Reduction in lattice thermal conductivity of porous materials due to inhomogeneous porosity

A physical model for the reduction in lattice thermal conductivity KL based on the diffuse scattering of phonons at the pore–medium interfaces is developed in case of inhomogeneous porosity. In “gray-medium” approximation, a theoretically sound expression is derived for the KL and the variation of that as a function of porosity, pore sizes and the number of pore groups with different sizes is studied. A condition is found at which the reduction in KL of a composite with inhomogeneous porosity is much more effective than that in the case of homogeneous porosity.

► We model a porous material with inhomogeneous porosity.
► A sound expression for the effective thermal conductivity of the material is derived for a wide range of porosity.
► We investigate the opportunities for the reduction in lattice thermal conductivity.