Particle Velocity Profiles Research Articles

Comparative analysis of counter-current and co-current downer reactors using particle image velocimetry and computational particle-fluid dynamics

We investigated the hydrodynamics in co- and counter-current downer operations using particle image velocimetry (PIV) and computational particle fluid dynamics simulations (CPFD). Pilot-scale experiments were conducted for fluid catalytic cracking (FCC) catalysts and sand, which verified the system stability and provided the validation basis for the simulation strategy. We compared the reactor characteristics of counter-current and co-current downers under different operating modes and conditions using PIV experiments and CPFD simulations. PIV experiments showed that the counter-current downer exhibits a more uniform particle velocity profile, with a gradient of only 8 % of the maximum velocity, compared to the co-current operation, which shows a significantly steeper gradient of 39.5 % from the maximum. Simulations confirmed that the counter-current downer reactor has 69 % higher solid holdup and 98 % longer residence time than the co-current operation. Thus, the counter-current downer reactor demonstrated intermediate behavior between the classical co-current downer and riser reactors, offering flexibility for industrial applications.

Effect of Rate-Dependent Breakage on Strength and Deformation of Granular Sample—A DEM Study

The mechanical response of granular materials is influenced significantly by both the magnitude and strain rate. While traditionally considered rate-independent in the quasi-static regime, granular media can exhibit rate effects in certain instances. This research uses two-dimensional discrete element modelling (DEM) to investigate the rate effects in one-dimensional compression tests by comparing non-crushable with crushable granular samples. This study indicates that micromechanical properties such as particle breakage and contact force distributions are predominant factors in dictating the macroscopic responses of the material. The DEM simulations highlight differences in macroscopic changes between crushable and non-crushable samples, demonstrating a clear correlation between mechanical properties and underlying microstructural features. Notably, the distribution of contact forces varies with strain rates, influencing the degree of particle breakage and, consequently, the overall rate-dependent behaviour. Further, this study explores the impact of post-breakage contact creation and progressive force redistribution, which contributes to observable differences in macroscopic stress under varying loading rates, which is quantified using coordination number, particle velocity, and fabric tensor profiles at two loading rates.

Application of Laplace and Sumudu transforms to the modeling of unsteady rotating MHD flow in a second-grade tetra hybrid nanofluid in a porous medium

Understanding and managing the complex rheological behavior of fluid models is crucial for many real-world applications, such as industrial fluid dynamics, biomedical engineering, and environmental management. This study aims to predict the unsteady magnetohydrodynamic (MHD) flow of a second-grade tetra hybrid nanofluid in a porous medium containing uniformly dispersed dust particles. To address this challenge, we develop a mathematical model utilizing a non-fractional approach with ramping conditions. Our methodology incorporates Laplace and Sumudu transforms to analyze the velocity fields of both the fluid and dust particles. Additionally, we examine the heat transfer characteristics and the underlying dynamics of the magnetized second-grade tetra hybrid nanofluid flow. The momentum transfer of the dust particles is modeled using a separate equation. Key outcomes of this research include visual representations of novel findings, facilitating comparison with existing literature. Numerical simulations based on Sumudu and Laplace transformations produce velocity profiles for both fluid and dust particles, as well as temperature distributions, aligning with theoretical expectations. These results demonstrate the effectiveness of Laplace and Sumudu transforms in analyzing and simulating the turbulent MHD flow of nanofluids through porous media with dispersed dust particles.

Couette flow of viscoelastic dusty fluid through a porous oscillating plate in a rotating frame along with heat transfer

AbstractUsually, suction/blowing is used to control the channel's fluid flow, which is why this worth‐noting effect is considered. The fluid velocity is considered along the x‐axis due to the oscillations of the right plate. The thermal effect on the flow due to the heated right plate is also considered. The fluid and dust particles have complex velocities due to the rotation, which are the sum of primary and secondary velocities. To convert the aforementioned physical phenomenon into mathematical form, partial differential equations are used for modeling the subject flow regime. Appropriate nondimensional variables are employed to nondimensionalize the system of governing equations. With the assistance of assumed periodic solutions, the system of partial differential equations is reduced to a system of ordinary differential equations which is then solved by the perturb solution utilizing Poincare–Lighthill perturbation techniques. The engineering interest quantities, the Nusselt number, and skin friction are also determined. The impact of various parameters on skin friction, viscoelastic fluid, and dust particle velocity profiles is also investigated. It is worth mentioning that suction controls the boundary layer to grow unexpectedly, even in the resonance case. The obtained solution is also valid in the case of injection. The radiation parameter, Grashof number, and second‐grade parameter cause a decrease in skin friction as their values increase. On the other hand, the suction, rotation, magnetic, dusty fluid, and Reynolds numbers cause a rise in skin friction.

Shock response of two epoxy resins at up to 330 GPa pressure

Experimental studies of the shock wave properties of two epoxy resins with the same composition but different curing temperatures (160 and 200 °C) at up to 330 GPa pressure have been carried out. Laser interferometry was used to record particle velocity profiles at up to 73 GPa pressure while measuring the shock wave velocity. The release sound velocity was experimentally determined in the 3–73 GPa pressure range. Cumulative explosive shock wave generators were used to study the shock Hugoniot of epoxy resins at pressures above 100 GPa. It was shown that the shock compressibility data of both samples are approximated by a single shock Hugoniot within the experimental error. A kink on Hugoniot recorded close to 25 GPa pressure indicates a chemical decomposition in epoxy resin. Above this kink, a change in the shock wave front structure was recorded. Hugoniots of epoxy resin and unidirectional carbon/epoxy composite were compared at up to 370 GPa pressure.

Heat transfer analysis of magnetohydrodynamics peristaltic fluid with inhomogeneous solid particles and variable thermal conductivity through curved passageway

PurposeThe particle distribution in a fluid is mostly not homogeneous. The inhomogeneous dispersion of solid particles affects the velocity profile as well as the heat transfer of fluid. This study aims to highlight the effects of varying density of particles in a fluid. The fluid flows through a wavy curved passage under an applied magnetic field. Heat transfer is discussed with variable thermal conductivity.Design/methodology/approachThe mathematical model of the problem consists of coupled differential equations, simplified using stream functions. The results of the time flow rate for fluid and solid granules have been derived numerically.FindingsThe fluid and dust particle velocity profiles are being presented graphically to analyze the effects of density of solid particles, magnetohydrodynamics, curvature and slip parameters. Heat transfer analysis is also performed for magnetic parameter, density of dust particles, variable thermal conductivity, slip parameter and curvature. As the number of particles in the fluid increases, heat conduction becomes slow through the fluid. Increase in temperature distribution is noticed as variable thermal conductivity parameter grows. The discussion of variable thermal conductivity is of great concern as many biological treatments and optimization of thermal energy storage system’s performance require precise measurement of a heat transfer fluid’s thermal conductivity.Originality/valueThis study of heat transfer with inhomogeneous distribution of the particles in a fluid has not yet been reported.

Discrete Element Method Modelling of the Particle Flow in Centrifugal Solar Particle Receiver

The centrifugal solar particle receiver (CentRec) is a promising design compared to other particle receiver concepts because it allows for an active adjustment of particle residence time and particle outlet temperature by adjusting the rotational speed of the drum and particle mass flow rate. A Discrete Element Method (DEM) tool is utilized to model the particle flow in CentRec. However, the numerical modeling of the particle flow in large scale receiver is computationally infeasible because of excessive number of particles in the simulation. Thus, in this study, a scale down approach is developed and validated to be used to estimate the particle film characteristics in large scale receivers. The particle velocity profile and film thickness distribution are employed to compare different receiver sizes.

Analysis of particle dispersion and cavity formation during bulk particle water entry using fully coupled CFD-DEM-VOF approach

This paper presents the development and validation of a fully coupled computational fluid dynamics—discrete element method—volume of fluid (CFD-DEM-VOF) model to simulate the complex behavior of particle-laden flows with free surfaces. The coupling between the fluid and particle phases is established through the implemented continuity, momentum, and alpha transport equation. The coupled particle forces such as drag, pressure gradient, dense virtual mass, viscous, and interface forces are also integrated, with drag and dense virtual mass forces being dependent on local porosity. The integrated conservative alpha transport equation ensures phase volume conservation during interactions between particles and water. Additionally, we have implemented a trilinear interpolation method designed to operate on unstructured hexahedral meshes. This method has been tested for its ability to properly resolve the coupling effects in the numerical simulations, particularly in cases with a relatively low cell-size ratio. The model is validated through three distinct test cases: single particle water entry, dam break with particles, and water entry of a group of particles case. The experimental setup is built to study the dynamics of the water entry of a group of particles, where three key flow features are analyzed: the evolution of average particle velocity, cavity shape, and particle dispersion cloud profiles in water. The tests involve four different scenarios, including two different water levels (16.1 and 20.1 cm) and two different particle densities (2650 and 4000 kg/m3). High-speed videometry and particle tracking velocimetry (using ImageJ/TrackMate) methods are employed for experimental data acquisition. It is demonstrated that numerical results are in excellent agreement with theoretical predictions and experimental data. The study highlights the significance of vortices in cavity shaping and particle dispersion. The validated CFD-DEM-VOF model constitutes a robust tool for simulating particle-laden flows, contributing valuable insights into the complex interplay between particles and fluids.

A computational analysis of operational parameters influencing coal gasification in a lab-scale drop tube gasifier

This study uses a numerical simulation for coal gasification operation in a drop tube gasifier to investigate the effects of wall temperature and oxygen-to-coal (O/C) ratios on gasification. Coal gasification is an efficient approach to electricity generation, offering a cleaner alternative to conventional coal combustion methods. A 2D Computational Fluid Dynamics (CFD) model of the gasifier was employed to perform grid sensitivity analysis and subsequently compute the influences of varying wall temperatures (1000 K, 1250 K, and 1500 K) and O/C ratios (0.6, 0.8, 1, and 1.2) on the temperature profile, syngas composition, and velocity within the gasifier. Temperature profiling within the furnace defined a spectrum of maximum and minimum temperatures, with apex values recorded at 2100 K and lowest values at 1300 K for Cases 12 and 1, respectively. High O/C ratios favored the production of CO2 due to enhanced combustion reactions, whereas lower O/C ratios were conducive to higher yields of CO and H2, essential syngas components. Velocity profiles of particles within the gasifier increased with higher temperatures and O/C ratios, and the maximum velocity was 9 m/sec. In conclusion, this study offers valuable insights into optimizing operational parameters such as wall temperatures and O/C ratios to enhance the performance and efficiency of coal gasification processes in lab-scale gasifiers.

Molecular Dynamics Simulation on Shocked Nanocrystalline Aluminum

The characteristics of shocked nanocrystalline aluminum are investigated by using molecular dynamics method based on the embedded atom method potential function. The result presents the particle velocity profile and the width of shock front in detail. The simulated Hugoniot relations are basically consistent with the experimental data and other molecular dynamics results. The width of shock front decreases with the particle velocity exponentially.

The reactive flow evolution of the polymer-bonded explosive PBX 9502: Experiments and model validation in extreme pressure regimes

The shock-to-detonation transition properties of the triaminotrinitrobenzene based PBX 9502 high explosive (HE) are experimentally and computationally explored in extremely high input pressure conditions. These include both slightly sub-Chapman–Jouguet and overdriven input pressure conditions, namely, ∼25 and ∼31 GPa, respectively. Our experiments capture the transient buildup of a shock-induced reaction via measurement of HE and polymethyl methacrylate window interface particle velocity profiles for a variety of sample thicknesses for this insensitive HE. These observations necessitate extremely thin explosive samples, and the high rates of reaction provide a considerable challenge to optical diagnostics. Samples at these thicknesses also provide an opportunity for evaluation of potential micro-structure effects on the resulting shock-to-detonation-transition measurements. To address this, the thin samples are also characterized via x-ray micro-computed tomography. Finally, a pair of previously established continuum-level detonation performance modeling approaches for PBX 9502 were used to analyze the experiments. The employed model variants crucially differ in their definition of each model’s empirical reaction rate functional form, utilization of shock state quantities, and local flow variable dependencies. As a result, the present experiments provide a novel platform to evaluate the quantitative and qualitative consequences stemming from these modeling choices in a challenging initiation scenario, largely beyond the chosen calibration range of either model. This new experimental information will provide a platform for both improved physics and model parameterizations for this well-studied explosive.

An Analysis of CFD-DEM with Coarse Graining for Turbulent Particle-Laden Jet Flows

This paper presents the results of simulations of particle-laden air–solid jet flow in long straight tubes using CFD-DEM, along with an analysis of coarse-graining. Although previous studies have used CFD-DEM for similar flows, these have typically been in a dilute flow regime where uncoupled simulations can be used effectively. However, fully coupled simulations can introduce issues, necessitating validation studies to ensure that all coupling parameters are effectively used and that the physics is accurately represented. This paper validated the simulations against two different experimental studies, with fluid Reynolds numbers between 10,000 and 40,000 and Stokes numbers between 5.6 and 50. Interestingly, the profiles of the mean particle velocity exhibited fewer discrepancies as the Stokes number increased, but more discrepancies for the root-mean-squared velocity compared to the experiments. The particle number flux was consistent with the experiments after the nozzle exit. Coarse-graining was also applied to the same simulations, achieving relatively accurate results. However, as expected, the scaling of contact collision frequencies, forces, and stresses could not be achieved, meaning that coarse-graining may be useful for comparing designs or operating parameters on an industrial scale, but falls short when measuring the total energy dissipation of one experiment.

CFD simulations to study bed characteristics in gas–solid fluidized beds with binary mixtures of Geldart B particles: II quantitative analysis

Hydrodynamics of fluidized beds with binary mixtures of particles is important in many industrial applications. The binary particles are generally in the Geldart particle range. In our earlier work, (Part I) of this work simulations were carried out and qualitative analysis was presented. Quantitative predictions of gas velocity and particle velocity profiles have been presented in the present work, which is Part II of the two-part work on computational fluid dynamics (CFD) simulations of binary fluidized beds. It was observed that the dynamics of the bed vary for different binary mixtures and are a strong function of superficial velocity and bed height. Mixing and segregation in beds for two different initial bed heights and six different binary mixtures and superficial velocities have been identified. Segregation is prominent for binary mixtures with 20 wt.% and 80 wt.% of large particles, whereas mixing is observed in 40 wt.% and 60 wt.% large particle mixtures. Bypassing of gas near the walls is prominently seen for 60 wt.% large particles with gas velocities as high as 5 m/s. Time-averaged axial particle volume fractions have been observed to be lower in the dilute phase with large undulations in the middle whenever the bed is well mixed for central axial profiles. The axial volume fraction profiles also confirm the mixing and segregation for the 40 wt.% and 20 wt.% composition of large particles for the operating conditions considered for the study. Bed height expansion is linear until a certain superficial velocity with the increase or decrease depending on the superficial velocity or bed height of operation. Furthermore, correlations for minimum fluidization velocity and pressure drops from the literature have been compared with experimental results. The simulated data have been considered for the development of a correlation for minimum fluidization velocity. The predicted results match experimental data with a 10%–15% deviation.

Shock response of unidirectional carbon polymer composite up to pressures of 200 GPa

Carbon fiber reinforced composite materials are often used to protect spacecraft from hypervelocity impacts with micrometeoroids or space debris. Therefore, shock-wave properties of these materials at pressures corresponding to orbital impact velocities are of interest. Experimental studies of shock compressibility of unidirectional carbon fiber polymer composite with longitudinal and transverse fiber orientation relative to the direction of shock-wave propagation have been carried out in the pressure range of up to 200 GPa. Particle velocity profiles on the composite surface-water window interface were recorded with a multichannel laser interferometer. The formation of a two-wave structure with a precursor amplitude from 1.5 to 3 GPa was observed with longitudinally oriented fibers. We show that Hugoniot of the composite material almost does not depend on the orientation of the carbon fibers, except for low pressures, when the particle velocity does not exceed 1 km/s. The graphite/diamond phase transition and the destruction of epoxy resin result in a characteristic kink on the Hugoniot curve with a distinct two-phase state region in the 23–35 GPa pressure range.

Thermally progressive Particle-Cu/Blood peristaltic transport with mass transfer in a Non-Uniform Wavy Channel: Closed-form exact solutions

The motivation behind writing the current article is to mathematically study the thermally driven transport of solute particles (measured in micro to nano meters) suspended in blood in an Esophagus mathematically taken as a non-uniform channel. The aim of the present study is to see the effects of solute particles with blood and nanoparticles in Esophagus to see its application in drug delivery and biomedical engineering etc. It also has many applications in microscale phenomena in physiology. Here blood is taken as a base fluid and nanofluid is prepared by the suspension of copper oxide nanoparticles in blood. Copper oxide is extremely useful in the medical domain for drug delivery and cancer treatment. To further study the impact of nanomedicine delivery we considered copper nanoparticles embedded in blood along other small sized solute particles. The mathematical formulation is performed in a rectangular coordinate system and constitutive flow equations are linearized by the implementation of approximations of low Reynolds number and large wavelength. The exact solution of reduced coupled and nonlinear set of equations for fluid particle velocity, temperature and fluid-particle composition profiles is computed through Mathematica while pressure rise is calculated by applying numerical integration. The effect of notable emerging parameters is discussed through graphs. It is observed that velocity rises with an increase in suspension and Casson fluid parameter, whereas opposite results are observed for temperature distribution. Nanoparticles volumetric fraction contribute to decelerating fluid flow and upsurge temperature. Schmidt number influences the fluid-particle composition by lessening it. PACS number: 47.10. A−; 47.35.Pq; 47.85.-g.

Influence of combination of coaxial cylindrical explosives on fragmentation and shock waves of a shelled composite charge

AbstractThis paper investigates fragmentation and shock waves generated by a novel coaxial cylindrical composite charge composed of an inner explosive, an intermediate inert material and an outer explosive widely used in tunable ammunition. Charges containing two types of explosive combinations were designed, and explosion experiments were conducted in two initiation modes: detonating only an inner explosive and detonating inner and outer explosives simultaneously. Results suggest the composite charge with higher inner‐detonation velocity and lower outer‐detonation velocity achieves more differentiated power output under different initiations. The differences in the average fragment mass and peak overpressure are as high as 34.5 % and 39.9 %, respectively, which are larger than 4.4 % and 8.4 % under the contrary explosive combination. On the basis of this observation, corresponding 2‐D and 3‐D models were simulated using AUTODYN code to investigate the evolution of the detonation waveform and detonation energy release. The numerically simulated initial shell expansion and later shock wave propagation of the composite charge agreed well with the experimental data. The errors in expansion radius and shock wave parameters (peak overpressure and specific impulse) are less than 6.6 % and 16.9 %, respectively, between the simulations and experiments. It was found that the particle velocity profile in the charge with lower outer‐detonation velocity lagged behind that of the charge with higher inner‐detonation velocity under inner initiation, while a wave front collision zone close to the outer charge appeared in the non‐detonation layer under simultaneous initiation.

Study of fractional-order model on Casson blood flow in stenosed artery with magnetic field effect

In this research work, the impacts of magnetic fields on Casson blood flow with stenosed artery are studied. The flow under investigation is affected by a magnetic field and an oscillating pressure gradient. The Caputo–Fabrizio fractional-order derivative was used to express the governing system of partial differential equations with imposed boundary and initial conditions. The governing problem is solved using Laplace and Finite Hankel transformations. The exact solution for blood velocity, magnetic particle velocity, and temperature profiles are defined. For better understanding of the various physical parameter, numerical results are obtained for blood velocity, magnetic particle velocity and temperature profiles and presented through the graphs. It is seen that the magnetic fields tend to reduce the blood viscosity which can be used for controlling the blood flow rate. It is also seen that Casson fluid parameter tends to improve the blood flow rate. From the results, it is illustrated that the heat transfer process improves with thermal radiation and heat generation parameter.

CFD simulations to study bed characteristics in gas–Solid fluidized beds with binary mixtures of Geldart-B particles: A qualitative analysis

The bed dynamics of unary and binary fluidized beds play a key role in understanding the pressure drop and hence provides an opportunity for performance improvement of the beds. In the present work, characteristics of fluidized beds with binary mixtures of Geldart-B particles were investigated using CFD simulations. The phenomena of segregation and mixing using simulations were studied, both qualitatively and quantitatively, at a range of superficial gas velocities (0.3–0.6 m/s) and two different bed heights. The study was divided into two parts. In Part I, the current study, a qualitative analysis of flow patterns for seven different binary mixtures, is presented. The quantitative analysis, including particle and gas velocity profiles, particle volume fraction profiles, and correlations for minimum fluidization velocity and pressure drop, will be presented in Part II of this work. A mathematical model consisting of an Eulerian-Eulerian model with RNG k-ε model and KTGF model to capture the bubble dynamics was used. The standardized values of coefficients and plastic stresses have been used for all simulations. The CFD model was validated using experimental data from the literature. Qualitative predictions of volume fraction profiles of small-sized particles showed that, for mixtures within a range of 40%–60% Geldart-B type large particles, the bubble and solid particle dynamics were different from those of single particles of the superficial gas velocities considered. In contrast to the single particles in the given superficial gas velocity range that were in bubbling regime, the binary particles showed a transition from bubbling to slugging to turbulent regime, as demonstrated by qualitative analysis. A homogeneous regime was observed for lower superficial gas velocities for mixtures consisting of 0%–20% large particles.

Boundary integral simulations of boundary layers in linear viscoelastic flow

We investigate the disturbance flow generated by the oscillatory motion of a solid particle in linear viscoelastic (LVE) fluids. We begin with one-mode Maxwell fluids and then add Newtonian components so we can examine a spectrum of Weissenberg numbers and frequency parameters. We compute the fluid dynamics using an accurate boundary integral method with third-order accuracy in space. A unique feature of our method is that we can calculate the stress on the particle surface for a prescribed particle velocity profile. It is well known that a boundary layer develops along an infinite plate under oscillatory motion in a Newtonian fluid. However, when the flow becomes viscoelastic, the boundary layers are fundamentally different from those observed in Newtonian fluids. We perform a series of numerical simulations for the geometry of spheroids, dumbbells, and biconcave disks, and characterize streamlines around these particles and shear stress distributions on the surface of the particles. Specifically, two main results emerge from our investigations: (i) there is a sequence of eddies produced in LVE rather than a single one as in the Newtonian fluid case; and (ii) the eddies develop in the interior of the LVE and barely travel, while in the Newtonian fluid, the eddy is generated on the particle surface and propagates into the fluid. Our numerical findings go beyond the well-known dynamical regimes for Newtonian fluids and highlight the level of complexity of particle dynamics in viscoelastic fluids.

Effect of particle shape on packing fraction and velocity profiles at outlet of a silo

Many studies on how the particle shape affects the discharge flow mainly focus on discharge rates and avalanche statistics. In this study, the effect of the particle shape on the packing fraction and velocities of particles in the silo discharge flow are investigated by using the discrete element method. The time-averaged packing fraction and velocity profiles through the aperture are systematically measured for superelliptical particles with different blockinesses. Increasing the particle blockiness is found to increase resistance to flow and reduce the flow rate. At an identical outlet size, larger particle blockiness leads to lower velocity and packing fraction at the outlet. The packing fraction profiles display evidently the self-similar feature that can be appropriately adjusted by fractional power law. The velocity profiles for particles with different shapes obey a uniform self-similar law that is in accord with previous experimental results, which is compatible with the hypothesis of free fall arch. To further investigate the origin of flow behaviors, the packing fraction and velocity field in the region above the orifice are computed. Based on these observations, the flow rate of superelliptical particles is calculated and in agreement with the simulated data.