Study On The Heat And Mass Transfer And The Influence Of Color And Quality Characteristics Of Rhizome Tibetan Medicine Drying

The rhizome Tibetan medicine is a characteristic Chinese herbal medicine in Yunnan,which has the function of medicine and food homology.Due to the poor origin of the primary processing of Tibetan medicinal materials and the lag of processing technology,the quality of Tibetan medicinal materials dried in large quantities is unstable after drying,and the quality after drying is uneven,which seriously affects the economic value and medicinal value of medicinal materials.As a result,the heat and mass transfer law of rhizome Tibetan medicinal materials during hot air drying was theoretically investigated in this work.The influence of various parameters of the drying medium on drying was studied,and drying experiments were performed in hot air under different gradient changes of drying media parameters.Based on the theory of heat and mass transfer,a numerical calculation model of rhizome Tibetan medicinal materials was established,and the characteristics and distribution characteristics of water migration in single root Tibetan medicinal materials were analyzed.The influence of drying media parameters on color change in the drying process of medicinal materials was also investigated,and the relationship between color change and drying parameters was also obtained.This offered a solid theoretical and practical foundation for large-scale manufacturing and staged drying process optimization of rhizome Tibetan medicinal products.This paper’s main research work and conclusions are as follows:(1)Study on moisture migration in Chinese herbal medicine during the drying process.The calculation model of rhizome Tibetan medicine drying is given by numerical calculation method and verified by experiments,which shows that the model is feasible.The model was used to analyze the internal moisture change of medicinal materials.It was found that the gradient difference of moisture inside and outside the material was the main reason for the inconsistency of moisture distribution inside the material.The internal moisture migration was carried out by the diffusion of liquid water.The closer to the surface of the medicinal material,the greater the moisture concentration gradient,the faster the moisture migration.The evaporation interface of liquid water and water vapor inside the medicinal material will migrate to the inside with the drying,increasing the difference of water concentration inside the medicinal material,causing the medicinal material to be dry and wet outside,and reducing the drying efficiency.(2)Study on the influence of drying medium(moist air)parameters on drying in an unsteady drying process.Through experimental research,the drying characteristics of unsteady drying and uniform drying were analyzed.It was found that the temperature and relative humidity of the drying medium in unsteady drying showed multi-gradient changes.The relative humidity of the air would hinder the increase of temperature in the middle of drying,and the drying rate and moisture ratio would lag.The experimental analysis shows that the initial temperature of unsteady drying is set to 40 °C ～ 45 °C,and the moisture inhomogeneity of medicinal materials is less than10 %,which can ensure the quality of medicinal materials after drying.The relative humidity of air is less than 60 %,which can promote the temperature rise in the drying oven.(3)Study on the quality and color changes of Chinese medicinal materials during drying process.In this paper,the relationship between color change and drying parameters during the drying process of medicinal materials was studied by combining experiments with theory.It was found that the brightness of medicinal materials was mainly affected by temperature and relative humidity.The quantitative relationship between color and temperature and relative humidity during the drying process of medicinal materials was given.According to the change of Chinese herbal medicine composition in the drying process,by analyzing the browning of medicinal materials and the relationship between hue angle and drying parameters,it can be seen that high temperature and low humidity will promote the browning of medicinal materials,resulting in the decrease of medicinal components and blackening of color.In the process of batch drying medicinal materials,the temperature is controlled at 55 °C ～60 °C,and the relative humidity is controlled below 30 % to ensure the stability of the quality and the content of medicinal ingredients after drying.(4)Process optimization of large-scale drying of rhizome Tibetan medicine:A three-stage drying process for large-scale drying of Tibetan medicine was proposed.Considering the energy utilization and medicinal value,it is proposed that the first stage is mainly a heating process.The temperature is set at 40 °C ～45℃,and a holding time of 6 h～10 h.The second stage is mainly a reduce the relative humidity in the drying box process.The temperature is set at 40 °C ～45 °C,and the humidity in the drying box is reduced to 60 % ～50 %.The third stage is mainly a heating process.The temperature is set at 55 °C ～60 °C and reduces the relative humidity of the air in the drying box.Based on the perspective of energy efficiency and processing,the proposed process can reduce energy consumption by 3.67 % ～ 14.5 % compared with other drying processes.