Re: [PipingDesign] Flow Elements - Recommendation

From: <Steve>
Date: Mon Nov 26 2001 - 01:56:00 EST

Rakesh,
if you have a look at BS1042, it will tell you most of what you need to know, including expected accuracy. In addition you will have a widely accepted design method and not just a bunch of numbers off the internet. I would expect ISA have the same.
For magflows, ultrasonics etc, the instrument vendors will assist. Any flowmeter will give a reading with any up/downstream straight distances. The longer the distances the better the accuracy. However once the limit of accuracy of the flowmeter is reached, there is no point in going longer. For preliminary planning, I allow 20D upstream, 10 downstream if it is not a critical measurement. For critical flows I double these, although I often wish I had allowed more.

Cheers

Steve Mckenzie

> Also, Upstream and downstream lengths depend on the configuration of the
> fittings used, i.e. before and after the Flow Element, which varies from
> upstream 7D - 25D
> and downstream 5D - 15D. These straight lengths can be reduced using 'Flow
> Straightners' upstream of the FE.
>
> regards
> Sharma
>
> -----Original Message-----
> From: V.R.H.P. Macharla [mailto:macharla777@yahoo.com]
> Sent: Monday, November 26, 2001 8:51 AM
> To: PipingDesign@yahoogroups.com
> Subject: Re: [PipingDesign] Flow Elements - Recommendation
>
>
> Rakesh,
> I suppose you are looking for the philosophy behind
> deciding the straight lenths before and after flow
> element.
> It links to theory of Boundary Layer and Secondary
> Flows in fluid path. After any bend, there will be
> secondary flows induced near the pipe wall...it
> proportionately effects local velocity/pressure of the
> fluid. Considering the length of pipe required to
> reach to full velocity of liquid, standard straight
> lengths ahead of Flow Element are established.
> For after FE, also staright length is required to
> reach to full velocity after the Vena Contracta
> condition at FE.
> Hope it clarifies upto some extent.
>
> Macharla
> --- saud <saud@bushnak.com> wrote:
> > Dear Rakesh
> >
> > The standard recommended dimensions upstream and
> > downstream of a flow
> > measuring instrument sensor (paddle wheel type etc.)
> > is 10 times the
> > diameter of the pipe (D) for upstream and 5 D for
> > down stream.
> >
> > With latest magnetic flow meters, this dimension is
> > reduced to 5 D and 2 D
> > respectively.
> >
> > Regards
> >
> > Saud
> > ----- Original Message -----
> > From: "RAKESH PATIL" <rpa@epc.ltindia.com>
> > To: <PipingDesign@yahoogroups.com>
> > Sent: Friday, November 23, 2001 6:15 PM
> > Subject: [PipingDesign] Flow Elements
> >
> >
> > > ** High Priority **
> > >
> > > Can anybody give me the basic criteria behind
> > deciding the upstream and
> > downstream dimensions between Flow Element and
> > connecting Fitting /
> > accessories in piping?
> > >
> > > regards,
> > > rakesh
> > >
> > >
> > >
> > >
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Received on Mon Nov 26 01:56:00 2001

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