Numerical investigations of liquid–liquid extraction through a coiled tube integrated with an extraction outlet

This study numerically investigates the extraction of two immiscible liquids through coiled tubes integrated with an extraction outlet. Assuming a fully mixed initial state, representing the worst-case scenario, the research explores optimal conditions for achieving pure extraction of each liquid through different outlets. Two laminar Reynolds numbers of 225 and 563, along with seven different outlet split ratios, were analyzed for horizontal-axis coiled tubes. The effects of geometrical parameters and flow conditions on extraction efficiency were examined. For an inlet amine volume fraction of 50%, the results indicate that optimal extraction occurs at a split ratio of 0.5, with enhanced performance at Re = 563 compared to Re = 225. Sharp-edged, constant-diameter extraction tubes outperformed rounded and nozzle-type configurations while reducing the extraction tube diameter diminished the efficiency. Furthermore, an extraction at a coil angle of 675° (2 turns minus 45°) provided better efficiency compared to 765° (2 turns plus 45°). It is therefore recommended to operate near Re = 563, utilize a straight extraction tube with the same diameter as the coiled tube, and employ a sharp-edged connection at a coil angle of 675°. The extraction split ratio should align with the inlet rate of the lighter phase.