Study On Dry Characteristics And Heat And Mass Transfer Mechanism Of Angelica Sinensis Slices In Vacuum Far Infrared Drying

In order to solve the problems of long drying time and serious loss of medicinal ingredients in the process of drying,the vacuum far-infrared drying characteristics of Angelica sinensis slices were studied,and the effects of different drying processes on the quality and microstructure of dried products were discussed.On this basis,the theoretical model of heat and mass transfer in the drying process of Angelica sinensis slices was established,and the changes of internal temperature and moisture concentration in the drying process were simulated and verified by COMSOL multiphysics software.Finally,the processing parameters of vacuum far infrared of Angelica sinensis slices were optimized.Through the combination of experimental research,theoretical analysis and numerical simulation,the drying mechanism of heat and mass transfer in the drying process of Angelica sinensis slices was comprehensively elaborated,in order to provide a suitable drying process for the postpartum processing of Angelica sinensis and provide a theoretical basis for guiding the actual production.The main results are as follows（1）Through single factor experiment,the vacuum far infrared drying characteristics of Angelica sinensis slices were explored,and the corresponding drying kinetics model was determined.The results showed that the main drying process of Angelica sinensis slices was decreasing drying rate,and increasing the drying temperature was helpful to improve the drying efficiency,and the suitable drying temperature range was 40～50℃The results show that increasing the slice thickness can increase the heat and mass transfer path inside the material and reduce the infrared radiation efficiency,and the suitable slice thickness range is 3～5mm;reducing the irradiation height can shorten the time of absorbing infrared energy and accelerate the drying efficiency,and the suitable irradiation height range is 230～390 mm.Through the fitting analysis of drying characteristic curve,the fitting accuracy of logarithmic model is higher,which can better reflect and predict the change law of drying characteristics of materials in the drying process.（2）The effect of vacuum far infrared drying technology on the quality of Angelica sinensis slices was studied.The results showed that:when the drying temperature was between 40℃and 50℃,the content of ferulic acid and ligustilide in the dried products showed a downward trend,the content of Angelica polysaccharide showed an upward trend,the content of total phenol,total flavone,total color difference value and antioxidant capacity showed a trend of first rising and then declining;the slice thickness was between0 In the range of 3-5mm,the contents of ferulic acid,ligustilide,total phenol and total flavonoids increased,while the contents of Angelica polysaccharide decreased,and the antioxidant capacity and color difference value decreased first and then increased;in the range of 230-390mm,the contents of ligustilide and antioxidant capacity increased,while the contents of ferulic acid,total phenol and total flavonoids increased The content of Angelica polysaccharide decreased first and then increased.（3）A theoretical model of heat and mass transfer for vacuum far infrared drying of Angelica sinensis slices was established,and the heat and mass transfer process of Angelica sinensis slices was simulated by COMSOL multiphysics software.The results show that:in the temperature field,the material temperature first starts to gather from the inside,and gradually diffuses outward with the drying process;in the moisture field,with the drying process,the free water content in the material gradually diffuses outward,and the internal and external moisture gradient decreases.The mechanism of infrared radiation and the basic principle of electromagnetic heating are further revealed.（4）Based on the single factor experiment,the vacuum far infrared drying process of Angelica sinensis slices was optimized by response surface method with the drying temperature,slice thickness and irradiation height as the influencing factors,and the content of ferulic acid,ligustilide,color difference and average drying rate as the experimental indexes.The results showed that:the established multiple regression model could well describe the vacuum far infrared drying process of Angelica sinensis slices.The optimal drying parameters were drying temperature 45℃,slice thickness 3 mm,irradiation height 390 mm.Under these parameters,the content of ferulic acid was 0.12%,the content of ligustilide was 1.2%,the color difference was 18.26,and the average drying rate was 0.013%·min^-1.The verification test shows that the relative error is less than 2.46%,which indicates that the model fitting effect is good,and the optimization of process parameters has a certain application value for actual production.