Study on Fluidization Behaviour of Raw and Dry Sri Lankan Black Pepper

Fluidized bed drying of Sri Lankan black pepper is commercially feasible due to short drying time and uniform heating. Knowledge on the fluidization behavior is important in dryer design and performance calculations. Despite the fact, that the theoretical minimum fluidization velocity (U_mf) is a constant for a given solid-fluid system, recent studies have shown that U_mf is a function of the bed weight. In this study, fluidization behavior of both raw and dry black pepper at various bed weights was studied. Both raw and dry pepper found to exhibit aggregative fluidization and belong to group D of Geldart classification of solids. An empirical mathematical correlation was developed to relate Reynolds number at minimum fluidization velocity (Re_mf) and the bed weight per unit bed cross section for pepper. Additionally, Burke-Plummer equation of minimum fluidization was modified, and correlation coefficients were determined. Results thus obtained show that U_mf is a function of bed weight per unit cross section to the power 0.25 and 0.35 for raw and dry black pepper, respectively. Furthermore, it was observed that during drying of pepper from moisture content 465% to 13%, true density, bulk density and U_mf decrease by 54%, 36% and 32%, respectively.