# Analysis of Rewetting Characteristics and Process Parameters in Tobacco Strip Redrying Stage
## 4 Results and Discussion
### The Effect of the Relative Humidity on Moisture Content and Humidification Rate of Tobacco Strips  
Combined with the actual production process parameters of some cigarette factories, the rewetting conditions were selected as a relative humidity of 85% and temperature of 55 \({}^{\circ}\)C. Under this condition, the distribution and variation of the heaped tobacco strips' overall moisture content are shown in Figure 6. The time interval in Figure 6a-c is the same, and the real-time moisture content of tobacco strips from three-dimensional and lateral perspectives are shown. At 1 s, in Figure 6a, the forced convection occurs in the rewetting box, and the vapor migrates through the forced convection to condense on the lower surface of the heaped tobacco strips, increasing the surface moisture content of the heaped tobacco strips. At 25 s, in Figure 6b, the surface moisture content is higher than the interior, and is transferred to the interior by diffusion. It is also seen that the moisture distribution is uneven in the same section, and the moisture content of the lower surface's central area is lower than the boundary because the vapor dispersed around the tobacco strips when it met them. At 50 s, in Figure 6c, the moisture distribution and transfer trend are similar to that in Figure 6b, which spread from the bottom and side boundaries to the center and top. The overall moisture content was significant, reaching 11-13%, and meeting the production requirements of moisture content. Figure 5: The comparison of the experiment and simulation of the moisture content. Figure 6: Schematic diagram of the rewetting process (the values in the figure represent the moisture content, unit: %). **(a)** The moisture content and distribution of tobacco strips at 1 s; **(b)** the moisture content and distribution of tobacco strips at 25 s; **(c)** the moisture content and distribution of tobacco strips at 50 s.  
Based on Figure 6, the moisture content changes in the heaped tobacco strip sections A, B, and C under different relative humidity conditions are analyzed when the temperature is 55 \({}^{\circ}\)C, as shown in Figure 7. At three relative humidities, the trend of moisture content of each section is the same, which includes two stages of the accelerating increase stage and the approximate constant rate increase stage. The accelerated increase stage is 0 s to 10 s, where the moisture content of all sections increases rapidly and the increments are large. The approximate constant rate increase stage is 10 s to 50 s, where the moisture content of all sections increases slowly and the increments remain stable. The reason for two stages is that the gas-phase condensation increases first, and then decreases gradually. It is also for this reason that there is always a moisture gradient that increases rapidly first, and then slows down to a stable level in all sections of the tobacco strips, which also indicates that moisture has been transmitted within the tobacco strips in the form of diffusion during this period. From Figure 7, it can be seen that, at the same time as that of the same relative humidity, the moisture content of section C is higher and faster than that of sections A and B; this is followed by section B, and finally, section A. This is because section C makes contact with the vapor first, and it is stable and sufficient. A large amount of vapor condenses at section C first, whereas section A is in the geometric center of the heaped tobacco strips, and the reactions here lag behind the other sections. Figure 7 also shows that the moisture content increment and growth rate of the three sections are also different with different relative humidity levels. The higher the relative humidity, the higher the increment and growth rate of the moisture content at each section, which indicates that relative humidity has a greater effect on the moisture content of tobacco strips.