Anisotropic particles are common in many industrial and natural turbulent flows. When these particles are small and neutrally buoyant, they follow Lagrangian trajectories while exhibiting rich orientational dynamics from the coupling of their rotation to the velocity gradients of the turbulence field. This system has proven to be a fascinating application of the fundamental properties of velocity gradients in turbulence. When particles are not neutrally buoyant, they experience preferential concentration and very different preferential alignment than neutrally buoyant tracer particles. A vast proportion of the parameter range of anisotropic particles in turbulence is still unexplored, with most existing research focusing on the simple foundational cases of axisymmetric ellipsoids at low concentrations in homogeneous isotropic turbulence and in turbulent channel flow. Numerical simulations and experiments have recently developed a fairly comprehensive picture of alignment and rotation in these cases, and t...

Anisotropic Particles in Turbulence

Progress in particle resuspension from rough surfaces by turbulent flows

A new set of correlations of drag, lift and torque coefficients for non-spherical particles and large Reynolds numbers

Drag, lift and torque correlations for non-spherical particles from Stokes limit to high Reynolds numbers

Multiphase chemical reactors with characteristic multiscale structures are intrinsically discrete at the elemental scale. However, due to the lack of multiscale models and the limitation of computational capability, such reactors are traditionally treated as continua through straightforward averaging in engineering simulations or as completely discrete systems in theoretical studies. The continuum approach is advantageous in terms of the scale and speed of computation but does not always give good predictions, which is, in many cases, the strength of the discrete approach. On the other hand, however, the discrete approach is too computationally expensive for engineering applications. Developments in computing science and technologies and encouraging progress in multiscale modeling have enabled discrete simulations to be extended to engineering systems and represent a promising approach to virtual process engineering (VPE, or virtual reality in process engineering). In this review, we analyze this emerging trend and emphasize that multiscale discrete simulations (MSDS), that is, considering multiscale structures in discrete simulation through rational coarse-graining and coupling between discrete and continuum methods with the effect of mesoscale structures accounted in both cases, is an effective way forward, which can be complementary to the continuum approach that is being improved by multiscale modeling also. For this purpose, our review is not meant to be a complete summary to the literature on discrete simulation, but rather a demonstration of its feasibility for engineering applications. We therefore discuss the enabling methods and technologies for MSDS, taking granular and particle-fluid flows as typical examples in chemical engineering. We cover the spectrum of modeling, numerical methods, algorithms, software implementation and even hardware-software codesign. The structural consistency among these aspects is shown to be the pivot for the success of MSDS. We conclude that with these developments, MSDS could soon become, among others, a mainstream simulation approach in chemical engineering which enables VPE.

Discrete simulation of granular and particle-fluid flows: from fundamental study to engineering application

Drag, lift and torque coefficients for ellipsoidal particles: From low to moderate particle Reynolds numbers

A stochastic approach for the simulation of collisions between colloidal particles at large time steps

The intention of this article is to compare the containment performance of a Type II microbiological safety cabinet (MSC) confronted with the simultaneous generation of a saline nanoparticle aerosol and a tracer gas (SF(6)). The back dissemination coefficient, defined as the ratio of the pollutant concentration measured outside the enclosure to the pollutant flow rate emitted inside the enclosure, is calculated in order to quantify the level of protection of each airborne contaminant tested for three enclosure operating configurations: an initial configuration (without perturbations), a configuration exposing a dummy in front of the enclosure (simulation of an operator), and a configuration employing the movement of a plate in front of the enclosure (simulation of human movement). Based on the results of this study, we observed that nanoparticulate and gaseous behaviours are strongly correlated, thus showing the predominance of air-driven transport over particle-specific behaviour. The average level of protection afforded by the MSC was found systematically slightly higher for the nanoaerosol than for the gas in the studied configurations (emission properties of the source, operating conditions, and measurement protocols). This improved protection efficiency, however, cannot be considered as a warrant of protection for operators since operating condition and ventilation parameters are still more influential on the containment than the pollutant nature (i.e. nanoaerosol or gas).

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Assessing the containment efficiency of a microbiological safety cabinet during the simultaneous generation of a nanoaerosol and a tracer gas

A quadrature method of moments, based on the population balance approach, was chosen to model nanoparticle coagulation and transport. Such a way has been already validated using experimental results in a homogeneous closed chamber in a steady fluid. In order to model the spatiotemporal evolution of a nanoaerosol, we propose here to couple the population balance equation (PBE) with computational fluid dynamics (CFD) considering a uniform pipe flow. A source term describing coagulation is added in convection-diffusion equations. This method is evaluated by considering convection and coagulation of an aerosol in the pipe. Computational performances are then assessed by comparison with experimental results. This method seems to be suitable for the future modelling of nano-aerosol dynamics in the workplace.

Anne Tanière

Papers

A new set of correlations of drag, lift and torque coefficients for non-spherical particles and large Reynolds numbers

Drag, lift and torque coefficients for ellipsoidal particles: From low to moderate particle Reynolds numbers

A stochastic approach for the simulation of collisions between colloidal particles at large time steps

Assessing the containment efficiency of a microbiological safety cabinet during the simultaneous generation of a nanoaerosol and a tracer gas

Modelling of Nanoparticle Coagulation and Transport in Pipe Flow