A current review: Engineering design of greenhouse solar dryers exploring novel approaches

Abstract

This work reviews various engineering factors influencing the efficiency of greenhouse solar dryers, focusing on drying load/volume ratio, ventilation, circulation mode, roof shape, materials, energy storage, and auxiliary heating, as reported in the last decade. The shape of the dryer roof is the most studied factor, with the even span roof being the most effective in capturing solar radiation, thus maximizing dryer efficiency. Nano Enhanced paraffin wax thermal storage systems have been shown to maintain drying temperatures and continue drying overnight. Auxiliary heating, such as single-pass flat solar collectors, helps to increase the air temperature when solar radiation is low. The maximum drying capacity of a greenhouse was found to be approximately 6 $kg/m^{3}d$. Computational Fluid Dynamics (CFD) emerged as the most powerful tool for designing and simulating greenhouse solar dryers, allowing accurate predictions of dryer behavior by incorporating models for solar radiation, flow dynamics, buoyancy effects, and species transport, such as relative humidity. This review identifies key factors that significantly impact dryer efficiency, providing insight into optimizing greenhouse solar drying systems.