## 4 Analysis of Experimental Results
### Comparative Analysis of Experimental Phenomena and Numerical Simulation Results
Due to the high swirl and large pressure gradient in the flow field, the PRESTO format was chosen for pressure differences, and the Second Order Upwind and QUICK formats were used for fluid convection. The material properties were based on natural gas hydrate core data from the Shenhu area in the South China Sea, with the solid-phase particle size in the slurry assumed to be 50 \(\upmu\)m. The simulation maintained constant in situ temperature and pressure, and the physical property parameters for each phase are shown in Table 3. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Inlet velocity (m/s) & 10 \\ Inlet temperature (K) & 273.15 \\ Inlet turbulence intensity & 5\% \\ Outlet relative pressure difference (MPa) & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Geometric Parameters and Operating Conditions in the Numerical Simulation. Figure 5: The geometric model meshing of the separator. To avoid the impact of mesh size on the results and to save computational resources, we analyzed the effect of varying the mesh number on the simulation results. The simulations were performed with the same geometry, boundary conditions, and material properties, using different mesh sizes of 20 mm, 10 mm, 5 mm, and 2 mm, with corresponding mesh numbers of 48,050, 128,649, 774,018, and 7,160,945. The pressure drop results for the first three mesh sizes showed errors of 7.8%, 5.3%, and 1.6%, with errors below 5% considered acceptable. Therefore, when the mesh size is below 5 mm, the separation efficiency shows little change. To avoid excessive mesh numbers affecting computational speed, a 5 mm mesh size was chosen for subsequent simulations. As shown in Figure 6, the experimental phenomenon of the overall separation process of the spiral-cyclone separator is compared with the simulation results. From the experimental phenomenon of the spiral-cyclone separator, we can find the difference in the transparency of the liquid in the hydrate recovery area and the sediment separation area, which is caused by the difference in the volume fraction of the sediment phase. The experimental phenomenon can prove that the separator has the same separation effect as the numerical simulation from a macroscopic point of view, while the quantitative analysis of the separation efficiency of the separator needs to be determined by sampling the outlet and inlet fluids. As shown in Figure 7, by comparing the numerical simulation and the indoor experimental phenomena, it was found that the volume fraction of the sediment phase is higher at the wall of the separator, which is because the denser sediment is thrown to the wall of the separator under the action of the centrifugal force generated by the separator, and the separation of the hydrate and sediment is achieved. The phenomenon of violent turbulence occurs at the entrance of the spiral flow channel so that the multiphase mixed slurry to be separated obtains a greater disturbance, which is conducive to the subsequent separation of the mud and sand from the multiphase mixed slurry. At the same time, at the bottom of the separator, a large amount of sedimentation of mud and sand occurred, which verified that the designed model has a good performance in terms of separating mud and sand. Figure 6: A comparison of experimental setup and the simulation of the overall separation process of the spiral\(-\)cyclone separator. As shown in Figure 8, the accumulation of mud and sand at the entrance of the spiral runner indicates that the content of mud and sand in the multiphase mixed slurry is high at this time. As the multiphase mixed slurry flows through the spiral runner, the content of mud and sand in the slurry is significantly reduced, which proves that the mud and sand in the multiphase mixed slurry are separated, and the natural gas hydrate has achieved the effect of purification.