Measurement of Mass Transfer to Agglomerate Aerosols

The influence of geometric properties and particle size on mobility properties of fractal-like aggregates was studied in the mass and momentum-transfer transition regimes. Two methodologies were investigated. The Collision Rate Method (CRM) that determines the slip correction factor through the ratio of two fictitious Brownian particle-aggregate effective collision rates, and the Adjusted Sphere Method (ASM) that assumes the existence of a virtual, flowindependent adjusted sphere with the same slip correction factor as the aggregate over the entire transition regime. The simulated fractal-like aggregates were synthetic as they were generated via a cluster-cluster agglomeration algorithm. The CRM was used to calculate the adjusted-sphere radius of various aggregates: we found it to be weakly dependent on the monomer Knudsen number for Kn greater than 0.5. Numerical expressions for the aggregate orientationally-averaged projected area and the adjusted-sphere radius are proposed. Both expressions depend on geometric, nonensemble averaged quantities: the radius of gyration and the number of monomers. The slip correction factor and the mobility radius of DLCA and RLCA aggregates were calculated using the ASM: for a given number of monomers, fractal dimension and prefactor, and Knudsen number their values were approximately constant (averaged over aggregate realizations). A fractal-like scaling law based on the mobility radius was found to hold. The mobility fractal dimension and prefactor were determined for different aggregates. The hydrodynamic radius, proportional to the friction coefficient, © 2014 European Union Received 4 July 2014; accepted 8 October 2014. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons. org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium provide the original work is properly cited. The moral rights of the named author(s) have been asserted.Address correspondence to Yannis Drossinos, European Commission, Joint Research Centre, Ispra, VA I-21027, Italy. E-mail: ioannis. drossinos@jrc.ec.europa.eu Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uast. and the dynamic shape factor of DLCA and RLCA aggregates were also calculated.

Section: Collision Rate Methods (Crm)mentioning

confidence: 99%

Friction Coefficient and Mobility Radius of Fractal-Like Aggregates in the Transition Regime

Melas

Isella

Konstandopoulos

et al. 2014

“…Their results show that there is no difference in the response of an epiphniometer between singlet (such as NaCl) and carbon agglomerates for a given mobility diameter. Rogak et al (1991) also compared transfer rates of 211 Pb onto particles using the epiphaniometer for (NH 4 ) 2 SO 4 , PSL, and TiO 2 agglomerates. They concluded that spherical shape particles and agglomerates with the same mobility have nearly the same transfer rate of 211 Pb.…”

Section: Characterization Of Diffusion Chargers Using Soot Agglomeratesmentioning

confidence: 99%

Characterization of Aerosol Surface Instruments in Transition Regime

Jung

Kittelson

2005

106

The primary purpose of this study is to measure the size-and composition-dependent responses of aerosol surface instruments designed to measure surface area related properties. The secondary purpose of this study is to investigate the difference in charging rate between singlets (NaCl particles) and agglomerates (diesel particles) by using diffusion chargers. Agglomerates (diesel particles at engine load 75%) acquire more charge than singlets (NaCl particles) by 15 and 17% for LQ1-DC and EAD, respectively.

“…ASA is the surface area of a sphere with diameter d and density ρ having the same mobility or diffusivity as the particle (Rogak et al 1991). Thus, the mass/volume-related surface areas for a particle size distribution with surface median diameter d SMD and mass median diameter where the surface median and mass median diameters are calculated from the modal or median number diameter according to the Hatch-Choate equation (Reist 1984).…”

Section: Evaluation Of Particle Surface Areamentioning

confidence: 99%

Generation of Ultrafine Particles by Spark Discharging

Roth¹,

Ferron²,

Karg³

et al. 2004

104

Ultrafine carbon, metal, and metal oxide particles were generated with a commercially available spark generator designed for the production of carbon particles. Aerosols with number concentrations up to 10 7 cm −3 were produced at flow rates up to 150 lpm. Lognormal size distributions with modal diameters in the range of 18-150 nm and geometric standard deviations of about 1.5 were obtained. The chemical composition, size, number concentration, morphology, and surface area of the particles were varied, and the generation of particles with fixed characteristics could be maintained over many hours. The particle characteristics, however, could not be varied independently. for cadmium oxide, 120 m 2 g −1 for iridium, and 300 m 2 g −1 for ferric oxide), and carbon with a large BET surface area (750 m 2 g −1 ). Iridium, on the other hand, has a huge volume-related BET surface area (2800 m 2 cm −3 ). It was not possible to generate ultrafine carbon particles without contaminations with the generator. However, these contaminations could be decreased in this study from 25% to 6% by replacing organic components of the generator by pure inorganic components.