Low‐temperature drying characteristics of mint leaves in a continuous‐dehumidified air drying system

Low‐temperature drying seems a better alternative option for drying heat labile products, especially leafy vegetables. In this article, the thin layer drying characteristics of mint leaves are studied using a continuous‐dehumidified air produced by molecular sieve 13X based heatless pressure swing adsorption (PSA) system. The PSA system consists of an air compressor with after cooler, two adsorber towers, and drying chamber. The optimum process parameters of adsorption system are identified through Box Wilson Central Composite experimental design to produce continuous‐dehumidified air suitable for low‐temperature drying applications ranging from 35 to 37°C dry bulb temperature and 0.1% rh. The performance indices of the PSA system such as thermal effectiveness and dehumidification efficiency at optimal conditions are observed as 0.884 and 96.40%, respectively. The effect of the volume flow rate of continuous‐dehumidified air on mint leaves drying characteristics is also studied, and the initial moisture content of leaves is reduced from 83.45% (wb) to less than 10% (wb) in 6 hr at the volume flow rate of 0.160 m³/min. The effective moisture diffusivity value for varied volume flow rates of air is varying from 2.07534 × 10⁻¹¹ to 3.45817 × 10⁻¹¹ m²/s. The ascorbic acid retention percentage in dried mint leaves is increased with increase in volume flow rate of dehumidified air, and the maximum of 70.11% is achieved at 0.160 m³/min. Based on the regression analysis, the most suitable drying model to describe the low‐temperature drying characteristics of mint leaves is the Midilli and Kucuk model. It is noted that the low‐temperature drying is the most appropriate drying method for retaining the good amount of ascorbic acid. PRACTICAL APPLICATIONS: Highly suitable for heat‐sensitive products' drying especially medicinal herbs, spicy (leafy) vegetables. Production of continuous‐dehumidified air (with ultra‐low dew point) for sensitive applications like pharmaceutical, lithium battery manufacturing, defense, chemicals, electronics, leather, and so forth.