Fluids

Fluids

Inlet mass flow rate 0 kg/s

    • raju.chowdhury
      Subscriber

      Hi,


      I am simulating compressible gas flow through an annuls area (annuls diameter is 1 mm) . I have used following boundary conditions:


      Mass flow inlet: 0.12 kg/s, Initial gauge pressure 20 bar, Inlet temperature: 1238K


      Pressure outlet  with target mass flow rate: 0.12 kg/s. Outlet temperature: 950 K


      Simulation is running but Inlet mass flow rate showing 0 kg/s. What could be the reason?


       


      Image result for annulus area

    • RK
      Ansys Employee

      Hello, 


      What is the operating conditions that you have set?


      Regards,


      Rahul 

    • Kalyan Goparaju
      Ansys Employee

      Hello, 


      Any reason why you have target mass flow rate turned on? This option is used to change back pressure at the pressure outlet boundary in order to establish a flow with a specific mass flow rate. Since you already have a defined mass flow rate (because of the mass flow inlet), I don't see why you need to have this option turned on.


      Thanks, 


      Kalyan

    • raju.chowdhury
      Subscriber

      Hi Rahul,


      Here is the operating conditions:


      Mass flow inlet: 0.12 kg/s, Initial gauge pressure 20 bar, Inlet temperature: 1238K


      Pressure outlet  with target mass flow rate: 0.12 kg/s. Outlet temperature: 950 K


       


      I only know the Flow rate 200 Nm3/hr and supply pressure 20000kPa. I need to know the exit velocity.

    • raju.chowdhury
      Subscriber

      Hi Kalyan,


      I have set up the target mass flow rate because as I know inlet mass flow rate, I am wanting to same mass flow rate at outlet.


       


       

    • Karthik R
      Administrator

      Hello,


      Just like my colleague mentioned, please change the outlet BC to Pressure Outlet. Since you are solving the conservation equations in Fluent, specifying an inlet mass flow rate will automatically ensure that the outlet has the same flow rate.


      Thanks.


      Best Regards,


      Karthik

    • raju.chowdhury
      Subscriber

      Hi Karthik,


      I have done this but still getting 0 kg/s at inlet.


      While I have used Pressure inlet boundary condition instead of mass flow rate boundary condition, the simulation diverging showing "temperature limited to ... cells" message.

    • raju.chowdhury
      Subscriber

       Hi all,


      I have solved the inlet mass problem.


      Can you anyone explain the following problem:


      I have data: Mass flow rate 200 Nm3/hr at pressure 20000 kPa. If I use mass flow rate boundary condition at inlet, how will ensure that gas is flowing at desired pressure (20000 kPa)?


      How can I calculate the static pressure for a gas flow through annulus area? I have calculated by considering the Mach number=1 because as the annulus area is same from inlet to outlet, it is expected that flow will be chocked. I have set the static pressure in inlet BC (mass flow rate + Initial gauge pressure). But, I am not getting the expected pressure in the simulation results.

    • vinayak chauhan
      Subscriber

      Hi,


      You can set the your desired value in "initial gauge pressure value/supersonic" tab and keep it constant.


      I hope it works.


      Thanks,


      vinayak

    • raju.chowdhury
      Subscriber

      Hi Vinayak,


      How can I keep at constant? Are there any option for that?


      Can you give me any idea to calculate Turbulent Intensity if I don't know the inlet velocity.?


       


      Thanks.

    • vinayak chauhan
      Subscriber

      hi,


      u can open boundary conditions->mass-flow inlet menu-> initial gauge pressure value/supersonic 


      enter your value here (which is initially set to 0)


       

    • raju.chowdhury
      Subscriber

      I did similar way but it is seems constant. I am giving 9.6 bar but getting 10.32 bar.

    • vinayak chauhan
      Subscriber
      Hi Since your flow is compressible so there will be a slight change in pressure and density.
    • vinayak chauhan
      Subscriber
      Hi Also check if you have taken wall friction condition or not.
    • vinayak chauhan
      Subscriber
      Hi Regarding your turbulent intensity you will need either Reynolds no. or initial velocity , otherwise it will be difficult to calculate . Or you know the value of viscous force and inertial force .

      Thanks Vinayak
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