水稻负压混流干燥室结构优化设计与试验

Optimized design and experimental study on rice negative pressure mixed flow drying chamber

针对水稻竖箱式干燥过程中气流分布不均匀、干燥效率与干后品质同步性差等问题,基于不可逆热力学理论和负压原理,建立了水稻竖箱式干燥室的负压干燥特性解析模型。并结合混流干燥工艺,设计了一种变径开孔式角状管用于改善竖箱式干燥室角状管内风量分配关系,用于进一步提高水稻干燥均匀性。基于Fluent软件分别在空载和满载状态下,对干燥室内的流场进行数值模拟和试验验证。研究表明:采用变径开孔式角状管,可有效解决管内风速高、流动大等问题,干燥室风场不均匀性得到良好地改善,可为水稻均匀干燥提供设备保障。该研究采用自主研制的5HSN-1型负压循环干燥试验机,应用四因素五水平二次正交旋转试验方法进行了参数优化试验,建立了以热风温度、表现风速、排粮辊转速、初始含水率为试验因素,干燥速率和爆腰增值率为试验指标的回归模型,并通过优化分析,得出优化工作参数组合:表现风速为0.75 m/s,热风温度为40℃,排粮辊转速为3.2 r/min,初始含水率为16.9%时,干燥速率为1.407%/h,爆腰增值率为0.574%,试验验证值与优化值的相对误差为6.2%~7.4%,拟合良好,结果表明该模型有效,干燥效率高,干燥后综合品质优良,优化工艺参数具有实际应用价值。

Rice is a major food crop grown widely in south and northeast China,particularly on a total annual production of nearly 210 million tonnes with a high level of consumption.The rice must be dried in time to minimize the loss as a result of sprouting,molding,and bursting waists after harvest.A positive-pressure high-temperature dryer is mostly adopted for hot-air drying in the actual production at present,but it was easy to cause uneven drying and low quality of rice.A negative-pressure dryer can be expected to improve the uniformity of rice drying and further reduce the saturation temperature of materials with a high drying speed in low-temperature drying,while shortening the drying time for energy saving.The mechanism and arrangement of angle tubes determine the airflow in the chamber for the rice drying.In this study,an analytical model was established for the negative-pressure drying of rice in a vertical chamber using irreversible thermodynamics,in order to gain even air distribution for better drying efficiency and quality of the dried product.Combined with the mixed flow drying,a perforated air duct with variable diameter was designed to improve the air distribution in the air duct of the vertical chamber.FLUENT software was used to conduct the numerical simulation and experimental verification for the flow field in the drying chamber under the conditions of no-and full-load.The research results showed that the perforated air duct with variable diameter well improved the wind speed and flow in the pipe of the vertical chamber for the uniform drying of rice.A self-developed 5 HSN-1 dryer with a negative-pressure circulation system was used to optimize the drying parameters.In a quadratic orthogonal rotation test with four factors and five levels,the regression model was established with the temperature of hot air,the wind speed,the speed of discharging roller,and the initial moisture content as the experimental factors,while the drying rate,and increment rate of waist burst as the test indices.The optimal combination of working parameters was as follows:the wind speed of 0.75 m/s,the hot air temperature of 40℃,the rotation speed of discharging roller of 3.2 r/min,the initial moisture content of 16.9%,the drying rate of 1.407%/h,the increment rate of burst waist of 0.574%.The relative error between the experimental and optimized values was 6.2%-7.4%.The model with excellent fitting can offer practical application for better comprehensive quality of rice drying.