The conductivity of foams: a generalisation of the electrical to the thermal case

The foam conductivity model of Phelan et al. [R. Phelan, D. Weaire, E.A.J. Peters, G. Verbist, J. Phys.: Condens. Mat. 8 (1996) 475] was generalised from electrical to thermal conductivity. In the thermal case two complications arise: (i) a radiation contribution to heat transfer (which was determined experimentally) and (ii) unlike the electrical case, the gas conduction cannot be neglected. re conduction part was modeled using an effective-mean field approach to average gas and polymer phase contributions and also a vertex/strut/film model to account for structural aspects. The model is compared to polyurethane closed cell rigid (PUR) foam data. PUR foams are of major industrial importance for thermal insulation. They are widely used as an insulating mantle around heating pipes. In particular this model is necessary at higher densities and for higher conductivity gases whose presence is nowadays unavoidable, as low-conducting chlorofluorocarbons (CFCs) have been phased out due to environmental reasons. This knowledge is also useful in attempting to optimise the strength and conductance of foams.