Thermal conductivity electrons. In this case the mean velocity is the Fermi velocity which is temperature independent. The mean free path is determined by the impurities and the crystal imperfections which are temperature independent as well. So the only temperature-dependent quantity is the heat capacity "c", which, in this case, is proportional to "T". So with "k" a constant. For pure metals such as copper, silver, etc. "l" is large, so the thermal conductivity is high. At higher temperatures the mean free path is limited by the phonons, so the thermal conductivity tends to decrease with temperature. In alloys the density of
Thermal conductivity and it is measured in watts per square metre of surface area for a temperature gradient of 1 K per unit thickness of 1 m". Therefore, specific thermal conductivity is calculated as: where: formula_14 = temperature difference (K, or °C) = 1 K during measurement Absolute thermal conductivity, on the other hand, has units of formula_15 or formula_16, and can be expressed as where formula_18 = absolute thermal conductivity (W/K, or W/°C). Substituting formula_18 for formula_20 into the first equation yields the equation which converts from absolute thermal conductivity to specific thermal conductivity: Solving for formula_18, we get the equation