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-   -   Bai-Gosman droplet impaction model in StarCCM+ (https://www.cfd-online.com/Forums/star-ccm/131748-bai-gosman-droplet-impaction-model-starccm.html)

 crevoise March 20, 2014 07:51

Bai-Gosman droplet impaction model in StarCCM+

Hello all

I am working on droplet-wall interaction, modeling an injection into a pipe.

To model the droplet-wall interaction, I am using the Bai-Gosman model, on which I have two questions:

1/ In the user manual (version 8.04, page 4214), it is explained that for wall temperature above the boiling point (called the T12), the spreading and splash are set with no residual on the wall.
Thus, this mean that if the wall temperature is above the droplet boiling point, no wall film is able to form (I could understand this in the case of temperature above the Leidenfrost temperature).
I actually see this in my computations, as I am running them at 470K and am injecting droplets of pure water. I am not getting any wall film.
My question is simple: does anyone understood why StarCCM+ made the assumption that no wall film can be created above the boiling point? In the theory of the Bai-Gosman model, this was not the case.
Do I have to escape this by setting a value for T12 far above the droplet boiling point?

2/ Coming from the above question, I am wondering what does mean 'wall temperature'.
In the case of a wall with a wall film, the droplets impacting the wall are in fact impacting the wall film. Thus, does the wall temperature refers to the wall temperature, or to the wall-film temperature.
If the wall temperature will refer to the wall film temperature, thus this one will obviously be under the boiling temperature and thus allow further deposition.

Thanks a lot for your lights on these points.

 me3840 March 20, 2014 10:49

1. I think they chose to do this because, in reality, when the droplet hits the wall, a vapor will form in between the wall and the droplet which will prevent the droplet's mass transfer to a film. I think they try to explain this earlier on the page.

2. On pg 4209 the boundary temperature is the wall temperature provided from the energy solver.

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