Learning Forum

[saisantosh]

Hello!! nI am trying to simulate condensation of humid air as it passes over a set of cooling coils. I have modelled the fluid as a mixture of air and water vapour and given the corresponding mass fractions (which accounts for the rh). But I am not sure how to proceed with the simulation of the condensation phenomenon. nCan someone suggest a methodology of how to set up this phenomenon using ANSYS FLUENT ?n

[Rob]

Have a look at the multiphase models and wall films. n

[saisantosh]

Yes, I am aware that I will have to use the multiphase models (mixture model) and subsequently enable phase interactions (evaporation-condensation). But the option here suggests to enter the condensation frequency and saturation temperature. Is there an option to enter the dew point temperature.nWhen I try the above methodology, the rh at outlet is always increasing, but this is not true if condensation occurs.nI guess I am going wrong with specifying the proper temperatures (saturation, dew point) and am not sure how to translate these into FLUENT. nPlease guide me in this aspect.n

[Rob]

It depends on the model, hence reading through the options. The time factors are part of the Lee model, and there should be a saturation temperature in the settings. In some of the models this is in the material properties. n

[saisantosh]

Kindly let me know the other options/models available for modelling condensation phenomenon (other than Lee).nYes, there is an option available to set a reference temperature in material property, but not sure how it ties into the simulation. Kindly share your insights on this regard too.nIs there any example (document or video) available for this particular phenomenon?n

[Rob]

I don't think we've got a tutorial at present. Opening the manual and/or multiphase panels will show what's available: you can then decide what's most suitable for your system. We can guide you in that respect, but you need to work out the engineering. What drives the condensation, is it coil surface or free stream, where does the condensate go?n

[saisantosh]

Hello Rob, Sorry for the delayed response.nWe worked out the phenomenon of condensation, it is the coil surface that drives the condensation.nThe condensate is collected and removed after a few days of operation and we are interested in finding the amount of condensate formed when steady state reaches.nPlease guide us on how to set up the case for this condition.n

[Rob]

OK, read the wall film models then, I'd suggest Eulerian Wall Film and you need mass transfer. Note, you may need to revise the model run duration as we typically solve at the flow timescale which is usually in the order of parts of seconds, so a few days might take a while. n