Analysis of drying kinetics and performance evaluation of an indirect solar cabinet chili dryer

Abstract

In this study, an indirect forced convection solar cabinet dryer was developed and experimentally evaluated for drying red chili under Ethiopian climate conditions. Drying temperature, relative humidity, and mass loss of chili were measured at different sections of the dryer to investigate drying behaviour and system performance. Drying kinetics were analyzed using ten commonly applied thin-layer drying models to identify the most suitable model for describing the evaluated moisture removal characteristics. The results showed that the red chilies placed on the lower tray dried faster than those on the middle and upper trays due to higher drying air temperature and lower relative humidity near the collector outlet. The moisture content of chili was reduced from an initial value of approximately 80% (wet basis) to the safe storage level of 11-12% within 39-42 hours using the solar cabinet dryer, while open sun drying required about 72-75 hours. The page model provided the best fit to the experimental data. The average solar collector efficiency ranged from 48.2% to 66.01%, depending on solar radiation conditions. The average overall drying efficiencies of the solar cabinet chili dryer for the lower (tray 1), middle (tray 2), and upper (tray 3) were 24.79%, 23.10%, and 22.2%, respectively, compared to only 6.5% for open sun drying. The maximum drying rate was 0.35 kg/kg.h at Tray1. The solar cabinet dryer reduced the drying time by approximately 42 % as compared to open-sun drying. In a nutshell, the indirect solar cabinet dryer significantly improved drying rate, reduced drying time, and enhanced energy efficiency compared to traditional open sun drying. The results demonstrate the potential of the developed system as an effective and sustainable drying technology for chili processing, particularly for smallholder farmers in regions with similar climate conditions.