## 5 Conclusions  
Based on the above results, the following conclusions can be drawn:  
1. Installing spiral blades at the gas inlet significantly improves the overall mixing effect compared to installing them at the air inlet. 2. When spiral blades are installed at both the air and gas inlets, the direction of rotation of the blades has an impact: when the mixing zone is short, the pressure loss and spatial non-uniformity are relatively lower for the same rotation direction, but when the mixing zone is long, the opposite rotation direction has a greater advantage. 3. When no spiral blades are added to the front end of the mixing zone, the overall effect of the structure with only gas rotation is the best, and the effect of the structure with air and gas rotating in opposite directions is similar to that of the structure with only gas rotation at two meters in the mixing zone. 4. Adding spiral blades at the forefront of the mixing zone significantly improves gas uniformity but is not conducive to reducing pressure loss. The impact on pressure loss and gas uniformity is related to the direction of rotation. Adding a set of spiral blades with the opposite rotation direction to the blades at the low-concentration gas inlet at the forefront of the mixing zone can greatly improve the mixing uniformity at the outlet but will increase the system's mixing pressure loss. When the two rotation directions are the same, the impact on system pressure loss and mixing uniformity is relatively small. 5. Among the structures with spiral blades added at the forefront of the mixing zone, the b2 structure has the most ideal results, with an outlet spatial inhomogeneity of approximately 5.24%, significantly better than the requirement of less than 15% spatial non-uniformity in the \"Design Code for Low-Concentration Gas Oxidation and Utilization Engineering in Coal Mines\", and the spatial non-uniformity still tends to decrease as the mixing zone length increases. In summary, the proposed spiral blade configurations effectively enhanced mixing uniformity while balancing pressure loss. However, this study is based solely on numerical simulations. The lack of experimental validation is a limitation, and future studies will focus on laboratory or field experiments to further verify the findings. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Model**Length** & **0.5 m** & **0.75 m** & **1 m** & **1.25 m** & **1.5 m** & **1.75 m** & **2 m** \\ \hline a1 & 0.36846 & 0.28228 & 0.19744 & 0.14179 & 0.10695 & 0.08219 & 0.06236 \\ a2 & 0.32407 & 0.23786 & 0.16193 & 0.12253 & 0.09562 & 0.07371 & 0.06057 \\ b1 & 0.03589 & 0.02269 & 0.01741 & 0.01111 & 0.00650 & 0.00352 & 0.00170 \\ b2 & 0.31912 & 0.20955 & 0.13853 & 0.10213 & 0.08070 & 0.06508 & 0.05237 \\ c1 & 0.22191 & 0.14100 & 0.10767 & 0.08387 & 0.06398 & 0.04829 & 0.02696 \\ c2 & 0.19589 & 0.10601 & 0.06668 & 0.05474 & 0.04886 & 0.04247 & 0.03823 \\ d1 & 0.33088 & 0.23683 & 0.19968 & 0.17827 & 0.16091 & 0.14767 & 0.13642 \\ d2 & 0.12011 & 0.09312 & 0.07193 & 0.05260 & 0.03910 & 0.03032 & 0.02353 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Non uniformity of cross-sectional space at different positions. **Author Contributions:** Conceptualization, Q.H. ; Methodology, H.G. ; Software, X.G. and S.L. ; Validation, Y.L. ; Formal analysis, H.G. ; Investigation, H.G. ; Resources, X.G. ; Data curation, H.G. and S.L. ; Writing--original draft, H.G. and S.L. ; Writing--review & editing, Y.L. ; Visualization, Q.H. ; Project administration, Y.L. ; Funding acquisition, X.G., Q.H. and Y.L. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was financially supported by the National Key Research and Development Program of China (Project NO. 2023 YFF0615404). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.