[gartz89]

Hello, guys!

The model presents a physical and mathematical transient model of the Eulerian wall film (EWF) with phase change into the fixed regenerative heat exchanger - (solid body) operating with humid air specified like a species transport (air + water vapor). The body is micro-channel with a very small hydraulic diameter so the Reynolds number is around 80 i.e. the flow is laminar.
The Energy equation and species transport are turn on. The BC in the model is a constant inlet velocity 1 m/s and inlet temperature 293K, the species mass fraction of water vapor is 0.01 kg/kg. The solid-body temperature is from the initial conditions and it was specified with the patch option = 273K. Therefore there is a temperature difference between the solid body and the fluid known as conjugate heat transfer (CHT) and helps with this mass fraction will rise a condensation into the wall formatting a thin film. Unfortunately in nature there is a phenomenon name a Fog Formation. The fog rise when the condensation process becomes and when the mass of the condensate water becomes higher in the same time the fog “particles of droplets” start to evaporate this was associated with an intensive increasing of the temperature of the mixture fluid.
I tried to simulate this process with DPM coupled with EWF + species transport. The problem is that I don’t know, how to enter correct boundary conditions of the DPM simulate a fog. I tried to surface injection in the interior fluid with a very small flow rate, but the absorption and evaporation of the droplets into the film was with a lot number of particles that were very expensive for time calculations. I tried to trap the DPM but nothing. So I continue to research this problem and I’m asking for a piece of advice. Is there somebody that was working in this area or these phenomena – fog formation from moisture air, I know that the influence is very small from the heat transfer and mass transfer into the film, but the aim, in this case, is different. Maybe without writing UDF this model has no solution.

Thank you and regards!

[2phase]

Dear Gartz,

if I got you right, the following publication might be of interest to you.
If not... well, sorry for bothering you.

Numerical Simulation of Nucleation and Condensation in Nozzles and Radial Turbines
Tim Wittmann , Sebastian Lück, Christoph Bode, Jens Friedrichs

I came across that during some literature researc and even found a pdf, but right now I didn't find it again.

Best
Martin

[gartz89]

Thank you I appreciate it, but the concept is different. Regards!

[DnyanMiri]

Have tried VOF-to-DPM approach? In this case, when the liquid evaporates from the surface and as it converts into small size fraction it is tracked by DPM. otherwise, it's tracked as an eulerian phase only.

I have not done this, but this just came to my mind and may be useful to you.

[gartz89]

The VOF method in FLUENT phase-change models has been specified for evaporation and condensation problems in a very dynamic process and even the constants don't help. Most of the models must be built using UDF and they are quite accurate for boiling problems, which is very famous in the literature. But however, from my point of view, I understand that the results of condensation and evaporation of water vapor in humid air in CFD and in this number including EWF is not very good if you don't use UDFs, but you could also use them for fast appropriate results. Other methods for this phenomenon of condensation and evaporation process of humid air are better than CFD. And for my experience, the task for DPM becomes very complicated, and you can check our paper that verifies these hypotheses. Finally, we did some verification with analytical and numerical models from the literature, but the error analysis was bad.