Modeling the movement of hulled millet in agitated drum dryer with discrete element method

Abstract

In the agricultural, food, chemical and pharmaceutical industries, mixing operations of granular materials frequently occur during which fractions are homogenized or the blockage of particles is prevented. In order to select the appropriate agitator motors, it is necessary to know the rotational speed of the mixer and the power requirements of the drive motor, which remains a major challenge for design engineers to this day.The main aim of this research was to create a discrete element simulation model (DEM) suitable for determining the mixing power requirements of an agitated drum dryer pilot plant, which can be applied to the modelling of mixing granular materials of various moisture content. In order to validate the results of the model, measurements were conducted by mixing hulled millet in the drum dryer. The parameter sensitivity tests conducted in the DEM environment showed that of the micromechanical parameters applied in the model, it was the Young modulus, and the rolling and twisting resistance coefficients of the contacts which needed to be adjusted as a function of the rotational speed in order for the simulated power requirements to approximate the values measured.In the laboratory tests conducted on the agitated drum dryer, the mixing power requirement of hulled millet of various moisture contents (9.6–29.5%) was determined at different drum loading factors (10–25%) mixed at various rotational speeds (0.32–1.58 s−1). Test results suggested that a DEM simulation environment could be created to approximate measurement results with acceptable accuracy. Furthermore, the mixing power requirement was highly affected by the moisture content of the material and the rotational speed of the mixing unit, while the mixing torque requirement decreased by increasing the latter. The validated DEM model is suitable for simulations of mixing hulled millet in an agitated drum dryer in terms of both quality and quantity.