Resistance reduction of an elbow with a guide vane based on the field synergy principle and viscous dissipation analysis

In recent years, to reduce carbon emissions and increase energy efficiency, the local resistance represented by elbows in piping has received increasing attention in heating, cooling, and water supply systems. In this paper, a resistance reduction method is proposed for a novel low-resistance elbow with a guide vane. The reasonable form for inserting the guide vane is determined. The resistance reduction mechanism of the elbow is analyzed through the field synergy principle and the viscous dissipation principle. The local resistance coefficients of traditional and novel vaned elbows with different diameters and radii of curvature are compared. The resistance reduction effect of the elbow with a 60 degrees guide vane in this study is also compared with that of the elbow with a 90 degrees guide vane from Ito. The results indicate that the insertion of the optimal guide vane improves the synergy between the pressure gradient and the velocity vector downstream of the elbow and reduces the internal energy consumption caused by viscous dissipation. At different inlet Reynolds numbers, the effectiveness of the resistance reduction method is verified. The resistance reduction rate and average synergy angle no longer change when the inlet Reynolds number exceeds 2.5 x 105, and the resistance reduction rate can reach up to 20.1%. When the ratio of the curvature radii to the diameter is R/D = 1, the resistance reduction rate of the elbow with a 60 degrees guide vane is as high as 25.1%. This paper can provide a reference for research on the resistance reduction of local components of heating, cooling, and water supply pipelines.