Your fan will develop a specific pressure at 20000 cfm - let's say 3" w.c.
(to talk about 'a 20,000 cfm fan' is meaningless if you don't say what
pressure the fan is developing - several different fans could draw 20,000
cfm, all running at different speeds and pressures).
Now, the smallest duct you can use is a duct system that has a pressure
loss of 3" w.c. This depends on duct diameter, length of duct, number of
bends, tees, branches, density of the gas.
For preliminary sizing, the most economical duct velocity usually turns out
to be about 50 ft/sec. If you design for a high velocity, be careful - a
small change in duct configuration, or dirt buildup in the duct can cause a
huge increase in pressure loss.
Neil
At 08:40 AM 5/16/2001 +0530, you wrote:
>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
>
Received on Wed May 16 07:40:00 2001
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