THERMAL-CONDUCTIVITY OF PACKED-BEDS CONSISTING OF POROUS PARTICLES WETTED WITH BINARY-MIXTURES

The thermal conductivity of particles wetted with a binary mixture and packed beds of such particles has been investigated both theoretically and experimentally. The model of Zehner and Bauer has been used to combine the conductivites of the (wetted) pores and the solid matrix to provide an effective thermal conductivity for the particle as well as to predict the effective conductivity of the packed bed. The latter is obtained both from the conductivity of the single particles and from the conductivity of the moist gas in the cavities, the additional transport of energy via the evaporation and recondensation of the vapours of both components being taken into account through the introduction of an equivalent thermal conductivity. Two different techniques have been employed in the experimental investigations. The thermal conductivities of single particles were obtained by means of a transient method, in contrast to the conductivities of fixed beds which were measured in a steady-state apparatus. By fitting two unknown parameters to the results for the single particles, a good prediction of the thermal conductivities of packed beds was obtained showing a strong temperature dependence in the case of wet particles.