[Suryan]

Hi All,

How can I simulate the flow of air with a relative humidity of, say, 60% in FLUENT? And how to check the RH once the solution is converged?

Thank you

[vvvms]

you can use airpak to simulate the RH

[coglione]

If you define your fluid as a gas mixture of chemical species with one component being h20vap relative humidity is automatically available as variable in Fluent.

cheers

[savate moh]

Originally Posted by coglione

If you define your fluid as a gas mixture of chemical species with one component being h20vap relative humidity is automatically available as variable in Fluent.

cheers

hi suryan, i'd like to know what have you done with your work? did you find how to simulate it?? i'm simulating thins kind ,i was wondering if you could show me please thx

[aiouss]

Originally Posted by savate moh

hi suryan, i'd like to know what have you done with your work? did you find how to simulate it?? i'm simulating thins kind ,i was wondering if you could show me please thx

hello savate
did youfind how to simulate it in flueunt
I am doing the same thing but I did not know how to simulate it in fleunt

waiting for your answer
best regards

[A CFD free user]

Originally Posted by aiouss

hello savate
did youfind how to simulate it in flueunt
I am doing the same thing but I did not know how to simulate it in fleunt

waiting for your answer
best regards

My friends,
There is a relationship between relative humidity and water vapor pressure as follows:

RH = P_H2O/ P_sat;

in which, P_H2O is defined as P_tot *y_H2O and P_sat is saturate pressure which is dependent on operating temperature. y_H2O is also water vapor mass fraction. So, having the RH, let's say 0.6, you have, P_H2O = 0.6*P_sat. From which, the y_H2O is obtained as :

y_H2O = P_H2O /P_tot;

and hence if you have air as a gas mixture, then the values for Oxygen and Nitrogen are calculated as:

y_O2 = 0.21*(1-y_H2O);
y_N2 = 0.79*(1-y_H2O);

Finally, you need to input these values as species mass fraction values. You can do that manually or using UDF, if you want to change the RH values. That's all.

I hope it helps

[the901]

I am doing a simulation of humid air over a flat plate. I am waiting for my paper published then I can send you my work and the paper. General speaking, You need to transfer Relative Humidity to mass fraction of H20 by using the Psychrometrics chart. In material you'd better specify dry air mixing with water vapor in Fluent data. For boundary conditions you prescribe mass fraction for each Boundary in "species tab". Then run the calculation in Transient mode. For relative humidity contour, choose "species"/ relative humidity in "contours graphic". I hope it would help you!

[aiouss]

hallo my friends thanks for ur usefull replly

I am simulating heat and mass transfer of humid air in porous media using Fluent
please, I have some questions
1- when I use 0.45 as mass fraction for water vapor and I start my simulation for 10 sec and I want to see the variation of relative humidity, I found RH min(%)= 2133.051 and max(%)=2143.051 that is abnormal values. is it correct or no? or I must divide the mass fraction value by 100 (=0.45/100) firstly.?
2- What is the appropriate model to consider the evaporation and condensation phenomenen because there is condensation of vapor and evaporation with time and temperature variations
3- how can I plot the variation of thermal conductivity as a function of moisture content or as a function of relative humidity?

waiting for your reply
best regards

[aiouss]

Originally Posted by the901

I am doing a simulation of humid air over a flat plate. I am waiting for my paper published then I can send you my work and the paper. General speaking, You need to transfer Relative Humidity to mass fraction of H20 by using the Psychrometrics chart. In material you'd better specify dry air mixing with water vapor in Fluent data. For boundary conditions you prescribe mass fraction for each Boundary in "species tab". Then run the calculation in Transient mode. For relative humidity contour, choose "species"/ relative humidity in "contours graphic". I hope it would help you!

thank you the901 for your help
I hope you recieve the acceptation quickly
this is my email: asais83@yahoo.fr

thank you again best regards

[aiouss]

Originally Posted by A CFD free user

My friends,
There is a relationship between relative humidity and water vapor pressure as follows:

RH = P_H2O/ P_sat;

in which, P_H2O is defined as P_tot *y_H2O and P_sat is saturate pressure which is dependent on operating temperature. y_H2O is also water vapor mass fraction. So, having the RH, let's say 0.6, you have, P_H2O = 0.6*P_sat. From which, the y_H2O is obtained as :

y_H2O = P_H2O /P_tot;

and hence if you have air as a gas mixture, then the values for Oxygen and Nitrogen are calculated as:

y_O2 = 0.21*(1-y_H2O);
y_N2 = 0.79*(1-y_H2O);

Finally, you need to input these values as species mass fraction values. You can do that manually or using UDF, if you want to change the RH values. That's all.

I hope it helps

hallo azarafza
thank you for your important help
cheers

[amasugi14]

Originally Posted by the901

I am doing a simulation of humid air over a flat plate. I am waiting for my paper published then I can send you my work and the paper. General speaking, You need to transfer Relative Humidity to mass fraction of H20 by using the Psychrometrics chart. In material you'd better specify dry air mixing with water vapor in Fluent data. For boundary conditions you prescribe mass fraction for each Boundary in "species tab". Then run the calculation in Transient mode. For relative humidity contour, choose "species"/ relative humidity in "contours graphic". I hope it would help you!

Hi, actually im having the same problem, could you help me too? this is my email amasugi14@yahoo.com. thank you so much

[binit kumar]

can any one of you help me with the condensation over flat plate or nusselt model using pure vapor or humid air(water vapor+air), i am using star ccm+ software to deal with this problem if any one of you knows about it then please help me... or even if you have worked on fluent then let me know it... i can work on both software...

i tried many times but i am unable to get results for condensation over flat plate... I had used vof model, eulerian phase, and applied lee model as source term but solution is not stable...

[Bran]

Hi Binit Kumar,

Were you able to obtain results for condensation over the flat plate? I have a similar problem. Could you help me out?

All the best.