Jacques Vendel

CHARACTERIZATION OF SOOT PARTICLES IN THE PLUMES OF OVER-VENTILATED DIFFUSION FLAMES

Fire is one of the greatest industrial risks. In nuclear facilities this is complicated by the need to ensure the containment of airborne contamination at all times, in both normal and accidental situations. In the event of a fire, the soot particles emitted in the smoke may have a double impact, first on containment (clogging of filtration barriers in the ventilation network) and secondly on fire propagation, through the radiative properties of these particles. Consequently, a better understanding of their properties is needed, not only in the fire zones, but also in the smoke of diffusion flames encountered during a fire. Here, we present a study of the physical and optical parameters of soot particles sampled in the plumes of over-ventilated diffusion flames of acetylene, toluene and polymethyl methacrylate. For these three fuels, and relative to several global equivalence ratios, we have established the size distribution for the primary particles and soot aggregates, along with morphological parameters (prefactor and fractal dimension), soot emission factors and the mass specific extinction coefficient.

Influence of Carrier Gas Flow Rate, Laser Repetition Rate, and Fluence on the Size Distribution and Number of Nanoparticles Generated Per Laser Shot During Paint Laser Ablation

This study focuses on the influence of three operating parameters (gas flow rate, laser repetition rate, and fluence) on the number and size distributions of nanoparticles generated by laser ablation of acrylic paint. These particles, produced by gas-to-particle conversion of vapors generated by polymer vaporization, can have a spherical shape with a 16 nm diameter (called primary particles) but most of them are aggregated primary particles. The most critical parameter is the gas (air) flow rate in the ablation cell. Indeed, the total number of nanoparticles produced per shot increases with the air flow rate, whereas the aggregate size decreases. Indeed, the gas flow rate controls the transit time and the related aggregation duration, which decrease with increasing flow rates. The influence of the air flow rate on the nanoparticle total number produced per shot can be attributed to the evolution of the particle residence time in the setup with the flow rate. In order to validate this point, the setup has been modeled (model based on the Smoluchowski coagulation equations). The model has shown that the primary particle aggregation mainly takes place in a sphere of a few millimetres in diameter. This sphere varies in volume with the laser fluence but does not depend on the air flow rate in the cell. Moreover, the nanoparticle final number per shot does not depend on the primary particle initial number per shot but only on the size of the interaction volume, which is related to laser fluence.

Characterization of Aerosols Generated by Nanosecond Laser Ablation of an Acrylic Paint

This study focuses on particles produced during laser ablation of a green colored acrylic wall paint, which is frequently used in industrial buildings and in particular in nuclear installations. Ablation is carried out with a Nd:YAG laser at a wavelength of 532 nm and a pulse duration of 5 ns, in a cell at ambient pressure and temperature, which is ventilated by filtered air. The number of particles emitted was measured with a Condensation Particle Counter (CPC) and their size with an Engine Exhaust Particle Sizer (or EEPS) for the nanometric range, and an AEROSIZER (for the micrometric range). The mass and shape of particles were determined by sampling on filters as well as on the different impaction plates of a Low-Pressure Impactor (LPI). Two particle populations were detected: a population of aggregates of primary nanoparticles with an electrical mobility diameter ranging from 30 to 150 nm, and a population of spherical submicron particles with an aerodynamic diameter ranging from 400 to 1000 nm. The spherical particles are mainly composed of titanium dioxide, and the aggregates most likely of carbon. The presence of two types of particles with different size distributions, shapes, and chemical compositions, implies that particles originating from the ablation of paint are formed by two different mechanisms: agglomeration in the case of the nanometric aggregates, which is preceded by steps of nucleation, condensation, and coagulation of the primary particles, while the submicron spheres result from a direct ejection mechanism.

Measurement of the Mass Specific Extinction Coefficient of Acetylene, Toluene and Polymethyl Methacrylate Soot Particles In Visible and Near-Infrared Wavelengths

An experimental set-up has been developed to determine the mass specific σs and the dimensionless extinction Kt coefficients of soot particles at visible (632 nm) and near-infrared (1064 nm) wavelengths. Near-infrared measurements have been carried out with a multiple-path extinction cell to increase the measurement accuracy. The extinction coefficient Kext has been analysed as a function of the mass concentration, measured by a Tapered Element Oscillating Microbalance (TEOM 1105 R&P) in order to retrieve the soot mass specific extinction coefficient, σe, in the smoke plume of acetylene, toluene and PolyMethyl MethAcrylate (PMMA) burning under turbulent, well-ventilated and small-scale conditions. Results for mass specific extinction coefficient σ e are consistent with previous measurements (Mulholland & Croarkin [1] and Newman & Steciak [2]) obtained for a variety of fuels for small-scale fires. The mobility diameter distribution of the soot particles is measured using a Scanning Mobility Particle Sizer (SMPS 3936 TSI). The soot aggregate morphology is determined from Transmission Electronic Microscopy picture analysis. From these measurements, the soot volume fraction is determined and so the dimensionless extinction coefficient. Values at 632 and 1064 nm are given and discussed in comparison to other published data. It is found the scattering contribution to the extinction process is important for the present experimental conditions. For this reason, the use of the dimensionless coefficient is expected to provide a more accurate soot volume fraction value than the calculation which assumes the scattering is negligible.