9 Replies Latest reply on Aug 31, 2015 12:44 PM by Chris Michalski

    Air flow simulation when vacuuming two chambers

    Jure Rejc

      Hi,

       

      I checked the internet but I could not find the solution. I have a system with two small chambers; one has a volume of 250 mm3 and other 650 mm3 with pressure sensor attached. These two chambers are connected with small and short tube (d=0.6 mm). To this tube another small tube (like T) with the same diameter is connected and leads to the larger connector where the vaccum pump is connected. At the start inside the system is a normal air with normal pressure (1013 mBar). After the vacuum pump is switched on the air is sucked out of the system to cca. 10 mbar - measured with the attached pressure sensor. I need to set the simulation for air flow, pressure drop in 2 seconds and the air temperature simulation.

       

      Is this possible in SolidWorks Flow Simulation?

       

      Thank you for the answer!

       

       

      Jure

        • Re: Air flow simulation when vacuuming two chambers
          Chris Michalski

          Yes, Flow Simulation can perform transient studies which calculate the change in parameters (temperature, pressure, velocity, etc) with respect to time.

          • Re: Air flow simulation when vacuuming two chambers
            Christopher Schaefer

            For clarification, are you drawing a vacuum on both tanks?

            I concur with Chris Michalski that this is a transient problem.  Tank evacuation isn't the easiest but Flow Sim provides an internal calculator to solve tank evac problems that I would suggest you review the Help documentation on.

            You should find this article helpful:

            Tank Evacuation

              • Re: Air flow simulation when vacuuming two chambers
                Jure Rejc

                Yes, the air is sucked out of all chambers. Thank you for now, I will study the link and help.

                 

                Regards,

                 

                Jure

                • Re: Air flow simulation when vacuuming two chambers
                  Jure Rejc

                  I must admit that I did not come to the solution for my problem. I started with a much more simple example. I have a tiny tube connected to the closed chamber/tank. I need to have a simulation of the time dependent pressure inside the chamber. The pressure at the beginning of the tiny tube is 10 bar and the inital pressure inside the tank is 1 bar. As I can distinguish from the literature this is time dependent process-the project is set to time-dependent. I have only the innlet without the outlet. The Boundary condition for an innlet is Static pressure of 10 bar, the surface is the inner lind surface of the tiny tube. What about the goals? I am confused. I would appreciate if you can give me a few hints how to accomplish the task.

                   

                  Thank you very much for the help and time.

                   

                   

                  Jure

                    • Re: Air flow simulation when vacuuming two chambers
                      Chris Michalski

                      For goals I would start by creating dummy volumes in your 2 chambers.  Make a solid that is the same shape as the inner volume, select these volumes to define the goals and then decide which values are most meaningful (minimum pressure, average pressure, etc).  Then make sure to disable those solids otherwise flow will consider your chambers full of solid instead of gas.  You can then plot the goal (pressure) vs time.

                        • Re: Air flow simulation when vacuuming two chambers
                          Jure Rejc

                          Hi,

                           

                          I managed to accomplish something, but the results are not ok. Is there a way that you make an example of filling the chamber with a small tube, so that also some others can understand the solution. The main problem is also arranging inlet pressure and boundary condition for the chamber pressure. I am using SW2014 and maybe this will be the biggest problem. Or step by step solution.

                           

                          Thank you very much for any help!

                            • Re: Air flow simulation when vacuuming two chambers
                              Chris Michalski

                              I have attached a quick model I made up.  It has 2 chambers connected by a small tube, and Tee off that tube for the vacuum source.

                              I didn't use your volumes or pressures so you'll have to adjust those.

                              I ran it as a transient study and it takes milliseconds to stabilize.  I have added the goals for the internal volumes.

                              A big risk in such a condition is not accurately refining the mesh.  My first attempt was all over as far as pressure.  When I looked at the mesh and realized it was not recreating the small diameter passage well I changed that and the simulation ran much more realistically.

                              Once you know how long it will take to stabilize you can add periodic saving so you can analyze the progress.  Or if the goals are sufficient you can graph them over time.