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Hydrodynamic Conditions (hydrodynamic + condition)

Distribution by Scientific Domains

Life Sciences	44%
Chemistry	27%
Physics and Astronomy	11%
Engineering	11%

Selected Abstracts

Influence of Hydrodynamic Conditions on Biofilm Behavior in a Methanogenic Inverse Turbulent Bed Reactor

BIOTECHNOLOGY PROGRESS, Issue 3 2003
S. Michaud
This paper presents a study about the influence of gas velocity on a methanogenic biofilm in an inverse turbulent bed reactor. Experimental results indicate a dynamic response of the growing attached biomass to the changes of hydrodynamic conditions, mainly attrition constraints. Short but intensive increases of gas velocity (Ug) are shown to induce more detachment than a high but constant gas flow rate. Hydrodynamic conditions control the composition of the growing biofilm in terms of cells and exocellular polymeric substances (EPS). The cell fraction within the biofilm (Rcell) was found to be inversely proportional to the gas velocity. The specific activity expressed in methane production rate or COD removal rate is higher in biofilms formed under high hydrodynamic constraints. The control of the hydrodynamic conditions in a biofilm reactor should make it possible to obtain a resistant and active biofilm. [source]

Regional hydrodynamic gene delivery to the rat liver with physiological volumes of DNA solution

THE JOURNAL OF GENE MEDICINE, Issue 6 2004
Xiaohong Zhang
Abstract Background The major barrier to the clinical application of hydrodynamic gene delivery to the liver is the large volume of fluid required using standard protocols. Regional hydrodynamic gene delivery via branches of the portal vein has not previously been reported, and we have evaluated this approach in a rat model. Methods The pGL3 plasmid with the luciferase reporter gene was used at 50 µg/ml in isotonic solutions, and was administered with a syringe pump for precise control of the hydrodynamic conditions evaluated. Gene expression was individually measured in six anatomically distinct liver lobes. The effect of systemic chloroquine to promote endocytic escape and a (Lys)16 -containing peptide to condense the DNA into ,100-nm nanoparticles was also evaluated. Results Hydrodynamic conditions for excellent gene delivery were obtained by using 3-ml volumes (,12 ml/kg) of isotonic DNA solution delivered at 24 ml/min to the right lateral lobe (,20% of the liver mass). Under these conditions, >95% of gene delivery usually occurred in the targeted right lateral lobe. Outflow obstruction was essential for gene delivery, both at optimal and at very low levels of hydrodynamic gene delivery. The use of systemic chloroquine to promote endocytic escape did not augment hydrodynamic gene delivery, while condensation of DNA in non-ionic isotonic solutions (5% dextrose) to nanoparticles of ,100 nm completely abolished gene delivery. Conclusions Regional hydrodynamic gene delivery via a branch of the portal vein offers a physiological model of liver gene therapy, for experimental and clinical application. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Influence of Hydrodynamic Conditions on Biofilm Behavior in a Methanogenic Inverse Turbulent Bed Reactor

Kinetic studies on the influence of temperature and growth rate history on crystal growth

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008
P. M. Martins
Abstract Crystallization experiments of sucrose were performed in a batch crystallizer to study the effect of temperature and growth rate history on the crystal growth kinetics. In one of the growth methods adopted, the isothermal volumetric growth rate (RV) is determined as a function of supersaturation (S) at 35, 40 and 45 ºC. In the other, crystals are allowed to grow at constant supersaturation by automatically controlling the solution temperature as the solute concentration decreased. Using the latter method RV is calculated as the solution is cooled. The obtained results are interpreted using empirical, engineering and fundamental perspectives of crystal growth. Firstly, the overall activation energy (EA) is determined from the empirical growth constants obtained in the isothermal method. The concept of falsified kinetics, widely used in chemical reaction engineering, is then extended to the crystal growth of sucrose in order to estimate the true activation energy (ET) from the diffusion-affected constant, EA. The differences found in the isothermal and constant supersaturation methods are explained from the viewpoint of the spiral nucleation mechanism, taking into account different crystal surface properties caused by the growth rate history in each method. Finally, the crystal growth curve obtained in the batch crystallizer at 40 ºC is compared with the one obtained in a fluidized bed crystallizer at the same temperature. Apparently divergent results are explained by the effects of crystal size, hydrodynamic conditions and growth rate history on the crystallization kinetics of sucrose. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

On the Initial Stages of Electrooxidation of Aqueous Maleic Acid on Bi-Doped PbO2

ELECTROANALYSIS, Issue 15 2007
Carlos Borras
Abstract Oxidation of maleic acid in aqueous solution on bismuth-doped lead oxide has been studied. The effects of hydrodynamic conditions on the oxidation rate have been identified. The number of electrons transferred during the initial stages of oxidation as well as the apparent heterogeneous rate constant was obtained from the combined analysis of rotating ring-disk currents and the decrease of concentration at constant potential, determined from UV-vis measurements. The number of electrons involved during electrochemical oxidation was found to be 12, indicating full mineralization to CO2, and the heterogeneous rate constant for oxidation at 1.6,V was 9.8×105,cm s,1. [source]

Effect of mass-transfer limitations on bioavailability of sorbed naphthalene in synthetic model soil matrices

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2000
Hendricus Mulder
Abstract External and internal mass-transfer resistances influencing the bioavailability of sorbed naphthalene in a synthetic model matrix for soil aggregates were investigated in batch experiments in mixed reactors. Amberlite® adsorption resins (XAD4 and XAD7) were used as the synthetic model for soil aggregates. The effect of hydrodynamic conditions in the slurry phase on the diffusive transport across a stagnant film surrounding the model particles was studied. In addition, a mechanistic model was developed based on mass balances, diffusion equations, a nonlinear sorption isotherm, and microbial degradation kinetics. Experimental results could be explained well with this model. In the absence of external transfer limitations, intraparticle effective diffusion coefficients of (3.55 ± 0.10) × 10,9 m2/s and (5.29 ± 0.86) × 10,10 m2/s were determined for naphthalene in Amberlite XAD4 and XAD7, respectively. [source]

Microscopic observation of aerobic granulation in sequential aerobic sludge blanket reactor

JOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2001
J.-H. Tay
Aims: This paper attempts to provide visual evidence of how aerobic granulation evolves in sequential aerobic sludge blanket reactors. Methods and Results: A series of experiments were conducted in two column-type sequential aerobic sludge reactors fed with glucose and acetate as sole carbon source, respectively. The evolution of aerobic granulation was monitored using image analysis and optical and scanning electron microscopy. The results indicated that the formation of aerobic granules was a gradual process from seed sludge to compact aggregates, further to granular sludge and finally to mature granules with the sequential operation proceeding. Glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density and microbial activity. However, the microbial diversity of the granules was associated with the carbon source supplied. In this work, an important aerobic starvation phase was identified during sequential operation cycles. It was found that periodical aerobic starvation was an effective trigger for microbial aggregation in the reactor and further strengthened cell,cell interaction to form dense aggregates, which was an essential step of granulation. The periodical starvation-induced aggregates would finally be shaped to granules by hydrodynamic shear and flow. Conclusions: Aerobic granules can be formed within 3 weeks in the systems. The periodical starvation and hydrodynamic conditions would play a crucial role in the granulation process. Significance and Impact of the Study: Aerobic granules have excellent physical characteristics as compared with conventional activated sludge flocs. This research could be helpful for the development of an aerobic granule-based novel type of reactor for handling high strength organic wastewater. [source]

Hydrodynamic considerations on optimal design of a three-phase airlift bioreactor with high solids loading

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2003
Jaroslav Klein
Abstract The hydrodynamic study of a three-phase airlift (TPAL) bioreactor with an enlarged gas,liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca-alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal-loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross-sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable. Copyright © 2003 Society of Chemical Industry [source]

Flocculation analysis and control system by laser diffractometry at industrial scale

AICHE JOURNAL, Issue 1 2008
Mohamed Bizi
Abstract The flocculant injection control system efficiency was evaluated on-site in an aggregate quarry, by means of laser diffraction and analysis of the size and texture of flocs. The configuration of the feed tank and the laser particle size measurement cell installed at the facility (280,000 t/year of aggregates) allowed characterization of flocs with particle size between 4.2 and 3473 ,m under hydrodynamic conditions that were highly favorable for the examination of large and very fragile flocs. Two days of analysis of the floc formation process along the path followed by the slurry showed that flocculation was optimal during standard operation of the facility when the flow rate of waste fines and concentrations of solids were close to those used to calibrate the flocculant injection control system. Conversely, when the concentration of solids in the flocculator feed slurry dropped by 57.3%, the flocculant dosing fluctuated during stabilization of the mechanism, the kinetics of flocculation slowed, the mean size of flocs arriving at the settling tank dropped by 69%, and the mode of smaller flocs shifted from 77.8 to 10.4 ,m in relation to normal operation. On-site analyses confirmed that the measurements made with laser diffraction (using a methodology developed in the laboratory) allow determination of the effects of conditioning on the characteristics of flocs in terms of particle size, porosity, density, and volume fraction in the slurry. Evolution of these characteristics according to the local parameters of conditioning (mean detention time, mean slurry velocity, and mean velocity gradient) provides a significant part of basic information necessary to a diagnosis of the operation of an industrial circuit of flocculation. © 2007 American Institute of Chemical Engineers AIChE J, 2008 [source]

160 Copepodology for the Phycologist with Apologies to G. E. Hutchenson

JOURNAL OF PHYCOLOGY, Issue 2003
P. A. Tester
Heterocapsa triquetra is one of the most common bloom forming dinoflagellates found in estuaries and near shore regions around the world. In order to bloom, H. triquetra optimizes a suite of factors including low grazing pressure, increased nutrient inputs, alternative nutrient sources, and favorable salinity and hydrodynamic conditions, as well as the negative factors of temperature-limited growth, short day lengths, and periods of transient light limitation. The prevailing environmental conditions associated its wintertime blooms are largely the result of atmospheric forcing. Low-pressure systems moved through coastal area at frequent intervals and are accompanied by low air temperatures and rainfall. Runoff following the rainfall events supplies nutrients critical for bloom initiation and development. Heterocapsa triquetra blooms can reach chl a levels >100 mg L,1 and cell densities between 1 to 6×106 L,1. As the blooms develop, nutrient inputs from the river became insufficient to meet growth demand and H. triquetra feeds mixotrophically, reducing competition from co-occurring phytoplankton. Cloud cover associated with the low-pressure systems light limit H. triquetra growth as do low temperatures. More importantly though, low temperatures limit micro and macrozooplankton populations to such an extent that grazing losses are minimal. [source]

Preparation of Hydroxyapatite Lathlike Particles Using High-Speed Dispersing Equipment

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2001
George C. Koumoulidis
Hydroxyapatite lathlike monocrystalline particles were prepared using high-energy dispersing equipment in combination with a pH shock-wave method. The Ca/P atomic ratios were very close to theoretical, and the acidic group content was very small. The particles were nonporous, with anisotropic crystal growth and average grain size ,140,1300 nm in length, ,20,100 nm in width, and ,10,40 nm in thickness. The high-speed dispersing equipment created the proper hydrodynamic conditions for lathlike particle growth in the [001] direction. The hydroxyapatite particles formed aggregates of 1,5 ,m average diameter. [source]

Investigating the Fate and Transport of Escherichia coli in the Charles River, Boston, Using High-Resolution Observation and Modeling,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2008
Ferdi L. Hellweger
Abstract:, The processes affecting the fate and transport of Escherichia coli in surface waters were investigated using high-resolution observation and modeling. The concentration patterns in Boston's Charles River were observed during four sampling events with a total of 757 samples, including two spatial surveys with two along-river (1,500 m length) and three across-river (600 m length) transects at approximately 25-m intervals, and two temporal surveys at a fixed location (Community Boating) over seven days at hourly intervals. The data reveal significant spatial and temporal structure at scales not resolved by typical monitoring programs. A mechanistic, time-variable, three-dimensional coupled hydrodynamic and water quality model was developed using the ECOMSED and RCA modeling frameworks. The computational grid consists of 3,066 grid cells with average length dimension of 25 m. Forcing functions include upstream and downstream boundary conditions, Stony Brook, and Muddy River (major tributaries) combined sewer overflow (CSO) and non-CSO discharge and wind. The model generally reproduces the observed spatial and temporal patterns. This includes the presence and absence of a plume in the study area under similar loading, but different hydrodynamic conditions caused by operation of the New Charles River Dam (downstream) and wind. The model also correctly predicts an episode of high concentrations at the time-series station following seven days of no rainfall. The model has an overall root mean square error (RMSE) of 250 CFU/100 ml and an error rate (above or below the USEPA-recommended single sample criteria value of 235 CFU/100 ml) of 9.4%. At the time series station, the model has an RMSE of 370 CFU/100 ml and an error rate of 15%. [source]

Maximising the fuel efficiency of engine oils: The role of tribology

LUBRICATION SCIENCE, Issue 3 2001
Stefan Korcek
Abstract Improvement of engine fuel efficiency is one of the most important goals of current automotive development. Maximising the contribution of engine oils to fuel efficiency is a very important part of this process. Engine friction modelling, based on fundamental tribological considerations, has shown that further engine friction improvements are possible through engine oil reformulation. This reformulation should minimise friction under hydrodynamic conditions through modification of the rheological properties of oils, and also minimise friction under mixed and boundary lubrication conditions through changes in the chemical composition of the oils. These improvements can be achieved by appropriate selection of a base oil as well as by the use of effective friction-reducing additive systems. A very important consideration in formulating these highly fuel-efficient oils is their ability to retain their fuel efficiency during the entire oil service interval. This paper describes the role of tribological research in the development and introduction of advanced fuel-efficient engine oils. [source]

Influence of dynamic structure on the microstructure formation of a steel surface in the electrolyte in a steady magnetic field

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004
Svetlana Gorobets
Abstract The periodic microfabrication effect of metal element surfaces in an electrolyte solution in an external steady magnetic field was investigated. Authors have shown that corrosion velocity and periodic microstructure formation on the metal element surface can be controlled by magnetic field application. Geometric configuration of periodic microstructure depends on metal element characteristics, electrolyte solution, treatment time, magnetic field magnitude and other parameters. Investigation results have shown possibility of magnetic field influence on hydrodynamic conditions and metal surface structure under its etching in the nitric acid solution. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) Reactor

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
Mike Winterbottoma
Abstract The liquid phase hydrogenation of 2-butyne-1,4-diol (B) to cis-2-butene-1,4,-diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir-Hinshelwood mechanism. L'hydrogénation en phase liquide du butyne-2-diol-1,4 B en cis-butène-2-diol-1,4 C a été étudiée dans un réacteur à monolithe (CDC). On a déterminé l'effet de la température, de la pression, des différents solvants et des vitesses d'alimentation de gaz et de liquide sur la vitesse de réaction et la sélectivité. Des mesures de distribution de temps de séjour ont été effectuées pour différentes conditions hydrodynamiques. L'écoulement du liquide est largement laminaire avec un film de paroi stagnant évident. On a observé que la sélectivité pour C augmentait avec la pression de l'hydrogène et s'approchait de 1 à des vitesses de gaz superficielles élevées et à conversion de B élevée (>95%) quand l'écoulement piston devient piston. Le régime d'écoulement a une influence sur la sélectivité et la cinétique, et celle-ci est bien décrite par un mécanisme à site double de Langmuir-Hinshelwood. [source]

Regional hydrodynamic gene delivery to the rat liver with physiological volumes of DNA solution

Experimental Results and Models for Solid/Liquid Fluidized Beds Involving Newtonian and Non-Newtonian Liquids

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2004
M. Aghajani
Fluidization technology relies almost solely on fluid/particle interaction wherein the liquid phase may exhibit Newtonian or non-Newtonian behavior. The steady motion of particles and the velocity-voidage relationship are the most important design parameters for fluidization, providing the basis for the prediction of heat and mass transfer coefficients and information on hydrodynamic conditions. A summary of the literature on particle settling velocity, minimum fluidization velocity and velocity voidage relationship is supplemented by new experimental results, which extend the range of investigated solid and liquid phase physical properties. Correlations for particle settling velocity and velocity-voidage relationship are developed and verified against experimental data. [source]