A horizontal venturimeter with inlet diameter 20cm and throat dia 10cm is used to measure the flow of oil of specific gravity 0.8. The discharge of the oil through venturimeter is 60 lit/sec. Find the reading of the oil-Hg differential manometer, take Cd= 0.98.

 A horizontal venturimeter with inlet diameter 20cm and throat dia 10cm is used to measure the flow of oil of specific gravity 0.8. The discharge of the oil through venturimeter is 60 lit/sec. Find the reading of the oil-Hg differential manometer, take Cd= 0.98. 

Solution:

 At entry, d1=20cm 

 a1= (π/4)*202 = 314.16 cm2 

 At throat, d2 = 10cm 

 a2 = (π/4)*102 = 78.54 cm2 

 Cd = 0.98 

Q = 60 lit/sec= 60*1000 cm3 /sec 

Q = Cd[a1a2 /√( a1 2 - a2 2 )]* √(2gh) 

 60*1000 = 0.98[314.16*78.54/√( 314.162 -78.542 )]*√(2*9.81*h) 

√h= 17.029, h= 289.98 cm of oil 

To calculate reading of the oil-Hg differential manometer 

 we have 

 h =x[(sh/sp)-1] 

 Where sh = 13.6 –> sp. gravity of the mercury 

 sp = 0.8 --> sp. gravity of the oil 

 x = ? 

 x= 18.12 cm