Polymer drag reduction in dispersed oil–water flow in tubes

Drag reduction by polymers is a critical issue, with several applications first reported more than 70 years ago. The number of related works is vast, but most are restricted to single-phase flow. The few available works treating two-phase flow use drag reducers only in the water phase. One goal of the present work is to study the role of polymer additives in both phases for a range of water fractions. We conduct the main tests by considering the pressure drop in a fully developed turbulent flow in a pipeline and fixing each phase flow rate. In our tests, the pressure drop depends on the water fraction, mixing viscosity, mean phase densities, polymer concentration, and molecular weight. It is worth mentioning that, in small concentrations, the water drops also work as a drag reducer. We conduct the tests to compare the role of polymers in single and two-phase flow, paying particular attention to mechanical polymer degradation. Our main conclusion is that drag reducers are effective only in the external phase. In our tests, the water drag reducer is effective for water fractions larger than 0.5, and the oil drag reducer for water fractions smaller than 0.5. When both phases contain additives, the pressure drops, relatively to the case in the absence of additives, for an entire range of water fractions.