稻谷薄层热风干燥工艺优化及数学模型拟合

对稻谷进行薄层热风干燥,采用正交试验方法研究稻谷在不同热风温度、初始含水率和热风风速条件下的热风干燥特性,比较10种数学模型在稻谷热风干燥中的适用性。结果表明:稻谷在热风干燥过程中没有出现明显的恒速干燥阶段,且干燥主要发生在降速干燥阶段;热风温度是影响稻谷热风干燥的最主要因素,其次是初始含水率;取初始含水率20%、热风温度50℃、热风风速1.4 m/s的方案为稻谷的最优热风干燥工艺,此时的最佳数学模型为Page模型;缓苏可有效抑制稻谷的爆腰率,缓苏温度越高,缓苏时间越长,缓苏效果越好;当初始含水率24%、热风温度40℃时,实验值和模型值的相对平均误差分别为1.563%和1.474%,表明模型预测的干燥曲线和实验所得的干燥曲线一致性较好;随着热风温度的升高,稻谷的有效水分扩散系数变大,经热风温度从40℃升高到60℃,其有效水分扩散系数由9.69×10~(-10) m~2/s增加到10.77×10~(-10) m~2/s,稻谷的干燥活化能为47.1 k J/mol。

Optimization and Mathematical Modeling of Thin Layer Hot-Air Drying of Rough Rice

The thin layer hot-air drying characteristics of rough rice as a function of hot-air temperature, initial moisture content and air velocity were investigated by using an orthogonal array design and the applicability of 10 mathematical models for the hot-air drying process of rough rice was compared. The results showed that no apparent constant-rate drying period existed in the hot-air drying process, and moisture removal mainly occurred in the falling-rate drying period; hot-air temperature was the main factor that affects the hot-air drying, followed by air velocity. The optimal hot-air drying conditions for rough rice were determined as follows: initial moisture content, 20%; hot-air temperature, 50 ℃ and air velocity, 1.4 m/s. The Page Model was found to be the best mathematical model for describing the drying characteristics of rough rice under these conditions; tempering could effectively inhibit the occurrence of fissuring, and a better effect was observed by raising tempering temperature and prolonging tempering time. Under the conditions of initial moisture content of 24% and air velocity of 1.4 m/s, the relative mean deviation between the experimental and predicted results were 1.563% and 1.474%, respectively. The predictive drying curves fitted well the experimental data. With temperature increase from 40 ℃ to 60 ℃, the effective moisture diffusion coefficient of rough rice increased from 9.69 × 10-10 to 10.77 × 10-10 m2/s, and the activation energy for rough rice drying was 47.1 kJ/mol.