Experimental investigation of single- and two-phase pressure drop in slender rectangular 180 degrees return bends

摘要

The pressure drop of single-phase water flows and two-phase air-water flows through slender 180 degrees return bends with rectangular cross-section are investigated. The commonly used approaches consider return bends with relatively small curvature ratios whereas in this work the curvature ratios are 20, 40 and 58. The rectangular cross-section has a hydraulic diameter around 3.9 mm and an aspect ratio of 1.067 (4 mm x 3.75 mm). The measurements for the pressure drop are compared with other correlations. From the results, a relation is found to approximate the effects of curvature on the pressure drop with the principle of equivalent lengths. This relationship is also the base of the second proposed correlation of this work, which gives reasonable pressure drop predictions for air-water flows through slender 180 degrees curved ducts. It has a maximum deviation below 35% for all considered values.