A venturimeter is to be fitted in a pipe of 0.25 m dia. where the pressure head is 7.6 m of flowing liquid and max. flow is 8.1 m3 /min. Find the least dia. of the throat to ensure that the pressure head does not become negative, cd = 0.96.

 Solution: 

 Q= cd((a1a2)/(√a1 2 -a2 2 ))*√(2gh)

Q = (8.1/60) = 0.135 m3 /s, cd = 0.96 

a1 = (π/4)*(0.25)2 = 0.049 m2

 h = 7.6 m 

0.135 = 0.96*((0.049*a2)/(√0.0492 -a2 2 ))*√(2*9.81*7.6)

a2 = 0.0112 m2