Page 87 - ebook fluid mechanics_finalize

FLUID MECHANICS

The theoretical discharge Q can be converted to actual discharge by multiplying by

the coefficient of discharge Cd found experimentally.

2gH
Actual discharge, Q = C Q = C A —————(3)
d
1
actual
d
theory
m 2 − 1

If the leads of U-tube are filled with water,

p 1 − p 2 = x ( −  )
g

p − p  g 
H = 1 2 =  x  −1 

   

Example 4.9

A venture tube tapers from 300 mm in diameter at the entrance to 100 mm in diameter at

the throat; the discharge coefficient is 0.98. A differential mercury U-tube gauge is

connected between pressure tapping at the entrance at throat. If the meter is used to

measure the flow of water and the water fills the leads to the U-tube and is in contact
with the mercury, calculate the discharge when the difference of level in the U-tube is 55

mm.

Solution to Example 4.9

Using Equation (3),

2gH
Q = c A
d
actual
1
m 2 − 1

x = 55 mm

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