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Q9. A centrifugal pump runs at 500 rev/min and discharges sea water at the rate of 12 m³/min against a head of 12 m.

The impeller has an inner diameter of 200 mm and an outer diameter of 500 mm. At exit, the vanes are backward facing at an angle of 45 o to the plane of rotation. The thickness of the vanes reduces the flow area by 10 %. There is no velocity of whirl at inlet and the fluid has a constant radial velocity of 2 m/s.

(a) Sketch the blade tip velocity vector diagram identifying the velocities. (4)

(b) Calculate EACH of the following:

(i) The width of the blade at inlet and exit; (4)

(ii) The angle of the blade at inlet; (3)

(iii) The manometric efficiency. (5)