Hot-air drying characteristics of Millettia speciosa Champ. slice and establishment of the kinetic model

Abstract

[Objective] To explore the influence of different hot air temperatures, slice thicknesses and material loads on Millettia speciosa Champ. slice hot air drying rate, establish model of thermal wind drying kinetic, and provide reference for perfecting M. speciosa Champ. drying processing technology. [Method] Taking hot air temperature (50, 60, 70, 80 °C), slice thickness (2,4,6,8 mm) and material load (100,200,300 g) as investigating factors,real-time measurement of moisture changes during hot air drying of M. speciosa Champ. slices under various conditions. The 5 kinds of drying models were screened and fitted, calculated the effective water diffusion coefficient and theactivation energy in the drying process. [Result] With the increase of the hot air temperature, the slice thickness and material load decreased, the moisture content of dry basis was greatly reduced, and the drying rate was greatly increased. The hot-air drying process of M. speciosa Champ. slices was divided into two stages : acceleration and deceleration, and most of the drying process was the deceleration stage. The kinetic model of hot-air drying of M. speciosa Champ. slices conformed to the Page model, and the predicted value of the Page model had a good fit with the experimental value ( R 2=0.969). the fitting equation ln (-lnMR)= -3.174-0.242 H+0.029 T-0.006 L+(0.721+0.015 H+0.002 T)ln t, k=e -3.174-0.242 H+0.029 T-0.006 L , n=0.721+0.015 H+0.002 T, the effective diffusion coefficient D eff of M. speciosa Champ. under different drying conditions was 1.62114×10 -10-12.96913×10 -10 m 2/s, with the increase of hot air temperature and slice thickness, the material load decreased, and the overall trend was increasing, and the activation energy was 60.7388 kJ/mol. [Conclusion] The Page model can better reflect the moisture change law of hot air drying process of M. speciosa Champ. slice with different slice thicknesses, and by fitting the equation, the content of water ratio in the hot air drying process at a certain time can be accurately predicted. 摘要：【目的】探讨不同热风温度、切片厚度及装载量对牛大力切片热风干燥速率的影响, 并建立牛大力切片热风 干燥动力学模型, 为牛大力干燥工艺探索提供理论依据。 【方法】以热风温度 (50、60、70、80 °C)、切片厚度 (2、4、6、8 mm)和装载量 (100、200、300 g)为考察因素, 实时测定各条件下牛大力切片热风干燥过程中水分变化, 对常见的5种 干燥模型进行筛选, 并计算干燥过程中的有效水分扩散系数和活化能。 【结果】随着热风温度的升高, 切片厚度和装载 量的降低, 牛大力切片的干基含水量明显减少, 干燥速率明显增加。牛大力切片在热风干燥过程分为加速和降速2个 阶段, 其中大部分干燥过程为降速阶段。牛大力切片热风干燥动力学模型符合Page模型, 该模型预测值与试验值拟 合度较高( R 2=0.969), 拟合方程为ln(-lnMR)=-3.174-0.242 H+0.029 T-0.006 L+(0.721+0.015 H+0.002 T)ln t, 可求得K=e -3.174-0.242 H+0.029 T-0.006 L , n=0.721+0.015 H+0.002 T, 不同干燥条件下牛大力切片的有效水分扩散系数在1.62114×10 -10~12.96913×10 -10 m 2/s, 均随着热风温度的升高和切片厚度的增加, 总体呈上升趋势; 活化能为60.7388 kJ/mol。 【结论】Page模型可 较好地描述不同切片厚度的牛大力切片热风干燥过程中水分的变化规律, 且通过拟合方程能较准确预测热风干燥过 程中某时刻牛大力切片的水分比。