Phase inversion in dispersed liquid–liquid flows

Abstract

Phase inversion and its effect on pressure gradient during the dispersed flow of two immiscible liquids have been studied for two pipe materials (steel and acrylic) and two pipe sizes (60 and 32 mm ID). Water and oil (796 kg m −3 density and 2.19 mm 2 s −1 viscosity) were used as test fluids while the appearance of phase inversion in the acrylic pipes was confirmed with the use of impedance ring probes. In the large pipes (steel and acrylic with 60 mm ID) it was found that the phase inversion point (oil volume fraction where inversion appears) depended on whether the inversion was from oil to water continuous mixture or from water to oil. The difference in the phase inversion points between the two dispersion initialisation conditions increased with increasing mixture velocity. No effect of initial conditions on the inversion point was found for the small acrylic pipe. Phase inversion was in all cases preceded by a large increase in pressure gradient, which was sharply reduced immediately after the new continuous phase was established. The pressure gradient peak was sharper and larger at high mixture velocities than at low ones and in the acrylic pipe compared to the steel one. The change in phase continuity lasted a few minutes and was accompanied by large fluctuations in pressure gradient and mixture impedance.