CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT > Fluent Multiphase

Evaporative phase change modeling in FLUENT

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

Like Tree1Likes
  • 1 Post By Kimia

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 30, 2017, 15:23
Default Evaporative phase change modeling in FLUENT
  #1
New Member
 
Join Date: Jun 2016
Posts: 17
Rep Power: 10
Kimia is on a distinguished road
Hi all,
I am working on a micro scale simulation of evaporation inside a porous structure, using ANSYS FLUENT. It is a transient two phase model (VOF) considering water and vapor inside a micro scale pore. I am using UDF codes to apply the source terms relative to the mass transfer according to Schrage's model formulation.
The results that I get seem to be logical, but my problem is that the time steps that I have to use are very small ( in the order of ~1e-9 s), which make it impossible to reach convergence.
Every time I increase the time step, I face the error that the "Global Courant number is greater than 250.00. The velocity field is diverging. check the solution and reduce the time step".
I really appreciate it if you have any suggestions or solutions for this problem or you have any recommendations for me to increase the time steps to more realistic values.
Ahmed Alkaisi likes this.
Kimia is offline   Reply With Quote

Old   March 31, 2017, 05:36
Default
  #2
Member
 
Ahmed Alkaisi's Avatar
 
Ahmed Alkaisi
Join Date: Aug 2015
Location: Australia
Posts: 80
Rep Power: 11
Ahmed Alkaisi is on a distinguished road
Send a message via Skype™ to Ahmed Alkaisi
Decrease URF to (0.2-0.5)
Use implicit

Sent from my SM-G900I using CFD Online Forum mobile app
Ahmed Alkaisi is offline   Reply With Quote

Old   May 12, 2017, 00:39
Default
  #3
New Member
 
Hao su
Join Date: May 2017
Posts: 4
Rep Power: 9
blue-sky is on a distinguished road
Quote:
Originally Posted by Kimia View Post
Hi all,
I am working on a micro scale simulation of evaporation inside a porous structure, using ANSYS FLUENT. It is a transient two phase model (VOF) considering water and vapor inside a micro scale pore. I am using UDF codes to apply the source terms relative to the mass transfer according to Schrage's model formulation.
The results that I get seem to be logical, but my problem is that the time steps that I have to use are very small ( in the order of ~1e-9 s), which make it impossible to reach convergence.
Every time I increase the time step, I face the error that the "Global Courant number is greater than 250.00. The velocity field is diverging. check the solution and reduce the time step".
I really appreciate it if you have any suggestions or solutions for this problem or you have any recommendations for me to increase the time steps to more realistic values.
hi,I'm working on boiling flow inside a tube, and I meet the same problem with you. Can you have some new ways to solve this problem? And i meet other problems that the bobble couldn't separate from the wall. can you give me some advice. thank you very much
blue-sky is offline   Reply With Quote

Old   May 12, 2017, 07:53
Default
  #4
New Member
 
David Chou
Join Date: Nov 2015
Posts: 5
Rep Power: 10
hospital0968 is on a distinguished road
Courant number = v*dt/dx
if C is huge enough to lead to divergence, decrease dt or increase dx
hope this will help
hospital0968 is offline   Reply With Quote

Old   May 13, 2017, 02:43
Default
  #5
New Member
 
Hao su
Join Date: May 2017
Posts: 4
Rep Power: 9
blue-sky is on a distinguished road
Quote:
Originally Posted by hospital0968 View Post
Courant number = v*dt/dx
if C is huge enough to lead to divergence, decrease dt or increase dx
hope this will help
thanks for your reply. the problem is that i drcrease the time step size ,but the problem also appear. i think the problem may be caused by the surface tension
blue-sky is offline   Reply With Quote

Old   July 4, 2017, 02:44
Default
  #6
Member
 
Ahmed Alkaisi's Avatar
 
Ahmed Alkaisi
Join Date: Aug 2015
Location: Australia
Posts: 80
Rep Power: 11
Ahmed Alkaisi is on a distinguished road
Send a message via Skype™ to Ahmed Alkaisi
Quote:
Originally Posted by Kimia View Post
Hi all,
I am working on a micro scale simulation of evaporation inside a porous structure, using ANSYS FLUENT. It is a transient two phase model (VOF) considering water and vapor inside a micro scale pore. I am using UDF codes to apply the source terms relative to the mass transfer according to Schrage's model formulation.
The results that I get seem to be logical, but my problem is that the time steps that I have to use are very small ( in the order of ~1e-9 s), which make it impossible to reach convergence.
Every time I increase the time step, I face the error that the "Global Courant number is greater than 250.00. The velocity field is diverging. check the solution and reduce the time step".
I really appreciate it if you have any suggestions or solutions for this problem or you have any recommendations for me to increase the time steps to more realistic values.
Do you have any update?

Sent from my SM-G900I using CFD Online Forum mobile app
Ahmed Alkaisi is offline   Reply With Quote

Old   January 23, 2019, 02:22
Default UDF evaporation, standard state enthalpy specification?
  #7
Senior Member
 
vidyadhar
Join Date: Jul 2016
Posts: 138
Rep Power: 10
vidyadhar is on a distinguished road
Quote:
Originally Posted by Kimia View Post
Hi all,
I am working on a micro scale simulation of evaporation inside a porous structure, using ANSYS FLUENT. It is a transient two phase model (VOF) considering water and vapor inside a micro scale pore. I am using UDF codes to apply the source terms relative to the mass transfer according to Schrage's model formulation.
The results that I get seem to be logical, but my problem is that the time steps that I have to use are very small ( in the order of ~1e-9 s), which make it impossible to reach convergence.
Every time I increase the time step, I face the error that the "Global Courant number is greater than 250.00. The velocity field is diverging. check the solution and reduce the time step".
I really appreciate it if you have any suggestions or solutions for this problem or you have any recommendations for me to increase the time steps to more realistic values.

Hello Kimia,


I have also written an UDF to simulate evaporation. The UDF can be found in the link below:
UDF with VOF method to predict evaporation mass/heat flux at vapor-liquid interface


But, I am also facing similar problems:

1) The interface is moving but faster than predicted by analytical solution of Stefan problem.
2) For large time steps, I am also facing divergence problems.


I request you to go through the above link and kindly let me know if there is any mistake in the UDF.
Also, how to specify the Standard state enthalpy(J/kgmol) values in Fluent so that required Latent heat(J/kg) is accomplished. Can I specify any values of standard state enthalpy such that the difference (in values between the two phases) divided by molecular weight of liquid or vapor gives the desired latent heat?


Thanks in advance!
vidyadhar

Last edited by vidyadhar; January 23, 2019 at 02:23. Reason: text added
vidyadhar is offline   Reply With Quote

Old   May 26, 2020, 01:19
Default
  #8
New Member
 
Zicheng Li
Join Date: Dec 2019
Posts: 8
Rep Power: 6
Liz1219 is on a distinguished road
Can you upload your file and study it together?
Liz1219 is offline   Reply With Quote

Reply

Tags
courant number, evaporation, phase change, timestep, transient 2d

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Phase Change Modeling of water Amar Kad CFX 4 January 11, 2016 18:09
it is possible tu simulate water phase change with fluent 14 or 15? kh91 Fluent Multiphase 1 June 13, 2014 09:58
Modeling of evaporative cooling pad on ANSYS Fluent Vishnu_1991 Fluent Multiphase 0 June 5, 2014 16:17
modeling phase change and homogeneous bubbles in many cycles dwtme FLOW-3D 12 January 1, 2013 05:57
phase change with CFX aximefu CFX 5 March 28, 2012 04:38


All times are GMT -4. The time now is 22:44.