Performance comparison of mixed mode and indirect mode parallel flow forced convection solar driers for drying Curcuma zedoaria

This study focuses on energy and drying kinetic analyses of Curcuma zedoaria (white turmeric) dried in mixed and indirect active parallel flow solar dryers. Dryer efficiency, specific energy consumption and drying rate are studied. The overall dryer efficiency of mixed mode (MFSCD) is 26.5% higher than indirect mode (IFSCD) solar dryer. Two term model and Verma model fit best for Curcuma zedoaria drying in MFSCD and IFSCD, respectively, and Logarithmic model is quite suitable for open sun drying (OSD). The effective moisture diffusivity of the product dried under MFSCD is highest as compared to IFSCD and OSD products. The quality analyses show that higher values of TFC (78.11 mg GAE/g of sample) and DPPH (120.56 μ mol of TE/g of sample) are reported in the samples dried in MFSCD as compared to IFSCD and OSD samples.

Practical applications

Conventional open sun drying is a common practice followed by small farmers for drying herbs and spices. Products dried under open sun lose their nutritional and medicinal values due to slow drying rate and improper heating. The present work focusses on the development of a low cost solar dryer for drying of high value medicinal herbs like Curcuma zedoaria, curcuma caesia, and black cardamom. Study of drying kinetics helps in improving the design aspects of solar dryer and optimization of the drying systems. Drying time of the Curcuma zedoaria dried in the developed dryer is about 60% less than the open sun drying and the retention of color, antioxidant, and texture of the solar dried products is excellent. The developed solar dryer will be suitable for small small-scale farmers and can be scaled up to any size.