Experimental investigation of air-water-oil flow characteristics and pressure loss across vertical-horizontal transitions with 90-degree elbows

Predicting pressure loss and flow regimes in complex air-water-oil three-phase flows through pipe directional changes, such as 90° elbows, poses a significant challenge for industrial pipeline systems. This study experimentally investigates these flows across a vertical-to-horizontal transition to characterise flow patterns and quantify pressure loss. The research novelty lies in analysing all three phases separately within a small-diameter (0.024 m) Perspex pipe, in contrast to prior work that often treats the liquid phases as a single entity. Experiments spanned air velocities of 0.03–16 m/s, water velocities of 0.03–0.3 m/s, and oil velocities of 0.09–0.6 m/s. Results identified specific vertical flow patterns (bubble-air, plug-air, foam-air and annular-air with dispersed water-in-oil) that transitioned to horizontal patterns, such as stratified-air bubble and dispersed-annular air. Pressure decreased substantially with increasing pipe height; for instance, in the bubble flow regime, pressure dropped from 52.85 kPa at L/D = 62 to 0.94 kPa at L/D = 304. Furthermore, pressure loss increased with higher fluid velocities. This work is critically important because it provides essential experimental data for optimising the design and operation of industrial piping in the petroleum and chemical sectors. This enables improved accuracy in predicting multiphase flow behaviour and pressure drops in intricate geometries, thereby enhancing system efficiency and integrity.