Convective drying of black pepper: Experimental measurements and mathematical modeling of the process

Black pepper (Piper nigrum L.) is an important worldwide agricultural commodity. The post-harvest moisture (65%, wet basis) needs to be reduced to ensure its conservation and commercialization. Nowadays, large-scale drying is conducted in open-air sun-drying or adapted dryers, compromising the product's quality. A systematic and phenomenological analysis of the drying process is a required task. Thin-layer drying experiments and mathematical modeling of the process were conducted towards qualitative and quantitative information on the drying kinetics of black pepper. The experimental data were simulated using two approaches: a model consisting of a set of differential equations that described the coupling between heat and mass transfers, and an isothermal model based on diffusion theory, in which it was possible to estimate the effective diffusivity, whose values were in the range of 1.91 x 10-11 to 1.22 x 10-10 m2 s- 1, and the activation energy, value equal to 54 kJ mol-1. The mass transfer coefficient was in the range of 3.83 x 10-5 to 1.97 x 10-4 kg s- 1 m- 2 and the heat transfer coefficient in the range of 42.39-228.51 W m- 2 degrees C-1. Halsey's equation was selected to estimate the equilibrium moisture of the grains. Overall, the proposed mathematical models satisfactorily described the drying kinetics of black pepper.