# 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
### Optimization of the Internal Structure of Drying Device  
First, the internal tray is positioned such that it is equidistant from the drying chambers on both sides, enabling air to flow out from both sides and then into the tray section at the middle position. The time step is set to 1 s with a total of 600 steps, and changes in the temperature field, flow field, and pressure field within the drying chamber over 600 s are observed. The corresponding cloud diagrams are shown in Figure 4.  
As can be seen from the temperature field cloud diagram, Figure 4a the temperature does not rise uniformly after 600 s. The heat accumulates from both sides to the middle, while the temperature at the central position rises slowly. This will cause the _Fritillaria ussuriensis_ in the central interior to still have a high moisture content when the outer _Fritillaria ussuriensis_ is already dried. From the velocity cloud diagram and pressure cloud diagram Figure 4b,c, it can be observed that the air velocity near the air outlet is relatively high, which also causes uneven heat. Moreover, the large pressure difference results in unstable pressure in the drying device, potentially causing explosion hazards. Therefore, considering the above factors, the uneven airflow inside the _Fritillaria ussuriensis_ drying device constitutes the key issue. Thus, the tray position of _Fritillaria ussuriensis_ is optimally designed. After optimization, the trays are staggered at a certain distance to form an airflow transmission path, allowing hot air to fully contact each _Fritillaria ussuriensis_ and achieve the purpose of removing moisture. The cloud diagrams of the optimized structure (Structure 2) are shown in Figure 5. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Project** & **Parameter** & **Unit** \\ \hline Length \(\times\) height & 800 \(\times\) 500 & mm \\ thermal conductivity & 15 & W/(m K) \\ air velocity & 3 & m/s \\ inlet temperature & 338 & K \\ outlet temperature & 298 & K \\ discharge pressure & 101.235 & kPa \\ \hline \hline \end{tabular}
\end{table} 
Table 4: 2D Simulation Parameters. Figure 4: Cloud Diagram of Structure -Variation (**a**) Temperature variation cloud diagram, (**b**) Velocity variation cloud diagram, (**c**) Pressure variation cloud diagram. As shown in the temperature cloud diagram of Figure 5a, when the tray positions are staggered, the temperature rises uniformly. At 600 s of drying time, the fluid temperature nearly reaches 338 K, with only partial tray positions having temperatures lower than that at the inlet. From the velocity cloud diagram of Figure 5b, it is observed that no fluid flows through the second-layer tray near the inlet, which accounts for the low temperature at this tray position. Additionally, the pressure difference is excessively large. Considering factors such as fluid direction and pressure, a separate heating chamber is designed. Hot air generated by the heating chamber is blown into each layer of trays through an open baffle, while ventilation openings are installed in the inner box to ensure hot air passes through every tray. An external drying box is also configured to recycle the hot air generated by the drying device. The simulation of the external drying box with wall heating is conducted, and the variation cloud diagrams (Structure 3) are shown in Figure 6.  
Temperature monitoring was carried out for each structure, with monitoring points set at the second layer of each structure to track the temperature changes of the fluid in this layer over 600 s. The temperature comparison diagram is shown in Figure 7a. It can be seen from the temperature change curve that the temperature rise in the second layer of Structure 1 is slow, which is significantly lower than that in Structures 2 and 3.