In this study, the drying kinetics of papaya (Carica papaya L. 'Red Maradol') and banana (Musa acuminata (AAA Group) 'Gros Michel') was experimentally investigated in a lab-scale tunnel dryer. The drying experiments were performed at three air temperatures (50, 60, and 70 degrees C) and three air velocities (1.0, 1.5, and 2.0 m/s). A surface area shrinkage linear model from the literature was used to include the shrinkage effect on the drying process. From the drying curves, no constant rate period was observed and drying occurred in a falling rate period. It was found that the changes in air velocity had a slight effect on the drying process. In addition, a non-linear regression analysis was employed to determine the characteristic drying curve.

In this study, the drying kinetics of sweet pepper (Capsicum annuum L. 'Tres Cantos') and yellow onion (Allium cepa L. 'Yellow Granex F1') was experimentally investigated in a lab-scale tunnel dryer. The drying experiments were performed at three air temperatures (50, 60, and 70 degrees C) and three air velocities (1.0, 1.5, and 2.0 m/s). A volumetric shrinkage linear model from the literature was used to include the shrinkage effect on the drying process. From the drying curves, no constant rate period was observed. The drying process took place in a falling rate period. It was found that the changes in air velocity had essentially no effect on the drying process. In addition, a non-linear regression analysis was employed to determine the characteristic drying curve.

In this study, the drying kinetics of noni (Morinda citrifolia L.) was investigated in a laboratory tunnel dryer at air temperatures of 50, 60, and 70 degrees C and velocities of 1.0, 1.5, and 2.0 m/s. Noni showed only a falling drying rate period. Further, a non-linear regression procedure was used to determine the characteristic drying curve. The experimental drying data of noni were employed to fit thin-layer models. Under the evaluated experimental conditions, the Page model provided the best representation of thin -layer drying characteristics of noni. The effective moisture diffusivity ranged from 1.77 x 10-7 to 3.33 x 10-7 m2/s. The activation energy was found to be 3.34 kJ/mol.

In this work, the drying kinetics of ginger (Zingiber officinale Roscoe) was studied considering the shrinkage effect. The experimental data were obtained using three different temperatures (40, 60, and 80 degrees C). For the determination of shrinkage, two cutting orientations were employed. The volumetric and thickness shrinkage was evaluated by direct measurement. The shrinkage showed two periods during drying and had a considerable effect on the drying rate. An equation that relates the changes in the drying area as a function of the moisture content was determined. During drying, ginger showed only a falling rate period and exhibited a characteristic drying curve.

A model for simulating the drying of paddy (Oryza sativa L.) in a continuous fluidised bed dryer was employed. Equipment and material models were applied to describe the process. The equipment model was based on the differential equations obtained by applying mass and energy balances to each element of the dryer. In the case of the material model, mass and heat transfer rates in a single isolated particle were considered. Simulation results were verified by comparison with experimental data from the literature. There was a very good agreement between experimental data and simulation. The effects of gas temperature and velocity, particle diameter, dry solid flow, and solid temperature on the drying process were studied. It was found that the changes in gas velocity, dry solids flow, and solid temperature had essentially no effect on the drying process.

Mathematical models of thin-layer drying for brewer’s yeast (Saccharomyces cerevisiae) were studied and verified with experimental data. Twelve (12) different mathematical drying models were compared according to three (3) statistical parameters, i.e., correlation coefficient, root mean square error and chi (χ²)-square. The thin-layer drying kinetics of brewer’s yeast was experimentally investigated in a laboratory tunnel dryer and the mathematical modelling, using thin-layer dryingmodels present in the literature, was performed. Experiments were performed at air temperature of 40, 50 and 60 ºC at an airflow rate of 1.2 m/s. Drying curves obtained from the experimental data were fitted to the thin-layer drying models. The results show that the Page model is the most appropriate model for predicting the drying behaviour of the thin-layer brewer’s yeast.

A mathematical model for the drying of grain in a continuous vibrating fluidized bed dryer was developed. Simple equipment and material models were applied to describe the process. In the plug-flow equipment model, a thin layer of particles moving forward and well mixed in the direction of the gas flow was examined. Mass and heat transfer within a single wet particle was described by effective transport coefficients. Assuming constant effective mass transport coefficient and thermal conductivity, analytical solutions of the mass and energy balances were obtained. The variation in both transport coefficients along the dryer was taken into account by a stepwise application of the analytical solution in space intervals with averaged coefficients from previous locations in the dryer. Calculation results were in fairly good agreement with experimental data from the literature. However, the results depend strongly on relationships used to determine heat and mass transfer coefficients; because the results from correlations found in the literature vary considerably, the correlations should be adapted to the specific equipment in order to obtain reliable results.

In this work, simulation algorithms for contact drying of agitated particulate materials under vacuum and at atmospheric pressure were developed. The implementation of algorithms gives a predictive estimation of drying rate curves and bulk bed temperature during contact drying. The calculations are based on the penetration model to describe the drying process, where all process parameters such as heat and mass transfer coefficients, effective bed properties, gas and liquid phase properties are estimated with proper correlations. Simulation results were compared with experimental data from the literature. In both cases, simulation results were in good agreement with experimental data. Few deviations were identified and the limitations of the predictive capabilities of the models are discussed. The programs give a good insight of the drying behaviour of the analysed powders.