Efficiency (redirected from Effeciency)

efficiency.

1 In business and industry, see industrial management; productivity.

2 In physics, seemachine; work.

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efficiency

 or mechanical efficiency

In mechanics, the measure of the effectiveness with which a system performs. It is stated as the ratio of a system's work output to its work input. The efficiency of a real system is always less than 1 because of friction between moving parts. A machine with an efficiency of 0.8 returns 80% of the work input as work output; the remaining 20% is used to overcome friction. In a theoretically frictionless, or ideal, machine, the work input and work output are equal, and the efficiency would be 1, or 100%.

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efficiency [ə′fish·ən·sē]

Abbreviated eff.

(chemistry)

In an ion-exchange system, a measurement of the effectiveness of a system expressed as the amount of regenerant required to remove a given unit of adsorbed material.

(engineering)

Measure of the degree of heat output per unit of fuel when all available oxidizable materials in the fuel have been burned.

Ratio of useful energy provided by a dynamic system to the energy supplied to it during a specific period of operation.

(nucleonics)

The probability that a count will be produced in a counter tube by a specified particle or quantum incident.

(physics)

The ratio, usually expressed as a percentage, of the useful power output to the power input of a device.

(statistics)

An estimator is more efficient than another if it has a smaller variance.

An experimental design is more efficient than another if the same level of precision can be obtained in less time or with less cost.

(thermodynamics)

The ratio of the work done by a heat engine to the heat energy absorbed by it. Also known as thermal efficiency.

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Efficiency

The ratio, expressed as a percentage, of the output to the input of power (energy or work per unit time). As is common in engineering, this concept is defined precisely and made measurable. Thus, a gear transmission is 97% efficient when the useful energy output is 97% of the input, the other 3% being lost as heat due to friction. A boiler is 75% efficient when its product (steam) contains 75% of the heat theoretically contained in the fuel consumed. All automobile engines have low efficiency (below 30%) because of the total energy content of fuel converted to heat; only a portion provides motive power, while a substantial amount is lost in radiator and car exhaust.

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Efficiency 

a parameter characterizing the effectiveness of a system, device, or machine in converting or transmitting energy; it is defined as the ratio of the usefully consumed energy to the total energy received by a system. It is usually denoted as η = W_use/ W_tot- In electric motors the efficiency is the ratio of the mechanical work (useful work) performed to the electric power received from a source; in heat engines it is the ratio of the useful mechanical work to the amount of heat expended; in electric transformers it is the ratio of the electromagnetic energy produced in the secondary winding to the energy consumed by the primary winding.

In calculating efficiency, various forms of energy and mechanical work are expressed in the same units based on the mechanical equivalent of heat and other similar relationships. Because of its generality the concept of efficiency makes possible the comparison and evaluation of such dissimilar systems as atomic reactors, electric generators and motors, steam power plants, semiconductor devices, and biological substances from a single point of view.

Because of the unavoidable energy losses caused by friction, heating of surrounding bodies, and so on, the efficiency is always less than 1. Therefore, it is expressed in fractions of the energy consumed—that is, in the form of a proper fraction or percentages—and is a dimensionless quantity. The efficiency of steam power plants reaches 35-40 percent; that of internal-combustion engines, 40-50 percent; that of high-power dynamos and generators, up to 95 percent; and that of transformers, up to 98 percent. The efficiency of the process of photosynthesis is usually 6-8 percent; and for chlorella it attains 20-25 percent. By virtue of the second law of thermodynamics the upper limit of the efficiency of heat engines is determined by the characteristics of the thermodynamic cycle (a cyclic process) performed by the working substance. The Carnot cycle has the highest efficiency.

A distinction is made between the efficiency of one stage of a machine or installation and the efficiency that characterizes the entire energy conversion chain in a system. Efficiency of the first type may be mechanical, thermal, and so on, depending on the nature of the energy conversion. The second type includes the total, economic, and technical forms of efficiency. The total efficiency of a system is equal to the product of the partial or stage efficiencies.

In the technical literature efficiency is sometimes defined in such a manner that it can be greater than 1. Such a situation occurs if, in the determination of efficiency by means of the ratio W_use/W_con, the term W_use is the useful energy obtained at the “output” of a system and W_con is not all the energy put into the system but rather only the part that brings about the actual consumption. For example, during the operation of semiconductor thermoelectric heaters (heat pumps) the consumption of electric power is less than the amount of heat produced by the thermoelement. The excess energy is drawn from the environment. In this case, although the true efficiency is less than 1, the efficiency in question ö = W_use/W_con can be greater than 1.

REFERENCES

Artobolevskii, I. I. Teoriia mekhanizmov i mashin, 2nd ed. Moscow-Leningrad, 1952.
Obshchaia teplotekhnika, 2nd ed. Edited by S. la. Kornitskii and la. M. Rubinshtein. Moscow-Leningrad, 1952.
Obshchaia elektrotekhnika. Moscow-Leningrad, 1951.
Vukalovich, M. P., and I. I. Novikov. Tekhnicheskaia termodinamika, 4th ed. Moscow, 1968.