Re: Pressure Drop for Compressible Flow

Hi Amjad,

I assume isothermal flow because the pipeline is long, velocity is low and the pipeline is uninsulated (there is sufficient heat transfer to maintain thermal equilibrium with surrounding)

I know for adiabatic flow, I shall use Fanno (with friction) or Rayleigh (frictionless) flows. In both cases the approach is totally different than that of incompressible flow.

For isothermal flow, the approach is very much the same as incompressible flow. The only difference is, I think, on the formula used to calculate pressure at fluid outlet. Please correct me if I'm wrong.

Regards,
Indra

• In PipingDesign@yahoogroups.com, Syed Amjad Ahmed <rsaahmed@...> wrote:
  >
  > Dear Indra
  > The calculation procedure you have described is for
  > incompressible flow. This is totally different from
  > compressible flows. May I know the basis for assuming
  > Isothermal flow...
  > First, you need to classify the flow to either Fanno,
  > Rayleigh or Isothermal.Then you need to calculate the
  > parameters accordingly. Details on these flows should
  > be available in any fluid mechanics textbook.
  >
  > Regards
  > Amjad
  >
  >
  >
  >
  >
  > --- indra pratisto <yohcindrap@...> wrote:
  >
  > > Hi all,
  > >
  > > First of all, my background is Mechanical
  > > Engineering, so most of the time I'm only working
  > > with incompressible fluid. However, this time I've
  > > given a task to calculate pressure drop of
  > > compressible fluid along pipeline connected to
  > > safety valve (flow is from steam drum to safety
  > > valve to pipeline to atmosphere).
  > >
  > > I'm assuming isothermal compressible flow. Using
  > > pressure and temperature at the safety valve's
  > > discharge point I obtain the fluid properties
  > > (density, viscosity, Cp, Cv, etc). Afterwards, my
  > > step-by-step calculation is as follows:
  > > - Check for Mach number of inlet fluid: max
  > > possible velocity of a compressible fluid in a pipe
  > > is sonic.
  > > - Calculate friction loss using Reynolds number
  > > and relative roughness
  > > - Calculate loss coefficient due to fittings using
  > > Darcy's 3-K method
  > > - Calculate total loss (friction loss + loss due
  > > to fittings)
  > > - Calculate outlet pressure using Darcy's equation
  > > for compressible fluid
  > > - Get the pressue drop (Inlet pressure - Outlet
  > > pressure)
  > > - Check for Mach number of outlet fluid: max
  > > possible velocity of a compressible fluid in a pipe
  > > is sonic.
  > >
  > > Please let me know if my method is correct and
  > > complete enough to solve the problem. Thanks.
  > >
  > > Regards,
  > > - Indra -
  > > Engineer, Singapore
  > >
  > >
  > > ---------------------------------
  > > Never miss a thing. Make Yahoo your homepage.
  > >
  > > [Non-text portions of this message have been
  > > removed]
  > >
  > >
  >
  >
  >
  >
  

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