Abstract
Drying agricultural products in open sun drying (OSD) is a well-known and ancient technology. OSD has a lot of limitations and these can be eliminated by employing various solar dryers. Integration of thermal energy storage (TES) units with solar dryers is an interesting and emerging area of research as it makes the dryers functional throughout the day. Among the sensible and latent heat storage substances, paraffin wax is widely used in solar dryers because of its easy availability, cheapness and its high TES capacity per unit volume. This work extensively reviews the solar dryers integrated with the TES units where paraffin wax is used. The different types of paraffin wax and their thermo-physical properties are presented. The thermal performances of various solar dryers with and without paraffin wax are reviewed and their effect on the drying time and drying efficiency is reported. Various kinds of TES unit locations inside the dryer were reviewed. Different methods available to enhance the thermal conductivity and heat transfer rate between paraffin wax and drying air are reviewed. Perspectives and challenges of solar drying with paraffin wax are also addressed. The thermal efficiency of solar dryers was enhanced up to 50% when paraffin, n-docosane with kerosene were mixed with a 2:1 ratio.
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