Concentrated pressure drop across sudden diameter contractions of oil-water flows in horizontal pipes: an experimental investigation

Two-phase flows of liquid (water) – gas (air, vapor, steam) throughout singularities have been widely investigated both by experimental and theoretical approaches. On the contrary, there are very few works dealing with liquid – liquid mixtures, such as water – light/heavy hydrocarbons, even though their industrial interest is not negligible. In particular, both experimental data and numerical models are available for oil-water flows almost only in horizontal straight pipes. To extend the knowledge in such a field, an experimental investigation was carried out about tap water and high viscosity oil (density 890 kg/m3, viscosity 0.838 Pa s at 20 °C, surface tension 0.035 N/m) two-phase flows within pipes including sudden area contractions. Flow pattern, pressure gradient and concentrated pressure drop were analyzed for two test sections, with a sudden contraction 50/40 mm i.d. and with a 50/30 mm i.d. respectively. Models and correlations for the prediction of the pressure variations were tested, both developed for oil-water and gas-water flows. No one gave good agreement with the experimental data, and particularly the gas-liquid ones heavily failed. Therefore, the need of deepening the experimental database appears of utmost importance also in order to formulate appropriated flow models.