Cell and quasihomogeneous models for determining of the effective thermal conductivity in packed beds are compared and their evidence is investigated by own experimental data both in the high and low temperature range under consideration of the stationary fluid. The quasihomogeneous model is extended to packed beds with spheres of relatively low thermal conductivity. The void radiation heat transfer is considered theoretically and is determined experimentally. Simplified formulas are presented for the computation of the effective thermal conductivity on the core of a high temperature reactor within a temperature range of 2500 °C