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rafat June 7, 2001 22:53

moist air density
Hi, I am trying to simulate a natural-draft wet cooling tower performance. I want to use a single phase simulation using Fluent 5.4 . I am trying to define the density of the moist air at the inelt. my problem is the interaction between the air and water "theoritically". I wonder if anyone has come by such a problem to help me.

I mean what sort of function should I use to express the change in the air density.

thanks for your help in advance.

Bart Prast June 8, 2001 04:03

Re: moist air density
If you do not include phase transition (condensation of water) you can do this by assuming a mixture of 2 ideal gases (air/water vapour): P = Pvapour + Pair with Pvapour the partial vapour pressure (saturation ratio * saturated vapour pressure)

rafat June 8, 2001 04:37

Re: moist air density
This has opend the door to another variable Pvabour. I am affraid I do not have enogh skill to play around with fluent. I am trying to find the way of mixing two fluid together.

Bart Prast June 8, 2001 04:47

Re: moist air density
If you need the density of moist air specifically (as opposed to dry air), you need the properties of the water vapour. You can also do this in terms of mass fractions.

Sergei Zhubrin June 12, 2001 11:49

Re: moist air density
Check out PHOENICS User Support pages at

Under 'On-line CFD calculators' you will find one called 'Air-water saturation' for the estimation of some air-water saturation data .

Give it a try and look at what it says re underlying methods.


Sergei Zhubrin

rafat June 13, 2001 21:36

Re: moist air density
Thank you for this, I tried to run it but it send me an error in the page. I will try it later on. thnk you again.

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