Re: [PipingDesign] Pressure Drop for Compressible Flow

From: <Syed>
Date: Mon Jan 28 2008 - 01:28:00 EST

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.


> 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]


Never miss a thing. Make Yahoo your home page. Received on Mon Jan 28 01:28:00 2008

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