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using Bernoullis Equation to get flue gas flow rate inside pipe

using Bernoullis Equation to get flue gas flow rate inside pipe

using Bernoullis Equation to get flue gas flow rate inside pipe

(OP)
hi
i am doing a project where i need to measure the flow rate of hot flue gasses (co, co2, nitrogen). i have took the pressure inside the heat exchanger mounted on fireplace rather than having flow velocity. then i use bernoullis equation as following to get flow rate.
Dia of pipe= 51mm
inner dia = 38mm
Corrugated pipe
pressure 300 pa
to find velocity from pressure (Bernoulli equation):
(po + p1) + rho v1^2 / 2 = (po + p2) + rho v2^2 / 2
where
p - pressure
v - velocity
1 and 2 subscripts indicate initial and exit values, while po is atmospheric pressure
(there is no height term since the pipe is horizontal)
if we assume that v1 = 0, and p2=0 (pipe exit)
v2 = sqrt (2 p1 / rho)
where p1 = 300 Pa
rho = 1000 kg/m^3
v2 = 0.77 m/s
Flow rate:
Q = A v2 = (25.5^2 pi / 4) * 0.77 = 393 m^3/s

result seems to me so weierd. it should not be so much high. can any one have any idea where i went wrong or the results are good enough.
thanks

RE: using Bernoullis Equation to get flue gas flow rate inside pipe

Density is not 1000 kg/m3 and  .. maybe ... just upstream of the outlet the pressure is not zero.  To not consider change of volume with pressure, the pressure drop must not be greater than 30 kPa, or even better at these low pressures, even less.

From "BigInch's Extremely simple theory of everything."

RE: using Bernoullis Equation to get flue gas flow rate inside pipe

You might want to see if you can get hold of a copy of Crane's Technical Paper 410 -- Flow of Fluids.  It has a section on flow of compressible gases, with a lot of formulas.

Patricia Lougheed

******

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RE: using Bernoullis Equation to get flue gas flow rate inside pipe

(OP)
thanks guys,
i also tried micro manometer to find flow rate but the difference between these results vary. so i am not sure about the compressible flow parameters.
Nuclear- can u post the same cran's technical paper here or any link i tried but could not find it

Thanks

RE: using Bernoullis Equation to get flue gas flow rate inside pipe

dgau008

Here's a link to the webpage where you can buy it: http://www.flowoffluids.com/.  You can also find it on Amazon (and probably on e-bay), though for MUCH higher prices (even when you take shipping into account.)

IMO, it is well worth the price to buy it.   

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

RE: using Bernoullis Equation to get flue gas flow rate inside pipe

(OP)
cool.... money doesnt matter as the importance of project..... i will buy that, hope will get useful info. by the way thank you very much

RE: using Bernoullis Equation to get flue gas flow rate inside pipe

Schaum's outline has a section on the application of the Bernoulli's equation on compressible fluids.

RE: using Bernoullis Equation to get flue gas flow rate inside pipe

Only if the fluid IS water at atmospheric pressure.
If a compressible fluid, it needs to be the density of the fluid at flow conditions at the point of interest.

From "BigInch's Extremely simple theory of everything."

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