Experimental studies on the dual continuous flow pattern in oil-water flows

The dual continuous flow pattern (both phases retain their continuity at the top and bottom of the pipe while there is interdispersion), which occurs during the pipe flow of two immiscible liquid phases, was studied in detail, and pressure gradient, in situ volume fraction and phase distribution data were obtained. The experimental work was performed in a 38 mm diameter, horizontal, stainless steel test section, using water and oil (6 mPa s viscosity and 828 kg/m(3) density) as test fluids. The identification of the dual continuous flow pattern boundaries was achieved with the use of an impedance and a conductivity probe. Measurements were made for mixture velocities from 0.8 to 3 m/s and input oil volume fractions from 10% to 90%. Dual continuous flow appeared at intermediate mixture velocities between stratified and dispersed flows and resulted in pressure gradients less than those of single phase oil flow; the velocity ratio increased with increasing input oil fraction, and was above 1 at high oil fractions apart from the highest mixture velocities where it was reduced to values below 1. This behaviour was explained by the in situ phase distribution data and the shape of the oil-water interface. The standard two-fluid model was unable to predict the pressure gradient and hold-up during dual continuous flow. (C) 2004 Elsevier Ltd. All rights reserved.