digplanet beta 1: Athena
Share digplanet:

Agriculture

Applied sciences

Arts

Belief

Business

Chronology

Culture

Education

Environment

Geography

Health

History

Humanities

Language

Law

Life

Mathematics

Nature

People

Politics

Science

Society

Technology

Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy would ideally be the amount of heat required to warm the metal to its temperature, but this quantity is not well-defined, as there are many ways to obtain a given body at a given temperature, and each of them may require a different amount of total heat input. Thermal energy, unlike internal energy, is therefore not a state function.

Thermal energy refers to the internal energy present in a system in a state of thermodynamic equilibrium by virtue of its temperature.[1] The average translational kinetic energy possessed by free particles in a system of free particles in thermodynamic equilibrium may be referred to as the thermal energy per particle.[2]

The internal energy of a system, also often called the thermodynamic energy, includes other forms of energy in a thermodynamic system in addition to thermal energy, namely forms of potential energy that do not influence temperature and do not absorb heat, such as the chemical energy stored in its molecular structure and electronic configuration, and the nuclear binding energy that binds the sub-atomic particles of matter.[citation needed]

Microscopically, the thermal energy may include both the kinetic energy and potential energy of a system's constituent particles, which may be atoms, molecules, electrons, or particles in plasmas. It originates from the individually random, or disordered, motion of particles in a large ensemble, as consequence of absorbing heat. In ideal monatomic gases, thermal energy is entirely kinetic energy. In other substances, in cases where some of thermal energy is stored in atomic vibration, this vibrational part of the thermal energy is stored equally partitioned between potential energy of atomic vibration, and kinetic energy of atomic vibration. Thermal energy is thus equally partitioned between all available quadratic degrees of freedom of the particles. As noted, these degrees of freedom may include pure translational motion in gases, in rotational states, and as potential and kinetic energy in normal modes of vibrations in intermolecular or crystal lattice vibrations. In general, due to quantum mechanical reasons, the availability of any such degrees of freedom is a function of the energy in the system, and therefore depends on the temperature (see heat capacity for discussion of this phenomenon).[citation needed]

Macroscopic, the thermal energy of a system at a given temperature is related proportionally to its heat capacity. However, since the heat capacity differs according to whether or not constant volume or constant pressure is specified, or phase changes permitted, the heat capacity cannot be used to define thermal energy unless it is done in such a way as to insure that only heat gain or loss (not work) makes any changes in the internal energy of the system. Usually, this means specifying the "constant volume heat capacity" of the system so that no work is done. Also the heat capacity of a system for such purposes must not include heat absorbed by any chemical reaction or process.[citation needed]

As noted, thermal energy is not a state function, or a property of a system, since the total thermal energy needed to warm a system to a given temperature depends on the path taken to attain the temperature, unless all forms of work and chemical potential change in the system are zero or negligible (in which case thermal energy is a subset of the internal energy). Thus, thermal energy is process-dependent except in systems in which processes to change internal energy other than heating, can be neglected. Nevertheless, when this is true, thermal energy and heat capacity may be a useful concept in the study of heat transfer in solids and liquids, in engineering and other disciplines.[citation needed]


Differentiation from heat[edit]

Heat, in the strict use in physics, is characteristic only of a process, i.e. it is absorbed or produced as an energy exchange, always as a result of a temperature difference. Heat is thermal energy in the process of transfer or conversion across a boundary of one region of matter to another, as a result of a temperature difference.[3] In engineering, the terms "heat" and "heat transfer" are thus used nearly interchangeably, since heat is always understood to be in the process of transfer. The energy transferred by heat is called by other terms (such as thermal energy or latent energy) when this energy is no longer in net transfer, and has become static.[4] Thus, heat is not a static property of matter. Matter does not contain heat, but rather thermal energy, and even the thermal energy is subject to transformations into and out of other types of energy, and so can be considered to be "conserved" only when these processes are small. The heat transfer rate or heating rate is the amount of energy per unit time being transferred as heat, or the heat power.

When two thermodynamic systems with different temperatures are brought into diathermic contact, they spontaneously exchange energy as heat, the exchange being transfer of thermal energy from the system of higher temperature to the colder system. Heat may cause work to be performed on a system, for example, in form of volume or pressure changes. This work may be used in heat engines to convert thermal energy into other forms of energy. When two systems have reached a thermodynamic equilibrium, they have attained the same exact temperature and the net exchange of thermal energy vanishes, and heat flow ceases.

Definitions[edit]

Thermal energy is the portion of the thermodynamic or internal energy of a system that is responsible for the temperature of the system.[1][3] The thermal energy of a system scales with its size and is therefore an extensive property. It is not a state function of the system unless the system has been constructed so that all changes in internal energy are due to changes in thermal energy, as a result of heat transfer (not work). Otherwise thermal energy is dependent on the way or method by which the system attained its temperature.

From a macroscopic thermodynamic description, the thermal energy of a system is given by its constant volume specific heat capacity C(T), a temperature coefficient also called thermal capacity, at any given absolute temperature (T):

U_{thermal} = C(T) \cdot T.

The heat capacity is a function of temperature itself, and is typically measured and specified for certain standard conditions and a specific amount of substance (molar heat capacity) or mass units (specific heat capacity). At constant volume (V), CV it is the temperature coefficient of energy.[5] In practice, given a narrow temperature range, for example the operational range of a heat engine, the heat capacity of a system is often constant, and thus thermal energy changes are conveniently measured as temperature fluctuations in the system.

In the microscopical description of statistical physics, the thermal energy is identified with the mechanical kinetic energy of the constituent particles or other forms of kinetic energy associated with quantum-mechanical microstates.

The distinguishing difference between the terms kinetic energy and thermal energy is that thermal energy is the mean energy of disordered, i.e. random, motion of the particles or the oscillations in the system. The conversion of energy of ordered motion to thermal energy results from collisions.[6]

All kinetic energy is partitioned into the degrees of freedom of the system. The average energy of a single particle with f quadratic degrees of freedom in a thermal bath of temperature T is a statistical mean energy given by the equipartition theorem as

E_{thermal} = f \cdot \tfrac 1 2 kT \,\!

where k is the Boltzmann constant. The total thermal energy of a sample of matter or a thermodynamic system is consequently the average sum of the kinetic energies of all particles in the system. Thus, for a system of N particles its thermal energy is[7]

U_{thermal} = N \cdot f \cdot \tfrac{1}{2} kT.

For gaseous systems, the factor f, the number of degrees of freedom, commonly has the value 3 in the case of the monatomic gas, 5 for many diatomic gases, and 7 for larger molecules at ambient temperatures. In general however, it is a function of the temperature of the system as internal modes of motion, vibration, or rotation become available in higher energy regimes.

Uthermal is not the total energy of a system. Physical systems also contains static potential energy (such as chemical energy) that arises from interactions between particles, nuclear energy associated with atomic nuclei of particles, and even the rest mass energy due to the equivalence of energy and mass.

Thermal energy of the ideal gas[edit]

Thermal energy is most easily defined in the context of the ideal gas, which is well approximated by a monatomic gas at low pressure. The ideal gas is a gas of particles considered as point objects of perfect spherical symmetry that interact only by elastic collisions and fill a volume such that their mean free path between collisions is much larger than their diameter.

The mechanical kinetic energy of a single particle is

E_{kinetic} = \tfrac 1 2 m v^2 \,\!

where m is the particle's mass and v is its velocity. The thermal energy of the gas sample consisting of N atoms is given by the sum of these energies, assuming no losses to the container or the environment:

U_{thermal} = \tfrac 1 2 N m \overline{v^2} = \tfrac{3}{2} N k T,

where the line over the velocity term indicates that the average value is calculated over the entire ensemble. The total thermal energy of the sample is proportional to the macroscopic temperature by a constant factor accounting for the three translational degrees of freedom of each particle and the Boltzmann constant. The Boltzmann constant converts units between the microscopic model and the macroscopic temperature. This formalism is the basic assumption that directly yields the ideal gas law and it shows that for the ideal gas, the internal energy U consists only of its thermal energy:

 U = U_{thermal}.\;

Historical context[edit]

In an 1847 lecture entitled On Matter, Living Force, and Heat, James Prescott Joule characterized various terms that are closely related to thermal energy and heat. He identified the terms latent heat and sensible heat as forms of heat each effecting distinct physical phenomena, namely the potential and kinetic energy of particles, respectively.[8] He describes latent energy as the energy of interaction in a given configuration of particles, i.e. a form of potential energy, and the sensible heat as an energy affecting temperature measured by the thermometer due to the thermal energy, which he called the living force.

Distinction of thermal energy and heat[edit]

In thermodynamics, heat must always be defined as energy in exchange between two systems, or a single system and its surroundings.[9] According to the zeroth law of thermodynamics, heat is exchanged between thermodynamic systems in thermal contact only if their temperatures are different, as this is the condition when the net exchange of thermal energy is non-zero. For the purpose of distinction, a system is defined to be enclosed by a well-characterized boundary. If heat traverses the boundary in direction into the system, the internal energy change is considered to be a positive quantity, while exiting the system, it is negative. As a process variable, heat is never a property of the system, nor is it contained within the boundary of the system.[3]

In contrast to heat, thermal energy exists on both sides of a boundary. It is the statistical mean of the microscopic fluctuations of the kinetic energy of the systems' particles, and it is the source and the effect of the transfer of heat across a system boundary. Statistically, thermal energy is always exchanged between systems, even when the temperatures on both sides is the same, i.e. the systems are in thermal equilibrium. However, at equilibrium, the net exchange of thermal energy is zero, and therefore there is no heat.

Thermal energy may be increased in a system by other means than heat, for example when mechanical or electrical work is performed on the system. No qualitative difference exists between the thermal energy added by other means. Thermal energy is not a state function, although it may be closely related to the internal energy of some systems, which is a state function. There is also no need in classical thermodynamics to characterize the thermal energy in terms of atomic or molecular behavior. A change in thermal energy induced in a system is the product of the change in entropy and the temperature of the system.

Heat exchanged across a boundary may cause changes other than a change in temperature. For example, it may cause phase transitions, such as melting or evaporation, which are changes in the configuration of a material. Since such an energy exchange is not observable by a change in temperature, it is called a latent heat and represents a change in the potential energy of the system.

Rather than being itself the thermal energy involved in a transfer, heat is sometimes also understood as the process of that transfer, i.e. heat functions as a verb.

Today's narrow definition of heat in physics contrasts with its use in common language, in some engineering disciplines, and in the historical scientific development of thermodynamics in the caloric theory of heat. The phenomenon of heat in these instances is today properly identified as the entropy.[5]

The origin of heat energy on Earth[edit]

Earth's proximity to the Sun is the reason that almost everything near Earth's surface is warm with a temperature substantially above absolute zero.[10] Solar radiation constantly replenishes heat energy that Earth loses into space and a relatively stable state of near equilibrium is achieved. Because of the wide variety of heat diffusion mechanisms (one of which is black-body radiation which occurs at the speed of light), objects on Earth rarely vary too far from the global mean surface and air temperature of 287 to 288 K (14 to 15 °C). The more an object's or system's temperature varies from this average, the more rapidly it tends to come back into equilibrium with the ambient environment.

Thermal energy of individual particles[edit]

The term thermal energy is also often used as a property of single particles to designate the kinetic energy of the particles. An example is the description of thermal neutrons having a certain thermal energy, which means that the kinetic energy of the particle is equivalent to the temperature of its surroundings.

See also[edit]

References[edit]

  1. ^ a b Thermal energy entry in Britannica Online
  2. ^ Thermal energy entry in Hyperphysics web site
  3. ^ a b c Robert F. Speyer (2012). Thermal Analysis of Materials. Materials Engineering. Marcel Dekker, Inc. p. 2. ISBN 0-8247-8963-6. 
  4. ^ Frank P. Incropera; David P. De Witt and D. P. Dewitt (1990). Fundamentals of Heat and Mass Transfer (3rd ed.). John Wiley & Sons. p. 2. ISBN 0-471-51729-1.  See box definition: "Heat transfer (or heat) is energy in transit due to a temperature difference." See page 14 for the definition of the thermal component of the thermodynamic internal energy.
  5. ^ a b Hans U. Fuchs (2010). The Dynamics of Heat: A Unified Approach to Thermodynamics and Heat Transfer (2 ed.). Springer. p. 211. ISBN 978-1-4419-7603-1. 
  6. ^ S. Blundell, K. Blundell (2006). Concepts in Thermal Physics. Oxford University Press. p. 366. ISBN 0-19-856769-3. 
  7. ^ D.V. Schroeder (1999). An Introduction to Thermal Physics. Addison-Wesley. p. 15. ISBN 0-201-38027-7. 
  8. ^ J. P. Joule (1884), "Matter, Living Force, and Heat", The Scientific Papers of James Prescott Joule (The Physical Society of London): 274, retrieved 2 January 2013, "I am inclined to believe that both of these hypotheses will be found to hold good,—that in some instances, particularly in the case of sensible heat, or such as is indicated by the thermometer, heat will be found to consist in the living force of the particles of the bodies in which it is induced; whilst in others, particularly in the case of latent heat, the phenomena are produced by the separation of particle from particle, so as to cause them to attract one another through a greater space." 
  9. ^ Thomas W. Leland, Jr., G. A. Mansoori, ed., Basic Principles of Classical and Statistical Thermodynamics 
  10. ^ The deepest ocean depths (3 to 10 km) are no colder than about 274.7–275.7 K (1.5–2.5 °C). Even the world-record cold surface temperature established on July 21, 1983 at Vostok Station, Antarctica is 184 K (a reported value of −89.2 °C). The residual heat of gravitational contraction left over from earth's formation, tidal friction, and the decay of radioisotopes in earth's core provide insufficient heat to maintain earth's surface, oceans, and atmosphere "substantially above" absolute zero in this context. Also, the qualification of "most-everything" provides for the exclusion of lava flows, which derive their temperature from these deep-earth sources of heat.

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Thermal_energy — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
1000000 videos foundNext > 

Heat Temperature and Energy

Thermal Energy Demonstration

Sixth-grade science students saw an example this week of what a quick change in temperature can cause. Liquid Nitrogen is colder than --200 degrees Celsius, ...

Bill Nye The Science Guy on Heat (Full Clip)

Heat flows. It's the energy of moving molecules. Heat makes things go; it can make things burn. From snow to ice floe, things may look cold, but they've got ...

Transfer of Thermal Energy

Heat (thermal energy) always moves from a place with a HIGHER temperature to a place with a LOWER temperature. This is called TRANSFER OF THERMAL ENERGY.

Geothermal Energy

Heat and cool your home naturally and comfortably with geothermal energy.

Temperature and Thermal Energy

This video lecture covers thermal energy, temperature, thermal expansion, convection, conduction, and radiation.

Thermal Energy and Temperature

An Introduction to what "temperature" measures, and how kinetic energy within a substance determines its temperature and its phase of matter.

Thermal Electricity - How it Works

How fossil fuels are used to generate electricity.

Thermal Energy Cell Candle Fan

http://www.TeamThinkTank.net http://www.twitter.com/TeamThinkTank This product was created by Team Think Tank. It uses a thermal energy cell (TEC) to extract...

Heat and Thermal Energy

Created using PowToon -- Free sign up at http://www.powtoon.com/ . Make your own animated videos and animated presentations for free. PowToon is a free to...

1000000 videos foundNext > 

556 news items

 
MarketWatch
Thu, 10 Jul 2014 04:10:07 -0700

Jul 10, 2014 (ACCESSWIRE via COMTEX) -- OTTAWA, ONTARIO / ACCESSWIRE / July 10, 2014 / Thermal Energy International Inc. ("Thermal Energy" or the "Company") (CVE:CA:TMG) , a global provider of energy efficiency and emission reduction ...
 
Greentech Media
Mon, 28 Jul 2014 09:03:52 -0700

740 kilowatts of thermal energy storage from Dimplex North America Ltd., North America's largest maker of electric heaters and equipment. Thermal energy storage involves getting water heaters and other electrical heating loads -- as well as air ...
 
Caribbean Journal
Tue, 22 Jul 2014 05:22:30 -0700

Ocean thermal energy uses the heat energy stored in the ocean to generate electricity, capitalizing on the temperature difference between the warmer top layer of the ocean and colder, deep ocean water. While there are several versions of the concept ...
 
MarketWatch
Tue, 15 Jul 2014 04:03:45 -0700

Jul 15, 2014 (ACCESSWIRE via COMTEX) -- OTTAWA, ONTARIO / ACCESSWIRE / July 15, 2014 / Thermal Energy International Inc. ("Thermal Energy" or the "Company") (CVE:CA:TMG) , a global provider of energy efficiency and emission reduction ...
 
SYS-CON Media (press release)
Mon, 21 Jul 2014 02:56:15 -0700

LANCASTER, PA and LONDON, UNITED KINGDOM -- (Marketwired) -- 07/21/14 -- Ocean Thermal Energy Corporation (GXG: OTEC) (ISIN: SE0006028023) ("OTE" or the "Company") is pleased to announce that its securities have been admitted to trade on ...
 
Prensa Latina
Wed, 23 Jul 2014 00:18:45 -0700

2 Imagen activa 3 de julio de 2014, 02:30Fort-de-France, July 23 (Prensa Latina) Martinique intends to develop a project of ocean thermal energy to generate electricity, the government reported today. According to a statement from the office of the ...
 
Renewable Energy Magazine (press release)
Tue, 29 Jul 2014 04:48:45 -0700

The company has also commercialised its molten salt solar thermal energy storage technology in a power tower configuration. This enables the company to operate its CSP power plants on-demand day and night, thereby delivering a stable and predictable ...

Newswire Today (press release)

Renewable Energy Focus
Thu, 10 Jul 2014 01:26:15 -0700

After a 12-month audit led by the European Investment Bank, the NEMO "New Energy for Martinique and Overseas" project for the development of an offshore pilot ocean thermal energy conversion plant in Martinique was awarded under the NER300 ...
Loading

Oops, we seem to be having trouble contacting Twitter

Talk About Thermal energy

You can talk about Thermal energy with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!