Two phase liquid-liquid stratified flow

In comparison to gas-liquid studies, the understanding on liquid-liquid two-phase flows is relatively inadequate. As is shown herein, gas-liquid results cannot readily be translated to liquid-liquid flow predictions. The concern of the present paper is the flow of two immiscible stratified layers. Utilizing a simple approach, based on 'adjustable definitions' for the hydraulic diameters of two layers, enables the analysis, under a common framework, of all possible flow situations of laminar-laminar, turbulent-turbulent or mixed flow regimes, for wide ranges of density and viscosity ratios. Basically, predictions of liquid-liquid systems require two parameters (φ-χ_s²), compared to a single parameter in gas-liquid flows. As is usually relevant in liquid-liquid systems, the two-phase pressure drop is discussed in terms of pressure drop reduction or power saving. Comparison with available experimental data is satisfactory, supporting the proposed simple approach as a reasonable predictive tool.