Design of drying drying system and investigation of drying parameters of medical aromatic products

Freeze drying process is based on dehydration sublimation of frozen product. Because of the low temperatures and pressure and long drying period required for the process, freeze drying technology is feasible to the process of sensitive products. Long drying times in freeze drying lead to high energy consumption and high capital costs. In this study, mint leaves were freeze dried at three different temperatures (40, 50, 60oC) and three different pressures (30, 50, 80 kPa). The drying behavior of dried mint leaves was investigated. With exergy analysis of the process specified the operating conditions that allow minimizing the exergy losses and maximizing the exergy efficiency. In addition to energy and exergy analysis, when the product appearance is evaluated, 30 kPa cabin pressure and 50oC drying temperature are found to be the most ideal conditions for freeze drying of mint. Wang and Singh model was found to be the most suitable mathematical model in the ideal drying conditions. Heat and mass transfer analyzes were performed for mint leaves. The heat transfer coefficient of dried mint was determined as 0.33 W/m2K. The mass transfer rate of the product ranged from 3.33x10-10 to 2.27x10-9 m/s. Both heat transfer coefficients and mass transfer rate increased with temperature increase and decreased with increase in cabin pressure. It was also found that the drying temperature accelerates the moisture diffusion. These results will provide information to help improve the system the optimization of a freeze-dryer and the operating parameters.