Decreasing Particle Concentration Research Articles

PEGylated Gold Nanoparticle Toxicity in Cardiomyocytes: Assessment of Size, Concentration, and Time Dependency.

Gold Nanoparticles (GNPs) have shown promising capabilities for use in many in-vivo applications such as gene and drug delivery, photothermal ablation of tumors, and tracking in many imaging modalities. Yet GNPs have thus far had limited use in cardiovascular medicine. Polyethylene glycol functionalized (PEGylated) GNPs have been extensively studied in a wide array of in vitro and in vivo models with results showing no apparent toxicity, but to our knowledge an investigation has never been performed to determine direct cardiomyocyte toxicity. In this study, we assessed if PEGylated GNPs exhibited direct toxicity to a primary culture of neonatal rat cardiomyocytes in order to establish PEGylated GNPs for potential future use in cardiovascular medicine applications. We present novel results that demonstrate both a particle size and concentration dependent relationship on cell viability. Cell viability was found to be significantly enhanced for many concentrations and sizes as compared to the control and increased linearly as a function of particle diameter. Additionally, viability increased in a parabolically dependent manner as a function of decreasing particle concentration. These new results could advance understanding of nanoparticle-cell interactions and lead to the development of new applications involving the use of gold nanoparticles in cardiovascular medicine.

Glacier sediment plumes in small bays on the Danco Coast, Antarctic Peninsula

AbstractGlacimarine sedimentary environments provide information about climate and oceanographic evolution in the Antarctic Peninsula. This study focuses on the generation of sediment plumes from glaciers. In February 2013 and 2014, two Chilean Antarctic Institute (INACH) Scientific Expeditions were carried out on board the Chilean Navy vessel Aquiles. Five relatively small bays were visited: Curtiss Bay, Recess Cove, Beaupre Cove, Paradise Harbour/Oscar Cove and Salvesen bay. Hydrography and turbidity profiling was carried out up to 100 m depth using an SBE19 Plus-V2 CTD-T. In general, the results showed sediment plumes at two levels: an upper plume from the surface up to 10 m deep and a deeper plume at 40–100 m. These plumes were identified by higher turbidity concentrations and their association with colder water tongues. The deeper plume tended to remain below the 1027.5 kg m-3 isopycnal and extended ~4 km from the glacier, maintaining its shape with a gradually decreasing particle concentration. This longitudinal extension was favoured by ebb tides. The characteristics of the sediment plumes may be influenced by the heat input from water masses. The contribution of the sediments from these small bay systems could play an important role in regional sedimentary processes.

Charging and separation behavior of gluten–starch mixtures assessed with a custom-built electrostatic separator

Electrostatic separation is a novel and sustainable process for dry separation of food ingredients. To establish guidelines for electrostatic separation, well-defined charging and separation experiments of model mixtures prepared from wheat gluten and starch were carried out. For this a custom-built bench-scale electrostatic separator was developed. Charging behavior of mixtures improved with decreasing particle concentration and increasing gas flow rate, which was similar compared to charging behavior of single materials. However, the charge of mixtures was not simply the sum of the charge of single materials because particle–particle interactions also largely influence the charging. Separation efficiencies for mixtures were found lower than could be expected on the basis of behavior of single materials in the equipment. This was attributed to formation of agglomerates by particles having opposite charge, which was further confirmed by the observation that dispersibility of the mixtures was poorer than for the single materials. Agglomeration of particles during electrostatic separation can be minimized by using high gas flow velocity, low feed dosing and higher field strength.

Inhomogeneity in breakup of suspensions

During pinch-off of a non-Brownian suspension or a slurry, the particle concentration in the pinch-off zone is found to decrease as its minimal diameter decreases, resulting in a pure liquid interstitial fluid. Snapshot images feature three successive stages during suspension pinch-off, referred to as suspension, transition, and liquid stages. We focus on the characteristics of the final liquid stage. Particles are jammed above and below the pinch-off zone when the minimal diameter of the thread created in pinch-off approaches the particle size. The volume of pure liquid is found to be proportional to the particle size and increases with decreasing particle concentration. The particle size and concentration also influence strongly the length of the thread in the liquid stage, the properties of which are quantified and analyzed.

Computational Fluid Dynamics (CFD)–Discrete Element Method (DEM) Simulation of Gas–Solid Turbulent Flow in a Cylindrical Spouted Bed with a Conical Base

Three dimensionally coupled computational fluid dynamics (CFD) and discrete element method (DEM) were studied for modeling the turbulent gas–solid flow in a cylindrical spouted bed with a conical base. The particle motion was modeled by the DEM, and the gas motion was modeled by the k–ε two-equation turbulent model. Drag force, contact force, Saffman lift force, Magnus lift force, and gravitational force acting on an individual particle were considered in establishing the mathematical models. Calculations on the cylindrical spouted bed with an inside diameter of 152 mm, a height of 700 mm, and a conical base of 60° were carried out. Experimental results from the University of British Columbia [He, Y. L.; Qin, S. Z.; Lim, C. J.; Grace, J. R.Particle velocity profiles and solid flow patterns in spouted beds. Can. J. Chem. Eng. 1994, 72 (8), 561−568] were used as a numerical benchmark to quantitatively assess the simulations. Despite the somewhat larger simulated spout diameter found, the present simulated results were in well-agreement with the experiments. The average error of particle velocity was less than 15%. On the basis of the simulations, the development of spout with time and distributions of particle velocity, particle concentration, and spout diameters at various spouting gas velocities were obtained. Besides, detailed information on particle collision and drag forces adding on particles at different bed regions was discussed. The results showed that particle velocity gradually decreases along the radial direction, with speeds of particles moving upward decreasing with an increasing bed height, while in the annulus region, particles decelerate downward in the cylindrical section and then accelerate in the conical base. The particle concentration increases in the spout region, is kept nearly constant in the annulus region, but decreases in the fountain region along the radial axis. An increasing bed height leads to an increasing particle concentration in the spout region but a decreasing particle concentration in the annulus and fountain regions. Particle collision number, particle turbulent intensity, and the transient collision force and drag force are significantly larger in the spout region than in the annulus and fountain regions. Besides, an increasing spouting gas velocity leads to a remarkable increased speed of particles moving upward or downward, spout diameter, particle collision, drag force, and particle turbulent intensity but decreased particle concentrations.

Effect of Sample Concentration on the Determination of the Anisotropy Constant of Magnetic Nanoparticles

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Techniques such as equilibrium (DC) and dynamic (AC) magnetic measurements have been used to determine the anisotropy constant of a variety of magnetic nanoparticles, obtaining values that are often an order of magnitude higher than the corresponding bulk material. Unfortunately, the effect of particle–particle interactions is often neglected, hence the reported values are an effective collective parameter , rather than an intrinsic property. In this study we used DC and AC magnetic measurements to determine the anisotropy constant of magnetic nanoparticles fixed in a cross-linked polymer matrix. We used nanoparticle concentrations of 0.1%, 1%, 6%, and 33%(w/w) in order to determine the effect of concentration, and hence interactions, on the value determined for the anisotropy constant. The effect of interaction on determining the magnetocrystalline anisotropy constant was accounted for by using the Néel and Vogel-Fulcher relaxation models, the latter with an effective interaction temperature determined from independent measurements. A decrease in the anisotropy constant determined from these measurements was observed with decreasing particle concentration from <formula formulatype="inline"><tex Notation="TeX">${\sim} 6100$</tex></formula> kerg/cm<formula formulatype="inline"><tex Notation="TeX">$^{3}$</tex></formula> to <formula formulatype="inline"><tex Notation="TeX">${\sim} 500$</tex></formula> kerg/cm<formula formulatype="inline"><tex Notation="TeX">$^{3}$</tex></formula> using the Vogel-Fulcher model and from <formula formulatype="inline"><tex Notation="TeX">${\sim} 9100$</tex></formula> kerg/cm<formula formulatype="inline"><tex Notation="TeX">$^{3}$</tex> </formula> to <formula formulatype="inline"><tex Notation="TeX">${\sim} 1100$</tex> </formula> kerg/cm<formula formulatype="inline"><tex Notation="TeX">$^{3}$</tex> </formula> using the Néel model. The values obtained for the most dilute samples using the Vogel-Fulcher model are of comparable magnitude to bulk values for magnetite. More importantly, the value of <formula formulatype="inline"> <tex Notation="TeX">$\tau_{0}$</tex></formula> obtained from AC susceptibility decreased from <formula formulatype="inline"><tex Notation="TeX">$10^{- 32}$</tex> </formula> to <formula formulatype="inline"><tex Notation="TeX">$10^{- 9}$</tex> </formula> s with decreasing particle concentration. As <formula formulatype="inline"> <tex Notation="TeX">$\tau_{0}$</tex></formula> is expected to be of the order of <formula formulatype="inline"><tex Notation="TeX">$10^{- 9}$</tex></formula> s, these results indicate that the value of magnetic anisotropy determined for the dilute sample represents an intrinsic rather than effective property. These measurements and analysis illustrate the importance of particle concentration/interactions in determining the intrinsic magnetic properties of nanoparticles, particularly the anisotropy constant . </para>

Effect of grinding conditions on mechanochemical grafting of poly(1-vinyl-2-pyrrolidone) onto quartz particles

Grinding of quartz in an aqueous solution of 1-vinyl-2-pyrrolidone (VP) in a stirred media mill results in grafting of poly(1-vinyl-2-pyrrolidone) (PVP) onto the quartz particles as proven by FTIR-spectroscopy. The grinding kinetics, the particle size of the final product and the amount of PVP grafted onto the silica particles depend on grinding conditions like VP and quartz concentration, pH and size of grinding media. The grinding kinetics becomes slower in the presence of VP due to the damping effect of the forming PVP chains. The final particle size, however, is almost independent on VP concentration. The amount of PVP grafted onto the silica particles ground for 12h increases with growing VP concentration because the amount of adsorbed VP and the polymerization rate increase with growing VP concentration.The primary particle size and the kinetics of particle breakage do not depend on the pH-value of the dispersing medium, whereas the degree of agglomeration of the particles decreases with increasing pH-value of the medium. Under alkaline conditions, however, less PVP is grafted onto the quartz particles than under neutral or strong acidic conditions. The reasons for these effects are pH-dependent interactions between the grafted PVP chains and the surface hydroxyl groups on the quartz particles. If the quartz concentration in the suspension decreases the grinding kinetics becomes much faster because the specific energy input increases with decreasing particle concentration if the other process parameters are kept constant. For a very low quartz concentration (1wt.%), however, after 7h of grinding the particle size measured by dynamic light scattering starts to increase with grinding time. SEM investigations reveal that grinding of 1wt.% quartz in aqueous VP solution for longer than 7h results in the formation of plate-like particles.

Bioaccessibility of Platinum Group Elements in Automotive Catalytic Converter Particulates

The bioaccessibilities of the platinum group elements (PGE): Rh, Pd, and Pt; and the catalyzator poison, Pb, have been determined in particles derived from milled automotive catalytic converters using a physiologically based extraction test (PBET) that simulates, sequentially, the chemical conditions encountered in the human stomach and intestine. PGE accessibility, relative to total metal concentration, was generally less than a few percent, but increased in the stomach with decreasing pH (from 4 to 1) and/or increasing chloride concentration, and with decreasing particle concentration. In most cases, bioaccessibility increased from the acidic stomach to the neutral, carbonate-rich intestine. Bioaccessibility of Pb displayed similar pH and particle concentration dependencies to PGE in the stomach, but this metal exhibited significantly greater mobilization (up to 80%) overall and a reduction in accessibility from the stomach to intestine. Reaction kinetics of PGE dissolution in the stomach at pH 2.5 were modeled using a combined surface reaction-diffusion controlled mechanism with rate constants of 0.068, 0.031, and 0.015 (microg L(-1))(-1) h(-1) for Rh, Pd, and Pt, respectively. For Pb, however, mobilization proceeded via a different mechanism whose time-dependence was fitted with an empirical, logarithmic equation. Overall, PGE bioaccessibility appeared to be controlled by dissolution rates of metallic nanoparticles in the stomach, and solubility and kinetic constraints on inorganic species (chlorides, hydroxychlorides, and carbanatochlorides) and undefined organic complexes formed in the simulated gastrointestinal tract. Further studies are required to elucidate any effects engendered by the long-term oral exposure of small quantities of these species.

Drag on a sphere in a spherical dispersion containing Carreau fluid

The drag on a rigid sphere in a spherical dispersion containing Carreau fluid is investigated theoretically based on a free surface cell model for Reynolds number in the range [0.1,100], Carreau number in the range [0,10], the power-law index in the range [0.3,1], and the void fraction in the range [0.271,0.999]. The influences of the particle concentration, the nature of the Carreau fluid, and Reynolds number, on the drag coefficient are examined. We show that the drag coefficient declines with the decreasing particle concentration, and the reversal of the flow field in the rear region of a sphere is enhanced by the shear-thinning nature of the fluid. An empirical relation, which correlates the drag coefficient with the void fraction (= 1 − particle concentration), the nature of the Carreau fluid, and Reynolds number, is proposed.

Freeze casting of porous hydroxyapatite scaffolds. I. Processing and general microstructure

Freeze casting of aqueous suspensions on a cold substrate was investigated as a method for preparing hydroxyapatite (HA) scaffolds with unidirectional porosity. In the present paper, we report on the ability to manipulate the microstructure of freeze-cast constructs by controlling the processing parameters. Constructs prepared from aqueous suspensions (5-20 volume percent particles) on a steel substrate at -20 degrees C had a lamellar-type microstructure, consisting of plate-like HA and unidirectional pores oriented in the direction of freezing. Sintering for 3 h at 1350 degrees C produced constructs with dense HA lamellas, porosity of approximately 50%, and inter-lamellar pore widths of 5-30 microm. The thickness of the HA lamellas decreased but the width of the pores increased with decreasing particle concentration. Decreasing the substrate temperature from -20 degrees C to -196 degrees C produced a finer lamellar microstructure. The use of water-glycerol mixtures (20 wt % glycerol) as the solvent in the suspension resulted in the production of finer pores (1-10 microm) and a larger number of dendritic growth connecting the HA lamellas. On the other hand, the use of water-dioxane mixtures (60 wt % dioxane) produced a cellular-type microstructure with larger pores (90-110 microm). The ability to produce a uniaxial microstructure and its manipulation by controlling the processing parameters indicate the potential of the present freeze casting route for the production of scaffolds for bone tissue engineering applications.

Number‐size distributions of free tropospheric aerosol particles at Mt. Norikura, Japan: Effects of precipitation and air mass transportation pathways

Number‐size distributions of free tropospheric aerosol particles of 9–300‐nm diameter were observed at Mt. Norikura (36.1°N, 137.5°E, 2770 m a.s.l.) in central Japan in August and September 2002. We observed two distinct air masses transported from over the Pacific Ocean and continental Asia. Size distributions of aerosol particles were analyzed in terms of their relation to the air mass transportation pathway, cumulative precipitation amount in the air mass for the last 24 h, and local precipitation rate. Particle concentrations of the accumulation mode range (100–300 nm) decreased by an order of magnitude when cumulative precipitation amount increased from 0 to 20 mm. The cumulative precipitation amount is suggested as an important factor to modify the size distribution by decreasing particle concentration. Considering data for air masses without experience of precipitation scavenging before arrival, concentrations of accumulation mode particles were almost identical (approximately 400 cm−3) in air masses transported from over the Pacific Ocean and continental Asia. Concentration of Aitken mode particles was high (890 cm−3 as a median value) in the air mass subsiding from over the subtropical Pacific Ocean (&gt; 4 km a.s.l.). Based on the relationship with the controlling factors described above, this study provides number‐size distribution parameters of free tropospheric aerosol particles in the west Pacific area.

Removal of platinum group elements in an estuarine turbidity maximum

The particle–water interactions of Rh(III), Pd(II) and Pt(IV) (or platinum group elements, PGE) have been studied in an estuarine turbidity maximum (Tamar, south west England) by spiking suspensions with mixed standards to concentrations of 10 μg L − 1 and analysing acidified filtrates and digested particles by ICP–MS. Adsorption of PGE to estuarine particles was defined by the Frendlich equation, with Freundlich constants on the order of a few thousand mL g − 1 and the degree of convexity between about 0.7 and 0.9. Along an axial transect of the turbidity maximum, all metals exhibited increasing removal from the aqueous phase with increasing particle concentration. However, for a given metal, removal could not be accounted for by a single sediment–water distribution coefficient, K D, since the magnitude of this coefficient decreased with increasing particle concentration. This reduction in K D could not be accounted for by the non-linearity of the adsorption isotherms. However, it was partly replicated in experiments in which different quantities of the same, fractionated and filtered sediment were added to filtered river water, and was greatly accentuated when the experiment was repeated after sediment suspensions had been allowed to settle for different time periods, resulting in a reduction in net particle size with decreasing particle concentration. Thus, variations in both particle size (and presumably sorptive character) and particle concentration (through some undefined mechanism or artefact) appear to be responsible for controlling the partitioning, hence removal of PGE from the estuarine water column. The results of this study significantly improve our understanding of and ability to predict the likely transport and fate of PGE in an estuarine turbidity maximum, once these elements have been mobilised from secondary sources such as road dust.

The dispersion-stability diagram of boehmite nanoparticles in aqueous AOT solutions

The dispersion stability of hydrophilic boehmite nanoparticles in aqueous sodium bis(2-ethylhexyl) sulfosuccinate (AOT) solutions was studied in a wide range of particle and surfactant concentrations. The two experimental parameters significantly influence the dispersion stability and span a stability diagram. With increasing surfactant concentration and decreasing particle concentration, the system changes from stable via moderately stable to unstable and back. In concentrated AOT solutions, fully redispersed particles are present, stabilized by a surfactant bilayer or admicelles on the surface. The redispersion can be reversibly induced by dilution or concentration of the samples. The positions of two transitions, namely for complete precipitation and for beginning redispersion, can be fitted accurately using a simple model based on H-type adsorption and including the specific surface area of the particle and the molar area of the surfactant. The transitions are controlled by the concentration of free surfactant molecules in solution as well as the saturation surface coverage and were corroborated by turbidity measurements.

Interaction effects on the coercivity and fluctuation field in granular powder magnetic systems

In this paper, the interaction effects on the coercivity ( H c) and Fluctuation fields ( H f) of doped barium–ferrite particles at different concentrations are examined. Samples with different concentrations are prepared by mixing the original powder with a non-magnetic host. Coercivity measurements at different particle concentrations showed that for high concentrations, the coercivity decreases with decreasing particle concentration. This attributed to the reduction of positive dipolar interactions that arise from stacking effects. However, at very low concentrations, H c is observed to increase with decreasing concentration due to the reduction in the predominant negative dipolar interactions. Measurements of fluctuation field using the waiting time technique show that the behavior of H f at different concentrations is greatly influenced by particle interactions. This result can be understood since H f is governed by the distribution of effective energy barriers F(Δ E eff).

Theoretical calculation of the reduced viscosity of aqueous suspensions of charged spherical particles

AbstractThe origin of the variety of characteristics of the reduced viscosity of aqueous suspensions of charged spherical particles has been an unsolved problem. To solve the problem, the reduced viscosity due to interparticle electrostatic interactions between charged spherical particles are calculated as a function of particle concentration with scanning various parameters, such as diameter of particle, number of charges per particle, and added‐salt concentration. The result successfully reproduced the variety of characteristics. Of all the scanned parameters, the diameter of the particle has a significant role to display the variety of characteristics when other parameters are fixed. When the diameter is very small (∼0 Å), the calculated reduced viscosity of aqueous suspensions of charged spherical particles increases with decreasing particle concentration and it shows a maximum. This behavior is very similar to the reduced viscosity of linear chain polyelectrolyte solutions. Whereas, when the diameter is large (&gt;2000 Å), the calculated reduced viscosity decreases with decreasing particle concentration and it does not show a maximum. When the diameter is &lt;1000 Å, the calculated reduced viscosity shows both the maximum and minimum. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1068–1074, 2004

Effect of suspended clay on the feeding and growth of bacterivorous flagellates and ciliates

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 34:181-192 (2004) - doi:10.3354/ame034181 Effect of suspended clay on the feeding and growth of bacterivorous flagellates and ciliates Jens Boenigk1,2,*, Gianfranco Novarino2 1Institute of Limnology, Austrian Academy of Sciences, Mondseestr. 9, 5310 Mondsee, Austria 2The Natural History Museum, Department of Zoology, Protista & Mathematics Division, Cromwell Road, London SW7 5BD, UK *Email: jens.boenigk@oeaw.ac.at ABSTRACT: The effect of suspended fine sediment on protist growth and behaviour was investigated using kaolinite-dominated clay with a mean grain size of 0.9 μm. Suspended sediment particles about the same size as potential food items of picovorous organisms, i.e. bacteria, were expected to interfere with feeding. Growth rates of Halteria sp. and Tetrahymena pyriformis were 0.056 and 0.15 h-1 irrespective of the clay concentration, Cyclidium sp. showed slightly higher but significant growth rates in the presence of clay, as did most flagellates. The largest difference in growth was found for Spumella sp., which showed rates of 0.19 and 0.14 h-1 with and without clay, respectively. An exception was the gliding flagellate Entosiphon sulcatum, which was covered by clay particles and therefore hardly came in contact with food particles. Flagellates discriminated strongly against sediment particles prior to food uptake. With decreasing particle concentration this selection mechanism became less important compared to differential digestion especially in Spumella sp. and an unidentified groundwater flagellate. Both Bodo saltans and Monosiga ovata showed differential digestion as well, but their importance in overall selectivity was low even at a low particle concentration. In contrast to flagellates, the ciliates collected many particles, including clay particles and bacteria, and incorporated them into 1 food vacuole. Discrimination against clay was of minor importance in ciliates, but a high feeding capacity seems to compensate for this low selectivity. In contrast to many zooplankton species, it can be concluded that protists are generally well adapted to environmental situations of high sediment load. KEY WORDS: Microbial food web · Suspended matter · Feeding strategy · Bacterivory · HNF · Plankton · Runoff · Resuspension Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 34, No. 2. Online publication date: February 04, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Minor hysteresis loop phenomena in particulate recording media

In this article measurements of minor hysteresis loops in substituted BaFe powder systems with different particle concentrations have been made. The area of minor loop is observed to decrease with decreasing particle concentration. In addition, the variation of magnetization with time along the upper and lower sections of the minor loop have also been measured and show an inflection point at particular field points. The field at which the rate of magnetization changes sign is believed to be equal to a positive (magnetizing) local interaction field, i.e., the negative applied field is balanced by a local positive field. These results suggest that minor hysteresis loops originate from interactions driving irreversible changes of magnetization during the cycling process of the magnetic field. Hence the opening of minor loops in these systems is governed by the ratio of interaction to anisotropy fields.

Features in coherent transmittance of a monolayer of particles.

Coherent and incoherent transmittance values of a monolayer of particles are considered. Such a monolayer is a set of particles whose centers are located in the same plane. We set forth the conditions for the effect of coherent-transmittance quenching, which takes place as a result of the interference between incident and forward-scattered waves. Using the single-scattering approximation we determined size parameters and particle refractive indexes for this interference effect in the case of identical isotropic spherical particles. The influence of polydispersity and the fine structure of light-scattering characteristics on the quenching effect has been estimated. It is shown that the polydispersity destroys this interference effect only at large widths of particle-size distribution functions. The influence of multiple scattering on this effect is considered in the quasi-crystalline approximation. Multiple scattering results in increasing size parameters and decreasing particle concentration at which coherent transmittance quenching takes place in comparison with the case of single scattering. Our theoretical results for suspensions of latex particles in water are in fairly good agreement with the experimental results.

Transport and Retention of Hydrophobic Organic Micropollutants in Estuaries: Implications of the Particle Concentration Effect

An increase in the particle–water distribution coefficient with decreasing particle concentration, or particle concentration effect (PCE), is a common phenomenon observed in both laboratory and field studies of many hydrophobic organic micropollutants (HOMs), and is demonstrated in this work by14C-labelled benzo[a]pyrene sorption to estuarine sediment. While the focus of most studies has been the precise cause of the PCE, a more immediate requirement from a regulatory and impact assessment standpoint is its empirical definition and incorporation into any pollution modelling or management tool.A compilation of literature data on the sorption of HOMs to natural particles indicates that the relationship between distribution coefficient, KD, and suspended particle concentration, SPM, is of the form: KD=aSPM−b. The constants a and b are compound- and site-specific and are dependent to some extent on the inadequacy of particle-aqueous phase separation (or the concentration of colloids or non-settling particles encompassed by the aqueous phase). It is proposed that, for chemical flux calculations and pollution transport considerations, a PCE algorithm of the same form is appropriate:KD ′=a′SPMs−b′. Here, a transport distribution coefficient represents the ratio of HOM concentrations discriminated according to contaminant transport properties (i.e. contaminant bound to particles which are subject to gravitational settlement, and contaminant in an aqueous phase which embraces non-settling particles), SPMsis the concentration of particles which are subject to gravitational settlement, and a′ and b′ are empirical constants which define the PCE derived in this way. The implications of this algorithm for the transport and fate of HOMs in estuaries are examined, and a simple model for the estuarine retention of HOMs, incorporating the PCE and accounting for compound degradation in the aqueous phase, is presented. Estuarine retention increases with increasing magnitude of a′, the particle concentration-normalized partitioning or ‘hydrophobicity index’, and increasing degradation half-life. For b′<1, retention increases with increasing particle concentration; for b′>1, the reduction in KD′ more than offsets the accompanying increase in particle concentration and a decrease in retention with increasing particle concentration is predicted.In the absence of necessary site-specific sorption and degradation data, and hydrological and sediment transport parameters, these calculations are largely hypothetical. Nevertheless, they demonstrate the factors that affect the overall retention of HOMs by estuaries and highlight the requirement for incorporation of the PCE in any contaminant modelling framework and environmental impact evaluation.

RESIDENCE TIME DISTRIBUTION OF FOOD AND SIMULATED PARTICLES IN A MODEL HORIZONTAL SWEPT SURFACE HEAT EXCHANGER1

ABSTRACTThe residence time distribution (RTD) of food and inert particles flowing in a swept surface heat exchanger at room temperature was investigated. The effects of selected experimental conditions on RTD include particle shape (cube, cylinder, and sphere), particle concentration (10, 20, and 30% w/v), particle type (potato, carrot, turkey, green peas, and polystyrene), fluid viscosity (water, 0.5% CMC, and 1.0% CMC), bulk flow rate (5.8 × 10−4, 7.28 × 10−4, and 8.71 × 10−4 m3/s) and shaft rotational speed (30, 60, and 90 rpm). Although turkey cubes were denser than other food particles, they moved faster than potato and carrot particles. Mean particle normalized residence time (MNPRT) of food particles (green peas) were found to be significantly higher than that of simulated particles (polystyrene). Cylindrical particles stayed longer than cubic particles in water, but not significantly in CMC solution. MNPRT values were found to be dependent on viscosity. Increasing particle concentration (up to 30%) tended to decrease MNPRT. Both bulk flow rate and shaft rotational speed tend to decrease MNPRT, thus reducing the lethality achieved. The distribution of residence time curves were narrowed by decreasing particle concentration, bulk flow rate, and shaft rotational speed, and by using fluids with high viscosity. In general, particle velocity was found to be higher than the average bulk velocity. The fastest particle velocity was found to be 3.23 times the average bulk velocity while the ratio was 0.382 for the slowest.