Physics
Efficiency in Physics
Efficiency in physics refers to the ratio of useful work output to the total energy input. It is a measure of how well a system or process converts input energy into useful output. In physics, efficiency is often quantified using the formula: Efficiency = (useful energy output / total energy input) x 100%.
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4 Key excerpts on "Efficiency in Physics"
- Prof. Olav Bolland, Prof. Lars O. Nord(Authors)
- 2020(Publication Date)
- Wiley-VCH(Publisher)
7 Power Plant Efficiency CalculationsThere is diversity in the methodology for calculating power plant efficiencies, which causes a lot of uncertainty when comparing plant options. Several terms are used inconsistently, and often with a lack of definition, for the term efficiency. Terms such as ‘efficiency’, ‘thermal efficiency’, ‘cycle efficiency’, ‘process efficiency’, ‘net/gross efficiency’, ‘net plant efficiency’, ‘electrical efficiency’, ‘total efficiency’, ‘exergy efficiency’, ‘second law efficiency’, ‘fuel efficiency’, and ‘fuel utilisation’ are used, some of them are interchangeable. In addition, many publications dealing with efficiencies give insufficient information about the computational assumptions, e.g. pressure drop, heat loss, temperature differences, and component efficiencies. Further, different software is used with various thermodynamic property models. The definition of system boundaries is often omitted. The diversity observed in efficiency calculation methods is not peculiar to power plants with CO2 capture but can be observed for energy conversion process analysis in general. In the following, an attempt is made to clarify efficiency calculations.7.1 General Definition of Efficiency
Efficiency is the ratio between two energy quantities: the numerator being the energy product of the process and the denominator being the energy input to the process.The energy product from a power plant is the power (or electricity) being delivered at a given boundary. It may also be both power and heat in the case of a cogeneration plant. When there is more than one energy product, the efficiency often becomes confusing, as energy products of different thermodynamics and economic values are added together. In some cases, one of the products of the process may be a substance, such as hydrogen or methanol.The energy input
- Lucien Borel, Daniel Favrat(Authors)
- 2010(Publication Date)
- PPUR(Publisher)
402 Thermodynamics and Energy Systems Analysis: from Energy to Exergy in which is the transformation energy received in the network n: (10.10) Particular cases 10.1.2 Effectiveness (or First Law efficiency) Definition Considering that the energy balance (10.7) expresses the conservation of energy, it is in principle inadequate to highlight the notion of thermodynamic loss. In general, the manipulation of a system always consists of receiving energy in one form or another as well as giving it in one form or another. Strictly speaking, the result of this is that the correct definition of “thermal efficiency” must approach a value of 1, i.e., 100 % – a value which in and of itself is, of course, of no interest. We know, however, that in practice it is opportune to define characteristic num- bers that can be used to express an interesting property of the considered system. In a general way, we denote by effectiveness the ratio between the useful energy and the used or dispensed energy. It is not possible to give a general definition for this ratio since the concept of usefulness and used vary from case to case. However, it is generally admitted that, considering the fact that it has no inter- est for the practitioner, the heat energy Q a transferred between the system and the atmosphere can neither be considered as an energy service received nor given by the system. This is why the term Q a will not be taken into account in the various formu- lations of the effectiveness. In other words, it has no value when we provide it and it The introduction of the concept of transformation energy is of great interest as it permits the inclusion in a single theory of closed systems, steady-state open sys- tems and non steady-state open systems.
- Efstathios Michaelides(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
They are ratios of variables associated with energy or power and have a specific meaning for those who defined and use them. For example, the thermal efficiency of the cyclic engines, defined in Eq. (1.24), represents a benefit-cost ratio for thermal power plants: the numerator, W, is a measure of the revenue derived by the sale of electricity and the denominator, Q H , is a measure of the cost of the fuel. Improving the efficiency of the cycle always increases the benefit-cost ratio for the thermal power plant. The efficiency (coefficient of per- formance) of refrigeration systems, defined in Eq. (1.31), is also a benefit (the coolness effect) to cost (electricity input) ratio. All the efficiency expressions in Eqs. (1.24)–(1.32) represent benefit/cost ratios for the operators of the engines. A characteristic of these expressions is the usage of heat and work, quantities related to the first law of thermodynamics. These efficiencies are referred to as the first law efficiencies. Exergy represents the maximum work and power and one may use these maxima as the benchmark for processes and systems and define the ratios: W act E and W act _ E , as figures of merit for the operation of engines. These figures of merit signify how closely the operation of the system/engine is to producing maximum work or power. The figures of merit, which are based on exergy – and, therefore, make use of the first and second laws of thermodynamics – are called exergetic efficiency. The term utiliza- tion factor has also been used in the past [1, 3], but the use of this term has faded. In general, the exergetic efficiency of any system is defined as: 7 η II Sum of all work and exergies leaving Sum of all work and exergies entering : (2.58) For simple closed and open systems that only produce work or power, Eq. (2.58) may be expressed as follows: 7 A few authors have used the symbol ε for exergetic efficiency.
eBook - ePubEnergy and Society
An Introduction, Second Edition
- Harold H. Schobert(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
low, respectively.The pool of water at the bottom of the waterfall still had some ENERGY . Analogously, the cold side of the steam engine still contains heat. Conceptually, more WORK could be extracted from the water in the pool until all the available gravitational potential energy of the water was used up—until we had reached the center of the Earth, which is the zero point of gravitational energy. Quite similarly, suppose that the condenser on a steam engine is at, say, 25°C. The water produced in the condenser could, in principle, be cooled further and further, until we reached a point at which no more work could be extracted from it. This point would be the temperature analog of the center of the Earth, the zero point of potential energy below which it is impossible to go. In a thermal system, this zero point of energy is the temperature called absolute zero. The total energy of the thermal system would be represented by the difference between the temperature of the hot side and absolute zero: Th − 0, or, simply Th .The heat engine efficiency is a measure of the ENERGY that can be converted to WORK as a fraction of the total ENERGY . This concept can be expressed mathematically in an equation for calculating efficiency:η =()T h−T 1T hUsing this equation, the numerical value of efficiency will be a fraction having a value between 0 and 1. Often it is more convenient or easier to express efficiency as a percentage, rather than as a fraction. This is done readily by using the comparable formula:% η = 100()T h−T 1T hIn this case, efficiency has a value between 0% and 100%. The equations are equivalent and provide the same information; the difference is whether the calculated efficiency is expressed as a fraction or as a percentage. However, there is one crucial fact in the use of efficiency calculations: these equations only provide the correct answer if the temperature is expressed in kelvins
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