Modeling of Drying Process and Energy Consumption of Onion (Ex-gidankwano Spp.) Slices in a Hybrid Crop Dryer

摘要

High consumption of energy in the drying industry has prompted extensive research regarding various aspects of crop drying energy consumption. Specific energy consumption, moisture ratio and thermal efficiency in drying of fresh ex-gidankwano onions variety were determined using a hybrid electric-gas dryer at air temperatures of 50, 60 and 70 o C, and at air velocities of 0.5, 1.0 and 1.5m/s. Thin layer models were selected by carrying out statistical analyses to fit the drying rate data to themodels. The Page drying model was found more suitable to describe the drying behaviour of onions slices based on its highest average R 2 -values of 0.99 and lowest average RMSE of 3.91for all temperatures and air velocitiesirrespective of the heat source. Records of drying rates and energy consumption were made using electronic weighing balances and the Arduino microprocessor respectively. Results obtained show that the specific energy consumption decreases with increase in air temperature but increases with increase in air velocity in both heat sources. The minimum and maximum specific energies for the electric and gas heat sources were 48.73MJ/kg and 90.21MJ/kg, and 36.83MJ/kg and64.65MJ/kg of moisture evaporated respectively.The thermal efficien cy of the heat sources increased proportionally with increasing drying air temperature and decreased with increase in drying air velocity with maximum values of 54.8 % and 68.2% for the electric and gas heaters respectively. The gas heat source performed more efficiently in terms of energy consumption and thermal efficiency at different temperatures and air velocities.