CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

Evaporation of droplet

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 18, 2005, 18:43
Default Evaporation of droplet
  #1
Jan
Guest
 
Posts: n/a
Dear, Is it possible to calculate "analytically-or semi" the evaporation of a water droplet carried by steam. I would like to get a rough estimate of time before the droplet is evaporated and the diameter as function of time. I assume everything constant for the steam. I know I can just start a CFD calculation for finding the solution, but I would like to get an idea and a feeling with the problem before just doing some calculations Thank in advance Jan
  Reply With Quote

Old   January 18, 2005, 19:00
Default Re: Evaporation of droplet
  #2
Dr Strangelove
Guest
 
Posts: n/a
Your entire problem will depend on the relative humidity of the atmosphere surrounding your droplet.

Secondly, on the temperature of the droplet and its relative velocity to the ambient.

Look up the heat transfer coefficient for spheres. Using that information and the latent heat of evaporization and the initial size of the droplet you should be able to get a rough idea of how long it will take for your droplet to disappear.
  Reply With Quote

Old   January 19, 2005, 03:46
Default Re: Evaporation of droplet
  #3
Rami
Guest
 
Posts: n/a
Hi Jan,

I vaguely remember a similar problem was presented and its solution discussed in detail in an old textbook by Spalding. It might be difficult to obtain it, though.

Spalding, Dudley Brian, Combustion and mass transfer : a textbook with multiple-choice exercises for engineering students, Oxford, Pergamon, 1979

Good luck, Rami

  Reply With Quote

Old   January 19, 2005, 12:39
Default Re: Evaporation of droplet
  #4
Chris Bailey
Guest
 
Posts: n/a
Droplet evaporation is a special and weird thing because the equilibration of humidity and evaporation / condensation at the droplet surface is a function of the curvature of the surface. That's why clouds are supersaturated. Since the curvature can also be negative, in a fine capillary, that's also why physical sorbents like silica gel work as dehumidifiers. This is called the "Kelvin effect". You can read about it in the book "Aerosol Technology" by W. C. Hinds. There are experts in the subject at the University of Minnesota, dep't of Mechanical Engineering, the aerosol science group of Dr. Ben Liu. Small droplets evaporate much faster than CFD would predict - if they are small enough they almost explode as they evaporate.
  Reply With Quote

Old   January 26, 2005, 03:59
Default Re: Evaporation of droplet
  #5
Jan
Guest
 
Posts: n/a
Thankyou very much for all the valuable input. I do not understand the concern about the relative humidity. I want to evaporate water droplets in superheated steam, so I cant figure why the humidity is important.

Anyway I tried the suggestion from Dr. Strangelove and it results in timescales of the right decade, for a start that is sufficient, but I will try to investigate this further.

"I am a bit plesaed that it is difficult, it was a pain for me that I could not solve it"

Thanks Jan
  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
how to simulate single droplet transcient evaporation using fluent6.3 Dhb FLUENT 0 May 15, 2009 09:28
DPM Modelling: Colloid droplet evaporation Meng Wai Woo FLUENT 1 August 1, 2007 00:27
Droplet Evaporation Christian Main CFD Forum 2 February 27, 2007 07:27
can CFX5 or 10 do this (about droplet evaporation) steven CFX 0 February 19, 2006 18:02
Water droplet motion and evaporation Julie Polyakh CD-adapco 0 November 16, 2002 15:16


All times are GMT -4. The time now is 00:44.