Suspension Mass Research Articles

Impact of diameter on carbon nanotube transport in sand

Carbon nanotubes are the subject of intense research due to their unique properties: light weight, significant strength, excellent conductivity, and outstanding chemical resistance. This has led to their application in a wide variety of industries (e.g., in composite materials). As a result of their potential impact to humans and ecosystems, there is increasing interest in understanding the factors that control the transport of carbon nanotubes in the environment, and of particular interest to this study, their transport in porous media. In this work, the transport behavior of multiwall carbon nanotubes (MWCNTs) is investigated in sand packed column experiments. To determine the importance of MWCNT diameter, experiments were conducted using four commercially available MWCNTs. Results suggest that smaller MWCNTs are less mobile than their larger counterparts, likely due to the increase in Brownian motion leading to more MWCNT collisions with the porous media with decreasing MWCNT size. A numerical model was used to simulate observed MWCNT transport behavior and facilitate comparison with published studies. These results suggest that careful characterization of MWCNT characteristics (i.e., dimensions and initial MWCNT mass in suspension) is essential to adequately interpret observed results. Results from this study suggest that MWCNTs may be mobile under conditions expected in subsurface aquifers.

Robust H∞ control of active vehicle suspension under non-stationary running

Due to complexity of the controlled objects, the selection of control strategies and algorithms in vehicle control system designs is an important task. Moreover, the control problem of automobile active suspensions has been become one of the important relevant investigations due to the constrained peculiarity and parameter uncertainty of mathematical models. In this study, after establishing the non-stationary road surface excitation model, a study on the active suspension control for non-stationary running condition was conducted using robust H∞ control and linear matrix inequality optimization. The dynamic equation of a two-degree-of-freedom quarter car model with parameter uncertainty was derived. The H∞ state feedback control strategy with time-domain hard constraints was proposed, and then was used to design the active suspension control system of the quarter car model. Time-domain analysis and parameter robustness analysis were carried out to evaluate the proposed controller stability. Simulation results show that the proposed control strategy has high systemic stability on the condition of non-stationary running and parameter uncertainty (including suspension mass, suspension stiffness and tire stiffness). The proposed control strategy can achieve a promising improvement on ride comfort and satisfy the requirements of dynamic suspension deflection, dynamic tire loads and required control forces within given constraints, as well as non-stationary running condition.

Gas-liquid-solid Operation of a High Aspect Ratio Self-ingesting Reactor

Gas-liquid stirred vessels are widely employed to carry out chemical reactions involving a gas reagent and a liquid phase. The usual way for introducing the gas stream into the liquid phase is through suitable distributors placed below the impeller. An interesting alternative is that of using “self ingesting” vessels where the headspace gas phase is injected and dispersed into the vessel through suitable surface vortices. In this work the performance of a Long Draft Tube Self-ingesting Reactor (LDTSR) dealing with three-phase (gas-liquid-solid) systems, is investigated. Preliminary experimental results on the effectiveness of this contactor for particle suspension and gas-liquid mass transfer performance in the three-phase system, are presented. Mass-transfer parameter kLa was measured by the recently introduced Simplified Dynamic Pressure Method (SDPM). It is found that the presence of low particle fractions causes a significant increase of the minimum speed required for vortex ingestion of the gas. Impeller pumping capacity and gas-liquid mass transfer coefficient are found to be affected by the presence of solid particles.

A Research of Vibration Signal Processing of Air Suspension System

Wavelet transform was utilized in vibrant signal processing of air suspension system. A dynamic model of 1/4 engineering vehicle with air suspension system was established. Road surface signal of B grade was input to the dynamic model. Vibrant acceleration curve of under spring mass and dynamic load curve of air suspension was gained. Noise signal of under spring mass acceleration and dynamic load of air suspension system were filtrated by wavelet decomposition. Vibrant acceleration signal of under spring mass and dynamic load signal of air suspension were extracted by wavelet reconstruction. It can provide a theoretical foundation for identifying dynamic load of air suspension system.

Influence of Suspension Mass Variation on Dynamic Characteristic of Magnetic Suspension System

Magnetic suspension system is nonlinear and unstable essentially. It is according to the principle of nonlinear system having same topological structure near the operation point with the linear system that linear control arithmetic for a nonlinear system is adopted. The system is easy to lose stabilize and diverge when subjected to interference or system parameters variation. Suspension mass is a key parameter of a magnetic suspension system and suspension mass variation has great influence on the dynamic characteristic of a magnetic suspension system. The influence of suspension mass variation on the dynamic characteristic of a magnetic suspension system under the PID control condition is discussed. The relationship between dynamic characteristic and structure as well as control parameters of the magnetic suspension system is reached by means of experimental method.

Assessment of mixing quality for an industrial pulp mixer using electrical resistance tomography

AbstractThe quality of mixing of a pulp suspension and chlorine dioxide by a static mixer in an industrial chlorine dioxide bleaching stage was evaluated using electrical resistance tomography (ERT) as a function of process operating conditions, including chemical flow rate, suspension flow rate, and suspension mass concentration. The uniformity was quantified by a mixing index based on the coefficient of variation of the individual conductivity values in each image pixel. An increase in the mixing index, indicating lower mixing quality, was observed when the chemical flow rate increased. In addition, the mixing quality decreased with a decrease in suspension flow rate. On the other hand, a decrease in the suspension mass concentration at a constant volumetric suspension flow rate gave better mixing quality. The results show that ERT can be used to evaluate industrial‐scale mixer performance and to monitor the changes in the mixing quality as a function of process operating conditions. The results are in good agreement with those in the literature based on other measurement techniques for similar mixer installations.

Bubble shape, gas flow and gas–liquid mass transfer in pulp fibre suspensions

AbstractGas–liquid mass transfer in pulp fibre suspensions in a batch‐operated bubble column is explained by observations of bubble size and shape made in a 2D column. Two pulp fibre suspensions (hardwood and softwood kraft) were studied over a range of suspension mass concentrations and gas flow rates. For a given gas flow rate, bubble size was found to increase as suspension concentration increased, moving from smaller spherical/elliptical bubbles to larger spherical‐capped/dimpled‐elliptical bubbles. At relatively low mass concentrations (Cm = 2–3% for the softwood and Cm ≅ 7% for the hardwood pulp) distinct bubbles were no longer observed in the suspension. Instead, a network of channels formed through which gas flowed. In the bubble column, the volumetric gas–liquid mass transfer rate, kLa, decreased with increasing suspension concentration. From the 2D studies, this occurred as bubble size and rise velocity increased, which would decrease overall bubble surface area and gas holdup in the column. A minimum in kLa occurred between Cm = 2% and 4% which depended on pulp type and was reached near the mass concentration where the flow channels first formed.

An alternative method to the traditional NASA hindlimb suspension model in mice

Animal models are used to induce atrophy and to evaluate interventions. The Morey‐Holton hindlimb unloading (HU) method is widely accepted.PURPOSEEvaluate an alternative to the Morey‐Holton HU technique in mice.METHODSForty adult female mice were HU for 14 days with (n=24) or without (n=16) recovery. Ambulatory controls (n=49) were used for comparison. A thin stainless steel wire was passed through the intervertebral disc spaces between the 5th and 7th sacral vertebrae and shaped into a ring from which the mice were suspended. The vertebral location was selected to appropriately balance the animal's body weight but not interfere with defecation. Success of this novel hindlimb unloading technique was assessed by percent body weight lost during suspension, soleus atrophy and adrenal mass.RESULTSBody mass of the mice prior to HU (24.8 ± 3.8g) was not significantly different immediately after HU (23.8 ± 2.8g), or after 3 days recovery (24.7 ± 2.5g. Soleus mass declined (−35.6%) with HU (p<0.001. Adrenal gland weights did not significantlyCONCLUSIONThe new method allows for ease of tail examination during suspension; decreases the likelihood of cyanotic, inflamed, and/or necrotic tails frequently observed with tail‐taping; and of mice chewing the traction tape (and becoming unsuspended). This tail‐ring method also ensures rapid recovery following HU. Support HD058834, MU Life Sciences Fellowship.

Gas holdup in pulp fibre suspensions: Gas voidage profiles in a batch-operated sparged tower

Abstract Gas holdup in a semi-batch operated slurry (pulp fibre suspension) bubble column was investigated for two pulp types (softwood and hardwood kraft pulps) over a range of suspension mass concentrations ( C m =0–9% by mass) and superficial gas velocities ( U g =0.0027–0.027 m/s). Three techniques were used: height difference between gassed and ungassed operation; pressure difference as a function column height; and electrical resistance tomography (ERT). Depending on the technique used the average, axial and radial holdup profiles could be determined. In the pulp suspensions, the ERT determined gas holdups correlated well with those determined using the differential height method. In water, the ERT determined gas holdups were significantly lower, but the agreement was significantly improved by increasing the background conductivity by adding 1 g/L salt to the water. This, however, reduced the overall gas holdup due to the effect of the electrolyte on bubble coalescence. Other differences between the three measurement techniques were attributed to limitations in the detection methods and the averaging procedures used to compare results. The presence of pulp fibres reduced gas-holdup at all gas flow rates and suspension concentrations studied and is attributed to increased bubble coalescence which increases bubble size and consequently bubble rise velocity through the suspension. Gas holdup (as determined by ERT) increased with column height. The radial gas profiles were non-uniform and more peaked than the corresponding water profiles. At low suspension concentrations this was attributed to asymmetric suspension recirculation within the column. As suspension concentration increased, channels formed in the suspension with the average void fraction leveling off to a plateau.

Aerobic Pollution Abatement of Pulp mill Effluent with the White Rot fungus <i>Phanerochaete chrysosporium</i> in Three-phase Fluidized Bed Bioreactor

The ligninolytic fungus Phanerochaete chrysosporium was used to treat the pulp and paper-mill effluent. It was pelletized and used for batch and continuous experiments in a two-litre fluidized bed bioreactor. The continuous experiment was initiated with concentrated effluent without any extra carbon source and the average removal of color was 3.8%. Then, it was fed with 50% diluted effluent which was enriched with glucose. At first, the glucose was consumed by the fungus, which is indicated by a COD removal of 38.5% and a 26.5% removal of color. This indicates the need for an extra carbon source for the fungal treatment. Using the mycelial mass in suspension, two experiments were carried out. The best results were obtained with 20% fungus and shaking of the effluent. During the last three days of the experiment using the mycelium mass the average removal of color, COD and BOD was 86.4%, 78.8% and 70.5%, respectively. The result indicates the potential of Phanerochaete chrysosporium for use in the treatment of pulp and paper-mill effluent. Keywords: Pulp and paper-mill effluent, fungal treatment, Phanerochaete chrysosporium . DOI = 10.3329/cerb.v13i1.2613 Chemical Engineering Research Bulletin 13 (2009) 13-16

Modeling aerosol suspension from soils and oceans as sources of micropollutants to air

Soil and marine aerosol suspension are two physical mass transfer processes that are not usually included in models describing fate and transport of environmental pollutants. Here, we review the literature on soil and marine aerosol suspension and estimate aerosol suspension mass transfer velocities for inclusion in multimedia models, as a global average and on a 1 × 1 scale. The yearly, global average mass transfer velocity for soil aerosol suspension is estimated to be 6 × 10 −10 m h −1, approximately an order of magnitude smaller than marine aerosol suspension, which is estimated to be 8 × 10 −9 m h −1. Monthly averages of these velocities can be as high as 10 −7 m h −1 and 10 −5 m h −1 for soil and marine aerosol suspension, respectively, depending on location. We use a unit-world multimedia model to analyze the relevance of these two suspension processes as a mechanism that enhances long-range atmospheric transport of pollutants. This is done by monitoring a metric of long-range transport potential, phi-one thousand ( ϕ 1000 ), that denotes the fraction of modeled emissions to air, water or soil in a source region that reaches a distance of 1000 km in air. We find that when the yearly, globally averaged mass transfer velocity is used, marine aerosol suspension increases ϕ 1000 only fractionally for both emissions to air and water. However, enrichment of substances in marine aerosols, or speciation between ionic and neutral forms in ocean water may increase the influence of this surface-to-air transfer process. Soil aerosol suspension can be the dominant process for soil-to-air transfer in an emission-to-soil scenario for certain substances that have a high affinity to soil. When a suspension mass transfer velocity near the maximum limit is used, soil suspension remains important if the emissions are made to soil, and marine aerosol suspension becomes important regardless of if emissions are made to air or water compartments. We recommend that multimedia models designed to assess the environmental fate and long-range transport behavior of substances with a range of chemical properties include both aerosol suspension processes, using the mass transfer velocities estimated here.

Effect of particulate aggregation in aquatic environments on the beam attenuation and its utility as a proxy for particulate mass

Marine aggregates, agglomerations of particles and dissolved materials, are an important particulate pool in aquatic environments, but their optical properties are not well understood. To improve understanding of the optical properties of aggregates, two related studies are presented. In the first, an in situ manipulation experiment is described, in which beam attenuation of undisturbed and sheared suspensions are compared. Results show that in the sheared treatment bulk particle size decreases and beam attenuation increases, consistent with the hypothesis that a significant fraction of mass in suspension is contained in fragile aggregates. Interestingly, the magnitude of increase in beam attenuation is less than expected if the aggregates are modeled as solid spheres. Motivated by this result, a second study is presented, in which marine aggregates are modeled to assess how the beam attenuation of aggregates differs from that of their constituent particles and from solid particles of the same mass. The model used is based on that of Latimer [Appl. Opt. 24, 3231 (1985)] and mass specific attenuation is compared with that based on homogeneous and solid particles, the standard model for aquatic particles. In the modeling we use recent research relating size and solid fraction of aquatic aggregates. In contrast with Mie theory, this model provides a rather size-insensitive mass specific attenuation for most relevant sizes. This insensitivity is consistent with the observations that mass specific beam-attenuation of marine particles is in the range 0.2-0.6m(2)/gr despite large variability in size distribution and composition across varied aquatic environments.

Particle migration and suspension structure in steady and oscillatory plane Poiseuille flow

A structure-tensor-based model is used to compute the microstructure and velocity field of concentrated suspensions of hard spheres in a fully developed, pressure-driven channel flow. The model is comprised of equations governing conservation of mass and momentum in the bulk suspension, conservation of particles, and conservation of momentum in the particle phase. The equations governing the relation between structure and stress in hard-sphere suspensions were developed previously and were shown to reproduce quantitatively results obtained by Stokesian dynamics simulations of linear shear flows. In nonhomogeneous, pressure-driven flows, the divergence of the particle contribution to the stress is nonzero and acts as a body force that causes particles to migrate across streamlines. Under steady conditions, the model predicts that the resulting migration causes particles to move to the center of the channel, where the concentration approaches the maximum packing for hard-sphere suspensions. In oscillatory flow, the behavior depends strongly on the amplitude of the strain. For oscillations with large strains, the particles migrate to the channel center. However, when the strain is small, the maximum concentration is located either at a position between the channel center and walls or, in the limit of very small strains, at the wall. The migration to the wall induced by small-strain oscillation occurs in conjunction with the suspension microstructure becoming ordered. This behavior agrees qualitatively with experimental observations reported in the literature. However, the predicted rate of migration toward the wall in the simulations is significantly slower than what is observed experimentally.

Characterization of axial flow impellers in pulp fibre suspensions

Two axial flow impellers commonly used in pulp agitation applications were characterized in hardwood and softwood low-consistency pulp fibre suspensions. The impellers operated in the laminar and transition-to-turbulence regimes with the suspension mass concentration significantly affecting both power and axial thrust numbers. Axial force numbers could be collapsed to a single operating curve using the yield stress Reynolds number, but the power number remained a function of suspension properties. CFD was used to model impeller flow using a Bingham approximation to describe the suspension rheology. Model agreement with the experimental measurements was generally good, with the values of N P and N f determined to within 24 and 16%, respectively. The error can be explained by the uncertainty in the rheological characterization of the pulp suspension, particularly the yield stress.

Cavern formation in pulp suspensions using side-entering axial-flow impellers

Pulp fibre suspensions display non-Newtonian rheology, including a yield stress. In mixing operations, this creates regions of active motion around the impellers with the cavern size affecting the quality of mixing attained. Due to the opacity of the suspensions, two non-invasive techniques were evaluated for determining cavern dimensions: electrical resistance tomography (ERT) and ultrasonic Doppler velocimetry (UDV), with ERT chosen for most tests due to the speed of data acquisition. Cavern volume as a function of impeller speed is reported for a range of mixing conditions (hardwood and softwood pulp, suspension mass concentrations from one to five percent, two impeller offsets from the wall, and three suspension height-to-chest diameter ratios). A scaled version of a commercial axial flow impeller was used in a standard side-entering configuration. Measured cavern diameters were compared against model predictions available in the literature. The discrepancy between experimental data and model predictions were significant and were attributed to interaction between the developing cavern and the vessel walls. An alternative model was developed for predicting cavern volume taking this interaction into account.

Scalable Selection of Hepatocyte- and Hepatocyte Precursor-Like Cells from Culture of Differentiating Transgenically Modified Murine Embryonic Stem Cells

Potential therapeutic applications of embryonic stem cell (ESC)-derived hepatocytes are limited by their relatively low output in differentiating ESC cultures, as well as by the danger of contamination with tumorigenic undifferentiated ESCs. To address these problems, we developed transgenic murine ESC clones possessing bicistronic expression vector that contains the alpha-fetoprotein gene promoter driving a cassette for the enhanced green "live" fluorescent reporter protein (eGFP) and a puromycin resistance gene. Under established culture conditions these clones allowed for both monitoring of differentiation and for puromycin selection of hepatocyte-committed cells in a suspension mass culture of transgenic ESC aggregates ("embryoid bodies" [EBs]). When plated on fibronectin, the selected eGFP-positive cells formed colonies, in which intensely proliferating hepatocyte precursor-like cells gave rise to morphologically differentiated cells expressing alpha-1-antitrypsin, alpha-fetoprotein, and albumin. A number of cells synthesized glycogen and in some of the cells cytokeratin 18 microfilaments were detected. Major hepatocyte marker genes were expressed in the culture, along with the gene and protein expression of stem/progenitor markers, suggesting the features of both hepatocyte precursors and more advanced differentiated cells. When cultured in suspension, the EB-derived puromycin-selected cells formed spheroids capable of outgrowing on an adhesive substrate, resembling the behavior of fetal mouse hepatic progenitor cells. The established system based on the highly efficient selection/purification procedure could be suitable for scalable generation of ESC-derived hepatocyte- and hepatocyte precursor-like cells and offers a potential in vitro source of cells for transplantation therapy of liver diseases, tissue engineering, and drug and toxicology screening.

Evaluation of a Sugarcane Bagasse Acid Hydrolysis Technology

AbstractConceptual process synthesis (CPS) is an important issue in chemical processing industries. In this paper, the general steps of the life cycle of an acid hydrolysis industrial project are evaluated. Chemical route synthesis, process development (experiments for kinetics and fluid dynamics) and process engineering (definition of basic equipment for economic evaluation) are all investigated. A mathematical model was used to generate the most favorable operating conditions for glucose and furfural production from sugarcane bagasse. The material and energy balances were performed by UNISim™ software. The suspension mass fraction and the thermal energy consumption are key issues to account for the profitable operation of the plant.

LPV Model Based Gain-scheduling Controller for a Full Vehicle Active Suspension System

This article addresses the design of a gain-scheduling type nonlinear controller for a full-vehicle active suspension system. The proposed method is based on a Linear Parameter Varying (LPV) model of the system. In this model, the variations in suspension deflection and mass are chosen as the scheduling parameters. During the simulations, the full-vehicle system that is controlled by the proposed method is tested with different road profiles, having high and low bumps, hollows and combinations of the two. The simulation results demonstrate that the proposed method successfully maximizes the ride comfort when suspension deflection is far away from the structural limits and minimizes the suspension deflection by changing its behavior when the suspension limits are reached.

On hydrodynamic optimisation of multi-channel counter-flow lamella settlers and separation efficiency of cohesive particles

In process and wastewater treatment applications, lamella settlers (LS) are well-known for their relatively high space-time-yield compared to ordinary settling basins. However, they are still characterised by relatively poor performance mainly due to poor hydrodynamic design and the application of incomprehensive models for the overall separation efficiency. These have both led to non-uniform feed distribution in multi-channel separators and poor capacity sizing causing some discontent in practical applications. In this work, a comprehensive description of the critical fluid-suspension-sediment interactions is proposed and used to interpret the results from secondary sludge separation using a CFD-flow optimised multi-channel counter-flow LS unit. Unlike contemporary models that are limited to particle-fluid interactions derived from single channel experiments, the suggested approach considers the effects of feed distribution and the consequent evolving hydrodynamic conditions on the particle population dynamics and deposit flow in a multi-channel separator. The overall separation efficiencies based on suspension mass balance show unique tendencies that are dependent on the feed rate, suspension concentration and the angle of inclination. For further clarity, a comparison is drawn between the LS and a hypothetical idealised batch sedimentation results to illuminate the effect of hydrodynamics and sediment flow on the average deposit flux and hence the overall system separation efficiency.

A Modified Differential Scanning Calorimetry Method for Determining Water Transport Properties in Biological Cells During the Freezing Process

A modified analytical and experimental method using differential scanning calorimeter (DSC) was applied to determine the cell water transport properties of human erythrocytes during the freezing process. Using DSC, samples containing human erythrocyte cell suspensions of human erythrocytes with different cytocrits were cooled to −40°C at slow cooling rates (5°C/min) after nucleation. It was shown that latent heat release from one unit mass of the cell suspension was a linear function of cytocrits (cell numbers), with a temperature-dependent slope and intercept. Based on the theoretical model, cell volumes were calculated from the slope and intercept at corresponding temperatures. Cell water transport properties (lpg,Ea) were next calculated by curve fitting of the cell volume change during the freezing process. The results revealed that, for human erythrocyte, Lpg (Tr = 273.15 K) is 0.10 ± 0.01 μm/min ċ atm and Ea is 279.1 ± 0.7 kJ/mol at the cooling rate of 5°C/min. For comparison, both DSC and cryomicro...