Technology & Engineering
Fluid Pumps
Fluid pumps are devices used to move liquids or gases by increasing the fluid's pressure. They are commonly used in various applications, including industrial, commercial, and residential settings. Fluid pumps come in different types, such as centrifugal pumps, positive displacement pumps, and axial flow pumps, each designed for specific fluid-handling needs.
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5 Key excerpts on "Fluid Pumps"
eBook - PDF- Carl J. Schaschke(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
99 5 Pumps Introduction The transport or movement of fluids from one place to another presents a number of challenges depending on the physical properties of the fluid, the volume and pressure to be transported, and other environmental require-ments. Numerous means of transporting have been devised over the cen-turies. From ancient times, water has been raised from wells using buckets and other containers including sacks or bags made from animal skin in which the rate of water raised is dependent on the volume of the sack and the frequency of fill and lift which operates using rope haulage or a balanced fulcrum (Figure 5.1). The Archimedes’ screw is another ancient mechani-cal invention devised for transferring water from a low-lying body of water into elevated irrigation ditches. It is attributed to the Greek mathematician and philosopher Archimedes (287–212 BC) on his visit to Egypt. Today, more sophisticated machines have been invented that can transport a wide variety of fluids from gases to highly viscous and non-Newtonian fluids. The two major types of fluid-transfer machines or pumps are classified as being positive-displacement for bulk handling or metering, and nonposi-tive displacement pumps, which are also known as rotodynamic pumps (Figure 5.2). Rotodynamic pumps, which include centrifugal and axial pumps, operate by developing a high liquid velocity (kinetic energy) and converting it to pressure. To produce high rates of discharge, such pumps tend to operate at high speeds, although their optimal efficiency is often lim-ited to a narrow range of delivered flows. Positive displacement pumps operate by drawing liquid into a chamber or cylinder by the action of a piston with the liquid being discharged in the required direction by the use of check valves. This results in a pulsed flow. Positive displacement pumps are, however, capable of delivering significantly higher heads than rotodynamic pumps.
- Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
18 Fluid Machinery Chapter Objectives • To describe the various types of fluid machines. • To provide the theoretical considerations for centrifugal pumps. • To discuss the problem of cavitation and the use of the net positive suction head. • To show how the performance of a system is matched to the performance of a centrifugal pump the system contains. • To derive the scaling laws for pumps and fans. • To discuss axial and mixed flow pumps and turbines. 18.1 Introduction The term fluid machinery is commonly used to categorize mechanical devices that exchange fluid energy and mechanical work. When mechanical energy is applied to a fluid, producing flow or higher pressure—or both, the machine is a pump . When the reverse is true, and fluid energy drives the machine to produce mechanical work, we call the machine a turbine . There are two principal types of fluid machines, positive displacement machines and turbo machines. In a positive displacement machine, a fluid is confined in a chamber whose volume is varied. The human heart and a bicycle tire pump are both positive displacement pumps. Examples of such devices are shown in Figure 18.1. Turbo machines involve rotary motion as the name implies. Window fans and aircraft propellers are examples of unshrouded turbo machines. Pumps used with liquids generally have a shroud that surrounds the impeller and thus contains and guides the flow. Two categories of pumps are shown in Figure 18.2, the radial flow pump and the axial flow pump. The designations radial and axial refer to the direction of flow relative to the axis of rotation of the blades. The term pump is generally used with flows of liquids. When a gas or vapor is the fluid of interest, the following terms apply: • Fans , which are generally associated with relatively low pressure changes with P in the neighborhood of 35-cm H 2 O (1/2 psi). • Blowers , which are in positive and variable displacement configurations with P up to 2.8-m H 2 O (40 psi). 563
eBook - PDF- William Graebel(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
These pumps are sometimes used as electrically driven automotive fuel pumps. The gear-, or lobe-, type of positive displacement pump consists of two counterrotating gears, or lobes, which trap the fluid and carry it through the pumps. These pumps have the advantage of being self-priming, but are easily injured by suspended grit. The screw-type positive displacement pump, frequently referred to as an Archimedes screw, consists of a helical screw inclined at an angle with the horizontal, usually between 30 and 40°. The angle of the inclination is less than 547 the helix angle of the screw, so admitted fluid always is running downhill. These pumps typically run at very low speeds, but are capable of very high efficiencies, and can be made in very large diameters. A typical head would be less than 10 ft. A simple example of a reciprocating pump is the manually operated bucket pump, seen in Figure 11.10. On the upstroke, the piston reduces the chamber pressure closing the piston check valve, and fluid is drawn in through the check valve at the bottom of the pump. On the downstroke, the bottom check valve closes, and the fluid is forced through the piston check valve. Such pumps are not self-priming, but can lift fluids approximately 2/3 of an atmosphere. A variation of this pump is the diaphragm pump, sometimes used as a mechanically driven fuel pump in an automobile. 5. Axial Flow Fans and Pumps An axial flow fan or pump (the usual distinction is that a fan handles gas, while a pump handles liquid) is fundamentally one or more propellers in a duct, casing, or shroud. The term axial means that the flow is substantially parallel to the axis of the impeller. It can be used as a pump to transport fluid, or it can provide a thrust for propulsive purposes. The casing allows a static pressure to develop. There are usually fixed or moveable (variable pitch) vanes that keep the flow direction axial.
eBook - PDF- DENNIS A SNOW(Author)
- 2013(Publication Date)
- Newnes(Publisher)
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 18.1. 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. 18.2 Pump principles 18.2.1 Rotodynamic pumps Taking a typical centrifugal pump (Figure 18.2) the Euler equation can be written, at best efficiency flow, in the form gH = u \ - ~ M cot ^2 (18.1) where u 2 = oeD 2 /2, A 2 = nD 2 b 2 , Q is flow rate and is head rise. This ignores flow losses, so that actual performance is less than the Euler (Figure 18.3). Figures 18.4-18.6 give typical pump performance curves for a constant driver speed. The inflections in the mixed and axial flow curves are due to flow instability over blades and through impeller passages. The hydraulic efficiency 1h s (18.2) and >7o = or 1o z Hydraulic power Input power IN r IN (18.3) Typical pump cross-sections are shown in Figures 18.7-18.10.
- Robert W. Fox, Alan T. McDonald, John W. Mitchell(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
• Determine the performance of a propeller or wind turbine. • Use the dimensionless parameters to scale compressor performance between operating conditions. Humans have sought to harness the forces of nature to offset human labor nature since antiquity. The first fluid machines developed were bucket wheels and screw pumps to lift water. The Romans introduced paddle wheels around 70 B.C.E. to obtain energy from streams [1]. Later, windmills were developed to harness wind power, but the low power density of the wind limited output to a few hundred horsepower. Development of waterwheels made it possible to extract thousands of horsepower at a single site. Today we take many fluid machines for granted. On a typical day we draw water pressurized by pumps from the tap, drive a car in which Fluid Pumps operate the lubrication, cooling, and power steering systems, and work in a comfortable environment provided lights and cooling systems powered by electricity produced by steam or gas turbines. The list could be extended indefinitely. A fluid machine is a device that either performs work on or extracts work from a fluid. This is a very large field of study, so we will limit ourselves mostly to incompressible flows. First the terminology of the field is introduced and machines are classified by operating principle and physical characteristics. We will focus on machines in which energy transfer to or from the fluid is through a rotating element. Basic equations are reviewed and then simplified to forms useful for analysis of fluid machines. Performance characteristics of typical machines are considered. We will use as examples pump and turbine applica- tions in typical systems and then discuss propellers and wind turbines. A discussion of compressible flow machines concludes the chapter. 10.1 Introduction and Classification of Fluid Machines Fluid machines may be broadly classified as either positive displacement or dynamic.
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