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Encyclopedia > Energy density

Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context. In some cases it is obvious from context which quantity is most useful: for example, in rocketry, energy per unit mass is the most important parameter, but when studying pressurized gas or magnetohydrodynamics the energy per unit volume is more appropriate. In a few applications (comparing, for example, the effectiveness of hydrogen fuel to gasoline) both figures are appropriate and should be called out explicitly. (Hydrogen has a higher energy density per unit mass than does gasoline, but a much lower energy density per unit volume in most applications.) For other uses, see Volume (disambiguation). ... For other uses, see Mass (disambiguation). ... A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust from within a rocket engine. ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Petrol redirects here. ...

Energy density per unit volume has the same physical units as pressure, and in many circumstances is an exact synonym: for example, the energy density of the magnetic field may be expressed as (and behaves as) a physical pressure, and the energy required to compress a gas may be determined by multiplying the pressure of the compressed gas times its final volume. This article is about pressure in the physical sciences. ... Synonyms (in ancient Greek, ÏƒÏ…Î½ (syn) = plus and ÏŒÎ½Î¿Î¼Î± (onoma) = name) are different words with similar or identical meanings. ...

## Energy density in energy storage and in fuel GA_googleFillSlot("encyclopedia_square");

In energy storage applications, the energy density relates the mass of an energy store to its stored energy. The higher the energy density, the more energy may be stored or transported for the same amount of mass. In the context of fuel selection, that energy density of a fuel is also called the specific energy of that fuel, though in general an engine using that fuel will yield less energy due to inefficiencies and thermodynamic considerations—hence the specific fuel consumption of an engine will be greater than the reciprocal of the specific energy of the fuel. And in general, specific energy and energy density are at odds due to charge screening. Energy storage is the storing of some form of energy that can be drawn upon at a later time to perform some useful operation. ... For other uses, see Mass (disambiguation). ... For other uses, see Fuel (disambiguation). ... The fuel value or relative energy density is the quantity of potential energy in fuel, food or other substance. ... For other uses, see Engine (disambiguation). ... The term inefficiency has several meanings depending on the context in which its used: Economic inefficiency refers to a situation where we could be doing a better job, i. ... Thermodynamics (from the Greek Î¸ÎµÏÎ¼Î·, therme, meaning heat and Î´Ï…Î½Î±Î¼Î¹Ï‚, dynamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... Specific fuel consumption, often shortened to SFC, is an engineering term that is used to describe the fuel efficiency of an engine design w/ a mechanical output. ... Look up reciprocal in Wiktionary, the free dictionary. ... The shielding effect describes the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell. ...

Gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline article): Petrol redirects here. ...

(Notes: Some values may not be precise because of isomers or other irregularities. See Heating value for a comprehensive table of specific energies of important fuels. The symbol ** indicates the item is an energy carrier, not an energy source.)
storage type energy density recovery efficiency
by mass by volume peak practical
MJ/kg MJ/L  %  %
**mass-energy equivalence 89,876,000,000
**binding energy of helium nucleus 675,000,000 8.57x1024
nuclear fusion of hydrogen (energy from the sun) 300,000,000 423,000,000
nuclear fission (of U-235) (Used in Nuclear Power Plants) 77,000,000 1,500,000,000 30% 50%
**liquid hydrogen 143 10.1
**compressed gaseous hydrogen at 700 bar[1] 143 4.7
**gaseous hydrogen at room temperature[citation needed] 143 0.01079
beryllium (toxic) (burned in air) 67.6 125.1
lithium borohydride (burned in air) 65.2 43.4
boron [2] (burned in air) 58.9 137.8
compressed natural gas at 200 bar 53.6[3] 10
gasoline[4] 46.9 34.6
diesel fuel/residential heating oil[5] 45.8 38.7
polyethylene plastic 46.3[6] 42.6
polypropylene plastic 46.3[7] 41.7
gasohol (10% ethanol 90% gasoline) 43.54 28.06
lithium (burned in air) 43.1 23.0
Jet A aviation fuel[8] 42.8 33
biodiesel oil (vegetable oil) 42.20 30.53
DMF (2,5-dimethylfuran) 42[9] 37.8
crude oil (according to the definition of ton of oil equivalent) 41.87 37[10]
polystyrene plastic 41.4[11] 43.5
body fat metabolism 38 35 22-26%[12]
butanol 36.6 29.2
LPG 34.39 22.16
**specific orbital energy of Low Earth orbit 33 (approx.)
graphite (burned in air) 32.7 72.9
anthracite coal 32.5 72.4 36%
silicon (burned in air)[13] 32.2 75.1
aluminum (burned in air) 31.0 83.8
ethanol 30 24
polyester plastic 26.0[14] 35.6
magnesium (burned in air) 24.7 43.0
bituminous coal [15] 24 20
PET pop bottle plastic ?23.5 impure ?
methanol 19.7 15.6
**hydrazine (toxic) combusted to N2+H2O 19.5 19.3
**liquid ammonia (combusted to N2+H2O) 18.6 11.5
PVC plastic (improper combustion toxic) 18.0[16] 25.2
sugars, carbohydrates & proteins metabolism 17 26.2(dextrose) 22-26% [17]
Cl2O7 + CH4 - computed 17.4
lignite coal 14-19
calcium (burned in air) 15.9 24.6
dry cowdung and cameldung 15.5[18]
wood 6–17[19] 1.8–3.2
**liquid hydrogen + oxygen (as oxidizer) (1:8 (w/w), 14.1:7.0 (v/v)) 13.333 5.7
sodium (burned to wet sodium hydroxide) 13.3 12.8
Cl2O7 decomposition - computed 12.2
nitromethane 11.3 12.9
household waste 8-11[20][21]
sodium (burned to dry sodium oxide) 9.1 8.8
iron (burned to iron(III) oxide) 7.4 57.9
Octanitrocubane explosive - computed 7.4
ammonal (Al+NH4NO3 oxidizer) 6.9 12.7
Tetranitromethane + hydrazine explosive - computed 6.6
Hexanitrobenzene explosive - computed 6.5
zinc (burned in air) 5.3 38.0
Teflon plastic (combustion toxic, but flame retardant) 5.1 11.2
iron (burned to iron(II) oxide) 4.9 38.2
**TNT 4.184 6.92
Copper Thermite (Al + CuO as oxidizer) 4.13 20.9
Thermite (powder Al + Fe2O3 as oxidizer) 4.00 [22] 18.4
**compressed air at 300 bar 4 0.14 ?
ANFO 3.88
hydrogen peroxide decomposition (as monopropellant) 2.7 3.8
Lithium Thionyl Chloride Battery 2.5
Regenerative Fuel Cell 1.62[23]
**hydrazine(toxic) decomposition (as monopropellant) 1.6 1.6
**ammonium nitrate decomposition (as monopropellant) 1.4 2.5
Molecular spring ~1
**sodium-sulfur battery ? 1.23[24] ? 85%[25]
**liquid nitrogen 0.77[1] 0.62
**lithium ion battery 0.54–0.72 0.9–1.9 95%[26]
**lithium sulphur battery 0.54-1.44 ?
kinetic energy penetrator 1.9-3.4 30-54
5.56 × 45 mm NATO bullet 0.4-0.8 3.2-6.4
**Zn-air batteries 0.40 to 0.72 ? ? ?
**flywheel 0.5 ? ? 81-94%[www.ccm.nl]
melting ice 0.335 0.335
**zinc-bromine flow battery 0.27–0.306[27]
**compressed air at 20 bar 0.27 ? 64%[28]
**NiMH Battery 0.22[29] 0.36 ? 60% [30]
**NiCd Battery 0.14-0.22 ? ? 80% [31]
**lead acid battery 0.09–0.11[32] 0.14–0.17 ? 75-85%[33]
**commercial lead acid battery pack 0.072-0.079[34] ? ? ?
**vanadium redox battery .09[35] .1188 ? 70-75%
**vanadium bromide redox battery .18[36] .252 ? 81%
**ultracapacitor 0.0206 [37] ? ? ?
**ultracapacitor by EEStor (claimed capacity) 1.0 [38] ? ? ?
**supercapacitor 0.01 ? 98.5% 90%[39]
**capacitor 0.002 [40] ? ? ?
water at 100 m dam height 0.001 0.001 ? 85-90%[41]
**spring power (clock spring), torsion spring 0.0003[42] 0.0006 ?
zero point energy 0 0

Energy density (how much energy you can carry) does not tell you about energy conversion efficiency (net output per input) or embodied energy (what the energy output costs to provide, as harvesting, refining, distributing, and dealing with pollution all use energy). Like any process occurring on a large scale, intensive energy use creates environmental impacts: for example, global warming, nuclear waste storage, and deforestation are a few of the consequences of supplying our growing energy demands from fossil fuels, nuclear fission, or biomass. Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. ... Embodied Energy refers to the quantity of energy required to manufacture, and supply to the point of use, a product, material or service. ... The energy industry is a generic term for all of the industries involved the production and sale of energy, including fuel extraction, manufacturing fuel and refining, and fuel distribution. ... A refinery is composed of a group of chemical engineering unit processes and unit operations used for refining certain materials or converting raw material into products of value. ... Air pollution Pollution is the introduction of pollutants (whether chemical substances, or energy such as noise, heat, or light) into the environment to such a point that its effects become harmful to human health, other living organisms, or the environment. ... Global warming refers to the increase in the average temperature of the Earths near-surface air and oceans in recent decades and its projected continuation. ... Political Punk band from Victorville, Ca WWW.MYSPACE.COM/NUCLEARWASTEX ... This article is about the process of deforestation in the environment. ...

By dividing by 3.6 the figures for megajoules per kilogram can be converted to kilowatt-hours per kilogram. Unfortunately, the useful energy available by extraction from an energy store is always less than the energy put into the energy store, as explained by the laws of thermodynamics. No single energy storage method boasts the best in specific power, specific energy, and energy density. Peukert's Law describes how the amount of energy we get out depends how quickly we pull it out. The laws of thermodynamics, in principle, describe the specifics for the transport of heat and work in thermodynamic processes. ... In engineering, specific power (sometimes also power per unit mass or power density) refers to the amount of power delivered by an energy source, divided by some measure of the sources size or mass. ... The fuel value or relative energy density is the quantity of potential energy in fuel, food or other substance. ... Peukerts Law defines a way to measure the capacity of a Battery (electricity) over a range of discharge rates. ...

## Energy density of electric and magnetic fields

Electric and magnetic fields store energy. In a vacuum, the (volumetric) energy density (in SI units) is given by In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

$U = frac{varepsilon_0}{2} mathbf{E}^2 + frac{1}{2mu_0} mathbf{B}^2$,

where E is the electric field and B is the magnetic induction. In the context of magnetohydrodynamics, the physics of conductive fluids, the magnetic energy density behaves like an additional pressure that adds to the gas pressure of a plasma. Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic field. ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ... This article is about pressure in the physical sciences. ... Kinetic theory attempts to explain macroscopic properties of gases, as pressure, temperature, or volume, by considering their molecular composition and motion. ... For other uses, see Plasma. ...

In normal (linear) substances, the energy density (in SI units) is

$U = frac{1}{2} ( mathbf{E} cdot mathbf{D} + mathbf{H} cdot mathbf{B} )$,

where D is the electric displacement and H is the magnetic field. Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

## Energy density of empty space

In physics, "vacuum energy" or "zero-point energy" is the volumetric energy density of empty space. More recent developments have expounded on the concept of energy in empty space. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Vacuum energy is an underlying background energy that exists in space even when devoid of matter (known as free space). ... In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess and is the energy of the ground state of the system. ...

Modern physics is commonly classified into two fundamental theories: quantum field theory and general relativity. Quantum field theory takes quantum mechanics and special relativity into account, and it's a theory of all the forces and particles except gravity. General relativity is a theory of gravity, but it is incompatible with quantum mechanics. Currently these two theories have not yet been reconciled into one unified description, though research into "quantum gravity" seeks to bridge this divide. Modern physics may refer to: Quantum mechanics Theory of relativity 20th-century physics in general See also History of physics This is a disambiguation page: a list of articles associated with the same title. ... Quantum field theory (QFT) is the quantum theory of fields. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... Gravity is a force of attraction that acts between bodies that have mass. ... Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ...

In general relativity, the cosmological constant is proportional to the energy density of empty space, and can be measured by the curvature of space. It is subsequently related to the age of the universe, as energy expands outwards with time its density changes. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Î›) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ...

Quantum field theory considers the vacuum ground state not to be completely empty, but to consist of a seething mass of virtual particles and fields. These fields are quantified as probabilities—that is, the likelihood of manifestation based on conditions. Since these fields do not have a permanent existence, they are called vacuum fluctuations. In the Casimir effect, two metal plates can cause a change in the vacuum energy density between them which generates a measurable force. In physics, a virtual particle is a particle which exists for such a short time and space that its energy and momentum do not have to obey the usual relationship. ... The magnitude of an electric field surrounding two equally charged (repelling) particles. ... In physics, the Casimir effect is a physical force exerted between separate objects, which is due to neither charge, gravity, nor the exchange of particles, but instead is due to resonance of all-pervasive energy fields in the intervening space between the objects. ...

Some believe that vacuum energy might be the "dark energy" (also called quintessence) associated with the cosmological constant in general relativity, thought to be similar to a negative force of gravity (or antigravity). Observations that the expanding universe appears to be accelerating seem to support the cosmic inflation theory—first proposed by Alan Guth in 1981—in which the nascent universe passed through a phase of exponential expansion driven by a negative vacuum energy density (positive vacuum pressure). In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... Look up Quintessence in Wiktionary, the free dictionary. ... AntiGravity is a group of New York gymnasts/performance artists. ... In physical cosmology, cosmic inflation is the idea that the nascent universe passed through a phase of exponential expansion that was driven by a negative-pressure vacuum energy density. ... Alan Harvey Guth (born February 27, 1947) is a physicist and cosmologist. ...

## Energy density of food

Energy density is the amount of energy (kilojoules or calories) per amount of food, with food amount being measured in grams or milliliters of food. Energy density is thus expressed in cal/g, kcal/g, J/g, kJ/g, cal/mL, kcal/mL, J/mL, or kJ/mL. This is the energy released when the food is metabolised by a healthy organism when it ingests the food (see food energy for calculation) and the food is metabolized with oxygen, into waste products such as carbon dioxide and water. Typical values of food energy density for high energy-density foods, such as a hamburger, would be 2.5 kcal/g. Purified fats and oils contain the highest energy densities—about 9 kcal/g. What is popularly referred to as the number of "calories" in a portion of food is therefore technically the number of kilocalories in the portion. A kilojoule (abbreviation: kJ) is a unit of energy equal to 1000 joules. ... Etymology: French calorie, from Latin calor (heat), from calere (to be warm). ... Food energy is the amount of energy in food that is available through digestion. ... A few of the metabolic pathways in a cell. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... A calorie refers to a unit of energy. ...

 Energy Portal

Image File history File links Crystal_128_energy. ... A Figure of merit is a quantity used to characterize the performance of a device relative to other devices of the same type. ... While all CO2 gas output ratios are calculated to within a less than 1% margin of error (assuming total oxidation of the carbon content of fuel), ratios preceded by a Tilde (~) indicate a margin of error of up to (but no greater than) 9%. Ratios listed do not include emissions... It has been suggested that this article or section be merged with Heating value. ... Heating value (or calorific value) is used to define the amount of heat released during the combustion of a fuel or food. ... A rechargeable lithium polymer Nokia mobile phone battery. ... Specific impulse (usually abbreviated Isp) is a way to describe the efficiency of rocket and jet engines. ... Vacuum energy is an underlying background energy that exists in space even when devoid of matter (known as free space). ...

## External references

### Zero point energy

1. Eric Weisstein's world of physics: energy density [43]
2. Baez physics: Is there a nonzero cosmological constant? [44]; What's the Energy Density of the Vacuum?.
3. Introductory review of cosmic inflation [45]
4. An exposition to inflationary cosmology [46]

### Density data

• ^  "Aircraft Fuels." Energy, Technology and the Environment Ed. Attilio Bisio. Vol. 1. New York: John Wiley and Sons, Inc., 1995. 257-259

### Books

• The Inflationary Universe: The Quest for a New Theory of Cosmic Origins by Alan H. Guth (1998) ISBN 0-201-32840-2
• Cosmological Inflation and Large-Scale Structure by Andrew R. Liddle, David H. Lyth (2000) ISBN 0-521-57598-2
• Richard Becker, "Electromagnetic Fields and Interactions", Dover Publications Inc., 1964

## References

1. ^ C. Knowlen, A.T. Mattick, A.P. Bruckner and A. Hertzberg, "High Efficiency Conversion Systems for Liquid Nitrogen Automobiles", Society of Automotive Engineers Inc, 1988.

Results from FactBites:

 energy: Definition, Synonyms and Much More from Answers.com (9829 words) The chemical energy of a substance is due to the condition of the atoms of which it is made; it resides in the chemical bonds that join the atoms in compound substances (see chemical bond). The dominant model of energy policy that emerged from this period and existed unchanged until the 1970s was one of support for conventional resources and regulation of industries whose natural monopolies required some government oversight to ensure that their public purpose served a public interest. Energy diffusion from more to less concentrated forms (net increase in entropy for the universe) is the driving force of all biological processes as all biochemical processes are a subset of chemical processes.
 Energy density - Wikipedia, the free encyclopedia (810 words) Energy density is the amount of energy stored in a given system or region of space per unit volume or per unit mass, depending on the context. In Physics, "Vacuum energy" or "zero-point energy" is the volumetric energy density of empty space. Energy density is the amount of energy (kilojoules or calories) per milliliter of food.
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