RADIATIVE AND CONDUCTIVE HEAT-TRANSFER IN POROUS-MEDIA - ESTIMATION OF THE EFFECTIVE THERMAL-CONDUCTIVITY

The effective thermal conductivity kappa(eff) of porous media has been studied when both radiation and conduction is present. Expressions fo r kappa(eff) of a solid containing dispersed, equisized, disconnected spherical pores are derived within an extended effective medium theory . When no radiation is present, the results agree very well with exact results for an fcc lattice of spheres. The effective medium approach is also used to calculate the transverse effective thermal conductivit y of a solid containing aligned, infinitely long, equisized, disconnec ted, cylindrical pores. When no radiation is present, the result is in excellent agreement with exact results for a hexagonal array of cylin ders. In the direction parallel to the cylinder axes, the effective th ermal conductivity is found exactly. An estimation of kappa(eff) for a system of random, overlapping, solid spheres in a gas matrix is prese nted.