Maximum Surface Load Research Articles

An improved model for predicting froth recovery

In froth flotation, froth recovery is a key factor as it quantifies the effect that the froth has on the overall cell recovery. Froth recovery is affected by a number of variables, including froth stability, particle size and density, and the operating conditions of the flotation cell. Despite its importance, modelling froth recovery is challenging due to the large number of competing effects involved. In this paper, we present a model for froth recovery that takes into account the effects of detachment and subsequent transport of particles. The model is phenomenological and is derived from a set of coupled partial differential equations used to describe both liquid and particle motion within a froth. An analytical algebraic solution is obtained for the froth recovery by making a number of assumptions, which are discussed and justified in the paper. This model is related to a previous model produced by the authors, in which froth recovery was described in terms of a constant particle detachment fraction. Conversely, this enhanced model includes an improved description for particle detachment behaviour during coalescence events, allowing for a variable particle detachment fraction. The key parameters in the model are two dimensionless groups. The first group combines the particle settling velocity, the air addition rate and froth stability parameters such as air recovery and the change in bubble size over the froth, while the second key dimensionless group is the ratio of the surface loading on the incoming bubbles to the maximum surface loading. This model is compared to experimental results and is shown to accurately describe the evolution of the froth recovery behaviour down a bank of cells in response to the decreasing froth stability.

Development of a flotation recovery model with CFD predicted collision efficiency

In this study, a novel flotation recovery model based on a first-order kinetics is proposed. The collision efficiency in the recovery model was directly obtained from 3D computational fluid dynamics (CFD) simulations involving a single-bubble-multi-particle aggregate system with typical flotation operating conditions (bubble diameter of 1 mm and particles diameter of 30 μm). The effect of the fluctuating flow field on collision was accounted using a large eddy simulation (LES) turbulence model for two turbulence intensity cases namely 4% and 20%, respectively. It was noted that the collision efficiency decreased in the radial direction away from the symmetry axis of the bubble. The normalized equivalent critical radius K1 for the overall collision efficiency, was found to be optimum at the lower turbulence intensity of 4%. A maximum bubble surface loading, 0.142 was determined by fitting the model-predicted bubble velocity with available experimental data. With this maximum bubble surface loading constraint, the recovery model predicted two regimes namely a loading regime in the early flotation period and a saturated regime wherein the bubble loading capability was entirely exhausted. Simulation of a batch flotation system suggested that loss in bubble surface loading capacity occurred faster in a dense pulp compared to a dilute pulp system and the predicted recovery decreased with increasing solids concentration for the same gas volume fraction. Similar to the collision efficiency, the optimum recovery was obtained at Ti = 4%. Further, the model predicted recovery was compared to a lab scale coal flotation test and reasonable agreement was obtained.

An investigation on dynamic characteristics of herringbone planetary gear system with torsional flexibility between the left and right teeth of the sun gear

Herringbone planetary gear system (HPGS) has high power density and complex structure. The torsional flexibility of the left and right teeth of the sun gear is closely related to the dynamic characteristics of the HPGS. In this research, considering the coordination conditions of both sides torsional stiffness and axial slide of the sun gear, a new dynamic model of the HPGS considering the meshing phase difference between left and right teeth of the sun gear is developed based on the lumped-parameter method, and the influence mechanism of torsional stiffness and axial sliding is studied. Moreover, the dynamic parameters and dynamic characteristics of the HPGS are analyzed in the case of varying torsoinal stiffness and axial slide. The results show that the torsional stiffness of left and right teeth and the axial slide of sun gear have significant impacts on the dynamic parameters and dynamic mesh force response. With the increase of the torsional flexibility (the decrease the torsional stiffness), the sun gear and planet gear meshing stiffness and the maximum tooth surface load are both increased on the left side (input side) and decreased on the right side, but the main peak values and peak frequencies of dynamic response on both sides of the s-p meshing pairs decrease significantly. In addition, when the sun gear slides toward the output side axially, meshing stiffness and dynamic mesh force response main peak values decreased on the left side (input side) and increased on the right side, but the main resonance peaks frequencies keep the same.

Research on vibration and noise reduction of electric bus gearbox based on multi-objective optimization

Aiming at noise problem of electric bus gearbox, this paper presents a method of reducing vibration and noise by using multi-objective optimization algorithm, which can reduce noise excitation sources such as peak to peak value of transmission error and its harmonics and maximum tooth surface load. Considering that optimization process requires a lot of iteration operations, this paper establishes a calculation model for calculating transmission error, time-varying meshing stiffness and tooth surface load of gear pair, which considers both computation speed and accuracy. An improved multi-objective optimization algorithm is used to optimize gear micro-geometry, so as to determine the optimal micro-modification strategy quickly. Finally, aiming at the noise problem of an electric bus gearbox, firstly, noise excitation source is identified by means of order tracking analysis. Secondly, the method proposed in this paper is applied to reduce vibration and noise. Finally, the effectiveness of the proposed method is verified by bench test. The optimization results show that the proposed optimization method can reduce vibration and noise of gearbox effectively and rapidly.

A NUMERICAL PARAMETRIC STUDY ON THE LOAD CARRYING BEHAVIOR UNDER BENDING OF HONEYCOMB GIRDERS

A honeycomb girder (HCG) is defined by a mirror symmetric arrangement of two trapezoidal corrugated steel sheets (TCSS). Mechanical fasteners such as screws or rivets connect them. The high bending stiffness of HCGs provides the opportunity to span distances up to 14.0 m. Especially in the application as a cladding of roofs and facades of industrial steel-framed buildings this new construction type promises the potential to improve the resource and economic efficiency of these buildings. Former experimental investigations verified a numerical model. Based on this finite element method (FEM) model a parametric study on HCGs with an equidistant fastener arrangement has been carried out. By applying three design criteria on the numerical results the maximum characteristic surface loads for 360 HCG constellations have been determined. This paper investigates the influence of a graduated arrangement of mechanical fasteners in HCG systems on their maximum characteristic surface load.

Full Scale Evaluation on Anionic Polyacrylamide Applied in Ferric Flocs Sludge Treatment

The Polyacrylamide (PAM) is a frequently used flocculant for high concentration suspensions removal in water treatment characterized by the generation of large and dense flocs. In this paper, by using the anionic PAM as flocculant, a full-scale experimental study was carried out on flocculating ferric flocs sludge with pelleting flocculation blanket process under scale of 19~38 m3/h. The investigation aimed to optimum the dosage of the PAM and evaluate the application of the PAM in ferric flocs sludge treatment. The experimental results indicated that the increasing of PAM dosage could improve both outlet turbidity and thicken sludge concentration obviously, under the raw wastes concentration of 285~1022 mg/L, the system could achieve ideal operation effect with PAM dosage of 0.3~2.7 mg/L and treatment unit surface loading of 19~38 m3/m2·H. The investigation results also proved that there exists an approximately linear relationship between optimal PAM dosage and raw sludge concentration, that is, the increasing of raw sludge concentration would require synchronously rising of the optimal dosage. While the relationship between maximum surface loading and raw sludge concentration appeared negatively linear dependence, the maximum surface loading would decreased linearly with the increasing of inlet sludge concentration.

Lamella settlers for storm water treatment – performance and design recommendations

Three lamella settlers were monitored over a period of 4 years. The main objective was to determine removal efficiencies for total suspended solids and associated pollutants. For this purpose a new sampling method based on large volume solid samplers was developed allowing a detailed analysis of solids. With regard to total suspended solids the average removal efficiency of the plants range from 49 to 68%. Similar values could be achieved for phosphorus and heavy metals mainly because of the high portion of fine particles in treatment plants' influent. A clear dependency between solid removal efficiency and the parameters maximum surface load and influent concentration could be observed on a single event basis. The aggregation of all findings result in a recommended maximum design surface loading rate (SLR) of 4 m/h. A solid removal rate of 50%, which is defined as minimum long-term efficiency, can be achieved safely at this SLR. In addition to the definition of the maximum SLR, a proper dissipation of the inflow energy and an equal collection of the clear water above the lamellas turn out to be essential.

Pilot Scale Evaluation of Pellet Fluidized Bed Process for the Conditioning of Alum Sludge

As a burgeoning technology based on conventional clarifier technology, pellet fluidized bed (PFB) technology has been widely applied in kinds of high SS water treatment process. In this paper, PFB process was used to thicken the alum sludge in a water plant in south China with scale of 1.0~2.5m3/h. The experimental results showed that, increasing flocculent (PAM) dosage could decrease outlet turbidity, and average up pellets settling behavior. Under the experimental condition, there exist negatively linear relationship between process maximum flow rate which ranged from 1.6m3/h to 2.2 m3/h and raw sludge concentration. Moreover, because of the improvement of pH environment and flocs chemical structure, additional lime dosage would enhance maximum surface loading and save PAM dosage. The pilot scale experiment proved that by applying PFB, alum sludge conditioning could achieve satisfied results characterised by high surface loading, low outlet turbidity, and high concentration thicken sludge with fine dewaterability.

Using carrier surface loading to design heterotrophic denitrification reactors

This article tests the theory of using nitrate carrier surface loading (SL) as the primary design criterion for heterotrophic denitrification of drinking water. Two load‐increase tests (flow rate and nitrate concentration) with a pilot‐scale heterotrophic biofilm reactor identified that the maximum SL was approximately 6 g nitrogen/m2/d and was controlled by the effluent nitrite concentration. A comparison of SL values obtained from the literature also showed that the maximum SLs were similar for a wide range of heterotrophic denitrification processes. All of the SL values are consistent, even though the empty bed contact time and the nitrate volumetric loading varied widely. The experimental results confirm that the electron donor should be supplied at the stoichiometric requirement to achieve simultaneously low concentrations of nitrate, nitrite, and organic carbon.

Properties and Stability of Solid Lipid Particle Dispersions Based on Canola Stearin and Poloxamer 188

AbstractSolid lipid particles (SLP) are one strategy for encapsulating lipophilic molecules, including for controlled release and enhanced bioavailability applications. SLP based on fully hydrogenated canola stearin (CaSt, 5, 10, 20, and 30 wt%) and the non‐ionic surfactant Poloxamer 188 (P188, 0.0, 0.5, 1.0, 2.5, 5.0 and 10.0 wt%) were produced by high pressure melt homogenization using a microfluidizer. Spherical particles in the region of 140 nm were formed, depending on compostion and processing parameters. Surfactant concentration and pressure had a significant influence on particle diameter (P < 0.05), although number of homogenization cycles did not (P > 0.05). A maximum surfactant surface load of approximately 4 mg m−2 was observed and, at or above 2.5% P188, excess surfactant was present in the continuous phase after production. P188 had the effect of decreasing particle size and facilitating transitions from the α to the β polymorph (P < 0.05) both through surface nucleation and size reduction effects. A stability study of the 10% CaSt SLP with 0.0, 1.0, or 5.0% P188 revealed particle growth for the 0.0 and 1.0% P188 SLP, especially at 20 versus 4 °C, but no changes in the 5.0% P188 SLP, which were exclusively in the β form, at both temperatures for up to 240 days.

The adsorption of salicylic acid onto γ-alumina and kaolinite from solution in hexane studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT)

It was possible to determine the maximum loading of salicylic acid adsorbed onto γ-alumina and kaolinite clay after exposure to salicylic acid dissolved in hexane by examination using diffuse reflectance infrared Fourier transform infrared spectroscopy (DRIFTS). The maximum surface loading of salicylic acid (which resisted washing with fresh hexane) on γ-alumina was four times that observed using water as a solvent (approximately 3.0 compared with 0.7 molecules/nm 2). Washing the sample with water removed the organic which was in excess to the maximum level observed for samples prepared with aqueous solution. The spectra of samples prepared with a loading up to the maximum observed with aqueous solution showed no significant differences to those of samples where the organic had been adsorbed from hexane (with the same surface loading). New peaks were observed for loadings greater than 1 molecules/nm 2, but the salicylic acid was still present as carboxylate (with no clear evidence for the carbonyl group). Salicylic acid adsorbed more readily to the surface of kaolinite from solution in hexane than from aqueous solution (up to maximum average loading of 2 molecules/nm 2). Washing the samples with water removed the organic to a loading in the region of 0.2 molecules/nm 2, independent of the initial loading. Salicylic acid was adsorbed onto kaolinite as the carboxylate. The findings indicate that uptake is mediated by a surface water layer even in the absence of bulk water.

Competitive Adsorption of Water Soluble Plasma Proteins from Egg Yolk at the Oil/Water Interface

Water soluble plasma proteins were fractionated from hen's egg yolk, and the molecular weight and pI of the most abundant protein species were characterized with gel electrophoresis. The proteins were identified by mass spectrometry. The protein fraction was used to produce oil-in-water emulsions, both at various protein concentrations and at various pH values, and the surface load was determined through serum depletion. The competitive adsorption was studied through the determination of nonadsorbing species with gel electrophoresis. The results show that it was possible to form an oil-in-water emulsion for which droplet size and maximum surface load depended on the protein concentration and pH. Serum albumin and YGP40 adsorbed selectively at the oil/water interface throughout the pH range investigated, and for albumin the selectivity increased close to its pI. It is suggested that this selective adsorption is due to long hydrophobic stretches in the polypeptide chain, which are present in the selectively adsorbing species but absent in less adsorbing species.

A Study of the Kinetics of I2 Deposition on Stainless Steel Sampling Lines

In this study, deposition of I2(g) on stainless steel tubing was investigated. The purpose was to quantify the rate of iodine deposition and desorption, as well as to elucidate the underlying mechanisms. The parameters included I2 gas phase concentration (10–7 to 10–11 M), relative humidity (<25 to 100%), tube surface temperature (23 to 90°C), and steel type (SS-304L and SS-316L). Gaseous I2 was found to deposit through both physical and chemical adsorption with deposition velocities ranging from 5 × 10–3 to 1.0 cm/s. At concentrations below 10–9 M, I2 rapidly deposited and was easily desorbed, consistent with physical adsorption. At concentrations above 10–9 M and low relative humidity (<25%), both adsorption and desorption were slow, consistent with a slow chemisorption process. At high relative humidity (>75%), rapid chemisorption with pitting corrosion occurred. Under some conditions, adsorption became inhibited resulting in an apparent maximum surface loading. At high iodine concentration, high relative humidity, and tube temperatures of 40 or 60°C, no such inhibition occurred, resulting in rapid and continuous iodine adsorption.

Scaling Up of Plugflow-Dissolved Air Flotation

In a conventional rectangular flotation basin, acceptable separation efficiencies in excess of 90% can rarely be achieved with an operational surface loading in excess of 5 m/h, because of the great degree of dispersion, turbulence, and dead space present in the basin. A pilot-scale coaxial cylinder-type flotation column was built to fulfill the required plugflow performance, to reduce dead space, and to optimize the size. This coaxial plugflow flotation column was used in a pilot-scale flotation unit capable of handling 10 m3/h of wastewater, operating at a maximum surface loading of 12 m/h. Near-plugflow was established using baffles in the different sections. Flotation efficiencies in excess of 90% were obtained for industrial wastewater at high surface loadings (up to 12 m/h) and a low recycle ratio (9%). Efficiencies obtained in a traditional unit are significantly lower. Experience with the coaxial unit has enabled us to formulate scale-up guidelines for the plugflow dissolved air flotation, and the use of a modular design is required. The process can be described by a model using two parameters, i.e., the bubble-floc attachment efficiency, αpb, and the air-to-solid volume ratio in the agglomerate, β. Fitting experimental data and model predictions defines both model parameters, which are in line with the literature data and with values obtained in a laboratory-scale unit, thus justifying the possible use of small-scale experiments for scale-up purposes.

Dephosphorylation-induced structural changes in β-casein and its amphiphilic fragment in relation to emulsion properties

To promote the understanding of the relationship between emulsifying and molecular properties of proteins/peptides, intact β-casein (βCN) and its amphipathic fragment, i.e., βCN (1–105/107) were dephosphorylated. Dephosphorylation was found not to change significantly their emulsifying properties. Since it is known that the structure of proteins can change upon adsorption onto an interface, the secondary structure of intact β-casein, its amphipathic fragment, and their dephosphorylated forms, both in solution and after adsorption onto a hydrophobic teflon/water interface, were studied by far-UV circular dichroism spectroscopy. An increased content of secondary structure, especially α-helix, was found for all samples after adsorption onto teflon. Dephosphorylation increased the helix-forming propensity, especially for amphipathic fragment of β-casein. No influence of the secondary structure properties on the emulsion-forming and -stabilizing properties was observed, but a relationship between the maximum surface load and the emulsion-stabilizing properties was found.

The Skin Effect of the Anelastic Earth

—Assuming that the rheology of the earth’s crust is defined by stress-strain relations containing a memory mechanism, it is seen that the stress field and the maximum shear stress (mss), caused by elongated mountain ranges, are limited mostly to the crust. In a geological, relatively short time, where relaxation is reached, the mss assumes the depth distribution (2πx)exp(–2πx) where x is the depth h measured in units of wavelength w of the mountain range; the mss reaches its maximum value, of about 1/3 the surface load, at the depth x = 1/2π (x = h/w). Contrary to the case of the perfectly elastic earth model, where the mss at the surface is about 0.25 the maximum surface load, in the case of the anelastic earth model the mss is asymptotically nil at the surface and for depths larger than w, the mss is less than 1.2% the maximum surface load. It is seen that the relaxation of the medium causes a rotation of the planes of the mss in a layer near the surface and that, in the case when the surface load is applied periodically, there is a phase shift between the surface load and the stress at depth which is less than four days when the period is one year; it is smaller for shorter periods. It is also seen that the creation of reservoirs lasting a finite time causes a small variation of the mss in the crust which, when the reservoir is removed, leaves a residual mss with maximum at the surface and decreasing exponentially with depth; for a load lasting one year it takes 250 days to reduce to 40% the stress at depth. As a consequence of the residual mss, caused by the load of the topography, after earthquakes the local mss will not drop to zero; this decreases the time required by tectonic forces to release the next earthquake and increases the rate of seismicity.

Reducing dust, lead, dust mites, bacteria, and fungi in carpets by vacuuming

Old carpets may be reservoirs of dust, lead (Pb), and dust mite allergen. The purpose of this study was to determine if the dust, Pb, dust mite allergen, bacteria, and fungi on the surface of carpets could be reduced by 90% in 1 week with the use of a Hoover Self Propelled Vacuum with Embedded Dirt Finder (HSPF). A high-volume surface sampler (HVS3) was used to measure surface dust and pollutants before and after the use of the HSPF to remove deep dust in carpets 12 to 20 years old in nine middle-class homes and two small offices. The minimum, median, and maximum surface loading for the first and final samples are as follows: first fine dust loading: min 0.32 g/m2, max 14.4 g/m2, median 1.30 g/m2; final fine dust loading: min 0.019 g/m2, max 0.289 g/m2, median 0.102 g/m2; first Pb loading: min 38 &mgr;g/m2, max 3,871 &mgr;g/m2, median 471 &mgr;g/m2; final Pb loading: min 13 &mgr;g/m2, max 2,023 &mgr;g/m2, median 86 &mgr;g/m2; first mite loading: min 0.11 &mgr;g/m2, max 12. 88 &mgr;g/m2, median 2.82 &mgr;g/m2; final mite loading: min 0.06 &mgr;g/m2, max 3.67 &mgr;g/m2, median 0.28 &mgr;g/m2. Data were insufficient to determine if the loadings of bacteria and fungi were reduced a similar amount. Six to 45 min/m2 of vacuuming with the HSPF removed deep dust from these carpets. The median surface loadings of fine dust, Pb, and dust mite allergen in these 11 carpets were reduced by 91, 82, and 94%, respectively, in 1 to 15 h of vacuuming. The loading of the deep dust collected with the HSPF ranged from 8 to 171 g/m2 with a median of 66 g/m2.

The adsorption-induced secondary structure of β-casein and of distinct parts of its sequence in relation to foam and emulsion properties

Changes in the secondary structure upon adsorption of β-casein (βCN) and of distinct parts of its sequence were investigated by far-ultraviolet circular dichroism in order to find suggested relationships with foam and emulsion-forming and -stabilising properties of the same protein/peptides. A teflon/water interface was used as a model system for foam and emulsion interfaces. The maximum surface loads of β-casein and its derived peptides were investigated. The main secondary structure element of all samples in solution was the unordered random coil, but upon adsorption ordered structure, especially α-helix, was induced. At lower pH more ordered structure was induced, just as at lower ionic strength. Apparently, both hydrophobic and hydrophilic groups influence the change of secondary structure induced at a hydrophobic interface. The results suggest that the hydrophobic C-terminal half of βCN accounted for the high maximum surface load on teflon, while the N-terminal half of βCN seemed to be responsible for the secondary structure induction upon adsorption. A relation between the maximum surface load and the foam-stabilising properties was found, but an influence of the secondary structure properties on the foam and emulsion-forming and -stabilising properties was not observed.

Cutinase binding and activity at the triolein–water interface monitored by oil drop tensiometry

Changes of the oil–water interfacial tension resulting from binding of Fusarium solani pisi cutinase and subsequent lipid hydrolysis were investigated using the oil drop technique. An ELISA was developed to determine the amount of cutinase bound to the triolein–water interface after biotinylation of the enzyme. Cutinase irreversibly adsorbs to a maximum value of about 2 mg/m 2. A minimal specific activity of 110 μmol/min/mg was calculated for cutinase acting on a single oil droplet, which is close to the activity found for triglyceride emulsions. At a maximum surface load cutinase could generate one monolayer of fatty acid products per second at the interface. It was found that oleic acid rapidly dissolves into the oil phase under the conditions used. The interfacial tension measured reflects the adsorption of cutinase to the oil droplet and also responds to the fate of the hydrolysis products. A model is presented that describes the catalytic events at the oil–water interface during lipid hydrolysis.