# Simulation and Experimental Research on the Energy Loss of Confluence Pipelines
## 5 Conclusions  
In the present study, the energy loss in confluence pipelines was studied, with a particular focus on this type of pipeline throughout the study. Through numerical simulation, we used the RNG turbulence model and SIMPLE algorithm to solve the energy loss of the pipeline. The energy loss of polymethyl methacrylate arc confluence pipelines with different pipe diameters, curvature radii, and Reynolds numbers were analyzed in the experimental research, and the main conclusions are as follows:  
1. For arc confluence pipes with diameters of 12 mm, 16 mm, and 20 mm, as the curvature radius of the arc confluence pipe increases, its energy loss coefficient first decreases and then increases, with the curvature radius corresponding to the minimum energy loss being approximately 65 mm. This phenomenon may be related to the flow separation and reattachment when the fluid flows through the confluence pipe, especially under smaller curvature radii, where flow separation is more severe, leading to increased local energy loss. As the curvature radius increases, the flow becomes smoother, reducing energy loss. However, when the curvature radius is too large, the along-pipe losses begin to dominate, leading to an increase in total energy loss.
2. For arc confluence pipes with the same curvature radius and diameters of 8 mm, 12 mm, 16 mm, 20 mm, and 25 mm, the energy loss coefficient gradually decreases as the pipe diameter increases. This may be because a larger diameter helps to reduce the local velocity of the flow, thereby reducing the energy loss caused by turbulence and flow separation.
3. For an arc confluence pipeline with different pipe diameters and curvature radii, there is no established rule to follow between the ratio of curvature radius to pipe diameter R/D and confluence energy loss. This indicates that a single geometric parameter is not sufficient to predict energy loss, and it may be necessary to consider more flow characteristics and boundary conditions.  
We conducted quantitative calculations on the energy loss and suction height of the PSP1500 vehicle-mounted fire pump produced by AMPRO. They indicated that the application of circular arc confluence pipes in the combined inlet pipeline of fire truck water supply pumps can increase the suction height, which is of great significance for improving the on-site performance of fire trucks and enhancing firefighting efficiency. Our future work will focus on sensitivity analysis of other independent variables like fluid properties and temperature and developing and validating more accurate numerical models to predict energy loss.  
Conceptualization, S.Z.; methodology, S.Z.; software, C.P.; validation, C.P.; formal analysis, C.P.; resources, S.Z.; data curation, C.P.; writing--original draft preparation, C.P.; writing--review and editing, S.Z. and J.L.; visualization, C.P.; supervision, Z.L. and Q.H.; project administration, Z.L.; funding acquisition, S.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Science and Technology Major Project, grant number: J2019-I-0008-0008.  
Not applicable.  
**Informed Consent Statement:** No applicable.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflicts of interest.