The results of Portillo et al. (Superfices y Vacío 15, 19-21, 2002) on the phase transition in CdS are analysed entirely by a different route here. With CdS single crystal taken in wafer form, photoacoustic measurements are carried out in the presence of carbon and air. Phase transformation from CdS to CdCO3 is obtained at a temperature of 80°C which agrees well with the results of Portillo et al.

A simplified model for drying solids in the constant rate period in a batch fluidised bed was developed.It assumes the bed to be divided into dense and bubble phases with heat and mass transfer between the phases.The model predicts the constant-rate drying period, provided the fluid bed shape and material characteristics are known.The model is compared with experimental data reported in the literature covering a wide range of materials, gas flow rates, column diameters, material hold-ups, air temperatures and humidities.Model predictions compare satisfactorily with the experimental data.