## 2 Design and Processing of Experimental Prototype of Spiral-Swirl Separator
### The Design, Machining, and Installation of the Experimental Spiral-Cyclone Separator Prototype  
To reduce the cost, speed up the progress, and facilitate the processing and later assembly of the experiment, the prototype used in the experiment adopts a split design and uses flanges to realize the connection of each component. The split experimental prototype can be optimized for a single component while other components remain unchanged, reducing the experimental cost. In this study, the spiral-cyclone in situ separator was divided according to its characteristics, as shown in Figure 2a, the in situ separator was divided into five parts from its toe, and each part was connected by flanges, and individual parts were processed separately. The internal flow path of the split experimental prototype and the internal flow path of the spiral-cyclone separator are kept consistent to ensure the scientific nature of the experiment. Because it is difficult to achieve real seabed conditions under the existing experimental conditions, and it is not realistic to build a simulated seabed ultrahigh-pressure and low-temperature experimental environment, the natural gas hydrate mixed slurry cannot enter into the separator from the suction port of the spiral-cyclone separator, so it is necessary to change the structural setup of the hydrate suction port, and the structure of the other components remains unchanged, and the area of the suction port is the same as the designed inlet area to ensure the separator processing  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Sign** & **Value** \\ \hline Total height of separator & H & 1200 mm \\ Separator inner diameter & D\({}_{1}\) & 140 mm \\ Number of cyclone inlet guide ports & N\({}_{0}\) & 4 \\ Cyclone inlet helical pitch & h\({}_{1}\) & 900 mm \\ Cyclone inlet helix turns & N\({}_{1}\) & 0.25 \\ Cyclone inlet helix length & L & 180 mm \\ Distance from the bottom of the cyclone & H\({}_{2}\) & 1000 mm \\ inlet to the bottom of the separator & & \\ Spiral runner pitch & h\({}_{2}\) & 78 mm \\ Overflow pipe inner diameter & D & 72 mm \\ Overflow pipe insertion length & L\({}_{1}\) & 0 \\ Number of spiral turns of spiral runner & N\({}_{2}\) & 5.25 \\ Vortex deflector position & E\({}_{1}\) & 136 mm \\ Sedimentation depth & H\({}_{1}\) & 317.5 mm \\ Vortex deflector diameter & D\({}_{2}\) & 120 mm \\ \hline \hline \end{tabular}
\end{table}
Table 1: Structural parameters of the spiral-cyclone in situ separator.  
Figure 1: An overview of the in situ separator–discharge sand backfill device. 1, sand discharging spray cylinder; 2, spring I; 3, sand discharging slip sleeve; 4, spring II; 5, spring cover; 6, conical steady-flow glue cylinder; 7, fixed ring I; 8, positioning casing; 9, cyclone-generating plate; 10, fixed ring II; 11, outer pipe of the separator; 12, power liquid pipe; 13, spiral broken glue junction harvesting cylinder; 14, centering bracket; 15, fixed ring III; 16, cyclone inlet.  
capacity. The area of the suction inlet is the same as the designed inlet area, to ensure that the capacity of the separator is consistent.  
To facilitate clear the observation of the experimental phenomena in the in situ spiral-cyclone separator, the separator is made of high-strength Plexiglas (acrylic). Figure 2b shows the experimental prototype machining of the components; due to the separator using a split design, the geometric optimization only needs to be processed separately in the spiral flow channel, vortex deflector, cyclone inlet, separator shell, and sedimentation chamber. The other parts do not need to change, and components that need to be optimized can be replaced.