Technology & Engineering
Mechanical Efficiency
Mechanical efficiency refers to the ratio of useful work output to the total energy input in a mechanical system. It measures how well a machine converts input energy into useful output work, taking into account factors such as friction and heat loss. High mechanical efficiency indicates minimal energy wastage, making it a key consideration in the design and performance evaluation of mechanical systems.
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5 Key excerpts on "Mechanical Efficiency"
eBook - PDFEnergy and Society
An Introduction, Second Edition
- Harold H. Schobert(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
In modern terminology, we would refer to the amount of work done per amount of fuel consumed as the efficiency of the engine. In broad terms, engineering efficiency is defined as the ratio of the output to input: Efficiency = output/input * It might be argued that, if steam engines were being used to pump water from coal mines, the coal would be free too, because it was available right there on the job site. However, coal consumed by the engines operating the pumps represented coal that could not be sold to customers. Such internal con-sumption of coal also represented a financial burden to the mining company, because it reduced the income from the sale of coal. † In British units, a bushel is a measure of volume, sometimes still used for selling farm products, such as a bushel of apples. A bushel is equivalent to about 36 liters. The weight of coal that could be packed into a bushel container depends on the size of coal particles, so that a large weight of pebble-sized pieces of coal could make up a bushel, but a lesser weight of football-sized pieces. 148 Energy and Society The ratio can be expressed in terms of any convenient engineering parameter, such as energy, raw materials and products, money flow, or the use of time. At first the steam engine, and earlier atmospheric engines, had been simply a means of raising water from coal mines. These early engines were being continually improved by hunches, trial and error, and tinkering. The science of steam engines was developed only later. (It comes, as we shall see in the following text, in part from the study of the behavior of gases by the French physicists Charles and Gay-Lussac.) The relation-ship between science and technological development is complicated. Sometimes use-ful, functioning devices are invented and improved with little understanding of their underlying scientific principles.
- Alexander V. Dimitrov(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
2Conversion of Thermal Energy into Mechanical Work (Thermal Engines)Energy-related (power) technologies may be treated as a combination of engineering-technical methods of energy and work conversion employed to facilitate human life. They are divided into two main groups. The first group comprises technologies of heat conversion into another type of energy (mechanical, electrical, electromagnetic, etc.) while the second one comprises technologies of heat transfer, accumulation, and regeneration. Each thermal technology discussed herein will be illustrated by specific physical schemes and devices. We shall consider them in the following order:•Technologies of mechanical work performance (so called thermomechanical technologies) •Technologies of generation of electrical energy (thermoelectric technologies) •Technologies of heat transformation (regeneration and recuperation) •Technologies of heat transfer and collection (transfer and accumulation) •Technologies creating comfortable environment (air conditioning and ventilation)Thus, we will treat a certain technology as an object of study of respective scientific-applied research fields, on one hand, and we will follow the teaching programs on “Power engineering,” “Transport management” and “General mechanical engineering,” on the other hand.2.1 Evolution of Engine TechnologiesAs is known from physics, energy conversion follows a natural course, that is, energy of motion of macro- and microbodies (popular as mechanical energy) is converted into heat by mechanisms that are studied by tribology (including dry, semi-dry, viscous, or turbulent friction). No opposite transformation is observed in nature. Heat conversion into energy needed for the operation of machines and mechanisms was an impossible task for primitive people as well as for those living in slave-holding* and feudal†
eBook - PDFEngine Testing
Theory and Practice
- A. J. Martyr, M.A. PLINT(Authors)
- 2011(Publication Date)
- Butterworth-Heinemann(Publisher)
It is a curious fact that, in the long run, all the power developed by all the road vehicle engines in the world is dissipated as friction: either mechanical friction in the engine and transmission, rolling resistance between vehicle and road or wind resistance. Mechanical Efficiency, a measure of friction losses in the engine, is thus an important topic in engine development and therefore engine testing. It may exceed 80 per cent at high power outputs, but is generally lower and is of course zero when the engine is idling. Under mixed driving conditions for a passenger vehicle between one third and one half of the power developed in the cylinders is dissipated either as mechanical friction in the engine, in driving the auxiliaries such as alternator and fan, or as pumping losses in the induction and exhaust tracts. Since the improvement of Mechanical Efficiency is such an important goal to engine and lubricant manufacturers, an accurate measure of mechanical losses is of prime importance. In fact the precise measurement of these losses is a particularly difficult problem, to which no completely satisfactory solution exists. Fundamentals The starting point in any investigation of mechanical losses should ideally be a precise knowledge of the power developed in the engine cylinder. This is represented by the indicator diagram, Fig. 13.7, which shows the relation between the pressure of the gas in the cylinder and the piston stroke or swept volume (also see Chapter 14). For a four-stroke engine, account must be taken of both the positive area A 1 , representing the work done on the piston during the compression and expansion strokes, and Thermal efficiency, measurement of heat and mechanical losses 277 p p 0 V c V s A 2 A 1 V 1 4 3 2 Figure 13.7 Indicator diagram, four-stroke engine.
eBook - PDF- Donald F. Elger, Barbara A. LeBret, Clayton T. Crowe, John A. Roberson(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Chapter 7: The Energy Equation 260 7.5 Mechanical Efficiency Figure 7.6 shows an electric motor connected to a centrifugal pump. Motors, pumps, turbines, and similar devices have energy losses. In pumps and turbines, energy losses are caused by fac- tors such as mechanical friction, viscous dissipation, and leakage. Energy losses are accounted for by using efficiency. Mechanical Efficiency is defined as the ratio of power output to power input: η ≡ power output from a machine or system _________________________________ power input to a machine or system = P output _ P input (7.32) The symbol for Mechanical Efficiency is the Greek letter η, which is pronounced as “eta.” In addition to Mechanical Efficiency, engineers use thermal efficiency, which is defined using ther- mal energy input into a system. In this text, only Mechanical Efficiency is used, and we some- times use the label “efficiency” instead of “Mechanical Efficiency.” EXAMPLE Suppose an electric motor like the one shown in Fig. 7.6 is drawing 1000 W of electrical power from a wall circuit. As shown in Fig. 7.7, the motor provides 750 J/s of power to its output shaft. This power drives the pump, and the pump supplies 450 J/s to the fluid. FIGURE 7.6 CAD drawing of a centrifugal pump and electric motor. (Image courtesy of Ted Kyte; www.ted-kyte.com.) Physics: The head provided by the pump (67.3 m) is balanced by the increase in pressure head (42.3 m) plus the increase in elevation head (20 m) plus the head loss (5 m). 4. Power equation: P = γQ h p = (9810 N / m 3 ) (1.0 m 3 / s) (67.3 m) = 660.2 kW = (660.2 kW) ( 1.0 hp _ 0.746 kW ) = 885 hp Review the Solution and the Process Discussion. The calculated power represents the work/time being done by the pump impeller on the water. The electrical power supplied to the pump would need to be larger than this because of energy losses in the electrical motor and because the pump itself is not 100% efficient.
eBook - PDF- Roderick A. Macleod, Jim Corlett, Roderick A. Macleod, Jim Corlett(Authors)
- 2012(Publication Date)
- De Gruyter Saur(Publisher)
23 Mechanical Engineering Michael Richards The purpose of offering information sources is twofold: to provide students, practitioners, librarians and information scientists with the necessary contacts to obtain the information they require; and to equip them with enough details to establish a physical working library of any size or depth. While this is an enormous task with even small subject areas, mechanical engineering offers its own particular set of questions and ambiguities -mainly in the area of definitions. Mechanical engineering, succinctly defined by James (1998), is the 'process, skills and technology used to achieve optimised >metamorphosis= of materials into components, machines and structures'. Thus, in engi-neering terms, anything - and everything - manmade, whatever its degree of sophistication, can healthily be argued to come under the heading of mechanical engineering. Even if the notion of machinery, defined by The Oxford Shorter Dictionary as 'an apparatus for applying mechanical power, consisting of a number of parts, each having a definite function', is introduced to reduce this universal manufactory warehouse, none of its components is actually obsoleted. Gloriously, the history of mechanical engineering traces the history and evolution of the human race. Clearly, for our present purpose, such a broad perspective will not do, even before considering concepts such as fuel, energy, control, power and heat, so definitions provided by EEVL; the Internet guide to engi-neering, mathematics and computing (www.eevl.ac.uk/engineering/ engsubjectguide.htm) are largely followed. • Mechanical engineering: mechanics, design, drives and transmission, lubricants and lubrication, measuring instruments. • A u t o m o t i v e engineering: automotive engines, buses, tractors, trucks. • C o n t r o l engineering: automatic control principles, applications, devices.
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