Design and Thermal Performance Enhancement of a Passive Solar Dryer Using a Rotating Ventilator Mechanism

Passive solar drying is a sustainable and energy-efficient method widely used for agricultural preservation, particularly in rural and small-scale applications. However, conventional passive solar dryers rely solely on buoyancyd-driven natural convection, which often results in weak airflow circulation, thermal stratification, and non-uniform moisture removal across drying trays. These limitations reduce overall drying efficiency and product quality.

This study presents the design and thermal performance enhancement of a passive solar dryer integrated with a rotating ventilator mechanism to improve internal airflow distribution. The proposed system utilizes a greenhouse-based solar collector with a blackened absorber surface to maximize solar heat gain. A rotating ventilator positioned at the outlet of the drying chamber induces controlled air extraction, promoting improved mixing, reduced stagnant air zones, and enhanced convective heat and mass transfer.

The system is designed to maintain predominantly passive operation while incorporating an optional low-power sensor-based control unit to stabilize airflow during fluctuating thermal conditions. Theoretical performance assessment indicates that enhanced airflow can reduce internal temperature gradients and potentially improve drying efficiency by approximately 15-25% compared to traditional passive configurations.

The proposed design offers a low-cost, scalable, and renewable solution for sustainable agricultural drying, contributing to improved energy utilization and reduced post-harvest losses.