Microwave Vacuum Drying Characteristics Of Angelica Slices And Heat And Mass Transfer Mechanism Research

Angelica is an authentic Chinese medicinal material rich in medicinal properties,but because it contains more water,it is prone to rot and deterioration during storage and transportation,which greatly reduces the quality of its dried products.Drying is an ancient processing method that can increase the shelf life of materials by reducing water activity.The conventional drying method has the disadvantages of long drying time,high energy consumption and large pollution.Microwave vacuum drying technology is a combination drying technology.Because of its advantages such as high heating efficiency,high product quality and low energy consumption,it is used in fruit and vegetable drying.Has a wide range of applications.In this paper,the dielectric parameters of materials under different drying conditions were measured with a parallel-plate capacitor,and the change law of the dielectric parameters of Angelica sinensis slices was studied.Secondly,the influence of material characteristics and equipment parameter changes on the microwave vacuum drying characteristics of Angelica slices was studied,and the heat and mass transfer laws during the material drying process were analyzed.Finally,based on the previous single-factor test,a response surface optimization test was performed to find its better microwave vacuum drying process.The main findings are as follows:(1)Study on microwave vacuum drying characteristics of Angelica slicesTaking angelica slices as research objects,the drying temperature,vacuum degree and slice thickness were taken as experimental factors to study the variation rules of microwave vacuum drying characteristics,and five drying models were used to fit the drying process.Studies have shown that the suitable range of material drying temperature in the process of microwave vacuum drying of Angelica slices is 40 ~ 50 ?,the more suitable degree of vacuum is-0.065 ~-0.075 MPa,and the more suitable slice thickness is 3 ~ 5mm;The distribution model can well simulate the single factor test of microwave vacuum drying process,and the Page drying model can fit the single factor test of drying temperature and slice thickness.(2)Study on Dielectric Parameters of Angelica SinensisTaking the drying time,drying temperature,slice thickness and vacuum degree as experimental factors,the change law of dielectric parameters of Angelica sinensis during microwave vacuum drying was studied.It was found that as the test frequency increased,the capacitance,resistance,and dielectric constant of the materials showed a decreasing trend.Atthe same time,the influence of drying temperature,slice thickness,and vacuum on the dielectric parameters of the Angelica slice microwave vacuum dry product was analyzed.With the increase of drying temperature,vacuum degree and slice thickness,the permittivity of the material decreases first and then increases.(3)Optimization of microwave vacuum drying process of angelica slicesOn the basis of the previous single-factor test,the appropriate factor ranges of drying temperature,slice thickness and vacuum degree were selected,and the microwave vacuum drying process of Angelica slices was studied with the rehydration ratio,color difference value and porosity as the test indicators.At the same time,the medicinal ingredients and microstructure of the dried products obtained under different drying conditions were compared.The results show that the significant order of the influence of various factors in the microwave vacuum drying process of angelica slices is: drying temperature,vacuum degree,slice thickness;the optimal parameter combination of microwave vacuum drying process of angelica slices is: drying temperature 40 ?,slice thickness 3mm,The degree of vacuum is-0.065 MPa,the maximum value of the rehydration ratio is 5.49,and the optimal values of color difference and porosity are 3.15 and 77.68%,respectively.By comparing the quality of the materials obtained under different drying conditions,it is found that microwave vacuum drying technology can Ferulic acid sliced with Angelica sinensis is preserved to the greatest extent to improve the quality of dried products.(4)Study on heat and mass transfer of microwave vacuum drying process of Angelica sinensisIn order to explore the heat and mass transfer laws of materials in the microwave vacuum drying process,according to the microwave vacuum drying mechanism of the materials,this paper established the heat and mass transfer equations of the materials in the drying process,theoretically describing the heat and heat of Angelica slices in the microwave vacuum drying process The law of moisture change.At the same time,the drying cavity and angelica slices were geometrically modeled,and the heat and mass transfer phenomena were modeled and simulated using comsol software.The changing trends of the temperature and moisture of angelica slices in different drying stages were observed.It conforms to the changing trend of the moisture ratio of the drying curve.Therefore,microwave vacuum drying technology canprovide a drying technology with low energy consumption,high efficiency and high quality for the processing of Chinese medicinal materials.