Single-droplet drying experiments were conducted with solutions of dairy materials in water (skim milk and its constituents, namely lactose, whey protein, and a lactose–whey mixture) at both moderate and elevated temperatures, at which inflation/deflation phenomena are observed. The experimental data were used to obtain parameters of a spatially resolving single-droplet drying model, which was extended to empirically account for inflation/deflation. Inflation/deflation parameters and conditions for crust formation at the transition from the first to the second drying stage were clearly solute dependent, and respective correlations with drying conditions were developed for the investigated dairy materials. The parametrized model was shown to satisfactorily describe measured data in respect to drying curve, drying time, and the diameter of product particles.

Recent initiatives covered in this review can be divided into three broad categories. The first category concerns mathematically describing the spray drying process using a plug-flow model which allows quick what-if evaluations of the process. Intricacies associated with capturing the drying of a range of droplet sizes are discussed. Challenges in adapting the plug-flow simulation approach to counter-current spray drying, which is common in the production of non-heat sensitive detergent powder, was further elaborated. The second broad category features modeling the spray drying process using the Computational Fluid Dynamics technique. A critical review was provided to guide readers on a common dilemma plaguing this area of spray drying modeling. Recent developments in agglomeration modeling in spray dryers are discussed as well. The final part of this review touches on modeling techniques which can be used to predict the development of specific powder qualities. This includes modeling the degree of protein denaturation during spray drying, predicting the characteristics of crystalline type spray dried powder, and determining the properties of the powder surface at the molecular scale.

This study examines the performance of a parabolic greenhouse-type solar dryer used for drying of cayenne pepper (Capsicum annuum) in Nan (northern Thailand). The dryer has a base area of 6.0 m × 8.2 m and a height of 3.25 m with the loading capacity of 100–200 kg for fruit or vegetables. It has a parabolic roof structure covered with polycarbonate sheets and is placed on a concrete floor. It is ventilated by three DC fans powered by a 50-Watt solar cell module. The produce is placed on trays with wire mesh base and located on steel supports. Among the advantages of this type of dryer is that the product is protected from rain, dust and insects. The pepper samples consisted of whole pods or cut pods. The drying experiments were carried out in the solar dryer and in an electrical (convective) tray dryer. The study was focusing on drying kinetics and on the effects of the drying treatments on one of the main quality attributes namely the capsaicin content in the dried products.