Performance Evaluation and Optimization of a Solar-Assisted Multi-Belt Conveyor Dryer Based on Response Surface Methodology

Drying process is an important post-harvest stage of food crops production which accounts for about 20 % of the world’s energy consumption in the industrial sector. One of the effective ways to reduce the share of fossil fuel consumption in the food drying process is to develop new drying systems based on the use of renewable energy sources. In this research, a novel solar-assisted multi-belt conveyor dryer was developed and its performance was analysed. The required thermal energy for drying process was supplied by the combination of solar-gas water heaters and four solar-powered infrared (IR) lamps. The experimental factors included the speed and temperature of the drying air and the power of IR lamps. The performance characteristics were drying time, Overall Specific Energy (OSE), Non-Solar Specific Energy (NSE), Overall Energy Efficiency (OEE), and Solar-Assisted Energy Efficiency (SEE). The optimization process of the drying system was carried out using Response Surface Methodology (RSM) by defining two general modes for the energy sources of the drying system, namely overall mode and solar-assisted mode. Based on the results, the lowest OSE (17.30 MJ/kg water evaporated) was obtained when the speed and temperature of the drying air were equal to 7 m/s and 40 °C, respectively, without using IR power. The lowest NSE (2.71 MJ/kg water evaporated) was achieved by applying the treatment of 7 m/s * 40 °C * 300 W. The maximum OEE was equal to 13.92 % whilst the maximum SEE was obtained as 88.71 %. Both of the mentioned maximum values were obtained at the speed and temperature combination of 7 m/s and 40 °C and their difference was applying     300 W IR power to gain maximum SEE and no IR utilization for the maximum OEE. According to RSM analysis, the optimum working conditions for the drying system included the treatment of 7 m/s * 39.96 ºC * 300 W. Under this condition, the drying time, NSE, and SEE values were equal to 180.95 min, 1.062 MJ/kg water evaporated, and 84.63 %, respectively.