Thermal and mass transfer properties of ashrinkable industrial sludge: experimentaldetermination and modeling approach

International audienceIn this study the thermo-physical and mechanical properties of an industrial sludge like shrinkagecoefficient, density, water activity, apparent moisture diffusivity, effective thermal conductivity andheat capacity are determined experimentally. These properties constitute a major part of therequired input data to model the sludge drying. The sludge shrinks linearly until reaching acritical 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 mostappropriate statistical model to describe the water sorption isotherm of the sludge. Theapparent moisture diffusivity is determined from the numerical solution of Richards law ofdiffusion with shrinkage. The results show that the effective thermal conductivity and the heatcapacity decrease with the reduction of the water content from 2.60 W m-1 K-1 and 2.52 J g-1K-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. Therelationships between thermo-physical / mechanical properties and the water content /temperature of the sludge are established to be introduced in the created numerical drying mode