Turbulent Coagulation Research Articles

Important role of turbulence on the distribution of particle radioactivity in the nuclear explosions

The distribution of particle radioactivity is one of the most important source items of radioactive fallout prediction model for nuclear explosion. For radioactive particles with the diameter larger than 0.5 μm, the influence of turbulent coagulation cannot be ignored. However, few scholars have considered the role of turbulence in the study of the distribution of particle radioactivity. The General Dynamic Equation (GDE), which is solved using the Multi-Monte Carlo method, is used in this study to establish a new model of the distribution of particle radioactivity that takes the impact of turbulent coagulation into account. The results present that the surface and volume distributions of particle radioactivity are closer to those of the Defense Land Fallout Interpretative Code (DELFIC) model, and the relative error of the surface (volume) distribution reduces from 1.243 (0.687) to 0.945 (0.284) when compared to the previous model that simply takes Brownian coagulation into account. The geometric median diameter of total particle radioactivity increases as the solidification temperature increases and as the particle size range increases when considering the influence of various geological conditions. When considering the effects of turbulent coagulation, the differences in the particle radioactivity produced under different geological conditions are smaller than those only considering the Brownian coagulation. This study highlights the importance of turbulent coagulation on the distribution of particle radioactivity in the nuclear explosions.

Turbulence enhancement of coagulation: The role of eddy diffusion in velocity

A Smoluchowski type model of coagulation in a turbulent fluid is given, first expressed by means of a stochastic model, then in a suitable scaling limit as a deterministic model with enhanced diffusion in the velocity component. A precise link between mean intensity of the turbulent velocity field and coagulation enhancement is obtained by numerical simulations, and a formula for the mean velocity difference, in agreement with the gas-kinetic model, is proved by a new method.

Congenital Bleeding Disorders and COVID-19 - An Emphasis on the Role of Thrombosis as One of the Main Causes of Morbidity and Mortality in COVID-19

A turbulent coagulation system is a prominent feature of Coronavirus Disease 2019 (COVID-19), with venous thromboembolism (VTE) a leading cause of death. Our hypothesis is that patients with inherited hypocoagulability, like congenital bleeding disorders (CBD), enjoy a protective effect against COVID-19-induced hypercoagulability and related fatal consequences. Our primary and follow-up observations revealed this effect, at least among patients with moderate to severe congenital bleeding disorders, particularly coagulation factor deficiencies. Theoretically, patients with inherited hypocoagulobility have only a potential protective effect against COVID-19-related hypercoagulability. Yet the lower rate of morbidity and mortality in patients with CBDs suggests that hypercoagulability and thrombotic events are the main cause of death in COVID-19. Therefore, appropriate and timely administration of anticoagulants could significantly decrease the rate of morbidity and mortality in COVID-19.

Analysis of turbulent coagulation in a jet with discretised population balance and DNS

The objective of the present study is to investigate turbulence–coagulation interaction via direct numerical simulation (DNS) coupled with the population balance equation (PBE). Coagulation is an important process in several environmental and engineering applications involving turbulent flow, including soot formation, gas-phase synthesis of nanoparticles and atmospheric processes, but its interaction with turbulence is not yet fully understood. Particle dynamics can be described by the PBE, whose Reynolds decomposition leads to unclosed terms involving correlations of number density fluctuations. In this work, we employ a discretisation (sectional) method for the solution of the PBE, which is free ofa prioriassumptions regarding the particle size distribution (PSD), and couple it with a DNS for the flow field in order to study the behaviour and significance of the unknown correlations. At present, it is not feasible to resolve the Batchelor scales that result from diffusion at high Schmidt number, hence a unity Schmidt number is employed. The investigation is conducted on a three-dimensional planar jet laden with monodisperse nanoparticles, and coagulation in the free-molecule regime is considered. The correlations due to turbulent fluctuations of the particle number density are calculated at several points in the domain and found to be positive in most cases, except close to the jet break-up. The transport equation for the moments of the PSD is also studied, and it is found that the correlations make a considerable contribution to the time-averaged coagulation source term, up to$20\,\%$on the jet centreline and$40\,\%$close to the edges.

Specificfeatures of evolution of dense atomized superheated water plumes and peculiarities of its diagnostics

Experimental study of evolution of plumes of atomized metastable superheated water during its discharge through convergent-divergent nozzles is conducted. Dispersion characteristics of dense plumes in micron and submicron droplet diameter ranges are obtained. Theoretical and prediction analyses of different coagulation mechanisms in the considered two-phase flow are performed. The negligible effect of Brown-type coagulation is shown. It is also demonstrated that turbulent coagulation can change the fraction of micron-diameter droplets within 9%. In addition, for the first time, an “inertial” mechanism of coagulation is considered for the studied plumes under the conditions of plume baking in a cocurrent flow or in the ambient air. It can lead to a considerable decrease in the submicron-droplet mass fraction, which is observed in experiments even at a small distance from the nozzle cut. The predicted data are compared with experimental ones obtained at theexperimental setup.

Effect of Impeller and Gas Stirring on Agglomeration Behavior of Polydisperse Fine Particles in Liquid

Agglomeration, coalescence and flotation of non-metallic inclusions in steel melt are effective for obtaining “clean steel.” In this study, the agglomeration and breakup behaviors of particles with a primary particle size distribution (hereinafter, polydisperse particles) in a liquid under impeller and gas stirring were compared by numerical calculations and model experiments. The particle-size-grouping (PSG) method in the numerical agglomeration model of particles was combined with a breakup term of agglomeration due to bubble bursting at the free surface. Polydisperse and monodisperse polymethylmethacrylate (PMMA) particles were used in the agglomeration experiments. The agglomeration rate of the polydisperse particles under impeller stirring was increased by an increasing energy input rate, whereas the agglomeration rate under gas stirring decreased under this condition due to the larger contribution of the breakup of agglomerated particles during bubble bursting in gas stirring. At the same energy input rate, agglomeration of polydisperse particles was larger under impeller stirring than under gas stirring. The agglomeration rate of polydisperse particles was larger than that of monodisperse particles under both impeller and gas stirring at the same energy input rate. The computational temporal changes in the total number of particles were in good agreement with the experimental results. This means that the difference in the agglomeration behaviors observed in impeller and gas stirring can be explained by the turbulent coagulation and subsequent agglomerated particle breakup in gas stirring. The computational temporal change in the number of each group approximately agreed with the experimental change in both impeller and gas stirring.

Study on Dust Turbulence-Chemical Agglomeration for Electrostatic Precipitation Technology

Due to the turbulent mixing between agglomeration agent and dust, the number of collisions per unit time between particles and droplets increases with the particle size in the process of chemical agglomeration, and the agglomeration efficiency increases accordingly. Turbulent agglomeration can promote the agglomeration effect of subsequent chemical agglomeration by strengthening the collision between particles and agglomerant droplets. The author used chemical agglomeration and turbulent mixing to cooperate in order to improve the efficiency of dust removal. Turbulent mixing can promote chemical agglomeration from agglomeration effect and dust removal efficiency, which can greatly improve electric dust removal technologyTurbulent mixing is the most intense at the inlet box position, and the agglomeration effect is the best. Turbulent mixing synergistic effect has an effect on dust removal efficiency. Compared with the three curves, it can be seen that the dust removal efficiency increases rapidly with the increase of agglomeration concentration, the curve trend changes obviously. The dust removal efficiency can reach 98.36 % and it is the highest in the middle section when the wind speed is greater than 11.2m/s. Through the experiment, the turbulent mixing and chemical coagulation method has a good application prospect in the electrostatic precipitators.

MODERNIZATION OF DEVICES FOR PURIFICATION OF AIR FROM SOLID HIGH-DISPERSED AEROSOLS

A device for cleaning solid particles with a dispersion of 0.1 μm is proposed. The principle of the apparatus is based on coagulation of particles on slots perforated in the form of slots, using irrigation of contaminated air with water through nozzles with a dispersed composition from 2.0 microns to 10 microns. When a threephase fl ow passes through the slots of the fi rst separator plate, turbulent coagulation occurs due to turbulence of the fl ow in streams with a small turbulence scale, which leads to particle coarsening. When the jet runs onto the second plate, a boundary layer is formed that has an increased viscosity to the components of the jet. Viscosity is formed due to the sedimentation and mixing of water particles and dust (including coarsened) on the surface of the second plate, where particles are mainly deposited. The dependences of the apparatus effi ciency on the width of the slots and their mutual arrangement on the fi rst and second plates, the combination of which provides a mode of increased coagulation and high effi - ciency of particle capture by the apparatus, are revealed.

Turbulent coagulation of micron and submicron particles in swirling flow

Coagulation of fine particles in turbulent swirling flow is investigated experimentally and numerically. First, different swirl producers are compared and helical blade is adopted due to its enhanced diffusion and convection in the radial direction. Then, study on structural parameters of helical blade is carried out, the result shows that smaller diameter of inner blades or shorter axial spacing between inner and outer blades can create better performance. Finally, research on the effect of operating parameters is conducted. The result implies that lower velocity or higher particle concentration helps improve coagulation performance, since diffusion and particle interaction are strongly affected by the turbulent two-phase flow field. The patterns of coagulation for micron and submicron particles are slightly different due to varied particle dynamics, specifically, breakup is an important factor for larger particles. Rising temperature has positive effect on coagulation of submicron particles because of enhanced thermal motions. Comparatively, the thermal effect is negligible for the micron particles. The study analyzed the mechanism behind turbulent coagulation in swirling flow, from which directions for optimal design are provided.

Determination of the Rate of Salt-Induced Rapid Coagulation of Polystyrene Latex Particles in Turbulent Flow Using Small Stirred Vessel

In our study, we revisited a previously reported method for evaluating the mixing intensity of uniform colloidal spheres in terms of their collision frequency, with the aim of evaluating the validity of this method in the case of a small stirred vessel equipped with an impeller with four paddles. The rates of the salt-induced rapid coagulation of polystyrene latex (PSL) particles with five different diameters were measured as functions of the rotation rate. The ad-hoc assumption of the linear additivity of the perikinetics and the orthokinetics of the coagulation process was used for the analysis. Our previously proposed equation for the rate of turbulent coagulation as a function of the particle diameter, determined for an end-over-end rotation mixing device, was confirmed to be valid. However, it was found that, for small particles and low-mixing rates, i.e., for low Peclet numbers, the rate of coagulation becomes larger than that predicted on the basis of linear additivity because of the coupling effect of Brownian motion and the fluid flow during turbulent mixing. This increase occurred even though the rate was lowered by the wall effect, which resulted in an inhomogeneous distribution of the mixing intensity.

The numerical simulation of flow field characteristics for single vortex column in different shapes

The coagulation technology of turbulence can improve the PM2.5 removal efficiency of ESP effectively, which is a hot technology researched by the scholars and manufacture. The turbulence produced by vortex column is the main power supply in the turbulence coagulation device, the velocity distribution, turbulence intensity, turbulence viscosity and pressure loss of single vortex column in different shapes and sizes were calculated in this paper. The turbulence produced by angle-steel had a better velocity and character than cylindrical vortex, and if the size of angle-steel and cylindrical vortex was bigge, the turbulence effect of the flow field would become better, but the pressure loss of different shapes would increase. We need to ensure the turbulence effect as well as minimize unnecessary pressure loss in practical applications.

Hybrid method of moments with interpolation closure–Taylor-series expansion method of moments scheme for solving the Smoluchowski coagulation equation

This paper presents a hybrid method of moments with interpolation closure–Taylor-series expansion method of moments (MoMIC–TEMoM) scheme for solving the Smoluchowski coagulation equation. In the proposed scheme, the exponential function, which arises in the conversion from a particle size distribution space to a space of moments, is expressed in an additive form using the third-order Taylor-series expansion; the implicit moments are approximated using two Lagrange interpolation functions, namely the newly defined normalized moment function and the normalized moment function defined by Frenklach and Harris (1987). The new hybrid scheme allows implementation of the method of moments with an arbitrary type of moment sequence, and it overcomes the shortcomings of the Taylor-series expansion moment method proposed by Frenklach and Harris. The proposed scheme is verified with three aerosol dynamics, namely Brownian coagulation in the free molecular regime, Brownian coagulation in the continuum-slip regime, and turbulence coagulation. The results reveal that the hybrid MoMIC–TEMoM scheme has similar accuracy to currently recognized methods including the quadrature method of moments, MoMIC, and TEMoM, and its accuracy can be further enhanced as the fractional moment sequence type is used for Brownian coagulation in the free molecular regime. Thus, the proposed scheme is a reliable for solving the Smoluchowski coagulation equation.

A coupled CFD-Monte Carlo method for simulating complex aerosol dynamics in turbulent flows

A coupled computational fluid dynamics (CFD)-Monte Carlo method is presented to simulate complex aerosol dynamics in turbulent flows. A Lagrangian particle method-based probability density function (PDF) transport equation is formulated to solve the population balance equation (PBE) of aerosol particles. The formulated CFD-Monte Carlo method allows investigating the interaction between turbulence and aerosol dynamics and incorporating individual aerosol dynamic kernels as well as obtaining full particle size distribution (PSD). Several typical cases of aerosol dynamic processes including turbulent coagulation, nucleation and growth are studied and compared to the sectional method with excellent agreement. Coagulation in both laminar and turbulent flows is simulated and compared to demonstrate the effect of turbulence on aerosol dynamics. The effect of jet Reynolds (Rej) number on aerosol dynamics in turbulent flows is fully investigated for each of the studied cases. The results demonstrate that Rej number has significant impact on a single aerosol dynamic process (e.g., coagulation) and the simultaneous competitive aerosol dynamic processes in turbulent flows. This newly modified CFD-Monte Carlo/PDF method renders an efficient method for simulating complex aerosol dynamics in turbulent flows and provides a better insight into the interactions between turbulence and the full PSD of aerosol particles.Copyright © 2017 American Association for Aerosol Research

Reynolds-number dependence of turbulence enhancement on collision growth

Abstract. This study investigates the Reynolds-number dependence of turbulence enhancement on the collision growth of cloud droplets. The Onishi turbulent coagulation kernel proposed in Onishi et al. (2015) is updated by using the direct numerical simulation (DNS) results for the Taylor-microscale-based Reynolds number (Reλ) up to 1140. The DNS results for particles with a small Stokes number (St) show a consistent Reynolds-number dependence of the so-called clustering effect with the locality theory proposed by Onishi et al. (2015). It is confirmed that the present Onishi kernel is more robust for a wider St range and has better agreement with the Reynolds-number dependence shown by the DNS results. The present Onishi kernel is then compared with the Ayala–Wang kernel (Ayala et al., 2008a; Wang et al., 2008). At low and moderate Reynolds numbers, both kernels show similar values except for r2 ∼ r1, for which the Ayala–Wang kernel shows much larger values due to its large turbulence enhancement on collision efficiency. A large difference is observed for the Reynolds-number dependences between the two kernels. The Ayala–Wang kernel increases for the autoconversion region (r1, r2 < 40 µm) and for the accretion region (r1 < 40 and r2 > 40 µm; r1 > 40 and r2 < 40 µm) as Reλ increases. In contrast, the Onishi kernel decreases for the autoconversion region and increases for the rain–rain self-collection region (r1, r2 > 40 µm). Stochastic collision–coalescence equation (SCE) simulations are also conducted to investigate the turbulence enhancement on particle size evolutions. The SCE with the Ayala–Wang kernel (SCE-Ayala) and that with the present Onishi kernel (SCE-Onishi) are compared with results from the Lagrangian Cloud Simulator (LCS; Onishi et al., 2015), which tracks individual particle motions and size evolutions in homogeneous isotropic turbulence. The SCE-Ayala and SCE-Onishi kernels show consistent results with the LCS results for small Reλ. The two SCE simulations, however, show different Reynolds-number dependences, indicating possible large differences in atmospheric turbulent clouds with large Reλ.

Solution of general dynamic equation for nanoparticles in turbulent flow considering fluctuating coagulation

A new averaged general dynamic equation (GDE) for nanoparticles in the turbulent flow is derived by considering the combined effect of convection, Brownian diffusion, turbulent diffusion, turbulent coagulation, and fluctuating coagulation. The equation is solved with the Taylor-series expansion moment method in a turbulent pipe flow. The experiments are performed. The numerical results of particle size distribution correlate well with the experimental data. The results show that, for a turbulent nanoparticulate flow, a fluctuating coagulation term should be included in the averaged particle GDE. The larger the Schmidt number is and the lower the Reynolds number is, the smaller the value of ratio of particle diameter at the outlet to that at the inlet is. At the outlet, the particle number concentration increases from the near-wall region to the near-center region. The larger the Schmidt number is and the higher the Reynolds number is, the larger the difference in particle number concentration between the near-wall region and near-center region is. Particle polydispersity increases from the near-center region to the near-wall region. The particles with a smaller Schmidt number and the flow with a higher Reynolds number show a higher polydispersity. The degree of particle polydispersity is higher considering fluctuating coagulation than that without considering fluctuating coagulation.

Experimental Parametric Study of Frequency and Sound Pressure Level on the Acoustic Coagulation and Precipitation of PM2.5 Aerosols

ABSTRACTThe efficiency of particle removal for PM2.5 aerosols using conventional separation systems is generally low. In this paper, acoustic precipitation and coagulation of aerosols as a preconditioning system is investigated experimentally. The results of experimental study concerning the effect of frequency and sound pressure level (SPL) on the acoustic coagulation and precipitation of PM2.5 aerosols are presented. An acoustic particle conditioning setup was used to perform experiments at the resonance frequencies of 204, 550, 650 and 749 (Hz), and SPLs 140, 150, 155, 162 dB. All experiments were performed under ambient condition and similar initial concentration. The experimental results showed that the effect of acoustics on filtration efficiency is amplified by increasing the frequency and intensity. Eventually, at the frequency of 749 (Hz) and 162 (dB) the acoustic coagulation and precipitation efficiency reaches about 83% which is significant. The results of this study (experimentally and theoretically) prove the existence of a threshold in SPL (≥ 155 dB) at which the acoustic precipitation and coagulation efficiency increase rapidly, implying the importance of turbulence coagulation interactions at high intensity acoustic waves. In addition, a new empirical correlation was developed for the acoustic coagulation and precipitation efficiency with reasonable accuracy.

Orthokinetic aggregation of charged colloidal particles in the presence of repulsive double layer force: A trajectory analysis with the solution of non-linear Poisson–Boltzmann equation

Abstract We studied turbulent coagulation rates of well-characterized carboxyl-terminated latex particles as a function of pH at different KCl concentrations. The negative charge of the studied particles increases and thus develops the electrical double layer repulsion with increasing pH. The pH-dependent coagulation rate was analyzed on the basis of the trajectory analysis with the Derjaguin, Landau, Verwey, and Overbeek theory using the solution of non-linear Poisson–Boltzmann (PB) equation under the charge regulation boundary condition, in which the electrostatic boundary conditions such as surface potential depends on surface separation distance. It should be noted that this is the first attempt to compare the calculated results with the experimental data of the effect of surface charge on turbulent coagulation rates. The calculation using the trajectory analysis can well describe the experimental data. However, to obtain the good agreement between the experimental data and the calculation, we need to decrease the Hamaker constant A H with increasing KCl concentration. The dependence of A H on salt concentration is probably ascribed to the fact that the origin of the van der Waals attraction is essentially electrostatic dipole–dipole interaction between molecules. That is, we consider that the van der Waals attraction is increasingly screened by the charge of ions with increasing salt concentration.

Numerical Investigation of Brownian, Gradient, and Turbulent Coagulation Under Moving Vehicle Conditions in an Underground Garage

Particle coagulation behavior can affect particle formation and dispersion in vehicle plumes. An Eulerian particle transport model combining a Realizable k–ϵ model, Brownian, gradient, and turbulent coagulation has been developed to analyze particle coagulation behavior in an underground garage under moving-vehicle conditions. The results show that prominent coagulation of nanoparticles occurs within a limited region, which is at a distance of less than 0.2 m in the vertical direction and no more than 0.4 m in the exhaust direction from a given vehicle. The coagulation of small particles with diameters of less than 130 nm is dominated by Brownian motion, while gradient and turbulent coagulation significantly affect the coagulation of particles with median diameters of 420 nm and larger diameters of 600–950 nm, respectively. The influence of turbulent coagulation increases as vehicle speed and particle size increase. The half-time due to coagulation is approximately two times and 10–20 times larger than the corresponding value due to dilution in the regions less than 0.2 and 1.5 m along the tailpipe centerline, respectively. It is demonstrated that coagulation has considerable influence on particle dispersion in the region less than 0.2 m from the tailpipe, compared with dilution.

The Research Progress of Coagulation Technology on Fine Particles

This article reviewed some of the measures taken to control particulate matters by combining the latest fine particles dominating technologies both at home and abroad. The coagulation technological principles and research achievements of fine particles were suggested. The research highlightly analyzed the technical principles and characteristics of electric coagulation technology, acoustic coagulation technology, vapor condensation technology, thermal coagulation technology,chemical coagulation technology, magnetic coagulation technology, turbulent coagulation technology and light coagulation technology.On the basis of comprehensive analysis of these technologies, it pointed out the development trend of fine particle control technology.

Absolute rate of turbulent coagulation from turbidity measurement

Turbidity method has been applied to assess colloid stability. While the method is simple and easy, it is not straightforward in evaluating absolute coagulation rates of colloidal particles. That is, the method requires the evaluation of the extinction cross section of doublets. Recently, the turbidity measurement has been successfully utilized to evaluate the absolute Brownian coagulation rate constant with the T-matrix method, which calculates the extinction cross section of doublets at arbitral size range. The present work was performed to extend the applicability of the method to turbulent coagulation. To this end, we measured the turbidity change of coagulating latex suspensions in a turbulent flow. The measurement was performed as a function of particle size. From the turbidity vs. time relationship, we evaluated turbulent coagulation rate constant using the T-matrix method. Obtained values of the constants agreed well with theoretical ones, demonstrating the usefulness of turbidity method for turbulent coagulation.