Transcript Document
Pumps • • • • • Outline: Where are pumps used Pumps, fans, compressor differences General HP and mechanical efficiency Types of Pumps – Displacement – Dynamic • Reading: – Handouts: • Chapter 4 Principles of Process Engineering • Fluide Design Inc. Centrifugal Pump Fundamentals (download) Dr. C. L. Jones Biosystems and Ag. Engineering 1 Pumps, Fans, Compressors-Turbomachines • Turbomachines: change energy level of flowing fluid by means of momentum exchange • 2nd only to electric motors in number • Wide spread in ALL industries – – – – – – – Power units: cars/trucks, tractors Computers Grain elevators Oilfield Water supply/treatment Food processing And……. Dr. C. L. Jones Biosystems and Ag. Engineering 2 Pumps, Fans, Compressors-Turbomachines • Differences between pumps, fans, compressors – Pumps: move liquids – Fans: move gases with little increase in pressure – Compressors: move gases with greater increase in pressure Dr. C. L. Jones Biosystems and Ag. Engineering 3 Mechanical Efficiency PowerOutput PowerInput • Ratio: • Power Output: Po WQ g • English Units, HP: • Efficiency Po QP 1714 Po em Pi Dr. C. L. Jones Biosystems and Ag. Engineering 4 Pump example 1 • A pump provides 0.009 m^3/s of water and total head of 10.6 m. Determine the power output of the pump. If the power input is 1310 W, determine the mechanical efficiency of the pump. 5 Pumps • Two types Flow rates Pressure Flow characteristics Displacement - plunger - piston - rotary Low High Pulsating Dynamic - centrifugal - jet - airlift High Low Steady Flow Dr. C. L. Jones Biosystems and Ag. Engineering 6 Displacement Pumps Dr. C. L. Jones Biosystems and Ag. Engineering 7 Displacement Pumps • Reciprocating and Piston Pumps – – – – – Crank Connecting rods Pistons or plungers Vol. efficiencies > 97%, Mech. eff. approx. 90% For more stable flow, increase number of cylinders Dr. C. L. Jones Biosystems and Ag. Engineering 8 Displacement Pumps • Rotary Pumps (gear, lobe, screw, vane) – Most popular: gear pumps – 90%+ mechanical eff. – Relatively constant output Dr. C. L. Jones Biosystems and Ag. Engineering 9 10 11 Dynamic Pumps • Centrifugal – – – – – – Relative simplicity Mech. eff. as high as 90% Can handle fluids containing suspended solids Ease of maintenance…good for food products 2 parts: impeller and casing Radial, mixed, axial flow Dr. C. L. Jones Biosystems and Ag. Engineering 12 Dr. C. L. Jones Biosystems and Ag. Engineering 13 Performance Curves Dr. C. L. Jones Biosystems and Ag. Engineering 14 Performance Curves Dr. C. L. Jones Biosystems and Ag. Engineering 15 Centrifugal Pump Affinity Laws Q1 N1 D1 Q2 N2 D2 3 2 W1 N1 D1 W2 N2 D2 3 2 5 Po1 N1 D1 1 Po 2 N2 D2 2 Dr. C. L. Jones Biosystems and Ag. Engineering 16 Centrifugal Pump Affinity Laws 300 1750 13" Q2 2000 13" 1601 1750 W2 2000 20 1750 Po 2 2000 3 2 3 13 13 2 5 13 13 1 Dr. C. L. Jones Biosystems and Ag. Engineering 17 Centrifugal Pump Fundamentals • Static head: the height of a column of liquid – Units: feet or meters • Pump imparts velocity to liquid…velocity energy becomes pressure energy leaving the pump. Head developed = vel. energy at the impeller tips. H v 2 v rpm D 2g 229 • Why do we use “feet” or “head” instead of “psi” or “pressure”? – Pump with impeller D will raise a liquid to a certain height regardless of weight of liquid Dr. C. L. Jones Biosystems and Ag. Engineering 18 Converting pressure to head in feet head, ft 2.31 Psurface Pvapor specific gravity Dr. C. L. Jones Biosystems and Ag. Engineering 19 Suction Lift Dr. C. L. Jones Biosystems and Ag. Engineering 20 Suction Head Dr. C. L. Jones Biosystems and Ag. Engineering 21 Static Discharge Head • Static Discharge Head = vertical distance from pump centerline to the point of free discharge or the surface of the liquid in the discharge tank. Dr. C. L. Jones Biosystems and Ag. Engineering 22 Total Static Head • Vertical distance between the free level of the source of supply and the point of free discharge or the free surface of the discharge liquid. Dr. C. L. Jones Biosystems and Ag. Engineering 23 Total Dynamic Suction Lift or Head • (fluid below suction) Static suction lift velocity head at suction + total friction head in suction line • (fluid above suction) Static suction head + velocity head at pump suction flange – total friction head in suction line • Velocity head = energy of liquid due to motion, Usually insignificant h v 2 v 2g Dr. C. L. Jones Biosystems and Ag. Engineering 24 Total Dynamic Discharge Head • Static discharge head + velocity head at pump discharge flange plus discharge line friction Total Dynamic Discharge Head (TH or TDH) (this is what we design for!!!) • Total dynamic discharge head – total dynamic suction head (tank above suction)…. Or…. • Total dynamic discharge head + total dynamic suction lift (tank below suction) Dr. C. L. Jones Biosystems and Ag. Engineering 25 Total Dynamic Discharge Head (TH or TDH) (this is what we design for!!!) TDH includes friction losses due to piping and velocity Dr. C. L. Jones Biosystems and Ag. Engineering 26 One last item to consider… NPSH (net positive suction head) Dr. C. L. Jones Biosystems and Ag. Engineering 27 NPSHR Dr. C. L. Jones Biosystems and Ag. Engineering 28 NPSHA NPSH Available 2.31 Psurface Pvapor sp.gr . static head, ft friction losses, ft Dr. C. L. Jones Biosystems and Ag. Engineering 29 NPSHA Dr. C. L. Jones Biosystems and Ag. Engineering 30 Capacity, Power, Efficiency • Capacity Q, gpm = 449 x A, ft2 x V, ft/sec Where A = cross-sectional area of the pipe in ft2 V = velocity of flow in feet per second • Bhp = actual power delivered to pump shaft Q TDH Sp.Gr . by driver bhp required 3960 pumpefficiency • Whp = pump output or hydraulic Q TDH Sp.Gr . horsepower whp 3960 Dr. C. L. Jones Biosystems and Ag. Engineering 31 Pump Efficiency Ratio of whp to bhp: whp Q TDH Sp.Gr . PumpEfficiency bhp 3960 bhp Dr. C. L. Jones Biosystems and Ag. Engineering 32 System Example: 80 ft of 4” ID galv. iron pipe with 3 elbows, 75’ lift, pumps from an open tank, discharges through a pipe to a tank at atm. Pressure (find rate, imp. dia., eff., motor size, rpm) Ratio of whp to bhp: Dr. C. L. Jones Biosystems and Ag. Engineering 33 Homework Handout http://biosystems.okstate.edu/Home/jcarol/Class_Notes/ BAE2023_Spring2011/pump hw.pdf Questions??? Dr. C. L. Jones Biosystems and Ag. Engineering 35