## Fluids

#### Microlayer Evaporation

• zakmt293
Subscriber

Greetings

Respected experts I hope you are in good health. I am working on simulation of single bubble growth in super heated domain. There is a very thin liquid layer beneath the bubble and above heat transfer surface known as micro layer as shown

Image showing microlayer (Image taken from Thermal-Fluid Pedia from the discussion of nucleation and inception)

If  you can see above in the image there is a mention of micro layer. Its thickness is in micro meter and in a very short interval of time it evaporates. The heat flux for micro layer  is obtained by assuming 1-D heat conduction

Heat flux per unit area= kl*(Tw-Tsat)/(t_m)

eq(1)

kl= Thermal conductivity of water                       Tw= Wall temp                    Tsat= 373;       t_m= Microlayer thickness

If we multiply eq (1) with interfacial area and then divide it by latent heat to get mass in kg/m3-sec it leads to a very high value of mass and leads to courant number crossing its limit.

To maintain courant number in its limit time step of 1e-12 is  adopted. But it would take huge time to reach upto 46 milli seconds which would be needed to compare it with experimental data.I am just interested in increase in volume that would occur due to the evaporation of this thin layer. Can the experts give me any idea so that I could incorporate this mass to just see the behavior of bubble. Any idea in any form would be highly appreciated. I would be thankful for suggestions of experts.

Thank You

• DrAmine
Ansys Employee

I remember I saw this micro-layer evaporation as part of a sub-grid wall boiling model. The effects have been modeled and not resolved.

What do you want to do? Resolve the whole process or model the boiling here?

• zakmt293
Subscriber

Thank You

Now  there is a hopeful chance. No I am not interested in resolving the whole process but interested in mass transfer and heat flux. Can you more elaborate how could this be made possible. I would be very thankful for your suggestions.

Thank You

• DrAmine
Ansys Employee

Micro-Layer evaporation Model is still state of research:

https://www.casl.gov/sites/default/files/docs/CASL-U-2013-0099-000.pdf

In Fluent you can deal with thin-film model (after Kolev)

• zakmt293
Subscriber

Greetings

Can you tell me more about thin film model of Kolev. I am not getting it properly. Can you share with me any link that could describe it.

Thank You

• DrAmine
Ansys Employee