## Fluids

#### Modelling evaporation from a microchannel

Tagged:

• d.weragoda
Subscriber

Hi,

I'm trying to model evaporation through a rectangular (open) microchannel.

Therefore to simplify the problem initially, I modelled the capillary rise through this rectangular microchannel (3D) and determined the average velocity of capillary rise. Afterwards I modelled a simplified version (2D) to determine the evaporation from this rectangular channel to the surrounding air. However, I'm having trouble modelling the evaporation across the liquid-air interface in the domain shown below.

For this scenario (i.e. 2D), I am having trouble defining the liquid-air interface. I believe I will have to define a UDF for the interface BC (allowing only vapour to flow, to make things simple). But not sure if that is the right approach and if so how to do it. Any guidance in this regard in highly appreciated. I am currenly using steady state, VOF, implicit and using simple for P-V coupling. I have also defined the saturation temperature to be 303K and the corresponding operating pressure to be 4.2kPa and set the reference pressure location at the surrounding air domain, with operating density (user-input) to be 1.225kg/m^3. (I can see that the heat is absorbed by the water-liquid and phase change taking place in the liquid domain, however, there isn't any vapour flowing to the surrounding air domain)

Many thanks.

• Danica
Ansys Employee

Hi,

Would it be possible to see some flow vectors and pictures of results? Additionally, please post a screen grab of the non conformal interface panel.

Thanks

• d.weragoda
Subscriber

Hi Danica,

So, I played around a bit and was able to see that vapour is transferred to the air domain as well. I ran the simulation at steady state and set the saturation temp at 373.15K.
However, in this case both vapour and water (liquid) are both transferred (which would not be the case in a microchannel). Is there any way to define the interface BC (liquid-air) so that only vapour is allowed to pass across?

Please see the results you requested.

Fig 1: Vapour volume fraction

Fig 2: Liquid volume fraction

Vector plot

Any guidance would be really appreciated.

Many thanks

Deli

• Rob
Ansys Employee

Why would the liquid stick to the wall?  Given the flow images I'm not sure you've got a converged solution, the speed is a little high for a microchannel and you've lost the free surface too. Finally, why use an interface? You really want a conformal mesh with an interior at the bounding position: read up on share topology and/or multibody parts.