# Design of and Experimental Study on Drying Equipment for _Fritillaria ussuriensis_
## 4 Optimization of Structural and Process Parameters of Drying Device Based on Fluent Simulation
### Simulation Analysis of Drying Effect of Fritillaria Ussuriensis  
In the drying process, the determination standard for the dry-based moisture content of _Frtillaria ussuriensis_ is calculated with reference to the drying method specified in national food safety standards, and it is specifically shown in the Formula (3) above. The FLUENT software is used to simulate the drying process of _Frtillaria ussuriensis_. During the drying process, as the moisture content of _Frtillaria ussuriensis_ changes continuously with temperature, it is necessary to introduce a UDF (User-Defined Function) to control the drying of _Frtillaria ussuriensis_. The source terms for moisture and mixture in _Frtillaria ussuriensis_ are set respectively. During the test, the room temperature was measured at 17 \({}^{\circ}\)C, and the initial moisture content of _Frtillaria ussuriensis_ was 66.4%. The initial moisture content was programmed into the UDF, and the humidity program for _Frtillaria ussuriensis_ was set accordingly. Patch initialization is performed to supplement the flow field initialization. When simulating the drying process, the optimal process parameters are selected as follows: inlet temperature of 338 K (65 \({}^{\circ}\)C), inlet air velocity of 3 m/s, and drying time of 10 h. The specific thermal-fluid-solid coupling simulation parameter values are provided in Table 7. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Serial Number** & **Item** & **Parameter** \\ \hline
1 & Thermal conductivity of stainless steel [W/(m\(\cdot\)K)] & 48 \\
2 & Initial temperature (K) & 290 \\
3 & Outlet temperature (K) & 298 \\
4 & Outlet pressure (kPa) & 101.325 \\
5 & Viscous drag coefficient of _Frtillaria ussuriensis_ & 3,444,859 \\
6 & Inertial drag coefficient of _Frtillaria ussuriensis_ & 3396 \\
7 & Porosity of _Frtillaria ussuriensis_ (\%) & 29.69 \\
8 & Thermal conductivity of _Frtillaria ussuriensis_ & 0.5 \\
9 & Specific heat capacity [J/(kg\(\cdot\)K)] & 2175 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Table of thermo-fluid-solid coupling simulation parameters. Based on the three optimized structural schemes proposed in Section 4.3, drying simulations of _Fritillaria ussuriensis_ were conducted, with the humidity of _Fritillaria ussuriensis_ at the central position of each layer monitored. The obtained humidity nephograms are shown in Figure 10. Through a comparative analysis of the drying effects of different schemes, it can be seen from Figure 10 that _Fritillaria ussuriensis_ in Structure 3 has a lower humidity, which stabilizes at approximately 11.5% once a steady state is reached. Additionally, the temperature and air velocity distributions are more uniform, resulting in a better drying effect. In the actual drying process, the drying rates of _Fritillaria ussuriensis_ may vary at certain special positions. For example, the moisture content of _Fritillaria ussuriensis_ located far from the air inlet is higher than that near the inlet. When the _Fritillaria ussuriensis_ near the air inlet is dried, that which is far from the air inlet may have a moisture content higher than the expected value. To avoid this phenomenon, this study conducts a drying simulation analysis on _Fritillaria ussuriensis_ in special positions. The moisture content of _Fritillaria ussuriensis_ at the left, middle, and right positions of each ray (numbered L1-3, M1-3, R1-3 from top to bottom) and the temperature changes at the middle position of each layer in the drying chamber (Line1-3) were monitored, with a total of 12 temperature and humidity monitoring points set. The final nephograms showing changes in moisture content and temperature of _Fritillaria ussuriensis_ at special positions, obtained through monitoring, are shown in Figure 11.  
It can be seen from Figure 11 that heat transfer occurs sequentially from the position close to the hot air toward the right (L-M-R).