# Modelling wet steam

indiaMember

Hello,

i am working with steam quality improvement through moisture separators (vane type moisture separator), My problem has the inlet steam has a quality of 80 percentage.

I know the problem is a multiphase because of the condenstion process. But the difficulty what  i face is correction in the modelling of Inlet steam with the desired quality.

How to model the steam in fluent with the steam quality of 80 percentage .??? someone please me through this.

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• UKForum Coordinator
edited January 20

Maybe start by working out (and stating) what 80% quality means in terms of mass fractions etc.  What are you trying to determine from your model?

• indiaMember
edited January 20
Exactly as you said, mass fraction of 80 % of steam and 20% water content in the steam.
I am trying to increase the efficiency of the wet steam through condensation inside the separator..
• GermanyForum Coordinator
edited January 20
Check the wet steam model in Fluent. Can be a way.
• indiaMember
edited January 20
I already tried that model sir and i found that the maximum mass fraction of water in the steam is limited to 0.2..But at the 0.2 the problem tends to fluctuate more...No convergence occured in the transport quantities..
• GermanyForum Coordinator
edited January 20
Then use CFX droplet condensation model.
• indiaMember
edited January 21

I dont have access to CFX sir. Is it possible to model my Problem in FLUENT??

• GermanyForum Coordinator
edited January 21

Yes: You need to write a couple of User defined mass transfer routines and implement the wet steam model in the pressure based solver. That is tough step but feasible.

Why do you not have CFX?

• indiaMember
edited January 22

thanks for the reply sir, My objective is to do the Condensation in Fluent only to check with the Experimental.

And another doubt is what material that i have to define to simulate steam at the inlet other than the wet steam model. ??????

• GermanyForum Coordinator
edited January 22
Wet steam so vapor and water liquid.
• indiaMember
edited January 22

FLUENT calculates the Mass flow rate based on the proportions of volume fractions. If i give 0.9 for vapour and 0.1 for the water liquid then the mass flow rate is getting adjusted based on this volume fractions. say for example velocity inlet of 30m/s has a mass flow inlet of 12000kg/hr experimentally means it wont match with the simulated .

If combining the mixture o vapour and liquid is the key means How to overcome this problem sir.

• GermanyForum Coordinator
edited January 22

You need to provide the volume fractions. You might calculate them out of the mass fractions.

• indiaMember
edited January 23
If my steam quality is 90% then i have to define volume fraction as 0.9 for water vapour and 0.1 for Liquid is it right sir???
And i tried this one sir If i give this the fluent calculates the Flow rates based on fraction i dont know how..but for 30m/s velocity inside a 80mm dia the flow rate is around 243kg/s .

Could you please clarify me on this sir??

• GermanyForum Coordinator
edited January 23

No: steam quality is per mass basis. You need to convert it to volume fraction /wetting fraction at the inlet temperature / density.

• indiaMember
edited January 23

Could you please elaborate this thing with an example value sir?  Because i am more confused with that of the mass fraction and volume fraction.....

• GermanyForum Coordinator
edited January 23

Mass fraction is Mass Concentration (Density of component)/Mixture Density. The Mass concentration it self is volume fraction time the real vapor density.

• indiaMember
edited January 23

i have tried that thing sir. The problem is in attaining the correct mass flow rate with respect to the velocity. my steam has a quality of 90% so the volume fraction of the steam is 99.987% and the liquid is about 0.013 % .With the specified velocity of 30m/s I couldnt get the Mass flow rate of 0.09 kg/s at 1 bar absolute pressure. i have updated the properties of vapour and water wth respect to the 100 degreee celcius and 1 bar abs pressure from steam table.

• GermanyForum Coordinator
edited January 23

I am not sure about your question now: what is the density of water and water vapor at temperature at inlet? What is the velocity applied here? This is just math and you do not need any phase change model or anything to get the right value at inlet.

• indiaMember
edited January 23

I have an experimental value of the velocity (30m/s) for the maximum flow rate  0.09 kg/s . so i thought of having an cross check by monitoring the mass flow rate for the velocity 30m/s.

• GermanyForum Coordinator
edited January 23
List your input at the boundary and density of vapor and water at inlet . Better as screenshot. Are you having same area as in the exp.?
• indiaMember
edited January 23