Settling Model Research Articles

Validation of Modified ART Mod 2 Code through Comparison with Aerosol Deposition of Cesium Compound in Phébus FPT3 Containment Vessel

Evaluation of aerosol deposition in the containment vessel is an important step for the assessment of radioactive material release to the environment. ART Mod 2 is a calculation code that is used for evaluation of aerosol deposition in the containment vessel. The authors modified aerosol deposition models of ART Mod 2, namely, gravitational settling model, Brownian diffusion model, diffusiophoresis model, and thermophoresis model in order to increase potential of capturing the deposition phenomena. This study aims to compare the simulated results of modified ART Mod 2 with aerosol deposition of cesium compounds in the containment vessel of Phébus FPT3 experiment, in order to validate modified ART Mod 2 code. It is found that aerosol deposition using modified ART Mod 2 agrees with Phébus FPT3. Prediction of Brownian diffusion is significantly improved due to the consideration of turbulent damping process. Cesium mass flow rate and aerosol size are factors that can significantly influence the uncertainty of the results. When conditions of single volumes are carefully selected to match those of the Phébus FPT3 experiment, modified ART Mod 2 can predict aerosol deposition in Phébus FPT3 with relative accuracy.

Scale-independent model of gravitational settling of particulate suspension in a fractal channel

Gravitational settling of solid particles into a fractal-shaped channel was investigated experimentally and theoretically. Previous studies have reported that the settling behavior of particles in liquid-filled channels depends strongly on particle properties and suspension conditions. At small particle size and high concentration, particles settle collectively like an immiscible fluid with respect to the surrounding one. In this study, we examined the gravitational dispersion behavior of solid particles in a three-dimensional fractal-shaped channel under various collective conditions. The experimental results showed that the settling behavior varies with the collectivity of suspended particles. In the case of high collectivity conditions, settling velocity is enhanced by a density-driven instability, which depends not only on the physical properties of the particles and fluid but also on channel geometry. We developed a model of temporal change in the volumetric occupancy ratio of the suspended particles region. This model describes the invasion of particles into a fractal channel. Our model comprises only the fractal characteristics of the channel, such as a homothetic ratio and a bifurcation number. Consequently, This model could provide a rough prediction of the gravity-induced invasion behavior of particles into any fractal-shaped channel.

Influence of Temperature and De-Icing Salt on the Sedimentation of Particulate Matter in Traffic Area Runoff

Stormwater quality improvement devices use sedimentation as a pre-treatment step to separate contaminant laden particulate matter (PM) from traffic area runoff. Multiple studies describe worse settling behavior during the cold season. This paper is written in response to a decreased PM retention that was observed in the cold season during a 20-month monitoring of a sedimentation tank. However, the data was insufficient to assess the two factors that influence sedimentation during the cold season—temperature and de-icing salt application. Therefore, simplified discrete particle settling models were used to determine the influence of temperature and de-icing salt. These influences were compared to other factors, like overflow rate, particle density, and particle size distribution. To calculate the effect of temperature and de-icing salt on density and viscosity, two empirical models were applied for the first time in this field. The calculations showed that de-icing salt (NaCl) had a negligible influence on the retention of PM. However, reducing the temperature from 20 °C to 5 °C was shown to decrease the total suspended solid removal efficiency by up to 8%. The order of influencing factors was found to be particle size distribution >> overflow rate > particle density > temperature.

The SAMI Galaxy Survey: stellar and gas misalignments and the origin of gas in nearby galaxies

Misalignment of gas and stellar rotation in galaxies can give clues to the origin and processing of accreted gas. Integral field spectroscopic observations of 1213 galaxies from the SAMI Galaxy Survey show that 11% of galaxies with fitted gas and stellar rotation are misaligned by more than 30 degrees in both field/group and cluster environments. Using SAMI morphological classifications and Sersic indices, the misalignment fraction is 45+/-6% in early-type galaxies, but only 5+/-1% in late-type galaxies. The distribution of position angle offsets is used to test the physical drivers of this difference. Slower dynamical settling time of the gas in elliptical stellar mass distributions accounts for a small increase in misalignment in early-type galaxies. However, gravitational dynamical settling time is insufficient to fully explain the observed differences between early- and late-type galaxies in the distributions of the gas/stellar position angle offsets. LTGs have primarily accreted gas close to aligned rather than settled from misaligned based on analysis of the skewed distribution of PA offsets compared to a dynamical settling model. Local environment density is less important in setting the misalignment fractions than morphology, suggesting that mergers are not the main source of accreted gas in these disks. Cluster environments are found to have gas misalignment driven primarily by cluster processes not by gas accretion.

A novel technique for online slurry grade detection based on EDXRF

The accuracy of energy dispersion X-ray fluorescence spectrometry (EDXRF) decreases via the online detection of slurry grade, which is due to the matrix difference caused by varying slurry components and processes. Among these, the most significant influence is the water content in the slurry, which reduces the X-ray fluorescence intensity of target elements that the detector receives. In this paper, a novel online detection method based on a correction model of X-ray fluorescence intensity is proposed. Using the mineral particle settling model as a foundation, the minimum slurry velocity was first derived to satisfy the condition of pulp content uniformity. Then, the impact of slurry concentration on the X-ray fluorescence intensity was analyzed. An intensity correction model was built, which accounted for the impact of water in slurry on the characteristic X-ray fluorescence intensity of the target elements. The overall methodology was thoroughly validated through several experiments, and was compared with the traditional EDXRF method. The experimental results indicated that the standard deviation of the target’s elemental slurry grade dropped by more than 60% for lead and 40% for zinc. Meanwhile, the average relative error of the slurry’s elemental grade was reduced by more than 80% for lead and 90% for zinc. The accuracy and stability of online slurry grade detection were therefore significantly improved.

Modeling, Simulation, and Implementation of Fast Settling Switched PI Controller for MOX Integrated Pt Microheater

This paper presents a sensor system with temperature control of platinum microheater using a combined control strategy of open-loop and closed-loop control. The method proposed in this paper modifies the proportional integral control for faster response under sampling time constraint of large sampling interval, as a large sampling interval between two control commands slow the response. The initial quick temperature rising open-loop response of microheater contributes to faster rise time, and then, it is switched to closed-loop control when the quick initial rise has taken place, hence termed open-loop to closed-loop switched proportional integral (OLCLS PI) control. The settling time obtained by OLCLS PI and PI are 3 and 14 s, respectively, for 2% accuracy, thereby providing faster response than PI. The work is studied with elaborate modeling and simulation using MATLAB, and a practical implementation on embedded platform is presented using an in-house developed MOX-based gas sensor, which utilizes a platinum microheater.

Large Eddy simulations of particulate flows inside a square differentially heated cavity at Rayleigh numbers up to 1011

The Differentially Heated Cavity (DHC) has often served as a suitable geometric model for naturally driven particulate flows inside closed volumes. While providing deep insights of the flow dynamics, 3D DNS or 3D LES simulations of DHC flows are very time-consuming and their potential extension to higher Rayleigh (Ra) numbers typical of room dimensions is problematic. In this study, therefore, a 2D-LES Euler-Lagrange approach is used to predict turbulent particle transport in a DHC.We first validate our predictions against a 2D DNS database at Ra 109 and 1010 with particles having diameters greater than 15 μm. We show that our LES results are in very agreement with the DNS data. In a second step, we extend our simulations to a fully turbulent Ra number 1011 and particle diameters between 0.5 and 10 m. Details are provided on the particle deposition locations and airborne concentration decay rate with time. We show in particular that as the flow becomes more turbulent, the particle settling rates approach those predicted by the simple stirred settling model.

Measurements and LES computations of a turbulent particle-laden flow inside a cubical differentially heated cavity

The estimation of particle removal rates in closed atmospheric environments such as rooms or airplanes is of great interest because it is directly relevant to air quality and disease transmission. In this work we investigate experimentally and numerically the depletion of micron-sized particles inside a turbulent, naturally driven enclosure flow. The enclosure is a cubical cavity with side 0.7 m in which two opposite vertical walls are held at different temperatures while other walls are adiabatic. The transport of monodisperse SiO2 particles with diameter 0.5, 1.0, and 2.5 μm was studied at Rayleigh numbers varying in the range of 3 × 108 to 109, corresponding to temperature differentials ΔT from 10 to 40 K. The decay time constant of the airborne particle concentration was calculated from discrete measurements performed with an Electrical Low-Pressure Impactor. It is found that the temperature difference greatly influences the deposition of particles with sizes equal to or less than 1 μm in diameter. For this particle range, thermophoresis becomes important and hence the larger the ΔT, the larger the deposition, a significant part of which taking place on the cold wall by the thermophoretic effect. As a result, the decay time constant of submicron particles is up to 5 times smaller than predicted by the stirred settling model, depending on the imposed ΔT. For the largest particles with diameter 2.5 μm, the influence of thermophoresis and hence ΔT is negligible, and particle removal rates are in line with the stirred settling model predictions, with mostly gravity dominated deposition on the bottom wall. A Large Eddy Simulation of the tests was performed using an Euler-Lagrange approach, and predictions of the decay time constant are within less than 20% of the measured values.

Characterization and modeling of sediment settling, consolidation, and suspension to optimize coastal Louisiana restoration

Many research efforts have been undertaken over many decades in the field of Louisiana coastal restoration, but long-term experiments for sediment suspension and consolidation in diversion-receiving basins are still limited, despite significance of this topic to ongoing restoration strategies. Sediment samples were collected from two active diversions on the Mississippi River: West Bay, a semi-enclosed bay located on the Mississippi River Delta and fed by the West Bay Diversion, and from Big Mar pond, a receiving basin of the Caernarvon freshwater diversion from the lower Mississippi River, Louisiana, USA. A dual-core Gust Erosion Microcosm System was used to measure time-series (0.5, 1, 2, 3, 4, 5, and 6-months after initial settling) erodibility at seven shear stress regimes (0.01–0.60 Pa) using experimental cores prepared with two initial sediment concentrations (60 and 120 kg m−3). A 230-cm tall settling column with nine sampling ports was used to measure the consolidation rates for initial sediment concentrations ranging from fluid mud (10 kg m−3) to dredge effluent (120 kg m−3), in combination with two levels of salinity (1 and 5). The erodibility of West Bay sediment decreased with increasing time of consolidation. The critical shear stress for resuspension increased from 0.2 Pa after 2 months to 0.45 Pa after 4 months of consolidation. The consolidation rates were inversely and exponentially related to initial sediment concentrations. Consolidation tests in salinity of 1 generally settled faster than that in salinity of 5, and consolidation tests with low sediment concentration tests generally settled faster than high-concentration tests. An exponential coefficient was added in the Sanford (2008) model to better predict the consolidation profile of both rapid early settling and slow self-weight consolidation processes. Our study suggests that enclosed basin, low salinity, relatively low sediment concentration and minimized disturbance for 4 months all favor of mud deposition and retention, and these factors should be considered in the design of coastal restoration projects such as dredging effluent placements and sediment diversions.

Application of modified concrete to remove surfactants from water

In these studies two types of modified concretes in photocatalytic mineralization of anionic surfactant sodium dodecylbenzenesulfonate (NaDBS) were used. Commercial TiO2-P25 and nitrogen modified TiO2-N as photocatalysts for concrete modification were employed. The studies were conducted in the special designed reactor which was a simple model of the secondary settler used at the sewage treatment plant. The mineralization of anionic surfactant NaDBS after 18 h of UV light irradiation amounted to 48% for concrete modified by TiO2-P25 and 37% for concrete modified by TiO2-N.

A simulation model for settling tanks with varying cross-sectional area

ABSTRACTA quasi-one-dimensional model of the process of continuous sedimentation in clarifier-thickeners (settlers) with variable cross-sectional area is presented. The partial differential equation (PDE) model extends the settler model advanced by Bürger et al. (2013), which assumes a constant cross section. A reliable numerical method that handles the special features of the nonlinear PDE is presented along with an advantageous time-step condition for continuous and batch sedimentation under the condition of a variable cross-sectional area. Simulations of continuous sedimentation show the effect of change of cross-sectional area in the concentration inside the vessel and in the underflow. Simulations of batch settling in cones illustrate the versatility of the numerical scheme to include a vertex, where the area shrinks to zero.

Predicting the fate of micropollutants during wastewater treatment: Calibration and sensitivity analysis

The presence of micropollutants in the environment and their toxic impacts on the aquatic environment have raised concern about their inefficient removal in wastewater treatment plants. In this study, the fate of micropollutants of four different classes was simulated in a conventional activated sludge plant using a bioreactor micropollutant fate model coupled to a settler model. The latter was based on the Bürger-Diehl model extended for the first time to include micropollutant fate processes. Calibration of model parameters was completed by matching modelling results with full-scale measurements (i.e. including aqueous and particulate phase concentrations of micropollutants) obtained from a 4-day sampling campaign. Modelling results showed that further biodegradation takes place in the sludge blanket of the settler for the highly biodegradable caffeine, underlining the need for a reactive settler model. The adopted Monte Carlo based calibration approach also provided an overview of the model's global sensitivity to the parameters. This analysis showed that for each micropollutant and according to the dominant fate process, a different set of one or more parameters had a significant impact on the model fit, justifying the selection of parameter subsets for model calibration. A dynamic local sensitivity analysis was also performed with the calibrated parameters. This analysis supported the conclusions from the global sensitivity and provided guidance for future sampling campaigns. This study expands the understanding of micropollutant fate models when applied to different micropollutants, in terms of global and local sensitivity to model parameters, as well as the identifiability of the parameters.

Numerical solution of a multi-class model for batch settling in water resource recovery facilities

• The numerical solution for several batch settling unit processes in WRRFs is computed. • Multi-class concentration-driven model based on settling velocity distributions used. • Non-linear convection–diffusion equations appear due to the multi-class extension. • IMEX-RK schemes combined with high order shock-capturing technology are applied. In Torfs et al. (2017) a new unified framework to model settling tanks in water resource recovery facilities was proposed providing a set of partial differential equations (PDEs) modelling different settling unit processes in wastewater treatment such as primary and secondary settling tanks (PSTs and SSTs). The extension to a multi-class framework to deal with the distributed properties of the settling particles leads to a system of non-linear hyperbolic-parabolic PDEs whose solutions may contain very sharp transitions. This necessitates the use of a consistent and robust numerical method to obtain well-resolved and reliable approximations to the PDE solutions. The use of implicit–explicit Runge–Kutta (IMEX-RK) schemes, along with the weighted essentially non-oscillatory (WENO) shock-capturing technology for the discretization of the set of equations, is advocated in this work. The versatility of the proposed unified framework is demonstrated through a set of numerical examples for batch settling occurring in both PSTs and SSTs, along with the efficiency and reliability of the numerical scheme.

Predicting settling performance of ANAMMOX granular sludge based on fractal dimensions

The settling performance of ANAMMOX granular sludge determines the biomass retention in reactors, and finally determines the potential reaction capacity. In this paper, Stokes equation was modified by fractal dimensions to describe the settling performance of ANAMMOX granular sludge. A new method was developed to obtain fractal dimensions, and a fractal settling model was established for ANAMMOX granular sludge. The fractal settling model was excellent with only a small deviation of 0.8% from the experimental data. Assuming normal distribution of all Feret diameters, 88% experimental data fell into the 90% confidence interval of settling velocities. Further assuming logarithmic normal distribution, 95% experimental data fell into the 90% confidence interval. The fractal settling model is helpful for the prediction of settling velocities of granular sludge and the optimization of bioreactor performance.

On the hindered settling of sand-mud suspensions

Hindered settling, the process by which the settling of sediment particles becomes impeded due to the proximity of other sediment particles, can be an important process for the coastal modeller, especially in highly muddy environments. It is also a significant process in other disciplines such as chemical engineering, the modelling of debris flow, the study of turbidites, piping of slurries and the understanding of processes occurring within a dredger hopper. This study first examines the hindered settling behaviour of monodisperse suspensions in order to create a framework for polydisperse hindered settling that works for both non-cohesive and cohesive suspensions. The Richardson–Zaki equation is adapted to make it compatible with the changes with viscosity that occur near the point at which suspensions become solid. The modified monodisperse settling equation is then compared to data for hindered settling of cohesive suspensions and shown to be consistent with the transition between hindered settling and the initial permeability phase of consolidation. Based on the monodisperse framework developed initially, this paper proposes a hindered settling model for sand/mud mixtures which is based on a modification of the Masliyah (1979) and Lockett and Bassoon (1979) hindered settling equation. The model is shown to reproduce the hindered settling of a variety of different sediment mixtures whilst reducing the extent of empiricism often associated with the modelling of polydisperse hindered settling of mud/sand mixtures.

Strangers No More: Immigration and the Challenges of Integration in North America and Western Europe. By Richard Alba and Nancy Foner. Princeton, NJ: Princeton University Press, 2015. Pp. 336. $35.00 (cloth); $24.95 (paper).

Strangers No More: Immigration and the Challenges of Integration in North America and Western Europe. By Richard Alba and Nancy Foner. Princeton, NJ: Princeton University Press, 2015. Pp. 336. $35.00 (cloth); $24.95 (paper).

Experimental metrics to predict the flocculent settling coefficient in a 1D settler model

Experimental metrics to predict the flocculent settling coefficient in a 1D settler model

Sedimentation in a small lake following conversion of bottomland forest to row cropping

Areas of native bottomland hardwood forest in the lower Red River basin in Louisiana were cleared for row cropping around 1970. Erosion and sediment deposition in channels and lakes presumably increased, affecting hydrologic connectivity and lake ecosystems. Sediment deposited in a representative small lake after land conversion was determined in 2000 from the distribution of cesium (137Cs) with depth. Sediment consisted of low-density clay deposited above dense silt loam. Organic carbon (C) and 137Cs profiles had lower and upper concentration maxima. The lower maxima established the circa 1970 lakebed at ≤0.9 m (3 ft) above the morphological discontinuity and from 2.1 to 1.3 m (6.9 to 4.3 ft) below the 2000 lakebed at positions midlake and halfway to the bank, respectively. The upper maxima were likely due to progressive land conversion around the lake, coupled with increasing clay content of sediment upwards to the 2000 lakebed. A quiescent settling model was used to estimate the composition of runoff water necessary to produce the depth, texture, and density of sediment above the lower 137Cs maxima. The Annualized Agricultural Nonpoint Source water quality model was calibrated to match this composition, and sediment accumulation under alternative management scenarios was calculated. Compared to conventional-till (CT) soybeans (Glycine max L.) for 30 years, CT with cover crop (CC), no-till (NT), NT with CC management, and forest might have reduced sedimentation in the lake by about 20%, 40%, 60%, and 98%, slowing changes in light penetration, temperature, turbidity, and chemistry that affect the lake ecosystem.

Dynamic modelling of solids in a full-scale activated sludge plant preceded by CEPT as a preliminary step for micropollutant removal modelling.

The presence of micropollutants in the environment has triggered research on quantifying and predicting their fate in wastewater treatment plants (WWTPs). Since the removal of micropollutants is highly related to conventional pollutant removal and affected by hydraulics, aeration, biomass composition and solids concentration, the fate of these conventional pollutants and characteristics must be well predicted before tackling models to predict the fate of micropollutants. In light of this, the current paper presents the dynamic modelling of conventional pollutants undergoing activated sludge treatment using a limited set of additional daily composite data besides the routine data collected at a WWTP over oneyear. Results showed that as a basis for modelling, the removal of micropollutants, the Bürger-Diehl settler model was found to capture the actual effluent total suspended solids (TSS) concentrations more efficiently than the Takács model by explicitly modelling the overflow boundary. Results also demonstrated that particular attention must be given to characterizing incoming TSS to obtain a representative solids balance in the presence of a chemically enhanced primary treatment, which is key to predict the fate of micropollutants.

On constitutive functions for hindered settling velocity in 1-D settler models: Selection of appropriate model structure

Advanced 1-D models for Secondary Settling Tanks (SSTs) explicitly account for several phenomena that influence the settling process (such as hindered settling and compression settling). For each of these phenomena a valid mathematical expression needs to be selected and its parameters calibrated to obtain a model that can be used for operation and control. This is, however, a challenging task as these phenomena may occur simultaneously. Therefore, the presented work evaluates several available expressions for hindered settling based on long-term batch settling data. Specific attention is paid to the behaviour of these hindered settling functions in the compression region in order to evaluate how the modelling of sludge compression is influenced by the choice of a certain hindered settling function. The analysis shows that the exponential hindered settling forms, which are most commonly used in traditional SST models, not only account for hindered settling but partly lump other phenomena (compression) as well. This makes them unsuitable for advanced 1-D models that explicitly include each phenomenon in a modular way. A power-law function is shown to be more appropriate to describe the hindered settling velocity in advanced 1-D SST models.