This document discusses pumps and turbines as energy conversion devices. It begins by defining key terms like head, power, and efficiency as they relate to pumps and turbines. It then describes the main types of pumps and turbines, distinguishing between impulse and reaction turbines, and positive-displacement and dynamic pumps like centrifugal pumps. The document outlines how to determine the duty point by matching pump and system characteristics. It also discusses hydraulic scaling laws for relating pump performance at different speeds. Finally, it provides an overview of common pump and turbine designs and the problem of cavitation.
The document discusses different types of water pumps, including their definitions, classifications, main parts, mechanics, efficiencies, characteristic curves, and considerations for selection. Water pumps are devices that convert mechanical energy to hydraulic energy in order to lift water from lower to higher points. They are classified based on how the water leaves the rotating part, with the main types being centrifugal, axial, mixed-flow, screw, and reciprocating pumps. Pump selection involves matching the system characteristic curve with the pump curve to determine the operating point that satisfies the required performance.
The document discusses different types of pumps used in fluid transport systems. It describes positive displacement pumps which use a fixed volume cavity to trap and transport fluid with each cycle. Dynamic pumps are also discussed, which add momentum to fluid without a fixed volume. Centrifugal pumps are described in detail, with their construction, working principle, performance parameters and efficiency calculations explained. The key aspects covered are the use of impellers to impart energy and velocity to fluid which is then converted to pressure by the volute casing.
Pumps and turbines are fluid machines that either add energy to or extract energy from a fluid. Pumps add energy by doing work on the fluid, while turbines extract energy from the fluid as it does work on the turbine. Specifically, centrifugal pumps have an impeller and casing. The impeller adds energy to the fluid by increasing pressure and velocity as it rotates and throws the fluid outward. The casing then converts the kinetic energy into increased pressure before the fluid exits.
Centrifugal pumps are best suited for large volume applications or smaller volumes with a high volume to pressure ratio. The selection of a centrifugal pump depends on system throughput, viscosity, specific gravity, and head requirements. Key parameters that impact applications are pump performance curves showing differential head and capacity. It is important to ensure sufficient net positive suction head to avoid cavitation. Centrifugal pumps can be operated singly, in series, or in parallel to achieve desired throughput and pressure conditions.
1. The document presents information on centrifugal and reciprocating pumps, including their basic workings, components, uses, and efficiencies.
2. Centrifugal pumps use centrifugal force to accelerate and move fluid outwards from the center to increase pressure, while reciprocating pumps use pistons or plungers that move back and forth to displace fluid.
3. Key components of centrifugal pumps include casings, impellers, while reciprocating pumps have cylinders, pistons, valves. Both are used widely for irrigation, industry, buildings and other purposes.
This document provides information on various types of pumps, with a focus on centrifugal pumps. It defines different types of pumps and discusses why centrifugal pumps are commonly used. It then provides details on the components and operating principles of centrifugal pumps. The document also discusses pump performance curves, cavitation, net positive suction head (NPSH), affinity laws, and best practices for pumping systems.
Centrifugal pumps in series and parallelphysics101
Centrifugal pumps work by using a rotating impeller to increase the velocity of a liquid and discharge it out of the pump housing. They have advantages like being simple, compact, and able to handle high rpm, but disadvantages like poor suction power and needing multiple stages to increase pressure. Proper installation requires a tight suction line, independently supported piping, minimal fittings, and protection against air intake to optimize performance. Pumps can be arranged in series to increase total head or in parallel to increase overall flow rate.
This document discusses water pumps, including their definition, classification, components, and operation. It describes how pumps work to convert mechanical energy into hydraulic energy to move water from lower to higher points. Pumps are classified as either turbo-hydraulic (centrifugal or positive displacement). Centrifugal pumps are the most common and their components and operation are explained in detail. Key concepts discussed include pump efficiency, cavitation, net positive suction head (NPSH), and selecting the appropriate pump based on system characteristics.
The document discusses different types of water pumps, including their definitions, classifications, main parts, mechanics, efficiencies, characteristic curves, and considerations for selection. Water pumps are devices that convert mechanical energy to hydraulic energy in order to lift water from lower to higher points. They are classified based on how the water leaves the rotating part, with the main types being centrifugal, axial, mixed-flow, screw, and reciprocating pumps. Pump selection involves matching the system characteristic curve with the pump curve to determine the operating point that satisfies the required performance.
The document discusses different types of pumps used in fluid transport systems. It describes positive displacement pumps which use a fixed volume cavity to trap and transport fluid with each cycle. Dynamic pumps are also discussed, which add momentum to fluid without a fixed volume. Centrifugal pumps are described in detail, with their construction, working principle, performance parameters and efficiency calculations explained. The key aspects covered are the use of impellers to impart energy and velocity to fluid which is then converted to pressure by the volute casing.
Pumps and turbines are fluid machines that either add energy to or extract energy from a fluid. Pumps add energy by doing work on the fluid, while turbines extract energy from the fluid as it does work on the turbine. Specifically, centrifugal pumps have an impeller and casing. The impeller adds energy to the fluid by increasing pressure and velocity as it rotates and throws the fluid outward. The casing then converts the kinetic energy into increased pressure before the fluid exits.
Centrifugal pumps are best suited for large volume applications or smaller volumes with a high volume to pressure ratio. The selection of a centrifugal pump depends on system throughput, viscosity, specific gravity, and head requirements. Key parameters that impact applications are pump performance curves showing differential head and capacity. It is important to ensure sufficient net positive suction head to avoid cavitation. Centrifugal pumps can be operated singly, in series, or in parallel to achieve desired throughput and pressure conditions.
1. The document presents information on centrifugal and reciprocating pumps, including their basic workings, components, uses, and efficiencies.
2. Centrifugal pumps use centrifugal force to accelerate and move fluid outwards from the center to increase pressure, while reciprocating pumps use pistons or plungers that move back and forth to displace fluid.
3. Key components of centrifugal pumps include casings, impellers, while reciprocating pumps have cylinders, pistons, valves. Both are used widely for irrigation, industry, buildings and other purposes.
This document provides information on various types of pumps, with a focus on centrifugal pumps. It defines different types of pumps and discusses why centrifugal pumps are commonly used. It then provides details on the components and operating principles of centrifugal pumps. The document also discusses pump performance curves, cavitation, net positive suction head (NPSH), affinity laws, and best practices for pumping systems.
Centrifugal pumps in series and parallelphysics101
Centrifugal pumps work by using a rotating impeller to increase the velocity of a liquid and discharge it out of the pump housing. They have advantages like being simple, compact, and able to handle high rpm, but disadvantages like poor suction power and needing multiple stages to increase pressure. Proper installation requires a tight suction line, independently supported piping, minimal fittings, and protection against air intake to optimize performance. Pumps can be arranged in series to increase total head or in parallel to increase overall flow rate.
This document discusses water pumps, including their definition, classification, components, and operation. It describes how pumps work to convert mechanical energy into hydraulic energy to move water from lower to higher points. Pumps are classified as either turbo-hydraulic (centrifugal or positive displacement). Centrifugal pumps are the most common and their components and operation are explained in detail. Key concepts discussed include pump efficiency, cavitation, net positive suction head (NPSH), and selecting the appropriate pump based on system characteristics.
The document discusses considerations for selecting a pumping system, including fluid characteristics, system requirements, pump types, drive selection, and standby requirements. Key factors in pump selection are fluid type, system head curve, potential modifications, operational mode, required margins, and space/layout constraints. Reciprocating pumps are used for small liquid chemical metering while centrifugal pumps are common for a wide range of head and capacity needs. Net positive suction head (NPSH) must also be considered to ensure proper pump operation and avoid cavitation.
This document discusses various types of pumps used to move water from lower to higher points. It describes centrifugal pumps, which use centrifugal force to move water radially outward, and positive displacement pumps like screw and reciprocating pumps. Key parts of centrifugal pumps are identified, including the impeller, casing, suction pipe, and delivery pipe. Concepts discussed include total dynamic head, pump efficiency, cavitation, net positive suction head, and the process of selecting a pump by matching its characteristic curve to the system curve.
This document provides an overview of pumping systems and opportunities for improving their energy efficiency. It discusses the types of pumps commonly used, including centrifugal and positive displacement pumps. The document explains how to assess pump performance by calculating hydraulic power, shaft power, and efficiency. It also outlines several methods for improving energy efficiency, such as selecting the properly sized pump, controlling flow rates through variable speed drives, using parallel pumps to meet varying demand, and eliminating inefficient flow control valves and bypass lines. The overall aim is to educate about pumping systems and identify opportunities to reduce the significant energy demands of pump operations.
The document provides an introduction to pump analysis. It discusses that the purpose of a pump is to increase the mechanical energy in a fluid by transporting it from a lower elevation to a higher elevation. It then covers key pumping concepts like capacity, head, efficiency, and power input. Specific types of pumps are defined, including centrifugal pumps which are most commonly used for wastewater applications. Methods for analyzing pump performance including head-capacity curves and affinity laws are also introduced.
This document provides information on pump efficiency, power requirements, and system curves for sprinkler irrigation systems. It defines key terms like total dynamic head (TDH), water horsepower (WHP), and brake horsepower (BHP). An example calculation is shown to determine the TDH, WHP, and BHP required for a centrifugal pump discharging into air. Different types of system curves are described for scenarios involving static lift, friction loss, and multiple laterals or center pivots. Affinity laws relating flow, head, speed, and power are also covered, along with using these laws to adjust a pump's operating point to match a system curve.
The document discusses various types of pumps including centrifugal pumps, positive displacement pumps, and reciprocating pumps. It describes the main components and working principles of centrifugal pumps, including the impeller, casing, suction and delivery pipes, and shaft. Centrifugal pumps work by using an impeller to impart kinetic energy to the fluid and a volute casing to convert this to pressure. Reciprocating pumps use pistons while positive displacement pumps include gear pumps.
Basics of centrifugal. Topics covered are operating principles, energy conversion, components in centrifugal pump, the concept of NPSH, pump rating calculation and affinity laws
The document discusses pumps, motors, and hydraulic cylinders. It begins by introducing hydraulic pumps and describing the two main types: rotodynamic pumps (like centrifugal pumps) and reciprocating pumps. It then compares centrifugal and positive displacement (reciprocating) pumps, noting key differences in how they handle flow rate, pressure, viscosity, efficiency, and net positive suction head (NPSH). The document dives deeper into technical terms related to pumps like static pressure, pressure head, specific weight, and flow rate. It provides diagrams of components like centrifugal pumps and reciprocating pumps. In summary, the document provides an overview of hydraulic pump types and technical concepts as well as comparisons between centrifugal and reciprocating pump
This document provides an overview of centrifugal pumps. It defines a pump and discusses the main components and classifications of centrifugal pumps. The key components of a centrifugal pump are the impeller, casing, suction pipe, and delivery pipe. Centrifugal pumps are classified based on impeller design and casing shape. The document also covers topics such as work done by the centrifugal pump, head of a pump, losses and efficiencies, and minimum speed for starting a centrifugal pump. Several example problems are provided to calculate values like inlet vane angle, work done, and minimum starting speed.
Centrifugal pumps impart velocity energy to fluid using a rotating impeller, converting it to pressure energy. Positive displacement pumps physically move a fixed volume of fluid using movable boundaries. The main types are centrifugal, reciprocating, and rotary pumps. Centrifugal pumps are best for medium/high flows at low/medium pressures while reciprocating pumps work well for low flows at high pressures. Pump performance is represented through curves showing relationships between flow rate, pressure, and efficiency. Cavitation can damage pumps and occurs when local pressure drops below vapor pressure as bubbles form and violently collapse.
Pumps theory www.chemicallibrary.blogspot.comFARRUKH SHEHZAD
This document discusses various terms related to pumps, including types of pumps (positive displacement, centrifugal), pump components (impeller, casing), pump operation concepts (head, suction lift, cavitation, NPSH), and pump performance parameters (specific speed, affinity laws). It provides definitions and formulas for key terms like head, specific speed, NPSH, cavitation, and discusses how different types of pumps like centrifugal and rotary pumps operate.
It is Allah who controls the seas so that ships may sail upon them and people benefit from His bounties and be grateful. There are two main types of pumps - positive displacement pumps and non-positive displacement (dynamic) pumps such as centrifugal pumps. Centrifugal pumps come in various configurations like vertical pumps with two stages for higher discharge used as fire pumps, and vertical pumps with double suction and single discharge for lower discharge used as ballast pumps.
This document discusses pumps and pumping systems. It begins by stating that pumping systems account for nearly 20% of global electrical energy demand. It then provides an overview of the main components of a pumping system, which include pumps, prime movers, piping, valves and other fittings. The document discusses different types of pumps, separating them into positive displacement pumps and dynamic pumps. It focuses on describing centrifugal pumps in more detail, stating they are the most common pumps used for industrial water applications.
The document discusses the selection and application of pumps. It begins by defining different types of pumps, including piston pumps, plunger pumps, diaphragm pumps, and centrifugal pumps. It then discusses key considerations for pump selection like fluid characteristics, pressure requirements, and space availability. The document also covers pump performance concepts like net positive suction head (NPSH), total dynamic head, brake horsepower calculations, and affinity laws relating pump parameters like flow, head, and rpm. Overall, the document provides an overview of different pump types and the important technical factors to examine when choosing a pump for a given application.
Three key points about reciprocating pumps from the document are:
1) Reciprocating pumps use pistons or plungers that oscillate back and forth to move water from lower to higher points, converting mechanical energy to hydraulic energy. They are commonly used for applications requiring variable flow rates or high pressures.
2) The main types are piston pumps, plunger pumps, and diaphragm pumps. Piston pumps are often used to transmit fluids under pressure, while plunger pumps are efficient and can develop very high pressures. Diaphragm pumps can handle viscous or toxic liquids.
3) Reciprocating pumps can be single acting, where water is moved in one direction, or double
This document summarizes a presentation on the design and analysis of a reciprocating pump. It includes a timeline of the project tasks that have been completed, such as market surveys, material selection, and progress reports. It also discusses the dimensions and drafting of pump components in SolidWorks. Finally, it notes that CFD analysis software will be used to model fluid flow, turbulence, heat transfer, and reactions for optimizing the pump performance.
The document discusses piston pumps, including their basic components like the cylinder block and piston. It describes how piston pumps work and the principles behind fixed and variable displacement pumps. The remainder of the document outlines Eaton's various piston pump product lines for industrial and mobile applications, ranging from small fixed displacement pumps to large high-pressure variable pumps. It also discusses integrated motor pump units that combine an electric motor and pump.
This document discusses pump and pumping systems. It describes different types of pumps including positive displacement pumps like reciprocating and rotary pumps, and dynamic pumps like centrifugal pumps. It also discusses components of solar pumping systems and assessing pump performance through calculations of pump shaft power and hydraulic power. The document concludes with several energy efficiency opportunities for pumps like maintenance, monitoring, controls, installing more efficient pumps, proper sizing, adjustable speed drives, and improved sealing.
This document provides an introduction to different types of pumping equipment, including their principles of operation and categories. It discusses the main differences between rotodynamic pumps (like centrifugal pumps) and positive displacement pumps (like reciprocating and rotary pumps). Centrifugal pumps are best for medium to high flow rates and low to medium pressures, while positive displacement pumps can achieve very high pressures or handle low flows. The document also compares characteristics like flow patterns, pressure capabilities, cost considerations, and fluid handling for different pump categories.
This document discusses centrifugal pumps and reciprocating pumps. It describes the key parts and working of a centrifugal pump, including the impeller, casing, suction and delivery pipes. The impeller rotates and increases the kinetic energy and pressure of the fluid. Characteristic curves showing variations in head, power and discharge with speed are also explained. For reciprocating pumps, the mechanical energy is converted to hydraulic energy by a piston moving back and forth in a cylinder.
Hydraulic machines use liquid flow to transfer mechanical energy between the liquid and a rotating component. There are two main types: hydraulic turbines, where the rotating component receives energy from the liquid flow; and pumps, where energy is transferred from the rotating component to the liquid. Common hydraulic turbines include impulse turbines like the Pelton wheel, which use jet momentum changes, and reaction turbines like the Francis turbine, where pressure and kinetic energy changes drive the rotating runner. Turbines are classified based on factors such as the type of energy used, direction of liquid flow, operating head, and specific speed. Hydraulic power plants typically include a dam, penstock, water turbine, and tailrace to harness potential and kinetic energy of water
The pdf contains explanation about the centrifugal pumps. It is usually studied by Mechanical or Civil engineering students. This pdf file will help for the students from these fields.
The document discusses considerations for selecting a pumping system, including fluid characteristics, system requirements, pump types, drive selection, and standby requirements. Key factors in pump selection are fluid type, system head curve, potential modifications, operational mode, required margins, and space/layout constraints. Reciprocating pumps are used for small liquid chemical metering while centrifugal pumps are common for a wide range of head and capacity needs. Net positive suction head (NPSH) must also be considered to ensure proper pump operation and avoid cavitation.
This document discusses various types of pumps used to move water from lower to higher points. It describes centrifugal pumps, which use centrifugal force to move water radially outward, and positive displacement pumps like screw and reciprocating pumps. Key parts of centrifugal pumps are identified, including the impeller, casing, suction pipe, and delivery pipe. Concepts discussed include total dynamic head, pump efficiency, cavitation, net positive suction head, and the process of selecting a pump by matching its characteristic curve to the system curve.
This document provides an overview of pumping systems and opportunities for improving their energy efficiency. It discusses the types of pumps commonly used, including centrifugal and positive displacement pumps. The document explains how to assess pump performance by calculating hydraulic power, shaft power, and efficiency. It also outlines several methods for improving energy efficiency, such as selecting the properly sized pump, controlling flow rates through variable speed drives, using parallel pumps to meet varying demand, and eliminating inefficient flow control valves and bypass lines. The overall aim is to educate about pumping systems and identify opportunities to reduce the significant energy demands of pump operations.
The document provides an introduction to pump analysis. It discusses that the purpose of a pump is to increase the mechanical energy in a fluid by transporting it from a lower elevation to a higher elevation. It then covers key pumping concepts like capacity, head, efficiency, and power input. Specific types of pumps are defined, including centrifugal pumps which are most commonly used for wastewater applications. Methods for analyzing pump performance including head-capacity curves and affinity laws are also introduced.
This document provides information on pump efficiency, power requirements, and system curves for sprinkler irrigation systems. It defines key terms like total dynamic head (TDH), water horsepower (WHP), and brake horsepower (BHP). An example calculation is shown to determine the TDH, WHP, and BHP required for a centrifugal pump discharging into air. Different types of system curves are described for scenarios involving static lift, friction loss, and multiple laterals or center pivots. Affinity laws relating flow, head, speed, and power are also covered, along with using these laws to adjust a pump's operating point to match a system curve.
The document discusses various types of pumps including centrifugal pumps, positive displacement pumps, and reciprocating pumps. It describes the main components and working principles of centrifugal pumps, including the impeller, casing, suction and delivery pipes, and shaft. Centrifugal pumps work by using an impeller to impart kinetic energy to the fluid and a volute casing to convert this to pressure. Reciprocating pumps use pistons while positive displacement pumps include gear pumps.
Basics of centrifugal. Topics covered are operating principles, energy conversion, components in centrifugal pump, the concept of NPSH, pump rating calculation and affinity laws
The document discusses pumps, motors, and hydraulic cylinders. It begins by introducing hydraulic pumps and describing the two main types: rotodynamic pumps (like centrifugal pumps) and reciprocating pumps. It then compares centrifugal and positive displacement (reciprocating) pumps, noting key differences in how they handle flow rate, pressure, viscosity, efficiency, and net positive suction head (NPSH). The document dives deeper into technical terms related to pumps like static pressure, pressure head, specific weight, and flow rate. It provides diagrams of components like centrifugal pumps and reciprocating pumps. In summary, the document provides an overview of hydraulic pump types and technical concepts as well as comparisons between centrifugal and reciprocating pump
This document provides an overview of centrifugal pumps. It defines a pump and discusses the main components and classifications of centrifugal pumps. The key components of a centrifugal pump are the impeller, casing, suction pipe, and delivery pipe. Centrifugal pumps are classified based on impeller design and casing shape. The document also covers topics such as work done by the centrifugal pump, head of a pump, losses and efficiencies, and minimum speed for starting a centrifugal pump. Several example problems are provided to calculate values like inlet vane angle, work done, and minimum starting speed.
Centrifugal pumps impart velocity energy to fluid using a rotating impeller, converting it to pressure energy. Positive displacement pumps physically move a fixed volume of fluid using movable boundaries. The main types are centrifugal, reciprocating, and rotary pumps. Centrifugal pumps are best for medium/high flows at low/medium pressures while reciprocating pumps work well for low flows at high pressures. Pump performance is represented through curves showing relationships between flow rate, pressure, and efficiency. Cavitation can damage pumps and occurs when local pressure drops below vapor pressure as bubbles form and violently collapse.
Pumps theory www.chemicallibrary.blogspot.comFARRUKH SHEHZAD
This document discusses various terms related to pumps, including types of pumps (positive displacement, centrifugal), pump components (impeller, casing), pump operation concepts (head, suction lift, cavitation, NPSH), and pump performance parameters (specific speed, affinity laws). It provides definitions and formulas for key terms like head, specific speed, NPSH, cavitation, and discusses how different types of pumps like centrifugal and rotary pumps operate.
It is Allah who controls the seas so that ships may sail upon them and people benefit from His bounties and be grateful. There are two main types of pumps - positive displacement pumps and non-positive displacement (dynamic) pumps such as centrifugal pumps. Centrifugal pumps come in various configurations like vertical pumps with two stages for higher discharge used as fire pumps, and vertical pumps with double suction and single discharge for lower discharge used as ballast pumps.
This document discusses pumps and pumping systems. It begins by stating that pumping systems account for nearly 20% of global electrical energy demand. It then provides an overview of the main components of a pumping system, which include pumps, prime movers, piping, valves and other fittings. The document discusses different types of pumps, separating them into positive displacement pumps and dynamic pumps. It focuses on describing centrifugal pumps in more detail, stating they are the most common pumps used for industrial water applications.
The document discusses the selection and application of pumps. It begins by defining different types of pumps, including piston pumps, plunger pumps, diaphragm pumps, and centrifugal pumps. It then discusses key considerations for pump selection like fluid characteristics, pressure requirements, and space availability. The document also covers pump performance concepts like net positive suction head (NPSH), total dynamic head, brake horsepower calculations, and affinity laws relating pump parameters like flow, head, and rpm. Overall, the document provides an overview of different pump types and the important technical factors to examine when choosing a pump for a given application.
Three key points about reciprocating pumps from the document are:
1) Reciprocating pumps use pistons or plungers that oscillate back and forth to move water from lower to higher points, converting mechanical energy to hydraulic energy. They are commonly used for applications requiring variable flow rates or high pressures.
2) The main types are piston pumps, plunger pumps, and diaphragm pumps. Piston pumps are often used to transmit fluids under pressure, while plunger pumps are efficient and can develop very high pressures. Diaphragm pumps can handle viscous or toxic liquids.
3) Reciprocating pumps can be single acting, where water is moved in one direction, or double
This document summarizes a presentation on the design and analysis of a reciprocating pump. It includes a timeline of the project tasks that have been completed, such as market surveys, material selection, and progress reports. It also discusses the dimensions and drafting of pump components in SolidWorks. Finally, it notes that CFD analysis software will be used to model fluid flow, turbulence, heat transfer, and reactions for optimizing the pump performance.
The document discusses piston pumps, including their basic components like the cylinder block and piston. It describes how piston pumps work and the principles behind fixed and variable displacement pumps. The remainder of the document outlines Eaton's various piston pump product lines for industrial and mobile applications, ranging from small fixed displacement pumps to large high-pressure variable pumps. It also discusses integrated motor pump units that combine an electric motor and pump.
This document discusses pump and pumping systems. It describes different types of pumps including positive displacement pumps like reciprocating and rotary pumps, and dynamic pumps like centrifugal pumps. It also discusses components of solar pumping systems and assessing pump performance through calculations of pump shaft power and hydraulic power. The document concludes with several energy efficiency opportunities for pumps like maintenance, monitoring, controls, installing more efficient pumps, proper sizing, adjustable speed drives, and improved sealing.
This document provides an introduction to different types of pumping equipment, including their principles of operation and categories. It discusses the main differences between rotodynamic pumps (like centrifugal pumps) and positive displacement pumps (like reciprocating and rotary pumps). Centrifugal pumps are best for medium to high flow rates and low to medium pressures, while positive displacement pumps can achieve very high pressures or handle low flows. The document also compares characteristics like flow patterns, pressure capabilities, cost considerations, and fluid handling for different pump categories.
This document discusses centrifugal pumps and reciprocating pumps. It describes the key parts and working of a centrifugal pump, including the impeller, casing, suction and delivery pipes. The impeller rotates and increases the kinetic energy and pressure of the fluid. Characteristic curves showing variations in head, power and discharge with speed are also explained. For reciprocating pumps, the mechanical energy is converted to hydraulic energy by a piston moving back and forth in a cylinder.
Hydraulic machines use liquid flow to transfer mechanical energy between the liquid and a rotating component. There are two main types: hydraulic turbines, where the rotating component receives energy from the liquid flow; and pumps, where energy is transferred from the rotating component to the liquid. Common hydraulic turbines include impulse turbines like the Pelton wheel, which use jet momentum changes, and reaction turbines like the Francis turbine, where pressure and kinetic energy changes drive the rotating runner. Turbines are classified based on factors such as the type of energy used, direction of liquid flow, operating head, and specific speed. Hydraulic power plants typically include a dam, penstock, water turbine, and tailrace to harness potential and kinetic energy of water
The pdf contains explanation about the centrifugal pumps. It is usually studied by Mechanical or Civil engineering students. This pdf file will help for the students from these fields.
This document discusses hydraulic turbines and pumps. It defines turbines as machines that convert hydraulic energy to mechanical energy, and pumps as the opposite, converting mechanical to hydraulic energy. It describes the key components and classifications of impulse and reaction turbines like the Pelton wheel and Francis turbine. It also covers turbine characteristics such as head, power, and efficiency. Characteristic curves are presented to show turbine and pump performance under varying operating conditions.
This document provides information on hydraulic turbines, including their definition, history, parts, types, and classifications. It focuses on the Pelton turbine, describing its working principle and key design aspects. The Pelton turbine uses the kinetic energy of water directed through a nozzle to spin buckets on a wheel. It is well-suited for high heads. Design considerations for the Pelton wheel include the velocity of its jet and buckets, the jet deflection angle, wheel and jet diameters, bucket dimensions, and the number of jets and buckets.
Southern Methodist UniversityBobby B. Lyle School of Engineeri.docxwhitneyleman54422
This document discusses pump selection and piping systems for fluid flow. It provides definitions for different types of pumps (e.g. centrifugal, positive displacement) and describes how they are used for various applications. It also discusses concepts like pump curves, system curves and selecting a suitable pump for a given piping system. Finally, it covers topics like multiple pipe systems with pipes in series, parallel and branching configurations, and how to analyze flow through such complex pipe networks.
1. Turbomachines such as centrifugal pumps transfer energy from a rotor to a fluid. Centrifugal pumps are classified based on the extent and type of fluid flow, and whether they absorb or produce energy.
2. Centrifugal pumps use a rotating impeller to impart velocity to the fluid and increase its pressure. They are commonly used to transport liquids through conversion of rotational kinetic energy.
3. Positive displacement pumps move fluid by trapping a fixed volume and forcing that volume into the discharge pipe. They are classified based on construction and include gear pumps, vane pumps, piston pumps, and more. Flow is constant with changing pressure in positive displacement pumps.
This document discusses various topics related to hydraulic turbines, including:
1. Classification, selection, and design of impulse turbines like the Pelton wheel and reaction turbines like the Francis and Kaplan turbines.
2. Components like the draft tube, surge tanks, and governing systems.
3. Concepts like unit speed, unit discharge, unit power, and characteristic curves used to analyze turbine performance.
4. Cavitation in hydraulic turbines.
Hydraulic turbines convert hydraulic energy from flowing water into mechanical energy. They are classified as either reaction turbines or impulse turbines. Reaction turbines experience pressure changes through both fixed and moving blades, while impulse turbines only experience velocity changes from jet impacts. Common reaction turbines are Francis and Kaplan turbines, which are used in low- and medium-head applications like dams. The Pelton wheel is an example of an impulse turbine, where individual jets strike rotating buckets to generate torque. Power developed depends on factors like efficiency, density, head, flow rate.
A water turbine is a rotary engine that captures energy from moving water. It was developed in the 19th century for industrial power production. There are two main types - reaction turbines, which rely on changes in water pressure, and impulse turbines, which rely on changes in water velocity. Francis turbines are the most widely used reaction turbine, while Pelton wheels are common impulse turbines. Water turbines come in various designs depending on factors like available water head and flow rate. They are designed to efficiently harness hydraulic energy with high mechanical efficiencies over 90% for power generation.
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Turbines and recipocating pumps and miscellaneous hydraulic machinesMohit Yadav
This document provides information about various topics related to hydraulic machines covered in a fluid mechanics project. It includes 3 sections: turbines, centrifugal pumps, and reciprocating pumps. For turbines, it discusses the basic working principles and types of turbines such as Pelton, Kaplan, and Francis turbines. It provides details on the components and working of each turbine. For centrifugal pumps, it explains the working principle and components like impeller, casing, and discusses concepts such as priming. It also includes the velocity triangle and equations for work done.
The document discusses different types of hydraulic turbines used to convert hydraulic energy into mechanical energy. It defines hydraulic turbines and provides examples such as the Pelton wheel, Francis, and Kaplan turbines. It then classifies hydraulic turbines based on factors like the energy at the inlet, direction of flow through the runner, head available at the inlet, and specific speed. The key components and working of Pelton wheel, Francis, and Kaplan turbines are explained along with diagrams. Concepts like velocity triangles, work done, efficiencies, and design aspects are covered for Pelton wheel turbines. Draft tubes, their functions and types are also summarized.
The document discusses different types of hydraulic turbines used to convert hydraulic energy from flowing water into mechanical energy. It describes Pelton, Francis, and Kaplan turbines, their main components, working principles, and classifications. Pelton turbines use impulse and are suitable for high heads. Francis turbines are reaction turbines that can achieve over 95% efficiency and are most commonly used. Kaplan turbines have adjustable blades and are used for low heads. The document also covers hydraulic turbine efficiencies, velocity triangles, draft tubes, and factors considered in turbine selection and design.
An Experimental Prototype for Low Head Small Hydro Power Generation Using Hydram - University of Nairobi
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Different power generatrion diagram and its breif explain by swapnil dSwapnil Dhage
The document describes different types of power plants:
1) Hydroelectric plants use falling water to rotate turbines and generate electricity. Key components include dams, penstocks, turbines, generators, and transformers.
2) Thermal plants burn fuels to create high-pressure steam that drives turbines connected to generators. They include boilers, steam turbines, condensers, and feedwater pumps.
3) Wind turbines use rotor blades to convert wind's kinetic energy into mechanical energy that spins generators. Their components are rotors, drive trains, nacelles, towers, and machine controls.
4) Solar plants use photovoltaic panels to convert sunlight into direct current, then inverters transform it into alternating
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1. Hydraulics 2 T4-1 David Apsley
TOPIC T4: PUMPS AND TURBINES AUTUMN 2013
Objectives
(1) Understand the role of pumps and turbines as energy-conversion devices and use,
appropriately, the terms head, power and efficiency.
(2) Be aware of the main types of pumps and turbines and the distinction between impulse
and reaction turbines and between radial, axial and mixed-flow devices.
(3) Match pump characteristics and system characteristics to determine the duty point.
(4) Calculate characteristics for pumps in series and parallel and use the hydraulic scaling
laws to calculate pump characteristics at different speeds.
(5) Select the type of pump or turbine on the basis of specific speed.
(6) Understand the mechanics of a centrifugal pump and an impulse turbine.
(7) Recognise the problem of cavitation and how it can be avoided.
1. Energy conversion
1.1 Energy transfer in pumps and turbines
1.2 Power
1.3 Efficiency
2. Types of pumps and turbines
2.1 Impulse and reaction turbines
2.2 Positive-displacement and dynamic pumps
2.3 Radial, axial and mixed-flow devices
2.4 Common types of turbine
3. Pump and system characteristics
3.1 Pump characteristics
3.2 System characteristics
3.3 Finding the duty point
3.4 Pumps in parallel and in series
4. Hydraulic scaling
4.1 Dimensional analysis
4.2 Change of speed
4.3 Specific speed
5. Mechanics of rotodynamic devices
5.1 Centrifugal pump
5.2 Pelton wheel
6. Cavitation
References
White (2006) – Chapter 11
Hamill (2001) – Chapter 11
Chadwick and Morfett (2004) – Chapter 7
Massey (2005) – Chapter 12
2. Hydraulics 2 T4-2 David Apsley
1. Energy Conversion
1.1 Energy Transfer in Pumps and Turbines
Pumps and turbines are energy conversion devices:
pumps turn electrical or mechanical energy into fluid energy;
turbines turn fluid energy into electrical or mechanical energy.
The energy per unit weight is the head, H:
g
V
z
g
p
H
2ρ
2
The first two terms on the RHS comprise the piezometric head. The last term is the dynamic
head.
1.2 Power
Power = rate of conversion of energy.
If a mass m is raised through a height H it gains energy mgH. If it does so in time t then the
rate of conversion is mgH/t.
For a fluid in motion the mass flow rate (m/t) is ρQ. The rate of conversion to or from fluid
energy when the total head is changed by H is, therefore, ρQgH, or
gQHpower ρ
1.3 Efficiency
Efficiency, η, is given by
in
out
power
power
η
where “powerout” refers to the useful power; i.e. excluding losses.
For turbines:
gQH
powerout
ρ
η
For pumps:
inpower
gQHρ
η
Example.
A pump lifts water from a large tank at a rate of 30 L s–1
. If the input power is 10 kW and the
pump is operating at an efficiency of 40%, find:
(a) the head developed across the pump;
(b) the maximum height to which it can raise water if the delivery pipe is vertical, with
diameter 100 mm and friction factor λ = 0.015.
Answer: (a) 13.6 m; (b) 12.2 m
3. Hydraulics 2 T4-3 David Apsley
2. Types of Pumps and Turbines
2.1 Impulse and reaction turbines
In a pump or turbine a change in fluid head (
g
V
z
g
p
H
2ρ
2
) may be brought about by a
change in pressure or velocity or both.
An impulse turbine (e.g. Pelton wheel; water wheel) is one where the change in head
is brought about primarily by a change in velocity. This usually involves unconfined
free jets of water (at atmospheric pressure) impinging on moving vanes.
A reaction turbine (e.g. Francis turbine; Kaplan turbine; windmill) is one where the
change in head is brought about primarily by a change in pressure.
2.2 Positive-Displacement and Dynamic pumps
Postive-displacement pumps operate by a change in volume; energy conversion is
intermittent. Examples in the human body include the heart (diaphragm pump) and the
intestines (peristaltic pump). In a reciprocating pump (e.g. a bicycle pump) fluid is sucked in
on one part of the cycle and expelled (at higher pressure) in another.
In dynamic pumps there is no change in volume and energy conversion is continuous. Most
pumps are rotodynamic devices where fluid energy is exchanged with the mechanical energy
of a rotating element (called a runner in turbines and an impeller in pumps), with a further
conversion to or from electrical energy.
This course focuses entirely on rotary devices.
Note that, for gases, pumps are usually referred to as fans (for low pressures), blowers or
compressors (for high pressures).
2.3 Radial, Axial and Mixed-Flow Devices
The terms radial and axial refer to the change in direction of flow through a rotodynamic
device (pump or turbine):
Radial Axial Mixed
4. Hydraulics 2 T4-4 David Apsley
In a centrifugal pump flow enters
along the axis and is expelled
radially. (The reverse is true for a
turbine.)
An axial-flow pump is like a propeller;
the direction of the flow is unchanged
after passing through the device.
A mixed-flow device is a hybrid device,
used for intermediate heads.
In many cases – notably in pumped-storage power stations – a device can be run as either a
pump or a turbine.
Inward-flow reaction turbine centrifugal pump (high head / low discharge)
(e.g. Francis turbine)
Propeller turbine axial-flow pump (low head / high discharge)
(e.g. Kaplan turbine; windmill)
Volute
'Eye' (intake)
Impeller vane
flow
rotation
Blades
Guide vanes
Hub
Blades
Guide vanes
Inlet Outlet
5. Hydraulics 2 T4-5 David Apsley
2.4 Common Types of Turbine
Pelton wheels are impulse turbines used in
hydroelectric plant where there is a very high head
of water. Typically, 1 – 6 high-velocity jets of
water impinge on buckets mounted around the
circumference of a runner.
Francis turbines are used in many large
hydropower projects (e.g the Hoover Dam), with an
efficiency in excess of 90%. Such moderate- to
high-head turbines are also used in pumped-storage
power stations (e.g. Dinorwig and Ffestiniog in
Wales; Foyers in Scotland), which pump water
uphill during periods of low energy demand and
then run the system in reverse to generate power
during the day. This smooths the power demands
on fossil-fuelled and nuclear power stations which
are not easily brought in and out of operation. Francis turbines are like centrifugal pumps in
reverse.
Kaplan turbines are axial-flow (propeller) turbines. In the
Kaplan design the blade angles are adjustable to ensure
efficient operation for a range of discharges.
Wells turbines were specifically developed for wave-energy applications. They have the
property that they rotate in the same direction irrespective of the flow direction.
Bulb generators are large-diameter variants of the Kaplan propeller turbine, which are
suitable for the low-head, high-discharge applications in tidal barrages (e.g. La Rance in
France). Flow passes around the bulb, which contains the alternator.
The Archimedes screw has been used since ancient
times to raise water. It is widely used in water
treatment plants because it can accommodate
submerged debris. Recently, several devices have been
installed beside weirs in the north of England to run in
reverse and generate power.
Jet
Bucket
Spear valve
6. Hydraulics 2 T4-6 David Apsley
3. Pump and System Characteristics
3.1 Pump characteristics
Pump characteristics are the head (H), input power (I) and efficiency (η) as functions of
discharge (Q). The most important is the H vs Q relationship. Typical shapes of these
characteristics are sketched below for centrifugal and axial-flow pumps.
Q
I
H
Q
I
H
centrifugal pump axial-flowpump
Given the pump characteristics at one rotation rate (N), those at different rotation rates may
be determined using the hydraulic scaling laws (Section 4).
Ideally, one would like to operate the pump:
as close as possible to the design point (point of maximum efficiency);
in a region where the H-Q relationship is steep; (otherwise there are significant
fluctuations in discharge for small changes in head).
3.2 System characteristics
In general the pump has to supply enough energy to:
lift water through a certain height – the static lift Hs;
overcome losses dependent on the discharge, Q.
Thus the system head is
lossess hHH
Typically, losses (whether frictional or due to pipe fittings) are proportional to Q2
, so that the
system characteristic is often quadratic:
2
aQHH s
The static lift is often decomposed
into the rise from sump to the level
of the pump (the suction head, Hs1)
and that between the pump and the
delivery point (Hs2). The first of
these is limited by the maximum
suction height (approximately 10 m,
corresponding to 1 atmosphere) and
will be discussed later in the context
of cavitation.
Sump
Delivery reservoir
Suction main
Delivery main
Static lift
Hs
Suction head
Pump
7. Hydraulics 2 T4-7 David Apsley
3.3 Finding the Duty Point
The pump operates at a duty point where the head supplied by the pump precisely matches
the head requirements of the system at the same discharge; i.e. where the pump and system
characteristics intersect.
Q
H
System
characteristic
Pump
characteristic
Duty
point
Hs
Example. (Examination 2005 – part)
A water pump was tested at a rotation rate of 1500 rpm. The following data was obtained. (Q
is quantity of flow, H is head of water, η is efficiency).
It is proposed to used this pump to draw water from an open sump to an elevation 5.5 m
above. The delivery pipe is 20.0 m long and 100 mm diameter, and has a friction factor of
0.005.
If operating at 1500 rpm, find:
(a) the maximum discharge that the pump can provide;
(b) the pump efficiency at this discharge;
(c) the input power required.
Answer: (a) 37.5 L s–1
; (b) 0.67; (c) 3.7 kW
In practice, it is desirable to run the pump at a speed where the duty point is close to that of
maximum efficiency. To do this we need to determine how the pump characteristic varies
with rotation rate N – see below.
Q (L s–1
) 0 10 20 30 40 50
H (m) 10.0 10.5 10.0 8.5 6.0 2.5
η 0.0 0.40 0.64 0.72 0.64 0.40
8. Hydraulics 2 T4-8 David Apsley
3.4 Pumps in Parallel and in Series
Pumps in Parallel
Same head: H
Add the discharges: Q1 + Q2
Advantages of pumps in parallel are:
high capacity: permits a large
total discharge;
flexibility: pumps can be
brought in and out of service if
the required discharge varies;
redundancy: pumping can
continue if one is not operating
due to failure or planned
maintenance.
Pumps in Series
Same discharge: Q
Add the heads: H1 + H2
Pumps in series may be necessary to
generate high heads, or provide
regular “boosts” along long pipelines
without large pressures at any
particular point.
Q
H
Single pump
Double the flow
Pumps in parallel
Q
H
Single pump
Pumps in series
Double
the
head
9. Hydraulics 2 T4-9 David Apsley
Example. (Examination, January 2004)
A rotodynamic pump, having the characteristics tabulated below, delivers water from a river
at elevation 102 m to a reservoir with a water level of 135 m, through a 350 mm diameter
cast-iron pipe. The frictional head loss in the pipeline is given by hf = 550 Q2
, where hf is the
head loss in m and Q is the discharge in m3
s–1
. Minor head losses from valves and fittings
amount to 50 Q2
in the same units.
Pump characteristics: Q is discharge, H is head, η is efficiency.
(a) Calculate the discharge and head in the pipeline (at the duty point).
If the discharge is to be increased by the installation of a second identical pump:
(b) determine the unregulated discharge and head produced by connecting the pump:
(i) in parallel;
(ii) in series;
(c) determine the power demand at the duty point in the case of parallel operation.
Answer: (a) 0.137 m3
s–1
and 44 m;
(b) (i) 0.185 m3
s–1
and 53.5 m; (ii) 0.192 m3
s–1
and 55.1 m; (c) 155 kW
Q (m3
s–1
) 0 0.05 0.10 0.15 0.20
H (m) 60 58 52 41 25
η (%) --- 44 65 64 48
10. Hydraulics 2 T4-10 David Apsley
4 Hydraulic Scaling
4.1 Dimensional Analysis
Provided that the mechanical efficiency is the same, the performance of a particular
geometrically-similar family of pumps or turbines (“homologous series”) may be expected to
depend on:
discharge Q [L3
T–1
]
pressure change ρgH [ML–1
T–2
]
power P [ML2
T–3
] (input for pumps; output for turbines)
rotor diameter D [L]
rotation rate N [T–1
]
fluid density ρ [ML–3
]
fluid viscosity μ [ML–1
T–1
]
(Rotor diameter may be replaced by any characteristic length, since geometric similarity
implies that length ratios remain constant. Rotation rate is typically expressed in either rad s–1
or rpm.)
Since there are 7 variables and 3 independent dimensions, Buckingham’s Pi Theorem yields a
relationship between 4 independent groups, which may be taken as (exercise):
31Π
ND
Q
, 222Π
DN
gH
, 533
ρ
Π
DN
P
, Re
μ
ρ
Π
2
4
ND
For fully-turbulent flow the dependence on molecular viscosity μ and hence the Reynolds
number (Π4) vanishes. Then, for geometrically-similar pumps with different sizes (D) and
rotation rates (N):
2
3
1
3
ND
Q
ND
Q
,
2
22
1
22
DN
gH
DN
gH
,
2
53
1
53
ρρ
DN
P
DN
P
For pumps (input power P, output power ρgQH), any one of Π1, Π2, Π3 may be replaced by
)(η
ρ
Π
ΠΠ
3
21
efficiency
P
gQH
The reciprocal of this would be used for turbines.
Example.
A ¼-scale model centrifugal pump is tested under a head of 7.5 m at a speed of 500 rpm. It
was found that 7.5 kW was needed to drive the model. Assuming similar mechanical
efficiencies, calculate:
(a) the speed and power required by the prototype when pumping against a head of 44 m;
(b) the ratio of the discharges in the model to that in the prototype.
Answer: (a) 303 rpm and 1710 kW; (b) Qm/Qp = 1/38.8 = 0.0258
11. Hydraulics 2 T4-11 David Apsley
4.2 Change of Speed
For the same pump (i.e. same D) operating at different speeds N1 and N2:
1
2
1
2
N
N
Q
Q
,
2
1
2
1
2
N
N
H
H
,
3
1
2
1
2
N
N
P
P
Thus,
NQ , 2
NH , 3
NP
(This might be expected, since Q velocity, whilst H energy velocity2
).
These are called the hydraulic scaling laws or affinity laws.
Speed Scaling Laws For a Single Pump
1
2
1
2
N
N
Q
Q
,
2
1
2
1
2
N
N
H
H
,
3
1
2
1
2
N
N
P
P
, 21 ηη
Given pump characteristics at one speed one can use the hydraulic scaling laws to deduce
characteristics at a different speed.
4.2.1 Finding the Duty Point at a New Pump Speed
Scale each (Q,H) pair on the original
characteristic at speed N1 to get the new
characteristic at speed N2; i.e.
1
1
2
2 Q
N
N
Q
, 1
2
1
2
2 H
N
N
H
Where this scaled characteristic intercepts the
system curve gives the new duty point.
Q
Systemcharacteristic
Newduty point
Hs
N1
N2
H
12. Hydraulics 2 T4-12 David Apsley
4.2.2 Finding the Pump Speed For a Given Duty Point (Harder)
To find the pump speed for a given
discharge or head plot a hydraulic-
scaling curve back from the required
duty point (Q2, H2) on the system
curve, at unknown speed N2:
2
22
Q
Q
H
H
Very important: the hydraulic
scaling curve is not the same as the
system curve.
Where the hydraulic scaling curve cuts the original characteristic gives a scaled duty point
(Q1, H1) and thence the ratio of pump speeds from either the ratio of discharges or the ratio of
heads:
1
2
1
2
Q
Q
N
N
or
1
2
2
1
2
H
H
N
N
Example.
Water from a well is pumped by a centrifugal pump which delivers water to a reservoir in
which the water level is 15.0 m above that in the sump. When the pump speed is 1200 rpm its
pipework has the following characteristics:
Pipework characteristics:
Discharge (L s–1
): 20 30 40 50 60
Head loss in pipework (m): 1.38 3.11 5.52 8.63 12.40
Pump characteristics:
Discharge (L s–1
): 0 10 20 30 40
Head (m): 22.0 21.5 20.4 19.0 17.4
A variable-speed motor drives the pump.
(a) Plot the graphs of the system and pump characteristics and determine the discharge at
a speed of 1200 rpm.
(b) Find the pump speed in rpm if the discharge is increased to 40 L s–1
.
Answer: (a) 32 L s–1
; (b) 1290 rpm
Q
Systemcharacteristic
Newduty point
Hs
N1
N2
Scaling curve
through
duty point
H
),( 22 HQ
),( 11 HQ
13. Hydraulics 2 T4-13 David Apsley
4.3 Specific speed
The specific speed (or type number) is a guide to the type of pump or turbine required for a
particular role.
4.3.1 Specific Speed for Pumps
The specific speed, Ns, is the rotational speed needed to discharge 1 unit of flow against 1 unit
of head. (For what “unit” means in this instance, see below.)
For a given pump, the hydraulic scaling laws give
constant
ND
Q
31Π , constant
DN
gH
222Π
Eliminating D (and choosing an exponent that will make the combination proportional to N):
4/3
2/1
4/1
3
2
2
1
)(Π
Π
gH
NQ
or, since g is constant, then at any given (e.g. maximum) efficiency:
constantldimensiona
H
NQ
)(4/3
2/1
The constant is the specific speed, Ns, when Q and H in specified units (see below) are
numerically equal to 1:
Specific speed (pump)
4/3
2/1
H
NQ
NS
Notes.
The specific speed is a single value calculated at the normal operating point (i.e. Q
and H at the maximum efficiency point for the anticipated rotation rate N).
With the commonest definition (in the UK and Europe), N is in rpm, Q in m3
s–1
, H in
m, but this is far from universal, so be careful.
In principle, the units of Ns are the same as those of N, which doesn’t look correct
from the definition but only because that has been shortened from
4/3
2/1
4/3
2/113
)m1(
)sm1(
H
NQNs
Because of the omission of g the definition of Ns depends on the units of Q and H. A
less-common (but, IMHO, more mathematically correct) quantity is the dimensionless
specific speed Kn given by
4/3
2/1
)(gH
NQ
Kn
If the time units are consistent then Kn has the same angular units as N (rev or rad).
High specific speed ↔ large discharge / small head (axial-flow device).
14. Hydraulics 2 T4-14 David Apsley
Low specific speed ↔ small discharge / large head (centrifugal device).
Approximate ranges of Ns are (from Hamill, 2011):
Type Ns
Radial (centrifugal) 10 – 70 large head
Mixed flow 70 – 170
Axial > 110 small head
Example.
A pump is needed to operate at 3000 rpm (i.e. 50 Hz) with a head of 6 m and a discharge of
0.2 m3
s–1
. By calculating the specific speed, determine what sort of pump is required.
Answer: Ns = 350; axial-flow pump
4.3.2 Specific Speed for Turbines
For turbines the output power, P, is more important than the discharge, Q. The relevant
dimensionless groups are
222Π
DN
gH
, 533
ρ
Π
DN
P
Eliminating D,
4/5
2/1
4/1
5
2
2
3
)(
)ρ/(
Π
Π
gH
NP
or, since ρ and g are usually taken as constant (there does seem to be a presumption that
turbines are always operating in fresh water) then at any given efficiency:
constantldimensiona
H
NP
)(4/5
2/1
The specific speed of a turbine, Ns, is the rotational speed needed to develop 1 unit of power
for a head of 1 unit. (For what “unit” means in this instance, see below.)
Specific speed (turbine)
4/5
2/1
H
NP
NS
Notes.
With the commonest definition (in the UK and Europe), N is in rpm, P in kW (note),
H in m, but, again, this is not a universal convention. As with pumps, the units of Ns
are the same as those of N.
As with pumps, a less-commonly-used but mathematically more acceptable quantity
is the dimensionless specific speed Kn, which retains the ρ and g dependence:
4/5
2/1
)(
)ρ/(
gH
NP
Kn
15. Hydraulics 2 T4-15 David Apsley
Kn has the angular units of N (revs or radians) – see Massey (2005).
High specific speed ↔ small head (axial-flow device)
Low specific speed ↔ large head (centrifugal or impulse device).
Approximate ranges are (from Hamill, 2001):
Type Ns
Pelton wheel (impulse) 12 – 60 very large head
Francis turbine (radial-flow) 60 – 500 large head
Kaplan turbine (axial-flow) 280 – 800 small head
16. Hydraulics 2 T4-16 David Apsley
5. Mechanics of Rotodynamic Devices
5.1 Centrifugal Pump
Fluid enters at the eye of the impeller and flows
outward. As it does so it picks up the tangential
velocity of the impeller vanes (or blades) which
increases linearly with radius (u = rω). At exit the
fluid is expelled nearly tangentially at high velocity
(with kinetic energy subsequently converted to
pressure energy in the expanding volute). At the
same time fluid is sucked in through the inlet to take
its place and maintain continuous flow.
The analysis makes use of rotational dynamics:
power = torque angular velocity
torque = rate of change of angular momentum
where angular momentum is given by “(tangential) momentum radius”.
The absolute velocity of the fluid is the vector sum of:
impeller velocity (tangential)
+
velocity relative to the impeller (parallel to the vanes)
Write:
u for the impeller velocity (u = rω)
w for the fluid velocity relative to the impeller
v = u + w for the absolute velocity
The radial component of absolute velocity is determined primarily
by the flow rate:
A
Q
vr
where A is the effective outlet area. The tangential part (also called
the whirl velocity) is a combination of impeller speed (u = rω) and
tangential component relative to the vanes:
βcoswuvt
Only vt contributes to the angular momentum.
With subscripts 1 and 2 denoting inlet and outlet respectively,
)(ρ 1122 rvrvQTtorque tt
)ωω(ρω 1122 rvrvQTpower tt
But head
gQ
power
H
ρ
, whilst ur ω . Hence:
Euler’s turbomachinery equation:
)(
1
1122 uvuv
g
H tt
2w
2β 1w
ω22 ru
ω11 ru
Vane
v,Resultant
w β
ωru
v
tv
rv
17. Hydraulics 2 T4-17 David Apsley
The pump is usually designed so that the initial angular momentum is small; i.e. vt1 ≈ 0. Then
22
1
uv
g
H t
Effect of Blade Angle
Because in the frame of the impeller the fluid leaves the blades in a direction parallel to their
surface, forward-facing blades would be expected to increase the whirl velocity vt whilst
backward-facing blades would diminish it.
Tangential and radial components of velocity:
A
Q
wvr βsin , βcoswuvt ,
Eliminating w:
βcot
A
Q
uvt
Hence, if inlet whirl can be ignored,
)βcot( 2
2
A
Q
u
g
u
H
This is of the form bQaH , where
H initially decreases with Q for backward-facing blades (β < 90°; cot β > 0)
H initially increases with Q for forward-facing blades (β > 90°; cot β < 0)
This gives rise to the typical pump characteristics shown. Of the two, the former (backward-
facing blades) is usually preferred because, although forward-facing blades might be
expected to increase whirl velocity and hence output head, the shape of the characteristic is
such that small changes in head cause large changes in discharge and the pump tends to
“hunt” for its operating point (pump surge).
Non-Ideal Behaviour
The above is a very ideal analysis. There are many sources of losses. These include:
leakage back from the high-pressure volute to the low-pressure impeller eye;
frictional losses;
“shock” or flow-separation losses at entry;
non-uniform flow at inlet and outlet of the impeller;
cavitation (when the inlet pressure is small).
Example.
A centrifugal pump is required to provide a head of 40 m. The impeller has outlet diameter
0.5 m and inlet diameter 0.25 m and rotates at 1500 rpm. The flow approaches the impeller
radially at 10 m s–1
and the radial velocity falls off as the reciprocal of the radius. Calculate
the required vane angle at the outlet of the impeller.
Answer: 9.7°
Q
H
90β
90β
90β
(backward-facing blades)
(forward-facing blades)
18. Hydraulics 2 T4-18 David Apsley
5.2 Pelton Wheel
A Pelton wheel is the most common type of impulse turbine. One
or more jets of water impinge on buckets arranged around a
turbine runner. The deflection of water changes its momentum
and imparts a force to rotate the runner.
The power (per jet) P is given by:
power = force (on bucket) velocity (of bucket)
Force F on the bucket is equal and opposite to that on the jet; by the momentum principle:
velocityinchangefluxmassfluidonforce )(
Because the absolute velocity of water leaving the bucket is the vector resultant of the runner
velocity (u) and the velocity relative to the bucket, the change in velocity is most easily
established in the frame of reference of the moving bucket.
Assuming that the relative velocity leaving the buckets
is k times the relative velocity of approach, v – u (where
k is slightly less than 1.0 due to friction):
)θcos1)((
)(θcos)(
kuv
uvuvkx-velocitychange in
where θ is the total angle turned (here, greater than 90°). The maximum force would be
obtained if the flow was turned through 180°, but the necessity of deflecting it clear of the
next bucket means that θ is typically 165°.
From the momentum principle:
)θcos1)((ρ kuvQF
The power transferred in each jet is then
)θcos1()(ρ kuuvQFuP
The velocity part of the power may be written
2
2
12
4
1
)()( uvvuuv
Hence, for a given jet (Q and v), the power is a maximum when the runner speed u is such
that vu 2
1 , or the runner speed is half the jet speed. (At this point the absolute velocity
leaving the runner at 180° would be 0 if k = 1, corresponding to a case where all the kinetic
energy of the fluid is transferred to the runner.) In practice, the runner speed u is often fixed
by the need to synchronise the generator to the electricity grid, so it is usually the jet which is
controlled (by a spear valve). Because of other losses the speed ratio is usually slightly less
than ½, a typical value being 0.46.
The jet velocity is given by Bernoulli’s equation, with a correction for non-ideal flow:
gHcv v 2
where H is the head upstream of the nozzle (= gross head minus any losses in the pipeline)
and cv is an orifice coefficient with typical values in the range 0.97– 0.99.
bucket
jet u
v
k(v-u)
v-u
19. Hydraulics 2 T4-19 David Apsley
Example.
In a Pelton wheel, 6 jets of water, each with a diameter of 75 mm and carrying a discharge of
0.15 m3
s–1
impinge on buckets arranged around a 1.5 m diameter Pelton wheel rotating at
180 rpm. The water is turned through 165° by each bucket and leaves with 90% of the
original relative velocity. Neglecting mechanical and electrical losses within the turbine,
calculate the power output.
Answer: 471 kW
6. Cavitation
Cavitation is the formation, growth and rapid collapse of vapour bubbles in flowing liquids.
Bubbles form at low pressures when the absolute pressure drops to the vapour pressure and
the liquid spontaneously boils. (Bubbles may also arise from dissolved gases coming out of
solution.) When the bubbles are swept into higher-pressure regions they collapse very
rapidly, with large radial velocities and enormous short-term pressures. The problem is
particularly acute at solid surfaces.
Cavitation may cause performance loss, vibration, noise, surface pitting and, occasionally,
major structural damage. Besides the inlet to pumps the phenomenon is prevalent in marine-
current turbines, ship and submarine propellers and on reservoir spillways.
The best way of preventing cavitation in a pump is to ensure that the inlet (suction) pressure
is not too low. The net positive suction head (NPSH) is the difference between the pressure
head at inlet and that corresponding to the vapour pressure:
g
pp cavinlet
ρ
NPSH
The net positive suction head must be kept well above
zero to allow for further pressure loss in the impeller.
The inlet pressure may be determined from Bernoulli:
lossheadHH sumpinletpump
f
atm
inlet
inlet
h
g
p
g
V
z
g
p
ρ2ρ
2
Hence,
finlet
atminlet
h
g
V
z
g
p
g
p
2ρρ
2
To avoid cavitation one should aim to keep pinlet as large as possible by:
keeping zinlet small or, better still, negative (i.e. below the level of water in the sump;
keeping V small (large-diameter pipes);
keeping hf small (short, large-diameter pipes).
The first also assists in pump priming.
Sump
pump inlet
zinlet
patm