A new expression for spherical aerosol drag in slip flow regime

Moshfegh, Abouzar; Shams, Mehrzad; Ahmadi, Goodarz; Ebrahimi, Reza

doi:10.1016/j.jaerosci.2010.01.010

Cited by 24 publications

(8 citation statements)

References 44 publications

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“…We note that the simulations presented were serial (single-processor) computations; hence, much more extensive DSMC studies could be performed in the future on large parallel-computing clusters, enabling simulation of the drag on a larger number of aerosol particles of greater morphological complexity. Not accounted for in this study, but of interest in future studies of aerosol particle transport, are the viscous interactions arising between particles during close approach in the momentum transfer transition regime (Gopinath and Koch 1999); higher-Re, higher-Ma influences (Moshfegh et al 2010); and the influence of particle rotation (Loyalka and Griffin 1994;Peters 1999) on drag.…”

Section: Downloaded By [Swansea University] At 15:51 04 November 2014mentioning

confidence: 99%

Determination of the Scalar Friction Factor for Nonspherical Particles and Aggregates Across the Entire Knudsen Number Range by Direct Simulation Monte Carlo (DSMC)

Zhang

Thajudeen

Larriba

et al. 2012

Aerosol Science and Technology

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The friction factor of an aerosol particle depends upon the Knudsen number (Kn), as gas molecule-particle momentum transfer occurs in the transition regime. For spheres, the friction factor can be calculated using the Stokes-Millikan equation (with the slip correction factor). However, a suitable friction factor relationship remains sought-after for nonspherical particles. We use direct simulation Monte Carlo (DSMC) to evaluate an algebraic expression for the transition regime friction factor that is intended for application to arbitrarily shaped particles. The tested friction factor expression is derived from dimensional analysis and is analogous to Dahneke's adjusted sphere expression. In applying this expression to nonspherical objects, we argue for the use of two previously developed drag approximations in the continuum (Kn → 0) and free molecular (Kn → ∞) regimes: the Hubbard-Douglas approximation and the projected area (PA) approximation, respectively. These approximations lead to two calculable geometric parameters for any particle: the Smoluchowski radius, R S , and the projected area, PA. Dimensional analysis reveals that Kn should be calculated with PA/π R S as the normalizing length scale, and with Kn defined in this manner, traditional relationships for the slip correction factor should apply for arbitrarily shaped particles. Furthermore, with this expression, Kn-dependent parameters, such as the dynamic shape factor, are readily calculable for nonspherical objects. DSMC calculations of the orientationally averaged drag on spheres and test aggregates (dimers, and open and dense 20-mers) in the range Kn = 0.05-10 provide strong support for the proposed method for friction factor calculation in the transition regime. Experimental measurements of the drag on aggregates composed of 2-5 primary particles further agree well with DSMC results, with differences of less than 10% typically between theoretical predictions, numerical calculations, and experimental measurements.

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Section: Downloaded By [Swansea University] At 15:51 04 November 2014mentioning

confidence: 99%

Determination of the Scalar Friction Factor for Nonspherical Particles and Aggregates Across the Entire Knudsen Number Range by Direct Simulation Monte Carlo (DSMC)

Zhang

Thajudeen

Larriba

et al. 2012

Aerosol Science and Technology

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“…Further, the for diffusion can be expressed as a linear function of the d p , as in Eq. 5and (10). Table 1 depicts the expressions for the single fiber efficiency by diffusion; the previous expression by Lee and Liu [2], and the currently derived expression are presented.…”

Section: Fiber Efficiencymentioning

confidence: 99%

“…(1) are compared with the approximated values calculated using Eq. (10). The filter diameter (D f ) is set at 0.02 mm, and the packing density and flow velocity are set at 0.08 and 1 cm/s, respectively.…”

Section: Fiber Efficiencymentioning

confidence: 99%

“…In cases where the aerosol-particle size in air approaches the mean free path of gas molecules, the discontinuities of the medium should be considered. C c accounts for these discontinuities and can be useful for describing aerosol properties, such as sedimentation and diffusion [1,[8][9][10]. For the interaction of gases and particles, Kn, the ratio of mean free path (λ) to particle diameter (d p ), is widely used [11].…”

Section: Introductionmentioning

confidence: 99%

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Approximation of most penetrating particle size for fibrous filters considering Cunningham slip correction factor

Jung

Yoon

et al. 2019

Environmental Engineering Research

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In the estimation of the aerosol single fiber efficiency using fibrous filters, there is a size range, where the particles penetrate most effectively through the fibrous collectors, and a corresponding minimum single fiber efficiency. For small particles in which the diffusion mechanism is dominant, the Cunningham slip correction factor (C c) affects the single fiber efficiency and the most penetrating particle size (MPPS). Therefore, for accurate estimation, C c is essential to be considered. However, many previous studies have neglected this factor because of its complexity and the associated difficulty in deriving the appropriate parameterization particularly for the MPPS. In this study, the expression for the MPPS, and the corresponding expression for the minimum single fiber efficiency are analytically derived, and the effects of C c are determined. In order to accommodate the slip factor for all particle-size ranges, C c is simplified and modified. Overall, the obtained analytical expression for the MPPS is in a good agreement with the exact solution.

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“…24–30 Recently, numerical studies on rarefaction effects on the sphere drag coefficient have been performed in Stokes’ flow regime 31 and also at intermediate Reynolds numbers. 32,33 However, not much information is available related to the heat transfer characteristics of spheres in the slip flow regime.…”

Section: Introductionmentioning

confidence: 99%

Heat transfer characteristics of slip flow over solid spheres

Anbarsooz

Niazmand

2016

Proceedings of the Institution of Mechanical Engineers, Part C:

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In this study, heat transfer characteristics of slip flow over an isolated impermeable solid sphere are investigated numerically. An isothermal solid sphere is considered at intermediate Reynolds numbers (0 ≤ Re ≤ 50) for Prandtl numbers in the range of 0.7–7.0. The Navier–Stokes and energy equations are solved by a control volume technique in conjunction with the velocity slip and temperature jump boundary conditions. It was found that the size of the thermal wake region according to the Knudsen number depends on the Prandtl number. At lower Prandtl numbers (0.7 ≤ Pr ≤ 2.0), the thermal wake region shrinks as the Knudsen number increases, while at higher Prandtl numbers, it grows as the Knudsen number increases. The maximum temperature jump occurs at the front stagnation point where the local Nusselt is itself maximum, owing to the maximum temperature gradient at this point. The results show that due to the opposing effects of the velocity slip and temperature jump, the average Nusselt number variation with the Knudsen number depends nonlinearly on both the Prandtl and Reynolds numbers. Furthermore, for the limiting case of Re → 0, an analytical solution for the problem is presented which has also served as a validation case.

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A new expression for spherical aerosol drag in slip flow regime

Cited by 24 publications

References 44 publications

Determination of the Scalar Friction Factor for Nonspherical Particles and Aggregates Across the Entire Knudsen Number Range by Direct Simulation Monte Carlo (DSMC)

Determination of the Scalar Friction Factor for Nonspherical Particles and Aggregates Across the Entire Knudsen Number Range by Direct Simulation Monte Carlo (DSMC)

Approximation of most penetrating particle size for fibrous filters considering Cunningham slip correction factor

Heat transfer characteristics of slip flow over solid spheres

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