scholarly journals Can terminal settling velocity and drag of natural particles in water ever be predicted accurately?

2020 ◽  
Author(s):  
Onno J. I. Kramer ◽  
Peter J. de Moel ◽  
Shravan K. R. Raaghav ◽  
Eric T. Baars ◽  
Wim H. van Vugt ◽  
...  
Keyword(s):  
Drinking Water ◽  
Measurement Errors ◽  
Settling Velocity ◽  
Particle Density ◽  
Fixed Bed ◽  
Drinking Water Treatment ◽  
Liquid System ◽  
Solid Particles ◽  
Spherical Particles ◽  
Fluidised Bed

Abstract. Natural particles are frequently applied in drinking water treatment processes in fixed bed reactors, in fluidised bed reactors, and in sedimentation processes to clarify water and to concentrate solids. When particles settle, it has been found that in terms of hydraulics, natural particles behave differently when compared to perfectly round spheres. To estimate the terminal settling velocity of single solid particles in a liquid system, a comprehensive collection of equations is available. For perfectly round spheres, the settling velocity can be calculated quite accurately. However, for naturally polydisperse non-spherical particles, experimentally measured settling velocities of individual particles show considerable spread from the calculated average values. This work aimed to analyse and explain the different causes of this spread. To this end, terminal settling experiments were conducted in a quiescent fluid with particles varying in density, size and shape. For the settling experiments, opaque and transparent spherical polydisperse and monodisperse glass beads were selected. In this study, we also examined drinking water related particles, like calcite pellets and crushed calcite seeding material grains, both applied in drinking water softening. Polydisperse calcite pellets were sieved and separated to acquire more uniformly dispersed samples. In addition, a wide variety of grains with different densities, sizes and shapes were investigated for their terminal settling velocity and behaviour. The derived drag coefficient was compared with well-known models such as Brown–Lawler. A sensitivity analysis showed that the spread is caused to a lesser extent by variations in fluid properties, measurement errors and wall effects. Natural variations in specific particle density, path trajectory instabilities and distinctive multi-particle settling behaviour caused a slightly larger degree of spread. In contrast, greater spread is caused by variations in particle size, shape and orientation.

scholarly journals Can terminal settling velocity and drag of natural particles in water ever be predicted accurately?

2021 ◽  
Vol 14 (1) ◽  
pp. 53-71
Author(s):  
Onno J. I. Kramer ◽  
Peter J. de Moel ◽  
Shravan K. R. Raaghav ◽  
Eric T. Baars ◽  
Wim H. van Vugt ◽  
...  
Keyword(s):  
Drinking Water ◽  
Measurement Errors ◽  
Settling Velocity ◽  
Particle Density ◽  
Fixed Bed ◽  
Drinking Water Treatment ◽  
Solid Particles ◽  
Spherical Particles ◽  
Fluidised Bed ◽  
Natural Variations

Abstract. Natural particles are frequently applied in drinking water treatment processes in fixed bed reactors, fluidised bed reactors, and sedimentation processes to clarify water and to concentrate solids. When particles settle, it has been found that, in terms of hydraulics, natural particles behave differently when compared to perfectly round spheres. To estimate the terminal settling velocity of single solid particles in a liquid system, a comprehensive collection of equations is available. For perfectly round spheres, the settling velocity can be calculated quite accurately. However, for naturally polydisperse non-spherical particles, experimentally measured settling velocities of individual particles show considerable spread from the calculated average values. This work aims to analyse and explain the different causes of this spread. To this end, terminal settling experiments were conducted in a quiescent fluid with particles varying in density, size, and shape. For the settling experiments, opaque and transparent spherical polydisperse and monodisperse glass beads were selected. In this study, we also examined drinking-water-related particles, like calcite pellets and crushed calcite seeding material grains, which are both applied in drinking water softening. Polydisperse calcite pellets were sieved and separated to acquire more uniformly dispersed samples. In addition, a wide variety of grains with different densities, sizes, and shapes were investigated for their terminal settling velocity and behaviour. The derived drag coefficient was compared with well-known models such as the one of Brown and Lawler (2003). A sensitivity analysis showed that the spread is caused, to a lesser extent, by variations in fluid properties, measurement errors, and wall effects. Natural variations in specific particle density, path trajectory instabilities, and distinctive multi-particle settling behaviour caused a slightly larger degree of the spread. In contrast, a greater spread is caused by variations in particle size, shape, and orientation. In terms of robust process designs and adequate process optimisation for fluidisation and sedimentation of natural granules, it is therefore crucial to take into consideration the influence of the natural variations in the settling velocity when using predictive models of round spheres.

Settling Behavior of Particles in Bubble Containing Newtonian Fluids: Experimental Study and Model Development

2021 ◽  
Author(s):  
Silin Jing ◽  
Xianzhi Song ◽  
Zhaopeng Zhu ◽  
Buwen Yu ◽  
Shiming Duan
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Volume Concentration ◽  
Settling Velocity ◽  
Particle Density ◽  
Particle Diameter ◽  
Newtonian Fluids ◽  
Spherical Particles ◽  
Bubble Volume ◽  
Particle Reynolds Number

Abstract Accurate description of cuttings slippage in the gas-liquid phase is of great significance for wellbore cleaning and the control accuracy of bottom hole pressure during MPD. In this study, the wellbore bubble flow environment was simulated by a constant pressure air pump and the transparent wellbore, and the settling characteristics of spherical particles under different gas volume concentrations were recorded and analyzed by highspeed photography. A total of 225 tests were conducted to analyze the influence of particle diameter (1–12mm), particle density (2700–7860kg/m^3), liquid viscosity and bubble volume concentration on particle settling velocity. Gas drag force is defined to quantitatively evaluate the bubble’s resistance to particle slippage. The relationship between bubble drag coefficient and particle Reynolds number is obtained by fitting the experimental results. An explicit settling velocity equation is established by introducing Archimedes number. This explicit equation with an average relative error of only 8.09% can directly predict the terminal settling velocity of the sphere in bubble containing Newtonian fluids. The models for predicting bubble drag coefficient and the terminal settling velocity are valid with particle Reynolds number ranging from 0.05 to 167 and bubble volume concentration ranging from 3.0% to 20.0%. Besides, a trial-and-error procedure and an illustrative example are presented to show how to calculate bubble drag coefficient and settling velocity in bubble containing fluids. The results of this study will provide the theoretical basis for wellbore cleaning and accurate downhole pressure to further improve the performance of MPD in treating gas influx.

Nitrogen and phosphorus removal from secondary effluent using drinking water treatment residuals fixed-bed column with intermittent operation

2014 ◽  
Vol 14 (5) ◽  
pp. 812-819
Author(s):  
Leilei Bai ◽  
Changhui Wang ◽  
Yuansheng Pei
Keyword(s):  
Drinking Water ◽  
Water Treatment ◽  
Fixed Bed ◽  
Drinking Water Treatment ◽  
Great Promise ◽  
Secondary Effluent ◽  
Water Treatment Residuals ◽  
Fixed Bed Column ◽  
Drinking Water Treatment Residuals ◽  
N Removal

This work aims to explore a novel intermittently operated fixed-bed column with drinking water treatment residuals (WTR) as main medium to remove nitrogen (N) and phosphorus (P) from secondary effluent under different hydraulic loading rates (HLRs). The results showed that the WTR was beneficial for N removal and the average removal efficiency reached 59%. The denitrification was the primary pathway for N removal and the denitrification rate (2.19 g N/m3 d) was higher than the theoretical value based on the organic matter removal rate (7.35 g CODcr/m3 d). The P removal was excellent and the efficiency still remained 98% after 260-day operation. The lifetime of the WTR fixed-bed column regarding P saturation was estimated to be 7.9 years under the highest HLR of 0.45 m3/m3 d. Moreover, the efficiency and stability of the nutrients removal further increased with the reduction of HLR. Based on regulations, the system holds great promise as a technology for water environment restoration and WTR recycling.

Relationship between di-(2-ethylhexyl) phthalate concentration and chemical structure of organic matter on solids in drinking water treatment processes

2004 ◽  
Vol 4 (5-6) ◽  
pp. 321-333 ◽  
Author(s):  
Y. Thaveemaitree ◽  
F. Nakajima ◽  
H. Furumai ◽  
S. Kunikane
Keyword(s):  
Drinking Water ◽  
Organic Matter ◽  
Water Treatment ◽  
Toxic Substance ◽  
Drinking Water Treatment ◽  
Solid Particles ◽  
High Concentration ◽  
Fragment Composition ◽  
Treatment Processes ◽  
Ethylhexyl Phthalate

Di-(2-ethylhexyl) phthalate (DEHP), regarded as a toxic substance, is widely used and abundantly contaminated in environments. Via contamination of freshwater, DEHP can enter into drinking water treatment and be adsorbed on solid particles. This study was aimed at understanding the concentration phenomenon of DEHP in drinking water treatment process, focusing on the relationship between DEHP concentration and characteristics of organic matter on the solids formed in the processes as scum, suspended solid and sludge. Solid samples were collected from five drinking water treatment processes in Japan and analyzed by pyrolysis GC/MS. The solids were categorized by the sampling locations, solid types and fragment composition. The specificity of the pyrolysis fragments in each group was summarized into a matrix. When compared with concentration of DEHP and characteristics of organic matter, a solid specifically containing many specific aliphatic fragments contained significantly high concentration of DEHP.

METHODOLOGY OF CALCULATION THE TERMINAL SETTLING VELOCITY DISTRIBUTION OF SPHERICAL PARTICLES FOR HIGH VALUES OF THE REYNOLD’S NUMBER

2014 ◽  
Vol 59 (1) ◽  
pp. 269-282 ◽  
Author(s):  
Agnieszka Surowiak ◽  
Marian Brożek
Keyword(s):  
Particle Size ◽  
Probability Density Function ◽  
Velocity Distribution ◽  
Density Distribution ◽  
Probability Density ◽  
Settling Velocity ◽  
Particle Density ◽  
Random Variable ◽  
Spherical Particles ◽  
Settling Velocity Distribution

Abstract The particle settling velocity is the feature of separation in such processes as flowing classification and jigging. It characterizes material forwarded to the separation process and belongs to the so-called complex features because it is the function of particle density and size. i.e. the function of two simple features. The affiliation to a given subset is determined by the values of two properties and the distribution of such feature in a sample is the function of distributions of particle density and size. The knowledge about distribution of particle settling velocity in jigging process is as much important factor as knowledge about particle size distribution in screening or particle density distribution in dense media beneficiation. The paper will present a method of determining the distribution of settling velocity in the sample of spherical particles for the turbulent particle motion in which the settling velocity is expressed by the Newton formula. Because it depends on density and size of particle which are random variable of certain distributions, the settling velocity is a random variable. Applying theorems of probability, concerning distributions function of random variables, the authors present general formula of probability density function of settling velocity for the turbulent motion and particularly calculate probability density function for Weibull’s forms of frequency functions of particle size and density. Distribution of settling velocity will calculate numerically and perform in graphical form. The paper presents the simulation of calculation of settling velocity distribution on the basis of real distributions of density and projective diameter of particles assuming that particles are spherical.

Insight From Recent Experimental and Empirical-Model Studies on Flow-Regime Characteristics in Debris Bed Formation Behavior

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Songbai Cheng ◽  
Ting Zhang ◽  
Jinjiang Cui ◽  
Pengfeng Gong ◽  
Yujia Qian
Keyword(s):  
Flow Regime ◽  
Empirical Model ◽  
Particle Density ◽  
Model Development ◽  
Solid Particles ◽  
Spherical Particles ◽  
Experimental Investigations ◽  
Nonspherical Particles ◽  
Model Studies ◽  
Formation Behavior

Studies on debris bed formation behavior are important for improved evaluation of core relocation and debris bed coolability that might be encountered in a core disruptive accident (CDA) of sodium-cooled fast reactors (SFR). Motivated to clarify the flow-regime characteristics underlying this behavior, both experimental investigations and empirical-model development are being performed at the Sun Yat-sen University in China. As for the experimental study, several series of simulated experiments are being conducted by discharging various solid particles into water pools. To obtain a comprehensive understanding, a variety of experimental parameters, including particle size (0.000125– 0.008 m), particle density (glass, aluminum, alumina, zirconia, steel, copper, and lead), particle shape (spherical and nonspherical), and water depth (0–0.8 m) along with the particle release pipe diameter (0.01–0.04 m) were varied. It is found that due to the different interaction mechanisms between solid particles and water pool, four kinds of flow regimes, termed, respectively, as the particle-suspension regime, the pool-convection dominant regime, the transitional regime, and the particle-inertia dominant regime, were identifiable. As for the empirical-model development, aside from a base model which is restricted to predictions of spherical particles, in this paper considerations on how to cover more realistic conditions (esp. debris of nonspherical shapes) are also discussed. It is shown that by coupling the base model with an extension scheme, respectable agreement between experiments and model predictions for regime transition can be achieved for both spherical and nonspherical particles given our current range of conditions.

Saltation and incipient suspension above a flat particle bed below a turbulent boundary layer

2000 ◽  
Vol 417 ◽  
pp. 77-102 ◽  
Author(s):  
K. NISHIMURA ◽  
J. C. R. HUNT
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Settling Velocity ◽  
Particle Density ◽  
Surface Wind ◽  
Spherical Particles ◽  
Flux Profile ◽  
Horizontal Flux ◽  
The Mean ◽  
The Impact

Experiments were conducted in a wind tunnel in which a turbulent boundary layer was naturally grown over flat beds of three types of nearly mono-disperse spherical particles with different diameters, densities and coefficient of restitution (r) (snow, 0.48 mm, 910 kg m−3; mustard seeds, 1.82 mm, 1670 kg m−3, r = 0.7; ice particles, 2.80 mm, 910 kg m−3, r = 0.8–0.9). The surface wind speeds (defined by the friction velocity u∗) were varied between 1.0 and 1.9 times the threshold surface wind speed (defined by u∗t). The trajectories, and ejection and impact velocities of the particles were recorded and analysed, even those that were raised only about one diameter into the flow.Measurements of the average horizontal flux of saltating particles per unit area, f(z), at each level z above the surface showed that, for u∗/u∗t [les ] 1.5, f(z) is approximately independent of the particle density and decreases exponentially over a vertical scale length lf, that is about 3 to 4 times the estimated mean height of the particle trajectories 〈h〉. Numerical simulations of saltating grains were computed using the measured probabilities of ejection velocities and the mean velocity profile of the air flow, but neglecting the direct effect of the turbulence. The calculated mean values of the impact velocities and the trajectory dimensions were found to agree with the measurements in the saltation range, where u∗/u∗t < 1.5. Similarly, in this range the simulations of the horizontal flux profile and integral are also consistent with the measurements and with Bagnold's u∗3 formula, respectively.When u∗/u∗t [ges ] 1.5, and u∗/VT [ges ] 1/10, where VT is the settling velocity, a transition from saltation to suspension occurs. This is indicated by the change in the mean mass flux profile which effectively becomes uniform with height (z) up to the top of the boundary layer. An explanation is provided for this low value of turbulence at transition relative to the settling velocity in terms of the random motion of the particles under the action of the turbulence when they reach the tops of their parabolic trajectories. The experiments show that, as u∗/u∗t increases from 1.0 to 1.9 the normalized mean vertical impact velocity 〈V3I〉/u∗ decreases by nearly 60% to about 0.6, which is less than 50% of the value for fluid particles. There is also a decrease in the vertical and horizontal component of the ejection velocity to values of 0.8 and 2.3, which are much less than their values in the saltation regime. We hypothesize that at the transition from saltation to suspension the ejection process changes quite sharply from being determined by impact collisions to being the result of aerodynamic lift forces and upward eddy motions.

Production process of zeolite X using alum sludge issued from drinking water treatment plants

2012 ◽  
Vol 1380 ◽  
Author(s):  
F. Espejel-Ayala ◽  
R. M. Ramírez Z.
Keyword(s):  
Drinking Water ◽  
Water Treatment ◽  
Production Process ◽  
Raw Materials ◽  
Drinking Water Treatment ◽  
Fecal Coliforms ◽  
Spherical Particles ◽  
Zeolite X ◽  
Water Treatment Plants ◽  
Alum Sludge

ABSTRACTThe present work describes a patent applied for registration at the IMPI (Instituto Mexicano de la Propiedad Industrial) of a production process of zeolite X using as raw materials alum sludges issued from drinking water treatment plants. Sludge sample was collected in a water drinking plant located northern Mexico City. The sample was dried and then physicochemical and microbiological analyses were carried out (metal content, main oxides content, mineralogical analysis, helminth eggs content, fecal coliforms). In accordance with its characterization, two main steps of the zeolites production process were performed: 1) alkaline fusion of alum sludge-NaOH mixture for increasing the dissolved precursor’s content and 2) alkaline hydrothermal treatment. Spherical particles of zeolite X were identified by SEM and XRD respectively. The best synthesized zeolite showed a CEC=2.11 meq/g, value being similar to the data reported for clinoptilolite (the most commonly zeolite used for water treatment in the removal of heavy metals). Thus, the synthesized zeolite X in this work can be used for the same purpose.

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