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%.
4 Key excerpts on "Efficiency in Physics"
eBook - ePubAutomotive Electricity
Electric Drives
- Joseph Beretta, Joseph Beretta(Authors)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
...Chapter 2 Basic Definitions 1 2.1. Basic concepts 2.1.1. Basics of automotive energy Most of the energy introduced into a vehicle is lost during transfers (friction, heat, pumping). Manufacturers continue to explore a number of possibilities for reducing these losses. To talk about energetic concepts, we need to talk about efficiency. Efficiency is the ratio of energy used with respect to the work involved in setting the vehicle in motion. It directly affects the consumption: the greater the efficiency, the lower the fuel consumption of the car. – Let us examine how energy in a car is reduced. When energy is introduced into an engine, only 30% remains when it comes to setting the wheels in motion. There are, throughout the process, losses which lower the efficiency. We estimate that 30% of energy is lost in the form of heat from the engine, approximately 30% leaves in the exhaust gas and 10% is dissipated by mechanical friction and driving the accessories (water pump, air-conditioning, etc.). On arrival, the remaining 30% are reduced slightly further by the mechanical efficiency of the gear box and the transmissions. Some of these losses are used to provide other services: the heat released by the cooling system is thus used for heating the cabin, the heat released through the exhaust supports the post-treatment mechanisms. – Each transformation has its own efficiency. The total efficiency of an engine (equal to 0.3 in the best cases) is the relationship between the energy supplied to the crankshaft and the energy supplied by the fuel...
eBook - ePub- Adrian Waygood(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...However, it is thought to have been used in its modern sense only since the beginning of the nineteenth century. ‘ Energy ’ is probably one of the most fundamental concepts in physics, but also one of the hardest to define. In fact, it’s one of those rare scientific terms where it’s very much easier to explain what it does or how it behaves, rather than what it is. That’s why practically all technical dictionaries and textbooks define energy simply as ‘ the ability to do work ’. Energy is defined as ‘ the ability to do work ’. But this definition doesn’t address the question of what energy actually is! And it also assumes we know what is meant by ‘work’! So it is a rather unsatisfactory definition. So, what is energy? Well, whatever it is, we know that it never appears from nowhere nor does it disappear into nothingness! We call this, ‘the First Law of Thermodynamics’, which states that ‘ the total energy of an isolated system is constant; it can be transformed from one form to another, but can be neither created nor destroyed ’. As good an explanation of this was presented during a lecture to undergraduate students, in 1961, by the American Nobel Laureate, Richard Feynman (1918–1988): There is a fact, or if you wish, a ‘law’, governing those natural phenomena that are known to date. There is no known exception to this law – it is exact so far we know. The law is called ‘the Conservation of Energy ’; it states that there is a certain quantity, which we call ‘energy’ that does not change in those many changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens...
eBook - ePubEssentials of Energy Technology
Sources, Transport, Storage, Conservation
- Jochen Fricke, Walter L. Borst(Authors)
- 2013(Publication Date)
- Wiley-VCH(Publisher)
...Chapter 3 Thermodynamic Energy Efficiency The conversion of most forms of primary energy to useful energy is still highly inefficient today. Only about one-third of the primary energy is actually put to use (Figure 3.1). There are several reasons for this: relatively low energy costs (especially in the United States), marginal incentives for higher efficiency, and fundamental thermodynamic limitations. Figure 3.1 Typical flow of energy in an industrialized country, here Germany. Most primary energy comes from coal, natural gas, oil, and uranium. The end energies are electricity, gasoline, and diesel fuel, for industry, trade, heating and air conditioning, transportation, and so on. (Source: Adapted from Ref. [1].) 3.1 Carnot's Law The proper application of thermodynamics is the key for higher energy efficiency. The upper limit for the conversion of heat into useful work is given by Carnot's law: 3.1 where η C is the energy efficiency of the Carnot engine (Figure 3.2) operating between two reservoirs at absolute temperatures T h (hot) and T c (cold). First described by Sadi Carnot in 1824, this law shows that the higher the temperature T h is for a fixed T c, the higher is the efficiency. In the Carnot engine, all processes are assumed to be reversible and infinitely slow so that the system is in equilibrium at all times. Figure 3.2 (a) Energy flow chart for the Carnot process. (b) Pressure-Volume (pV) diagram. The shaded area of the closed loop is the extracted work W. (c) Temperature–Entropy (TS) diagram. Vertical transitions represent isentropic (adiabatic) processes. Two adiabatic and two isothermal processes make up the closed cycle, in which heat Q 34 at high temperature T h is used to produce work W, with heat Q 12 discharged at low temperature T c. The efficiency η C in Eq. (3.1) is defined as the work W divided by the provided heat Q 34. Applying the first law of thermodynamics (conservation of energy), we know that 3.2 and we obtain 3.3 Problem 3.1 Derive Eq...
eBook - ePubIntroduction to Energy, Renewable Energy and Electrical Engineering
Essentials for Engineering Science (STEM) Professionals and Students
- Ewald F. Fuchs, Heidi A. Fuchs(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
...The combination of heat, cooling, and electric generation increases total overall power efficiency up to 90%. Gas turbines have greater power efficiency than steam turbines, as will be shown later. Energy efficiencies, η energy, are mostly smaller than the rated power efficiencies, η power, due to low‐power operation periods where the power efficiency is relatively small. In most cases, the nameplate of an apparatus gives the power efficiency and sometimes, when the operating time is important, also lists energy efficiency. The generation of electricity via solar PV cells is governed by the solar cell energy conversion efficiency, η solar_cell, the ratio of the maximum electric output power of a solar cell to the incident power of sunlight at a maximum insolation of E = 1 kW/m 2 as it occurs on Earth. This conversion efficiency is the percentage of the insolation power to which the cell is exposed that is converted into electric energy [ 1 ]. This is calculated by dividing a cell's power output (in watts) at its maximum power point (P m) by the input light power per unit area (E, in W/m 2) and the surface area of the solar cell (A c, in m 2): (1.2) Under laboratory conditions, researchers have achieved solar cell efficiencies of more than η solar_cell = 44%...
