Single layer drying kinetics of papaya amidst vertical and horizontal airflow

The impact of airflow direction, namely through-flow and over-flow modes, on drying kinetics of osmotically-pretreated papayas was investigated in a convective-type dryer under varied conditions (temperature, humidity and velocity). The Newton model was used to describe thin-layer drying characteristics and the dependence of drying air parameters on the drying constant (k) was expressed by an Arrhenius-type relationship. It was found that a more uniform airflow distribution in the through-flow chamber resulted in higher product temperature as well as faster drying rate, especially during the initial stage of drying. For both airflow modes, drying kinetics was most significantly influenced by temperature and velocity of the air, whereas the specific humidity had less effect on the drying rate. The value of k increased in parallel with temperature and velocity of the drying air, whereas it was reduced by increasing humidity. A model incorporating the conditions of drying air was developed for each airflow mode, which can help with optimization of practical drying operations.