Predicting Droplet Size Distributions of Emulsions Produced in a Sonolator

Abstract

Producing emulsions continuously compared to in batch production has many benefits, such as increased speed and agility of production. A Sonolator, a device similar to a high-pressure homogenizer, is capable of this continuous production. In this paper, the size of droplets produced during emulsification has been investigated for various orifice pressure drops, dispersed phase viscosities, and orifice sizes. The phase fraction of the dispersed phase, up to 10% v/v, and the presence of a blade after the orifice were found not to affect the droplet size distribution (DSD). The mode droplet size decreased with increasing pressure drop and the DSDs were mostly bimodal, due to the formation of satellite droplets, meaning that d 3,2 is a poor benchmarking parameter. We propose a model capable of predicting the full DSD of the emulsion. This reveals key parameters for scale-up of production using Sonolators and can help to improve product quality and process efficiency.

Thermodynamic and Kinetic Pathways to Agitated and Spontaneous Emulsification

“…The pressure fluctuation-driven emulsification is the first step to the process, which is taken over by the viscous stress at the smallest scale of the turbulent eddies. The average droplet size is expected to lie between the Hinze and Kolmogorov scales, d K and d H , which has received ample supports in various studies. − …”

“…This scenario is valid if the entire system evolves quasistatically toward equilibrium, and when the free energy of dispersion compensates for the increase of interfacial free energy. In reality, emulsification occurs, largely, under nonequilibrium conditions assisted by the difference of the chemical potentials between the initial and final states. ,, While the chemical potentials are equilibrated, various diffusive, chaotic, and dissipative transports are induced, which lead to the formation of various kinetically stable morphologies. − When oil is dispersed in water, or vice versa, with a surfactant dissolved in one of the phases, emulsification occurs readily − with agitation even when the interfacial tension is positive. The issues of agitated and agitation-less emulsification are highly relevant to bilge water that is transferred to a central oily waste holding tank from the point of generation through sliding-shoe and cavity feed pumps .…”

“…The issues of agitated and agitation-less emulsification are highly relevant to bilge water that is transferred to a central oily waste holding tank from the point of generation through sliding-shoe and cavity feed pumps . As the bilge water is transferred, there are splashes into the tank and sloshing with ship motion that often lead to non-negligible agitation. − The oily water in the bilge also ages with time, where emulsification can proceed, seemingly, in the absence of any external agitation.…”

“…The literature is replete with excellent studies on the turbulence-induced emulsification, in which the Kolmogorov–Hinze models are the starting points in predicting the size of the droplets and its distribution. While the field is substantially enriched with these studies, − further research is warranted for various reasons. For example, we do not find convincing evidence with such a seemingly trivial issue as to whether the aqueous phases in the previous experiments were always free of dissolved air.…”