Drying kinetics and mathematical modeling of Erzhi Pills during hot-air drying process / 中草药

ABSTRACT

Objective: To study the change rule of water content in the drying process of hot air drying of thin layer drying characteristic and model research, and to provide reference for improving the quality of Erzhi Pills (EP). Methods: The moisture ratio, drying rate of dry basis, and drying rate curves along with the change of drying time and relationship between dry basis moisture content and drying rate of EP were studied using a hot air dryer at five levels of drying air temperature in the range of 50-90 ℃. The model was fitted and verified by the empirical model Henderson & Pabis model, Newton model, Page model, Logarithmic model, two term exponential model, Wang & Singh model, Midilli et al. model, etc. Meanwhile, based on Fick's diffusion law, the effective diffusion coefficients of water (Deff) and activation energy value in EP were calculated. Results: The drying curves of EP show that the moisture ratio and drying rate of EP were closely related to the temperature of drying medium, and the moisture of the material decreases with the prolonged drying time. It could be seen from the drying rate curve that the drying rate increased with the increase of hot air temperature, and the migration of moisture was accelerated. By comparing the correlation coefficient (R2), chi-square (χ2) and standard error (RMSE), we could see that the mean value of R2 of model number 7 was the maximum, the χ2 and RMSE mean were the smallest (0.996 86, 2.43 × 10−4, and 1.93 × 10−4), respectively. The results showed that the model number 7 could describe and predict the drying process of the pills. The experimental data had the effective diffusion coefficient (Deff) value of 8.6 × 10−11—3.13 × 10−10 m2/s, and the activation energy (Ea) was 30.97 kJ/mol. Conclusion: The hot air drying process of EP can be modeled and verified. The research provides a new way to explore the drying characteristics and quality of pills.