Learning Forum

[Mehrnoush Dardashti]

I am trying to simulate the evaporation of a falling droplet. Here is the link to the video that I want to simulate:

I followed the steps that are mentioned in a youtube video, but I wasn't successful. The main problem is the terminal velocity. I tried to use terminal velocity based on droplet radius. However, it doesn't change during the simulation.

Thanks.

[Rob]

Please can you post what's happening in your model? 

[Mehrnoush Dardashti]

It is a 2D model of water drop evaporation free falling in air by the simultaneous heat and mass transfer model. I used  ANSYS Fluent 2021 R1 (2d, dp, pbns, eulerian, spe, lam, transient) Heat transfer: ranz-marshall, Mass transfer: mass transfer coefficient per phase, piecewise-liner saturation pressure [Pa].

https://youtu.be/i1p78532Ubg

I have two major problem :

1. I attached the animation of volume fraction of droplet change here. as you can see after some time, the maximum volume fraction of droplet start decreasing. In my opinion, the evaporation must be from the surface of the droplet and the maximum volume fraction must be 1 (It shouldn't decrease).
2. The air temperature here is 300 K. Based on analytical results it must take more than 5 seconds to evaporate droplet with this diameter (1 mm). As you can see from the video, the volume fraction of droplet decreases very fast. The total time of this video is 0.1 seconds.

[Rob]

Remember in 2d it's a circle, not a sphere. Check mesh and temperature. There's nothing in Fluent to fix evaporation to the surface only without coding it in.