Two-stage solar tunnel chili drying: Drying characteristics, performance, product quality, and carbon footprint analysis

Abstract

An indirect two-stage solar tunnel dryer has been developed to study the drying characteristics of two chili pepper varieties. The effect of chili layer density on the drying time and moisture loss was investigated. Thirteen thin layer-drying models have been analyzed to fit the experimental data. The results showed that the drying process occurred in the falling rate period. A safe storage moisture content of 11–12% (w.b) was achieved within 50–80 h. The moisture diffusivity of both varieties varied from 2.94 E−09 to 4.47E−09 m2 s−1. The Modified Henderson and Pabis and Verma et al. model accurately described the drying characteristics of the MF and BL chili varieties respectively. The efficiencies of the collectors range from 66.44% to 76.53%. The overall system efficiency was found in the range of 24.12–31.3%. The specific energy consumption of the dryer ranged from 2.1 to 2.44 kWh/kg and the CO2 emission was calculated as 53.8 kg/kWh. The energy payback period varied from 2.1 to 2.36 years and the net CO2 mitigation varied from 10.9 to 13 tons per year. The two-stage solar tunnel dryer provide good quality attributes compared to open sun drying. The carbon footprint mitigation of the solar dryer showed that renewable energy-based drying technologies provide better benefit compared to conventional drying systems and the maximum and minimum of the earned carbon credit (ECC) in US dollar was found to be 162.880 and 136.250 per year respectively.