Evaluation of effective thermal conductivity from the structure of a packed bed

This paper presents a method to evaluate the effective thermal conductivity from the packing structure of a packed bed of mono-sized spheres in the presence of a stagnant fluid. The evaluation is based on two aspects: (i) the heat transfer between particles, which is obtained under some simplified conditions; and (ii) the connectivity of particles in a packing, which is determined from the packing structure measured by Finney. Three heat transfer mechanisms or paths are considered in the present modelling, including the conduction through the solid particles and stagnant fluid between non-contacted particles, the conduction through the solid particles and stagnant fluid and the conduction through the contact area between contacted particles. The validity of this approach is verified by the good agreement between measured and calculated results for a packed bed over a wide range of solid-to-fluid thermal conductivity ratio and for packed beds with particles of different thermal conductivities. (C) 1999 Elsevier Science Ltd. All rights reserved.