Analysis of Rewetting Characteristics and Process Parameters in Tobacco Strip Redrying Stage

Abstract

To study the rewetting characteristics of tobacco strips during the redrying stage, a conjugate heat and mass transfer model of tobacco strips was established based on their physical properties. The fundamental relationship between the multiphysical fields and humidity fields of tobacco strips and the key process parameters was considered in this model, and the feasibility of the model was verified via experiments. Based on this model, the transfer and variation laws of the moisture content, humidification rate, and temperature of tobacco strips under different relative humidity and temperature conditions were studied, and the rewetting process parameters of tobacco strips were determined using COMSOL Multiphysics. The results show that this model can be used to study the rewetting characteristics of tobacco strips during the redrying stage. The rewetting of tobacco strips can be divided into two stages, namely, the accelerated stage and approximate constant rate increase stage, where the former stage has a greater impact on the rewetting effect. The higher the relative humidity and temperature, the greater the change in the moisture content, humidification rate, and effective moisture diffusivity, and the faster the increase rate. The best rewetting effect was achieved when the relative humidity was 85% and the temperature was 55 °C. Under these conditions, the moisture content of the tobacco strips was 11% to 13%, the humidification rate was 0.03 %/s to 0.29 %/s, the highest effective moisture diffusivity was 7.8 × 10−10 m2/s, and the maximum activation energy was 37.86 kJ/mol. This study provides a theoretical basis and data support for analyzing the characteristics of the rewetting process and for optimizing the process parameters.

Keywords

• rewetting
• tobacco strips
• redrying
• heat and mass transfer model
• relative humidity