Evacuated Tube Solar Collector-Based Drying System: Analytical Modeling, Influencing Factors, and Recent Progress in Drying of Agri-Commodities

Evacuated tube solar collector (ETSC) has gained significant attention due to its high thermal efficiency and ability to harness solar energy more effectively as compared to flat plate solar collector. The present review analyzed the in-depth mechanism of analytical modeling of ETSC, different factors influencing the performance, and applications in drying of Agri-commodities. Evacuated tubes with and without heat pipes are used for air heating purposes. ETSC with tracking and non-tracking, selective coating techniques, and for reducing heat loss during drying operations are reported. The system performance is greatly influenced by the ETSC design, absorber coating, heat transfer fluid, mass flow rate of working fluid, inclination or tilt angle, collector size, and distance between tubes. Moreover, Computational fluid dynamic (CFD) simulations of the various ETSC-based drying systems were compiled to investigate their flow patterns, heat transfer characteristics, and overall system performance. This literature inherently provides the way for the development of evacuated tube-based innovative and sustainable solar dryers in small and industrial scale.