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O-K-State BAE 2023 - Review from Lecture 1: Pumps

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Review from Lecture 1: PumpsSlide 2Slide 3Review: Dynamic PumpsPerformance CurvesSlide 6Review: Centrifugal Pump Affinity LawsCentrifugal Pump Affinity LawsCentrifugal Pump FundamentalsConverting pressure to head in feetSuction LiftSuction HeadStatic Discharge HeadTotal Static HeadTotal Dynamic Suction Lift or HeadTotal Dynamic Discharge HeadSlide 17One last item to consider… NPSH (net positive suction head)NPSHRNPSHASlide 21Capacity, Power, EfficiencyPump EfficiencySystem 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)Homework HandoutSlide 261Dr. C. L. JonesBiosystems and Ag. EngineeringReview from Lecture 1:Pumps•Difference between pumps, fans, and compressors•Mechanical Efficiency1714oQPP =omiPeP=2Dr. C. L. JonesBiosystems and Ag. EngineeringReview from Lecture 1:Pumps•Two typesFlow rates Pressure Flow characteristicsDisplacement - plunger - piston - rotaryLow High PulsatingDynamic - centrifugal - jet - airliftHigh Low Steady Flow3Dr. C. L. JonesBiosystems and Ag. EngineeringReview from Lecture 1:Pumps•Recip Pumps have a crank, connecting rods, and pistons or plungers •Rotary gear pumps provide more constant output•Recip Pump eqtns.Q D VE= �231A S n rpmD� � �=1714Q PBHPME�=�4Dr. C. L. JonesBiosystems and Ag. EngineeringReview: Dynamic Pumps•Centrifugal–Relative simplicity–Can handle fluids containing suspended solids–Ease of maintenance…good for food products–2 parts: impeller and casing–Radial, mixed, axial flow5Dr. C. L. JonesBiosystems and Ag. EngineeringPerformance Curves6Dr. C. L. JonesBiosystems and Ag. EngineeringPerformance Curves7Dr. C. L. JonesBiosystems and Ag. EngineeringReview: Centrifugal Pump Affinity Laws2 21 1 12 2 2W N DW N D� �� �=� �� �� �� �31 1 12 2 2Q N DQ N D� �� �=� �� �� �� �3 511 1 12 2 2 2ooPN DP N Drr� �� �� �=� �� �� �� �� �� �•Example 4.3 pg 107 Henderson & Perry and ITT handout8Dr. C. L. JonesBiosystems and Ag. EngineeringCentrifugal Pump Affinity Laws2 2121601750 132000 13W� �� �=� �� �� �� �32300 1750 13"2000 13"Q� �� �=� �� �� �� �( )3 5220 1750 1312000 13oP� �� �=� �� �� �� �•ITT handout example: N1 = 1750 rpmD1 = 13”N2 = 2000 rpm9Dr. C. L. JonesBiosystems and Ag. EngineeringCentrifugal Pump Fundamentals22vHg=•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. •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 229rpm Dv�=10Dr. C. L. JonesBiosystems and Ag. EngineeringConverting pressure to head in feet( )2.31,surface vaporP Phead ftspecific gravity-=11Dr. C. L. JonesBiosystems and Ag. EngineeringSuction Lift12Dr. C. L. JonesBiosystems and Ag. EngineeringSuction Head13Dr. C. L. JonesBiosystems and Ag. EngineeringStatic 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.14Dr. C. L. JonesBiosystems and Ag. EngineeringTotal 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.15Dr. C. L. JonesBiosystems and Ag. EngineeringTotal 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 insignificant22vvhg=16Dr. C. L. JonesBiosystems and Ag. EngineeringTotal Dynamic Discharge Head •Static discharge head + velocity head at pump discharge flange plus discharge line frictionTotal 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)17Dr. C. L. JonesBiosystems and Ag. EngineeringTotal Dynamic Discharge Head (TH or TDH) (this is what we design for!!!)TDH includes friction losses due to piping and velocity18Dr. C. L. JonesBiosystems and Ag. EngineeringOne last item to consider…NPSH (net positive suction head)Absolute pressure at suction nozzle = vapor pressure of liquid…..vapor pockets or BUBBLES  Cavitation19Dr. C. L. JonesBiosystems and Ag. EngineeringNPSHRNPSH Required = positive head in feet absolute at the pump suction required to overcome the pressure drops through the pump and maintain the majority of the liquid above its vapor pressureA function of the pump design…Information comes from the pump manufacturer…usually given on the pump performance curve…varies with speed and capacity20Dr. C. L. JonesBiosystems and Ag. EngineeringNPSHANPSH Available = excess pressure of the liquid in feet absolute over its vapor pressure at pump suction, function of the system design( )2.31, ,. .surface vaporAvailableP PNPSH static head ft friction losses ftsp gr-= + -21Dr. C. L. JonesBiosystems and Ag. EngineeringNPSHA22Dr. C. L. JonesBiosystems and Ag. EngineeringCapacity, Power, Efficiency. .3960requiredQ TDH Sp Grbhppumpefficiency� �=�•Capacity Q, gpm = 449 x A, ft2 x V, ft/secWhere A = cross-sectional area of the pipe in ft2 V = velocity of flow in feet per second•Bhp = actual power delivered to pump shaft by driver •Whp = pump output or hydraulic horsepower. .3960Q TDH Sp Grwhp� �=23Dr. C. L. JonesBiosystems and Ag. EngineeringPump Efficiency. .3960whp Q TDH Sp GrPumpEfficiencybhp bhp� �= =�Ratio of whp to bhp:24Dr. C. L. JonesBiosystems and Ag. EngineeringSystem 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:Homework Handout26Dr. C. L. JonesBiosystems and Ag.


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O-K-State BAE 2023 - Review from Lecture 1: Pumps

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