# Analysis of Rewetting Characteristics and Process Parameters in Tobacco Strip Redrying Stage
## 1 Introduction  
The rewetting of tobacco strips during the redrying stage (hereinafter referred to as rewetting) is a more complex and difficult part of the whole redrying process [1], which aims to make the internal moisture and temperature of heaped tobacco strips reach the specified process index [2, 3] while being conducive to natural alcoholization. Traditional rewetting methods have been eliminated due to their large number of problems, and now, rewetting with a forced hot and humid airflow is commonly used [4]. No matter which rewetting method is used, it is greatly influenced by the process parameters. Because of the numerous and complex process parameters [5, 6, 7] and because adjustment mainly relies on manual experience [8], various problems arise, such as reduced tobacco quality and high moisture and vapor consumption [9]. The influence of relative humidity and temperature on rewetting characteristics is a problem that urgently needs to be solved.  
In the process of rewetting, relative humidity and temperature are critical for consistent rewetting quality and strip yield [10]. [PERSON] [1] used the BP neural network algorithm to control and optimize the moisture and temperature of a tobacco redrying machine, and this algorithm greatly improved the rewetting quality of tobacco strips. [PERSON] et al. [11] proposed a novel dual-control algorithm to control the exit moisture and to reduce the fluctuation amplitude of the outlet moisture during the tobacco redrying process. [PERSON] et al. [12]designed a serial predictive compensation control strategy based on the serial relationship between the moisture content of tobacco strips at the outlet of the redryer and that of tobacco strips packed in cases, which solved the problem of the unstable moisture content of tobacco strip packing in the drying line. Based on the thermodynamic theory, [PERSON] et al. [13] simulated the temperature field and flow field of tobacco in a reversion machine and optimized the structure of the reversion machine based on simulation and experimental results to improve the quality of tobacco rewetting. [PERSON] et al. [14] built a mathematical model of the internal flow field of the box and the motion of the strips and silk particles based on the fluid dynamics theory to optimize the tobacco conditioner, and improve the utilization rate of strips and product quality. [PERSON] et al. [15] established a loose rewetting network model of tobacco strips using the Bayesian network analysis method to explore the complex relationship between the process parameters and quality indicators in the process of rewetting during production. [PERSON] et al. [16] improved the number and layout of nozzles in a rewetting cylinder, optimized the moisture addition and proportion, and solved the problem of wet mass after rewetting. In summary, these studies on improving the quality and qualified rate of tobacco strips by changing the process parameters, such as relative humidity and temperature, were realized by improving algorithms based on simulations to optimize the structure of rewetting machines. In terms of the mechanism, there are few studies on the influence of the transfer and diffusion of external relative humidity and temperature on rewetting.  
In this paper, a conjugate heat and mass transfer model of tobacco strips was established, and the reliability of the model was verified by experiments. Based on the established model, the transfer and distribution of moisture and temperature at different positions and thicknesses of tobacco strips were calculated. The influence of the relative humidity and temperature on the moisture content, humidification rate, effective moisture diffusivity, and activation energy of the tobacco strips was studied, and the rewetting characteristics and process parameters were explored.