Effective Viscosity for Dispersed Oil–Water Pipe Flow in Different Diameters

Abstract

Existing prediction models for the effective viscosity of emulsions are typically empirical relations tuned to experimental measurements. Experimental methods like the preparation of stirred oil–water mixtures for rheometers and the use of small-scale flow loops have been used to characterize emulsions. Nevertheless, the extrapolation of these small-scale results to large-scale real systems is still uncertain and deserves further attention. This work reports a study of the effect of the pipe diameter on the effective viscosity of water-in-oil emulsions. Pipe flow experiments were performed with water-in-oil surfactant stabilized emulsions in acrylic pipes with 16, 32, 60, and 90 mm ID. Salt water (3.5% w/v of NaCl, pH = 7.3) and the oils Exxsol D80 (µ = 1.8 mPa s) and Marcol 52 (µ = 10 mPa s) with 0.25% v/v of Span 80 (lipophilic surfactant, HLB = 4.3) were used in the experiments. Pressure drop and droplet sizes were measured for different water fractions and mixture velocities. The effective viscosities calculated from pressure drop results were similar in all pipes up to about 40% water cut. Above 40%, the difference in effective viscosity increases with water cut, being significantly higher for the larger diameters.