Re: [PipingDesign] Pressure Drop for Compressible Flow

From: <>
Date: Mon Jan 28 2008 - 10:25:00 EST


First, I want to thank you for the professional manner in which you have presented the question.

Your basic approach is sound. Realize that it is an iterative process. You also need to consider the possiblity of condensation thru the pressure wave, and evaluate possible major wear locations based on Mach number within any geometry changes, and I would also suggest consideration of a second set of conditions for wear, if any are suspected (based on condensation and geometry changes). This is a complex issue. You do not mention the fluid or service, both of which will impact your decisions and calculations. If there is a reasonble chance of condesnation or other phase change, this can become very complex, and you may want to consider very rigorous methods, some of which are included in DIERS methodology (developed by AIChE).

... Bruce D. Bullough ...
Lead Process Engineer
Foth Production Systems, LLC
8550 Hudson Boulevard North, Suite 100
Lake Elmo, MN 55042
Direct: +651-288-8598 Fax: +651-288-8551

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indra pratisto <>
Sent by:
01/27/2008 11:56 PM
Please respond to


[PipingDesign] Pressure Drop for Compressible Flow

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

Please let me know if my method is correct and complete enough to solve the problem. Thanks.

- Indra -

Engineer, Singapore Received on Mon Jan 28 10:25:00 2008

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