分程变温对不同商品等级党参干燥特性及动力学模型的影响

Effects of the Process of Variable Temperature on Drying Characteristics and Kinetic Models of Different Commercial Grades of Codonopsis Radix

关键词:  党参  等级  变温  干燥动力学  水分有效扩散系数  偏倚活化能

Key words:  Codonopsis Radix  commercial grades  process of variable temperature  drying kinetics  effective diffusion coefficient of water  bias activation energy

摘要:

目的 比较不同干燥方式对党参的干燥特性、水分有效扩散系数以及偏倚活化能的影响，明确3种分程变温（45-55-60，60-55-45，60-45-60℃）和3种恒温（45，55，60℃）对不同商品等级党参干燥特性曲线的影响。方法 以R²、χ²和RMSE为评价指标，选用10种典型干燥动力学模型对党参的干燥曲线进行拟合，并计算不同干燥方式下有效水分扩散系数和偏倚活化能。结果 Midilli模型能较好地描述不同商品等级的党参药材的干燥过程，党参的水分比呈现指数下降的趋势。若初始干燥温度>55℃，能在2 h内达到最大干燥速率。商品等级和温度对党参有效水分扩散系数有一定影响，同一温度条件下，党参干燥过程中水分迁移的平均速度：一等品＞二等品＞三等品，其D_eff依次为10.433 9×10^–8，5.545 2×10^–8，2.249 6×10^–8·m²·s。计算党参的偏倚活化能在2.943×10⁴~4.378×10⁴J·mol^–1，不同干燥方式的偏倚活化能排序为60-55-45℃变温<60-45-60℃变温<45-55-60℃变温<55℃恒温<60℃恒温<45℃恒温，说明分程变温干燥与恒温干燥相比，药材中水分更容易溢出，耗能更少，尤其60-55-45℃分程变温的偏倚活化能仅为其他2种变温干燥的77.54%和81.86%，是3种恒温干燥的67.22%，75.13%和74.26%。结论 干燥过程中运用分程变温中的降温模式更省时节能，可为党参干燥技术的提升和干燥工艺优化提供实验依据。

Abstract:

OBJECTIVE To compared the effect of different drying methods on drying characteristics, water effective diffusion coefficient and biased activation energy of Codonopsis Radix and to definite 3 different drying methods of varying temperature(45-55-60, 60-55-45, 60-45-60℃) and 3 constant temperature(45, 55, 60℃) on drying characteristic curves of different commercial grades of Codonopsis Radix. METHODS Used R², χ² and RMSE as evaluation indexes, 10 typical drying kinetic models were selected to fit the drying curve of Codonopsis Radix, and the effective moisture diffusion coefficient and biased activation energy under different drying method were calculated. RESULTS It was found that the Midilli model could well describe the drying process of different commercial grades of Codonopsis Radix, the water ratio of Codonopsis Radix showed an exponential downward trend. If the initial drying temperature was set above 55℃, the maximum drying rate could be reached within 2 h. And commercial grades temperature had certain influence on the effective water diffusion coefficient of Codonopsis Radix. Under the same temperature condition, the average speed of moisture migration during drying of Codonopsis Radix was:first-class> second-class>third-class, and the D_effwere 10.433 9×10^-8, 5.545 2×10^-8, 2.249 6×10^-8·m²·s, respectively. The calculated bias activation energy of Codonopsis Radix was 2.943×10⁴-4.378×10⁴ J·mol^-1, the order of bias activation energy of different drying methods was as follows:60-55-45℃ variable temperature<60-45-60℃ variable temperature<45-55-60℃ variable temperature<55℃ constant temperature<60℃ constant temperature <45℃ constant temperature, which indicated that the moisture in the medicinal materials was more likely to evaporate and overflow and consumes less energy than the constant temperature drying. In particular, the bias activation energy of 60-55-45℃ drying method was 77.54% and 81.86% of the other 2 variable temperature drying methods, which were 67.22%, 75.13% and 74.26% of the 3 kinds of constant temperature drying. CONCLUSION The use of cooling mode in the drying process can save more time and energy, and can provide experimental basis for the improvement of drying technology and optimization of drying process of Codonopsis Radix.