Development of a photovoltaic driven ventilation system to modified traditional Ethiopian gombisa for on-cobs-maize drying

Abstract

Mycotoxin-producing fungal growth commonly reported from traditional maize storage system in southwestern Ethiopia. Un-safe moisture content at loading and non-climatically controlled nature of gombisa results in mycoflora growth and development on maize in storage system. Therefore, this paper was aimed to develop a photovoltaic driven ventilation system fitted to modified gomibsa for natural air in-bin drying of on-cobs-maize and increase the shelf life of the product. Modified gombisa was constructed from locally available materials for the current experiment. An appropriate fan type and size, humidistat set at >70% and two 20 W_p photovoltaic panels were used for ventilation purpose, fan control and power the fan, respectively. In total 1.76 m³ of on-cobs-maize with an average moisture content of 22% was used in this study. Solar irradiance, photovoltaic array, current, air velocity and; both temperature and relative humidity inside the storage system and ambient condition data collected for both experiments. Computational fluid dynamics simulation results showed the uniformity of the air velocity rapidly after certain distances above the plenum chamber.  The trend of temperature revealed high variability and fluctuation for ambient compared with inside the store. A similar result was observed for the relative humidity during both experiments. Throughout fan operating hours, inlet temperatures significantly higher by 7.8^oC and 7.2^oC than outlet temperatures for the first and second experiment, respectively. However, outlet relative humidity was higher by an average value of 22.9% and 15.1% compared to inlet relative humidity for the first and second experiments, with the respective order. Hourly average of energy output for the selected day was 658 Wm^-2. Ventilation of on-cobs-maize for 10-12 days resulted in a reduction of moisture content to almost 14 (db). Solar irradiance data obtained from Jimma area, Ethiopia showed better energy output compared to the current experiment, demonstrating a possibility to apply ventilation and drying system to the tropical region. Generally, storing maize inside modified gombisa plays a role in protecting the stored product from outside weather conditions. Also, monitored temperature, relative humidity, and energy output showed the system was able to reduce to safe moisture content for storage without mould development. This promising research result needs to be tested and validated in tropical regions of the world.