Floc Diameter Research Articles

Ageing of aluminium hydroxide flocs

The ageing processes of kaolinite suspensions flocculated with Al 2(SO 4) 3 under a variety of different but well-controlled flocculation conditions were studied by measuring their average diameter, diameter distribution, strength and electrophoretic mobility. Three periods could be distinguished in the ageing process. Initially shrinkage of the flocs is mainly due to cementation-aggregation. In the first 6–8 h, dependent on the flocculation conditions, the average diameter reduces from ⋍500 to ⋍220 μm. During the following 4 days a shrinkage to ⋍180 μm occurs, mainly due to condensation-polymerization and crystallization. In the third period, the average diameter increases because of Oswald ripening of the crystals. During each period the change of the diameter as a function of age can mathematically be described by: d f, i = d∞ + d′· t i + i− ω . With d ∞, d′ and ω constants dependent on the flocculation conditions. During ageing, the floc diameter distribution narrows. The shrinkage of the flocs during ageing is definitely not due to erosion of particles from the floc surface. The change of the electrophoretic mobility during ageing provides information on the thickness and homogeneity of the layer of insoluble hydroxides around the destabilized clay particles. The influence of a wide range of different flocculation process parameters on the floc ageing process is summarized, as is the influence of the ageing process on floc strength and floc density. The evolution of the effective floc density can be described by: P e| t=t i = a·d (3−K p) ƒ,0 d 3 ƒ,i . The constants K p and a are functions of the ratio quantity of suspended solids vs coagulant dose.

Magnetic Flocs Build up on a Single Magnetic Wire

Studies on magnetic flocs buildup on a single magnetic wire were described. Red tide plankton and kaolin were used as nonmagnetic granules, and magnetite was added to a kaolin-water slurry, with a PAC cohesive agent and reagents to adjust the pH. On either raising the magnetite content to above 150 mg/l, or raising the field to 5 kOe, bumpy formations on both sides of the floc were observed. Changes in floc diameter when other conditions are varied are also described.

Estuarine flocs: Their size, settling velocity and density

The size and settling velocity of flocs of suspended sediments from the Chesapeake Bay were measured in laboratory experiments and in the field. The curves between floc diameter and settling velocity showed a non‐Stoke's relationship that was best described by the following: settling velocity (cm/s) = 1.73 (floc diameter, cm)0.78. Furthermore, the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size. In addition to changing density, a cylinder shape was found to be the best shape factor.

Settling Velocity, Diameter, and Density for Flocs of Illite, Kaolinite, and Montmorillonite

ABSTRACT The relation between floc settling velocity and diameter was measured for illite, kaolinite and montmorillonite. The curves between floc diameter and settling velocity show a non-Stokes' relation that indicated the floc density decreased or drag properties increased as the floes increased in size.

Acoustic microscopy improves internal reliability of IC packaging : Thomas E. Adams. Semiconductor Int. 100 (February 1985)

The aggregation kinetics of the aqueous dispersion of allophane was measured by dynamic light scattering as functions of pH and ionic strength. The sample was purified from natural Kanuma soil (Tochigi, Japan). A notable feature is that the dispersion is composed of aggregated flocs of allophane particles. The experiments were performed adjusting the initial floc diameter by centrifugation. The aggregation was induced by charge neutralization or compression of the electrical double layers, by merely mixing the suspension with an electrolyte solution of controlled pH and ionic strength. After the initial mixing operation, the suspension was placed in a static condition and the temporal variation of the average hydrodynamic diameter was monitored in situ. In the initial stage, the diameter dramatically increased reflecting the aggregation induced by the hydrodynamic mixing. Due to the Brownian aggregation, this initial enhancement was followed by a moderate increase. Under the Brownian aggregation, the aggregation rates were found to take a certain limiting value denoting fast coagulation irrespective of charge neutralization or compression of the electric double layers. When the salt concentration is not sufficiently high, the rate of aggregation against pH gradually increases and approaches the fast-coagulation domain; however, the rate decreases rather rapidly as the pH increases. This behavior was interpreted considering pH-dependent charge distribution generated on the surface of allophane particles with peculiar morphology. This interpretation was supported by electrophoretic mobility data. In contrast with the Brownian aggregation, the rate of orthokinetic aggregation induced by charge neutralization was detected to be slightly faster than that induced by compression of the electric double layers.

Characteristics of Suspended Cohesive Sediment of the Severn Estuary, U.K.

Characteristics of suspended cohesive sediment from the benthic boundary layer of the Bristol Channel/Severn Estuary were examined at one location (51°27.66′N. 2°53.20′W). Samples were collected in vertical profiles over the bottom 2 m of the water column at times near to, and at low and high slack water periods on spring and neap tides. Primary particle size distributions obtained using a Coulter Counter (range 1.59–50 μm) and electron microscopy (range 0.1–20 μm) reveal bimodal (volume) frequency distributions with a lower mode fixed at 1.59 μm and a higher mode variable between 6 and 30 μm. When these data are converted to number frequency distributions, the higher mode effectively vanishes, while the lower is retained. Suspended sediment mineralogy, of dispersed samples, was determined by individual and multiple particle examination using analytical electron microscopy. Average suspended sediment composition was found to be illite 44%, quartz 23%, chlorite 19%, calcium carbonate 5%, kaolinite 4%, and organic carbon 3% (by weight). Floc diameters estimated from hindered settling experiments were ≈ 140 μm possessing a sedimentation velocity in the range 1.8–2.0 mm∙s−1, in good agreement with field observations of temporal changes in the vertical distribution of turbidity.Key words: suspended cohesive sediment, flocculation, Bristol Channel.

Floc breakage in agitated suspensions: Effect of agitation rate

A population balance equation that governs the floc size distribution in turbulent flow, incorporating both the splitting and erosion mechanisms of floc breakage has been presented in previous studies[6,7]. Experiments have been conducted in which transient floc size distributions of dilute suspensions of Kaolin-hydrous ferric-oxide flocs undergoing breakage in agitated batch system are obtained over turbulent microscale shear rates ranging from 60 to 400 sec −1. Floc size distributions over a range of floc diameters from about 1 to 100 μ m are measured by overlapping techniques, including computerized optical scanning of photographs and rapid electronic sizing of individual flocs using a light blockage transducer. The experimentally determined size distributions are then fit to those computed from the population balance equation, using constrained nonlinear least squares. The splitting frequency of parent flocs is found to vary as the 0.33 power of the parent floc volume and 0.71 power of the shear rate. The average number of daughter fragments produced upon splitting of individual flocs is found to be about 2.5. The mean and standard deviation of the daughter fragments produced upon splitting are found to be in fixed ratio to one another, independent of the parent floc size and shear rate. An appropriately nondimensionalized coefficient characterizing floc erosion has been found to be independent of shear rate.

Der Einfluß der Flockenbildung auf die Versorgung der Hefezellen mit Sauerstoff bei der Fermentation flüssiger Kohlenwasserstoffe

AbstractFloc formation, especially the influence of floe diameter variations on the total velocity of the process, was investigated in aerobic growth processes of yeast on the hydrocarbons of crude oil.The experimental results show that the diameter of the flocs is a function of the rheological properties of the fluids and the flow conditions.The floc diameter varies between 0,1 mm and a few millimeters. About 90% of the total yeast cells are situated in the interior of the flocs.Since oxygen must be transferred to all yeast cells their oxygen supply was studied.Thus, the yeast cells in the floc interior were not sufficiently supplied with oxygen, if the floc diameter reached a critical value.In such cases a decrease of the biomass formation rate was observed, although the dissolved oxygen concentration of the aquaeous fermentation medium was greater than zero. Therefore, aerobic microbial growth processes in multicomponent systems must be carried out without floc formation or under such conditions as cause very small floc diameters.

Physical characteristics of flocs—I. The floc density function and aluminium floc

Some characteristics of floc density were illuminated by experiments and model floc simulation by using clay-aluminium flocs. As an aluminium floc is a very fragile particle, the authors adopted an experimental method in which the settling velocity and diameter of a discrete floc were measured in a quiescent water column. Floc density was calculated by introducing the measured values and some constants such as water density and viscosity into a suitable settling velocity equation. In this study a modified Stokes equation was used. From the experimental results, the following conclusions were obtained. 1. (1) Floc density decreases as floc size increases, and the floc diameter and the floc effective density (buoyant density = floc density — water density) have a straight line relationship on a logarithmic paper. This line is characterized by two constants, K p and a, which show the slope of the line and the floc effective density of 1 cm diameter floc. The authors have designated this relationship as the floc density function. 2. (2) ALT ratio (aluminium ion concentration dosed/suspended particle concentration) greatly affects the clay-aluminium floc density. As ALT ratio decreases, the floc density at the fixed size increases. Other effects of coagulation condition upon floc density function were also discussed. 3. (3) The floc density function of coagulated colored water was studied. Iron, magnesium and calcium flocs with clay were also studied for reference purposes. 4. (4) The floc density function was verified by the model floc simulation. Model flocs were produced by computer and the floc density function was derived by substituting the number of the primary particles contained in a floc and the model floc diameter into a mass balance equation of a floc particle.

Physical characteristics of flocs—II. Strength of floc

Characteristic features of floc strength were examined by theoretical and experimental studies by using clay-aluminium flocs. From the studies, the following conclusions were obtained. 1. (1) Maximum floc diameter d max under an agitation intensity is evaluated by the following equations: ▪ where, ϵ 0: the effective rate of energy dissipation [erg cm −3·s], K p : the exponent of the floc density function [−], λ 0: micro scale of the isotropic turbulence [cm], d max: the maximum diameter of flocs [cm], K,K ∗ : constants. In practice, however, the latter equation is possibly used. 2. (2) From the above equation in viscous subrange, and K p -value of the floc density function evaluated in the previous paper, d max will be changed with the rate of energy dissipation ϵ o or the rate of the agitation blades rotation Nr as the following equation: ▪ 3. (3) Relative floc binding strength can be evaluated by the following equation: ▪ where, σ: the floc binding strength, a: coefficient of the floc density function, d: diameter under an agitation intensity, Suffixes 1 and 2 denote the characteristic values of flocs 1 and 2, respectively. 4. (4) After the theory and experimental studies, characteristic features of clay-aluminium flocs were evaluated.

Turbulent disruption of flocs in small particle size suspensions

AbstractIn the absence of turbulent fluctuations the main effect of a velocity gradient on the floc properties is a rearrangement of particles within the floc producing a more dense floc structure. When the suspension is sufficiently dilute that floc‐floc collisions are negligible, the limits on the floc diameter are (1 + α)5/3 < (Df/Dp) ⩽ (1 + α)2, where α is the ratio of the volume of fluid immobilized in the floc structure to volume of solids in the floc structure as determined from hindred‐settling measurements. These results set an upper limit on the floc size.Under turbulent flow conditions the principle mechanism leading to floc rupture is pressure differences on opposite sides of the floc which cause bulgy deformation and rupture. The breakup of the floc is resisted by the yield stress τy and is promoted by an increase in the energy dissipation per unit mass of fluid ϵ. Because the energy dissipation per unit mass is at a maximum near the pipe wall, the floc size is at a minimum in this same region.By application of the concepts of local isotropy, the floc size is found to be proportional to (τy9/ϵ5)1/2once the turbulent intensity is sufficient to overcome the yield stress. In the wall region the floc diameter is proportional to (du/dr)3 (τy9/ϵ8)1/2.