Influence of Draft Tube on Drying Behaviour of Black Pepper in Spouted Bed

Black pepper was dried in two different spouted bed dryer configurations namely a spouted bed equipped with a non-porous draft tube and a spouted bed equipped with a porous draft tube. The spouted bed equipped with a non-porous draft tube requires the lowest value of minimum spouting velocity while the non-porous draft tube fitted spouted bed requires the highest minimum spouting velocity for the given bed heights. The influence of the geometric factors of non-porous and porous draft tubes such as tube height, tube diameter, and height of entrainment zone on the drying kinetics of black pepper was analyzed. Effective moisture diffusivity, activation energy, and pre-exponential factor were evaluated for black pepper drying in each configuration. Effective moisture diffusivity was increased when the drying air temperature was increased from 45°C to 75°C. Effective diffusivity values ranged from $4.11 \times 10^{-11}$ $\mathrm{m}^{2} / \mathrm{s}$ to $1.71 \times 10^{-10} \mathrm{~m}^{2} / \mathrm{s}$ for the above-mentioned drying air temperatures in two spouted bed configurations at minimum spouting conditions. A spouted bed equipped with a porous draft tube has higher moisture diffusivity and lower activation energy compared to a spouted bed equipped with a non-porous draft tube.