Core-annular flow in horizontal and slightly inclined pipes: Existence, pressure drops, and hold-up

An analysis of high viscosity oil/water flow in horizontal and slightly inclined pipe is presented. We propose experimental flow maps – in particular we focus on the core-annular flow pattern boundary – pressure drops, and oil hold-up measurements. Experimental data are used to validate some models present in literature. Since hold-up measurement in liquid–liquid systems is particularly challenging and, therefore, only few data are available in literature, they are analyzed and commented in detail. The slip ratio computed by hold-up data is also provided and analyzed.