Fluid Pumps

5 Key excerpts on "Fluid Pumps"

• 

  eBook - ePub

  Fluid Mechanics, Hydraulics, Hydrology and Water Resources for Civil Engineers

  • Amithirigala Widhanelage Jayawardena(Author)
  • 2021(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 12 Fluid machinery

  12.1 Introduction

  Fluid machinery can be broadly classified into two types; namely, pumps and turbines. Pumps convert mechanical energy into fluid energy, thereby increasing the energy of the fluid (increase of pressure). Turbines convert the fluid energy into mechanical energy, thereby decreasing the energy of the fluid.

  Compressor is also a pump. Its primary function is to increase the pressure of the gas. Fan and Blower are machines used only for causing the movement of gas.

  12.2 Types of pumps

  There are various types of pumps; some have only historical importance. Examples include.

  12.2.1 Chain or bucket pumps

  This is the simplest type of pump that uses gravity lift. It has a valve which opens when it goes below the water line and closes when lifted above the water line.

  12.2.2 Static or positive displacement pumps

  Positive displacement type functions by changes of the volume occupied by the fluid within the machine. They create an expanding cavity on the suction side and a contracting cavity on the delivery side. The operation of a positive displacement type machine depends only on mechanical and hydrostatic principles. Only a few principles of fluid dynamics are involved. Positive displacement pumps are more suitable for low flow high-pressure situations, and their efficiency is relatively independent of the pressure. They are preferred for moving viscous fluids such as oil, asphalt, etc. There are several types of positive displacement pumps.

  12.2.2.1 Reciprocating type

  They are usually of piston−cylinder combination with inlet and exit valves involving suction and compression. Work done by pump is ∫pdv

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  eBook - ePub

  Food Process Engineering and Technology

  • Zeki Berk(Author)
  • 2018(Publication Date)
  • Academic Press

    (Publisher)

  shaft work , that is, mechanical work, delivered through a shaft) are discussed in this section. One of the nonmechanical devices of widespread industrial application (the ejector) is considered in a subsequent section.

  One of the main engineering characteristics of a pump is the relationship between the volumetric flow rate (capacity) and the total head increment (usually expressed as the increase in pressure). The graphical presentation of this relationship is called a characteristic curve . Characteristic curves usually provide information on additional interrelated values as power, pump efficiency, and net suction pressure (to be defined later).

  One of the important factors of pump performance is the mechanical power required to operate the pump. Theoretically, at a volumetric flow rate Q (m3  s− 1 ), the net energy input to the fluid as its pressure is increased by ΔP (Pa s) is

  W th

  = Q Δ P

    (2.35)

  where W th (W) is the theoretical power requirement.

  The actual power requirement W may be considerably higher than the theoretical value. The ratio of the theoretical to the actual value is the

  mechanical efficiency ηm

  of the pump.

  η m

  =

  W th

  W

    (2.36)

  Pumps are classified into two major groups, namely, kinetic pumps and positive displacement pumps.

  Kinetic pumps : kinetic pumps impart to the fluid a velocity, hence kinetic energy, which is then converted to pressure according to the Bernoulli law. The most widespread type of kinetic pumps is the centrifugal pump . The mode of operation of a centrifugal pump is shown in Fig. 2.12 . The fluid is admitted at the center of the pump housing. A rapidly rotating impeller (rotor) imparts to the fluid a rotational movement at high velocity. The fluid moves in radial direction away from the center to the periphery under the action of centrifugal forces. The velocity is gradually reduced in the volute (the space between the impeller and the pump housing) as the fluid advances from the tip of the impeller toward the pump outlet. Most of the velocity head is converted almost quantitatively to pressure head. The impeller consists of curved vanes. Impellers can be open , semiopen , or closed (or shrouded ) (Fig. 2.13

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  eBook - ePub

  Surface Production Operations: Volume IV: Pumps and Compressors

  • Maurice Stewart(Author)
  • 2018(Publication Date)
  • Gulf Professional Publishing

    (Publisher)

  The engineer must be able to select the proper pump for each application, determine horsepower requirements, design the piping system associated with the pump, and specify materials and details of construction for bearings, seals, and so on. On standard applications the engineer may allow the vendor to specify materials and construction details for the specified service conditions. Even then, the engineer should be familiar with different alternatives so that he or she can better evaluate proposals and alternative proposals of vendors.

  There are a number of factors that should be considered when selecting a pump for a specific application. The primary goal is the same, that is, providing a pump that maximizes company profits (low cost) while providing safe, reliable (trouble free) equipment that satisfies operating requirements and meets local environmental constraints. Selecting the right pump is difficult due to the number of different kinds of pumps available.

  Meeting the primary goal involves optimizing the following primary factors:

  • •  Minimizing the initial pump cost
  • •  Meeting safety and environmental concerns
  • •  Reducing installation and commissioning expenses
  • •  Reducing maintenance expenses
  • •  Maximizing reliability
  • •  Starting up on time
  • •  Maintaining maximum production

  Sound engineering judgment is important when deciding which of the listed factors are the most important.

  2.1.2 Types of fluids

  Pumps are used to move fluids. Fluids include liquids, dissolved gases, and solids. Gases include dissolved air and hydrocarbon vapors. Solids include sand, clay, and scale. Most common types of fluids pumped in upstream operations are water, crude oil, condensate, lube oils, glycols, and amines.

  Each fluid has different physical properties. Physical properties that must be taken into consideration when sizing and selecting a pump are as follows:

  • •  Suction temperature
  • •  Specific gravity
  • •  Viscosity
  • •  Vapor pressure
  • •  Solids content (if predictable)
  • •  Lubricity (slipperiness)

  2.1.3 Pump classification

  A pump can be defined as “as mechanical device that adds energy to a liquid for the purpose of increasing its flow rate and static pressure.” Pumps are divided into two major categories: positive displacement and kinetic energy. These two categories are further divided into numerous subdivisions.

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  eBook - ePub

  Plant Engineer's Handbook

  • R. Keith Mobley(Author)
  • 2001(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  32 Pumps and Pumping

  Keith Turton Loughborough University of Technology

  Contents

  32.1. Pump functions and duties

  32.2. Pump principles

  32.2.1. Rotodynamic pumps

  32.2.2. Scaling laws and specific speed

  32.2.3. Positive displacement pump principles

  32.3. Effects of fluid properties on pump behavior

  32.4. Flow losses in systems

  32.4.1. Friction losses

  32.4.2. Losses in bends, valves and other features

  32.4.3. Presentation of system loss

  32.5. Interaction of pump and system

  32.5.1. Steady-state matching of pump and system

  32.5.2. Flow control

  32.5.3. Multiple-pump layouts

  32.5.4. Suction systems

  32.6. Cavitation

  32.6.1. Net positive suction head (NPSH)

  32.7. Priming systems

  32.8. Seals: selection and care

  32.8.1. Centrifugal pump and rotary pump seal systems

  32.8.2. Reciprocating pump seal systems

  32.9. Pump and drive selection

  32.9.1. Pump selection

  32.9.2. Drive selection

  32.9.3. Economics of pump selection and running maintenance

  32.9.4. Reliability considerations

  32.10. Pump testing

  32.10.1. Factory tests

  32.10.2. Scale-model testing

  32.1 Pump functions and duties

  Pumps impart energy to the liquids being transferred by mechanical means using moving parts. They can be classified as rotodynamic or positive displacement. Rotodynamic pumps cause continuous flow, and the flow rate and discharge pressure are effectively constant with time. Positive displacement pumps deliver fixed quantities at a rate determined by driving speed. The main types of pump commonly used are listed in Figure 32.1 .

  Figure 32.1 Pump family trees

  Pumps are used to transfer liquids, such as moving blood and other biological fluids; delivering measured quantities of chemicals; in firefighting; in irrigation; moving foods and beverages; pumping pharmaceutical and toilet products; in sewage systems; in solids transport; in water supply and in petrochemical and chemical plant. They are utilized in power transfer, braking systems, servomechanisms and control, as well as for site drainage, water-jet cutting, cleaning and descaling. Pumps thus give a wide range of pressure rises and flow rates with pumping liquids that vary widely in viscosity and constituency.

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  eBook - ePub

  Plant Engineer's Reference Book

  • DENNIS A SNOW(Author)
  • 2001(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  20

  Pumps and pumping

  Keith Turton, BSc(Eng), CEng, MIMechE,     Visiting Fellow, School of Mechanical Engineering Cranfield University

  Contents

  Pump functions and duties

  Pump principles

  Rotodynamic pumps Scaling laws and specific speed Positive displacement pump principles

  Effects of fluid properties on pump behaviour

  Flow losses in systems

  Friction losses Losses in bends, valves and other features Presentation of system loss

  Interaction of pump and system

  Steady-state matching of pump and system Flow control Multiple-pump layouts Suction systems

  Cavitation

  Net positive suction head (NPSH)

  Priming systems

  Seals: selection and care

  Centrifugal pump and rotary pump seal systems Reciprocating pump seal systems

  Pump and drive selection

  Pump selection Drive selection The economics of pump selection and running maintenance Reliability considerations

  Pump testing

  Factory tests Scale-model testing

  20.1 Pump functions and duties

  Pumps impart energy to the liquids being transferred by mechanical means using moving parts. They can be classified as rotodynamic or positive displacement. Rotodynamic pumps cause continuous flow, and the flow rate and discharge pressure are effectively constant with time. Positive displacement pumps deliver fixed quantities at a rate determined by driving speed. The main types of pump commonly used are listed in Figure 20.1 .

  Figure 20.1 Pump family trees

  Pumps are used to transfer liquids, moving blood and other biological fluids, delivering measured quantities of chemicals as in dosing in water treatment, in firefighting, in irrigation, moving foods and beverages, pumping pharmaceutical and toilet products, in sewage systems, in solids transport, in water supply and in petrochemical and chemical plant. They are utilized in power transfer, braking systems, servomechanisms and control, as well as for site drainage, water-jet cutting, cleaning and descaling. Pumps thus give a wide range of pressure rises and flow rates with pumping liquids which vary widely in viscosity and constituency.

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