scholarly journals The Influence of Internal Intermittency, Large Scale Inhomogeneity, and Impeller Type on Drop Size Distribution in Turbulent Liquid-Liquid Dispersions

Entropy ◽  
2019 ◽  
Vol 21 (4) ◽  
pp. 340 ◽  
Author(s):  
Wioletta Podgórska
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Drop Size ◽  
High Efficiency ◽  
High Viscosity ◽  
Drop Size Distribution ◽  
Dispersed Phase ◽  
Power Number ◽  
Scale Inhomogeneity ◽  
Impeller Type

The influence of the impeller type on drop size distribution (DSD) in turbulent liquid-liquid dispersion is considered in this paper. The effects of the application of two impellers, high power number, high shear impeller (six blade Rushton turbine, RT) and three blade low power number, and a high efficiency impeller (HE3) are compared. Large-scale and fine-scale inhomogeneity are taken into account. The flow field and the properties of the turbulence (energy dissipation rate and integral scale of turbulence) in the agitated vessel are determined using the k-ε model. The intermittency of turbulence is taken into account in droplet breakage and coalescence models by using multifractal formalism. The solution of the population balance equation for lean dispersions (when the only breakage takes place) with a dispersed phase of low viscosity (pure system or system containing surfactant), as well as high viscosity, show that at the same power input per unit mass HE3 impeller produces much smaller droplets. In the case of fast coalescence (low dispersed phase viscosity, no surfactant), the model predicts similar droplets generated by both impellers. In the case of a dispersed phase of high viscosity, when the mobility of the drop surface is reduced, HE3 produces slightly smaller droplets.

scholarly journals Statistics of Drop Size Distribution Parameters and Rain Rates for Stratiform and Convective Precipitation during the North Australian Wet Season

2013 ◽  
Vol 141 (9) ◽  
pp. 3222-3237 ◽  
Author(s):  
Guillaume Penide ◽  
Vickal V. Kumar ◽  
Alain Protat ◽  
Peter T. May
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Drop Size ◽  
Drop Size Distribution ◽  
The Other ◽  
Convective Precipitation ◽  
Trade Wind ◽  
High Concentration ◽  
Wet Season ◽  
Rain Rates

Abstract C-band polarimetric radar measurements spanning two wet seasons are used to study the effects of the large-scale environment on the statistical properties of stratiform and convective rainfall around Darwin, Australia. The rainfall physical properties presented herein are the reflectivity fields, daily rainfall accumulations and raining area, rain rates, and drop size distribution (DSD) parameters (median volume diameter and “normalized” intercept parameter). Each of these properties is then analyzed according to five different atmospheric regimes and further separated into stratiform or convective rain categories following a DSD-based approach. The regimes, objectively identified by radiosonde thermodynamic and wind measurements, represent typical wet-season atmospheric conditions: the active monsoon regime, the “break” periods, the “buildup” regime, the trade wind regime, and a mixture of inactive/break periods. The large-scale context is found to strongly modulate rainfall and cloud microphysical properties. For example, during the active monsoon regime, the daily rain accumulation is higher than in the other regimes, while this regime is associated with the lowest rain rates. Precipitation in this active monsoon regime is found to be widespread and mainly composed of small particles in high concentration compared to the other regimes. Vertical profiles of reflectivity and DSD parameters suggest that warm rain processes are dominant during this regime. In contrast, rainfall properties in the drier regimes (trade wind/buildup regimes) are mostly of continental origin, with rain rates higher than in the moister regimes. In these drier regimes, precipitation is mainly formed of large raindrops in relatively low concentration due to a larger contribution of the ice microphysical processes on the rainfall formation.

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