Experimental Study On Uniformity And Quality Change Of Negative Pressure Drying In Rice

Rice is the main food crop in China,and its planting range is relatively wide,mainly distributed in the south and northeast regions.The total annual output is nearly 100 million tons,and the consumption is also large.In order to avoid the phenomenon of germination,mildew and burst waist after rice harvest,it is necessary to carry out drying treatment in time to reduce the loss.At present,the positive pressure high temperature dryer is often used for hot air drying in actual production,which is easy to cause uneven drying of rice,and the quality after drying is difficult to guarantee.In the quality analysis process of rice after baking,a single method is mostly used,and the quality evaluation lacks integrity.The structure of angular tube was designed and optimized for the problems in the quality analysis process after the rice is dried and baked in this paper,and simulated and analyzed the flow field in the drying section using Fluent software.Rice negative pressure drying technology is the main research object,analyze the drying characteristics of rice under negative pressure and optimize the drying parameters.And analyze the quality of the dried rice,establish a quality evaluation index screening and evaluation model,comprehensively evaluate the quality of negative pressure dried rice,and provide a theoretical basis for the uniformity drying and quality evaluation of rice.The main research contents are as follows:(1)The structural optimization design is carried out on the basis of the variable-angle angular tube,and the variable-angle variable-opening angular tube with different opening ratios is designed.And the finite element analysis software is used to analyze the structural stress of the angular tube,and the best opening rate is 19.14%.The range of the performance wind speed is determined to be 0.6m/s-0.8m/s,which provides a basis for the selection of the performance wind speed in the rice negative pressure drying test.(2)In the case of no-load and full-load,the flow field in the dry section is simulated by using variable diameter angular tube and variable diameter open porosity angular tube respectively.The results show that the hot air can flow out through the air outlets on the two sides of the angled tube after the variable-diameter open-angled angled tube is used,and the unevenness of the wind field is well improved.And the fluidity of hot air is enhanced,and the pressure field is evenly distributed.Wind field test results show that: after using variable-diameter open-pored angular tubes,the coefficient of variation of wind speed is significantly reduced,the performance wind speed in the drying section is also significantly reduced,and the wind field is evenly distributed.This is consistent with the simulation results and can provide a theoretical basis for the uniform drying of rice.(3)The effects of hot air temperature,performance wind speed,grain stick speed,initial moisture content and other factors on rice drying characteristics were studied through experiments.At the same time,the reliability of the negative pressure drying characteristics model of rice was verified by analyzing the changes of moisture ratio and drying rate of rice with time under different experimental factors.And through the optimization analysis of response surface,the best working parameter combination is: the performance wind speed is 0.75m/s,the hot air temperature is 45?,the speed of the grain discharge roller is 3.2r/min,the initial moisture content is 17.90%,the rice is dry The rate prediction value is 0.0305%/min.The drying rate measured by the verification test is 0.0309%/ min,which is 0.0004%/min different from the predicted value,and the fitting is good.The results show that the model is effective and the best process parameters have practical application value.(4)Establish a rice quality evaluation index screening and evaluation model.The comprehensive evaluation results of rice quality are: when the performance wind speed is0.75m/s,the hot wind temperature is 45?,and the grain is discharged When the roller speed is3.2r/min,the initial moisture content is 17.90%,the drying rate is 0.0302%/min,and its quality comprehensive evaluation score is the highest at 3.955.It is 0.0003%/min different from the predicted value of drying rate by response surface analysis.It can be seen that the comprehensive evaluation model of rice drying quality can be well combined with the regression model of rice negative pressure drying,reflecting the changing law of rice drying quality.