初烤烟叶主脉与叶片的吸附等温线及其热力学性质研究

Adsorption Isotherms and Thermodynamic Properties of the Main Veins and Blades of First⁃cured Tobacco Leaves

为探究初烤烟叶主脉与叶片在吸湿过程中所表现出的水分吸附特性,测定初烤烟叶主脉与叶片在环境温度20、25、30、35、40℃以及环境相对湿度50%、60%、70%、80%、90%下的吸湿情况,绘制初烤烟叶主脉与叶片的吸附等温线,采用5种常用的农产品吸附等温线模型对试验数据进行拟合,并在此基础上探究初烤烟叶主脉与叶片的热力学性质。结果表明,初烤烟叶主脉与叶片的吸附等温线属于Ⅲ型等温线,在环境相对湿度相同的条件下,初烤烟叶主脉与叶片的平衡含水率随环境温度的升高而降低。MHAE模型是描述初烤烟叶主脉与叶片吸附等温线的最佳模型,决定系数(R^(2))为0.99877~0.99905,平均相对百分率误差(MRE)为1.45515%~2.94968%。热力学性质研究结果表明,在平衡含水率发生变化时,初烤烟叶主脉与叶片的净等量吸附热(Q_(st))与微分吸附熵(ΔS)有相似的变化趋势,均随平衡含水率的升高而下降,且两者与温度之间都没有明显关系。在初烤烟叶主脉与叶片的水分吸附过程中,熵-焓补偿理论也同样存在并适用,并且水分吸附过程是自发的由焓所驱动的反应。综上,初烤烟叶主脉与叶片在水分吸附过程中的热力学性质较为相似,MHAE模型适合用来描述初烤烟叶主脉与叶片在温度20~40℃的吸附等温线。

In order to explore the moisture adsorption characteristics of the main vein and blade of first⁃cured tobacco during the moisture adsorption process,the moisture absorption of the main vein and blade of first⁃cured tobacco was measured at ambient temperatures of 20,25,30,35,40℃and ambient relative humidity of 50%,60%,70%,80%,90%,and the adsorption isotherms of the main vein and blade of first⁃cured tobacco were drawn.Five commonly used agricultural product adsorption isotherm models were used to fit the test data,on this basis,the thermodynamic properties of the main vein and blade of first⁃cured tobacco were explored.The results showed that the adsorption isotherm of the main vein and blade of first⁃cured tobacco belonged to typeⅢisotherm.Under the same relative humidity,the equilibrium moisture content of the main vein and blade of first⁃cured tobacco decreased with the increase of ambient temperature.The MHAE model was the best model to describe the adsorption isotherm of the main vein and blade of first⁃cured tobacco leaves.The determination coefficient(R^(2))was 0.99877—0.99905,and the average relative percentage error(MRE)was 1.45515%—2.94968%.The results of thermodynamic properties showed that when the equilibrium moisture content changed,the net isotherm adsorption heat(Q_(st))and differential entropy(ΔS)of the main vein and blade of first⁃cured tobacco leaves had a similar trend of change,which decreased with the increase of equilibrium moisture content,and there was no obvious relationship between them and temperature.The entropy enthalpy compensation theory also existed and applied in the process of moisture adsorption of the main vein and blade of first⁃cured tobacco blade,and the moisture adsorption process was spontaneous and driven by enthalpy.To sum up,the thermodynamic properties of the main vein and blade of first⁃cured tobacco leaves in the process of water adsorption are similar,and the MHAE model is suitable for describing the adsorption isotherm of the main vein and blade of first⁃cured tobacco leaves at 20—40℃.