Study On Drying Properties And Kinetics Of Paddy

In order to ensure the safety of paddy storage,the freshly harvested paddy with high moisture content needs to be dried properly.The study of drying kinetics is helpful to study drying characteristics and is of great significance for exploring on the mechanism of moisture diffusion and dryer design.The isothermal drying kinetics of paddy at different temperatures with initial dry basis moisture content of 17.18%,21.05%and 30.12%was studied based on thermogravimetric analysis.Results indicate that for the same initial moisture content of paddy,the higher drying temperature,the lower final moisture content.At the same drying temperature,the higher initial moisture content,the higher final moisture content.The drying rates and the peak drying rates increase with increasing temperature and initial moisture content.Five different isothermal drying models were utilized to fit and analyze the experimental data,and the fitting results are all good.The Midilli and Kucuk model is the most appropriate model for this experiment.Along with the increasing initial moisture content and drying temperature,the effective moisture diffusion coefficient increase from 3.97×10^-10 m²/s to 5.25×10^-10 m²/s.Meantime,the activation energy also increased from 3.92 kJ/mol to 6.82 kJ/mol with the decreasing initial moisture content.In order to study the dynamic characteristics of paddy vacuum drying,a dry kinetics experimental platform,which can accurately control the vacuum degree as well as temperature and measure the quality in real time,was designed.The platform includes vacuum control system,temperature control system,mass weighing system,real-time data acquisition and control system as well as data processing system.After the test of vacuum control,temperature control and quality measurement performance,the results indicated that the platform can achieve accurate control of vacuum degree as well as temperature,and achieve real-time accurate acquisition of dry data.The effects of relative pressure and temperature on the vacuum drying characteristics were studied on paddy with the dry basis moisture content of 28.02%.The results indicate that the relative pressure has little effect on the drying of paddy,and the effect of temperature on the vacuum drying of paddy is obvious.The higher the drying temperature,the shorter the time required to reach the target moisture content,the greater drying rate and peak drying rate.Nine different isothermal drying models were utilized to analyze the experimental results at different drying temperatures.The correlation coefficients R² of the models fitting were all higher than 0.9860,which means the fitting results are good.Among them,the Midilli and Kucuk model owes the best fitting effect with the highest R² which larger than 0.9990.Under vacuum conditions,the effective moisture diffusion coefficient of paddy increase with the increasing drying temperature,and the activation energy was 37.43 kJ/mol.