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98-Mar-B5 December 2014 Page 4 of 16 QUESTION 4 PUMP DESIGN Refer to the Examination Paper Attachments Page 10 Pump Velocity Diagram. A preliminary analysis for a particular centrifugal pump to deliver water under ambient conditions has yielded the following parameters: Impeller inlet radius Impeller outlet radius Impeller inlet width Impeller outlet width Rotational speed Volumetric flow rate Delivery head 100 mm 180 mm 50 mm (in axial direction) 30 mm (in axial direction) 1720 rev/min 0.25 m/s 40 m As a next step determined. the design of the pump the impeller blade angles need to be (a) Calculate the power required by the pump assuming ideal conditions (no friction). (b) Calculate the mechanical torque required on the shaft. (c) Calculate the blade inlet and outlet tangential velocities. Calculate the water inlet and outlet radial velocities neglecting blade thickness. (d) (e) Calculate the tangential water velocity at the outlet assuming pure radial flow at the inlet. (1 Draw to scale the inlet and outlet velocity diagrams and determine the inlet and outlet blade angles. Note: The velocity vector diagrams must be drawn sufficiently large to obtain a suitably accurate answer (10 mm = 5 m/s minimum). While calculation of velocities by trigonometric ratios is acceptable it is longer and more time consuming. [10 marks ]
98-Mar-B5 December 2014 Page 10 of 16 QUESTION 4 PUMP VELOCITY DIAGRAM Nomenclature for velocity vectors and angles V2T B2 V2 VR V82 VAT 02 VIR vi V81 V Absolute water velocity at inlet V81 Blade velocity at inlet VIR Radial water velocity at inlet vт Tangential water velocity at inlet V2 Absolute water velocity at outlet V81 Blade velocity at outlet V2R Radial water velocity at outlet V2T Tangential water velocity at outlet