On the steady‐state drop size distribution in stirred vessels. Part I: Effect of dispersed phase viscosity

Abstract

Previous studies on emulsification have used the maximum drop size (dmax) or Sauter mean diameter ( trued¯32) to investigate the effect of viscosity on the drop size distribution (DSD), however, these parameters fall short for highly polydispersed emulsions. In this investigation (Part I), the steady‐state DSD of dilute emulsions is studied using of silicon oils with viscosities varying across six orders of magnitude at different stirring speeds. Different emulsification regimes were identified; our modeling and analysis is centered on the intermediate viscosity range where interfacial cohesive stresses can be considered negligible and drop size increases with viscosity. The bimodal frequency distributions by volume were well described using two log‐normal density functions. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3293–3302, 2018

On the steady‐state drop size distribution in stirred vessels. Part II: Effect of continuous phase viscosity

“…For very high μ d , the droplet's viscous forces become the dominant cohesive force and the interfacial ones become negligible . As shown by Calabrese et al and by Padron, the mechanistic models become explicit functions for very large μ d .…”

“…Eight of the Fluid XX Silicon Oils (SiOil, dimethyl siloxane, Dow Corning, Michigan) used in Part I with nominal dynamic viscosity in the 10‑100,000 cSt range. and blends were emulsified for this investigation.…”

“…The relevant properties of the continuous phases are shown in Table . The ρ c were obtained using a pycnometer, and the μ c was obtained using the same methods used to determine the properties of the SiOils in Part I …”

“…Maaß et al reported that for 2 mm petroleum drops, ternary breakup was the most probable, however, they reported that a maximum of 97 drops per breakup event; for 0.50 mm drops they found that binary breakup was the most likely. In Carrillo De Hert and Rodgers, the increase in the amount of small daughter drops was attributed this breakup mechanism.…”

“…The former models consider that the interfacial forces are the only cohesive forces balancing the disruptive stresses. However, as the viscosity of the dispersed phase μ d increases, the viscous internal resistance becomes important . Dimensionless numbers have been proposed to relate the viscous forces to the inertial and the interfacial ones such as the Viscosity group Vi H (also known as Ohnesorge number) by Hinze (Vi H = μ d ( ρ d σd ) −1/2 ) and the one by Calabrese et al (Vi C = μ d NDσ −1 ( ρ c / ρ d ) 1/2 ).…”