Effect of turbulence intensity and surface tension on the emulsification process and its stationary state—A numerical study

Abstract

We study turbulent emulsions and the emulsification process in homogeneous isotropic turbulence (HIT) using direct numerical simulations (DNS) in combination with the volume of fluid method (VOF). For generating a turbulent flow field, we employ a linear forcing approach augmented by a proportional‐integral‐derivative (PID) controller, which ensures a constant turbulent kinetic energy for two phase flow scenarios and accelerates the emulsification process. For the simulations, the density ratio of dispersed and carrier phases is chosen to be similar to that of oil and water (0.9), representing a typical application. We vary the turbulence intensity and the surface tension coefficient. Thus, we modulate those parameters that directly affect the Hinze scale, which is expected to be the most stable maximum droplet diameter in emulsions in HIT. The considered configurations can be characterized with Taylor Reynolds numbers in the range of 100–140 and Weber numbers, evaluated with the velocity fluctuations and the integral length scale, of 4–70. Using the 3‐D simulation results, we study the emulsification process as well as the emulsions at a statistically stationary state. For the latter, droplet size distributions are evaluated and compared. We observe a Hinze scale similarity of the size distributions considering a fixed integral length scale, that is, similar Hinze scales obtained at different turbulence intensities or for different fluid properties result in similar distributions.

Ultrasound-enhanced interfacial adsorption and inactivation of soy trypsin inhibitors

“…In addition, the TIs at hexane and VTO presented different reduction trends in interfacial tension with the increased time. Generally, the formation (i.e., break-up and coalescence) of emulsion droplets highly depends on the turbulence energy, interfacial energy and viscosity [43] , [44] , [45] . It has been reported that the break-up rate of droplets decreased from around 70 s −1 to<10 s −1 when the interfacial tension increased from 1 mN/m to 30 mN/m [45] .…”

Effect of the Density Ratio on Emulsions and Their Segregation: A Direct Numerical Simulation Study

“…They investigated the bubble formation mechanisms in breaking waves, as well as the correlation of bubble sizes and energy dissipation proposed by Garret et al [8]. However, the scaling laws of droplet distribution are not yet fully understood and require further discussion [9,10].…”

“…Dodd and Ferrante [18] showed the relationship between turbulent kinetic energy evolution and droplet deformation, breakup, and coalescence processes in decaying isotropic turbulence, for a range of different Weber numbers and density and viscosity ratios. Crealesi-Esposito et al [10] and Begemann et al [9] studied emulsions using the VoF method, which is also applied in this work. Crealesi-Esposito et al [10] varied the volume fractions, viscosity ratio, and surface tension.…”

Preface to the computational fluid dynamics for chemical and process engineering special issue section

“…While the previously mentioned studies are concerned with simulations at the apparatus‐scale, detailed numerical studies by Konstantinidis et al, [ 4 ] Raju et al, [ 5 ] Begemann et al, [ 6 ] and Vasquez Giuliano et al [ 7 ] focus on local phenomena and processes at the micro‐ to nano‐scale. Both Konstantinidis et al [ 4 ] and Raju et al [ 5 ] are motivated by wetting process simulations.…”

“…This is also discussed by Raju et al, [ 5 ] which provides a free and publicly available means for the verification of the Navier‐slip boundary condition using a transient start‐up flow solution with slip. In Begemann et al’s study, [ 6 ] the emulsification process in homogeneous isotropic turbulence is studied using a VOF method, disclosing the effects of turbulence intensity and surface tension. In order to study the response of shear‐activated nanotherapeutic particles in obstructed blood vessels, Vasquez Giuliano et al [ 7 ] have combined CFD and the discrete element method (DEM).…”