Adsorption Isotherms and Thermodynamic Properties of the Main Veins and Blades of First-cured Tobacco Leaves
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(R2)was 0.998 77-0.999 05,and the average relative percentage error(MRE)was 1.455 15%—2.949 68%.The results of thermodynamic properties showed that when the equilibrium moisture content changed,the net isotherm adsorption heat(Qst)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℃.
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