Experimental study and mathematical model for soya bean drying in thin layer

Thin-layer drying tests were conducted for soya bean in the temperature range 45–120 °C, velocity range 0–3 m s−1, initial grain moisture content 0.13–0.32 dec., d.b., with variations in relative air humidity 5–50%. To generate air of required humidity the water vapour was injected after the air heater. The influence of velocity on drying dynamics essentially depends on initial grain moisture content. At low values of initial grain moisture content (<0.22 dec., d.b.) influence of velocity was practically absent. At high moisture content (>0.32 dec., d.b.) increases in air velocity (from 0.12 m s−1 up to 0.37 m s−1) led initially to acceleration in the drying process. Subsequent increases in velocity (from 0.5 m s−1 up to 2.5 m s−1) did not practically influence drying dynamics. In the absence of airflow the drying ratio is less essential than even the lowest velocity (0.12 m s−1) used in the experiments. The increases in air humidity that slows down the drying process are related with the increase in value of the equilibrium moisture content. The dependences of the moisture ratio with time under identical initial condition did not practically depend on air humidity. To describe the experimental results obtained it was proposed to consider the soya bean seed as composed of two compartments with different transfer coefficients. The resulting thin-layer drying model consisted of two ordinary differential equations, considered the influence of all the studied parameters and satisfactorily described all experimental data.