3 Replies Latest reply on Sep 23, 2010 10:53 AM by 1-TCDKTI

    Problem modeling evaporation from a lake's surface

      Hi all,

       

      I have to model the evaporation rate from a water surface (a lake) under several wind and geometry conditions, in Cosmofloworks (SW 2008)

      The lake is a flat static surface (no two-phase problem, just air flow + moisture). I consider, at least for now, no thermal effect.

       

      I started with a parallelepiped fluid domain (see attachment), with an air inlet and an outlet, two ideal walls on the sides. The upper and lower faces are enviroment-pressure openings.

      I set the upper face to correspond to the environmental humidity (e.g. 30%, like for the inlet).

      The lower face is in contact with the water surface, and I set humidity to be 100% (saturated layer).

       

      I expect, in this basic situation, that, after a while, the system will get to an equilibrium: in particular, moisture distribution  will be stable.

      Then, I guess, if I take a control volume anywhere in the domain, the water mass content will be constant and, therefore, the total water flux through its surface will be 0.

       

      My idea was, then, to take a control volume with the lowest face close to the water surface, and to consider the flux thorugh this face as the evaporation rate.

       

      The problem is that, even after many trials and corrections, the flow through the surface of the control volume never becomes 0. So, I don't know how to interprete the results... in particular, I don't know if

      1. my "equilibrium idea" is wrong,
      2. my model is wrong, or it could be done much better,
      3. ...

      (I already checked that there is no condensation in the control volume)

       

      Do anybody has some clue or suggestion?

       

      Thank you!

       

      Guido

        • Re: Problem modeling evaporation from a lake's surface
          Stefan Wozniak

          If I understand correctly, you will not get 0 value because of flow in direction paralel to water surface.

          I'm not sure if you will get in FlowSimulation movement in relation to humidity.

          Perhaps In order to get water vaporation you need to apply some temperature.

          • Re: Problem modeling evaporation from a lake's surface

            Hi all,

             

            I try to better explain my basic question, because I realized it is not so straightforward...

             

            I have to model the evaporation rate from a water surface (a lake) under several wind conditions, in Cosmofloworks (SW 2008)

            I would like to find an evaporation rate under different wind velocities.

             

            I can start with a simplified problem, where the water is static and air and water temperature are constant.

             

            How could I model this system well in SW? Internal or external flow? How to represent the water surface? ...

            The first attempt I tried is in my previous post, but I am not sure at all it is the good way!

             

            Thank you

             

            Guido