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Evaporation and film forming

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Old   May 19, 2016, 02:15
Default Evaporation and film forming
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amrrhm
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Hi all,

I am trying to model a cylinder containing water (the water doesn't fill the cylinder completely). The bottom and the top of the cylinder have different temperatures. The idea is that the higher temperature at the bottom and low pressure cause the water to evaporate and reaches the top wall and at the top wall the vapor condensate and form a film. I tried gas simulations + parcel simulations + spray modeling. However I get the following error:

error in spray.in, evaporation is on but parcel species for H2O_WATER does not exist as a gas species.

I have H2O_WATER in parcel and H2O in gas.

I did add the H2O_WATER to the gas and added H2O_WATER to the therm.dat using H2O numbers but it messed the densities.

Do you have any suggestions?
Thanks
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Old   May 20, 2016, 12:02
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Yanheng Li
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Hi,
For the error message, I think you have to name the gas species the same as the parcel species (H2O_WATER). CONVERGE has H2O gas phase data in therm.dat and just make sure two species has the same name.
For the density issues, make sure you are using correct critical temperature and pressure for the water (crit_temp and crit_pres). The default values are for air.

For this case, if the water is stored in the cylinder, then it acts like a continuum and there is little parcel collision or break-up modelling involved, hence you'd better turn off these collision-breakup models if you want to stick to spray modelling. Ideally for such continuum-based multiphase flow case the Eulerian approach in CONVERGE (Volume of Fluid modelling) should be a better practice, although currently there are some limitations in our VOF model in well resolving the water-vapor interface while handling the evaporation-condensation at the same time.
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Old   May 23, 2016, 17:49
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Dear Yli,

Thanks for the help. I tried VOF, but I neither evaporation nor condensation happened at the temperatures and pressures they should happen. I am not sure where I am making mistake.

Thanks
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Old   May 24, 2016, 14:56
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Dear amrrhm,
This is because currently CONVERGE VOF modelling does not have a specialized model to handle evaporation(although we do have a cavitation model but it is designed for cases with large pressure-gradient) . So for now spray modelling is the best way to simulate this problem, which has evaporation model. Remember to turn off collision-break-up for the spray modelling as they should be minimum in this case.

Let us know if you have further questions. Thanks!
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