4 Replies Latest reply on Jul 10, 2013 8:10 PM by Jerry Pham

    Boundary Condition for Enclosed Air?

    Jerry Pham

      Hi,

       

      If I want to simulate the air temperature change within an enclosed container (no inlet/outlet flow), initially at 1 atm and 300K ordinary condition, the container being a glass bottle. What should I do? The only influencing factor is some a 3cm deep moderately hot water at 80°C.

       

      bnd.jpg

        

      I have problems in understanding the inner wall boundary condition:

      1. I should not use inlet/outlet type.
      2. Nor should the 2nd option (pressure) type suffice. Pressure of the air was already specified in the initial conditions.
      3. Walls:

      Ideal wall, not appropriate because the glass bottle is not adiabatic.

      Out wall, not appropriate because it is inner wall.

      Real wall: first I cannot specify constant temperature or it will become a heat source; But if I select heat transfer coefficient, how should I choose the “T of external fluid”? I this scenario the glass has thickness, and the 3cm deep 80°C water will heat the glass by convection/conduction, as well as by heating first the above air and the air then imparts some energy to the glass, so the glass temperature constantly changes. Is it logical to select  “T of external fluid” in this context?

      On the other hand, there is also an option “Interpolated” and “Dynamic Boundary Layer Thickness”, but both the “Technical Reference” and “Solving Engineering Problems” has no mentioning of it. What does it mean here?

       

      I actually guess that I should NOT need to specify INNER boundary condition in this case. But if I don’t, the “Run” command will prompt an error that “There is no fluid volume in the project. Please check geometry or boundary conditions”, so it seems that a boundary condition is required even when it is unnecessary. Is there a way to continue without using any of the inner wall boundary conditions?

       

        

      Jerry

        • Re: Boundary Condition for Enclosed Air?
          Jared Conway

          Internal or external analysis.

          Do not exclude cavities without flow conditions.

          If you use an internal analysis, apply the appropriate external boundary conditions as outer walls.

          If you use external analysis, use the appropriate external conditions.

          On the inside, whatever fluid you have defined will be calculated appropriately as a fluid dynamics problem.

           

          have you considered taking the flow simulation training class from a local reseller? I think you've got some really good questions but you're one step ahead of where you need to be. break the problems down as internal or external first and then worry about the boundary conditions. this topic should be covered well in the training class and also the tutorials. We also offer our customers one-on-one training for their specific needs. For example in this case, i can think of about 5 different ways to solve the problem and that is what we would go over.