Thermal and mass transfer properties of a shrinkable industrial sludge: experimental determination and modeling approach
Résumé
In this study the thermo-physical and mechanical properties of an industrial sludge like shrinkage
coefficient, density, water activity, apparent moisture diffusivity, effective thermal conductivity and
heat capacity are determined experimentally. These properties constitute a major part of the
required input data to model the sludge drying. The sludge shrinks linearly until reaching a
critical water content Xcr = 23% and then maintains a constant volume until the end of drying.
Therefore, the density increases with decreasing the water content until the critical value (Xcr =
23%) then it decreases until the end of drying. The Henderson equation seems to be the most
appropriate statistical model to describe the water sorption isotherm of the sludge. The
apparent moisture diffusivity is determined from the numerical solution of Richards law of
diffusion with shrinkage. The results show that the effective thermal conductivity and the heat
capacity decrease with the reduction of the water content from 2.60 W m-1 K-1 and 2.52 J g-1
K-1 for a wet sludge to 1.71 W m-1 K-1 and 0.78 J g-1 K-1 for a dry sludge respectively. The
relationships between thermo-physical / mechanical properties and the water content /
temperature of the sludge are established to be introduced in the created numerical drying model