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Encyclopedia > Thermal contact conductance
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In physics, thermal contact conductance is the study of heat conduction between solid bodies in contact. The thermal contact conductance coefficient, hc, is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact. The inverse of this property is termed thermal contact resistance. Image File history File links Wiki_letter_w. ... The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... Heat flow along perfectly insulated wire Heat conduction is the transmission of heat across matter. ... In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. ... In physics, heat, symbolized by Q, is defined as energy in transit. ...

Contents


Definition

Fig. 1: Heat flow between to solids in contact and the temperature distribution.
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Fig. 1: Heat flow between to solids in contact and the temperature distribution.

When two solid bodies come in contact, such as A and B in Figure 1, heat flows from the hotter body to the colder body. From experience, the temperature profile along the two bodies varies, approximately, as shown in the figure. A temperature drop is observed at the interface between the two surfaces in contact. This phenomenon is said to be a result of a thermal contact resistance existing between the contacting surfaces. Thermal contact resistance is defined as the ratio between this temperature drop and the average heat flow across the interface [1]. In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... In thermodynamics, temperature is the physical property of a system that underlies the common notions of hot and cold —something that is hotter has the greater temperature. ...


According to Fourier's law, the heat flow between the bodies is found by the relation: (1)
where q is the heat flow, k is the thermal conductivity, A is the cross sectional area and dT / dx is the temperature gradiant in the direction of flow. Heat flow along perfectly insulated wire Heat conduction is the transmission of heat across matter. ...


From considerations of energy conservation, the heat flow between the two bodies in contact, bodies A and B, is found as: (2)
One may observe that the heat flow is directly related to the thermal conductivities of the bodies in contact, kA and kB, the contact area, A and the thermal contact resistance, 1 / hc, which, as previously noted, is the inverse of the thermal conductance coefficient, hc. For the physical concepts, see conservation of energy and energy efficiency. ...


Importance

Thermal contact conductance is an important factor in a variety of applications, largely due to the fact that many physical systems contain a mechanical combination of two materials. Some of the fields where contact conductance is of importance are [2][3][4]: Mechanics (Greek ) is the branch of physics concerned with the behaviour of physical bodies when subjected to forces or displacements, and the subsequent effect of the bodies on their environment. ...

The field of electronics comprises the study and use of systems that operate by controlling the flow of electrons (or other charge carriers) in devices such as thermionic valves and semiconductors. ... A large copper heatsink. ... See parenthesis for an account of the rhetorical concept from which the name of the punctuation mark is derived. ... Core of a small nuclear reactor used for research. ... This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings. ... An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... A heat exchanger is a device for transferring heat from one fluid to another, where the fluids are separated by a solid wall so that they never mix. ... Flight is the process of flying: either movement through the air by aerodynamically generating lift or aerostatically using buoyancy, or movement beyond earths atmosphere by spacecraft. ... In aerodynamics, hypersonic speeds are speeds that are highly supersonic. ... Vehicles are non-living means of transport. ... Space has been an interest for philosophers and scientists for much of human history, and hence it is difficult to provide an uncontroversial and clear definition outside of specific defined contexts. ...

Factors influencing contact conductance

Fig. 2: An enlargement of the interface between two contacting surfaces. The finish quality is exaggerated for the sake of the argument.
Enlarge
Fig. 2: An enlargement of the interface between two contacting surfaces. The finish quality is exaggerated for the sake of the argument.

Thermal contact conductance is a complicated phenomenon, influenced by many factors. Experience shows that the most important ones are as follows:


Contact pressure

The contact pressure is the factor of most influence on contact conductance. As contact pressure grows, contact conductance grows (And consequentially, contact resistance becomes smaller). This is attributed to the fact that the contact surface between the bodies grows as the contact pressure grows. The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ...


Since the contact pressure is the most important factor, most studies, correlations and mathematical models for measurement of contact conductance are done as a function of this factor. Linear correlations between 1000 pairs of numbers. ... A mathematical model is an abstract model that uses mathematical language to describe the behaviour of a system. ...


Interstitial materials

No truly smooth surfaces really exist, and surface imperfections are visible under a microscope. As a result, when two bodies are pressed together, contact is only performed in a finite number of points, separated by rather large gaps, as can be shown in Fig. 2. Since that actual contact area is reduced, another resistance for heat flow exists. The gasses/fluids filling these gaps may largely influence the total heat flow across the interface. Air is the most common interstitial material. The thermal conductivity of the interstitial material and its pressure are the two properties governing its influence on contact conductance. A microscope (Greek: micron = small and scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ... Gass can mean:- William H. Gass, an American writer Craig Gass, a comedian Melbourne Gass, a Canadian politician Patrick Gass, a member of the Lewis and Clark Expedition Kyle Gass, a member of the band Tenacious D A.J. Gass, a Canadian football player Michael David Irving Gass, Colonial Secretary... A subset of the phases of matter, fluids include liquids and gases, plasmas and, to some extent, plastic solids. ... AIR is a three-letter abbreviation with multiple meanings, as described below: The Annals of Improbable Research, a monthly magazine devoted to scientific humour All India Radio - Indias Government Radio service AIR, a popular electronica band from France. ...


In the absence of interstitial materials, such as the bodies are in vacuum, the contact resistance will be much larger, since flow through the intimate contact points is dominant. Look up Vacuum in Wiktionary, the free dictionary. ...


Surface roughness, waviness and flatness

One can characterise a surface that has undergone certain finish operations by three properties: Rougness, waviness and flatness. Among these, roughness is of most importance, and is usually indicated by an rms value, σ. Finishing is the procedure that some single malt Scotch whisky undergoes whereby the spirit is matured in a cask of a particular origin and then spends time in a cask of different origin. ... RMS may mean: root mean square, a concept in statistics and electronics Richard M. Stallman, a computer programmer and founder of the GNU project. ...


Surface deformations

When the two bodies come in contact, surface deformation may occur on both bodies. This deformation may either be plastic or elastic, depending on the material properties and the contact pressure. When a surface undergoes plastic deformation, contact resistance is lowered, since the deformation causes the actual contact area to increase [5][6] In engineering mechanics, deformation is a change in shape due to an applied force. ... In engineering mechanics, deformation is a change in shape due to an applied force. ... In engineering mechanics, deformation is a change in shape due to an applied force. ...


Surface cleanliness

The presence of dust particles, acids, etc., can also influence the contact conductace. After just three years of use dust has blocked this laptop heat sink, making the computer unusable Dust is a general name for minute solid particles with diameter less than 500 micrometers (otherwise see sand or granulates) and, more generally, for finely divided matter. ... In physics, a particle is an object, or body, with only a few degrees-of-freedom, including position, and perhaps orientation in space. ... For alternative meanings see acid (disambiguation). ...


Measurement of thermal contact conductance

Going back to Formula 2, calculation of the thermal contact conductance may prove difficult, even impossible, due to the difficulty in measuring the contact area, A (A product of surface characteristics, as explained earlier). Because of this, contact conductance/resistance is usually found experimentally, by using a standard apparatus. An apparatus is: A machine; or Reference tools added to a book, apart from the text, such as variant readings or translations, textual notes, a concordance, a bibliography, or an index, designed for the use of scholars studying the book. ...


The results of such experiments are usually published in Engineering literature, on magazines such as Journal of Heat Transfer, International Journal of Heat and Mass Transfer, etc. Unfortunately, a centralized database of contact conductance coefficients does not exist, a situation which sometimes causes companies to use outdated, irrelevant data, or not taking contact conductance as a consideration at all. Engineering is the application of scientific and technical knowledge to solve human problems. ... Old book bindings at the Merton College library. ... This article is about the magazine as a published medium. ... A database is a collection of logically related data designed to meet the information needs of one or more users. ...


CoCoE (Contact Conductance Estimator), a project founded to solve this problem and create a centralized database of contact conductance data and a computer program that uses it, was started in 2006. See also: Other events of 2006 List of years in science . ...


References

  1. ^ Hollman, J. P. (1997). Heat Transfer, 8th Edition. McGraw-Hill.
  2. ^ Fletcher, L. S. (November 1988). "Recent Developments in Contact Conductance Heat Transfer". Journal of Heat Transfer.
  3. ^ Madhusudana, C. V.; Ling, F. F. (1995). Thermal Contact Conductance. Springer.
  4. ^ Lambert, M. A., Fletcher, L. S. (November 1997). "Thermal Contact Conductance of Spherical Rough Metals". Journal of Heat Transfer.
  5. ^ Williamson, M., Majumdar, A. (November 1992). "Effect of Surface Deformations on Contact Conductance". Journal of Heat Transfer.
  6. ^ Heat Transfer Division (November 1970). "Conduction in Solids - Steady State, Imperfect Metal-to-Metal Surface Contact". General Electric Inc..

The McGraw-Hill Companies logo. ... Springer Science+Business Media or Springer (IPA: ) is a worldwide publishing company based in Germany which focuses on academic journals and books in the fields of science, technology and medicine. ...

See also

Heat transfer is the study of the energy transfer via either conduction, convection, or radiation. ... In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat. ... Heat flow along perfectly insulated wire Heat conduction is the transmission of heat across matter. ...

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