## 6 Conclusions  
Based on the model established in this study, the influence of the mass transfer coefficient on the phase transition of the liquid film was calculated and analyzed. According to the optimized mass transfer coefficient, the influence of the spiral seal face groove structural parameters on the performance of the liquid film seal between the seal faces was calculated and analyzed. The following conclusions were obtained:  
1. The phase transition phenomenon of the spiral groove liquid film seal was simulated and calculated. Based on the calculation results, as the mass transfer coefficient increases, the average vapor phase volume fraction first increases and then stabilizes. The average vapor phase volume fraction changes in the same manner under different mass transfer coefficients. However, the difference between the calculated values is obvious, and the influence of the mass transfer coefficient cannot be ignored. However, the effect of the change in the mass transfer coefficient on the opening force and the leakage rate can be assumed to be negligible. Therefore, when performing the numerical analysis of the average vapor phase volume fraction simulation, it is necessary to determine the mass transfer coefficient before performing the subsequent calculation and analysis.
2. The average vapor phase volume fraction increases with an increase in the helix angle, groove-weir ratio, and groove depth. Moreover, the average vapor phase volume fraction first increases and then decreases with an increase in the groove-diameter ratio. The opening force decreases with an increase in the helix angle, groove-weir ratio, and groove depth. By comparison, the opening force first decreases and then increases with an increase in the groove-diameter ratio. The leakage rate first increases and then stabilizes with an increase in the helix angle. Moreover, the leakage rate increases continuously with an increase in the groove-diameter ratio, groove-weir ratio, and groove depth. The effect of the helix angle and the groove depth on the leakage rate is less obvious than the effect of the groove-diameter ratio and groove-weir ratio. As such, it can be assumed to be negligible.
3. This paper represents an analysis of the influence of single-factor structural parameters based on the optimal mass transfer coefficient on the phase transition of the spiral groove mechanical seal liquid film. In future works, the influence of structural parameters on the phase transition of the liquid film under the interaction of multiple factors will be discussed. Moreover, the effect of changes in operating conditions on the phase transition and sealing performance parameters will also be investigated.
4. The current study of the influence of the change in the mass transfer coefficient on the vaporization of liquid film fills an existing research gap. It has important theoretical and engineering significance for the design and application of mechanical seals with different structural parameters, controlling the degree of phase change, improving the sealing stability, and improving the sealing performance.  
[PERSON], [PERSON] and [PERSON] outlined the structure of the paper, [PERSON] wrote the paper, [PERSON], [PERSON] and [PERSON] revised the paper. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China (No. 2018 YFB2000800), the National Natural Science Foundation of China (No. 52075268), and the Key R&D Program of Jiangsu Province (No. BE2021062).  
The authors acknowledge the financial support provided by the National Key R&D Program of China (No. 2018 YFB2000800), the National Natural Science Foundation of China (No. 52075268), and the Key R&D Program of Jiangsu Province (No. BE2021062).  
The authors declare no conflict of interest.