air flow in a pipe

huangyhg

air flow in a pipe
i am looking for an equation to determine air flow (standard) in a frictionless short pipe given diameter and the pressure differential across it. for example a 2.5" diameter pipe of 1 ft length has 20" h20 pressure across it. how much air (cfm) is it flowing? thanks.
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this thread should give you the information needed to for the cfm with a given pressure drop.  
the flow of mass is m [kg/s]= rho*u*s
and this is constant in every section (if you are in a stable condition).
rho= density;
u=speed;
s=area of the section that is constant in this case.
if the pipe is frictionless and the flow is adiabatic the total rho is constant (1.225 kg/m^3) so you can calculate the rho in this way:
rho=total rho*(1+(gamma-1)*m^2/2)^(-1/(gamma-1));
where
gamma=cp/cv=1.4;
m=number of mach;