Augustin Charvet

Characterizing the effective density and primary particle diameter of airborne nanoparticles produced by spark discharge using mobility and mass measurements (tandem DMA/APM)

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®, 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 mass-mobility exponents and primary particle diameters were determined for these particles, and found to agree well with published data.

Can bubble columns be an alternative to fibrous filters for nanoparticles collection

The most effective and widely used dedusting techniques to separate nanoparticles of a carrier fluid are fibrous media. The main problem is the clogging of the filter that induces a pressure drop increase over time and thus requires a regular cleaning of the media (or its replacement). Following these observations, this study proposes to investigate the potential of bubble columns for nanoparticles collection. Despite collection efficiencies lower than those of fibrous filters, experimental results show that bubble columns present likely performances for the collection of nanoparticles and have collection efficiency even more important when the liquid height is high and bubbling orifices have low diameters. Experiments have also revealed the presence of a most penetrating particle size for a particle diameter range between 10 and 30 nm. The model developed in this article highlights a good agreement between the theoretical collection efficiency by Brownian diffusion and experimental collection efficiencies for particles lower than 20 nm. Nevertheless, the modelling may be extended to other collection mechanisms in order to explain the collection efficiency increase for particles higher than 20 nm and to confirm or infirm that electrostatic effects can be the cause of this efficiency increase.

Optimization of bubble column performance for nanoparticle collection

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.

Filtration of Liquid Aerosols

Liquid aerosols can make up a considerable portion of atmospheric pollution in mechanical industries (mists generated by oil application in the machining of metals or the production of compressed gas) and agricultural industries (phytosanitary products), among others. These liquid aerosols, in the form of oil mists, are mainly produced by three different processes: – Mechanical atomization : Many authors demonstrate that at very high rotational velocities (therefore with a very high shearing force), the liquid that comes into contact with the rotatory equipment acquires sufficient mechanical energy to disaggregate into small droplets.

An Introduction to Aerosols

Abstract: The term aerosol first appeared around 1920 to designate the suspension, in a gaseous medium, of solid or liquid particles with negligible settling velocity. In air and under normal conditions, these correspond to particles smaller than 100 μ m. Gives the dimensions of some of the impurities usually found in air with some comparative elements. An aerosol, by definition, refers to both the particles as well as the gas in which these particles are suspended. However, as a result of constant misuse, the term aerosol is often mistakenly used as a synonym for particles.