Study On Dehydration Dynamics Model And Characteristic Mechanism For Chinese Medicinal Materials Of Rhizome By Hot Air Drying

The number of Chinese medicinal materials of rhizomes accounts for more than 80% of the total number of Chinese medicinal materials of plants.However,the lacks in the processing technology of Chinese crude drugs led to the limited quality of Chinese crude drugs,which affected the sales volume.Therefore,the heat and mass transfer laws in the process of hot air drying of rhizome Chinese medicinal materials were theoretically studied,and the hot air drying experiments under different drying conditions were carried out.To provide an effective theoretical basis and experimental basis for the drying of rhizome Chinese medicinal materials,a dynamic model for predicting the water loss process of rhizome Chinese medicinal materials under different hot air drying conditions were established based on Fick's diffusion law.The effects of different drying conditions on the drying characteristics and drying quality of rhizome Chinese medicinal materials are analyzed.The main research work and conclusions of this paper are as follows:(1)Based on the law of mass conservation,and the heat conservation,the feck diffusion as well as the theory of liquid diffusion,the thermodynamic properties of rhizome Chinese medicinal materials was studied.The results show that the rate of heat and moisture transfer during the drying of wet materials were affected by different drying conditions.The drying process of wet materials goes through a short speed-up phase and a long-term speed-down phase,while a few of the wet materials also need to go through a short constant velocity stage.Increasing the drying parameters can effectively decrease the preheating time and improve the drying efficiency in the speedup phase;increasing the drying parameters has a small effect on the drying process of the constant velocity stage;in the speed reduction stage.Increasing the drying parameters can effectively increase the drying rate.If the drying parameters are too high,it is easy to harden the drying materials and affect the drying quality.(2)A dynamic model formula of predicting the water loss process of Chinese medicinal materials of rhizomes under the different conditions of hot air drying was established,which include the effecting factors of hot air temperature,wind speed,relative humidity of the air and slice thickness.The model was verified by the experimental data with the materials of the Gentiana macrophylla,the notopterygium and the rhizome under the conditions of the loading 850 kg,60kg and 200 kg,respectively.The results show that the data predicted by the model can agree with the actual value of more than 90%.The model can accurately predict the water loss process of rhizome Chinese medicinal materials under the hot air drying.(3)The experimental study of thermodynamic characteristics of the sliced Gastrodia elata and the Gentiana macrophylla were carried out under different hot air drying conditions.The results show that increasing the hot air temperature,air velocity,reducing air relative humidity,and the slice thickness can effectively increase the effective diffusion coefficient of rhizomes,and its activation energy ranges from 30-40 KJ/mol.(4)The main influencing factors of increasing the drying rate were the hot air temperature,also the main influencing factors in improving the drying quality were the hot air temperature and wind speed.Under the conditions of the temperature from 50? to 65?,with the wind speed of 2.0m/s to 3.5m/s,and the relative humidity less than or equal to 25%(the thickness of the dried rhizome Chinese medicinal materials section is 0.4cm),the rhizome Chinese medicinal materials have the highest drying rate and the best drying quality.The research works can provide the reference to establishing the drying standard system of rhizome Chinese medicinal materials.