Experiments on geometric effects of 90-degree vertical-upward elbow in air water two-phase flow

This study investigates the geometric effects of a 90-degree vertical-upward elbow on local two-phase flow-parameters in an air-water system, and develops an experimental database for interfacial area transport modeling. The experimental facility is constructed from 5.08 cm inner diameter acrylic pipes and includes vertical and horizontal sections interconnected by a 90-degree vertical glass elbow. The elbow has a radius of curvature of 15.24 cm and is installed at L/D = 63 from the inlet. A four-sensor conductivity probe is used to measure time-averaged local two-phase flow parameters including: void fraction, bubble velocity, interfacial area concentration, and bubble frequency at ten axial locations along the test section. It is observed that the bubbles moving through the vertical-upward elbow are entrained by the secondary flow leading to a bimodal distribution in bubbly flow conditions. For the flow conditions investigated within the study, this bimodal distribution occurs regardless of the bubble distribution upstream of the elbow. It is found that the change in bubble distribution downstream of the elbow is strongly correlated to the dissipation of the elbow effects. Furthermore, the dissipation characteristics as well as the length of dissipation region for the vertical-upward elbow are found to be a strong function of the liquid-phase flow rate.