As discussed previously in this section, the measurement of the thermal conductivity is notoriously difficult. The consequence is that, while the measurement accuracy by individual researchers is claimed to be of the order of 2%, laboratories participating in round-robin tests produce results differing from each other by 15% or more . Even the measurement of pure metals is no exception to this role.
About forty years ago, the published values of Nickel and Tungsten, for example, varied over an order of magnitude. Supposedly a wrong value for Tungsten used to calculate proper thickness for thermal shields of early space vehicles led to fatal re-entry problems. The large discrepancies found in ‘early’ literature could possibly be attributed to small impurity levels, for which the thermal conductivity is very sensitive. People in search of the most trustworthy data could best consult the series of books by Touloukian et al. .
The thermal conductivity of pure metals shows a rather complex dependency on temperature, but, in our range of interest (0-200°C), its value usually decreases slightly with increasing temperature. In almost all cases of practical interest the temperature dependency can be neglected, with the possible exception of Nickel, Tin and Tungsten. The following table lists values of pure metals most commonly used in electronics cooling, at three different temperatures.
Source: Beaton and Hewitt
1. Hulstrom L., Tye R., Smith S., Round Robin Testing of Thermal Conductivity Reference Materials, in Thermal Conductivity, vol.19, Plenum Press, 1988, pp. 199-211.
2.Touloukian Y. et al. (ed.) Thermophysical Properties of Matter, IFI/Plenum, 1970.
3.Beaton C., Hewitt G. (ed.), Physical Property Data for the Design Engineer, Hemisphere, 1989.