INFLUENCE OF AIR VELOCITY ON DRYING DYNAMICS OF ALFALFA

Alfalfa is widely used as feed for animals, and preservation of fodder is an important problem. This paper contains the experimental and theoretical investigations of alfalfa (Medicago sativa) drying by forced convection. This research is focused on verification of the influence of different air velocities on the drying process of alfalfa in thin layer in mild temperatures (22 degrees C) and rather high relative humidity of air (70 %). The initial moisture content of the material was determined by the gravimetric method using the hot air drying in the electric oven. Special device for convection drying with air flow passing through the material from the bottom through supporting trays with a sieve (dimensions of mesh 3 x 4 mm) by constant temperature was used for drying experiments, when the air velocity 0.7 m.s(-1), 1.0 m.s(-1), 1.2 m.s(-1) and 2.0 m.s(-1). Changes of alfalfa samples moisture were determined from the measured values of weight using the gravimetric method. The most preferable form of the alfalfa drying coefficient K(t) with forced air was power expression. Using the experimental data and the mathematical model of the thin layer drying process, it is possible to determine the unknown parameters at each speed of the drying agent. The theoretical results are compared with the experimental results and the average difference was lower than 6 %. The biggest difference was observed at lower air speeds and at the initial stage of the process. Using the experimental results relationships between the air velocity and the parameters included in the function of the drying coefficient were determined. This research allows theoretically predicting the drying process depending on the air velocity.