## 4 Materials and Methods
### Analysis of the Effect of the Tempering Process on Rice Drying
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Group**} & \(X_{1}\) & \(X_{2}\) & \(X_{3}\) & \(X_{4}\) \\  & (\({}^{\circ}\)C) & **(\%)** & **(\%w.b.)** & **(m/s)** \\ \hline \(1\) & 39 & 50 & 19 & 0.5 & 1.5/3/4.5 \\ \(2\) & 39 & 50 & 19 & 0.6 & 1.5/3/4.5 \\ \(3\) & 39 & 50 & 19 & 0.7 & 1.5/3/4.5 \\ \(4\) & 39 & 50 & 21 & 0.5 & 1.5/3/4.5 \\ \(5\) & 39 & 50 & 21 & 0.6 & 1.5/3/4.5 \\ \(6\) & 39 & 50 & 21 & 0.7 & 1.5/3/4.5 \\ \(7\) & 39 & 50 & 23 & 0.5 & 1.5/3/4.5 \\ \(8\) & 39 & 50 & 23 & 0.6 & 1.5/3/4.5 \\ \(9\) & 39 & 50 & 23 & 0.7 & 1.5/3/4.5 \\ \(10\) & 39 & 54 & 19 & 0.5 & 1.5/3/4.5 \\ \(11\) & 39 & 54 & 19 & 0.6 & 1.5/3/4.5 \\ \(12\) & 39 & 54 & 19 & 0.7 & 1.5/3/4.5 \\ \(13\) & 39 & 54 & 21 & 0.5 & 1.5/3/4.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Factor combination scheme. To make the comparison more intuitive, comparison diagrams were drawn, as shown in Figures 4-7. As can be seen from Table 13, when every three groups are taken as a unit, only the velocity of the hot air is different. When taking every nine groups as a unit, the difference is the initial moisture. When all 27 groups are compared as units, the difference is relative humidity. Therefore, every three data points were taken as a comparison group to obtain the influence of the velocity of the hot air on each coefficient; every nine data points were taken as a comparison group to obtain the influence of the initial moisture of the rice on each coefficient; and all 27 data points were taken as a comparison group to obtain the influence of the relative humidity of hot air on each coefficient. It can be seen from Figure 4 that the \(k\) value affected by tempering was more sensitive to the velocity of the hot air through the comparison of every three data points. According to the comparison of every nine data points, with the increase in the initial moisture content of the rice, the \(k\) value affected by tempering decreased by about 0.05-0.1, while the \(k\) value without the influence of tempering increased by about 0.05, indicating that the increase in the initial moisture content of the rice weakened the effect of the \(k\) value on the drying process. The effect of tempering on high moisture content rice was weaker than that on low moisture content rice. Through the comparison of all 27 data points, it was found that with the increase in the relative humidity of the hot air, the \(k\) values with and without the influence of tempering decreased slightly, indicating that the increase of the relative humidity of the hot air tends to weaken the effect of the tempering process. Figure 4: Comparison of the coefficient \(k\) of the two models. Figure 5: Comparison of the coefficient \(n\) of the two models. Figure 5 shows that through the comparison of every three data points, it was found that the characteristics of the influence of the velocity of the hot air on the \(n\) value change. When the tempering ratio was 1.5 and the relative humidity of the hot air was relatively low (50%), the \(n\) value increases with the increase of the velocity of the hot air. When the initial moisture of the rice and the relative humidity of the hot air increased, the \(n\) value showed a negative correlation with the velocity of the hot air, because the desorption equilibrium temperature decreased with the increase of the initial moisture of the rice. When the tempering ratio was 3 or 4.5, the velocity of the hot air and the \(n\) value showed a negative correlation, indicating that a higher tempering ratio would hinder the drying process because too long a tempering time would lead to the occurrence of rice adsorption. Through the comparison of every nine data points, it was found that the \(n\) value decreased with an increase in the initial moisture content of the rice, and that the phenomenon was more obvious with an increased tempering ratio; the reason was the same as that mentioned before.