Influence of cycles of high and low turbulent shear on the growth rate and equilibrium size of mud flocs

Keyvani, Ali; Strom, Kyle

doi:10.1016/j.margeo.2014.04.010

Cited by 64 publications

(79 citation statements)

References 82 publications

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“…This behavior of the variation of the median size with respect to time describes the flocculation process of type I, which includes three phases: fast floc growth, slow floc growth and a steady state, as already introduced in Section 1 of this paper. A similar method for classifying these phases has been used by Keyvani and Strom who studied the influence of cycles of high and low turbulent shear on the growth processes of mud flocs [19]. , respectively).…”

Section: G=14s -1mentioning

confidence: 99%

“…In the first trend, the median size distribution of the flocs rapidly increases with time at the beginning of flocculation development and then continually slows down until a steady state is approached [7][8][9][10][11][12][13][14][15][16][17][18][19]. This type of size-time profile is henceforth referred to as type I.…”

Section: Introductionmentioning

confidence: 99%

“…This type of size-time profile is henceforth referred to as type I. However, the profile is referred to as type II when the median size initially increases to a maximum value with time and then decreases again before reaching a steady state [9,11,[19][20][21][22][23][24]. This peak in the size-time curve during the aggregation process potentially occurs as a result of breakups and/or restructurings (breakages and re-aggregations) of the flocs according to recent studies conducted by Bubakova et al and Selomulya et al [9,22].…”

Section: Introductionmentioning

confidence: 99%

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Fractal Dimension of Cohesive Sediment Flocs at Steady State under Seven Shear Flow Conditions

Zhu

Wang

et al. 2015

Water

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Abstract:The morphological properties of kaolin flocs were investigated in a Couette-flow experiment at the steady state under seven shear flow conditions (shear rates of 5.36, 9.17, 14, 24, 31, 41 and 53 s −1 ). These properties include a one-dimensional (1-D) fractal dimension (D1), a two-dimensional (2-D) fractal dimension (D2), a perimeter-based fractal dimension (Dpf) and an aspect ratio (AR). They were calculated based on the projected area (A), equivalent size, perimeter (P) and length (L) of the major axis of the floc determined through sample observation and an image analysis system. The parameter D2, which characterizes the relationship between the projected area and the length of the major axis using a power function, , decreased as the shear rate increased almost linearly. The parameter AR, which is the ratio of the length of the major axis and equivalent diameter, decreased from 1.56, 1.59, 1.53 and 1.51 in the low shear rate group to 1.43, 1.47 and 1.48 in the high shear rate group. These changes in Dpf and AR show that the flocs become less convoluted and more symmetrical and that their boundaries become smoother and more regular in the high shear rate group than in the low shear rate group due to breakage and possible restructuring processes. To assess the effects of electrolyte and sediment concentration, 0.1 mol/L calcium chloride (CaCl2) and initial sediment concentration from 7.87 × 10 were used in this preliminary study. The addition of electrolyte and increasing sediment concentration could produce more symmetrical flocs with less convoluted and simpler boundaries. In addition, some new information on the temporal variation of the median size of the flocs during the flocculation process is presented.

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Section: G=14s -1mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fractal Dimension of Cohesive Sediment Flocs at Steady State under Seven Shear Flow Conditions

Zhu

Wang

et al. 2015

Water

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“…3) [22][23][24]. The first three images correspond to flocs produced by sand, fly ash, coal and PAM respectively and they were examined by optical microscopy.…”

Section: Morphological Analysismentioning

confidence: 99%

“…These particles are the building blocks of clusters which gather and flocculate with PAM to produce flocs. [22]. To better understand the effect of PAM, a clear and unambiguous SEM (scanning electron microscope) image was presented in Fig.…”

Section: Morphological Analysismentioning

confidence: 99%

Predicting the Floc Characteristics and Settling Velocity of Flocs under Variable Dosage of Polyacrylamide

Shi¹,

Zhang²,

Pei³

et al. 2017

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Abstract. In this study, floc characteristics such as fractal dimension and settling velocity were investigated through a flocculantion process with a polyacrylamide (PAM) flocculant over a range of suspended particle concentrations, suspension type and flocculant dosage. The floc's structure and morphology were characterized by optical microscopy and scanning electron microscopy (SEM) methods. Floc settling velocity was measured in a settling column in a laboratory. The results showed that, the surface fractal dimension ranged from 1.044 to 1.415, which quantitatively confirmed the round and layered structure of flocs observed in SEM analyses. The PAM flocculant was proved to be more effective in flocculantion process, increasing the settling velocity. Therefore, an appropriate PAM dosage is an excellent candidate as efficient flocculant. A possible flocculantion mechanism for PAM was further analyzed. For alkaline or neutral environments, adsorption and bridging effects are dominant while charge neutralization is favored in acidic conditions.

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Seasonal variation in concentration, size, and settling velocity of muddy marine flocs in the benthic boundary layer

Fettweis

Baeye

2015

JGR Oceans

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Suspended Particulate Matter (SPM) concentration profiles of the lowest 2 m of the water column and particle size distribution at 2 m above the bed were measured in a coastal turbidity maximum area (southern North Sea) during more than 700 days between 2006 and 2013. The long-term data series of SPM concentration, floc size, and settling velocity have been ensemble averaged according to tidal range, alongshore residual flow direction, and season, in order to investigate the seasonal SPM dynamics and its relation with physical and biological processes. The data show that the SPM is more concentrated in the near-bed layer in summer, whereas in winter, the SPM is better mixed throughout the water column. The decrease of the SPM concentration in the water column during summer is compensated by a higher nearbed concentration indicating that a significant part of the SPM remains in the area during summer rather than being advected out of it. The opposite seasonality between near-bed layer and water column has to our knowledge not yet been presented in literature. Physical effects such as wave heights, wind climate, or storms have a weak correlation with the observed seasonality. The argument to favor microbial activity as main driver of the seasonality lies in the observed variations in floc size and settling velocity. On average, the flocs are larger and thus settling velocities higher in summer than winter.

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Influence of cycles of high and low turbulent shear on the growth rate and equilibrium size of mud flocs

Cited by 64 publications

References 82 publications

Fractal Dimension of Cohesive Sediment Flocs at Steady State under Seven Shear Flow Conditions

Fractal Dimension of Cohesive Sediment Flocs at Steady State under Seven Shear Flow Conditions

Predicting the Floc Characteristics and Settling Velocity of Flocs under Variable Dosage of Polyacrylamide

Seasonal variation in concentration, size, and settling velocity of muddy marine flocs in the benthic boundary layer

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