二至丸热风干燥动力学及干燥过程数学模拟研究

Drying kinetics and mathematical modeling of Erzhi Pills during hot-air drying process

目的以二至丸为研究对象,探索丸剂热风干燥过程水分的变化规律,进行薄层干燥特性及模型研究,为改善裂丸、结壳、假干燥等现象提供理论依据。方法研究二至丸在不同热风干燥温度50、60、70、80、90℃下丸剂的水分比、干基含水率、干燥速率随干燥时间的变化曲线及干基含水率与干燥速率间的关系。利用经验模型Henderson&Pabis模型、Newton模型、Page模型、Logarithmic模型、Two term Exponential模型、Wang&Singh模型、Midilli et al.模型对丸剂干燥过程中水分比与时间的关系进行模型拟合与验证;以Fick扩散定律为依据,确定不同热风干燥温度丸剂的水分有效扩散系数(Deff)及活化能(E_a)。结果二至丸干燥曲线结果表明二至丸的水分比、干燥速率与干燥介质的温度密切相关,随着干燥时间的延长,物料的水分不断减少;由干燥速率曲线可知,随着热风温度的升高,干燥速率增加,加速水分的迁移。通过比较各模型的相关系数(R^2)、卡方(χ~2)和标准误差(RMSE),可知Midilli et al.模型的R^2平均值最大、χ~2及RMSE平均值最小,分别为0.996 86、2.43×10^(-4)及1.93×10^(-4),结果表明Midilli et al.模型能够很好地描述与预测丸剂的干燥过程;实验数据得到Deff值在8.6×10^(-11)~3.13×10^(-10) m^2/s,Ea为30.97 k J/mol。结论二至丸的热风干燥过程可以进行模型拟合并得到了验证,该研究为探索丸剂的干燥特性和品质提供新的思路。

Objective To study the change rule of water content in the drying process of hot air drying of thin layer drying characteristic and model research, and to provide reference for improving the quality of Erzhi Pills（EP）. Methods The moisture ratio, drying rate of dry basis, and drying rate curves along with the change of drying time and relationship between dry basis moisture content and drying rate of EP were studied using a hot air dryer at five levels of drying air temperature in the range of 50—90 ℃. The model was fitted and verified by the empirical model Henderson Pabis model, Newton model, Page model, Logarithmic model, two term exponential model, Wang Singh model, Midilli et al. model, etc. Meanwhile, based on Fick＇s diffusion law, the effective diffusion coefficients of water（Deff） and activation energy value in EP were calculated. Results The drying curves of EP show that the moisture ratio and drying rate of EP were closely related to the temperature of drying medium, and the moisture of the material decreases with the prolonged drying time. It could be seen from the drying rate curve that the drying rate increased with the increase of hot air temperature, and the migration of moisture was accelerated. By comparing the correlation coefficient（R^2）, chi-square（χ~2） and standard error（RMSE）, we could see that the mean value of R^2 of model number 7 was the maximum, the χ~2 and RMSE mean were the smallest（0.996 86, 2.43 × 10^（-4）, and 1.93 × 10^（-4））, respectively. The results showed that the model number 7 could describe and predict the drying process of the pills. The experimental data had the effective diffusion coefficient（Deff） value of 8.6 × 10^（-11）—3.13 × 10^（-10）m^2/s, and the activation energy（Ea） was 30.97 k J/mol. Conclusion The hot air drying process of EP can be modeled and verified. The research provides a new way to explore the drying characteristics and quality of pills.