Thermal conductivity of a foam

Several other more complex dependences accounting for the shape of grains and pores have been proposed. However, it should be pointed out that in most of these models the disperse phase consists of solid particles, while the dispersion phase is gas in the form of pores. Such models do not correspond to the process for they do not account for the effect of the liquid phase on heat transfer. Considering a cubic foam model Manegold [5] has suggested a relation between the thermal conductivity of a foam and the liquid content in it... 

Eqs. (8.66) - (8.68) show that thermal conductivity decreases with the increase in foam expansion ratio. Since the thermal conductivity of water (At = 0.63 V m 1 K1) is about 25 times higher than that of air (Ac = 0.024 V m 1 K 1), at n = 20-25 the thermal conductivity of a foam is mainly determined by that of the gas phase. 

Foams, also called e>q>anded plastics, possess inherent features that make them suitable for certain applications. For instance, the thermal conductivity of a foam is lower than that of the solid polymer. Also, a foamed polymer is more rigid than the solid polymer for any given weight of the material. Finally, compressive stresses usually cause foams to collapse while absorbing much energy, an obvious advantage in protective packaging. Properties such as these can be tailored to fit various applications by the choice of polymer and by the maimer of foam formation or fabrication. 

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