SECTION B: FLUID MECHANICS

3. The general expression for energy conservation in pipes, using standard notation, is

P₁+pU+pgh,

+pU+pgh, +pgh₁ + pgh

= P₂ +

a) Describe the physical significance of the pressure terms in this equation in terms

of the energy balance of the system.

[10 marks]

In a manufacturing facility, a sizable rooftop tank supplies water for cooling machinery in

the building, after which it collects in a tank in the basement tank for recirculation to the

tank on the roof. The outlet pressure required from the pump that recirculates the water to

the roof is a function of the required flow rate and the pressure losses in the flow path to

the roof. The flow path is formed from 40mm internal diameter copper pipe (a drawn

tubing) and exits from a tap, of the same internal diameter into the tank above the free

surface of the water. The water flow rate is 190 litres/minute.

The detailed flow path from the outlet of the pump is as follows: 5m horizontal pipe; 90°

threaded elbow (minor loss factor KL=1.5); 20m vertical pipe up to the roof; 90° threaded

elbow (KL=1.5); 2m horizontal pipe; wide open globe valve (KL=10); 2m horizontal pipe and

a tap in the tank (KL=2 for the given conditions). Assuming that the water flows with a

dynamic viscosity of 1x10-3 Pa.s and density 1000 kg/m³

b) Determine the pressure required at the start of the flow path, that is the outlet of

the pump.

[15 marks]