Thermal Conductivity of Porous Material

jeallison

does anyone know where this equation regarding the thermal conductivity of porous material K=K[itex]_{}0[/itex][(1-P)[itex]/(1-B P[/itex])] comes from? I know B has to do with thermal density, but I have no idea what P is? let alone the origins of the equation. This has to do with beds of spherical material.

background: I'm doing a lit review for a graduate student and I'm stuck on this particular equation, and she doesn't know much about it either.

thanks!