ME 388 – Applied Instrumentation Laboratory Centrifugal Pump Lab

References Streeter and Wylie, Fluid Mechanics (Ch.10) Holman, Experimental Methods for Engineers, (Ch.6) Munson (Ch.9) Any Fluid Mechanics book

Lab Objectives Understand operation of a dc motor Analyze fluid flow using –Centrifugal pump –Venturi flow meter Evaluate pump performance as a function of impeller (shaft) speed –Develop pump performance curves –Assess efficiencies

Lab Set-up

dc motor Figure 1. dc motor (howstuffworks.com) Armature or rotor Commutator Brushes Axle Field magnet DC power supply

Centrifugal pump

Cavitation

Centrifugal pump operation Rotating impeller delivers energy to fluid Governing equations or Affinity Laws relate pump speed to: –Flow rate, Q –Pump head, H p –Fluid power, P

Pump Affinity Laws N  Q N 2  H p N 3  P

Determination of Pump Head

Determination of Flow Rate Use Venturi meter to determine Q Fluid is incompressible (const.  )  Q = V fluid Area

Venturi Meter As V , kinetic energy   T = 0  Height = 0  Pv or P 

Calculate Q from Venturi data V 1 = inlet velocity V 2 = throat velocity A 1 = inlet area A 2 = throat area

Throat Velocity

Discharge Coefficient

Solve for Q Use MS EXCEL (or Matlab) Calculate throat velocity Calculate discharge coefficient using Reynold’s number and throat velocity Calculate throat area Solve for Q

Power and Pump Efficiency Assumptions – –No change in elevation –No change in pipe diameter –Incompressible fluid –  T = 0 Consider 1 st Law (as a rate eqn.)

Pump Power Derivation

Efficiencies

Summary of Lab Requirements Plots relating H p, P, and  pump to Q Plot relating P to  pump Regression analyses Uncertainty of  overall (requires unc. of Q) Compare H p, P, Q for two N’s –For fully open valve position –WRT affinity laws

Start-up Procedure 1.Fill pvc tube with water (3/4 full) 2.Bleed pump 3.Switch breaker to “on” 4.Push main start button 5.Make sure variac is turned counterclockwise 6.Make sure throttle valve is fully open 7.Turn lever to “pump” 8.Push “reset” button 9.Push “start” button 10.Adjust variac to desired rpm using tach.

Pump lab raw data Shaft speed (rpm) DC voltage (volts) DC current (amps) Inlet Pressure (in Hg) Outlet Pressure (kPa) Venturi DP (kPa) Dyna (lbs)

Shut-down Procedure 1.Fully open throttle valve 2.Turn variac fully counterclockwise 3.Push pump stop button 4.Turn pump lever to “off” 5.Push main stop button 6.Switch breaker to “off”