Centrifugal and Axial Flow Pumps

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Centrifugal and Axial Flow Pumps

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Centrifugal and Axial Flow Pumps

Centrifugal and Axial Flow Pumps

Pressure increases in the rotor due to centrifugal action.Fluid enters the impeller through the center and then flows outward which is discharged around the entire circumference into the casing.Kinetic energy is converted to pressure head.Widely used for high head applicationCentrifugal PumpsClassification

Volute Centrifugal PumpDiffuser Centrifugal Pump

Single StageDouble StageMultistageCentrifugal Pump Types

Single StageDouble StageMultistage

Common pump used for high volume requirements.Consists of a propeller incased inside a pipe.Propeller is typically direct driven by electric motor or an engineFluid particles remains in the axial direction as it enters and exits the pump and thus the term axial flow pump.Axial Flow Pumps

One way to size a pump is by the size of the discharge flange. However, this is not the best method.Best practice is rating the pump based on capacity in terms of flow rate, Q and Head, H at its maximum efficiency in a particular speed.Size and RatingPumps operated at constant speed will deliver varying head over varying flow rate.Efficiency varies as wellPump Characteristic Curve

Max Eff = 80%H = 7.5 mQ = 0.3 m3/min

Head Developed by pump

Ns = N x SQRT(Q)H3/4

Specific speed values indicates the type of pump and can be used to determine the appropriate pump needed for a particular application.

Specific Speed

Specific Speed

The diameter of the discharge pipe of a pump is 15cm and the intake is 20cm. The pressure gage at discharge reads 207Kpa and the vacuum gage at the intake reads 25.4cm Hg. If flow rate is 85 L/s of water and brake power is 35.0 KW calculate the efficiency.Example (Seatwork)Pump installed in a system of pipes and other related components will operate with a head and flow rate that correspond to the intersection of the pump characteristic curve and system curve.Pump Characteristic and System Curves

System curve is based on:H = Change in Elevation + HLHL head loss due to pipe friction and other connections such as elbows, valves and transitions

System Curves

The operating point may not be the efficient operating point of the pump and this means that the pump is not suited for the system.Design the pump system wherein the operation should be at peak efficiency. Otherwise energy will be wasted.Pump Characteristic and System CurvesChanging the speed of the pumpSelecting different size homologous pumpSelecting different size and changing speedUse series pump or parallel pumpsMethods to accomplish pumping requirements with good efficiency