Cette etude a permis d'acquerir une base de donnees experimentales sur l'evolution de la perte de charge d'un filtre plisse a Tres Haute Efficacite (THE), pendant son colmatage en presence d'humidite par un aerosol... more
Cette etude a permis d'acquerir une base de donnees experimentales sur l'evolution de la perte de charge d'un filtre plisse a Tres Haute Efficacite (THE), pendant son colmatage en presence d'humidite par un aerosol micronique non-hygroscopique d'oxyde d'aluminium et un aerosol submicronique hygroscopique de chlorure de sodium. Les resultats obtenus avec l'aerosol non-hygroscopique ont montre que la fermeture des plis est d'autant plus rapide que l'humidite de l'air est grande ; ainsi, pour une meme masse d'aerosol deposee, la perte de charge du filtre est plus importante lorsque l'humidite de l'air est proche de la saturation. Avec l'aerosol hygroscopique etudie et pour des taux d'humidite relative en dessous de son point de deliquescence, les resultats montrent qu'en debut de colmatage, l'accroissement de la perte de charge du filtre est d'autant plus faible que l'humidite de l'air est grande, comme pou...
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In air filtration, nonwoven materials are known to be pertinent structures for fine filtration and moderate pressure drop. In order to develop a filter that combines good permeability and high efficiency, it is important to identify the... more
In air filtration, nonwoven materials are known to be pertinent structures for fine filtration and moderate pressure drop. In order to develop a filter that combines good permeability and high efficiency, it is important to identify the relevant structural parameters of the nonwoven. The main criteria studied in this paper are fiber fineness, solid volume fraction and basis length (total length of fiber in unit area of nonwoven). The effect of combining different fiber diameters in order to reach the best compromise is also investigated. Our results show that the use of binary blends of different fiber diameters improves overall filtration behavior, in comparison to nonwoven filters with equivalent unimodal diameter distribution. A theoretical filtration model is used to predict filtration behavior for different structural characteristics and these predictions are compared to experimental results. However, this comparison demonstrates the limits of existing models in the case of fib...
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Dust and droplet filtration is an essential process step in many industries. Although many studies have been dedicated to the mechanisms of dust filtration, little is known about the behaviour of an air filter when challenged with solid... more
Dust and droplet filtration is an essential process step in many industries. Although many studies have been dedicated to the mechanisms of dust filtration, little is known about the behaviour of an air filter when challenged with solid and liquid particles at the same time. This research article answers questions about the pressure drop during the filtration of a solid/liquid
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ABSTRACT Thermal metal spraying or cutting (arc/air) processes produce large quantities of ultrafine particles which cause irreversible clogging of industrial dust collectors in the long-term. This study, conducted on a test system... more
ABSTRACT Thermal metal spraying or cutting (arc/air) processes produce large quantities of ultrafine particles which cause irreversible clogging of industrial dust collectors in the long-term. This study, conducted on a test system equipped with a pleated filter cartridge confirms the high clogging capacity of these fumes, and also shows that current pulsed-jet cleaning methods are ineffective. The study has shown that the pressure drop across filters rises during filtration primarily due to the presence of ultrafine particles in the aerosol. This explains why cyclone type pre-separation has proved inefficient in preserving filtration capacity. Filter pre-coating could overcome the problem of ineffective cleaning (if used in off-line mode), but this technique generates large quantities of waste requiring specific handling. Future research should be oriented either towards improving filter cleaning or developing alternative separation techniques.
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Fibrous media embody the most effective and widely used method of separating ultrafine particles from a carrier fluid. The main problem associated with them is filter clogging, which induces an increasingly marked pressure drop with time... more
Fibrous media embody the most effective and widely used method of separating ultrafine particles from a carrier fluid. The main problem associated with them is filter clogging, which induces an increasingly marked pressure drop with time and thus imposes regular media cleaning or replacement. This context has prompted the idea of investigating bubble columns, which operate at constant pressure drop, as alternatives to fibrous filters. This study examines the influence of different operating conditions, such as liquid height, air flow rate, bubble size and presence of granular beds on ultrafine particle collection. Experimental results show that bubble columns are characterised by high collection efficiency, when they feature a large liquid height and small diameter bubbling orifices, while their efficiencies remain lower than those of fibrous filters. Gas velocity does not greatly influence collection efficiency, but the inclusion of a granular bed, composed of beads, increases the bubble residence time in the column, thereby increasing the column collection efficiency.
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ABSTRACT
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ABSTRACT Formaldehyde is toxic to humans and is classed as a category 1 carcinogen. Methods have been developed to degrade this compound, but for industrial application, relevant mathematical models are required. This study models a fixed... more
ABSTRACT Formaldehyde is toxic to humans and is classed as a category 1 carcinogen. Methods have been developed to degrade this compound, but for industrial application, relevant mathematical models are required. This study models a fixed bed photocatalytic reactor designed to degrade formaldehyde constituted of TiO2-coated Raschig rings illuminated by UV-A lamps. Initially, the reactor's hydraulic behavior was described based on an experimental residence time distribution. This model takes into account hydraulics, light distribution, chemical kinetics and mass transfer in the reactor. The dispersion model satisfactorily represented the reactor's hydraulic behavior. This model, combined with a Langmuir-Hinshelwood kinetic model, was then used to calculate variations in concentration at the reactor output. By adding the transfer flux between the bulk and the surface to the material balance equation, it is possible to distinguish between mass transfer and chemical reaction limitation and determine the chemical kinetics. Experimental data from different initial concentrations were used to calculate the Langmuir-Hinshelwood kinetic constants. The dispersion model with chemical reaction was validated under various irradiation and flow rate conditions. The results show that the fixed bed photocatalytic reactor efficiently degrades formaldehyde in an aqueous solution. The chemical constants of photocatalytic degradation obtained for formaldehyde are necessary parameters if this technology is to become the basis of industrial applications. This study provides a new tool, integrating mass transfer limitations and light distribution, to design photo-reactors.
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... 02786821003674244 Benjamin Sutter a , Denis Bémer a , Jean-Christophe Appert-Collin b , Dominique Thomas b & Noël Midoux b pages 395-404. ... Powder Technology , 118(12): 171179. View all references and Raynor et al. (1999)17.... more
... 02786821003674244 Benjamin Sutter a , Denis Bémer a , Jean-Christophe Appert-Collin b , Dominique Thomas b & Noël Midoux b pages 395-404. ... Powder Technology , 118(12): 171179. View all references and Raynor et al. (1999)17. Raynor, PC and Leith, D. 1999. ...
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The effects on health of inhaled nanostructured particles (which constitutive elements have at least one dimension less than 100 nm) depend on several physical and chemical factors. If none of the three indicators (mass, surface, number)... more
The effects on health of inhaled nanostructured particles (which constitutive elements have at least one dimension less than 100 nm) depend on several physical and chemical factors. If none of the three indicators (mass, surface, number) is not yet clearly identified, it seems essential to develop means of measuring the surface-area of airborne nanostructured particles. In fact, there is no
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ABSTRACT We use a combination of Single-Photon Emission Computed Tomography and X-Ray Computed Tomography to visualize the behavior of a radioactively marked aerosol in pleated filters under different operating conditions. We first... more
ABSTRACT We use a combination of Single-Photon Emission Computed Tomography and X-Ray Computed Tomography to visualize the behavior of a radioactively marked aerosol in pleated filters under different operating conditions. We first validate this atypical method as a mean to comprehensively observe the filtration process in a filter at the macroscopic scale. This non-intrusive technique highlights the influence of the filtration velocity on the areas where the particles first tend to settle out in blank HEPA filter. We demonstrate that the pleating geometry and the local media permeability act on the flow and account for the preferential location of the deposit. Moreover, e show that the increase in the filtration rate leads to a more homogeneous distribution of the tracer on the entire height of the pleats and hence a more uniform arrangement of the flow. The rigid separators, placed on the media to increase the effective filtration surface, act as obstacles around which the flow is splitted, thus reducing the available area of filtration. Surface observations of loaded filters show that an inhomogeneous growth of the cake induces the formation of preferential channels for the solid aerosol to flow in. Caution should then be taken when carrying out the tomographic analyses because of the competition between the local air resistance and the local efficiency that can prevent from determining the areas where the radioactive aerosol accumulates.
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ABSTRACT Increasing numbers of workers are exposed to airborne nanoparticles, the health effects of which remain difficult to evaluate. Effective density is considered to be a key characteristic of airborne nanoparticles due to its role... more
ABSTRACT Increasing numbers of workers are exposed to airborne nanoparticles, the health effects of which remain difficult to evaluate. Effective density is considered to be a key characteristic of airborne nanoparticles due to its role in particle deposition in the human respiratory tract and in the conversion of number distributions to mass distributions. Because effective density cannot be measured directly, in this study the electrical mobility and aerodynamic equivalent diameters of airborne nanoparticles were measured simultaneously (tandem DMA/ELPI). Test aerosols consisted of spherical Di-Ethyl-Hexyl-Sebacate nanoparticles produced by nebulization (PALAS AGK 2000). To take into account the presence of multiple-charged particles at the DMA outlet, a theoretical model was developed in which the successive mechanisms undergone by particles are accounted for. Using this model, it is possible to determine the proportion of each population exiting the DMA (p = 1, 2,., 5 elementary charges) in each channel of the overall ELPI signal. Thus, particle effective density can be estimated for each population. The results indicate that using the ELPI signal alone could lead to significant misevaluation of particle effective density, with biases up to 150%. However, when the proportion of each population is taken into account, particle effective density is determined within +/- 15 % of the theoretical value.
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In the field of aerosol filtration, the theory of thermal rebound of nanoparticles developed by Wang and Kasper [10] has been subject of discussion for more than two decades since it does not fit the experiment. The main purpose of this... more
In the field of aerosol filtration, the theory of thermal rebound of nanoparticles developed by Wang and Kasper [10] has been subject of discussion for more than two decades since it does not fit the experiment. The main purpose of this theory is that the filtration efficiency of fibrous filters could decrease in the region of 10nm and below because of an excessive impact velocity of particles. However and despite numerous lab experiments leaded by different teams, the phenomenon has never been clearly observed. We demonstrate in this paper why no thermal rebound effect has ever been measured experimentally. According to our approach, the decrease in filtration efficiency, if any, might only happen below 1nm, even at high temperatures.
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ABSTRACT We present the main results and conclusions relating to cross flow filtration of gasses. These show that the thickness and the mass of deposit depend significantly on filtration and cross flow velocities. These velocities are... more
ABSTRACT We present the main results and conclusions relating to cross flow filtration of gasses. These show that the thickness and the mass of deposit depend significantly on filtration and cross flow velocities. These velocities are combined as the shear stress to give a parameter which characterizes the flow at a wall in a tube subjected to a wall suction. The presence of a deposit is characterized by a limiting shear stress which corresponds to the stress that fluid must exert in order to erode the deposit. From these two stresses, it is possible to predict the mass of deposit in steady state for given initial operating conditions.RésuméCet article présente les principaux résultats et conclusions relatifs à la filtration tangentielle des gaz. Nous montrons que l'épaisseur et la masse du dépôt sont fortement tributaires des vitesses tangentielle et de filtration. Ces dernières on pu être reliées à un paramètre caractéristique de l'écoulement à la paroi d'un fluide dans un tube poreux soumis à une aspiration pariétale: la contrainte tangentielle. Nous caractérisons le dépôt par une contrainte tangentielle limite qui correspond à celle que doit exercer le fluide pour arracher le dépôt. A partir de ces deux contraintes, il est possible de prévoir pour des conditions opératoires initiales données, la masse du dépôt mobilisé en régime permanent.
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The aim of this work is first to measured nanoparticles penetration through three different fiberglass filters intentionally-pierced with calibrated needles at different filtration velocity. Then a semi-empirical model based on the air... more
The aim of this work is first to measured nanoparticles penetration through three different fiberglass filters intentionally-pierced with calibrated needles at different filtration velocity. Then a semi-empirical model based on the air flow resistances of the new and perforated filter media and on the mechanism of Brownian diffusion for the collection of ultrafine particles by the media enables to well
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An increasing number of experimental and theoretical studies focus on airborne nanoparticles (NP) in relation with many aspects of risk assessment. Indeed, our understanding of the hazards, the actual exposures in the workplace and the... more
An increasing number of experimental and theoretical studies focus on airborne nanoparticles (NP) in relation with many aspects of risk assessment. Indeed, our understanding of the hazards, the actual exposures in the workplace and the limits of engineering controls and personal protective equipment with regard to NP are still under development. Several studies have already identified surface-area as an important
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ABSTRACT Due to the increasing use of nanomaterials in research and product development, it is probable that the number of situations of occupational exposure to them is also rising. The same is true for the number of workers. Although... more
ABSTRACT Due to the increasing use of nanomaterials in research and product development, it is probable that the number of situations of occupational exposure to them is also rising. The same is true for the number of workers. Although current research in nanotoxicology is far from conclusive, it is clear that relying on mass concentration and chemical composition alone is not appropriate in all cases and alternative measurement methods and approaches need to be developed. In this work, we propose a method based on simultaneous size-integrated measurements of two particle concentrations (number and lung-deposited surface area, CNC/NSAM), and on the estimation of the average size of potentially inhaled particles from the combination of these measurements. The proposed method could be part of a measurement strategy that is practical as it would use field-portable, commercially available aerosol instruments. In the absence of instruments providing real-time size-resolved measurements, this original approach can be carried out as considering that the ratio of these concentrations is a monotonous function of particle size. Indeed, the latter function depends only on the geometric standard deviation of airborne particle number size distribution, assumed to be lognormal. Compared to SMPS data for polydisperse aerosols having three chemical natures with count median diameters ranging from 64 to 177 nm, experimental results were obtained with acceptable relative discrepancies of ±30 %. Though the method proposed is less accurate than traditional instruments like SMPS, it can be used for workplace air monitoring or as a screening tool to detect the presence of airborne nanoparticles.
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ABSTRACT Nanoparticles are increasingly used in a wide variety of industries. As yet, their health effects are incompletely characterized. Effective density is among the key characteristics of airborne nanoparticles due to its role in... more
ABSTRACT Nanoparticles are increasingly used in a wide variety of industries. As yet, their health effects are incompletely characterized. Effective density is among the key characteristics of airborne nanoparticles due to its role in particle deposition in the human respiratory tract and in the conversion of number distributions to mass distributions. Because it cannot be measured directly, different methods have been developed to accede to this parameter. The approach chosen in this study is based on the tandem measurement of airborne nanoparticles electrical mobility and mass (tandem differential mobility analyzer/aerosol particle mass analyzer), which major advantage lies in the absence of hypothesis contrary to the tandem differential mobility analyzer/electrical low pressure impactor (DMA/ELPI). The methodology was first applied to spherical model particles to validate the associated data treatment and protocol. In particular, the influence of APM rotational velocity and airflow rate were investigated with regards to the separation of multiply charged particles and electrometer signal. It emerged from experimental data that a compromise between separation efficiency and detection limit shall be found, depending on the nanoparticles to characterize. Accounting for their wide use in different domains, airborne nanoparticles of constantan (R), copper, graphite, iron, silver and titanium, produced by spark discharge appear to be representative of ultrafine particles stemming from different industrial processes. In addition to their effective density, the massmobility exponents and primary particle diameters were determined for these particles, and found to agree well with published data.
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An experimental investigation was carried out on the influences of dust concentration, particle size distribution and humidity on aluminum dust explosion. Tests were mainly conducted thanks to a 20 L explosion sphere. The effect of... more
An experimental investigation was carried out on the influences of dust concentration, particle size distribution and humidity on aluminum dust explosion. Tests were mainly conducted thanks to a 20 L explosion sphere. The effect of humidity was studied by storing the aluminum particles at constant relative humidity until the sorption equilibrium or by introducing water vapour in the explosion vessel. The tested particles sizes ranged from a volume median diameter of 7 to 42 μm and the dust concentrations were up to 3000 g m−3.Among other results, the strong influence of the particle size was pointed out, especially when the Sauter mean diameter is considered. These results stressed the predominance of the specific surface area on the mass median particle diameter.The effect of water on aluminum dust explosion was decoupled: on the one hand, when water adsorption occurs, hydrogen generation leads to an increase of the explosion severity; on the other hand, when the explosion of dried aluminum powder occurs in a humid atmosphere, the inhibiting effect of humidity is put forward.A model based on mass and heat balances, assuming a shrinking core model with chemical reaction limitation, leads to a satisfactory representation of the pressure evolution during the dust explosion.