Low-resistance optimization and secondary flow analysis of elbows via a combination of orthogonal experiment design and simple comparison design

Abstract

The resistance of local piping components in HVAC systems significantly contributes to building energy consumption. Therefore, this study proposes a method combining orthogonal experiment design (OED) and simple comparison design (SCD) to optimize the position and angle of the double guide vanes in the elbow, resulting in a low-resistance modified elbow with double guide vanes. The resistance performance and secondary flow intensity of the traditional and modified elbow with double guide vanes are analyzed by full-scale experiments and numerical simulations. The effectiveness of the modified elbow with double guide vanes in reducing resistance is verified for different inlet Reynolds numbers, nominal diameters, and curvature ratios. The results show that the modified elbow has a good resistance reduction effect, and the resistance reduction rate is 11.4%–29.4% when the Re number ranges from 0.1 × 105 to 8.0 × 105. Under different nominal diameters (DN25-DN200) and curvature ratios (0.8–2.0), the resistance reduction rate of the modified elbow was 0%–38.1%. For long elbows with a curvature ratio greater than 2.0, resistance reduction by inserting double guide vanes is not recommended. The insertion of double guide vanes can inhibit the development of secondary flow in the elbow, cutting the double-vortex core with high vortex intensity into a four-vortex core with low vortex intensity, thus decreasing the secondary flow intensity and mechanical energy consumption. This study provides new optimization methods and perspectives for the low-resistance and standardized design of piping components in HVAC systems.