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Pump pipeline

1. 1. Water Supply and Wastewater Removal Pump-Pipeline Systems Instructor: Parjang Monajemi
2. 2. Introduction  Simply stated, a pump is a machine used to move liquid through a piping system and to raise the pressure of the liquid. A pump can be further defined as a machine that uses several energy transformations to increase the pressure of a liquid.  There are actually three distinct reasons for raising the pressure of a liquid with a pump: 1. Static elevation A liquid’s pressure must be increased to raise the liquid from one elevation to a higher elevation. This might be necessary, for example, to move liquid from one floor of a building to a higher floor. Water Supply and Wastewater Removal2 Spring 1390
3. 3. 2. Friction. It is necessary to increase the pressure of a liquid to move the liquid through a piping system and overcome frictional losses. Liquid moving through a system of pipes, valves, and fittings experiences frictional losses along the way. 3. Pressure. In some systems it is necessary to increase the pressure of the liquid for process reasons. In addition to moving the liquid over changes in elevation and through a piping system, the pressure of a liquid must often be increased to move the liquid into a pressurized vessel, such as a boiler or fractionating tower, or into a pressurized pipeline. Water Supply and Wastewater Removal3 Spring 1390
4. 4. Pressure and Head  It is important to understand the relationship between pressure and head. Pressure is measured in psi (pounds per square inch) or kilopascal (kPa), bar, or kilograms per square centimeter (kg/cm2), while the equivalent units for head are meters (m) or feet(ft). Water Supply and Wastewater Removal4 Spring 1390
5. 5. Classification of Pumps  There are many ways to classify pumps: according to their function, their conditions of service, materials of construction, etc. The pump industry trade association, the Hydraulic Institute, has classified pumps as follows: 1. Kinetic: In a kinetic pump, energy is continuously added to the liquid to increase its velocity. When the liquid velocity is subsequently reduced, this produces a pressure increase. Although there are several special types of pumps that fall into this classification, for the most part this classification consists of centrifugal pumps. Water Supply and Wastewater Removal5 Spring 1390
6. 6.  Centrifugal pumps, involve a collection of blades, buckets, flow channels, or passages arranged around an axis of rotation to form a rotor. Rotation of the rotor produces dynamic effects that either add energy to the fluid or remove energy from the fluid. centrifugal pumps are classified as axial-flow, mixed-flow, or radial-flow machines depending on the predominant direction of the fluid motion relative to the rotor’s axis as the fluid passes the blades Water Supply and Wastewater Removal6 Spring 1390
7. 7.  Positive Displacement In a positive displacement pump, energy is periodically added to the liquid by the direct application of a force to one or more movable volumes of liquid. This causes an increase in pressure up to the value required to move the liquid through ports in the discharge line. The important points here are that the energy addition is periodic (i.e., not continuous) and that there is a direct application of force to the liquid. Typical examples shown include the common tire pump used to fill bicycle tires, the human heart, and the gear pump. Water Supply and Wastewater Removal7 Spring 1390
8. 8.  The following are some key application criteria that would lead to the selection of a P.D. pump over a centrifugal pump: a) High viscosity b) Self-priming c) High pressure d) Low flow e) High efficiency f) Low velocity g) Low shear h) Fragile solids handling capability i) Accurate, repeatable flow measurement j) Constant flow/variable system pressure k) Two-phase flow Water Supply and Wastewater Removal8 Spring 1390
9. 9. (Volk, 2005) Water Supply and Wastewater Removal9 Spring 1390
10. 10. Cavitation in Turbomachines  Cavitation refers to conditions at certain locations within the turbomachine where the local pressure drops to the vapor pressure of the liquid, and as a result, vapor filled cavities are formed. As the cavities are transported through the turbomachine into regions of greater pressure, they will collapse rapidly, generating extremely high localized pressures. Signs of cavitation in turbopumps include noise, vibration, and lowering of the head- discharge and efficiency Water Supply and Wastewater Removal10 Spring 1390
11. 11.  On the suction side of a pump, low pressures are commonly encountered, with the possibility of cavitation occurring within the pump. The requiered head at the pump inlet to keep the liquid from cavitating or boiling is called Net Possitive Suction Head (NPSH).  Consider the shown operating pump. Location 1 is on the liquid surface on the suction side, and location 2 is the point of minimum pressure within the pump. 2 2 s s v required p V p NPSH g     Water Supply and Wastewater Removal11 Spring 1390
12. 12.  The design requirement for a pump is thus established as follows 22 1 1 1 2 1 2 2 2 2 2 s s s loss atm s s s loss atm s s loss atm v loss p Vp V z z h g g p p V z z h g p p V z h g p p z h NPSH                                atm v available loss p p NPSH z h       atm v loss p p N PS H z h       Water Supply and Wastewater Removal12 Spring 1390
13. 13.  A centrifugal pump is to be placed above a large, open water tank, as shown, and is to pump water at a rate of 0.5 cfs. At this flowrate the required net positive suction head, is 15 ft, as specified by the pump manufacturer. If the water temperature is and atmospheric pressure is 14.7 psi, determine the maximum height, that the pump can be located above the water surface without cavitation. Assume that the major head loss between the tank and the pump inlet is due to filter at the pipe inlet having a minor loss coefficient k=20. Other losses can be neglected. The pipe on the suction side of the pump has a diameter of 4 in. (Munson, 2009) Water Supply and Wastewater Removal13 Spring 1390
14. 14.   2 3 14.7 0.5069 15 20 62.2 / 2 atm v loss p p NPSH z h psi V z lb ft g                 2 3 0.5069 5.73 / 15 20 7.65 62.2 / 2 atm p psi ft s z z ft lb ft g         Water Supply and Wastewater Removal14 Spring 1390
15. 15.  Calculate NPSHa for this system and verify the adequacy of the selected pump. (Volk, 2005) Suction lift=12ft Design capacity Q=2000 gpm Design pump total head=175 ft Liquid=water at 80°F (s.g.=1.0) Hf=3ft P=14.2psia Water Supply and Wastewater Removal15 Spring 1390
16. 16.  Solve the previous problem, except using water at 160°F (Volk, 2005). 14.2 2.31 32.8 1.0 1.2 32.8 12 3 1.2 16.6 v a ft H ft NPSH ft         From previous figure, at 2000 gpm, NPSH = 11.2 ft, 16.6 11.2a r NPSH ft NPSH ft   14.2 2.31 33.5 0.98 11.2 33.5 12 3 11.2 7.3 v a ft H ft NPSH ft         7.3 11.2a r NPSH ft NPSH ft   Water Supply and Wastewater Removal16 Spring 1390
17. 17. Performance Characteristics  The flow system used to test a centrifugal pump at a nominal speed of 1750 rpm is shown. Data measured during the test are given in the table. Calculate the net head delivered and the pump efficiency at a volume flow rate of 1000 gpm. Plot the pump head, power input, and efficiency as functions of volume flow rate. (Pritchard, 2011) Water Supply and Wastewater Removal17 Spring 1390
18. 18. 2 1 p p p h      1 2 3 2 2 3 3 0.92 62.4 1 0.49 36.9 62.4 3 38.2 38.2 0.49 89.2 62.4 s d p lb lb p p z ft psi in ft lb lb p p z ft psi in ft h ft lb ft                     Water Supply and Wastewater Removal18 Spring 1390
19. 19. Basic Output Parameters  Usually V2 and V1 are about the same, z2 z1 is no more than a meter or so, and the net pump head is essentially equal to the change in pressure head  The power delivered to the fluid simply equals the specific weight times the discharge times the net head change This is traditionally called the water horsepower. The power required to drive the pump is the brake horsepower where ω is the shaft angular velocity and T the shaft torque. 2 1 p p p h    P Qh bhp T Water Supply and Wastewater Removal19 Spring 1390
20. 20.  Water at 10 °C (nu=1.3x10-6m2/s) is to flow from reservoir A to reservoir B through a cast- iron pipe of length 20 m at a rate of Q=0.015 m3/s as is shown. The system contains a sharp- edged entrance and six regular threaded 90° elbows. Determine the the required head of the pump that must be used if the pipe diameter is 5 cm. (Munson, 2009) Water Supply and Wastewater Removal20 Spring 1390
21. 21.     3 2 0.015 / 7.65 / 0.05 4 m sQ V m s A     7.65 0.05 Re 294231 0.0000013 VD VD            0.26 0.005 5 mm D cm    , Re 294000 0.03f           2 2 2 2 2 2 0.5 6 1.5 1 12 0.5 9 1 65.8 63.8 2 2 2 2 2 p p L V V V V V h f m h m D g g g g g             2 2 1 1 1 1 1 2 1 1 2 2 p p P V P V E h E headlosses z h z headlosses g g             Water Supply and Wastewater Removal21 Spring 1390
22. 22.  The given pump adds 25 kW to the water and causes a flowrate of 0.04 m3/s. Determine the flowrate expected if the pump is removed from the system. Assume f=0.016 for either case and neglect minor losses. (Munson, 2009)   2 2 2 2 1 1 2 2 1 2 1 1 31.8 30 14.2 62.5 0.16 68.7 2 2 20 0.06 20 P v P v Z hp Z head loss Z Z m g g                       3 3 10, 000 / 0.04 / 25000 100% 62.5 N m m s HQH P W H m                    3 3 2 2 2 2 0.04 / 0.04 / 14.2 / 31.8 / 0.06 0.04 4 4 pipe exit m s m s v m s v m s m m       Water Supply and Wastewater Removal22 Spring 1390
23. 23. 222 2 1 1 2 2 1 2 22 30 68.7 0.16 2 2 20 0.06 20 30 68.7 0.16 20 0.06 20 pipeexit pipeexit vvP v P v Z Z head loss g g vv                  2 2 2 2 0.06 0.04 0.44 4 4 pipe exit pipe exit v m v m v v                2 2 2 2 3 0.4430 68.7 0.16 23 / 20 0.06 20 23 / 0.04 0.03 / 4 ex itex it ex it vv v m s Q m s m m s        Water Supply and Wastewater Removal23 Spring 1390
24. 24.  The efficiency is basically composed of three parts: volumetric, hydraulic, and mechanical. 1. The volumetric efficiency is where QL is the loss of fluid due to leakage in the impeller-casing clearances 2. The hydraulic efficiency where hf has three parts: (1) shock loss at the eye due to imperfect match between inlet flow and the blade entrances, (2) friction losses in the blade passages, and (3) circulation loss due to imperfect match at the exit side of the blades. 3. the mechanical efficiency is v L Q Q Q    1 f h s h h    1 f m p php    Water Supply and Wastewater Removal24 Spring 1390
25. 25.  where Pf is the power loss due to mechanical friction in the bearings, packing glands, and other contact points in the machine.  By definition, the total efficiency is simply the product of its three parts v h m     Performance characteristics for a given pump gometry and operating speed are usually given in the form of plots of and bhp versus Q commonly referred to as capacity as is llustrated Water Supply and Wastewater Removal25 Spring 1390
26. 26.  Water is to be pumped from one large, open tank to a second large, open tank as shown. The pipe diameter throughout is 6 in. and the total length of the pipe between the pipe entrance and exit is 200 ft. Minor loss coefficients for the entrance, exit, and the elbow are shown on the figure, and the friction factor for the pipe can be assumed constant and equal to 0.02. A certain centrifugal pump having the given performance characteristics is suggested as a good pump for this flow system. With this pump, what would be the flowrate between the tanks? Do you think this pump would be a good choice?(Munson, 2009) Water Supply and Wastewater Removal26 Spring 1390
27. 27. Q H η 0 89 0 400 86 30 800 81 53 1200 75 73 1600 65 86 2000 53 88 2400 28 60 Water Supply and Wastewater Removal27 Spring 1390
28. 28. As can be seen, although the operating efficiency is not the peak efficiency, which is about 86%, it is close (about 84%). Thus, this pump would be a satisfactory choice Water Supply and Wastewater Removal28 Spring 1390
29. 29.  Solve the previous problem if two pumps were used (a) in series, (b) in parallel Q H η 0 89 0 400 86 30 800 81 53 1200 75 73 1600 65 86 2000 53 88 2400 28 60 Q H 0 178 400 172 800 162 1200 150 1600 130 2000 106 2400 56 Q H 0 89 800 86 1600 81 2400 75 3600 65 4000 53 4800 28 Single pump Two pumps in parallel Two pumps in series Water Supply and Wastewater Removal29 Spring 1390
30. 30. 0 20 40 60 80 100 120 0 400 800 1200 1600 2000 2400 Head,ft Flowrate, gal/min 2 Parallel pumps 0 20 40 60 80 100 120 140 160 180 200 0 400 800 1200 1600 2000 2400 Head,ft Flowrate, gal/min 2 pumps in series  1780 / min 88% Q gal     2100 / min 85% Q gal    Water Supply and Wastewater Removal30 Spring 1390
31. 31. Dimensionless Parameters and Similarity Laws  As we studied earlier, we know that the principal, dependent pump variables are the actual head rise ha, shaft power ẃshaft, and efficiency η. We expect that these variables will depend on the geometrical configuration, which can be represented by some characteristic diameter D, other pertinent lengths L, and surface roughness ε, In addition, the other important variables are flowrate Q, the pump shaft rotational speed ω, fluid viscosity μ, and fluid density ρ. Water Supply and Wastewater Removal31 Spring 1390
32. 32.  When the pump flow involves high Reynolds numbers experience has shown that the effect of the Reynolds number can be neglected. For simplicity, the relative roughness, can also be neglected in pumps since the highly irregular shape of the pump chamber is usually the dominant geometric factor rather than the surface roughness. Thus, with these 2 Re D    Water Supply and Wastewater Removal32 Spring 1390
33. 33. simplification and for geometrically similar pumps (all pertinent dimensions, scaled by a common length scale), the dependent pi terms are functions of only Q/ωD3 so that: 3 5 2 5 3 Power Coefficient Head Coefficient Flowrate Coefficient W H Q W C D gH C D Q C D         Water Supply and Wastewater Removal33 Spring 1390
34. 34.  An 8-in diameter centrifugal pump operating at 1200 rpm is geometrically similar to the 12-in diameter pump having the shown performance characteristics while operating at 1000 rpm. For peak efficiency, predict the discharge, actual head rise, and shaft horsepower for this smaller pump. The working fluid is water at 60 °F (Munson, 2009). Water Supply and Wastewater Removal34 Spring 1390
35. 35. For a given efficiency the flow coefficient has the same value for a given family of pumps. Water Supply and Wastewater Removal35 Spring 1390
36. 36.  A centrifugal pump provides a flowrate of 500 gpm when operating at 1750 rpm against a 200-ft head. Determine the pump’s flowrate and developed head if the pump speed is increased to 3500 rpm. (Munson, 2009)   3 1 2 2 23 3 3 3 1 1 2 2 1 2 Flowrate Coefficient 500 1000 1750 3500 Q Q C D Q Q Q Q gpm D D D D            2 5 1 2 2 22 5 2 5 2 2 1 1 2 2 Head Coefficient 200 800 1750 3500 H gH C D gH gH H H ft D D          Water Supply and Wastewater Removal36 Spring 1390
37. 37. Specific Speed, Suction Specific Speed  A useful pi term named specific speed can be obtained by eliminating diameter D between the flow coefficient and the head rise coefficient.  With an analysis similar to that used to obtain the specific speed pi term, the suction specific Speed Ss, can be expressed as Water Supply and Wastewater Removal37 Spring 1390
38. 38.  Select a pump to deliver 500 gal/min of water with a pressure rise of 65 psi. Assume a rotational speed not to exceed 3600 rpm. (Potter, 2012) (Munson, 2009)      3 3600 377 / 30 65 144 150 1.94 32.2 500 1.11 / sec 7.48 60 rad s p Hp ft g Q ft                    3 / 4 3 / 4 377 1.11 0.69 32.2 150 s p Q N gH      Water Supply and Wastewater Removal38 Spring 1390
39. 39.  References: 1. Munson B.R., Young D. F., Okishi T. H., and Huebsch W. W., Fundamentals of Fluid Mechanics, John Wiley and Sons inc, Sixth Edition, 2009. 2. Potter M. C., Wiggert D. C., and Ramadan B. H., Mechanics of Fluids, Cengage Learning, Fourth Edition, 2012. 3. Pritchard P. J., Fox and McDonald’s Introduction to Fluid Mechanics, John Wiley and Sons inc, Eighth Edition, 2011. 4. Volk M., Pump Characteristics and Applications, Taylor & Francis Group, Second Edition, 2005. Water Supply and Wastewater Removal39 Spring 1390