CE154 - Lecture 7 Pipe System Design

CE154 - Lecture 7 Pipe System Design - PipeS mDe yste sign...

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Fall 2009 CE154 1 Pipe System Design CE154 - Hydraulic Design Lecture 7
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Pump System Fall 2009 CE154 2
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Fall 2009 CE154 3 Pump Terminology Pump head (dynamic head) – H Pump discharge – Q Pump speed – n Pump power – P
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Centrifugal Pump Fall 2009 CE154 4
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Rotary Pump Fall 2009 CE154 5
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Reciprocating Pump Fall 2009 CE154 6
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Fall 2009 CE154 7 Pump Terminology Power P Motor efficiency η m Pump Efficiency η p Q, H
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Fall 2009 CE154 8 Pump Terminology Pump Output (Water) Power (Q in gpm, H in ft, s is specific gravity and dimensionless, and P in horsepower) Pump Input (Brake) Power 3960 QHs P w = η p QHs bhp 3960 =
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Fall 2009 CE154 9 Pump Terminology Electric Motor Power Typically motor efficiency is approximately 98% η m p QHs mhp 3960 =
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Fall 2009 CE154 10 Pump Terminology Single or Double suction pump Single or multiple stage pump
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Fall 2009 CE154 11 Pump Specific Speed Q is gpm per suction , n is rpm, H is ft per stage Pump Type N s (US unit) Radial Pump 500-4200 Mixed flow Pump 4200-9000 Axial flow Pump 9000-15000
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Fall 2009 CE154 12 Pump Performance Variable-Speed pumps – may be desirable when different operating modes require different pump head or flow Homologous laws Q 1 /Q 2 = n 1 /n 2 H 1 /H 2 = (n 1 /n 2 ) 2 P 1 /P 2 = (n 1 /n 2 ) 3
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Pump Performance Curves Fall 2009 CE154 13
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Fall 2009 CE154 14 Pump Terminology Static Lift – elevation difference between pump centerline and the suction water surface. If the pump is higher, static lift is positive. If pump is lower, static lift is negative. Static Discharge – elevation difference between the pump centerline and the end discharge point. If pump is higher, static discharge is negative. Total Static Head – sum of static lift and static discharge.
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Fall 2009 CE154 15 Pump Terminology Shutoff Head – head at 0 flow Operating point – the point where the pump curve and the system curve intersect. A system curve is a curve describing the head-flow relationship of the pipeline system. Q b a H 2 + =
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Fall 2009 CE154 16 System Curve friction losses
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Fall 2009 CE154 17 Operating Point
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Fall 2009 CE154 18 Pump Terminology Net positive suction head (NPSH) - to ensure that water does not vaporize at the pump impeller tip - NPSH available = available suction head + atmospheric pressure – vapor pressure – suction head loss = determined by local condition - NPSH required = characteristic of and provided by pump curve h h h h NPSH s vp s atm A - - + =
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Fall 2009 CE154 19 Example (p. 10.3 May’s HDH)
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Fall 2009 CE154 20 Atmospheric Pressure At mean sea level, 1 atomospheric pressure = 14.69 psia = 1.03 kg/cm2 = 760 mm Hg El.(ft) 0 1000 2000 4000 6000 8000 Patm (psia) 14.69 14.17 13.66 12.69 11.8 10.9
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Fall 2009 CE154 21 Vapor pressure Vapor pressure of water at atmospheric pressure T ( ° F) 32 40 50 60 68 80 90 P v (psia) 0.089 0.112 0.178 0.256 0.339 0.507 0.698 T ( ° F) 100 120 140 160 180 200 212 P v (psia) 0.949 1.69 2.89 4.74 7.51 11.53 14.70
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CE154 - Lecture 7 Pipe System Design - PipeS mDe yste sign...

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