2 Replies Latest reply on Feb 6, 2017 10:32 AM by Brian Kent

    Can I estimate pressure delta with FloXpress?

    Brian Kent

      I have run a FloXpress study, by entering the volumetric flow rate into the inlet opening, and it has reported the flow velocities throughout the model.  My understanding is that FloXpress reports results only as velocities.  I would like to know the pressure difference between the inlet and the outlet.  Since flow resistance is approximately proportional to the square of the velocity, I would also expect the pressure difference to vary with the velocity squared.


      I could repeat the study, except instead of entering volumetric flow rate, I would enter an inlet pressure, and then compare the resulting velocities with the ones generated by the simulation in which the volumetric flow rate at the inlet was entered.  I could repeat the study by entering various inlet pressures until the velocities are approximately equivalent to the velocities that were reported when the volumetric flow rate was entered.  Once I select the inlet pressure that results in approximately the same velocities reported by the volumetric flow rate run, is it valid to infer that the pressure delta gives rise to the flow rate of the first simulation?

        • Re: Can I estimate pressure delta with FloXpress?
          Ryan Dark

          Hi Brian,

          I just ran a quick test of the workflow you outlined using the full Flow Simulation package.  I use the full package so I could measure the pressure drop and apply it to a second flow project to check the difference in velocities.  The results was that the maximum velocities agreed within 4%.  So, if you don't want to buy full Flow Simulation and don't mind spending the time to iterate through to get an answer you could probably get away with that.


          I did also run the pressure boundaries I found in full Flow Simulation through FloXpress and it had a larger error (6%) so your millage may vary.

            • Re: Can I estimate pressure delta with FloXpress?
              Brian Kent


              Thank you for your prompt response, and for the help!


              I also ran my own example problem, consisting of a 10" long pipe with a 1.0 inch diameter inlet and a .10 inch diameter outlet, and a taper between the two diameters.  I ran FloXpress with an inlet pressure of 14.9 psi, and outlet pressure at the default value of 14.696 psi, about a .2 psi pressure delta.  Then, I did a few iterations entering different volume flow rates, and determined that a 9 cubic inch per second resulted in approximately the same maximum velocity at the outlet as what I saw with the .2 psi pressure delta.


              Then, as a second check, I doubled the volume flowrate at the inlet, to 18 cu in/sec, expecting to see 4x the pressure drop.  I ran it again, with an inlet pressure of 15.5 psi, representing four times the pressure drop.  Comparing the two runs, I found the maximum velocity at the outlet to compare pretty closely.


              Both your answer and my own experiment confirm to me that one can, indeed, use FloXpress to approximate the pressure delta in the system that results in an estimated volume flow rate by equalizing the reported velocities.


              Thanks again, Brian.