• Author / Uploaded
• Abhilash Tilak

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Assignment I.

The outer diameter of an impeller of a centrifugal pump is 400 mm and outlet width 50 mm. The pump is running at 800 r.p.m and is working against a total head of 15 m. The vanes angle at outlet is 400 and manometric efficiency is 75%. Determine: 1) Velocity of flow at outlet. 2) Velocity of water leaving the vane. 3) Angle made by the absolute velocity at outlet with the direction of motion at outlet. 4) Discharge.

II.

The impeller of a centrifugal pump is of 300 mm diameter and 50 mm width at the periphery, and has blades whose tip angle incline backwards 600 from the radius. The pump delivers 17 m3/min. of water and the impeller rotates at 1000 r.p.m. Assuming that the pump is designed to admit radially, calculate: 1) Speed and direction of water as it leaves the impeller. 2) Torque exerted by the impeller on water. 3) Shaft power required. 4) Lift of the pump. Take mechanical efficiency = 95% and hydraulic efficiency = 75%.

III.

A centrifugal pump impeller has at outlet a diameter of 360 mm and width 60 mm. The vanes are curved backwards at 350 to the tangent at outer periphery and thickness of vanes occupies 20 percent of the peripheral area and the velocity of flow is constant from inlet to outlet. The impeller rotates at 800 r.p.m. If the rate of flow through the pump is 0.13 m3/s, determine: 1) The pressure rise in the impeller, 2) The percentage of total work converted to kinetic energy.

IV.

A centrifugal pump, in which water enters radially, delivers water to a height of 165 mm. The impeller has a diameter of 360 mm and width 180 mm at inlet and corresponding dimensions at outlet are 720 mm and 90 mm respectively; its rotational speed is 1200 r.p.m. The blades are curved backward at 300 to the tangent at exit and the discharge is 0.389 m3/s. Determine: 1) Theoretical head developed 2) Manometric efficiency 3) Pressure rise across the impeller assuming losses equal to 12 percent of velocity head at exit. 4) Pressure rise and the loss of head in the volute casing. 5) The vane angle at inlet 6) Power required to drive the pump assuming an overall efficiency of 70%. What would be corresponding mechanical efficiency?

V.

A centrifugal pump lifts water under a static head of 36 m of water of which 4 m is water is suction lift. Suction and delivery pipes are both 150 mm in diameter. The head loss in suction pipe is 1.8 m and in delivery pipe is 7 m. The impeller is 380 mm in diameter and

25 mm wide at mouth and revolves at 1200 r.p.m. Its exit blade angle is 350. If the manometric efficiency of the pump is 82 percent, determine: 1) The discharge through the pump. 2) The pressure at the suction and delivery branches of the pump. VI.

The following data refer to a radial, single stage, double action, centrifugal pump: Discharge at the pump outlet = 90 litres/sec; Diameter at inlet = 100 mm; Diameter at outlet = 290 mm; Head = 36 m; Speed of impeller = 1750 r.p.m; Width at inlet = 25 mm per side; Width at outlet = 23 mm in total; Overall efficiency = 60 percent; Leakage loss = 2.7 litres/sec; Mechanical losses = 1.5 kW; Contraction factor due to vane thickness = 0.87; Outlet vane angle = 270 Assuming that water enters the impeller at inlet radially, determine:

VII.

i.

The inlet vane angle

ii.

The angle at which water leaves the wheel

iii.

The speed ratio

iv.

The absolute velocity of water leaving the impeller

v.

The manometric efficiency

vi.

The volumetric efficiency

vii.

The mechanical efficiency

The impeller of a centrifugal pump has an outer diameter of 250 mm and an effective area of 0.017 m2. The blades are bent backwards so that the direction of outlet relative velocity makes an angle of 1480 with the tangent drawn in the direction of impeller rotation, the diameters of suction and delivery pipes are 150 mm and 100 mm respectively. The pump delivers 0.031 m3/s at 1450 r.p.m. when the gauge points on the suction and delivery pipes close to the pumps show heads of 4.6 m below and 18.0 m above atmosphere respectively. The head losses in the suction and delivery pipes are 2.0 m and 2.9 m respectively. The motor driving the pump delivers 8.67 kW. Assuming that water enters the pump without shock and whirl, determine:

VIII.

i.

The manometric efficiency

ii.

The overall efficiency of the pump.

A centrifugal pump impeller, having outlet diameter 0.35 m is running at 960 r.p.m. the velocity of flow (assumed constant throughout the system) is equal to 2.4 m/s. The vane

angle at outlet is 280. The static suction lift is 4.03 m. The energy losses in suction pipe, impeller and volute casing are 0.88 m, 0.7 m, and 1.26 m of water respectively. Determine the readings of vacuum or pressure gauges placed at: i.

Inlet to the pump.

ii.

Impeller outlet (in clearance between impeller and outlet)

iii.

Pump outlet or delivery flange, 0.24 m above the centerline of the pump.