Study On The Law Of Quality Change And The Ventilation And Precipitation In The Drying Process Of Japonica Rice

In order to understand the storage quality changes of rice with different moisture content under different temperature conditions,and to understand the law of water migration in the process of ventilation and drying,a drying mathematical model of the effect of ventilation conditions on moisture changes was established.In this paper,rice paddies with different moisture ranges(14～15%,16～17%,1 8～19%,20～21%)were stored under different temperature conditions(15,25,35℃)for short-term storage to explore variation laws of rice quality with different moisture contents under different temperature conditions,such as the grain moisture content,fatty acid value,processing quality,rice cooking quality,texture characteristics and so on,at the same time,using fatty acid value of 20～21%rice as an indicator to establish a quality dynamic model could efficiently and accurately guide the fresh harvest rice paddies to be dried in time.At an ambient temperature of 15℃,the freshly harvested rice was placed in a simulated silo to complete the in-situ drying test of the freshly harvested rice under three different ventilation conditions(80,92,104 m3/h)to study the moisture content of the rice grain pile and the internal and external moisture distribution of the single grain rice were studied.According to the change of moisture in each layer of the grain pile,a mathematical model of drying was established to predict different ventilation conditions.The research results are as follows:1.The moisture content of rice showed a downward trend with the increase of storage time,and the value of fatty acid showed an upward trend;the roughness rate and head rice rate also showed an upward trend,but at 15℃,the increase was smaller;the water absorption rate and volume expansion rate of rice showed an upward trend in the environment of 35℃,but showed a downward trend under the other two temperature conditions.The loss rate of rice solids with 14～19%moisture content basically showed an upward trend,and the loss rate of rice solids with 16-18%moisture was 35℃ and 15℃showed a downward trend,and at 25℃,the increase was smaller;as the temperature increased,the faster the hardness and adhesion of rice increased,the elasticity showed an upward trend and then a downward trend with time.The chewability showed a slight upward trend,and the quality of rice slightly increased.At 35℃,the deterioration rate of rice is accelerated,while 15℃ environment can effectively delay the deterioration of rice quality;the dynamic model of rice fatty acid value change in the range of 20～21%was:lnA=0.0193e409.09/T.t+lnA0.2.Dry-in-place drying experiments were performed at room temperature of 15℃.The three ventilation conditions of the simulated warehouse were set to 80,92,and 104 m3/h.Under these three ventilation conditions,rice Grain pile water 1igration rules were:water migrates to the upper part of the grain pile,the greater the amount of ventilation,the faster the water decline rate,and the faster the upward movement of the grain pile water;the drying rate of the bottom layer of the rice grain pile basically includes:rapid precipitation,Slow precipitation and constant precipitation,but when the ventilation volume is 104 m3/h,the rice drying does not go through the slow precipitation stage;when the moisture content of the grain layer is greater than 18%,the drying rate of rice moisture is gradually accelerated,and when the moisture content is at In the range of 14～18%,the drying rate decreases.When the moisture content is lower than 14%,the moisture content inside and outside the rice balances,and the drying rate approaches a constant rate.The decline process of the absorbed water in the single-grain rice includes the slow precipitation stage and the rapid precipitation stage.The speed is reduced to the lowest value;while the free water inside the paddy rice has experienced rapid precipitation and slow precipitation after a slight gradual trend;the slow precipitation speed of adsorbed water is more compared with the rapid precipitation speed of free water fast.3.Carry out the in-situ drying experiment at 15℃,the moisture ratio of the grain layer showed a downward trend with the increase of ventilation and drying time,and the moisture ratio of the grain layer directly contacting the air distribution room at the bottom layer was the smallest;the effective moisture diffusion coefficient of the rice grain layer under the three ventilation conditions was 0.092～0.43 m2/d range,under 80 m3/h ventilation conditions,the effective diffusion coefficient of moisture in each layer of the grain stack was less than the other two ventilation conditions;by comparing the R2 and RMSE values of eight mathematical models,it was finally determined that they can be established based on the Ademiluyi model under different ventilation conditions,the mathematical model of the drying of each layer of the rice grain stack was used to predict the moisture change of the rice grain layer under different ventilation conditions.The moisture ratio at the 8th day of the bottom layer of the grain pile under three ventilation conditions was randomly selected and compared with the predicted value of the equation.The relative error is less than 10%,which is lower than the 15%accuracy requirement of general numerical simulation.This prediction model is credible.