Particle Diameter Ratio Research Articles

Optimizing parameter of particle damping based on Leidenfrost effect of particle flows

Abstract Particle damping (PD) has strongly nonlinearity. With sufficiently vigorous vibration conditions, it always plays excellent damping performance and the particles which are filled into cavity are on Leidenfrost state considered in particle flow theory. For investigating the interesting phenomenon, the damping effect of PD on this state is discussed by the developed numerical model which is established based on principle of gas and solid. Furtherly, the numerical model is reformed and applied to study the relationship of Leidenfrost velocity with characteristic parameters of PD such as particle density, diameter, mass packing ratio and diameter-length ratio. The results indicate that particle density and mass packing ratio can drastically improve the damping performance as opposed as particle diameter and diameter-length ratio, mass packing ratio and diameter-length ratio can low the excited intensity for Leidenfrost state. For discussing the application of the phenomenon in engineering, bound optimization by quadratic approximation (BOBYQA) method is employed to optimize mass packing ratio of PD for minimize maximum amplitude (MMA) and minimize total vibration level (MTVL). It is noted that the particle damping can drastically reduce the vibrating amplitude for MMA as Leidenfrost velocity equal to the vibrating velocity relative to maximum vibration amplitude. For MTVL, larger mass packing ratio is best option because particles at relatively wide frequency range is adjacent to Leidenfrost state.

Correlating the hydrodynamics of fluidized media with the extent of membrane fouling mitigation: Effect of bidisperse GAC mixtures

Abstract The anaerobic fluidized-bed membrane bioreactor (AnFMBR) makes use of fluidized granular activated carbon (GAC) to mechanically scour the membrane to mitigate fouling. The question addressed in the current study is whether fluidizing bidisperse mixtures (i.e., particles of two different sizes) can improve the energy-efficiency in mitigating membrane fouling. The hydrodynamic parameters (including particle velocity, particle concentration, particle momentum and extent of segregation) of the fluidized media numerically obtained via a Two-Fluid Model (TFM) were correlated with the fouling rate experimentally obtained. Three bidisperse mixtures with the same mean particle diameter (namely, 1 mm) but different particle diameter ratios (namely, d p2 /d p1 = 1.22 – 1.86) were studied over a range of superficial liquid velocities. The key highlights are that (i) the fouling rate decreased (i.e., fouling mitigation was more effective) as the particle diameter ratio increased, which indicates the benefits of fluidizing multi-sized particle mixtures over monodisperse ones, (ii) the fouling rate (dTMP/d t ) was positively correlated to the mixing index ( M ), which implies that segregated systems were more effective at mitigating membrane fouling, and (iii) the effect of bidispersity was more significant at the lower power input, which suggests that the advantages of fluidizing such bidisperse mixtures should only be harnessed at moderate power but not higher ones.

Numerical Study of Forced Convective Heat Transfer in Grille- Sphere Composite Packed Bed With Taguchi-CFD Method

In the present paper, a grille is inserted into the packed bed to construct a grille-sphere composite packed bed with small grille-sphere packed channels inside, which would be helpful to improve the flow homogeneity and heat transfer performance inside. The tube to particle diameter ratio of the packed bed is relatively large, while the tube to particle diameter ratio of the grill-sphere packed channel is relatively small. Due to the effect of grille on the porosity, the pressure drop and heat transfer characteristics in the grille-sphere packed channels are significant. Furthermore, the Taguchi-CFD method is used to study the grille effects in detail, including grille thermal conductivity, grille thickness and tube to particle diameter ratio of the channel. It is found that, the effect of the tube to particle diameter ratio (N) would be the most significant, while the effects of grille thermal conductivity and grille thickness would be relatively small. Therefore, the tube to particle diameter ratio is considered as the main factor for an optimum design in grille-particle composite packed bed.

Geosynthetic Protection for Buried Pipes Subjected to Surface Surcharge Loads

Geosynthetics have been extensively used as reinforcement in several geotechnical engineering applications. Regarding pressurised buried pipes, geosynthetics can protect the pipe against mechanical damages and reduce the consequences of explosions and leakages. This paper presents and discusses the use of geosynthetic reinforcement for the protection of buried pipes against the influence of localized surcharges on the ground surface. Model tests were carried out under plane-strain conditions where increasing surcharge pressures were applied on the surface of a dense sand layer containing a buried pipe. Three polymeric geogrids were used as reinforcements. Reinforcement arrangements consisting of a geogrid horizontal layer, an inverted U arrangement and an arrangement where the geogrid completely enveloped the pipe were tested. The results obtained showed that the presence of the reinforcement was effective in reducing the vertical stresses transferred to the pipe as well as in reducing pipe strains. The arrangement with the geogrid enveloping the pipe was the most efficient and the geogrid that combined satisfactory tensile stiffness and aperture to soil particle diameter ratio was the one which performed best. The testing programme showed the potentials for the use of geosynthetic reinforcement in reducing the effects of surface surcharges on buried pipes.

Hierarchically self-assembled hexagonal honeycomb and kagome superlattices of binary 1D colloids

Synthesis of binary nanoparticle superlattices has attracted attention for a broad spectrum of potential applications. However, this has remained challenging for one-dimensional nanoparticle systems. In this study, we investigate the packing behavior of one-dimensional nanoparticles of different diameters into a hexagonally packed cylindrical micellar system and demonstrate that binary one-dimensional nanoparticle superlattices of two different symmetries can be obtained by tuning particle diameter and mixing ratios. The hexagonal arrays of one-dimensional nanoparticles are embedded in the honeycomb lattices (for AB2 type) or kagome lattices (for AB3 type) of micellar cylinders. The maximization of free volume entropy is considered as the main driving force for the formation of superlattices, which is well supported by our theoretical free energy calculations. Our approach provides a route for fabricating binary one-dimensional nanoparticle superlattices and may be applicable for inorganic one-dimensional nanoparticle systems.

Impact of granular segregation on the solid residence time and active-passive exchange in a rotating drum

Via the discrete element method, a three-dimensional partially filled rotating drum operating in the rolling regime is numerically simulated to investigate the solid residence and inter-region exchange behaviors in the active and passive regions, and their dependence on the operating parameters of rotating speed and particle diameter ratio of the binary-size mixture. The results demonstrate the effects of size-segregation of the binary-size mixture: (i) for both particle displacement and residence time, the magnitude of large particles are greater, and the magnitudes in the passive region are greater than that in the active region; (ii) the solid exchange rate between the two regions is greater for the small particles; (iii) although the solid exchange rate of each particle type evolves with time due to the evolving size segregation, the exchanging rate between the active and passive regions is proven to be global parameter, which is not influenced by size-segregation; (iv) changes in the rotating speed has a greater influence than that in particle diameter ratio in the ranges investigated. Collectively, these results shed more light on the impact of size segregation of a binary-size mixture on the characteristics of the rotating drum.

Measurement of local wall heat transfer coefficient in randomly packed beds of uniform sized spheres using infrared thermography (IR) and water as working medium

The needs for compact and effective heat transfer equipments are in growing demand and porous media caters to this need. Packed beds are a simple type of porous media devices which help in transport of mass, momentum and heat. The applications of packed beds are in chemical reactors, distillation, catalysis, thermal energy storage, food processing, solar power plants and several other areas. They act as enhancement devices for different transport processes. In the present study, the behavior of wall heat transfer coefficient with randomized packing of uniformly sized spheres is investigated.In the present work, the local wall heat transfer coefficient is estimated from local wall temperature data obtained using infrared (IR) thermography for the packed beds with randomized packing of uniformly sized spheres under steady state conditions with water as the working fluid. The experiments are conducted for bed to particle diameter ratios of 6, 3 and 2 using random packing of mono-dispersed glass spheres. The two-layer model theory for heat transfer in packed beds is examined in terms of contribution or core zone and wall zone in packed beds. The comparison of heat transfer enhancement aspects with different insert configurations is done and packed beds are found effective.

Radial porosity peak at the centerline of packed beds with small tube to particle diameter ratios

Various mathematical models in literature conclude that the porosity profile varies in an oscillatory fashion and the amplitude decreases with increasing distance from the wall. However, scrutiny of the literature indicates a distinct deviation in the models that a strong porosity peak at the centerline is not amenable to the predictions for packed beds with small tube to particle diameter ratios. In this study, the radial porosity peak at the centerline of packed bed is investigated by experiments. According to the structure of packed beds at D/d<3.37, the bed is divided into two parts—the near wall part and the central part. The mean porosity value of different parts is obtained by counting method. In the experimental result, high porosity value at the central part is observed. Then, the reasons that lead to the porosity peak—the highly ordered ring structure and the internal channel similar to the bed at D/d<2—are identified. Moreover, the channel at the centerline promises that significant bypass flow would occur in the packing arrangement, which should be taken into account for the analysis of transport phenomena in packed beds.

Droplet impact onto a solid sphere: Effect of wettability and impact velocity

Collision of a droplet onto a still spherical particle was experimentally investigated. The effect of droplet impact velocity and wettability of the particle surface on collision outcomes was studied (0.05 &amp;lt; V0 &amp;lt; 5.0 and θ = 70°, 90°, 118°). Compared to the literature, the range of Weber number variations was significantly extended (0.1 &amp;lt; We &amp;lt; 1146), and while focus of the previous works was on impacts in which particle is larger than the droplet (Dr &amp;lt; 1), the drop to particle diameter ratio in this work was larger than one. Therefore, formation of a thin liquid film, i.e., lamella, was observed due to impact of a relatively high velocity droplet onto a hydrophobic particle. Temporal variations of various geometrical parameters of collision outcomes including lamella length and lamella base diameter were investigated during the impact. It was also shown that for hydrophobic targets, the extent of hydrophobicity of the particle does not affect the lamella geometry. A comprehensive map of all the available works in drop impact on a spherical target was also provided.

Spontaneous formation of bimodal particle size distributions: A novel one-step strategy for obtaining high solid content, low viscosity poly(vinyl acetate- co -ethylene) latexes

Abstract A novel one-step semi-batch method was developed as a means of synthesizing vinyl acetate- co -ethylene (VAE) latexes with bimodal particle size distributions (PSDs). This technique allows high solid content while maintaining extremely low viscosity. In contrast to previous methods, the formation of a bimodal PSD based on the limited auto-aggregation of particles was found to occur spontaneously. The effects of the reaction temperature, initiator concentration, surfactant concentration, sodium dodecyl sulfate (SDS)/nonionic surfactant ratio and reaction time on the PSD and solid content of the latex were all investigated. A stable VAE latex consisting of 78.4 vol% large particles and 21.6 vol% small particles with a large-to-small particle diameter ratio of 4.51 was readily synthesized using this approach. The viscosity of one such latex with a 71.83 wt% solid content was below 300 mPa s at a constant shear rate of 20 s −1 . This synthesis method was also demonstrated to be highly reproducible.

Design of a fuzzy differential evolution algorithm to predict non-deposition sediment transport

Since the flow entering a sewer contains solid matter, deposition at the bottom of the channel is inevitable. It is difficult to understand the complex, three-dimensional mechanism of sediment transport in sewer pipelines. Therefore, a method to estimate the limiting velocity is necessary for optimal designs. Due to the inability of gradient-based algorithms to train Adaptive Neuro-Fuzzy Inference Systems (ANFIS) for non-deposition sediment transport prediction, a new hybrid ANFIS method based on a differential evolutionary algorithm (ANFIS-DE) is developed. The training and testing performance of ANFIS-DE is evaluated using a wide range of dimensionless parameters gathered from the literature. The input combination used to estimate the densimetric Froude number (Fr) parameters includes the volumetric sediment concentration (CV), ratio of median particle diameter to hydraulic radius (d/R), ratio of median particle diameter to pipe diameter (d/D) and overall friction factor of sediment (λs). The testing results are compared with the ANFIS model and regression-based equation results. The ANFIS-DE technique predicted sediment transport at limit of deposition with lower root mean square error (RMSE = 0.323) and mean absolute percentage of error (MAPE = 0.065) and higher accuracy (R2 = 0.965) than the ANFIS model and regression-based equations.

Slope, grain size, and roughness controls on dry sediment transport and storage on steep hillslopes

AbstractExisting hillslope sediment transport models developed for low‐relief, soil‐mantled landscapes are poorly suited to explain the coupling between steep rocky hillslopes and headwater channels. Here we address this knowledge gap using a series of field and numerical experiments to inform a particle‐based model of sediment transport by dry ravel—a mechanism of granular transport characteristic of steep hillslopes. We find that particle travel distance increases as a function of the ratio of particle diameter to fine‐scale (&lt;1 m) topographic roughness, in agreement with prior laboratory and field experiments. Contrary to models that assume a fixed critical slope, the particle‐based model predicts a broad transition as hillslopes steepen from grain‐scale to hillslope‐scale mean particle travel distances due to the trapping of sediment on slopes more than threefold steeper than the average friction slope. This transition is further broadened by higher macroscale (&gt;1 m) topographic variability associated with rocky landscapes. Applying a 2‐D dry‐ravel‐routing model to lidar‐derived surface topography, we show how spatial patterns of local and nonlocal transport control connectivity between hillslopes and steep headwater channels that generate debris flows through failure of ravel‐filled channels following wildfire. Our results corroborate field observations of a patchy transition from soil‐mantled to bedrock landscapes and suggest that there is a dynamic interplay between sediment storage, roughness, grain sorting, and transport even on hillslopes that well exceed the angle of repose.

Experimental Study on the Influence of Filling Method and Particle Material on the Packed‐Bed Porosity

AbstractThe reliable prediction of the pressure drop of packed beds requires an accurate estimation of the packed‐bed porosity as its error propagation multiplies the occurring errors by a factor of about four. The commonly used correlations to determine porosity depend only on the tube to particle diameter ratio. To improve accuracy, the influence of the filling method and of material properties, in particular surface roughness, density, and restitution coefficient are investigated for random packings of spheres in cylindrical confining walls. Furthermore, statistical methods are applied to identify interconnecting effects between these influencing parameters.

A simple approach to describe hydrodynamics and its effect on heat and mass transport in an industrial wall-cooled fixed bed catalytic reactor: ODH of ethane on a MoVNbTeO formulation

The incorporation of hydrodynamics in an industrial wall-cooled packed bed reactor model is essential to describe the performance of highly exothermic oxidation reactions. Although the conventional hydrodynamic approach (CHA), Navier-Stokes equations coupled to Darcy-Forchheimer terms, has been the most used approximation to describe velocity profiles in these packed bed reactors, it is itself inconsistent and the computation time for its numerical solution, when coupled to the reactor model, is still demanding. This work is aimed at developing a practical but reliable hydrodynamic approach (PHA) to describe velocity profiles in packed bed reactors presenting a low tube to particle diameter ratio. In this approach, velocity profiles are described at the core and close to the wall of the reactor. The core model makes use of the Darcy-Forchheimer equation (DFE), and the wall model makes use of Navier-Stokes equations (NSE) using an effective viscosity to account for turbulence. The PHA predicts similar results to those obtained by the CHA and properly fits velocity observations from packed beds with a tube to particle diameter ratio (dt/dp) ranging from 3 to 6. The PHA allows the estimation of both turbulent viscosity (μt) involved in the viscous term of the NSE and parameters influencing viscous (α) and inertial (β) flow resistances in Darcy and Forchheimer terms, respectively. Then, hydrodynamics is coupled to a heat transport model accounting for conductive anisotropy to fit temperature observations in absence of reaction from a pilot-scale packed bed reactor with a dt/dp=3.048. Hydrodynamics and heat transfer results are, then, transferred to a pseudo heterogeneous reactor model to simulate the behavior of a novel technology to perform the oxidative dehydrogenation of ethane on a multimetallic MoVNbTeO formulation. This is the first study modeling this reactor system accounting for hydrodynamics, information that is essential for its conceptual design in future studies. Finally, it is worth stressing that the PHA, coupled to the heat transport model or the reactor model, leads to significantly lower computation times than the CHA, which is attributed to the analytical rather than numerical solution of the former.

Critical Condition for the Particle Combustion of Carbon Activated in a Hot, Quiescent Environment: Comparisons with Experimental Results

ABSTRACTAppropriateness and/or usefulness of the critical condition, being derived in a previous work related to the activation of solid fuel particles, have further been examined by conducting comparisons by use of such experimental data in the literature as are reported to burn-out in a quiescent environment. Results of various carbonaceous solid fuels used are those from anthracite to low-rank coal char, as well as petroleum coke, after confirming kinetic parameters for the surface reaction that are indispensable in evaluating combustion rate. Particle sizes reported are those from 25 μm to 4 mm; ambient temperatures are those higher than 1300 K. Use has been made of the Arrhenius plot of the extended comprehensive parameter consisting of frequency factor of the surface C–O2 reaction, particle diameter, oxygen mass-fraction, and pressure ratio, the upper half of which, separated by the critical condition, corresponds to that for particle burn-out with the surface reaction activated. As far as the trend and approximate magnitude are concerned, a fair degree of agreement has been demonstrated, in general, suggesting that the formulation used has captured the essential feature of the particle combustion, elucidation of which has not been made by the others. In addition, once again, it has been confirmed that the reduction in particle size does not necessarily favor the particle combustion, and that the surface reaction ceases to be activated when the particle size is reduced below the critical one.

Numerical investigation and comparison of coarse grain CFD – DEM and TFM in the case of a 1 MWth fluidized bed carbonator simulation

This work focuses on a comparison between the Euler-Euler Two Fluid Model (TFM) approach and the coupled coarse grain discrete element CFD-DEM numerical model for the simulation of a 1MWth CFB carbonator reactor located at TU Darmstadt (TUD). The effect of the drag force formulation and its associated application in the numerical model for both approaches in terms of their numerical accuracy, compared to experimental data is investigated, by implementing either the conventional Gidaspow model or the advanced EMMS one. Moreover, for the coarse grain CFD – DEM model, the range of values for important numerical parameters as the particle per parcel and cell to parcel size ratios are investigated to shed light on the necessary resolution such a model should have in order to reproduce valid and not parameter dependent numerical results. An adequate cell length to parcel diameter ratio is found to be around 2.6 while as concerns the parcel to particle diameter ratio a value around 58.5 proved to be sufficient, at least for the range of parameters investigated in this paper (size of riser, flow rates and particles average diameter). The EMMS model improved the accuracy of results derived by the coarse grain CFD – DEM model, while further research on the appropriate drag models for the coarse grain CFD – DEM is a sine qua non for its successful implementation in similar studies. For instance it is of interest to answer whether the individual particles slip velocity instead of the particles cell averaged slip, should be used for the calculation of the momentum interexchange coefficient (β) as well as the treatment of different particle diameters in the EMMS equation scheme.

Effect of two-body and three-body microcontacts under dry friction on contact characteristics

The wear debris generation is unavoidable between the contact interfaces of moving components. In three-body contact instances, friction and wear occur at these separate contact points. This paper discusses the characteristics of the three-body contact comprising the abrasive particle in the interface compared to the two-body contact. The results show that for the wear debris or foreign particles present in the interface of the three-body contact, as external load initially increases, the external load is fully borne by the contact characteristics of particle-to-surface. Until the external load rises to a particular critical external load, it enters the real three-body situation, and the critical external load thus increases with an increase in the ratio of particle diameter to surface roughness. For two contact surfaces, the summit deformation is the elastoplastic deformation in a wide range of external loads. As the external load is lower than the critical external load value of the three-body contact, the contact surface is under the particle-to-surface two-body contact, and the elastic deformation of surface peak has the largest proportion of contact area. When the external load is higher than the critical external load value, the elastoplastic deformation contact area quickly dominates, and the total contact area ratio approximates to the surface-to-surface two-body contact situation. In the range of engineering surface roughness (σ = 50–400 nm), at each external load and surface roughness, the total friction coefficient decreases with the increase in the ratio of particle diameter to surface roughness under the three-body contact, and this shows that the friction coefficient of surface-to-surface contact is larger than that of the sphere wear debris between the contact interface. At the same surface roughness, the friction coefficient may increase or decrease with an increase in the external load because it is determined by particle diameter. At the same ratio of particle diameter to surface roughness and external load, the friction coefficient increases with the decreasing surface roughness.

Lattice Boltzmann simulation of 3-dimensional natural convection heat transfer of CuO/water nanofluids

The present study investigated fluid flow and natural convection heat transfer in an enclosure embedded with isothermal cylinder. The purpose was to simulate the three-dimensional natural convection by thermal lattice Boltzmann method based on the D3Q19 model. The effects of suspended nanoparticles on the fluid flow and heat transfer analysis have been investigated for different parameters such as particle volume fraction, particle diameters, and geometry aspect ratio. It is seen that flow behaviors and the average rate of heat transfer in terms of the Nusselt number (Nu) are effectively changed with different controlling parameters such as particle volume fraction (5 % ≤ φ ≤ 10 %), particle diameter (d p = 10 nm to 30 nm) and aspect ratio (0.5 ≤ AR ≤ 2) with fixed Rayleigh number, Ra = 105. The present results give a good approximation for choosing an effective parameter to design a thermal system.

Origin of the scaling laws of sediment transport

In this paper, we discover the origin of the scaling laws of sediment transport under turbulent flow over a sediment bed, for the first time, from the perspective of the phenomenological theory of turbulence. The results reveal that for the incipient motion of sediment particles, the densimetric Froude number obeys the ‘(1 + σ )/4’ scaling law with the relative roughness (ratio of particle diameter to approach flow depth), where σ is the spectral exponent of turbulent energy spectrum. However, for the bedforms, the densimetric Froude number obeys a ‘(1 + σ )/6’ scaling law with the relative roughness in the enstrophy inertial range and the energy inertial range. For the bedload flux, the bedload transport intensity obeys the ‘3/2’ and ‘(1 + σ )/4’ scaling laws with the transport stage parameter and the relative roughness, respectively. For the suspended load flux, the non-dimensional suspended sediment concentration obeys the ‘ − Z ’ scaling law with the non-dimensional vertical distance within the wall shear layer, where Z is the Rouse number. For the scour in contracted streams, the non-dimensional scour depth obeys the ‘4/(3 − σ )’, ‘−4/(3 − σ )’ and ‘−(1 + σ )/(3 − σ )’ scaling laws with the densimetric Froude number, the channel contraction ratio (ratio of contracted channel width to approach channel width) and the relative roughness, respectively.

Liquid-like granular film from granular jet impact

Dynamic behaviors of dense granular jets impacting a flat target are experimentally studied and numerically simulated using the Discrete Element Method. Effects of the granular jet velocity (u0⩽6.5m/s), the particle diameter (82⩽d⩽350μm), the jet diameter (1⩽D⩽12mm), and the volumetric solid content ratio of the granular jet (0.05⩽xp<0.62) on the flow patterns are investigated. Two patterns were identified: the thin, liquid-like granular film and the diffuse pattern. The profile and thickness of granular films have been characterized. The transition critical parameters and maps of the two patterns are obtained in this work. Results show that the regimes of the granular jet impact are primarily determined by the ratio of jet diameter to particle diameter (D/d) and solid content ratio (xp). A compacted dead zone over the target forms with large D/d and xp, which subsequently causes rapid interparticle inelastic collisions and circular motion of the granular film.