Fluid FlowCENTRIFUGAL PUMPSCENTRIFUGAL PUMPSCentrifugal pumps are one of the most common components found influid systems. In order to understand how a fluid system containinga centrifugal pump operates, it is necessary to understand the headand flow relationships for a centrifugal pump.EO 1.37 DEFINE the terms net positive suction head andcavitation.EO 1.38 CALCULATE the new volumetric flow rate, head, orpower for a variable speed centrifugal pump using thepump laws.EO 1.39 DESCRIBE the effect on system flow and pump headfor the following changes:a. Changing pump speedsb. Adding pumps in parallelc. Adding pumps in seriesEnergyConversioninaCentrifugalPumpFluid entering a centrifugal pump is immediately directed to the low pressure area at the centeror eye of the impeller. As the impeller and blading rotate, they transfer momentum to incomingfluid. A transfer of momentum to the moving fluid increases the fluid’s velocity. As the fluid’svelocity increases its kinetic energy increases. Fluid of high kinetic energy is forced out of theimpeller area and enters the volute.The volute is a region of continuously increasing cross-sectional area designed to convert thekinetic energy of the fluid into fluid pressure. The mechanism of this energy conversion is thesame as that for subsonic flow through the diverging section of a nozzle. The mathematicalanalysis of flow through the volute is based on the general energy equation, the continuityequation, and the equation relating the internal properties of a system. The key parametersinfluencing the energy conversion are the expanding cross-sectional area of the volute, the highersystem back pressure at the discharge of the volute, and the incompressible, subsonic flow of thefluid. As a result of the interdependence of these parameters, the fluid flow in the volute, similarto subsonic flow in a diverging nozzle, experiences a velocity decrease and a pressure increase.Rev. 0 Page 47 HT-03
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