[namandoshi]

Can someone help me how to define moist air(using mass fraction or relative humidity in cfx-pre)

i have made new material-variable mixture material using
ideal air gas and water vapor(not ideal water gas) but density is coming 0.5(kg/m3) which is very low as expected(1.2kg/m3)

[ghorrocks]

You define a multicomponent mixture as you appear to have done. If it is not giving correct densities, check the temperatures and pressures it is using for density (ideal air gas will use the ideal gas EOS but water vapour is a fixed density regardless of temperature or pressure), check the mass fractions you are defining and check you are looking at the density of the gas mixture, not partial pressures.

[namandoshi]

Originally Posted by ghorrocks

You define a multicomponent mixture as you appear to have done. If it is not giving correct densities, check the temperatures and pressures it is using for density (ideal air gas will use the ideal gas EOS but water vapour is a fixed density regardless of temperature or pressure), check the mass fractions you are defining and check you are looking at the density of the gas mixture, not partial pressures.

Sir,
i have taken mass fraction of water as 0.04.
and vent as opening with relative pressure 1 atm.
also, i have set reference pressure as 0 atm (corrected just now , previously it was set to 1atm).
hoping for correct results any other suggestion which i may be doing wrong.

[namandoshi]

Originally Posted by ghorrocks

You define a multicomponent mixture as you appear to have done. If it is not giving correct densities, check the temperatures and pressures it is using for density (ideal air gas will use the ideal gas EOS but water vapour is a fixed density regardless of temperature or pressure), check the mass fractions you are defining and check you are looking at the density of the gas mixture, not partial pressures.

1. does it will affect if i use water ideal gas or water vapour?
2. I am viewing density contours on cfd post so i dont think there is error in selecting partial pressure.

[ghorrocks]

"water vapour" material uses the density of water vapour at 25C, 1atm (I think). If that does not match your conditions you will have to change the density to be correct.

"water ideal gas" uses the temperature and pressure and an ideal gas equation to calculate the density.

Using a reference pressure of 1 atm with a opening pressure of 0 atm is recommended over a reference pressure of 0 atm and an opening pressure of 1 atm. It minimises round off errors.

If you cannot work out the problem please post your output file and an image of the results you are getting which show the incorrect density.

[namandoshi]

Originally Posted by ghorrocks

"water vapour" material uses the density of water vapour at 25C, 1atm (I think). If that does not match your conditions you will have to change the density to be correct.

"water ideal gas" uses the temperature and pressure and an ideal gas equation to calculate the density.

Using a reference pressure of 1 atm with a opening pressure of 0 atm is recommended over a reference pressure of 0 atm and an opening pressure of 1 atm. It minimises round off errors.

If you cannot work out the problem please post your output file and an image of the results you are getting which show the incorrect density.

Thank you sir, made suggested changes.
Now density is coming within range thankyou.