Drop breakup in turbulent flow through an orifice
Pedro N. Azevedo1; J.H. Penuela1; M. S. Carvalho1
1 PUC-RIO
doi:10.20906/CPS/COB-2015-1375
Resumo
As the two-phase oil-water mixture flows through the producing wells, risers and valves, the disperse phase may break leading to stable emulsions. The size of the dispersed oil drops has a strong effect on the flow resistance and on the phase separation process. Most of the drop breakup occurs as the oil-water mixture flows in turbulent regime through valves and narrow passages. Despite the large volume of experimental work reported in the literature, the relationship between the drop size distribution downstream of an orifice and the flow conditions is not clearly understood. In this work, we study experimentally the drop breakup of an oil-water emulsion as it flows through an orifice. Two mineral oils of moderate viscosity were dispersed in two different continuous phases, tap water and a continuous phase formed by a mixture of substitute ocean water and the anionic surfactant STEOL® CS-330 (Stepan Company). The drop size distribution downstream of the flow restriction is measured as a function of the flow conditions, liquid properties and drop size distribution upstream of the orifice. Results show that, for each flow condition, there is a maximum stable drop diameter below which the drops do not break. Analysis of the data revealed that maximum stable drop sizes were in the inertial sub range, characterized exclusively by the energy dissipation rate per unit mass. Details of the breakup process was studied by visualizing the breakup of a single drop using a high-speed camera. The images show that drop breakup only occurs downstream of the restriction and takes place at a certain distance from the edge of the orifice. At this breakup length, the radial velocity gradient in the flow is large enough to overcome the resistance stresses (exerted by the droplet) and produce the rupture of the droplet. The visualization has also allowed the analysis of the relative influence of interfacial tension and dispersed phase viscosity.
Palavras-chave: Drop breakup; emulsions; visualization; turbulent flow