GC: n
CT: Heat transfer by conduction involves transfer of energy within a material without any motion of the material as a whole. The rate of heat transfer depends upon the temperature gradient and the thermal conductivity of the material. Thermal conductivity is a reasonably straightforward concept when you are discussing heat loss through the walls of your house, and you can find tables which characterize the building materials and allow you to make reasonable calculations.
More fundamental questions arise when you examine the reasons for wide variations in thermal conductivity. Gases transfer heat by direct collisions between molecules, and as would be expected, their thermal conductivity is low compared to most solids since they are dilute media. Non-metallic solids transfer heat by lattice vibrations so that there is no net motion of the media as the energy propagates through. Such heat transfer is often described in terms of “phonons”, quanta of lattice vibrations. Metals are much better thermal conductors than non-metals because the same mobile electrons which participate in electrical conduction also take part in the transfer of heat.
Conceptually, the thermal conductivity can be thought of as the container for the medium-dependent properties which relate the rate of heat loss per unit area to the rate of change of temperature.
S: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html (last access: 20 February 2015)
N: 1. – thermal (adj): 1756, “having to do with hot springs,” from French thermal (Buffon), from Greek therme “heat, feverish heat,” from PIE gwher- “to heat, warm” (cognates: Latin fornax “an oven, kiln,” formus “warm,” Old English wearm). Sense of “having to do with heat” is first recorded 1837. The noun meaning “rising current of relatively warm air” is recorded from 1933.
– conductivity (n): From adjective conductive (1520s, “having the power or property of leading” (a sense now obsolete), from conduct (v.) + -ive. Physics sense, “resulting from or pertaining to conduction,” is from 1840. Related: Conductivity, from 1837) and -ity (word-forming element making abstract nouns from adjectives and meaning “condition or quality of being,” from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -tas; roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. Fowler).
2. Thermal conductivity is the property of a material to conduct heat. Thermal conductivity can be defined as “the quantity of heat transmitted through a unit thickness of a material – in a direction normal to a surface of unit area – due to a unit temperature gradient under steady state conditions”
3. Thermal conductivity units are W/(m K) in the SI system and Btu/(hr ft °F) in the Imperial system.
4. Thermal conductivity of a homogeneous material not affected by thickness.
5. A physical property of materials which is their ability to conduct heat from a warmer to a cooler object.
S: 1. OED – https://bit.ly/2EkOPyE; https://bit.ly/2QE9bbP; https://bit.ly/2rocSnK (last access: 8 December 2018). 2 to 4. EngTB – http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html (last access: 20 February 2015). 5. TERMIUM PLUS – https://bit.ly/2zOFkUl (last access: 8 December 2018).
SYN: heat conductivity, heat conductibility.
S: TERMIUM PLUS – https://bit.ly/2zOFkUl (last access: 8 December 2018)
