Turbulent Two-Phase Flows and Particle Deposition in a Duct at High Concentrations

2010 ◽  
Author(s):  
Goodarz Ahmadi ◽  
Hojjat Nasr ◽  
John B. McLaughlin
Keyword(s):  
Particle Deposition ◽  
Deposition Velocity ◽  
Particle Collision ◽  
Duct Flow ◽  
Particle Collisions ◽  
Coupling Effects ◽  
Two Phase Flows ◽  
Two Phase ◽  
Mean Velocity ◽  
Navier Stokes Equation

Two-phase flows including particle-particle collisions and two-way coupling in a turbulent duct flow were simulated using a direct simulation approach. The direct numerical simulation (DNS) of the Navier-Stokes equation was performed via a pseudospectral method was extended to cover two-way coupling effects. The effect of particles on the flow was included in the analysis via a feedback force that acted on the fluid on the computational grid points. The point particle equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. Several simulations for different particle relaxation times and particle mass loading were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration were determined. It was found that when particle-particle collisions were included in the computation, the particle deposition velocity increased. When the particle collision was neglected but the particle-fluid two-way coupling was accounted for, the particle deposition velocity decreased slightly. When both inter-particle collisions and two-way coupling effects were taken into account in the simulations, the particle deposition velocity increased. Comparisons of the present simulation results with the available experimental data and earlier numerical results are also presented.

A DNS study of effects of particle–particle collisions and two-way coupling on particle deposition and phasic fluctuations

2009 ◽  
Vol 640 ◽  
pp. 507-536 ◽  
Author(s):  
HOJJAT NASR ◽  
GOODARZ AHMADI ◽  
JOHN B. MCLAUGHLIN
Keyword(s):  
Particle Deposition ◽  
Particle Concentration ◽  
Stokes Equations ◽  
Deposition Velocity ◽  
Relaxation Times ◽  
Time History ◽  
Navier Stokes ◽  
Wall Region ◽  
Particle Collisions ◽  
Coupling Effects

This study is concerned with the effects of particle–particle collisions and the two-way coupling on the dispersed and carrier phase turbulence fluctuations in a channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation of the Navier–Stokes equations via a pseudo-spectral method. The particle equation of motion included the wall-corrected nonlinear drag force and the wall-induced and shear-induced lift force. The effect of particles on the flow was included in the analysis via a feedback force that acted on the computational grid points. Several simulations for different particle relaxation times and particle mass loadings were performed, and the effects of particle–particle collisions, particle feedback force and inter-particle interactions on the particle deposition velocity, fluid and particle fluctuating velocities, and particle concentration profiles were determined. The effect of particle aerodynamic interactions was also examined for certain cases.The simulation results indicated that when particle–particle collisions were included in the computation but two-way coupling effects were ignored, the particle normal fluctuating velocity increased in the wall region causing an increase in the particle deposition velocity. When the particle collisions were neglected but the particle–fluid two-way coupling effects were accounted for, the two-way coupling and the particle normal fluctuating velocity decreased near the wall causing a decrease in the particle deposition velocity. In the case of the four-way coupling in which both inter-particle collisions and two-way coupling effects were present, it was found that the particle deposition velocity increased compared with the one-way coupling case. When the particle aerodynamic interactions were added to the four-way coupled case (termed six-way coupled case), no significant changes in the mean fluid and particle velocities and the fluid and particle fluctuating velocities were obtained.The results for the particle concentration profile indicated that the inclusion of two-way coupling or inter-particle collisions into the computation reduced the accumulation of particles near the wall. It was also observed that particle–particle collisions and two-way coupling weakened the preferential distribution of particles.

Direct Numerical Simulation of Four Way-Coupled Gas-Solid Flow and Deposition in a Turbulent Channel Flow

2009 ◽  
Author(s):  
Goodarz Ahmadi ◽  
Hojjat Nasr ◽  
John B. McLaughlin
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Channel Flow ◽  
Particle Deposition ◽  
Particle Concentration ◽  
Deposition Velocity ◽  
Time History ◽  
Wall Region ◽  
Particle Collisions ◽  
Coupling Effects

This study was concerned with the effects of particle-particle collisions and two-way coupling on the dispersed and carrier phase turbulence fluctuations in a channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle equation of motion included the drag and the shear induced lift forces. The effect of particles on the flow was included in the analysis via a feedback force that acted on the computational grid points. Several simulations for different particle relaxation times and particle mass loadings were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration profiles were determined. It was found that, when particle-particle collisions were included in the computation but two-way coupling effects were ignored, the particle normal fluctuating velocity increased in the wall region causing an increase in the particle deposition velocity. When the particle collisions were neglected but the particle-fluid two-way coupling effects were accounted for, the particle normal fluctuating velocity decreased near the wall causing a decrease in the particle deposition velocity. For the physical case that both inter-particle collisions and two-way coupling effects are present, a series of four-way coupling simulations was performed. It was found that the particle deposition velocity increased with mass loading. The results for the particle concentration profile indicated that the inclusion of either two-way coupling or inter-particle collisions into the computation reduced the accumulation of particles near the wall. Comparisons of the present simulation results with the available experimental data and earlier numerical results were also presented.

scholarly journals Particle Deposition Characteristics and Efficiency in Duct Air Flow over a Backward-Facing Step: Analysis of Influencing Factors

2019 ◽  
Vol 11 (3) ◽  
pp. 751
Author(s):  
Hao Lu ◽  
Li-zhi Zhang
Keyword(s):  
Particle Deposition ◽  
Air Flow ◽  
Deposition Velocity ◽  
Particle Diameter ◽  
Deposition Efficiency ◽  
Reynolds Stress Model ◽  
Expansion Ratio ◽  
Particle Model ◽  
Duct Flow ◽  
Backward Facing Step

Dry deposition of airborne particles in duct air flow over a backward-facing step (BFS) is commonly encountered in built environments and energy engineering. However, the understanding of particle deposition characteristics in BFS flow remains insufficient. Thus, this study investigated particle deposition behaviors and efficiency in BFS flow by using the Reynolds stress model and the discrete particle model. The influences of flow velocities, particle diameters, and duct expansion ratios on particle deposition characteristics were examined and analyzed. After numerical validation, particle deposition velocities, deposition efficiency, and deposition mechanisms in BFS duct flow were investigated in detail. The results showed that deposition velocity in BFS duct flow monotonically increases when particle diameter increases. Moreover, deposition velocity falls with increasing expansion ratio but rises with increasing air velocity. Deposition efficiency, the ratio of deposition velocity, and flow drag in a BFS duct is higher for small particles but lower for large particles as compared with a uniform duct. A higher particle deposition efficiency can be achieved by BFS with a smaller expansion ratio. The peak deposition efficiency can reach 33.6 times higher for 1-μm particles when the BFS expansion ratio is 4:3. Moreover, the “particle free zone” occurs for 50-μm particles in the BFS duct and is enlarged when the duct expansion ratio increases.

Direct numerical simulation of particle collisions in two-phase flows with a meshless method

2008 ◽  
Vol 63 (13) ◽  
pp. 3474-3484 ◽  
Author(s):  
Changfu You ◽  
Xi Wang ◽  
Haiying Qi ◽  
Ruichang Yang ◽  
Delong Xu
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Meshless Method ◽  
Particle Collisions ◽  
Two Phase Flows ◽  
Two Phase

Inter-Particle Collisions: Analytical Approach for Closure of Driving Equations of Dispersed Phase in Gas-Solid Particle Flows

2003 ◽  
Author(s):  
Alexander Kartushinsky ◽  
Efstathios E. Michaelides
Keyword(s):  
Stress Tensor ◽  
Eddy Viscosity ◽  
Solid Particles ◽  
Particle Collision ◽  
Viscous Drag ◽  
Dispersed Phase ◽  
Particle Collisions ◽  
Governing Equations ◽  
Two Phase ◽  
Particle Flows

Two mechanisms for the particle-particle collisions—with and without frictional sliding collision are considered in this paper to take into account the effect of the particle-particle collision on the motion of solid particles in two-phase turbulent pipe and channel flows. Based on these mechanisms the correlations of the various velocity components of colliding particles are obtained analytically by using an averaging procedure, which takes into account three collision coordinates, two angles and one geometrical distance between the centers of colliding particles. As a result the various stress tensor components are obtained and then introduced in the mass, linear momentum and angular momentum equations of the dispersed phase. They are considered as additional force factors together with the influence of the particle-turbulence interactions, the viscous drag force, the two types of lift force (Magnus and Saffman) and the gravitational force. The approach applies to the particle-particle collisions based both on the average velocity difference between colliding particles and to the turbulent velocity fluctuation of colliding particles. To close the governing equations of the dispersed phase, the pseudoviscosity (and pseudodiffusity) coefficients with collision origin are determined as well, using a Bousinesque-type eddy-viscosity approach. [To close the governing equations of the dispersed phase, the stress tensor components as well as the pseudoviscosity (and pseudodiffusity) coefficients defined with the help of using a Bousinesque-type eddy-viscosity approach are determined here.] In order to obtain these coefficients the time of the inter-particle collision is calculated from the information on the collision process. The model covers the motion and collisions of both polydisperse and monodisperse particulate systems. The model is validated by comparison with the experimental data of Tsuji et al. (1984) for a vertical pipe.

Large-eddy simulation of turbulent gas–particle flow in a vertical channel: effect of considering inter-particle collisions

2001 ◽  
Vol 442 ◽  
pp. 303-334 ◽  
Author(s):  
Y. YAMAMOTO ◽  
M. POTTHOFF ◽  
T. TANAKA ◽  
T. KAJISHIMA ◽  
Y. TSUJI
Keyword(s):  
Gas Flow ◽  
Vertical Channel ◽  
Stokes Number ◽  
Particle Collision ◽  
Experimental Measurements ◽  
Particle Collisions ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Agreement

The interaction between a turbulent gas flow and particle motion was investigated by numerical simulations of gas–particle turbulent downward flow in a vertical channel. In particular the effect of inter-particle collision on the two-phase flow field was investigated. The gas flow field was obtained by large-eddy simulation (LES). Particles were treated by a Lagrangian method, with inter-particle collisions calculated by a deterministic method. The spatial resolution for LES of gas–solid two-phase turbulent flow was examined and relations between grid resolution and Stokes number are presented. Profiles of particle mean velocity, particle wall-normal fluctuation velocity and number density are flattened as a result of inter-particle collisions and these results are in good agreement with experimental measurements. Calculated turbulence attenuation by particles agrees well with experimental measurements for small Stokes numbers, but not for large Stokes number particle. The shape and scale of particle concentrations calculated considering inter-particle collision are in good agreement with experimental observations.

scholarly journals The Lattice-Boltzmann Modeling of Microflows in a Cell Culture Microdevice for High-Throughput Drug Screening

2021 ◽  
Vol 11 (19) ◽  
pp. 9140
Author(s):  
Roman G. Szafran ◽  
Mikita Davykoza
Keyword(s):  
High Throughput ◽  
Drug Screening ◽  
Lattice Boltzmann ◽  
Plug Flow ◽  
Algebraic Solution ◽  
Duct Flow ◽  
Mean Velocity ◽  
Navier Stokes Equation ◽  
High Throughput Drug Screening ◽  
The Mean

The aim of our research was to develop a numerical model of microflows occurring in the culture chambers (CC) of a microfluidic device of our construction for high-throughput drug screening. The incompressible fluid flow model is based on the lattice-Boltzmann equation, with an external body force term approximated by the He-Shan-Doolen scheme and the Bhatnagar-Gross-Krook approximation of the collision operator. The model accuracy was validated by the algebraic solution of the Navier–Stokes equation (NSE) for a fully developed duct flow, as well as experimentally. The mean velocity prediction error for the middle-length cross-section of CC was 1.0%, comparing to the NSE algebraic solution. The mean error of volumetric flow rate prediction was 6.1%, comparing to the experimental results. The analysis of flow hydrodynamics showed that the discrepancies from the plug-flow-like velocity profile are observed close to the inlets only, and do not influence cell cultures in the working area of CC. Within its workspace area, the biochip provides stable and homogeneous fully developed laminar flow conditions, which make the procedures of gradient generation, cell seeding, and cell-staining repeatable and uniform across CC, and weakly dependent on perturbations.

Sign in / Sign up

Export Citation Format

Share Document