Liquid-liquid Dispersion in Batch and In-line Rotor-Stator Mixers

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This two-part dissertation investigates the behavior of batch and in-line rotor-stator mixers separately. In the first study, water was dispersed into viscous oil using a batch Silverson L4R rotor-stator mixer. The flow regime was determined by reference to published Power number data and by qualitative differences in drop size data. Drop breakup in laminar flow was analyzed by comparison to published single drop breakup experiments in idealized flow fields. The breakup mechanism in laminar flow was similar to that for simple shear flow and equal to about twice the nominal shear rate in the rotor-stator gap. Drop breakup in turbulent flow followed a mechanistic correlation for mean drop size for drops less than the Kolmogorov microscale, but still large enough that both inertial and viscous effects were manifest. Surfactants decreased drop size with Marangoni effects observed near the CMC for laminar, but not for turbulent flow. Below phase fractions of 0.05, d32 increased in a log-linear fashion with phase fraction for all conditions tested including: laminar and turbulent flow, presence of surfactant, and hydrophobically treated high-shear surfaces. The significant effect of phase fraction was caused by the flow structure being locally laminar near the drops, and was permitted by sufficiently low fluid viscosities which promoted film drainage. Above phase fractions of 0.1, drop sizes plateaued. This was attributed to decreasing coalescence rate and efficiency, along with increasing breakup. In the second study, the power consumption of an IKA 2000/4 in-line pilot scale rotor-stator mixer was measured with a purpose-built torque meter. The power spent by the mixer on pumping was insignificant compared to viscous dissipation. A constant power number was obtained for turbulent flow using constant power per stage with an empirically determined effective diameter for each generator type. For conditions where mean drop size was close to equilibrium, as determined by flowrate independence, previously reported mean drop size data were calculated using the well-known inertial subrange scaling law along with the power draw measurements of the present study. The maximum local energy dissipation rate was found to be nine times the average energy dissipation rate