Modeling and optimization of energy consumption and performance characteristics of a solar assisted fluidized bed dryer

The major problem regarding conventional rice mills is the use of fixed-bed drying systems, which is accompanied by high energy consumption. In this study, a novel solar-assisted fluidized-bed system for drying paddy grains was used. The system included a solar water heater, an infrared lamp powered by photovoltaic panels, along with a gas water heater, which were used together to provide the required thermal energy. The working factors were drying air temperature (۳۵, ۴۵, and ۵۵ °C), drying air velocity (۷, ۸, and ۹ m/s), and the angle of the desiccant wheel regeneration gate (۰, ۴۵, and ۹۰ degrees). The performance characteristics of the drying system were measured in terms of drying rate, total energy consumption, solar fraction and energy efficiency. Several mathematical models were also applied to fit the moisture ratio curves. In order to analyze the results and obtain the optimized working conditions of the drying system, Response Surface Methodology (RSM) based on the Box–Behnken technique was used. In all of the evaluated conditions, the model entitled “Approximation of diffusion” had the best results for fitting the moisture ratio curves with a correlation coefficient value of at least ۰.۹۷۲۹. The selected optimum point included drying air velocity of ۷ m/s, drying air temperature of ۵۲.۷۷ ºC and regeneration gate angle of ۰. Under the mentioned working conditions, the drying time of ۷۵.۹۹ min, the total energy consumption of ۰.۲۹۷ kWh, solar energy fraction of ۰.۵۴۰ and energy efficiency of ۴۷.۶۷% could be obtained with a desirability value of ۰.۹۷۰.