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Gas flow through a 90 deg Elbow

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Old   June 29, 2004, 16:08
Default Gas flow through a 90 deg Elbow
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I am a mechanical engineer, who does flow calculations occasionally. I have been asked to estimate the loss of pressure of a gas flowing through a 90 deg. elbow. Is there any ready formala for doing this, and is there any references somebody can help me. Thanks a lot for your assistance.
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Old   June 29, 2004, 19:59
Default Re: Gas flow through a 90 deg Elbow
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abhi
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The Diffrence Between pressure inlet and pressure outlet will be total pressure loss.
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Old   June 29, 2004, 21:12
Default Re: Gas flow through a 90 deg Elbow
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My problem is I only know the inlet pressure, and may not have an oppurtunity to plug a pressure gauge after the outlet. I have to predict the pressure loss before the equipment is built. Any input is greatly appreciated.
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Old   June 30, 2004, 07:36
Default Re: Gas flow through a 90 deg Elbow
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Tim
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Hi yes you can use an approximate loss coefficient approach.

The pressure head loss (h) can be approximated as...

h = (k*u*u)/(2g)

as h = dp/(rho*g) you can re-arrange to get

dp = k. 0.5*rho*u*u

I assume you know or can calculate the density and average flow velocity. The value of k can be found listed in tables for differend bends/valve/etc.

a 90 degree elbow has a k coefficient of 0.9

i.e.

loss of pressure = 0.9 * dynamic pressure

dp = 0.9 * 0.5* density * velocity squared

This is described fully in the book 'mechanics of fluids' by B.S. Massey . ISBN 0-412-34280-4

alternatively you can calculate the friction factor from a moody chart and use a l/d approximation to find the pressure loss

hf = f . (l/d) (vel squared/2g) Darcy weisbach equation

try http://www.engineering.uiowa.edu/~fl...Chapter_10.pdf

Good luck

Tim,

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Old   June 30, 2004, 10:43
Default Re: Gas flow through a 90 deg Elbow
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Tim,

Thanks a lot, appreciate your help.
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Old   July 4, 2004, 08:29
Default Re: Gas flow through a 90 deg Elbow
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James Date
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Have a look in:

Fluid Flow - Internal Flow Systems

2nd Edition by D.S. Miller

This has pretty much everything you need to know about doing pipe flow calculations.

Regards James
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