Optimization of the performance of a hybrid solar desiccant drier in grain storage systems

The remarkable need for alternative and renewable energy technologies is evidently an increasing feature in the developing countries. One such effort is represented in this study whose objective was to optimise the performance of a hybrid solar desiccant drier in grain storage systems. The performance of a solar collector in preconditioning the air for grain drying was investigated with the aim of developing a low cost grain drying and storage unit for small scale maize farmers. The effect of radiation concentrator convex lenses, extended surfaces (fins), lining material and exit air recirculation on the efficiency of a designed, developed and tested prototype was investigated. Effectively, perspex glazing was used to test the evacuated effect of the preventive heat losses in the collector plate due to its infrared penetration characteristics. The glazing of the collector plate was designed and moulded with a clear 2 mm acrylic material, a dome shape with a depth of 250mm onto which radiation concentrating lenses of variable focal lengths were embedded based on the length of their radiation concentration focal points and the day-arc trajectory of the sun. Additionally, the solar collector and back plate were welded with fins resulting to an increase in extended heat transfer surface area of 1.0046 m2. A desiccant fabric was used to line the collector to trap any apparent condensation of drops of water on the inner surface of the solar collector, recirculation conduits and later during storage, a black paint was used to coat the solar collector plate. Results from point time data logger indicated highest increase of temperature and lowest relative humidity parameters of drying air within the collector combination of fins, lenses and black coated collector plate. Re-circulated exit air in desiccant lined conduits decreased the relative humidity of the air gradually more than inlet ambient air. This presents the hybrid drier as a strong candidate for a low-cost, portable, high-efficiency hybrid solar- desiccant system that can be used in grain drying to benefit both the grain and seed industry for sustained food security