Average drop size in a liquid-liquid phase mixing vessel.

Abstract

Whentwo immiscible liquids are agitated, a dispersion is formed in which continuous breakup and coalescence of drops occur, and a dynamicequilibrium is attained betweenbreakup and coalescence after a certain time. Effects of the volume fraction of dispersed phase, viscosity of liquid, impeller speed and impeller-to-vessel diameter ratio on the average drop size of a dispersion in a mixing vessel are discussed and correlative equations are proposed. It is also found that the dominant process in deciding average drop sizes in a mixing vessel changes from breakup to coalescence whenthe average energy dissipation rate or the volumetric fraction of dispersed phase is increased.The mixing of immiscible liquid is among the most important chemical or biological engineering operations. In nuclear fuel reprocessing, the performance of mixer-settlers should be analyzed from drop size distribution for optimizing uranium and plutonium extraction.A number of investigators have presented correlative equations that related drop sizes in the mixing vessel to mixing parameters and physical properties of the system. Whentwo immiscible liquids are agitated, a dispersion is formed in which breakup and coalescence of drops occur. After a certain time, a dynamic equilibrium is attained between breakup and coalescence in the mixing vessel. Drops are believed to be broken up by turbulent fluctuations of the ambient liquid in the neighbourhood of the drops. In a dilute dispersion, coalescence may be negligible and the equilibrium spectrum of drop size distribution will depend on the breakup process. The coalescence process may be dominant in a dense dispersion because the probability of collision of drops increases.Effects of the volume fraction of dispersed phase, viscosity of liquid, impeller speed and impeller diameter on the drop sizes in a mixing vessel are discussed in this report and it is found that the coalescence process becomes dominating at higher energy dissipation rate or at larger volume fraction of dispersed phase. Drop sizes estimated by use of the correlative equations obtained in this study are compared with reported values by various authors.

On-line monitoring of drop size distributions in agitated vessels. 1. Effects of temperature and impeller speed

“…In the 200-300 rpm step change, the system quickly attains ita new steady state in about 90 min. A similar behavior has been reported (Nishikawa et al, 1987) for a system of 1.5% wax in water. On the other hand, in the 300-200 rpm step change, the system reaches a new steady state in about 9 h. This is due to a slow coalescence rate of the drops, which requires a1 longer equilibration period.…”

Continuous phase viscosity influence on maximum diameters of poly(styrene-divinylbenzene) beads prepared by suspension polymerization

“…From the experimental results presented in the literature these viscosities have opposite effects on the d max 31. When μ d increases the d max increases,13, 32 but when μ c increases the d max decreases 14–17…”

“…However, it should be noted that the knowledge of d max leads to that of d̄ because it is well established that d̄ is directly proportional to d max 17–20: The constant k 3 depends on the definition of d̄ (Table I).…”

Hydrodynamics of gas-agitated liquid-liquid extraction columns

“…Nishikawa et al (22) measured the effects of the volume fraction of dispersed phase, viscosity of liquids, impeller speed and impeller-to-vessel diameter on the average drop size of a dispersion in a mixing vessel for the two-phase: water (continuous phase)-honey bees` wax (dispersed phase). Hatate et al (23) also measured the mean droplet size for several systems using two columns and correlated it as a function of the superficial gas velocity, interfacial tension, and column diameter.…”