Hitest,
Let me help you to short of to find principle which can help you;
first you select of duct are (sq.ft) which using ie. 12 in, then 20000 cfm pass
through the nominal size duck. so now you define of fluid that is flowing
through s pipe/duck may move in two way different patterns, streamline and
turbulance. and the the deciding sd to ehether thr flow is streamline or
turbulent is the the Reynolds number. ( Output of fan we consider was streamline
< 2,000). then you find friction factor, inclding the roughness of the surface.
(for air closed to zero)
So direct we use formula standard : velocity (V) = capacity (Q) / duct are(A);
I am sure you can be developed that formula by adding some factors you
considered. (as neils said affect the 'maximum' velocity are the type of gas and
its density to be considered and in practice, most main ducts have velocities in
the range 40-75 ft/sec. As the duct diameter increases, the velocity can be
increased because the wall area decreases as a ratio to the cross section (less
friction)).
I hope this will be short of explained of all acknowledment.
regards,
<a href="/group/PipingDesign/post?postID=nQajO4IeBxfkVNczeg8Ac59YNONKuE6SVgowhLLdhluamv85EiFYmVTbQE3ylf8oNvbfCtfRYcrHpg">Rofinus@telkom.net</a>
> Hi Neil
> Here I have presented my problem in different way. Suppose I have a fan of
> 20000 CFM air capacity.
> This fan will not suck 20000 cfm air through 12 inch duct because it has
> limitation on fan suction velocity according to its impeller tip speed. So
> for a given fan say 20000cfm what should be the minimum duct diameter to
> suck 20000 cfm air. How do we calculate the minimum dia of duct requires so
> that it will convey/pass 100% flow of fan.
>
> Thanks all of you for giving your valuable time to my problem.
> Regards
> Hitesh
>
> > -----Original Message-----
> > From: Neil Stone [SMTP:jnstone@MNSi.net]
> > Sent: Tuesday, May 15, 2001 11:09 PM
> > To: <a href="/group/PipingDesign/post?postID=64d5m7YxK9XUPcSxtQruNqrehcs7vsGs4I-AaJXiW9h_IIWCNq0yn3lPEyrhK6_2p7sJZOHD3OIk4bXC51i_uU-8bkc">PipingDesign@yahoogroups.com</a>
> > Subject: Re: [PipingDesign] maximum duct velocity
> >
> > The maximum velocity you can take in a duct is when the duct pressure loss
> > just equals the fan head - this can be as high as you like, up to sonic
> > velocity. In practice, most main ducts have velocities in the range 40-75
> > ft/sec. As the duct diameter increases, the velocity can be increased
> > because the wall area decreases as a ratio to the cross section (less
> > friction),
> > BUT, in certain parts of a system, the velocity may be as low as 15
> > ft/sec,
> > or as high as 150 ft/sec. Other factors that affect the 'maximum'
> > velocity
> > are the type of gas and its density.
> > Neil
> >
> > At 04:47 PM 5/15/2001 +0530, you wrote:
> > >I have little problem in Duct velocity. For a given I.D. fan what will be
> > >the maximum velocity we can take in Duct. What is the limiting factor of
> > >duct velocity according to fan design.
> > >Regards
> > >Hitesh
> >
> >
> >
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[Non-text portions of this message have been removed] Received on Wed May 16 11:31:00 2001
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