Page 95 - ebook fluid mechanics_finalize

FLUID MECHANICS

Example 4.12

The water supply to a water heater contracts from 10mm in diameter at A (Figure 4.12) to

7 mm in diameter at B. If the pipe is horizontal, calculate the difference in pressure

between A and B when the velocity of water at A is 4.5 m/s.

The pressure difference operates the gas control through connections which is taken to a
horizontal cylinder in which a piston of 20 mm diameter moves. Ignoring friction and the

area of the piston connecting rod, what is the force on the piston?

d1 d2

p1 ,v1
p2 v2

Figure 4.12 : Venturi Meter

A B
b
Solution to Example 4.12

In the Figure 3.11 the diameter, pressure and velocity at A are d1, p1 and v1 ; and at B are

d2, p2 and v2.

By Bernoulli’s theorem, for horizontal pipe,

v 1 2 + p 1 = v 2 2 + p 2
2g  2g 

84