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

Mass Transfer & VOF

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 3, 2009, 10:39
Default Mass Transfer & VOF
  #1
R Liew
Guest
 
Posts: n/a
Dear all,

I'm trying to solve a condensation problem. To do this, I use the VOF model and have written a complex condensation model. There are several problems:

- 1) The Absolute Pressure drops BELOW zero.

This should not be possible ofcourse. My operating pressure is 4 bar abs.

- 2) The mass transfer works not like it should:

I've tested this with a very simple condensation model (UDF):

from species = water.

to species = steam.

DEFINE_MASS_TRANSFER(Condensation,cell,mix,from_in dex, from_species_index, to_index, to_species_index)

{

Thread *gas = THREAD_SUB_THREAD(mix, from_index);

Thread *liq = THREAD_SUB_THREAD(mix, to_index);

real T_sat = 406;

real m_lg;

if (C_T(cell,mix)>T_sat)

m_lg = 5000;

else

m_lg=-5000;

return m_lg;

}

This means that if the cell temperature exceeds the saturisation temperature, evaporation should occur. Otherwhise evaporation occurs.

But if I solve the problem (unsteady) this is not the case. In my simulation, at one place the mass transfer is 5000 kg/(m3-s) from water to steam. This is true indeed if I look to the temperatures, but if I look to the phase, the opposite occurs (condensation instead of evaporation).

I use the explicit VOF sceme, no turbulence models, energy equation. Unsteady with dt=1e-6 sec.

Solution controls:

p-v coupling: coupled

pressure: Presto

momentum: Quick

VOF : modified HIRC

energy: Quick.

Please, can anyone help me??

Thanks in advance!

R Liew, Technical University of Eindhoven

  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
Mass Transfer R Liew FLUENT 0 March 10, 2009 09:42
mass transfer houman CFX 2 October 20, 2005 06:01
correct units of mass transfer used in mass intera prasanth FLUENT 0 June 2, 2003 12:11
Mass transfer John FLUENT 2 April 23, 2003 21:15
mass transfer Ludwig Bauer FLUENT 1 January 7, 2003 07:11


All times are GMT -4. The time now is 05:47.