Time evolution of the drop size distribution for liquid–liquid dispersion in an agitated tank (original) (raw)
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Drop-breakage in agitated liquid—liquid dispersions
Chemical Engineering Science, 1974
Experimental data from batch vessels on cumulative volumetric drop-size distributions at various times are shown to yield useful information on probabilities of droplet-breakup as a function of drop-size. Such information is sufficient for a priori prediction of drop-sizes in agitated dispersions in batch and continuous vessels. It may also be useful in predicting heat and/or mass transfer in liquid-liquid dispersions by accounting for the simultaneity of transport processes from individual drops and droplet breakage processes:
Drop breakage in liquid–liquid stirred dispersions: Modelling of single drop breakage
Chemical Engineering Science, 2007
A new experimental approach has been set up for the identification of reasonable break-up mechanisms in stirred dispersions and of a physically-based model for the daughter drop size distribution. In the experiments, breakage of a single organic droplet and the subsequent fragments formation are analyzed by image processing techniques. The experimental data are then fitted by means of a daughter drop size distribution function written in terms of a probability density function (pdf). The mathematical approach that matches the theoretical requirements and that provides the best fit of the experimental data is the pdf proposed by . This is a purely statistical model that does not contain any dependence on physical parameters, such as turbulence intensity and mother drop size. Based on the experimental results, an extension of the Diemer and Olson model is derived, in which dependence on the Weber number as well as on the mother drop diameter can be inserted.
Analysis of drop size distributions in lean liquid-liquid dispersions
AIChE Journal, 1980
Experimental measurements of transient drop size distributions in a stirred liquid-liquid dispersion (with low dispersed phase fraction) have been used concomitantly with population balance theory to recover the transition probability of droplet breakage, based on a similarity concept. The data remarkably uphold the proposed similarity hypothesis, and the estimated probability function displays the same qualitative trend as the model due to Narsimhan et al. (1979).
Drop break-up and coalescence in a stirred tank
It is shown in the paper that drop size distribution in liquid-liquid dispersions is affected by both the fine-scale and the large-scale inhomogeneity of turbulence. Fine-scale inhomogeneity is related to the phenomenon of local intermittency and described using a multifractal formalism. Largescale inhomogeneity is related to inhomogeneous distributions of the locally averaged properties of turbulence, including the rate of energy dissipation and the integral scale of turbulence. Large-scale distributions of the properties of turbulence in a stirred tank are considered with a network of wellmixed zones. CFD methods are used to compute the properties of turbulence in these zones. A model taking into account inhomogeneity of both types explains the effect of the system's scale on drop size; it predicts smaller maximum stable drop sizes than the classic Kolmogorov theory of turbulence. The model predictions agree well with experimental data.
A model for transitional breakage probability of droplets in agitated lean liquid-liquid dispersions
Chemical Engineering Science, 1979
A model for transItional breakage probabfity of droplets m astated lean bqmd-hqmd dlsperslons IS proposed based on the mechamsm of breakage of droplets due to theu osculations resultmg from relative velocity Ructuahons A umvcrsal translhonal breakage probabhty m terms of non-dunenslonahzed drop diameter IS denved for all dispersed phases whose density and viscosity are almost the same as that of contmuous phase The maxunum stable drop diameter d,, denved from the model, shows a dependence of N$6
Chemical Engineering Science, 1996
Transient breakage drop-size distributions have been experimentally measured using an image analysis technique. The transient distributions show self-similar behavior. The breakage rate and daughterdrop distribution functions have been determined using an inverse-problem approach which takes advantage of this self-similarity. The inverse-problem results show that the breakage rate is not a power law function of the drop size. The breakage rate is found to increase sharply with the drop size and the stirrer speed while decreasing sharply with increase in the interfacial tension. It is also found to decrease with increase in the dispersed phase viscosity, though the dependence on the viscosity is weaker than on the other variables. The daughter drop distribution was found to be relatively insensitive to the stirrer speed and interfacial tension, but was found to depend on the dispersed phase viscosity. As the drop viscosity increases, the breakage becomes more erosive in nature, leading to a broader size distribution of daughter drops. Generalized correlations for the breakage rate and daughter-drop distribution which account for the effect of physical properties and experimental conditions are presented. These relations will be very useful in predicting the drop-size distributions in stirred dispersions. Models for the breakage functions are compared with those determined in this study and the model predictions of the transient-size distributions are compared with the experimental data.
Industrial & Engineering Chemistry Research, 1989
T h e microscopic phenomena occurring in an agitated vessel are extremely complex. The exact mechanisms of coalescence and breakage in bubble and drop systems are generally not very well understood. Several attempts have been made in the literature to improve our understanding of these phenomena in multiparticle systems. In the present work, the most comprehensive models describing the coalescence and breakage processes in a styrene/water dispersion system are incorporated in a numerical algorithm to calculate the steady-state drop size distributions in a batch stirred vessel. A new breakage distribution function is introduced that considers droplet broken into two daughter and several satellite droplets. As a result, bimodal diameter density distributions are obtained. It is shown that the proposed model has the ability t o fit reasonably well a series of experimental data obtained for a low-coalescence system a t different impeller speeds, temperatures, and dispersed phase hold-up fractions.
Droplets size evolution of dispersion in a stirred tank
EPJ Web of Conferences
Dispersion of two immiscible liquids is commonly used in chemical industry as wall as in metallurgical industry e. g. extraction process. The governing property is droplet size distribution. The droplet sizes are given by the physical properties of both liquids and flow properties inside a stirred tank. The first investigation stage is focused on in-situ droplet size measurement using image analysis and optimizing of the evaluation method to achieve maximal result reproducibility. The obtained experimental results are compared with multiphase flow simulation based on Euler-Euler approach combined with PBM (Population Balance Modelling). The population balance model was, in that specific case, simplified with assumption of pure breakage of droplets.