A small scale demonstration model consisting of a combined solar and biomass cabinet dryer with 3 equally spaced drying trays was designed, constructed and evaluated. The results, obtained using fresh yam chips as test material over a four day test period, were satisfactory and useful for optimization purposes. Maximum tray temperature of 53°C was obtained in combination with solar and biomass heating sources even though the ambient temperature for the test period was between 24 and 30°C. An optimal drying rate of 0.0142 kg/hr was achieved with the combined solar and biomass dryer, compared to the lower drying rate of 0.00732 kg/h for the solar drying and 0.0032 kg/h for the biomass drying. This study proved that the efficiency of agricultural dryers could be increased through the use of a combination of solar and biomass heating sources, compared to conventional dryers with only solar or only biomass heating sources. It implies that improvements in the design and construction of the various components of the system would lead to more efficient dryers for use in small and medium business enterprises for sustainable development of developing countries. Using combined solar and biomass dryers have the potential to increase the productivity and resultant economic viability of small and medium-scale enterprises producing and processing agricultural produce in developing countries. African countries, with large quantities of natural resources, like forests and solar radiation, could make the most use of these types of dryers.
Key words: Solar biomass dryer, drying rate, moisture loss, preservation, yam chips, solar radiation, small and medium-scale enterprises.
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