Range Of Solids Concentrations Research Articles

New Calibration Methods for Accurate Electrical Capacitance Tomography Measurements in Particulate-Fluid Systems

Three different calibration techniques have been developed to greatly improve the accuracy of the solid holdup distributions obtained from electrical capacitance tomography (ECT) measurements. First, liquid mixtures are used to calibrate the ECT system. Second, the relative permittivity of solid particles is obtained by immersing the solids in different fluids: the solid relative permittivity corresponds to the point where the fluid relative permittivity matches the relative permittivity of the liquid−solid mixture. Third, the best relationship between solid holdup and electrical permittivity, over the required range of solid concentrations, is determined, for each particulate system, by suspending the particles in a viscous liquid honey.

Modeling the Potential Influence of Particle Deposition on the Accumulation of Organic Contaminants by Submerged Aquatic Vegetation

Submerged aquatic vegetation can act as both a mitigating factor(e.g., reducing downstream impacts of pesticides following runoff/spray drift) and mobilizing factor (e.g., remobilization of contaminants from sediments) influencing the fate and distribution of organic contaminants in the environment. Consequently, there has been wide scientific and regulatory interest in assessing the role of these plants in different contamination scenarios. Mechanistic models describing the environmental fate of contaminants in submerged aquatic vegetation are useful tools for interpreting laboratory and field measurements in addition to providing valuable information to risk assessors. In this study, we developed a fugacity-based model to investigate the influence of particle deposition to plant surfaces on the fate and distribution of two substances in small ponds. The main motivation for conducting this study was to address the fact that the potential contribution of this process is not typically considered by many types of models describing contaminant dynamics in submerged aquatic vegetation. For the hydrophobic substance included in this evaluation (lambda-cyhalothrin), model performance was greatly improved by including this process. The model was also applied in a generic context to compare the importance of particle deposition versus directwater uptake as a function of chemical properties (log Kow) and concentration of suspended solids in the water column. The generic application demonstrated that contaminant mass transfer is dominated by particle deposition for chemicals with log Kow greater than approximately 5.5--6 across a wide range of suspended solid concentrations and can be important even for low log Kow substances in some circumstances. Further empirical and modeling studies are recommended to explore this process more comprehensively.

Hindered and compression settling: parameter measurement and modelling

The Vesilind settling velocity function forms the basis of flux theory used both in state point analysis (for design and capacity rating) and one-dimensional dynamic models (for dynamic process modelling). This paper proposes new methods to address known shortcomings of these methods, based on an extensive set of batch settling tests conducted at different scales. The experimental method to determine the Vesilind parameters from a series of bench scale settling tests is reviewed. It is confirmed that settling cylinders must be slowly stirred in order to represent settling performance of full scale plants for the whole range of solids concentrations. Two new methods to extract the Vesilind parameters from settling test series are proposed and tested against the traditional manual method. Finally, the same data set is used to propose an extension to one-dimensional (1-D) dynamic settler models to account for compression settling. Using the modified empirical function, the model is able to describe the batch settling interface independently of the number of layers.

Determining Cyclone Particle Holdup by Pressure Drop for a CFB Boiler

AbstractAn experimental study was conducted to assess the possibility of determining particle holdup by measuring the pressure drop of a conventional cyclone used in a circulating fluidized bed (CFB) boiler. It was found that within a wide range of inlet solid concentrations, i.e., 0.54–4.42 kg/kg‐gas, the cyclone pressure drop increased linearly with inlet solid concentration at a given gas velocity, while the pressure drop between the dust exit and the vortex finder of the cyclone remained almost constant. Since particle holdup increases virtually linearly with solid flow rate, the particle holdup in the cyclone can be derived from the cyclone pressure drop, and therefore, an equation set was proposed to calculate the particle holdup from the cyclone pressure drop.

Characterization of TiO2 nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO2 deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO2 nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3–2.5 wt.%) and at different shear rates ( $$ \dot \gamma $$ = 10–250 s−1). The influence of these parameters on the quality of TiO2 films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO2 nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s−1). For the suspension with 1 wt.% TiO2 containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕm) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕm = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO2 deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1–9, being pH ≈ 5 the optimal value for this system in terms of EPD results.

Slurry Viscosity Modification Effects on Classifying Cyclone Performance

Efforts to reduce the amount of ultrafine bypass in classifying cyclones by decreasing water recovery increased the particle size cut point and negatively affected classification efficiency due to the impact on slurry rheology. The addition of a viscosity modifier to the feed stream of a classifying cyclone improved the classification performance and decreased the particle size cut point over a range of feed solids concentrations. The detailed test program investigated the use of the modifier in conjunction with varying apex diameters to identify conditions that minimize ultrafine bypass. With small apex sizes, roping conditions were readily eliminated by the addition of viscosity modifiers.

Slurry Viscosity Modification Effects on Classifying Cyclone Performance

Efforts to reduce the amount of ultrafine bypass in classifying cyclones by decreasing water recovery increased the particle size cut point and negatively affected classification efficiency due to the impact on slurry rheology. The addition of a viscosity modifier to the feed stream of a classifying cyclone improved the classification performance and decreased the particle size cut point over a range of feed solids concentrations. The detailed test program investigated the use of the modifier in conjunction with varying apex diameters to identify conditions that minimize ultrafine bypass. With small apex sizes, roping conditions were readily eliminated by the addition of viscosity modifiers.

Feasibility study of the anaerobic digestion of dewatered pig slurry by means of polyacrylamide

Liquid livestock waste can be managed by separating liquid and solid fractions then treating each separately by applying best available technology, such as anaerobic digestion for the solid fraction. There is an increasing use of polyacrylamide (PAM) as a flocculant agent to improve solid–liquid separation. In the present work, the anaerobic toxicity of PAM residues and the optimal range of total solids concentration for maximum methane production were studied as a function of PAM dosage. Results showed that dry matter and its volatile solids content increased significantly with increasing PAM dosage. Batch anaerobic tests showed that methane yield decreased linearly with increasing total solids, while the methane production per unit of raw substrate reached a maximum at 16.4% total solids. No PAM toxicity was measured for PAM concentrations below 415 g/kg total solids, but some indirect inhibitory phenomena were observed, such as a limited hydrolysis rate due to particle aggregation, and inhibition of methanogenesis by high ammonia concentration.

NUMERICAL SIMULATION OF LAMINAR SOLID-LIQUID TWO-PHASE FLOW IN STIRRED TANKS

Laminar flow of solid-liquid suspension has been rarely reported in the literature. In this article, the laminar solid-liquid two-phase flow in a lab-scale stirred tank is measured with digital particle image velocimetry (DPIV) and numerically simulated with the improved inner-outer iterative method. The simulation results show good agreement with the present data. In the range of low solid volume concentration under investigation, solid particles have minor impact on two-phase flow, and the simulated flow fields of both phases are similar to the counterpart of single-phase laminar liquid flow. The comparison of simulation with experiments of single-phase laminar flow shows reasonable agreement. These observations suggest that the numerical method employed in the present study is reliable for analysis of stirred tanks. The influence of impeller off-bottom clearance on velocities is found significant: the lower the impeller, the smaller the radial and axial velocities, and the higher the solid concentration.

Effect of surfactants on bauxite residues suspensions viscosity

Measurement of the rheological property of bauxite residue samples received from an Australian alumina refinery (red mud and neutralised mud suspension) has been carried out using a Brookfield viscometer. The plant samples were treated with two anionic surfactants (sodium polyphosphate and sodium laurate) in the laboratory and the effect of the surfactants on the residues viscosity was determined. It was found that the addition of sodium laurate, prepared with an excess of sodium hydroxide causes reduction of the viscosity of both red mud and neutralised mud while sodium polyphosphate shows very little effect on either samples. The suspensions exhibit non-Newtonian behaviour and obey the power law model over a range of solid concentrations at 75 °C.

Sustainable Flux Fouling in a Membrane Bioreactor: Impact of Flux and MLSS

The long term sustainable flux behavior of a submerged membrane bioreactor operated under a steady state conditions at a range of mixed liquor suspended solids (MLSS) concentrations has been examined. Comparison of fouling rates at a number of imposed fluxes has been made between long term filtration trials and short term tests using the flux step method. Results indicate an exponential relationship between fouling rate and flux for both long and short term trials, although the value was an order of magnitude lower during long term tests. Moreover, operation during long term trials is characterised by a period of pseudo stable operation followed by a catastrophic rise in TMP at a given critical filtration time (tfilt) during trials at 6 g · L−1. This time of stable operation, tfilt, is characterised by a linear relationship between fouling rate and flux. Results have been compared with the literature. Data for membrane fouling prior to the end of tfilt yielded a poor fit with a recently proposed model. Trends recorded at t>tfilt revealed the fouling rate to follow no definable trend with flux, contrary to the notion that fouling beyond the critical filtration time relates to solids deposition.

Temperature Dependent Rheological Property of Copper Oxide Nanoparticles Suspension (Nanofluid)

A nanofluid is the dispersion of metallic solid particles of nanometer size in a base fluid such as water or ethylene glycol. The presence of these nanoparticles affects the physical properties of a nanofluid via various factors including shear stress, particle loading, and temperature. In this paper the rheological behavior of copper oxide (CuO) nanoparticles of 29 nm average diameter dispersed in deionized (DI) water is investigated over a range of volumetric solids concentrations of 5 to 15% and various temperatures varying from 278-323 degrees K. These experiments showed that these nanofluids exhibited time-independent pseudoplastic and shear-thinning behavior. The suspension viscosities of nanofluids decrease exponentially with respect to the shear rate. Suspension viscosity follows the correlation in the form ln(mus) = A(1/T)-B, where constants A and B are the functions of volumetric concentrations. The calculated viscosities from the developed correlations and experimental values were found to be within +/- 10% of their values.

Rheological measurements of sewage sludge for various solids concentrations and geometry

In order to control and scale up activated sludge's processes, such as aeration tanks in wastewater treatment plants, it is important to get precise rheological measurements of sludge flows in a sufficiently large range of solid concentration. Indeed, the development of new processes such as Membrane Bioreactors enhances the range of biomass concentrations encountered in wastewater treatment plants. As a consequence, in this paper, we are interested by measuring flows of sludge with solid contents varying from about 2.5 to 57 g/L (activated to concentrated sludge). Considering the consistency of these sludges, among available measuring geometries, concentric cylinders (CC) and double concentric cylinders (DCC) are tested. This leads to the conclusion that, in our case, only the CC system can be used to perform the experiments. Flow and dynamic measurements are then carried out using the CC geometry. The analysis of several rheological parameters is presented for various total suspended solid (TSS) values (27 g/L to about 57 g/L). Finally, empirical equations are proposed to model the influence of the TSS concentration on rheological parameters such as the yield stress, the flow index and also the consistency index and the energy of cohesion of the sludge material.

Settling and sediment bed behaviour of kaolinite in aqueous media

In the characterisation of solid–liquid separation of suspensions it has been common in the past to either focus on the free settling region of the suspension or on the behaviour of networked suspension either in the form of a sediment or a filter cake. Combination of results from these regimes is seldom completed and, if more complete knowledge of the characterisation from individual particles to a fully networked system is required, it is necessary consider the solid–liquid separation data over a wide range of solids concentration. The current paper investigates the settling behaviour (free settling region), gel point, ϕ g (transition point) and compressive yield stress, P y( ϕ) (sediment bed region) in the characterisation of the kaolinite–sodium chloride systems from the un-networked state through to the fully networked state. It was found that settling behaviour of kaolinite changes with both ionic strength and pH of the suspension. In acidic pH range (pH 2) particles settle in flocculated form regardless of electrolyte concentration: however, in basic pH ranges, the particles settle both, dispersed form (in low electrolyte concentration) and flocculated form (in high electrolyte concentration). On the other hand, the gel point and sediment bed behaviour are found to be very sensitive to the type of the inter-particle interactions. Face–face (F–F) flocculation produces higher gel points and higher apparent maximum packing fractions while edge–face (E–F) flocculation produces higher compressive yield stresses at all volume fractions. These results show good correlations between the settling behaviour, gel point, and compressive yield stress for the different kaolinite particle interactions.

Flow analysis of semi solid processing for grey cast iron

Fluidity tests for semi solid processed grey cast iron were conducted at different degrees of primary fraction solid using fluidity strips with 2·5, 5 and 14 mm wall thickness. The microstructure of the fluidity strip castings was examined. Fluidity parameters, such as slurry velocity, critical solid concentration and choking range were studied. It can be concluded that critical solid concentration increases with the increase of wall thickness. The slurry velocity drops suddenly at a certain fraction solid very near to the critical solid concentration. Choking range zone can be measured by observing microstructure. A solidification model for fluidity has been developed based on the literature and microstructure study of semi solid processed grey cast iron. A mathematical equation has been obtained from the solidification model by modifying Flemings' fluidity model in order to analyse cavity filling of semi solid grey cast iron.

The selective aggregation and separation of titania from a mixed suspension of silica and titania

The separation of fine-grained titania from silica is an important industrial problem as the demand for titania continues. In this study we demonstrate how high-purity, synthetic, micron and sub-micron silica and titania particles may be separated by selective aggregation from an aqueous suspension. Specific electrolyte concentration and suspension pH were chosen through a colloid stability analysis. High-efficiency (up to 99.6 wt.%) separation of titania from a mixed silica–titania suspension (50% : 50%) was achieved over a wide range of solid concentrations (0.03–2 wt.%) with an electrolyte concentration of 20 mM at pH 8. Analysis of the data revealed that separation efficiency improved as the solid concentration increased. The latter behaviour was attributed to a transition from ‘free’ to hindered settling of the flocs, which impacted on the entrapment of silica particles within titania flocs.

Postponed air entrainment in dilute suspension coatings

AbstractExperimental evidence is provided that the introduction of solid spheres significantly postpones the onset of air entrainment in a particular range of solid concentrations. Spherical poly(methylmethacrylate) particles were dispersed in Newtonian liquids at different weight fractions up to 1 wt %. Despite the monotonic increase in bulk liquid viscosity, the measured onset velocity of air entrainment first increased and then decreased with increasing particle number density. The maximum onset velocity was obtained at a certain particle number density that did not depend on either the particle diameter or the Bond number. A lubrication model was built by newly considering the forced air‐film splitting by particle contacts. The successive consistency between the model prediction and the experimental observation suggests some directions for broadening the applicability of the coating operation to higher surface speeds. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Further development of software for the design and simulation of industrial thickeners

Abstract The authors presented at the Engineering Foundation Conference on Solid–Liquid Separation Systems III-2001 in Davos, software for the simulation of batch and continuous thickeners. The steady state of a continuous cylindrical thickener was simulated using the solid feed flux density function, the critical concentration, the solid effective stress and the required underflow concentration as input, in addition to the solid and fluid material densities. If the thickener area is known, the capacity and the concentration profile in the equipment are predicted. On the other hand, if the capacity is known, the required settling area and the resulting concentration profiles are predicted. In the present work, the software is extended to thickeners having conical bottoms. As model functions, two choices are possible, a solid flux density function for the whole range of solid concentrations or a solid flux density function for concentrations less than the critical and a sediment permeability and an effective solid stress for concentration above the critical. The following outputs can be chosen, the unit area, the cross-sectional area for a given capacity and height of sediment, the plot of sediment height versus thickener area for a given capacity, the plot of sediment height versus capacity for a given thickener area and the concentration profiles and mass balances for any of these cases.

Milks and Milk Concentrates: Surface Tension Measurement

Surface tension is an important property of milk concentrates because it affects atomisation in spray drying. A Krüss tensiometer and Wilhelmy plate were used to measure surface tension. Skim milk and whole milk were tested at a range of solids concentrations and were compared with the surface tension of standard and reconstituted milks. It was found that surface tension was affected more by temperature than by fat content or solids concentration. The surface tensions for concentrates correspond to published values for standard milks below 60°C, but above 60°C, the surface tension increases markedly, which can be attributed to changes in the milk chemistry. The difficulty associated with using the Wilhelmy plate method is the time taken to perform each measurement, which allows a skin to form and reduces the accuracy of the measurements.

A comparison of ultrasound treatment on primary and secondary sludges

Ultrasound treatment of primary and secondary sludges was conducted to improve the qualities of sludges for the anaerobic digestion. The impacts of different sonication times, sonication densities and solids concentrations on ultrasonication efficiency were examined. The experimental results indicated that the significant reduction in particle size and increase in soluble organics could be achieved, implying that ultrasonication could offer a feasible treatment method to efficiently disintegrate sludge. The greater decrease in particle size and increase in soluble organics of sludge indicated that the secondary sludge has a more remarkable improvement after sonication over the primary sludge. With respects to the extent of disintegration and energy consumption, higher sonication density performed more effectively in terms of specific energy. There exists an optimal solids concentration range for both the sludges for optimum sonication. Within the optimal solids concentration range, efficient sonication can be effected and sludge would be disintegrated efficiently. The ultrasound would be attenuated by scattering and absorption if the solids concentration exceeds the optimal range. It appeared from the study that the mechanical shear forces caused by ultrasonic cavitation could be a key factor for sludge disintegration and collapse of cavitation bubbles could significantly alter the sludge characteristics.