RE: calculation diameter of pipe

From: <erwin>
Date: Sun Dec 14 2003 - 21:04:00 EST

Dear all,
For Gas pipe calculate, I found formula as follows:

        Q = 2826/G^0.425x ( P1^2 -P2^2)^0.575/L x d^2.725

Where : Q = Gas flow rate ( ft^3/hour ) 

              G = Specific grafity of gas ( 0.65 )
             P1 = Pipe inlet pressure (psia)
             P2 = Pipe outlet pressure ( psia )
             L   = Lengh of pipe
             d   = Internal diameter  ( inches )

Can this formula used ?

Regards

Erwin.

Steve McKenzie <mechproj@xtra.co.nz> wrote:

to chuck in my 2 bobs worth, two places to be careful:

  1. Units. In imperial/US units P=?H is right because ? is in lb weight per unit volume. The g term is already included. In SI units P = ?gH because ? is in mass per unit volume. Be careful with the units because they are even less forgiving than recommended velocity. Dimensional analysis is a useful check.
  2. Friction factor. There are two out there: The one given by Nashine in H=fL/d X V^2/(2g) is the one more commonly used by mechanical engineers The original equation was H = 4 X fL/d X V^2/(2g) and is occasionally used by chemical engineers. Both equations should give the same result but the original equation has a friction factor which is one quarter of that we normally use . When obtaining f, be sure to check Take care as it can be embarassing to be out by a factor of 4 - the wrong way.

Cheers

Steve McKenzie

-----Original Message-----
From: erwin alamsyah [mailto:erwinalam@yahoo.com] Sent: Friday, December 12, 2003 8:40 PM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] calculation diameter of pipe

Thanks for your help

Paul Bowers <pbowers@pipingdesign.com> wrote: "V= Recommended velocity of fluid". Careful with that, some fluids are less forgiving than others.

Paul

> Steps for calculation of pipe diameter :
>
> Step I : Calculate the approximate diameter of pipe on basis of
recommended velocity for the fluid. Using equation ; Q=AV.
>
> Here, Q = Flow rate of liquid, A = inner area of pipe, V= Recommended
velocity of fluid.
>
> Step II : Calculate the pressure loss in the system using formula
fenning's / Darcy's formula ; H=fLV2/2gd and P=?H
>
> Here, H= Head loss of fluid, f=friction factor which depends on surface
roughness for pipe, L=Equivalent length for piping comprising pipe fittings & valves etc, d= Inner diameter of pipe, g=gravitational acceleration, V= Recommended velocity of fluid, P=pressure drop, ?=Density of fluid
>
> Step III: Continue the above iteration till that pressure drop comes with
in acceptable limit for the system.
>
> Step IV : Having acceptable pressure drop use formula H=fLVa2/2gd again
to back calculate the actual velocity (Va).
>
> Step V: Use formula Q=Aa Va to back calculate the final annular / inside
area (Aa ).
>
> Step VI: Having inner diameter and pipe thickness (which is to be
separately calculated by strength calculation by using Tayler's formula or relevant piping codes) outer diameter can be selected from dimensional codes for pipe sizing e.g., ANSI B36.10/ANSI B36.19/ BS3600 etc.

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[Non-text portions of this message have been removed] Received on Sun Dec 14 21:04:00 2003

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