Particle Volume Fraction Distribution Research Articles

Analysis of Fouling in Six-Start Spirally Corrugated Tubes

Fouling on heat exchanger surfaces can weaken the heat-transfer capability, increase the energy consumption, and even cause the failure of the whole system. In coaxial heat exchangers, spirally corrugated tubes perform better than smooth ones concerning heat transfer and antifouling. In this article, a parametric study on the antifouling performance of a six-start spirally corrugated tube is carried out with a solid–liquid two-phase model. First, comparisons between a smooth tube and a specific sample six-start spirally corrugated tube on the solid particle volume fraction distributions are carried out. Then, the effects of solid particle diameter, the main geometric parameters, including pitch and the corrugation depth, are investigated. Analyzing the solid particle volume fraction with different geometries, solid particle diameters and Reynolds number, the roles played by the centrifugal force, drag force, and gravity of solid particles on fouling performance in six-start spirally corrugated tubes are obtained. In addition, the corrugation depth affects the volume fraction range more while the pitch affects more on the steady range of particle volume fraction. This work is of significance for further design of spirally corrugated tubes and analysis of fouling problems in heat exchangers.

Particle emission of organic brake pad material: A review

Wear of a brake pad emits airborne particles and is a major environmental issue. This review paper deals with the analysis of different brake pad composite materials and their wear phenomenon. The volume fraction and size distribution of non-asbestos organic airborne particles emitted from the brake pad material with time, load and speed have also been discussed under different braking conditions. The airborne particles are measured by different aerosol instruments. TSI P-Trak, GRIMM aerosol spectrometer and scanning mobility particle sizer were used by different researchers for measuring ultrafine particles, micron-sized particles and aerodynamic nanoparticles, respectively. This paper shows that the wear particles emitted from the brake pad material vary in diameter between 10 nm and 10 μm under various loads and sliding velocities. These airborne particles such as coarse fine (diameters > 1 μm), fine (diameters between 100 nm and 1 μm) and ultrafine (diameters < 100 nm) particles are responsible for health hazards to the human respiratory system. This study has accumulated the data of different ingredients of the brake pad with airborne particle emission from various studies, which may be helpful for the evolution of new composite materials in the near future.

3D Micro-Structural Modeling of Vibration Characteristics of Smart Particle-Reinforced Metal-Matrix Composite Beams

In this study, the effects of micro-structural parameters such as particle volume fraction, size and random distribution of Al 6061/SiC particulate metal-matrix composite (MMC) beams on free vibration response and the active vibration control are investigated. For this purpose, numerical particle-reinforced MMC (PRMMC) beam specimens were modeled with 3D finite elements, and the cubic-shaped reinforcing SiC particles were randomly distributed in Al 6061 metal matrix similar to an actual micro-structure. The particle size and especially volume fraction play an important role on the natural frequencies of the smart PRMMCs although they have no effect on the mode shapes. The random particle distribution has minor effect on the natural frequencies of the smart PRMMCs. With the increase of the feedback control gain, both the vibration amplitude and the suppression time are reduced reasonably. Increasing the particle volume fraction induces an important reduction in the damping time and the vibration amplitude for both the controlled and uncontrolled damped vibrations. Finally, increasing the particle size decreases the vibration suppression capacity and increases the vibration amplitude and time slightly. Random particle distribution had no obvious effect on the uncontrolled and controlled vibrations.

Investigation of gas–solid flow characteristics in the cyclone dipleg of a pressurised circulating fluidised bed by ECT measurement and CPFD simulation

To optimize the design and operation of a pressurised circulating fluidised bed (PCFB) system, it is necessary to understand the gas–solid flow characteristics and properly measure the solid circulation flux in the cyclone dipleg and loop-seal of the PCFB. In this research, electrical capacitance tomography (ECT) measurement and computational particle fluid dynamic (CPFD) simulation are combined to investigate the multiphase flow behaviour of a ‘cold’ PCFB, in particular the cyclone dipleg. A dual-plane ECT sensor is used for visualisation and online monitoring of the particle distribution. The particle velocity is measured by cross-correlation of two signals from capacitance electrodes, and the circulation flux is analysed. In addition, 3D full-loop CPFD simulation incorporating an energy-minimization multi-scale (EMMS) drag model is performed on a Barracuda platform, to understand the gas–solid hydrodynamic behaviour, validate and supplement the experimental measurements. The results show that the CPFD prediction agrees well with the ECT measurement in terms of the particle volume fraction distribution, velocity and circulation flux. The time-averaged gas–solid flow behaviour, instantaneous hydrodynamic features and the effects of operating pressure on particle distribution and the flow regime in the PCFB dipleg are unravelled. This is the first investigation of a solid circulation flux measurement in the cyclone dipleg and loop-seal of a PCFB system using a combination of ECT measurements, cross-correlation and CPFD simulation with high-pressure operational conditions.

Particle orientation and bulk properties of magnetoactive elastomers fabricated with aligned barium hexaferrite

Abstract

Multiple-inclusion model for the transport properties of porous composites considering coupled effects of pores and interphase around spheroidal particles

Understanding of the effects of particle geometries, pores and interphase characteristics on transport properties of porous composites is very crucial to the smart design of porous composites and the improvement of their durability. In this work, the authors devise a multiple-inclusion micromechanical model to predict the effective transport properties of multiphase porous composites, where spheroidal inclusions of diverse types are randomly dispersed in a homogeneous matrix. The multiple-inclusion model is then applied to estimate the effective diffusivity of four-phase porous composites containing impermeable particles, pores, highly permeable interphase and matrix. Specifically, the microstructural characteristics of pores, interphase and particles, and their physical properties are incorporated into the evaluation of the effective diffusivity of porous composites. It is shown that the present model leads the prediction of diffusivity of porous composites to reasonable accuracy by comparing with extensive experimental data. Moreover, utilizing the proposed model, we investigate the dependence of effective diffusivity of porous composites on the shape, volume fraction and size distribution of impermeable particles, the interphase thickness and volume fraction, and the porosity characterized by the hydration degree of cement and the water-cement ratio. The results reveal that the geometrical and physical properties of these components play a significant role in determining the diffusivity of porous composites. The multiple-inclusion model provides a powerful and convenient predictive toolkit for multiphase composite design and evaluation.

Numerical investigation of gas-particle hydrodynamics in a vortex chamber fluidized bed

Gas-particle hydrodynamic behaviour inside a vortex chamber fluidized bed is studied numerically with respect to different design and operating conditions. A three-dimensional computational fluid dynamics (CFD) model of a cylindrical vortex chamber is developed. Simulations are carried out with particles and without particles. In order to understand the gas-particle flow behavior velocity distribution, particle volume fraction distribution, radial pressure distribution and axial pressure distribution inside the vortex chamber are analyzed in detail. Particles of different diameters are used and its effect on the gas-particle flow behaviour is studied. Design parameters like the number of gas inlet slots and slot width are varied and their impact on the hydrodynamics of the vortex chamber is investigated. The numerical model is validated by comparing the numerical results with experimental results reported in literature.

In-situ laser diagnostic of nanoparticle formation and transport behavior in flame aerosol deposition

In this work, we investigate the flame aerosol deposition of TiO2 nanoparticles in a well-defined premixed stagnation flame based on two-dimensional phase-selective laser-induced breakdown spectroscopy (PS-LIBS). The deposited nanoparticles are in anatase phase with an average size of ∼10 nm. In PS-LIBS measurement, atomic emissions of titanium near the wavelength of 500 nm are extracted by spectral filter lenses and imaged for demonstrating the particle volume fraction distributions. The PS-LIBS signals can well depict the whole process of particle formation and transport, including the rapid gas-to-particle conversion near the flame front, dilution and concentrating of the nanoparticles induced by gas density variations, and dropping of particle volume fractions near the substrate. A quantitative model has been proposed to describe convection, thermophoresis, and diffusion of the nanoparticles. Combining the PS-LIBS measurement and the numerical simulation, it is found that, the nanoparticles concentrate outside the boundary layer at low substrate temperatures due to a joint effect of gas compression and thermophoresis. Further parametric analysis indicates that substrate temperatures and precursor loading rates can strongly affect the particle concentration boundary layer and the particle deposition rate.

Techno economic analysis of chemical looping system for Indian power plants

Abstract Chemical looping combustion (CLC) has been developed as a major new generation CO 2 capture technology which involves inherent CO 2 separation and high system conversion efficiency. The technology is well-known to have low energy penalty, as compared to other technologies. This paper intends to carry out a numerical investigation on the flow characteristics of the chemical looping combustion (CLC) process using the cold model fabricated and commissioned by CSIR-CIMFR, Dhanbad. It attempts to visualise the hydrodynamic viability of the system, which is very important to know the effect of the configuration of the system on circulation of the oxygen carrier particles. Cost analysis for a power plant implemented with chemical looping based capture system in Indian condition has also been presented. The pressure drop profile, volume fraction distribution of particles and fluidisation patterns are analysed and found to give expected results. The effects of gas phase and solid phase velocity are also studied, through which, similarity in flow pattern of ilmenite as well as air can be seen in both the plots. Through the cost analysis, higher temperature in both air reactor as well as fuel reactor has been found to increase plant efficiency while residence time in both reactor was found to have a little effect on the plant efficiency. As cost for O&M for gasifier was found to be more, change and modification of the gasifier unit will play a major role towards increasing the plant efficiency with incorporation of chemical looping as a carbon capture system.

Hydrodynamic Modelling of Coal-Biomass Mixture in a Bubbling Fluidized Bed Reactor

Biomass is a renewable and sustainable energy source. Co-firing of biomass with coal will increase the renewable energy share by decreasing the coal consumption. In the present paper, hydrodynamic behaviour of coal and biomass mixture is investigated in a fluidized bed reactor. A Computational Fluid Dynamic (CFD) model is developed and the hydrodynamic behaviour of gas and solid is investigated in detail. The CFD model is based on Eulerian-Eulerian multiphase modelling approach where the solid phase properties are obtained by applying the Kinetic Theory of Granular Flow (KTGF). Six different weight percentages of coal and biomass (100:0, 95:5, 90:10, 80:20, 70:30 and 50:50) are used for the present study. The hydrodynamic behaviour is analyzed in terms of the important hydrodynamic parameters like bed pressure drop, bed expansion ratio, particle volume fraction distribution and velocity distribution. The numerical model is also validated by comparing some of the numerical results with our own experimental data generated in a laboratory scale bubbling fluidized bed reactor.

Phase coarsening in multicomponent systems.

A theory for phase coarsening in multicomponent systems is developed in which both the multicomponent thermodynamic effect and kinetic effect from a nonzero volume fraction are considered. In contrast to previous theory, a diffusion screening zone for a coarsening particle due to nonzero volume fraction is introduced. The evolution equation for phase coarsening in multicomponent systems is derived in a rigorous way in the framework of the maximum rate of dissipation with the constraints of mass and energy conservation. Existing previous relations are recovered and generalized. Some findings such as the relationship between the maximum particle size and volume fraction and particle size distribution in multicomponent systems are discovered.

Numerical Prediction of Indentation Behavior of Metal Matrix Composites Using XFEM

In this study, the effects of particle volume fraction, particle size and particle distribution is investigated on the indentation behavior of metal matrix composites (MMCs) using extended finite element approach. The particles are assumed to be circular in shape. The matrix (Zr2.5Nb) is assumed to have an elasto-plastic behaviour whereas the particles (SiC) are assumed to have linear elastic behavior. The indentation response of the MMCs is investigated using random particles distribution for different reinforcement volume fractions (10 to 30%). Plastic behavior of matrix is described by the von-Mises yield criterion with Hollomon's power law equation. The large deformation under the indenter is modelled by updated Lagrangian approach. A penalty approach is employed to impose the contact constraints at the interface between the indenter and matrix. An efficient node-to-segment (NTS) frictionless contact algorithm is employed to model the contact behavior. The effect of particle size, distribution and volume fraction on the residual von-Mises stress and equivalent plastic strain is also investigated.

Effects of Initial Perturbations in the Early Moments of an Explosive Dispersal of Particles

Recent experiments have shown that when a dense layer of solid particles surrounding a high-energy reactive material is explosively dispersed, the particles cluster locally leading to jetlike patterns. The formation of these coherent structures has yet to be fully understood and is believed to have its origin in the early moments of the explosive dispersal. This paper focuses on the early moments of an explosive dispersal of particles. In particular, the effect of initial perturbations on both the gas and particulate phase is investigated, considering heavy particles with a low initial particle volume fraction. Two-dimensional simulations are carried out, and results suggest that a distinctive heterogeneity in the form of a single wavelength perturbation in the rapidly expanding detonation products does not have a significant impact on the early evolution of neither the gas phase nor the cloud of particles. In contrast, the equivalent distinctive heterogeneity in the initial particle volume fraction distribution lingers for the duration of our simulations. Developing instabilities in the gas phase and at the inner- and outer-most front of the particle bed display a dominant wavelength equal to the wavelength of the initial perturbation in the particle volume fraction.

Analytical effective elastic properties of particulate composites with soft interfaces around anisotropic particles

Understanding the effects of interfacial properties on effective elastic properties is of great importance in materials science and engineering. In this work, we propose a theoretical framework to predict the effective moduli of three-phase heterogeneous particulate composites containing spheroidal particles, soft interfaces, and a homogeneous matrix. We first derive the effective moduli of two-phase representative volume elements (RVEs) with matrix and spheroidal inclusions using the variational principle. Subsequently, an analytical model considering the volume fraction of soft interfaces around spheroidal particles is presented. The effective moduli of such three-phase particulate composites are eventually derived by the generalized self-consistent scheme. These theoretical schemes are compared with experimental studies, numerical simulations, and theoretical approximations reported in the literature to verify their validity. We further investigate the dependence of the effective elastic modulus on the interfacial properties and the geometric characteristics of anisotropic particles based on the proposed theoretical framework. Results show that the interfacial volume fraction and the effective elastic modulus of particulate composites are strongly dependent on the aspect ratio, geometric size factor, volume fraction, and particle size distribution of ellipsoidal particles.

Numerical study of forced convection flow and heat transfer of a nanofluid flowing inside a straight circular pipe filled with a saturated porous medium

In this paper, the problem of developing forced convection flow of a nanofluid in a constant-wall-temperature circular tube filled with a porous medium is considered. The flow is steady and Brinkman-Forchheimer-extended Darcy equation model is employed. The thermal-equilibrium model is assumed between nanofluid and solid phase. It is also assumed that nanoparticles are distributed non-uniformly inside the pipe, hence the particles volume fraction equation is also coupled with the governing equations. A numerical study has been performed using the Finite-Volume method to analyze heat transfer coefficient of Al2O3 -water nanofluid. The effects of nanoparticles volume fraction and porosity on fluid flow and heat transfer of nanofluids are studied. The results show that the Nusselt number is increased with increasing particles volume fraction. Moreover, the wall shear stresses are increased. Finally, the effect of porosity on particle volume fraction distribution is studied and discussed in detail. We are confident that the reported results are new and original.

Evaluating Dust Particle Transport Performance within Urban Street Canyons with Different Building Heights

ABSTRACTIn developing cities, buildings with different heights obstruct the diffusion of pollutants. In this study, dust particles transported within urban street canyons were simulated using Reynolds-averaged Navier–Stokes (RANS) method, and air-solid two-phase flow fields were obtained on a regional scale. Four typical street building models were used in this study: (a) low-rise buildings (H/b = 1), (b) step-up building arrangements (H/b = 1, 2, 3, 4, 5), (c) step-down building arrangement (H/b = 5, 4, 3, 2, 1), and (d) high-rise buildings (H/b = 5). The particle volume fraction distribution in the four models reflected the basic properties of particle transportation in the canyons. Vortices were observed on the roofs of street canyons, which prevented particles from being transmitted into the canyons, and the vortex regions were characterized as low particle concentration. To evaluate the dust particle transport performance in the models, three indices, namely particle transport efficiency, suspension fraction and suspension density, were defined. These concepts were based on the particle number concentrations, which were obtained using the Lagrange approach. The high-rise building model (H/b = 5) demonstrated the lowest transport efficiency among all four models, and it also had the lowest suspension density in the street canyons. This implied that the high-rise buildings hindered the particles from being transporting further and that the particles could not enter the deep canyons easily. In the step-down building arrangement model (H/b = 5, 4, 3, 2, 1), the particle concentration level and suspension density in the canyons were lower than those observed in the step-up building arrangement model (H/b = 1, 2, 3, 4, 5), indicating that a step-down building height arrangement is appropriate for creating construction plans for developing cities. Finally, the variation of the streamwise air velocity, vertical velocity and fluctuating velocity on the roof of canyons along the x direction were separately examined. Notably, the fluctuating velocity was the dominant mechanism of the particle suspension in the canyons.

Flash X-ray measurements on the shock-induced dispersal of a dense particle curtain

The interaction of a Mach 1.67 shock wave with a dense particle curtain is quantified using flash radiography. These new data provide a view of particle transport inside a compressible, dense gas–solid flow of high optical opacity. The curtain, composed of 115-µm glass spheres, initially spans 87 % of the test section width and has a streamwise thickness of about 2 mm. Radiograph intensities are converted to particle volume fraction distributions using the Beer–Lambert law. The mass in the particle curtain, as determined from the X-ray data, is in reasonable agreement with that given from a simpler method using a load cell and particle imaging. Following shock impingement, the curtain propagates downstream and the peak volume fraction decreases from about 23 to about 4 % over a time of 340 µs. The propagation occurs asymmetrically, with the downstream side of the particle curtain experiencing a greater volume fraction gradient than the upstream side, attributable to the dependence of particle drag on volume fraction. Bulk particle transport is quantified from the time-dependent center of mass of the curtain. The bulk acceleration of the curtain is shown to be greater than that predicted for a single 115-µm particle in a Mach 1.67 shock-induced flow.

The effect of the volume fraction and viscosity on the compression and tension behavior of the cobalt-ferrite magneto-rheological fluids

The purpose of this work is to investigate the effects of the volume fraction and bimodal distribution of solid particles on the compression and tension behavior of the Co-ferrite-based magneto-rheological fluids (MRFs) containing silicon oil as a carrier. Hence, Co-ferrite particles (CoFe2O4) with two various sizes were synthesized by the chemical co-precipitation method and mixed so as to prepare the bimodal MRF. The X-Ray Diffraction (XRD) analysis, Fourier Transform Infrared Spectroscopy (FTIR), Laser Particle Size Analysis (LPSA) and Vibrating Sample Magnetometer (VSM) were conducted to examine the structural and magnetic properties, respectively. The results indicated that the increase of the volume fraction has a direct increasing influence on the values of the compression and tension strengths of fluids. In addition, the compression and tension strengths of the mixed MRF sample (1.274 and 0.647 MPa) containing 60 and 550 nm samples were higher than those of the MRF sample with the same volume fraction and uniform particle size of 550 nm.

Multi-scale CFD simulation of hydrodynamics and cracking reactions in fixed fluidized bed reactors.

Fixed fluidized bed reactor is widely used to evaluate the crackability of heavy oils and the activity of catalysts. To understand the hydrodynamics, reaction kinetics and thermodynamics in conventional and modified fixed fluidized bed reactors, the computational fluid dynamics method, energy-minimization multi-scale-based two-fluid model coupled with a six-lump kinetic model was used to investigate the gas–solid flow and cracking reactions. The gas mixing and particle volume fraction distributions, as well as product yields in the conventional and modified fixed fluidized bed reactors were analyzed. The residence time distribution model was utilized to obtain the parameters indicating the back-mixing degree, such as mean residence time and dimensionless variance of the gas. The results showed that the simulated product distribution is in reasonable agreement with the experimental data; the modified fixed fluidized bed reactor is closer to the ideal plug flow reactor, which can efficiently enhance the gas–solid mixing, reduce the gas back-mixing degree, and hence improve the reaction performance.

SAXSEV 2.1 cross-platform application for data analysis of small-angle X-ray scattering from polydisperse systems

The present paper discusses development and implementation of the cross-platform application with a graphical user interface for estimation of the particle volume fraction distribution function and fitting specific surface area to this distribution pattern. SAXSEV implements the method of statistical regularization for ill-posed mathematical tasks being solved with the use of Numpy, Scipy and MathPlotlib libraries. The main features of this software application are the ability to adjust the arguments grid of the desired function and the ability to select the optimal value of the regularization parameter. This parameter is selected by several specific and one common criteria. The software application consists of modules written in Python3. The modules are combined by common interface based on Tkinter library. Current version SAXSEV 2.1 was tested on the basis of Windows XP / Vista / 7/8, Ubuntu 14.1. SAXSEV 2.1 was used successfully at effectiveness study of statistical regularization method for analyzing dispersed system by SAXS, at research of the powder consisting from nanoparticles and composite materials with nanoparticles inclusion.