RESUMO
Objective: To explore the law of temperature change in hot air drying process, and provide a theoretical basis for improving the drying efficiency and uniformity of Erzhi Pills (EP). Methods: Heat and mass transfer models were established to simulate the temperature distribution of the drying process of EP with no hole bottom and screen hole bottom based on COMSOL Multiphysics. The drying process of EP layer at 60, 80 and 100 ℃ was studied. The effective water diffusion coefficient (Deff) of EP layer was calculated by Fick’s second law plate model. A probe temperature sensor was used to monitor the temperature changes of the intermediate surface and interior of EP layer during the drying process to verify the drying model. Results: The surface and internal temperature of EP layer showed a trend of first sharp rise and then slow rise in the drying process of different hot air temperature. The inner temperature range of the drying model with no hole bottom and screen hole bottom was 55.3-56.0 ℃ and 57.5-57.7 ℃ respectively. The uniformity of drying temperature of EP can be improved by using drying plate with screen hole. The Deff range of the two model experiments were 0.76 × 10-7-2.82 × 10-7 m2/s and 1.15 × 10-7-3.94 × 10-7 m2/s, respectively. The experimental results showed that the model could well reflect the temperature variation of EP layer drying process within a certain drying temperature range. Conclusion: The change of drying temperature was directly reflected through the reliable hot air drying model of EP layer. The study provides reference for the optimization of EP drying process.
RESUMO
Objective: Taking Angelicae Sinensis Radix (ASR) slices as the research object, the far infrared drying characteristics and kinetic model of ASR slice were explored, which provided a theoretical basis for improving the quality of dry products and establishing a suitable processing method. Methods: The far-infrared drying technique was applied to the drying of ASR. The far-infrared drying characteristics and dry product quality of ASR were studied under different drying temperature, slice thickness and irradiation height, and the Weibull function was used to fit the drying curve. The quantitative relationship between test factors and model parameters were established. Results: With the increase of drying temperature and the decrease of the slice thickness and the irradiation height, the water ratio was decreased significantly, and the drying rate was increased significantly. The far-infrared drying process of the ASR slice obeyed the Weibull distribution function (R2 = 0.983 34-0.999 34, χ2 = 0.001 3-0.006 5), both the size parameter and the shape parameter were related to the drying temperature, slice thickness and irradiation height; The interval for estimating the water diffusion coefficient (Dcal) was 4.698 × 10-11-2.084 × 10-10 m2/s. The effective moisture diffusion coefficient (Deff) was in the range of 3.891 × 10-9-2.179 2 × 10-8 m2/s, both of which tended to increase with the increase of drying temperature, slice thickness and irradiation height. Compared with dry products from hot-hair drying, the color difference and water activity of far infrared drying were smaller, and it was easier to retain ferulic acid and volatile oil in ASR. Scanning electron microscopy analysis of the microstructure of dry products under different drying conditions showed that far infrared increased the interior of ASR slices. The number of micropores was increased, the cells were arranged more neatly, so as to increase the rate of thermal mass migration during the drying process and reduce the drying time. Conclusion: The Weibull distribution function can predict the water migration law of the drying process of ASR. It is of great significance for the prediction of the drying process of ASR and the process optimization.