Mathematical modeling and simulation of batch drying of foods in fixed beds with airflow reversal

A mathematical model based on the heat and mass transfer mechanisms between the air and the product was developed in order to simulate the fixed bed drying process of foods conducted with and without periodical reversals of the airflow direction. The proposed model considers the fixed bed of the product as a series of ideal stirred stages connected in series, and was validated with the experimental data obtained during the packed bed drying of carrot cylinders with various times of application of the airflow reversals (15 min, 30 min, and without air flow reversal). The drying experiments were performed using an air velocity of 2 m/s and two different particle thickness/bed height combinations (0.001/0.05 and 0.01/0.1 m/m) at the air temperatures of 50 and 70 °C. A good agreement was found between the experimental and the predicted data. Furthermore, the results showed that the proposed model is able to predict the distributions of moisture content and temperature within the packed bed of the food and a higher frequency of application of the airflow reversal promote slightly shorter drying times and flatter moisture and temperature profiles in the bed than those obtained without it.