Dense Oil in Water Emulsions using Vortex-Based Hydrodynamic Cavitation: Effective Viscosity, Sauter Mean Diameter, and Droplet Size Distribution.

Abstract

Vortex-based hydrodynamic cavitation offers an effective platform for producing emulsions. In this work, we have investigated characteristics of dense oil in water emulsions with oil volume fractions up to 60% produced using a vortex-based cavitation device. Emulsions were prepared using rapeseed oil with oil volume fractions of 0.15, 0.3, 0.45, and 0.6. For each of these volume fractions, the pressure drop as a function of the flow rate of emulsions through the cavitation device was measured. These data were used for estimating the effective viscosity of the emulsions. The droplet size distribution of the emulsions was measured using the laser diffraction technique. The influence of the number of passes through the cavitation device on droplet size distributions and the Sauter mean diameter was quantified. It was found that the Sauter mean diameter (d32) decreases with an increase in the number of passes as n-0.2. The Sauter mean diameter was found to be almost independent of oil volume fraction (αo) up to a certain critical volume fraction (αoc). Beyond αoc, d32 was found to be linearly proportional to a further increase in oil volume fraction. As expected, the turbidity of the produced emulsions was found to be linearly proportional to the oil volume fraction. The slope of turbidity versus oil volume fraction can be used to estimate the Sauter mean diameter. A suitable correlation was developed to relate turbidity, volume fraction, and Sauter mean diameter. The droplet breakage efficiency of the vortex-based cavitation device for dense oil in water emulsions was quantified and reported. The breakage efficiency was found to increase linearly with an increase in oil volume fraction up to αoc and then plateau with a further increase in the oil volume fraction. The breakage efficiency was found to decrease with an increase in energy consumption per unit mass (E) as E-0.8. The presented results demonstrate the effectiveness of a vortex-based cavitation device for producing dense oil in water emulsions and will be useful for extending its applications to other dense emulsions.