Assessment of a mixed-mode vertical solar dryer for experimental turmeric drying

Solar drying, an eco-friendly and sustainable approach harnesses solar radiations to remove moisture from a drying commodity, thereby preventing its spoilage and extending shelf life. Turmeric (Curcuma longa), a popular herb is being used for centuries in Ayurveda as a traditional medicine. Since, fresh turmeric contains 80-90 % moisture content, therefore, it is quite difficult to store for a longer period. An innovative and compact mixed- mode vertical solar dryer (MVSD) with a circular solar collector (solar tracking geometry) is developed and tested for turmeric slices drying under partial and fully loaded conditions. Turmeric samples of 2, 3 and 4 mm slices thicknesses were used for experimentation under partial loading condition. The thickness of the turmeric slices was observed to affect the performance of the MVSD. The drying rate and thermal efficiency were observed to be highest for 3 mm thick turmeric slices sample under partially loaded condition. The MVSD was further tested with full loading capacity for 3 mm thick turmeric slices drying under natural and forced convection (NC and FC), respectively modes. The drying behavior of turmeric slices was well described by Midilii-Kucuk model. Heat transfer coefficients and efficiency (thermal and exergy) were observed to be higher under FC mode. Embodied energy and energy payback time were observed as 554.44 and 585.53 kWh; and 4.39 and 4.55 years under NC and FC modes, respectively. Annualised cost and payback period were observed to be desirable for NC mode.