Comparative analysis of charcoal-starch composite as a heat absorber in solar drying of water yam (Dioscorea alata)

The objective of this study is to assess the feasibility of replacing the aluminium-plate absorber, which carries high embodied energy, with an environmentally friendly charcoal-based alternative in solar dryer design. Therefore, two solar dryers with aluminium-plated absorber (SDAPA) and charcoal bed absorber (SDCBA) were developed, and their thermodynamic performance and drying kinetics were compared for drying water yam. SDAPA raised the inlet air temperature by 2.1–6.3 ◦C, while it was 1.4–6.3 ◦C for SDCBA. The average thermal efficiencies were 44.93 % for SDAPA and 44.77 % for SDCBA, with an average heat utilization ratio of 46 % and 43 %, respectively. Drying water yam from initial moisture content of 69.45 %wb to 7.41 ± 0.32 % took 16 h for SDAPA, 17 h for SDCBA, and 24 h for sun-drying with average effective moisture diffusivities of 4.51 × 10—10, 3.3 × 10—10, and 2.56 × 10—10 m2/s, respectively. The specific energy utilisation varied from 0.239 to 14.07 W/ kg for SDAPA and 0.37 to 15.07 W/kg for SDCBA. The SDCBA mitigated 6782.404 tons of CO2 per year, translating to $98,344.87 in earned carbon credits, while it was 6465.87 tons and $93,755.12 for SDAPA. Modified Henderson and Pabis model best fitted the drying curve of water yam. This study demonstrates the potential of charcoal as a sustainable alternative to aluminium-plate as an absorber in solar dryers.