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

Melas, Anastasios; Isella, Lorenzo; Konstandopoulos, Athanasios G.; Drossinos, Yannis

doi:10.1080/02786826.2014.985781

Cited by 17 publications

(18 citation statements)

References 31 publications

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“…Figure 4 shows the K fm values of aggregates with varying k f and D f . At a fixed D f , a positive dependency between K fm and k f is clearly observed, which is in agreement with the findings of Melas et al (2014b). However, at a fixed k f , the relationship between K fm and D f is rather noisy and trivial: K fm fluctuates approximately by §3% around a mean.…”

Section: Influence Of Monomer Screening and Fractal Morphologysupporting

confidence: 81%

Sensitivity analysis of aggregate morphology on mass-mobility relationship and improved parameterizations

Liu

Chakrabarty

2015

Aerosol Science and Technology

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Past studies have shown that the diffusion-limited cluster aggregation mechanism yields aggregates with a mass fractal dimension (D f ) of around 1.8 and power-law prefactor (k f ) ranging between 1.2 and 2.5. For a fixed D f , an increasing k f physically manifests as decreasing shape anisotropy or the degree of "stringiness" of an aggregate. In this work, we investigate the effects of changing k f , monomer size (d), and number of monomers (N) of computer-simulated aggregates on their massmobility scaling exponent (D fm ) and prefactor (k fm ). Our simulation results for a statistically significant number of D f D 1.78 § 0.10 aggregates yielded D fm values of 2.20 § 0.05. These values are in excellent agreement with previous experimental observations. While variations in D fm were predominantly influenced by D f , k fm showed sensitivity to fluctuations in k f . The validity and accuracy of the empirical power-law exponent 1.08 used for estimating N in three dimensions from two dimensional projection images was also evaluated. It was found that the exponent was only valid for aggregates with k f close to unity. A correction has been proposed to account for the enhanced apparent screening effects at large k f . EDITOR Mark T. Swihart

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Section: Influence Of Monomer Screening and Fractal Morphologysupporting

confidence: 81%

Sensitivity analysis of aggregate morphology on mass-mobility relationship and improved parameterizations

Liu

Chakrabarty

2015

Aerosol Science and Technology

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“…To do so, we extend the continuum-regime methodology introduced by Isella & Drossinos (2011), a methodology used to calculate the hydrodynamic radius of power-law aggregates (Melas, Isella, Konstandopoulos, & Drossinos, 2014a), to the slip-flow regime. The methodology may be applied to calculate the friction coefficient of fractal-like aggregates, and in general, of any non-spherical structure, as a function of the monomer Knudsen number (Melas, Isella, Konstandopoulos, & Drossinos, 2014b). Herein, it is applied to one of the simplest realizations of power-law aggregates, straight chains composed of N touching, spherical monomers of radius R 1 .…”

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confidence: 99%

A methodology to calculate the friction coefficient in the transition regime: Application to straight chains

Melas

Isella

Konstandopoulos

et al. 2015

Journal of Aerosol Science

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a b s t r a c tA methodology is introduced, the Collision Rate Method (CRM), to calculate the friction coefficient of power-law aggregates across the entire momentum-transfer regime. The friction coefficient is calculated via the ratio of two fictitious particle-aggregate collision rates evaluated in the continuum and slip-flow regimes. The effective collision rates are obtained from the numerical solution of the Laplace equation with Robin boundary condition. The methodology was justified by comparing the slip correction factor of straight-chains composed of up to 50 spherical monomers with literature results. We determined the validity of the CRM to lie in an extended slip-flow regime, the maximum monomer Knudsen number being 2. We calculated the adjusted-sphere radius, the radius of a sphere with the same slip correction factor as the chain, in slip flow. We found it to be weakly dependent on flow conditions, as specified by the carrier-gas mean free path, a dependence that leads to a weak effect on calculated slip correction factors. The CRM was combined with the Adjusted-Sphere Method to extend its validity to all Knudsen numbers. Excellent agreement of calculated, straight-chain, slip correction factors with literature values was obtained for monomer Knudsen numbers up to 100. Various characteristic length scales, geometric (equivalent volume radius, radius of gyration) and dynamic (equivalent hydrodynamic and mobility radii), were calculated.

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“…A comparison of the predicted diffusion-equivalent spheres to the measured mobility equivalent diameters for a series of nanorods (Gopalakrishnan et al 2015b) showed excellent agreement (Tian et al 2016). Melas et al (2014Melas et al ( , 2015 investigated the friction coefficient and mobility radius of the fractal-like aggregates in the transition regime, and the application to straight chain agglomerates. These studies provided an opportunity to re-examine the high aspect ratio non-spherical particle dynamics, and the development of a convenient equivalent mobility diameter in high Knudsen number flows.…”

Section: Introductionmentioning

confidence: 85%

“…The "adjusted sphere" method has been supported by experiments (Cheng et al 1988;Rogak et al 1993), and most recently validated by Melas et al (2014Melas et al ( , 2015 For majority of the irregular-shaped particles, such as fractal-like agglomerates and straight chains, d adj is not available due to the lack of free molecular information. As a convenience, Equation (4) together with a volume equivalent diameter d ev, is frequently used to approximate the slip correction.…”

Section: Transition Regimementioning

confidence: 99%

“…A remarkable continued correlation between the agglomerates' mobility and the equivalent projected-area diameters was observed throughout the transition regime. More recently, by using the Collision Rate Method (CRM), Melas et al (2014Melas et al ( , 2015 described a method of calculating friction coefficient and mobility radius of the fractal-like aggregates in the transition regime.…”

Section: Applicability To Aerosol Agglomeratesmentioning

confidence: 99%

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Mobility of nanofiber, nanorod, and straight-chain nanoparticles in gases

Tian

Ahmadi

2017

Aerosol Science and Technology

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With the fast development of nanotechnology, accurate measurement and classification of nanoparticles are in great need. Nanoparticles frequently appear in non-spherical forms such as long aspect ratio nanofibers, nanotubes, and irregular nano-agglomerates. While the welldeveloped classical studies were mainly in continuum regime with spherical particles, dynamics of the non-spherical nanoparticles is not fully understood. In this study, orientation-averaged mobility of nanofiber and nanorod (with no preferred alignment) is examined by the methods of Brownian diffusion theory, a combination of collision limited reaction rate theory and the bipolar diffusion charging analysis. Comparisons to empirical predictions from the experimental measurements are also made. The study leads to the discovery of a surface-dominated mobility for high aspect ratio nanoparticles with characteristic Knudsen number greater than 5. In view of the extreme relative length scales between particle size and the gas mean free path, particles of all morphologies can be viewed as point collisions; therefore, the equivalent surface mobility diameter is reasonably justified. This finding has been verified in the current study with high aspect ratio particles. For non-spherical particles of more general forms, further investigation is needed. As expected, accuracy of this approximation reduces as the characteristic Knudsen number decreases. When Kn(d L ) < 0.1, the study shows that particle morphology starts to play an important role. A review of particle mobility for all Knudsen number flows is also provided.

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

Cited by 17 publications

References 31 publications

Sensitivity analysis of aggregate morphology on mass-mobility relationship and improved parameterizations

Sensitivity analysis of aggregate morphology on mass-mobility relationship and improved parameterizations

A methodology to calculate the friction coefficient in the transition regime: Application to straight chains

Mobility of nanofiber, nanorod, and straight-chain nanoparticles in gases

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