Abstract: 【Objective】In order to improve the drying quality of the bitter melon slice(BMS), shorten the drying time, the effects of the air-impingement drying conditions on the drying characteristics of the BMS were studied and the drying kinetics model was established to predict the moisture change in the drying process. 【Method】The BMS were dried by the air-impingement jet dryer made by the authors’ laboratory. The effects of different air temperatures (40, 50, 60, 70 and 80℃), air velocities (9, 10, 11, 12 and 13 m·s^-1) and slice thickness (2, 3, 4, 5 and 6 mm) on the drying characteristics of materials and effective moisture diffusion coefficient of water were studied, and the activation energy was calculated. With the R², χ² and RMSE as the evaluation indexes, the optimum model was screened within the five commonly used dry models fitting the experimental data by Origin 8.0 software, then the relationships between the model parameters and drying conditions was establish and the prediction effect of the optimum drying model was verified.【Result】The air-impingement jet drying of BMS occurred in the falling rate drying period, and there was no constant drying rate stage. Under the experimental condition, air temperature, air velocities and slice thickness all had a certain effect on dry characteristics of BMS in air-impingement jet drying process. With the increase of air temperature and air velocities, the decrease of the slice thickness, the moisture of material decreased more fast and the drying rate was rising, the drying time was short, but the influence of air velocities was less significant than air temperature and slice thickness. The water effective diffusion coefficient of the BMS during drying process could be calculated by Fick’s second law, and it increased with the increase of air temperature, air velocities and slice thickness. The maximum effective diffusion coefficient was 2.9668×10^-9 m²·s^-1. Arrhenius was used to calculate the activation energy of BMS in drying process and the value of E_a was 29.89 kJ·mol^-1. The five selected models all had good fitness (R²>0.98), they could predict the moisture change of the BMS in air-impingement jet drying process. Of the five models, the Two term exponential model had the highest coefficient of determination R² (0.99937), the lowest chi-square χ² (0.00876) and root mean square RMSE (0.000077), and it is the optimum model of the BMS in air-impingement jet drying. 【Conclusion】All the factors including the air temperature, air velocities and slice thickness had influence on the drying curve, the drying rate curve and moisture effective diffusion coefficient, and their influences were in an order of the air temperature＞air velocities＞slice thickness. Two term exponential model could properly describe the air-impingement jet drying behavior of BMS and could be used to predict the moisture change of the BMS in air-impingement jet drying process under the condition that the air temperatures between 40 and 80℃, air velocities between 9 and 13 m·s^-1 and slice thickness between 2 and 6 mm.

Key words: bitter melon, air-impingement jet, drying characteristics, drying model