CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Evaporation of thin water film

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree2Likes
  • 2 Post By Stephen Waite

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 3, 2014, 17:59
Default Evaporation of thin water film
  #1
New Member
 
Stephen Waite
Join Date: May 2013
Location: Auckland, New Zealand
Posts: 29
Rep Power: 13
Stephen Waite is on a distinguished road
Hello, I'm trying to simulate the evaporation of water from a thin film covering a wall boundary in CFX. The wall boundary represents biological tissue and the thin film of water represents the mucous layer above the tissue. A gas mixture of air and water vapor will flow over the (stationary) thin film of water and cause evaporation. The temperature and depth of the water film are to be held constant.

I'm unsure about how to specify this sort of boundary condition.
I've created two domains (one for the air flow and one for the film of water) and used a "Conservative Interface Flux" interface model for heat transfer.
The air domain contains both the air-water vapor gas mixture, the liquid water material and a homogeneous binary mixture containing liquid and gaseous water. The water film domain only contains the liquid water material but I'm not sure how to "fill" this domain so that it consists entirely of water that is stationary and constant in mass despite the evaporation.

Alternatively would a better approach be to specify a temperature and water source on the wall boundary?

Are there any tutorials with this sort of evaporation model?

Thanks in advance for any help.
Stephen Waite is offline   Reply With Quote

Old   July 3, 2014, 18:37
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,826
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
The best way to model this will depend on what you are trying to get out of the simulation. What is the thing you are trying to get out of this simulation? How the water vapour behaves as it leaves the area? Of the heat transfer involved in the evaporation? Or something else?
ghorrocks is offline   Reply With Quote

Old   July 3, 2014, 19:28
Default
  #3
New Member
 
Stephen Waite
Join Date: May 2013
Location: Auckland, New Zealand
Posts: 29
Rep Power: 13
Stephen Waite is on a distinguished road
I guess the evaporation rate and the heat transfer involved in causing this evaporation. We know what the surface temperature is at a given time (I'm just working on steady state simulations at the moment) and what the inlet and outlet temperature and humidities are and we want to know what the total evaporation rate and heat flux to cause this evaporation is in order to achieve the outlet temperature and humidity. I hope that makes sense.
6863523 and user321 like this.
Stephen Waite is offline   Reply With Quote

Old   July 3, 2014, 19:33
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,826
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
So would a simple simulation of the air flow only, with a mass source at the wall to generate the water vapour be a useful starting point? You can make the local mass source a function of water vapour concentration to make it more realistic. This will give you an idea of the water vapour flow and it is a much simpler simulation (a single domain and a single phase, but multicomponent). But it does simplify the heat transfer side of things.
ghorrocks is offline   Reply With Quote

Old   July 3, 2014, 20:21
Default
  #5
New Member
 
Stephen Waite
Join Date: May 2013
Location: Auckland, New Zealand
Posts: 29
Rep Power: 13
Stephen Waite is on a distinguished road
Thanks, so would I just need the gas mixture (air and water vapor) and have the source being a function of the water vapor partial pressure at the wall and wall temperature? Or just a function of the water vapor mass fraction?
Stephen Waite is offline   Reply With Quote

Old   July 3, 2014, 21:39
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,826
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Yes, the source would be a function of the local humidity. But as for partial pressure or vapor mass fraction - you will have to look into this and find out what is the best way to describe the mass transfer for your situation.
ghorrocks is offline   Reply With Quote

Old   July 3, 2014, 22:14
Default
  #7
New Member
 
Stephen Waite
Join Date: May 2013
Location: Auckland, New Zealand
Posts: 29
Rep Power: 13
Stephen Waite is on a distinguished road
Great thank you very much
Stephen Waite is offline   Reply With Quote

Reply

Tags
cfx, evaporation, thin water film

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
question about simulation of falling water film mengyue1 FLUENT 2 March 30, 2014 10:16
VOF - Eliminating shear on the surface of a thin liquid film saisanthoshm88 Fluent Multiphase 0 October 27, 2013 12:22
Reversed flow error with thin film heater MK FLUENT 1 February 12, 2009 10:26
Evaporation - Thin Film Mohsen Main CFD Forum 0 August 23, 2004 12:14
uptodate water distribution network fredius,magige,tanzanian,(e.a) Main CFD Forum 0 January 27, 2002 07:10


All times are GMT -4. The time now is 18:16.