Convective drying of phytotherapic leaves involves heat and mass transfer in packed-beds of deformable material, since the leaves shrink significantly when the moisture is removed. Therefore, the packing structure changes over time, and the transfer properties alter as well. An additional drawback in the analysis of this process is the challenge to obtain reproducible packings to investigate drying in fixed-packed beds, given the random nature of packing for such an irregular type of material. In this work, an experimental investigation will be conducted to analyze how basil leaves (Ocimum basilicum L.) behave during drying focusing in the challenging characteristics of this particulate phase. Aiming at evaluating reproducibility of drying kinetic curves (dimensionless moisture content versus time), a minimum of 10 drying experiments will be performed in cells 10 cm in diameter with height of 1 to 3 cm (corresponding to thin-layer beds), at a given condition of air velocity and temperature, adopting a standard packing procedure. The purpose is to identify the minimum number of assays to ensure statistically significant averages that allow a reliable fitting of parameters on drying kinetic curves. In a second approach will be evaluated drying in deep-fixed beds, in which shrinking worsen the reproducibility. In drying experiments with beds 10 cm high, the pressure drop across the bed and the variation of bed height throughout time will be measured at the same conditions of air temperature and velocity adopted in thin-layer drying. These data will be used to evaluate how bed permeability changes with time due to moisture reduction and shrinking.
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