Heat Conduction

Flow of internal energy (heat) from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles (atoms, molecules, ions, electrons, etc.) in the intervening space. The factors that affect the rate of heat transfer by conduction are the temperature difference (ΔT), length (l), cross-sectional area (A), and thermal conductivity of the material (k):

Conductivities are usually given in units of W/m·K. They are highest in metallic solids, lower in nonmetallic solids, very low in liquids, and extremely low in gases. The best ordinary metallic conductors are silver (429 W/m·K), copper (401), gold (317), aluminum (237), and tungsten (174). Among nonmetallic solids, diamond is best (895); most silicate minerals have low values (forsterite, 4.6; almandine, 3.6; diopside, 4.2; hornblende, 2.0; feldspar, 2.3–2.7; calcite, ~3). Some minerals show strong dependence of conductivity with crystal axes. For example, the conductivity of quartz is 6.2 ⊥c and 10.2 ||c at 30 °C. The material with the greatest thermal conductivity (105) is the super fluid helium II, which only exists at temperatures below 2.17 K.


Some or all content above used with permission from J. H. Wittke.


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