Thermo-economic analysis of sun drying patio coffee in the Sierra Mariscal, Chiapas-México

This study shows a thermo-economic analysis of patio coffee drying in the Sierra Mariscal Chiapas-México to optimize bed thickness. The drying time, specific energy, thermal efficiency, water-effective diffusivity, and drying batch costs were correlated with bed thickness and solar irradiation. The initial and final coffee moisture contents were 53 % and 11–12 % ( w.b ). The bed thickness was in terms of kilograms of coffee uniformly spread on a square meter (2.0, 5.0, 10.0, 15.0, and 20.0 kg/m 2 ). The five experimental campaigns involved five tests over a harvest season. The water-effective diffusion coefficient increases with bed thickness (0.38–91.2 × 10 −10 m 2 /s ). The solar irradiation requirement and the efficiency of the patio drying linearly increase with bed thickness while specific energy exponentially decreases. The lower specific energy was (7.1–10.4 MJ/kg) for the higher bed thickness (20.0 kg/m 2 ), with (24.0–38.0 h ) of drying time and (0.22–0.32) of efficiency. The optimized coffee bed thickness was 10 kg/m 2 , with a specific energy of 8.8–9.6 MJ/kg. When bed thickness increases, the thermal efficiency increases almost linearly 5.5 times, exponentially reducing the drying cost per batch five times. However, increasing drying times shall lessen the quality of physical-chemical and sensorial coffee. • Sun patio drying performance mainly depended on bed thickness and irradiation. • Highest efficiency of the patio drying reached up 0.318 at 20.0 kg/m 2 of bed thickness. • Lower specific energy was 8.8 MJ/kg at 10.0 kg/m 2 of bet thickness. • Optimum coffee bed thickness was 10.0 kg/m 2 and the standard 5.0 kg/m 2 . • Specific energy of patio drying was 41.76 % concerning reported coffee cherries.