: n/a
Dear All:

It really bothers me. Does anybody know how to set up a differential equation as a boundary condition?

It is a mass transfer problem within a control box. The equation governing the fluid is the Laplace Equation: d^2/dx_i^2 CA=0

Three surfaces all have the same and fixed boundary consition: CA=1 at x,y,z -> infinite

The other three: dCA/dx=0 at x=0 dCA/dy=0 at y=0 dCA/dz=hCA at z=0

I am stucked on the last one.

I'd very appreciated it if anyone could help.

Ray ^^
  Reply With Quote

Old   April 26, 2006, 02:09
Default Re: How to set up a differential equation for boun
  #2
rag
Guest
 
Posts: n/a
U can use symmetry BC for the same. For detailed understanding, check out details of symmetry BC in Fluent user's manual.
  Reply With Quote

Old   April 26, 2006, 18:41
Default Re: How to set up a differential equation for boun
  #3
Raphael
Guest
 
Posts: n/a
I did not see how the symmetry bc will happen with the last one. If you have a wall which only some species flow trhough you could use a pseudo "reaction" to impose the concentration gradient but I am not sure.

If your problem is a solution of a mixture where an interface exists and is where the mass transfer occurs you could create a UDF and solve the eq. dCa/dz=hCa(bulk)->

Ca(at boundary)= hCa dZ + Ca(at the neighbor cell of the boundary cell)

This concentration can be transformed to mass fraction whatever and used to specify the mass fraction defining the interface as a wall.
  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
Installation problems indy OpenFOAM Installation 7 April 3, 2009 09:40
boundary conditions of level set equation Amir Main CFD Forum 0 September 17, 2008 02:26
Level set equation in axisymmetric 2-D flow jinwon park Main CFD Forum 0 February 26, 2008 17:26
solving a differential equation with NEWTON.... myway Main CFD Forum 0 May 15, 2006 02:05
Differential equation solving cfd-user Main CFD Forum 1 November 12, 2003 03:42


All times are GMT -4. The time now is 16:32.