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Simulating Evaporation

  1. Aug 2, 2011 #1
    I'm looking to do a little flash animation illustrating evaporation at a surface however I've been having a lot of trouble implementing this.

    My initial Lennard-Jones approach was a disaster. I then tried hard-spheres and this wasn't really any better. I've considered something like a hard spheres model with some sort of attractive potential drawing particles to the surface, something like 1/(y_surface-y_particle)^n which would sort of simulate the coulomb or dipole force from all the atoms within the liquid. However, it all just ends up being chaos. Does anyone have any suggestions as to what a simple model might be that will illustrate the largest velocity particles in a liquid leaving the surface? Thanks in advance
  2. jcsd
  3. Aug 3, 2011 #2
    It's not my field of interest but I might provide some insight. I strongly suggest you to take a look at Blender (blender.org) if you want realistic illustrations. It has real world physics engine also fluid dynamics packs which will be enough for your need. It is an easy to learn gaming engine and will provide much better results than a flash animation. All the macroscopic mechanical phenomenas can be visually and precisely represented by the aid of this approach. When I first heard about it I didn't care that much because a gaming engine is a gaming engine and thought can not be used for scientific or research purposes/illustrations but it turned out that it has more potential than I could imagine. It's free and has a linux version - which was more than enough for us.

    Some basic searching yielded to ;

    Hope that helps.
    Last edited by a moderator: Sep 25, 2014
  4. Aug 3, 2011 #3
    Thanks for the link but I'm not quite sure what the relevance is. I'm trying to figure out the interactive force needed to do a molecular dynamics simulation that illustrates evaporation. This appears to be a graphics engine, regardless of how pretty the shader effects are on my particle I'd still need to know the interactive force necessary to illustrate evaporation.
    Last edited by a moderator: Sep 25, 2014
  5. Aug 3, 2011 #4
    Liquid molecules will start to earn kinetic energy from the heating/hot surface and will tend to move against gravity. At boiling temperature modelling the system should not be hard. Higher velocity particles will be the first ones to shift to gas phase and you need to know the approximated minimum velocity/heat required for your specific liquid molecules. Problem is evaporation will occur at any temperature also it's rate will change with the humidity level of environment and air flowing in contact surface (liquid - air).

    Some digging returned this ;

    E = K.A.(Xs - X)

    E = amount of evaporated liquid (kg/h)
    K = evaporation coefficient (kg/m2h)
    v = velocity of air above the liquid surface (m/s)
    A = liquid surface area (m2)
    Xs = humidity ratio in saturated air at the same temperature as the liquid surface (kg/kg)
    X = humidity ratio in the air (kg/kg)

    Once you find E you can get to number of molecules evaporated.
  6. Aug 3, 2011 #5
    Again, I am trying to do a MOLECULAR DYNAMICS simulation of evaporation. If you don't know what this is (and yet you posted anyways) an example animation can be found here http://en.wikipedia.org/wiki/Kinetic_theory The difficulty comes in finding the partial differential equation that governs the force between the particles that I can discretize to effectively simulate the evaporation of a liquid at a surface.
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