Assessment of energy, exergy, environmental, and economic study of an evacuated tube solar dryer for drying Krishna Tulsi

In the present work, experimental studies of drying Krishna tulsi leaves in an in-house fabricated evacuated tube solar collector (ETSC) connected with an indirect solar dryer are carried out. The acquired findings are compared to those obtained from drying the leaves in open sun drying (OSD). The developed dryer takes 8 h to dry Krishna tulsi leaves; it takes 22 h in the OSD to reach a final moisture content of 12% (db) from an initial moisture content of 47.26% (db). The collector and dryer efficiencies range from 42 to 75%, 0-18%, respectively, with an average solar radiation of 720 +/- 20 W/m(2). The ETSC and drying chamber exergy inflow and outflow vary from 200 to 1400 W, 0 to 60 W, and from 0 to 50 W, 0 to 14 W, respectively. The ETSC and cabinet exergetic efficiencies range from 0.6-4% and 2-85%, respectively. The exergetic loss of the overall drying process is estimated to be 0-40%. The drying system sustainability indices, including improvement potential (IP), sustainability index (SI), and waste exergy ratio (WER), are calculated and presented. The value of the embodied energy of the fabricated dryer is 349.874 kWh. For an expected life span of 20 years, the dryer will reduce CO2 by 13.2 tonnes and earn carbon credits worth between 10,894 and 43,576 INR. The proposed dryer has a payback period of 0.4 years.