Abstract
A mathematical model is proposed to predict temperature distribution profiles for the drying of a single droplet in a forced convection medium. The phenomenon of receding evaporation front and crust formation are taken into account. The governing heat transfer equations are derived and solved using finite difference methods, taking into account the effect of vapor diffusion through the crust. A suspended rotating glass nozzle was specially designed to measure the weight loss and core temperature of a suspended single droplet. The study covered sodium sulphate decahydrate solution, a concentrated fruit juice and an organic paste used for adhesive and coating applications over various drying conditions. The proposed model was compared with the experimental results for the various materials at different air temperatures. A good agreement was obtained between the predicted and the experimental results of temperature distributions within the droplet. The experimental results of the moisture contents at 75 degrees C and 140 degrees C showed the effect of crust formation on the mechanisms of drying. The mechanisms suggested are of interest for both single droplet drying and the optimization of spray drying equipment.