Study On Drying Characteristics And Mathematic Simulation Of Rice Seeds

Drying process is an important treatment after harvest for rice and it has a very significant influence for rice seeds vigour. If drying parameter is unreasonable, there will be some quality damage arising. The influence of dying process to rice seeds is mainly representation by decline of germination rate and seed vigour. The high temperature drying may make the seed protein denaturation, and the seeds with crack obtain fewer nutrients which will give a rise to the falling germination rate. There were a vast majority of grain drying studies while research on seed drying was very few at home. To solve this problem, following researches have been done.(1) The drying kinetics of rice seeds were studied systematically. It was very sensitive to drying process of rice seeds, and it request exuberant vitality after drying. Because the drying conditions for rice seeds is much more strictly, therefore low temperatures were chose for the drying process. Before drying process, a large number of rice data in literature of equilibrium relative humidity and equilibrium moisture content models were compared and analyzed. The results showed that modified GAB model with highest R2 and minimum errors was the most suitable model to describe the rice adsorption and desorption characteristics under different temperatures. Thus the equilibrium moisture content curves were obtained through this model and it can provide to calculate the end moisture content of rice drying. The random distribution of moisture content of rice seeds in drying duration was studied and found that the random distribution of initial moisture content was approximately normal distribution, while it was deviating from the normal distribution as the drying continues. The drying kinetics of different thin-layer drying temperatures (30℃、35℃、40℃、45℃、50℃ and 55℃, respectively) and velocity of drying air (0m/s,0.5m/s,1.0m/s, respectively) were studied. Ten classic drying models were selected and fitted, and found the Diffusion Approach model was simulated best. The regression analysis of the model parameters were calculated with drying temperatures and velocity of drying air.(2) The thermal properties of rice seeds after drying were investigated by differential scanning calorimeter (DSC). A series high DSC heating rates were used to improve the signal detection, however, this method also led to a lag of the characteristic values. In order to eliminate the effect of the high heating rates to the experiment results, the extrapolation values for the heating rate zero was obtained. The linear regression equation and Gordon Taylor equation were investigated between the relationship of glass transition temperature and moisture content of rice seeds.(3) The mechanical properties of rice seeds after drying were investigated by dynamic mechanical analysis (DMA) and the viscoelastic properties and creep relaxation characteristics were analyzed. Through detailed analysis of the tan delta peak value of rice seeds, the values of both storage modulus and loss modulus are significantly different while the significant difference among the values of tan delta only appeared for the rice seeds with very low moisture contents, or with significantly different moisture contents.5-element Kelvin model and 3-element Maxwell model could match the creep and relaxation behavior of rice seeds samples well. The creep behavior was significantly affected by its moisture content and length, while the relaxation behavior was only influenced by its moisture content.(4) The experiments of seed germination after drying were studied and analyzed the dying conditions on seed germination energy and germination rate. The results showed that seed germination energy was more vulnerable to dry conditions than germination rate. Simple analysis of rice seed deterioration has been done and a dynamic prediction model for seed germination rate was obtained. The parameters were also obtained and the model can be forecast the rice seed germination rate after drying process.(5) The heat and mass transfer models were established by assuming the rice seed as a three layer ellipsoid body. The internal temperatures and moisture content of each node were obtained by using the finite element method. Through the computer simulation and experimental validation of average temperature and moisture content, and the simulation of temperatures of each node internal the seeds, we found that the biggest temperature gradient was just appeared at the beginning of drying process. So if the initial drying temperature can be controlled, the seeds of crack would be reduced and improved the seed quality.