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

How to model moisture within Fluent?

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

Like Tree15Likes

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 2, 2007, 06:55
Default How to model moisture within Fluent?
  #1
Carlos
Guest
 
Posts: n/a
Hello,

Does anybody know how to model moisture within fluent? I understand that the species transport model has to be implemented but it is not clear how to set up the model.

I am looking at the humidity levels within a livestock trailer. I have modeled sheep as large blocks with a surface generating heat. I now need to set up a humidity model. Does anybody know how I would approach this problem? What type of boundary condition would I need to set? I assume it will simply be a wall with a base level of wetness but it is not clear to me.

If anybody can help that would be much appreciated. All the best,

Carlos.
  Reply With Quote

Old   August 3, 2007, 21:04
Default re: How to model moisture within Fluent?
  #2
AAA
Guest
 
Posts: n/a
Hi

Use the Species model and define the properties of the "mixture species" in the materials window to have H2O and Air (H2O must be the top one). Choose "volume-wheighted" for density and "mass-weighted" for thermal conductivity and viscousity. Then specify the moisture mass fraction for inlets to the domain (this is the humidity ratio in the psycrometric chart). Specify a "constant" mass fraction value for the body of the sheep.

djing, metmet, chinna and 3 others like this.
  Reply With Quote

Old   August 7, 2007, 09:23
Default re: How to model moisture within Fluent?
  #3
Carlos
Guest
 
Posts: n/a
Thanks for your help AAA, this method appears to work fine - much appreciated. Just wondered if you had any idea of typical mass fractions of vapour for my boundary conditions?

When postprocessing I find that contour plots of relative humidity show values of 1000's of %! Clearly the humidity cannot exceed 100% at any given temperature. If you have any ideas please let me know.

Best regards,

Carlos.
  Reply With Quote

Old   August 7, 2007, 18:03
Default re: How to model moisture within Fluent?
  #4
AAA
Guest
 
Posts: n/a
Hi

Relative humidity must never exeed 100%.

Have you heard about a Psychrometric chart? This chart is usually used by HVAC engineers (please find one) to find properties of air such as humidity ratio (mass fraction) by knowing the temperature and relative humidity, for example, among others. This will enable you to specify the mass fraction at the inlet and also predict the relative humidity at the outlet.

Now if you don't know any HVAC enngineers, kindly send me the temperature and relative humidity you are using for the inlet boundary and I will give you the values for the mass fraction. Still, if you can find some one to show you the chart and explain it to you, this will be better.

Kind Regards

  Reply With Quote

Old   August 7, 2007, 19:26
Default re: How to model moisture within Fluent?
  #5
Carlos
Guest
 
Posts: n/a
Hi AAA,

Thats great, thanks for your advice. I think I may be having problems because I am specifying the humidity on the inlet AND the outlet, maybe I should leave the outlet alone this time! Your help is much appreciated.

Thanks

Carlos.
  Reply With Quote

Old   August 7, 2007, 20:03
Default re: How to model moisture within Fluent?
  #6
AAA
Guest
 
Posts: n/a
Hi

You still have to specify a "practical" mass fraction for moisture at the inlet to get a reasonable relative humidity for the domain. This is done by knowing the temperature and relative humidity at the inlet and finding the corresponding mass fraction from a Psychrometric chart. Otherwise, you might cross the 100% relative humidity line again.

Regards
  Reply With Quote

Old   August 7, 2007, 21:15
Default re: How to model moisture within Fluent?
  #7
Carlos
Guest
 
Posts: n/a
Thats brilliant!

Thanks,

Carlos.
  Reply With Quote

Old   October 25, 2009, 11:36
Default
  #8
New Member
 
Join Date: Oct 2009
Posts: 13
Rep Power: 16
denise is on a distinguished road
Dear AAA,
i am trying to solve humidity transfer in enclosure, every where isolated except for ceiling..ceiling is cooled..but in Fluent i can see temperature gradient but there is no mass fraction of H2O gradient..it is almost same...i am trying to write UDF but, what is the source term? there is no generation of humidity in my room..how to include natural convection using bossinique model in simple species transport without reaction phenomenon.?please help me..
thank you


denise is offline   Reply With Quote

Old   October 2, 2015, 07:31
Default
  #9
Senior Member
 
Astio Lamar
Join Date: May 2012
Location: Pipe
Posts: 186
Rep Power: 13
asal is on a distinguished road
Sorry to bring this old topic up!

I f I have 20 oc for temperature, atmospheric pressure and 40% humidity, then from the Psychrometric chart I have the ration of 0.006. Should I specify this value for the H2o mass fraction in the inlet boundary condition?
thanks.
asal is offline   Reply With Quote

Old   October 2, 2015, 09:38
Default
  #10
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Quote:
Originally Posted by asal View Post
Sorry to bring this old topic up!

I f I have 20 oc for temperature, atmospheric pressure and 40% humidity, then from the Psychrometric chart I have the ration of 0.006. Should I specify this value for the H2o mass fraction in the inlet boundary condition?
thanks.
That is correct! Just make sure that's the dry bulb temperature and relative humidity.
LuckyTran is offline   Reply With Quote

Old   October 4, 2015, 10:13
Default
  #11
Senior Member
 
Astio Lamar
Join Date: May 2012
Location: Pipe
Posts: 186
Rep Power: 13
asal is on a distinguished road
Hello and thanks for your swift reply.
I have simulate the humidity based on H2o mass fraction calculated from Psychrometric chart. the question now is how to post process the the result in CFD-post based. I try different method, but I cannot show the humidity for example at plane.
Thanks in advance for your respond.
asal is offline   Reply With Quote

Old   October 4, 2015, 15:47
Default
  #12
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
What is your problem exactly? Are you unable to plot anything or are your missing "humidity" as a plottable variable? For example can you plot temperature on a plane?

If you need to calculate humidity:

The relative humidity is given by the partial pressure of water to the saturated vapor pressure at the same (dry bulb) temperature.

You can convert your mess fractions into mole fractions and calculate the partial pressure of water and then calculate the partial pressure at the same temperature.
LuckyTran is offline   Reply With Quote

Old   November 3, 2015, 01:19
Default
  #13
New Member
 
KEER AKSHAY TUSHAR
Join Date: Oct 2015
Posts: 3
Rep Power: 10
akky112 is on a distinguished road
what is mass fraction?
is it humidity ratio?
what is the formula for mass fraction?
akky112 is offline   Reply With Quote

Old   November 9, 2015, 00:35
Default Air condensation over the Wings
  #14
New Member
 
M MOHSIN's Avatar
 
M Mohsin Iqbal
Join Date: Jan 2014
Location: National University Sciencies & Technology, Pakistan
Posts: 17
Rep Power: 12
M MOHSIN is on a distinguished road
Hi
Sir i am carrying research on Air condensation over the wings.
I am having problem for making settings in the Fluent.
Kindly guide me how can i give prescribed humidity (say 65-70 %) to the computational domain.
Thank You
Looking Forward.
M MOHSIN is offline   Reply With Quote

Old   November 9, 2015, 00:51
Default
  #15
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
Quote:
Originally Posted by M MOHSIN View Post
Hi
Sir i am carrying research on Air condensation over the wings.
I am having problem for making settings in the Fluent.
Kindly guide me how can i give prescribed humidity (say 65-70 %) to the computational domain.
Thank You
Looking Forward.
Humidity is handled by using the species transport model and adding water vapor as the new species. You need to specify mass fractions. Note the earlier discussion on how to do this.

For water condensation, you need to do a multi-phase simulation.
M MOHSIN and PJTsai like this.
LuckyTran is offline   Reply With Quote

Old   November 30, 2015, 03:28
Default Air condensation over the Wings
  #16
New Member
 
M MOHSIN's Avatar
 
M Mohsin Iqbal
Join Date: Jan 2014
Location: National University Sciencies & Technology, Pakistan
Posts: 17
Rep Power: 12
M MOHSIN is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
Humidity is handled by using the species transport model and adding water vapor as the new species. You need to specify mass fractions. Note the earlier discussion on how to do this.

For water condensation, you need to do a multi-phase simulation.

sir and simulation will be steady or transient ??????
i want to capture the fog cloud over the wings caused due to the condensation of humidity .
looking forward
M MOHSIN is offline   Reply With Quote

Old   August 19, 2017, 13:48
Default
  #17
Senior Member
 
Have a nice time!
Join Date: Feb 2016
Location: mech.eng.ahmedmansour@gmail.com
Posts: 291
Rep Power: 11
Ahmed Saeed Mansour is on a distinguished road
Hello, I want to get the values of the relative humidity for a simulation contains moisture (humid air), I think I have followed the steps that are shown here...I have the steps in the snapshots..Is this right or there is another thing that has to be further done?
Thanks
Attached Images
File Type: png 1.PNG (66.9 KB, 370 views)
File Type: png 2.PNG (23.6 KB, 303 views)
File Type: png 3.PNG (37.7 KB, 296 views)
File Type: png 4.PNG (29.6 KB, 298 views)
File Type: png 5.PNG (41.6 KB, 293 views)
suiryagowtham likes this.
Ahmed Saeed Mansour is offline   Reply With Quote

Old   August 19, 2017, 13:50
Default
  #18
Senior Member
 
Have a nice time!
Join Date: Feb 2016
Location: mech.eng.ahmedmansour@gmail.com
Posts: 291
Rep Power: 11
Ahmed Saeed Mansour is on a distinguished road
These are the rest of the snapshots
Attached Images
File Type: png 6.PNG (37.6 KB, 266 views)
File Type: png 7.PNG (29.4 KB, 255 views)
File Type: png 8.PNG (17.9 KB, 244 views)
suiryagowtham likes this.
Ahmed Saeed Mansour is offline   Reply With Quote

Old   September 19, 2017, 02:18
Default
  #19
Member
 
Vignesh Lakshmanan
Join Date: Nov 2016
Posts: 79
Rep Power: 9
ViLaks is on a distinguished road
Dear Ahmed,

Your case seems to be fine as mentioned in this thread. Only thing you need to do, which I think, is that you need to enable source terms in the cell zone conditions.

Thanks
Vignesh
ViLaks is offline   Reply With Quote

Old   January 27, 2018, 13:11
Default
  #20
Senior Member
 
Have a nice time!
Join Date: Feb 2016
Location: mech.eng.ahmedmansour@gmail.com
Posts: 291
Rep Power: 11
Ahmed Saeed Mansour is on a distinguished road
Thank you dear Vignesh
Ahmed Saeed Mansour is offline   Reply With Quote

Reply

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
Seeking Macroscopic Particle Model in Fluent bzhang7 FLUENT 3 June 25, 2022 18:54
Fluent :- turbulence Model prince_pahariaa FLUENT 9 May 20, 2016 04:41
How to create a 3Ds Car Model importing to FLUENT? spysunny Main CFD Forum 1 January 11, 2012 00:40
Fluent 12 k-w SST turbulence model DarrenC FLUENT 0 December 13, 2009 09:33
Covert Star-CD model to FLUENT Lam Siemens 6 June 24, 2003 21:21


All times are GMT -4. The time now is 15:32.