196,080 research outputs found
Dependence of aggregate strength, structure, and light scattering properties on primary particle size under turbulent conditions in stirred tank.
No full textSizing Polydisperse Dispersions by Focused Beam Reflectance and Small Angle Static Light Scattering
No full text"Dependence of Initial Cluster Aggregation Kinetics on Shear Rate for Particles of Different Sizes Under Turbulence"
No full textInitial aggregation kinetics for three particle sizes and broad range of Péclet numbers were investigated under turbulent conditions in stirred tank. This allowed us to observe the transition from diffusion-controlled to purely shear-induced aggregation. The evolution of the root-mean-square radius of gyration, zero-angle intensity of scattered light, and obscuration was obtained by small-angle static light scattering. For a given particle sizethe measured evolution of all integral quantities obtained for various volume averageshear rates (G), scales with a dimensionless time, τexp = αexp × (G) × φ × t. The experimentally obtained aggregation efficiency αexp, follows the power law αexp = Pe-n, where Pe is the primary particle Péclet number. With increasing particle size a decrease in n is observed in accordance with theory and literature data. As previously predicted by population balance equation simulations three aggregationregimes were observed experimentally.</p
Dynamic response studies on aggregation and breakage dynamics of colloidal dispersions in stirred tanks
No full textAggregation and breakage of aggregates of fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tanks using small-angle static light scattering. It was found that the steady-state values of the root-mean-square radius of gyration are fully reversible upon changes of stirring speed as well as solid volume fraction. Steady-state values of the root-mean-square radius of gyration were decreasing with decreasing solid volume fraction as well as with increasing stirring speed. Moreover, it was found that the steady-state structure and shape of the aggregates is not influenced by the applied stirring speed
Effect of shear rate on aggregate size and morphology investigated under turbulent conditions in stirred tank
No full textAggregation and breakage of aggregates produced from fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tank. Detailed investigation of the initial kinetics showed that the collision efficiency, alpha, depends on the shear rate G according to alpha proportional to G(-b), with a power law exponent, b, equal to 0.18. After steady state was reached the dynamic response of the system on a change in stirring speed and solid volume fraction was investigated. It was found that the steady-state values of two measured moments of the cluster mass distribution (CMD) are fully reversible upon a change in stirring speed. This indicates that although the moments of CMD at steady-state depend on the applied shear rate, the aggregate structure is independent of the shear rate in the given range of stirring speeds. This was proved by independent measurement of the fractal dimension, d(f), using image analysis which provided a df equal to 2.62 +/- 0.18 independent of applied stirring speed. The critical aggregate size, below which breakage is negligible, determined by dilution experiments was consequently used to evaluate the aggregate cohesive force holding the aggregate together, which was found to be independent of the aggregate size and equal to 6.2 +/- 1.0 nN
"Role of Counterion Association in Colloidal Stability"
No full textA generalized model for colloidal stability has been validated against experimentally measured values of Fuchs stability ratio and critical coagulation concentration (ccc) for electrolytes with mono- or divalent cation, i.e., potassium chloride and magnesium chloride, respectively. Besides the classical DLVO theory, the generalized model accounts for the interplay between colloidal interactions and the association of cations with the particles surface charge groups. The model parameters are either obtained or estimated purely on the basis of independent information available in the literature. For the monovalent salt, the predictions agree well with literature experimental data, forecasting both the ccc values and stability ratios quantitatively. For the divalent salt the predictions for large values of the stability ratio tend to deviate from the experimental data produced in this work, but it is noted that the onset of stability, i.e., the ccc, and small stability ratios are correctly predicted. Moreover, a comparison of the above results with those neglecting the effect of counterion association with the particles surface charge groups indicates that the latter substantially overestimates stability ratios in the presence of high salt concentration in the case of the monovalent salt, and leads to unrealistic large values of the ccc for the divalent salt. Including the association of cations with the particles surface charge groups can explain the relatively low values of experimental ccc for divalent salts compared to the theoretical predictions by the classical DLVO theory neglecting ion association, which is a point of interest in industrial coagulation processes
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
- …
