Minimum Fluidization Velocity of Food Materials: Effect of Moisture and Shape

Abstract

Changes in fluidization behaviour of three geometrical shaped food particulates, with changes in moisture content during drying, were investigated using a fluidized bed dryer. The three food particulates were cylindrical (beans), parallelepiped (potato) and spherical (green peas). Fluidization behavior was characterised for cylindrical shape particles with three length diameter-ratios of 1:1, 2:1 and 3:1, parallelepiped particles with three aspect ratios of 1:1, 2:1 and 3:1 and spherical particles. All drying experiments were conducted at 50oC and 15% RH using a heat pump dehumidifier system. Fluidization experiments were undertaken for the bed heights of 100, 80, 60 and 40mm and at 10 moisture content levels.Data was analysed using SAS, and an empirical relationship of the form Umf = A + B e-Cm was developed for the change of minimum fluidization velocity with moisture content during drying for cylindrical particulates for the L:D ratio of 1:1, and spherical behaviour was best fitted to the linear model of Umf = A + Bm. Due to irregularities in shape, the minimum fluidisation velocity of parallelepiped particulates (potato) could not be fitted to any empirical model. The experimentally determined minimum fluidisation velocities were compared with predicted minimum fluidisation velocities using a generalised equation.