Determine the optimum operating conditions for black pepper drying in a tray dryer to minimize the total drying energy

Abstract

Open sun drying is the widely used passive method for black pepper drying, but due to its limitations, artificial dryers have become popular. Among these dryers, convective hot air tray dryers are extremely popular in black pepper processing industries. It is extremely important to identify the optimum drying temperature and the hot air velocity for black pepper drying process on a convective type tray dryer to minimize the total drying energy while improving the quality of the black pepper. During this study, the drying characteristics of black pepper were investigated in a convective type tray dryer. An experimental apparatus which was fabricated in-house was used to understand the variation of the moisture ratio with the drying time. The experiments were conducted for three different temperatures of 50°C, 55°C and 60°C and, for three different air velocities of $0.4 \text{ms}^{-1},0.8\text{ms}^{-1}$ and $1.2 \text{ms}^{-1}$. The observed experimental data were fitted with existing drying models. Model coefficients and constants were evaluated by using the MS Excel Solver software. The Logarithmic model was found to be the most suitable drying model describing the black pepper drying on a convective type tray dryer with an average RMSE (root mean square deviation) of 0.0140. The total drying time required to reduce the moisture content to 12% (minimum safe storage moisture content) in dry basis under different drying conditions was calculated using the logarithmic model equation. The total drying energy required to dry 1 kg of raw black pepper in different drying conditions was calculated and a surface plot of total drying energy against temperature and hot air velocity was generated. Based on the contours of the surface plot, the drying conditions which minimize the total drying energy required were determined.