Floc size distribution and settling velocities are crucial parameters for characterising cohesive sediments, as they influence how these sediments behave in various environmental settings. The accurate measurement of these properties is essential, with different methods available depending on the scope of the study. For long-term monitoring, in situ techniques based on laser diffraction are commonly used, while video microscopy techniques are preferred for shorter studies due to their ability to provide detailed information on individual particles. This study compares two high-magnification digital video camera setups, LabSFLOC-2 and FLOCCAM, to investigate the impact of particle concentration on settling velocity in flocculated sediments. Flocculated clay was introduced into settling columns, where both the size and settling velocities of the flocs were measured. The results obtained from both setups are in line with each other, even though the FLOCCAM was slightly more efficient at capturing images of small particles (of size less than 50 microns) and LabsFLOC-2 was better at detecting large size fraction particles (having a low contrast due to the presence of organic matter). Floc size and settling velocity measurements from both setups however exhibit mostly similar trends as a function of clay concentration and the same order of magnitudes for the recorded settling velocities.@en

The insights gained from deep-sea mining (DSM) research regarding sediment dynamics can be utilized to better predict turbidity plumes in shallow marine environments. Small-scale lab experiments can replicate deep-sea conditions effectively, offering an ideal model system to study turbidity currents, given the reduced hydrodynamics and low biota present in the deep sea. DSM operations involve the deployment of a Polymetallic Nodule Mining Tool (PNMT) that collects ore and discharges excess water and sediments. Organic matter, bound to mineral clay as floes, is a key driver of sediment transport in the deep sea. Understanding the dispersal and settling patterns of sediments, and the likelihood of flocculation occurring in DSM activities, can be generalized and applied to turbid flows in shallow water areas. Laboratory experiments demonstrate that the interaction between organic matter, mineral clay, and floes within turbidity currents, results in the reduction of their dispersion. Alongside this, factors like shear rate and sediment concentration significantly influence both floe growth, size and settling velocities. Combining these results with real-time data on sediment concentration, particle size distribution, turbidity, and flow dynamics can be helpful to make dredging decisions, reduce the environmental disruption, and guide dredging equipment selection. By understanding the factors that influence sediment flocculation, deposition, and resuspension, we can design engineered solutions to mitigate the impact of turbidity current. @en

Deep-sea mining Industry and academia are presently investigating the potential of deep-seamining for valuable resources such as poly-metallic nodules. Nevertheless, the process of manoeuvring, excavating, and processing these resources poses a threat to the deep-sea environment through the generation of plumes of suspended fine-grained solids, which have the potential to damage benthic fauna by smothering or burying them. Assessing the impact of plumes requires an understanding of how far they disperse through bottomcurrents and how their suspended loads change over time. The affected area may be overestimated by current numerical simulations as they neglect the crucial process of flocculation, whereby fine particles aggregate into larger and faster-sinking clumps. The effect of flocculation on plume dispersion is still not well comprehended, engendering ambiguity in monitoring techniques dependent on optronic and acoustic sensors that are sensitive to particle size but do not take into account flocculation. To tackle these concerns, it is essential to undertake research that centres on studying flocculation characteristics in marine sediments. This includes carrying out controlled laboratory experiments to gain a better understanding of the critical conditions for flocculation. Additionally, it involves scaling up these experiments to replicate real-world plume dispersion and devising precise measuring methods for flocculated particle suspensions. This thesis focuses only on benthic sediment plumes...@en

Turbidity flows are known to be affected by the density difference between sediment plumes and the surrounding water. However, besides density, other factors could lead to changes in flow propagation. Such a factor is the presence of suspended organic matter. Recently, it was found that flocculation does occur within plumes upon release of a sediment/organic matter mixture in a lock exchange flume. In the present study, mineral sediment (illite clay) was released into the outflow compartment containing water and synthetic organic matter (polyacrylamide flocculant). Even though the density of water was barely affected by the presence of flocculant, flow head velocity was observed to be larger in the presence of flocculant than without. Samples taken at different positions in the flume indicated that flocs were created during the small current propagation time (about 30–60 s) and that their sizes were larger with higher flocculant dosage. The size of flocs depended on their positions in the flow: flocs sampled in the body part of the flow were larger than the ones sampled at the bottom. All these properties are discussed as a function of sediment–flocculant interactions.@en

This article discusses whether or to what extent flocculation plays a role in the saline deep-sea environment and whether sediment plumes generated by deep-sea mining activities are affected by the process of flocculation. The results of our laboratory study demonstrate that deep sea mineral clay with a median floc size of 20 μm can flocculate quickly within 2.5 min of mixing to form flocs with a median floc size of about 50–150 μm and outliers as large as 500 μm in size due to the presence of natural organic matter. At high shear (turbulent mixing), a threshold of about 125 s−1 was found above which, organic matter can successfully bind to clay. Above 125 s−1, the steady-state floc size is also found to increase linearly with shear. In low energetic conditions (when flocs experience mainly differential settling), the median floc sizes are found to be 2 or 3 times larger than at turbulent mixing. As expected, the rate of flocculation is greater at higher clay concentrations. At long mixing times, the median floc size is found to decrease due to the breaking/reconformation of flocs. Experiments performed to study the ageing of flocs at rest demonstrated that a dynamic process was ongoing between the organic matter and the clay. It is hypothesized that the organic matter present has amphiphilic properties. Over time, the organic matter would rearrange itself such as to maximize its contact area with the mineral clay, resulting in two effects, depending on the structure of the flocs. In the case of flocs formed at high shear, it led to a rupture of flocs. A slow agitation of settled flocs, having previously experienced low shear conditions, on the other hand, led to aggregation. Overall, the results found in the present article show that flocculation likely plays a significant role in deep-sea areas.@en

In this work a high-magnification digital video camera in combination with a settling column is used to study in a first part the influence of the amount of flocs transferred into the settling column on their settling velocity. In a second part, the setup was used to study the properties of flocs prepared at different clay concentrations but at same flocculant to clay ratio (2.5mgg−1). Illite clay was used and flocculated in a 1 L jar with an anionic polyacrylamide (flocculant). Results show that the average settling velocity of flocs is a function of the amount of transferred flocs. It was also found that floc size and settling velocity depend on clay concentration. This is attributed to the fast aggregation happening in the jar when flocculant and clay are mixed: at higher clay concentrations, larger flocs are created in the first minutes of the experiment, with low densities that prevent them from settling to the bottom of the jar.@en

Recent research highlights the abundance of floccule (flocs) in rivers, formed by aggregation of clay particles with organic matter. These flocs affect the transport and the eventual fate of clay. Flocs exhibit distinct behaviour from the unflocculated sedimentary counterparts: they can deform and break, and have higher settling velocities, which may in turn cause flocs to deposit and possibly interact with the riverbed. Here, we conducted systematic experiments in a laboratory flume to identify the mechanisms by which flocs and bedforms interact. Flocs showed a saltating (bouncing) behaviour, and were incorporated in the sediment bed as single flocs, clusters, or strings, via deposition and burial in the lee of a dune. Dune geometry was negligibly impacted by the presence of flocs. In natural systems, the burial of flocculated clay particles can affect contaminant spreading, aquatic ecology, the interpretation of deposition patterns, and clay transport.

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This study explores the effect of silver nanoparticles on heat transfer and flow behavior within the context of the Ellis fluid model. It specifically considers electroosmotic forces in a nonuniform divergent channel with compliant walls. The analysis involves studying thermal transport in silver-blood nanofluid flow, using MATHEMATICA 13.2 software to obtain exact solutions for velocity and temperature distribution. Findings reveal that certain parameters, such as wall damping and wall elastic properties, increase skin friction, while compliant wall parameters generally reduce flow velocity. Additionally, wall rigidity and tension parameters lead to larger trapped boluses. Notably, a 1% concentration of nanoparticles enhances heat transfer by up to 13.75%, offering control over heat transfer rates. This research introduces a novel perspective by examining compliant wall impacts on heat transfer analysis in the context of electroosmotic flow within the Ellis fluid model, incorporating silver nanoparticles with potential therapeutic applications due to their antibacterial properties.

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Problem statement: The study offers theoretical formulations for high-viscosity particulate flows in inclined reservoirs, taking into account the presence of homogeneous spheroidal particles of various types to produce discrete two-phase suspensions. Purpose: The primary objective of this analytical and comparative study is to identify the most dependable nanoparticles among hafnium and crystal metals that are suspended in an Eyring–Powell fluid through an inclined channel while being subjected to external magnetic and gravitational forces. Solution methodology: The flow dynamics of multiphase flows are formulated utilizing the stress tensor of the base fluid. The regular perturbation method (RPM) is employed to attain a more closed-form solution. The perturbation method is frequently employed in engineering problems to obtain an approximated solution, even when demonstrating the convergence of the solution is challenging. The rough solution is also validated through a thorough parametric analysis that shows the role of relevant parameters that contribute to the multiphase flow. Results: A concise parametric study is carried out against some of the most pertinent parameters and reveals that additional particles have promising effects on the momentum of each multiphase flow, whereas Eyring–Powell multiphase suspensions lessen in momentum due to strong internal viscous forces. The velocity of fluid and particle phases diminish with Hartmann number M and Froude number Fr. The second-order material constant B and concentration of nanoparticles C boost the motion of the fluid. The velocities of the particulate phase are quicker than the fluid phase. The hafnium particle is more reliable than crystal particles. Solution benchmark: Numerical and graphical findings have also been compared with the existing literature for the limiting case and found to be fully in agreement. Applications: This study’s findings provide a wider understanding of subterranean flows, specifically within the petroleum sector, with a focus on multiphase flows. Originality: The current study represents the authors’ original work and has not been previously submitted or published elsewhere.@en

In the present article two flocculation models, given in Chassagne (2021) (LG model) and Winterwerp (1998) (S model) are compared. Both models give the time evolution dL/dt where L is the size of a particle undergoing flocculation, and t is the time. The LG model is based on logistic growth theory, whereas the S model is based on the theory originally derived by Smoluchowski. Both models have the advantage of easy implementation in, for instance, large-scale sediment transport numerical models. However, it is found that they do not obey the same kinetics. A series of laboratory experiments is presented where the flocculation of a mineral clay by polyelectrolyte is studied as a function of clay concentration and shear rate. From modelling these experiments, it is found that the LG model reproduces the time dependence of the floc sizes found experimentally, whereas the S model does not. It is shown that the LG model can be used to model the data over the whole range of clay concentration and shear investigated. Based on the study presented in this article, it was found that the average floc growth in time for the clay type and conditions applied in the experiments could be modelled by: dL/dt=40×10−4G0.75×[exp(−2×10−4G0.75t)]/[1+20exp(−2×10−4G0.75t)]L.@en

Flocculation between inorganic sediment, salt ions and microscopic organic
matter present in the marine environment might play an important role in the
dynamics of turbidity currents. The ability to predict, understand, and potentially
leverage the effect of flocculation on turbidity currents will help to minimize the
impact of human interventions such as dredging, trenching, and deep-sea
mining. To better characterize the effect of flocculation on the benthic turbidity
currents generated by these activities, a series of laboratory experiments were
performed. Turbidity currents were created by means of lock exchange
experiments. The present work focuses on the flocculation of clays that are
representative for abyssal regions where deep-sea mining is performed, but
most of the conclusions of this work are generic and can be applied to other
types of benthic flows, occuring in harbours and channels. The effect of salt and
organic material as flocculant agent was investigated. Various concentrations of
clay and organic flocculant were tested. Video analysis was used to determine
the head velocity of the plume. Samples at different run-out lengths were
collected at the end of the lock exchange experiments for particle size and
settling velocity measurements. The velocities of the turbidity currents in fresh
and saline water (when no organic matter was present) were found to be similar,
which was expected considering the timescales of salt-induced flocculation
(about 30 min or more compared to the duration of lock exchange
experiment <60 s). It was however demonstrated that, in presence of
organic matter, flocculation occurred during the short time (30–60 s) of the
experiment, leading to a reduced current propagation and a significant change
in floc sizes (from 20 to 1,000 μm) and settling velocities (from 1 to 60mms−1).
Salt ions contributed to flocculation in the sense that flocculation with organic
matter was improved in the presence of salt.@en

Turbidity currents are generated as a result of various processes such as dredging and deep-sea mining. In this work, we generate a turbidity current in a lock exchange setup [1] by using 100 g/l illite, as shown in figure 1. Two different flocculant dosages (0.25 mg/g & 0.75 mg/g of clay) were used with this illite. The material was mixed in the mixing section of the lock exchange before the lock gate was opened. Experiments were done both in fresh and salt water. The samples were collected after the end of the experiment, and their rheological properties were measured using a HAAKE MARS I rheometer (Thermo Scientific, Germany). Rheological studies were carried out using Couette geometry with a gap of 1mm. The sample was gently stirred before rheological measurements. Higher yield stress values were observed in freshwater experiments compared to saltwater experiments, which can be attributed to a larger floc size in freshwater. In addition, the structural recovery of the flocs was also found to be higher in freshwater than in salt water.@en

For green energy transition, the industry seeks alternative resources for nickel and cobalt, the main ingredients for energy storage devices and other applications. Polymetallic nodules lying at the abyssal plain are rich in these mineral resources, which leads to an increased interest in deep-sea mining (DSM) of polymetallic nodules. During the DSM operation, the seabed will be disturbed, resulting in a suspended sediment plume. Such a plume can have a significant environmental impact. As a result, defining the main processes and quantifying sediment plume dispersion is vital for predicting the possible ecological implications. Flocculation could play a key role in minimizing and better prediction of dispersion of turbidity flows generated by deep-sea mining equipment. In this work, we study the effect of flocculation on the propagation of deep-sea sediment plumes by means of conducting a series of lock exchange experiments using artificial deep-sea sediment. Experiments were conducted in fresh and saline water with different clay and synthetic organic matter concentrations. Experiments are conducted in freshwater for comparison with saline water. The head velocity is measured via video analysis. At the end of the lock exchange experiments, subsamples at various run-out lengths are collected for particle size and settling velocity measurements. When experiments are conducted with synthetic organic matter in saline water, the results show that the head velocity reduces significantly compared to freshwater conditions due to the formation of dense flocs. @en

Kaolin based suspensions have wide range of applications such as slurry wall, drilling fluids, adhesives, cosmetics, refractories and pharmaceuticals, due to their abundance in nature, low cost and non-swelling nature. On the other hand, the unique properties (i.e., biodegradability) of biopolymers make them suitable candidate for variety of applications including modification of clay suspensions. In this study, the rheological properties of kaolin suspensions modified with different biopolymers (xanthan gum (XG), sodium carboxymethyl cellulose (CMC), potato starch (PS), chitosan (Ch) and apple fibre (AF)) have been investigated by varying the biopolymer type, content and clay content. The main objective of the present study is to propose a substitute for the natural mud sample. Frequency sweep tests, stress ramp-up tests and time-dependent tests were performed by using the Couette geometry (coaxial cylinders) for the prepared suspensions. The rheological results showed that both viscosity and moduli were significantly influenced by adding different biopolymers into the kaolin suspensions. For instance, an increase in viscosity of modified suspensions was observed: 3 – 4 orders of magnitude by adding xanthan gum (1 wt%) or sodium carboxymethyl cellulose (5 wt%) and 6 orders of magnitude by adding apple fibre (5 wt%). Likewise, the incorporation of different biopolymers significantly affected the complex modulus of modified clay suspensions. For example, similar or higher values of complex modulus than the pure kaolin suspension were observed at low xanthan gum or sodium carboxymethyl cellulose content (0.1 wt%). In case of chitosan, the complex modulus of the modified suspensions was higher than the complex modulus of pure kaolin suspension, even at very low polymer content (1 wt%). In the case of potato starch, a decrease in complex modulus by increasing polymer content till 10 wt% was observed followed by an increase in complex modulus with polymer content. The shear rate ramp-up and ramp-down experiments showed that the time-dependent behaviour of kaolin suspensions was not strongly influenced by adding different biopolymers. This knowledge will provide a base to choose a suitable substitute for the natural mud sample.@en

The characterization of flocculation rates is often done through floc size distribution over time. This distribution in size also affects settling rates. Besides sizes, settling velocities are dependent on floc density. This density is estimated using Stokes law, by recording the velocity and equivalent radius of a settling particle. This work compares two experimental setups used to calculate the floc size distribution and their settling velocities. The two floc measurement instruments as shown in figure 1, one is called LabSFLOC-2 [1,2] and the other is referred to as FLOCCAM [3]. Both setups have a telecentric lens which effectively reduces the pixel distortion. Polystyrene particles are used to benchmark the results. Different clay types are used to create flocs with the addition of industrial flocculant zetag 4110. The post-processing of the recorded floc videos for size, settling velocities and shapes of flocs is done with the help of an image analysis tool based on Matlab for LabSFLOC-2, whereas FLOCCAM analysis is done with the help of Safas [4].@en