efficiency(redirected from Effeciency)
Also found in: Dictionary, Thesaurus, Medical, Legal, Financial.
efficiency.1 In business and industry, see industrial managementindustrial management,
term applied to highly organized modern methods of carrying on industrial, especially manufacturing, operations. The Rise of Factories
..... Click the link for more information. ; productivityproductivity,
in economics, the output of any aspect of production per unit of input. It is a measure of the output of a worker, machine, or an entire national economy in the creation of goods and services to produce wealth.
..... Click the link for more information. . 2 In physics, seemachinemachine,
arrangement of moving and stationary mechanical parts used to perform some useful work or to provide transportation. From a historical perspective, many of the first machines were the result of human efforts to improve war-making capabilities; the term engineer
..... Click the link for more information. ; workwork,
in physics and mechanics, transfer of energy by a force acting to displace a body. Work is equal to the product of the force and the distance through which it produces movement.
..... Click the link for more information. .
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 = Wuse/ Wtot- 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 Wuse/Wcon, the term Wuse is the useful energy obtained at the “output” of a system and Wcon 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 = Wuse/Wcon can be greater than 1.
REFERENCESArtobolevskii, 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.
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.