Evaluation of heat mass performances for freeze drying of mint leaves

Abstract

Mint leaves are one of the most used medicinal and aromatic plants in the world, having a wide range of minerals and vitamins. It is necessary to prevent nutrient content and quality loss during the drying of the leaves. This study aimed to perform the drying of mint leaves and to experimentally specified the effective diffusion coefficient, activation energy, and heat and mass transfer coefficients values throughout the drying process. Mint leaves were dried using a laboratory-scale dryer with three different drying temperatures (30, 40, and 50°C) and three different chamber pressures (50, 60, and 70 kPa). As a result, heat transfer coefficients varied from 0.3347 to 0.3353 W/m2K, and mass transfer coefficients varied from 3.33 × 10−10 to 2.27 × 10−9 m/s for different drying conditions. The effective moisture diffusivity during drying varied from 5.01 × 10−14 to 4.80 × 10−13 m2/s. The activation energy for mint leaves during drying varied from 79.07 to 76.44 kJ/mol at different drying temperatures. Practical applications Drying is an energy-intensive process that involves simultaneous heat and mass transfer. In this study, the heat and mass transfer coefficients of mint leaves at different drying temperatures and pressures were studied. In order to optimize the drying process, the heat and mass parameters of the product must be fully understood. Understanding these parameters can easily provide a basis for designing dryers with the best energy saving.