Lattice Boltzmann simulations of water-in-oil (W/O) type emulsions of moderate viscosity ratio (≃1/3) and with oil soluble amphiphilic surfactant were used to study the droplet size distribution in forced, steady, homogeneous turbulence, at a water volume fraction of 20%. The viscous stresses internal to the droplets were comparable to the interfacial stress (interfacial tension), and the droplet size distribution (DSD) equilibrated near the Kolmogorov scale with droplet populations in both the viscous and inertial subranges. These results were consistent with known breakup criteria for W/O and oil-in-water emulsions, showing that the maximum stable droplet diameter is proportional to the Kolmogorov scale when viscous stresses are important (in contrast to the inviscid Hinze-limit where energy loss by viscous deformation in the droplet is negligible). The droplet size distribution in the inertial subrange scaled with the known power law ~d(-10/3), as a consequence of breakup by turbulent stress fluctuations external to the droplets. When the turbulent kinetic energy was sufficiently large (with interfacial Péclet numbers above unity), we found that turbulence driven redistribution of surfactant on the interface inhibited the Marangoni effect that is otherwise induced by film draining during coalescence in more quiescent flow. The coalescence rates were therefore not sensitive to varying surfactant activity in the range we considered, and for the given turbulent kinetic energies. Furthermore, internal viscous stresses strongly influenced the breakup rates. These two effects resulted in a DSD that was insensitive to varying surfactant activity.

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Droplets in oil-water dispersions are measured using two different measurement techniques. Both 'focused beam reflectance measurements' (FBRM) and 'particle video microscopy' (PVM), are applied simultaneously in order to obtain direct comparison. A real time chord length distribution (CLD) is obtained from the FBRM. The picture series by the PVM are post-processed to obtain droplet size distributions (DSD). By measuring particle samples, it was shown that PVM is able to detect the correct size distribution.Using the PVM images, the uncertainty of the CLD was quantified. Two empirical approaches to convert the CLD to the correct DSD are documented. Downloaded by [University of Sherbrooke] at 12:09 12 April 2015 2

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The study demonstrates how a disturbance of the flow can affect the pressure gradient and further needs a considerable development length to recover. This is of importance for experimental studies as well as industrial applications. Oil-water experiments were conducted in the Well Flow Loop at the Institute for Energy Technology, Norway. Three different mineral oils (120 mPa*s, 60 mPa*s and 35 mPa*s) and tap water were used. Input water fractions from 0 to 100% and mixture velocities up to 1.1 m/s were tested. A static mixer was installed at the test section inlet to introduce mixing. Comparison with non-premixed data showed that onset of dispersion shifts towards lower mixture velocities when the inlet disturbs the flow. This will also have an impact on the pressure gradient. At low mixture velocities when the flow was semi-dispersed, the influence seems to be most serious. Formation of a dense packed droplet layer is assumed to be a major reason for an increasing pressure gradient. Comparing pressure gradient measurements along the pipe it was found that the development length of the flow was still not reached 200 diameters downstream of the inlet mixer.