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Encyclopedia > Thermal expansion
Material Properties
Specific heat $C=frac{T}{N}left(frac{partial S}{partial T}right)$
Compressibility $beta=-frac{1}{V}left(frac{partial V}{partial p}right)$
Thermal expansion
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In physics, thermal expansion is the tendency of matter to change in volume in response to a change in temperature. When a substance is heated, its constituent particles move around more vigorously and by doing so generally maintain a greater average separation. Materials that contract with an increase in temperature are very uncommon; this effect is limited in size, and only occurs within limited temperature ranges. The degree of expansion divided by the change in temperature is called the material's coefficient of thermal expansion and generally varies with temperature. The thermodynamic properties of materials are intensive thermodynamic parameters which are specific to a given material. ... Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval. ... Fluid Dynamics Compressibility (physics) is a measure of the relative volume change of fluid or solid as a response to a pressure (or mean stress) change: . For a gas the magnitude of the compressibility depends strongly on whether the process is adiabatic or isothermal, while this difference is small in... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other uses, see Volume (disambiguation). ... During heat transfer, the energy that is stored in the intermolecular bonds between atoms changes. ...

Common engineering solids usually have thermal expansion coefficients that do not vary significantly over the range of temperatures where they are designed to be used, so where extremely high accuracy is not required, calculations can be based on a constant, average, value of the coefficient of expansion.

Materials with anisotropic structures, such as crystals and composites, will generally have different expansion coefficients in different orientations. This article is being considered for deletion in accordance with Wikipedias deletion policy. ... Crystal (disambiguation) Insulin crystals A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Composite materials (or composites for short) are engineering materials made from two or more components. ...

To more accurately calculate thermal expansion of a substance a more advanced Equation of state must be used, which will then predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions. In physics and thermodynamics, an equation of state is a relation between state variables. ... In thermodynamics, a state function, or state quantity, is a property of a system that depends only on the current state of the system, not on the way in which the system got to that state. ...

For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the $frac{}{}epsilon_{thermal}$ ratio of strain: This article is about the deformation of materials. ...

is the initial length before the change of temperature and the final length recorded after the change of temperature.

For most solids, thermal expansion relates directly with temperature:

Thus, the change in either the strain or temperature can be estimated by: Look up strain in Wiktionary, the free dictionary. ...

where

and

is the coefficient of thermal expansion in inverse kelvins.
is the difference of the temperature between the two recorded strains, measured in celsius or kelvin.

A number of materials contract on heating within certain temperature ranges; we usually speak of negative thermal expansion, rather than thermal contraction, in such cases. For example, the coefficient of thermal expansion of water drops to zero as it is cooled to roughly 4 °C and then becomes negative below this temperature, this means that water has a maximum density at this temperature, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of sub-zero weather. Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... For other uses, see Kelvin (disambiguation). ... Negative Thermal Expansion (NTE) is a physicochemical process in which some materials contract upon heating rather than expanding as most materials do. ...

In many common materials, changes in size can also be due to water (or other solvents) being absorbed/desorbed, and many organic materials change size much more due to this effect than they do to thermal expansion. Common plastics exposed to water can, in the long term, expand many percent.

Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:

• Metal framed windows need rubber spacers
• Metal hot water heating pipes should not be used in long straight lengths
• Large structures such as railways and bridges need expansion joints in the structures
• One of the reasons for the poor performance of cold car engines is that parts have inefficiently large spacings until the normal operating temperature is achieved.
• a Gridiron pendulum uses an arrangement of different metals to maintain a more temperature stable pendulum length.

This phenomenon can also be put to good use, for example in the process of thermal shrink-fitting (also called "sweating"), parts are assembled with each at a different temperature, and sized such that when they reach the same temperature, the thermal expansion of the parts forces them together to form a stable joint. An expansion joint is an assembly designed to safely absorb the heat-induced expansion and contraction of metallic parts. ... The gridiron pendulum was an improvement of clocks developed by John Harrison, consisting of alternating brass and steel rods assembled so that the different expansion and contraction rates cancelled each other out. ... Shrink-fitting is a technique, in which pieces of a structure are heated or cooled, employing the phenomenon of thermal expansion, to make a joint. ...

Thermometers are another example of an application of thermal expansion – they contain a liquid which is constrained to flow in only one direction (along the tube) due to changes in volume brought about by changes in temperature.

Results from FactBites:

 Herguth - TOC - Thermal Expansion (231 words) The coefficient of thermal expansion is the ratio of the relative change of volume to a change in temperature. Thermal expansion is expressed as the ratio of volume change to the initial volume after heating 1 degree C. Therefore, the unit is reciprocal degree C, or degree C-1. Thermal expansion (or contraction) determinations require the measurement of the volume of a given mass of oil at various temperatures.
 thermal expansion: Definition and Much More from Answers.com (4301 words) For quartz, the coefficient of linear expansion is 0.05. In general, water—whose volume expansion coefficient in the liquid state is 2.1, and 0.5 in the solid state—exhibits a number of interesting characteristics where thermal expansion is concerned. Thermal expansion is a particularly serious problem where railroad tracks are concerned, since the tracks on which the trains run are made of steel.
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