Investigation of churn/annular and pseudo-slug flow characteristics before and after pipe elbows

Annular flow is one of the most observed flow patterns in oil and gas production systems, thus understanding annular flow characteristics is of great importance. When gas flow velocity is low, depending on the rate of liquid, annular flow transitions to slug flow and an annular/pseudo-slug flow pattern is developed. The aim of the present study is to examine the annular/pseudo-slug flow characteristics such as void fraction using a state-of-the-art experimental approach before and after an elbow. Wire Mesh Sensor (WMS) has been used to determine the void fraction distributions in an upward vertical orientation before a 3-inch elbow and in a horizontal orientation after the elbow for different flow conditions. In lower gas velocities and higher liquid velocities and viscosities, churn-annular transition and pseudo-slug flow patterns were observed for vertical (before bend) and horizontal sections (after bend), respectively. On the other hand, increasing the gas velocity and decreasing the liquid velocity and viscosity cause the flow structure to shift toward the annular and wavy stratified patterns in vertical and horizontal orientations, respectively.