Resuspension Behavior Research Articles

Effects of Surface Hydrophobicity of Lab Coat Fabrics on Nanoparticle Attachment and Resuspension: Implications for Fabrics Used for Making Protective Clothing or Work Uniform

Although nanoparticles have been incorporated in a range of applications, human exposure through surface contamination remains a concern and is under investigation. This is especially true in the context of industrial and research labs, where workers may become contaminated with nanoparticles. Development of appropriate personal protective equipment requires a deeper understanding of how nanoparticles interact with fabrics. The contamination and resuspension behavior of Al2O3, carbon black (CB), and carbon nanotubes (CNTs) with four common lab coat materials (100% cotton, 80/20 polyester/cotton blend, 100% polypropylene, and Tyvek) is presented in this study. To understand the effects of fabric weave pattern and surface chemistry on nanomaterial–fabric interactions, fabrics were treated with C3F8 or H2O(v) plasma to alter surface wettability while maintaining bulk morphology. Changes in surface chemistry and wettability were measured using X-ray photoelectron spectroscopy and water contact angle goniometry on untreated and plasma-treated materials. Contamination and release of nanomaterials were quantified by monitoring the change in mass after contamination and shaking of the fabrics and using scanning electron microscopy image analysis. Overall, the lowest contamination levels arose from exposure to CNTs. Plasma treatment results in differential contamination, with the H2O(v) plasma-treated fabrics demonstrating the lowest CB contamination, whereas the lowest Al2O3 contamination and resuspension occurs with the C3F8-plasma treated cotton. A complex mechanism for nanoparticle interaction with fabrics involving surface chemistry, morphology, and intermolecular forces is discussed. Notably, different surface treatments resulting in materials repellent to airborne particles could be used in treating fabrics used for making protective clothing or work uniforms to minimize the contamination and spread of unwanted particles.

Experiment and predicted model study of resuspended nanofluid pool boiling heat transfer under electric field

In the pool boiling, the deposition of nanoparticles leads to the instability of boiling heat transfer of nanofluids. While, electric field can actively control the movement of nanoparticles. Therefore, the nanoparticle resuspension behavior, boiling heat transfer of resuspended nanofluid and prediction models for boiling heat transfer of resuspended nanofluid under the electric field were studied in the present study. Concretely, the heat transfer performance under the coupling effect between electric field and resuspended nanofluid was discussed. Besides, pool boiling and critical heat flux (CHF) prediction model were proposed to research the heat transfer variation caused by the movement of nanoparticles under electric field. It is found that the nanoparticles can be resuspended by electric field, and the boiling heat transfer of resuspended nanofluid under electric field is significantly enhanced when comparing to the pure base fluid. However, there exists an optimal concentration for the best enhanced effect. Besides, the enhancement of heat transfer results from the heat exchange by nanoparticles, the reduced surface tension of gas-liquid interface and the thermal conductivity enhancement effect. The predicted curves of model agree well with the experimental data. Meanwhile, the models comprehensively consider the effect of heat exchange by nanoparticles, surface tension and thermal conductivity

Particle size-dependent adhesion forces and wind removal efficiency of anti-soiling coatings on textured solar glasses

Abstract

Resuspension of deposited nanoparticles during pool boiling

The resuspension of deposited nanoparticles within a boiling fluid is a nanoparticle behavior that may mitigate or even avoid the degradation of nanofluids, which is of great significance to the long-lasting heat transfer enhancement of nanofluids. In this study, the nanoparticle resuspension behavior during pool boiling was investigated experimentally and theoretically. Visualized pool boiling experiments were conducted for the nanoparticle-deposited surfaces which were prepared by boiling nanofluids. Various methods were employed to capture the resuspension phenomenon and characterize the morphology of nanoparticle deposition layer. The nanoparticle resuspension ratio was measured for various boiling durations, deposition area densities, and heat fluxes to elucidate the effects of these factors on the resuspension behavior. It was found that a part of deposited nanoparticles were resuspended to the bulk of the boiling liquid and then migrated with the internal flow during pool boiling, and the porous structure of nanoparticle deposition layer played a key role in the occurrence of resuspension. The measurement showed that heat flux was a main influential factor, and increasing heat flux can lead to a dramatical increase of resuspension ratio. A semi-theoretical model was developed to predict the resuspension ratio, which agreed well with the experimental results.

Plastic microbeads from cosmetic products: an experimental study of their hydrodynamic behaviour, vertical transport and resuspension in phytoplankton and sediment aggregates

Hydrodynamic behaviour and the transport pathways of microplastics within the ocean environment are not well known, rendering accurate predictive models for dispersal management of such pollutants difficult to establish. In the natural environment, aggregation between plastic microbeads and phytodetritus or suspended sediments in rivers and oceans further complicate the patterns of dispersal. In this laboratory study, the physical characteristics and hydrodynamic behaviour of a selection of common plastic microbeads, as used in exfoliation skincare cosmetic products, were investigated. Additionally, the potential for aggregation of these microbeads with phytodetritus and suspended sediments, as well as the subsequent sinking and resuspension behaviour of produced aggregates, were investigated with roller tanks, settling columns and erosion chamber. Physical characteristics of the plastic microbeads showed great heterogeneity, with various densities, sizes and shapes of plastic material being utilised in products designed for the same purpose. The majority of the plastics investigated were positively buoyant in both freshwater and seawater. Aggregation between plastic microbeads and phytoplankton was observed to be swift, with even extremely high concentrations of plastics being rapidly scavenged by suspended algal material. Following aggregation to sizes of 300 to 4400 μm diameter, some formerly buoyant plastics were observed to settle through the water column and enter the benthic boundary layer with settling velocities ranging between 32 and 831 m day–1. These aggregates could be resuspended in the laboratory under critical shear velocities of 0.67–1.33 cm s–1 (free stream velocities of > 10 cm s–1). This rapid aggregation and subsequent settling indicates a potentially important transport pathway for these waste products, a pathway that should be considered when modelling discharge and transport of plastic microbeads and determining the ecosystems that may be at risk from exposure.

Study on the resuspension of graphite dust based on the Rock'n'Roll model

The resuspension characteristics of graphite dust in a high temperature gas-cooled reactor significance impact the source terms in the reactor safety analysis. The present academic study analyzes resuspension behavior of graphite dust, including the effects of the distribution of the independent variables between the particle and substrate adhesion, the particle diameter and the time for the resuspension characteristics of graphite dust based on the Rock'n’Roll model. The results indicated that the distribution of the independent variables for the adhesion has an important influence on the resuspension characteristics of the particles and that the Biasi fitting distribution gives a better fit to the experimental data. Particles with larger mean values of adhesion between the particle and the substrate are less prone to resuspension. Hence, a larger standard deviation σa' will overestimate the resuspension fraction for a low-speed case and underestimate the resuspension fraction in the high-speed region. Graphite dust particles with larger particle diameters are more likely to be resuspended and have a greater resuspension fraction at the same friction velocity. For the conditions matching the operating parameters of HTR-10, the threshold friction velocity that enables 0.5 μm graphite dust particles to resuspend is 5.76 times larger than that of 5 μm particles and 16 times larger than that of 10 μm particles. In addition, these results also showed that the graphite dust particle fraction changes with time and can be divided into short-term and long-term effects. The critical time between the short-term and long-term effects decreases with increasing helium velocity and particle diameter.

Characterization of graphite dust produced by pneumatic lift

Graphite dust is an important safety concern of high-temperature gas-cooled reactor (HTR). The graphite dust could adsorb fission products, and the radioactive dust is transported by the coolant gas and deposited on the surface of the primary loop. The simulation of coagulation, aggregation, deposition, and resuspension behavior of graphite dust requires parameters such as particle size distribution and particle shape, but currently very limited data on graphite dust is available. The only data we have are from AVR and THTR-300, however, the AVR result is likely to be prejudiced by the oil ingress. In pebble-bed HTR, graphite dust is generally produced by mechanical abrasion, in particular, by the abrasion of graphite pebbles in the lifting pipe of the fuel handling system. Here we demonstrate the generation and characterization of graphite dust that were produced by pneumatic lift. This graphite dust could substitute the real dust in HTR for characterization. The dust, exhibiting a lamellar morphology, showed a number-weighted average particle size of 2.38μm and a volume-weighted average size of 14.62μm. These two sizes were larger than the AVR and THTR results. The discrepancy is possibly due to the irradiation effect and prejudice caused by the oil ingress accident. It is also confirmed by the Raman spectrum that both the filler particle and binder contribute to the dust generation.

Particle deposition and resuspension in gas-cooled reactors—Activity overview of the two European research projects THINS and ARCHER

The deposition and resuspension behaviour of radio-contaminated aerosol particles is a key issue for the safety assessment of depressurization accidents of gas-cooled high temperature reactors. Within the framework of two European research projects, namely Thermal Hydraulics of Innovative Nuclear Systems (THINS) and Advanced High-Temperature Reactors for Cogeneration of Heat and Electricity R&D (ARCHER), a series of investigations was performed to investigate the transport, the deposition and the resuspension of aerosol particles in turbulent flows. The experimental and numerical tests can be subdivided into four different parts: (1) Monolayer particle deposition, (2) Monolayer particle resuspension, (3) Multilayer particle deposition and (4) Multilayer particle resuspension. The experimental results provide a new insight into the formation and removal of aerosol particle deposits in turbulent flows and are used for the development and validation of numerical procedures in gas-cooled reactors. Good agreement was found between the numerical and the experimental results.

Resuspension of carbon dust collected in Tore Supra and exposed to turbulent airflow: Controlled experiments and comparison with model

This work presents the results of experiments conducted with carbon microparticles collected in the tokamak Tore Supra in order to characterize their resuspension behaviour from a stainless-steel substrate when exposed to turbulent airflow. Experiments were conducted in a wind tunnel with controlled velocity profiles and monitored environmental conditions. A consequent amount of dust has been collected in the vessel of the tokamak and a bimodal particle size distribution of samples is first demonstrated. Comparison with resuspension of alumina powders with equivalent particle size distributions under turbulent airflow is also discussed. Results for both carbon and alumina microparticles are then compared to a theoretical resuspension model. Data reveal that exposing multilayer deposits with bimodal particle size distributions to low-speed flows (i.e. 3–10m/s) induces a significant reduction of the mobilized fractions compared to what was predicted by the model. In addition, results helped to highlight some limitations in the model to physically describe changes in the adhesive strength that can occur with a polydisperse deposit.

Sediment microstructure and resuspension behavior depend on each other

The critical shear stress of resuspension and rates of erosion for cohesive and loosely structured sediments must be obtained by direct measurements since there is no theoretical calculation. An in situ experiment on sediment resuspension was performed in a shallow lake (Langer See, NE Germany; area = 1.27 km2, zmax = 3.8 m) in summer 2006 using a hydrodynamically calibrated erosion chamber (O 20 cm). Shear velocity (u*) was incrementally increased in 11 steps (0–2.19 cm s−1) to initiate resuspension events. Entrainment rates (E) of suspended particulate matter (ESPM), total P (ETP), chlorophyll a (EChl a), and soluble reactive P (ESRP) were determined by mass balance. Two subsequent critical u* (0.53 cm s−1 and 1.48 cm s−1) support the ‘two-layered bed’ model of a fluffy surface aggregate layer (freshly deposited phytodetritus prone to resuspension) and an underlying more consolidated biostabilised layer. Patterns in ESPM (2–106 g m−2 h−1), ETP (11–532 mg m−2 h−1), and EChl a (3–24 μg m−2 h−1) revealed a sediment surface maximum of TP and Chl a and their theoretical vertical logarithmic decrease within 4 mm sediment depth, the maximum thickness of sediment layer entrained. The advective ESRP flux (17 mg m−2 h−1) was 43 times higher than the diffusive SRP flux (0.4 mg m−2 h−1). The TP and Chl a micro-profiles suggest that cohesive sediment bed formation is a function of both settling (fluff) and consolidation (biostabilisation). Thus, sediment microstructure and resuspension behavior depend on each other.

Comparison of the Resuspension Behavior Between Liquid and Solid Aerosols

Resuspension of an aerosol from solid surfaces is an important phenomenon. The resuspension behaviors of solid aerosols and liquid aerosols are not necessarily the same. A whole solid particle detaches from the surface when the removal force is sufficient, while a portion of a droplet may detach even if the removal force is insufficient to detach the whole droplet. The objective of this article is to compare the resuspension behaviors between liquid and solid aerosols from a solid surface. Polystyrene particles and glycerol in micron sizes were generated and deposited on substrates. Two types of experiments, centrifugal detachment and vibrational resuspension, were carried out. In the centrifuge experiment, a constant removal force field was provided. Larger droplets split into smaller portions during detachment. In terms of the fraction remaining, the adhesion of the liquid aerosol has the same order of magnitude to that of the solid particle. A theoretical analysis analogous to the case of pendent drop was carried out, and the theoretical prediction agreed well with the experimental result. In the vibration experiment, a sinusoidal force field was applied. A same fraction of the solid particle detached with a much smaller force in vibration experiment than in the centrifuge experiment, whereas no resuspension was observed for liquid droplets. The adhesive forces of the liquid and solid aerosols have the same order of magnitude in the centrifuge case, but in the vibration case their adhesive forces have much greater difference. It poses a necessity for further investigation. Copyright 2013 American Association for Aerosol Research

Sediment dynamics in shallow Lake Markermeer, The Netherlands: field/laboratory surveys and first results for a 3-D suspended solids model

In 2007/08, a study was undertaken on sediment dynamics in shallow Lake Markermeer, The Netherlands. Firstly, the sediment characteristics median grain size, mud content and loss on ignition showed a spatial as well as water depth related pattern indicating wind-induced sediment transport. Sediment dynamics were investigated in a sediment trap field survey at two stations. Sediment yields, virtually all coming from sediment resuspension, were significantly correlated with wind speeds. Resuspension rates for Lake Markermeer were very high, viz. ca. 1,000 g/m(2)day as an annual average, leading to high suspended solids (SS) contents, due to the large lake area and its shallowness (high 'Dynamic Ratio'). Sediment resuspension behaviour was further investigated in preliminary laboratory experiments using a 'micro-flume', applying increasing water currents onto five Lake Markermeer sediments. Resuspension showed a clear exponential behaviour. Finally, a 3-D model was set up for water quality and SS contents in Lake Markermeer; first results showed a good agreement between modelled and actual SS contents. Construction of artificial islands and dams will reduce wind fetches and may be expected to cause a substantial decrease in lake water turbidity.

The influence of drill cuttings on physical characteristics of phytodetritus

Sinking of aggregated phytoplankton cells is a crucial mechanism for transporting carbon to the seafloor and benthic ecosystem, with such aggregates often scavenging particulate material from the water column as they sink. In the vicinity of drilling rigs used by the oil and gas industry, the concentration of particulate matter in the water column may at times be enriched as a result of the discharge of ‘drill cuttings’ – drilling waste material. This investigation exposed laboratory produced phytoplankton aggregates to drill cuttings of various composition (those containing no hydrocarbons from reservoir rocks and those with a <1% hydrocarbon content) and assessed the change in aggregate size, settling rate and resuspension behavior of these using resuspension chambers and settling cylinders. Results indicate that both settling velocity and seabed stress required to resuspend the aggregates are greater in aggregates exposed to drill cuttings, with these increases most significant in aggregates exposed to hydrocarbon containing drill cuttings.

Resuspension behaviour of aluminium treated lake sediments: effects of ageing and pH

Lake restoration with aluminium (Al) has been widely used in shallow lakes, but it is unknown how ageing of the Al floc affect resuspension behaviour, sediment stability and entrainment of Al and phosphorus (P). High primary production in shallow lakes can lead to high pH in the water column with a potential release of Al and P during resuspension events. A laboratory resuspension experiment at defined hydrodynamic conditions using a calibrated erosion chamber was performed with intact sediment cores (with intact vs. disturbed biofilm on the surface) from previously Al-treated shallow Lake Mollen, NE Germany. Newly applied Al reduced surface sediment stability, but ageing led to the same stability as untreated sediment within 2 months with an intact biofilm and within 4 months with a disturbed biofilm. Dissolved Al increased markedly at resuspension after 2 days and 2 weeks of ageing and with elevated pH (9–11) in the water. The Al floc were redissolved and dissolved Al increased with elevated pH and shear velocity. Dissolved P concentration was constantly low due to excess binding capacity of the Al floc. In conclusion, Al application to shallow lakes prone to resuspension and with a high production must be done in periods with less resuspension risk to allow 2–4 months time for floc stabilization. Otherwise, possible resuspension and high(er) pH may lead to elevated concentrations of dissolved Al in the water column.

Analysis of sedimentation and resuspension processes of aquaculture biosolids using an oscillating grid

Sedimentation and resuspension processes of aquaculture biosolids (non-ingested feed and faeces) are analysed using vertically oscillating grids as a source of turbulence in fluid tanks. An oscillating grid system consists of a container in which a grid is stirred vertically generating a well-known turbulent field that is function of amplitude and frequency of oscillation, distance between grid and measurement point, and mesh spacing of the grid. The grid used in this study had a mesh spacing of 1.2 cm, and was calibrated using different amplitudes (1, 1.5 and 2 cm), frequencies (from 1 to 6 Hz) and distances (2.4, 2.7 and 3 cm). After calibration, the turbulence needed to resuspend biosolids and to maintain them in the water column following different times of consolidation, and with biosolids of different origin, was analysed. It was observed that the turbulence needed to resuspend aquaculture biosolids increased with the time of consolidation. When the turbulence was decreased after a resuspension process, the next sedimentation of biosolids showed a hysteretic behaviour: turbulence needed to resuspend a fixed percent of biosolids from the tank bottom is substantially higher than that needed to maintain the same percentage suspended in the water column. Differences in resuspension behaviour of biosolids originated in different tanks were also observed. The method provides useful information that can be compared with turbulence generated by fish swimming activity, in order to determine the culture conditions, which can promote self-cleaning conditions in a particular tank.

Effect of physical variables on particle critical erosion shear stress: Hydrostatic pressure, slope and changes in water density

In recent years, the importance of organo-mineral aggregates (OMAs) in the transport of organic material from the continental shelf to the deep ocean floor has been recognized. Attempts to model the transport of these OMAs rely on measurements of several physical parameters, such as the critical erosion shear stress. However, due to technical constraints, such measurements are not done in situ, making it difficult to assess the impact of environmental parameters on the measurements made, and their accuracy in representing the study site. Changes in hydrostatic pressure, slope angle and water density potentially can affect the critical erosion shear stress of OMAs. Using new methodologies, we found no measurable effect of hydrostatic pressure variation on the OMAs' resuspension behavior. Changes in slope angle resulted in the decrease of u∗ cri up to 35%. The u∗ cri decreased by 9% with an exchange with denser water, and it increased by 6% with an exchange with lighter water. These changes were temporary, and after a 3-h stabilization the u∗ cri returned to the original value. We will discuss the future applications of these results on modeling of particle transport.

Resuspension of allergen-containing particles under mechanical and aerodynamic disturbances from human walking

This study presents and develops a controlled and characterized method to explore the influence of specific occupant activity on the aerosolization of allergen-containing particles. Indoor allergen-related diseases are primarily inhalation sensitized and developed, suggesting an aerobiological pathway of allergen-containing carrier particles from dust reservoir to occupant respiration. But the pathways are not well understood or quantified. The influence of occupant walking on particle aerosolization is simulated by a system in which complex floor disturbances are deconvoluted into aerodynamic and mechanical components. Time resolved particle size distributions are measured for particles resuspended from representative samples of flooring materials and different types of floor disturbances in an environmentally controlled experimental chamber. Results indicate aerodynamic disturbances, relative to mechanical, dominate the particle resuspension behavior. Dust type, dust load and floor type showed marginal influences on a normalized surface loading basis. Humidity effects were not clear since during experiments the floor samples may not have reached moisture partitioning equilibrium with the controlled air humidity. Average resuspension rates ranged from 10 −7 to 10 −3 min −1, having phenomenological consistency with previous, large room or chamber investigations, suggesting the method can be utilized to develop a database for particle resuspension rates.

Sand and mud flux estimates using acoustic and optical backscatter sensors: measurements seaward of the Wash, southern North Sea

Abstract Optical and acoustic backscatter sensors, more sensitive to fine and sandy sediment respectively, were used to measure the mud and sand components of a mixed suspension at a site seaward of the Wash embayment, in the southern North Sea. Data were acquired from a free-standing instrument frame during a five-week deployment in 12 m water depth about 6 km offshore. Suspended mud at this site was characterized by tidal advection of fine sediment along the coast resulting in semi-diurnal peaks in concentration near slack water. Suspended sand concentrations correlated well with tidal current speeds indicating local resuspension behaviour. Predicted sand flux direction followed the residual current while mud fluxes at the site were different in direction to both the residual current and sand flux. Residual fluxes may be biased by cumulative errors resulting from instrument calibration and inferred vertical concentration profiles. These factors are assessed in relation to both predicted flux magnitudes and directions.

Critical Shear Stress of Cohesive Bottom Sediments

The main purpose of this study is to obtain a simple critical shear stress function for cohesive soft bottom sediments. A series of experiments concerning threshold levels of mud transport and two series of tests of their rheological and setting properties were conducted to find some correlation among these indices. We defined two threshold levels for mud transport and divided muds into two groups by their characteristics (settling type, flow curve, resuspension behavior, etc.). In discussing the factors determining the characteristics of the two groups, we found that natural muds usually belong to the first group, in which the two critical shear stresses are given as a function of yield value τy1 (defined in paper) independent of material, following a new definition of threshold for sediment detachment from the bed. Finally, the correlation between this yield value and the final settling volume ratio is also discussed.

PHYSICAL PROPERTIES AND CRITICAL SHEAR STRESS OF COHESIVE BOTTOM SEDIMENTS

The main purpose of this experimental study is the estimation of critical shear stress of cohesive bottom sediments. The resistance properties against currents are mainly controlled by the electro-chemical bond between individual particles. Hydraulic experiment and physico-chemical test were performed. Bottom sediments were divided into two groups according to characteristics of settling form, flow curve and resuspension behavior. The main factor which controls those characteristics was found to be the nature of cations adhering to particle's surface. For bottom sediments two critical shear stresses were defined from the resuspension behaviors. They showed linear relation with respect to viscosity and yield value on log-log paper but the relations were different between two groups.