3 (a) Show that the NPSH available (NPSH) for a pump can be expressed as: P NPSH = arm-P pg - Given: NPSH P.-P. V + pg 2g where P, is pressure at pump suction, p, is vapour pressure of fluid, Pam is atmospheric pressure, V, is velocity at pump suction, (-21) refers to pump above suction level, and Hy is head loss in suction line. Discuss how the NPSH available can be affected (i) when the pump is located above/below the suction level, and (ii) when the pump is to operate at 5000 m above sea level. (10 marks) (b) A centrifugal pump is selected to draw water from a well. The centre line of the pump suction is 2 m above the water surface in the well. The suction pipe has a diameter of 20 cm and a length of 7 m. The designed flow rate is 0.16 m³/s. (i) Determine the pressure at the pump suction at the designed flow rate. (ii) Will cavitation occur when the suction level is 2 m below the pump? (iii) What is the lowest possible suction level to avoid cavitation? You may use the following information: Entry loss coefficient = 0.5 Valve loss coefficient = 1.2 Pipe friction factor = 0.01 Density of water 1000 kg/m³ Dynamic viscosity of water = 0.001 Ns/m² NPSH required by pump = 2.5 m Atmospheric pressure 101 kPa Vapour pressure of water = 2430 Pa (15 marks)