A study of mass transfer resistance in the hot air drying process of stacked flake materials
摘要
To investigate the mechanism of the influence of hot air drying quality for stacked flake materials, the mass transfer resistance of stacked flake materials in the hot air drying process was studied. A numerical simulation model for hot air drying of stacked flake materials has been established and the accuracy of the model is verified by a bidirectional alternating hot air drying test platform. The mass transfer resistance model was established, the influence laws of airflow velocity and airflow temperature on mass transfer resistance and drying quality were studied, and the influence mechanism of airflow direction on mass transfer resistance of stacked flake materials was analyzed using segmented hot air drying. The results show that the numerical simulated and experimental data are in good agreement, with average relative errors of 2.38% and 2.63% for the moisture content of the upper and lower layers of stacked flake materials, respectively. During the hot air drying process of stacked flake materials, the airflow velocity and temperature have a significant effect on the mass transfer resistance, which is inversely proportional to the airflow velocity and directly proportional to the airflow temperature. When a single airflow direction is used, the mass transfer resistance in the upward airflow direction is greater than that in the downward airflow direction, where the difference is greatest in the middle layer of stacked flake materials, about 2 times. The lower the mass transfer resistance, the more conducive to improving the drying uniformity of the stacked flake materials; the higher the mass transfer resistance, the more easily to cause the stacked flake materials over-drying (Mc < 8%) and insufficient drying (Mc> 11%). Changing the direction of airflow has a significant effect on mass transfer resistance, and the more times the direction of airflow is changed, the lower the drying efficiency and the lower the energy utilization, can only change the direction of the airflow for 1 time. The results of this study can provide a reference for improving the segmented hot air drying process of agricultural products.