Effective thermal conductivity of debris beds

The effective thermal conductivity ksub(E) of an isotropic composite material is ill-defined unless the geometric arrangement of the phases is sufficiently well specified. Nevertheless, Hashin and Shtrikman have obtained rigorous bounds of practical use provided the component conductivities are sufficiently close. For a two-component system, these bounds are the familiar Maxwell formulae. Effective medium theory gives an estimate of effective conductivity ignoring connectedness; it is the formula of Bruggeman. This appears to provide a further bound for characterising debris beds. (orig.)