This work presents a simple method developed for the design of indirect dryers in thin-film by boiling for an alumina sludge treatment. The method developed is based on decoupling of the internal and external transfers. In a first step, external transfers are characterized. A simple experimental device was built up in order both to provide and to estimate the heat flux density at the interface between a hot metallic plate and the drying sample. An analytical direct model is made using the quadripole formalism, and the system transfer function is calculated. The inverse problem is solved using the Beck's sequential function specification method, and the corresponding drying curve is deduced by an energy balance without weighing.
In the second part, the drying of sludge on an electrically heated laboratory drum dryer was studied. The aptitude of sludge to be coated on the cylinder is related to thermal effects. The drying kinetics are obtained by sampling and are compared with those obtained with the first experimental device. The curves are similars whereas the drying time is much longer. A simple model of the drum dryer is developed by taking into account the combined effects of the internal and external transfers. In this case, the importance of the internal transfers, which govern the drying time, are highlighted.