7 Replies Latest reply on Sep 3, 2010 9:14 AM by Rich Bayless

    Creating Suction/Vacuum in a venturi tube using FlowSimulation

    Eran Levi

      Hi all,

       

      I have encountered a problem while trying to create a suction effect using a venturi tube.

       

      I have attached several snapshots of the setting I chose, as well as some post-calculation snapshots.

       

      I know that there might be a problem with the nozzle minimal diameter which is 4 mm (don't think water can really pass through...),

       

      but it is the principle that I am trying to understand.

       

      my working fluid is water at 50 degrees Celsius.

       

      My goal is to lift water located at about 20-40 cm   below   the venturi nozzle, using a thin 5mm tube.

       

      the pressure at the venturi tube entrance is 700 kPa ; the pressure at the entrance to the thin tube is  103kPa;

       

      the flow rates should be:

       

      16 liter/min at the entrance to the venturi ;  2 liter/min through the thin 5mm tube ; and of course 18 liter/min at the venturi tube outlet.

       

      I have turned on gravity, and tried to run the simulation with Pressure Potential on and off, getting the same result:

       

      When the water entering the venturi reaches the thin tube, it immediately falls down, instead of creating suction and pulling the water (which is located below) up...

       

      I might be wrong here, but the calculation shows that in the throat the pressure drops to LESS than the pressure at the bottom of the thin tube, therefore, theoretically,

       

      there should be a suction effect...

       

      I am new to the flow simulation tool and therefore will be vary glad if anyone could help me.

       

      Thank you very much in advance,

       

      Eran.

        • Re: Creating Suction/Vacuum in a venturi tube using FlowSimulation
          Rich Bayless

          Hello,

           

          Please respond with the version of SW/Flow Sim that you are using, and your version of Windows.

           

          It would also help if you were to attach the solidworks part/assembly using 'pack and go'.

           

          Change the simulation to be an external study and see what happens.  You may need to apply an environmental pressure to one of the outside surfaces of the model.

           

          Rich.

            • Re: Creating Suction/Vacuum in a venturi tube using FlowSimulation
              Eran Levi

              Hello,

               

              The version of SW/Flow Simulation is 2010 (Premium) SP0.0  ; The version of Windows is Win 7 Ultimate 32-bit.

               

              I have attached the part/assambly files.

               

              Thank you for your time and effort.

               

              Eran.

                • Re: Creating Suction/Vacuum in a venturi tube using FlowSimulation
                  Rich Bayless

                  Hello,

                   

                  Search the Flow Sim forum for the words 'Gravity Flow Simulation', you will find a long thread about how to simulate the hydrostatic pressure of a column of water.

                   

                  This may give you some ideas to try out.

                   

                  Rich.

                    • Re: Creating Suction/Vacuum in a venturi tube using FlowSimulation
                      Eran Levi

                      Hello Rich,

                       

                      Thank you for your time.

                       

                      I ran an "External flow" test on the design, and now it really does show a suction effect through the thin 5mm vertical tube.

                       

                      My question is why didn't it work when the settings where set to internal flow, which is the what really happens in reality? there is no external flow around the venturi and the thin tube. only inside them.

                       

                      When I run the simulation with external flow, and after that, insert flow trajectories on the External surfaces, it shows flow in the opposite direction

                       

                      (snapshot attached).

                       

                      Do you by any chance know the reason for that happaning?

                        • Re: Creating Suction/Vacuum in a venturi tube using FlowSimulation
                          Rich Bayless

                          Hello Eran,

                           

                          the developers posted this answer to a question of how to model hydrostatic pressure in an internal study.

                           

                          I haven't tried creating a model example using their numbers, but perhaps you may have some time to give it a try?

                           

                          Thanks,  Rich.

                           

                          >>>Start of quote

                          Solution Id: S-015123 
                           
                            Product:  
                           
                            Updated: 8/27/2009 04:41:05 AM
                           
                            Area: COSMOSFloWorks
                           
                            Sub-Area: FW Fluid mechanics
                           
                            Question: Can Flow Simulation model the pressure hydrostatic effects of a drain where there is an elevation change within the drain?
                            
                           
                            Answer: To correctly model the hydrostatic effect of the water the developers wrote the following to calculate the pressure potential (grZ).

                          Absolute pressure is related to the pressure potential by the formula: Pabs=Ppot+grZ.

                          Here Pabs – absolute pressure level, Ppot – pressure potential, g=9.81 m/s2, r - water density, Z – coordinate (representing the height term.

                          The pressure potential term for COSMOSFloWorks is equal to the absolute pressure at Z=0. For example a drain model with the Z coordinate from top to bottom of the drain is equal to 0.3 m. The gravitation pressure term is then equal to grZ= 2943 Pa. Looking at the pressure potential at the top point where absolute pressure is equal to 101325 Pa. Pressure potential is equal to Ppot=Pabs- grZ=98382 Pa.

                          Therefore, to solve this problem the following boundary conditions can be set:

                          -  on the top surface: absolute pressure is equal to 101325 Pa;

                          -  on the exit of the drain: absolute pressure is equal to 101325 Pa.

                          The initial condition in the General Settings can be set with a pressure potential of 98,382 Pa.

                          Pabs=Ppot+grZ
                          Ppot =  Pabs - grZ
                          grZ  = 9.81 * 1000 * .3 = 2943
                          Ppot = 101325 – 2943
                          Ppot = 98,382 Pa

                           

                          <<<End of quote

                  • Re: Creating Suction/Vacuum in a venturi tube using FlowSimulation
                    Satit Nilyai

                    Hi all

                    The pressure at the entrance to the thin tube is 103kPa. (Pressure at bottom) Do you calculate from? (high of water, pressure gage)

                     

                    Note :I just finished the solving. If we input boundary condition in this case. the results are true. but theory of venturi isn't correct. I think, we will be to put value really of boundary condition by check from pressure input the model.