Design and Performance of Solar Tunnel Dryers: A Comprehensive Review

Abstract

An inadequate postharvest preservation results in considerable food loss, especially in poor areas where there is little access to efficient drying processes. Open sun drying is the traditional approach but is typically associated with contamination, poor product quality, prolonged drying durations and high postharvest losses. The purpose of this review is to assess the design features, drying performance, economic viability and environ-mental impacts of solar tunnel dryers for agricultural products. A detailed review of available literature on direct, indirect and hybrid solar tunnel dryers working under natural and forced convection modes has been performed. The examined studies were analyzed with respect to dryer configuration, drying efficiency, moisture reduction, product quality, economic performance and environmental impact. The results show that solar tunnel dryers may shorten the drying time by around 25–57% compared to the typical open sun drying with superior nutritional, sensory and sanitary quality of dried items. Reported thermal efficiency ranged from about 19% to over 80% as a function of dryer type, operating circumstances and product qualities. Economic assessments indicated positive benefit-cost ratios and short payback times ranging from 1 to 4 years. The thermal energy storage and hybrid energy systems can also improve the performance and continuity of operation of the dryer. In conclusion, solar tunnel dryers are a low-cost, energy-efficient and ecologically sustainable drying technology that can considerably minimize postharvest losses and increase food security, particularly for smallholder farmers and rural populations.