scholarly journals Numerical Simulations on Mixing Dynamics of Spherical and Non-Spherical Tablets in a Pan Coater

2019 ◽  
Vol 9 (6) ◽  
pp. 5029-5032
Author(s):  
R. Chand ◽  
R. Hadj Lajimi ◽  
S. Uddin ◽  
S. Meghwar ◽  
U. Farooq ◽  
...  
Keyword(s):  
Rotational Velocity ◽  
Contact Dynamics ◽  
Spherical Particles ◽  
Mixing Efficiency ◽  
Valuable Insight ◽  
Spherical Type ◽  
Numerical Work ◽  
Mixing Dynamics ◽  
Pan Coater ◽  
Type 3

Discrete element simulations provide valuable insight into the mixing dynamics of granular materials in industry. In this paper, numerical work is conducted in order to find the influence of pan rotational velocity and particle shape on mixing behavior. Four types of particles of different shapes were chosen: spherical, non-spherical type 1 (disk shape), non-spherical type 2 (capsule shape), and non-spherical type 3 (triangular shape). The pan mixer was filled with ~ 30 % volume of the same shape with the particles and was rotated at 15 RPM, 30 RPM, 45 RPM, and 60 RPM. The particles were colored as bottom-particles, middle-particles, and top-particles in order to visualize mixing efficiency. The homogeneity of the mixtures was determined by using contact dynamics of particles. The results show that fast-rotating pan (30-60 RPM) provides good mixing for all shapes of particles. However, non-spherical particles do not show as good mixing as spherical particles.

Pre-Operative Planning of Total Hip Arthroplasty on Dysplastic Acetabuli

2016 ◽  
Vol 27 (1) ◽  
pp. 55-59 ◽  
Author(s):  
Dror Lakstein ◽  
Zachary Tan ◽  
Nugzar Oren ◽  
Tatu Johannes Mäkinen ◽  
Allan E. Gross ◽  
...  
Keyword(s):  
Total Hip Arthroplasty ◽  
Hip Arthroplasty ◽  
Weighted Kappa ◽  
Valuable Insight ◽  
High Porosity ◽  
Total Hip ◽  
Structural Support ◽  
Operative Planning ◽  
Type 3 ◽  
Dysplastic Hip

Background When performing total hip arthroplasty (THA) on a dysplastic hip, proper positioning of the acetabular component may not allow for more than 70% coverage. Structural support in the form of an autograft or a high porosity metal augment may be necessary. The purpose of the study was to investigate the value of pre-operative templating and deformity classification in predicting cup coverage and the need for structural support. Methods 65 cases of THA for DDH were retrospectively analysed. 2 observers independently classified each dysplastic hip according to Hartofilakidis and determined the extent of cup coverage via templating software on pre-operative digital AP pelvic radiographs. Results Weighted kappa interobserver agreement was 0.68 for cup coverage and 0.76 for Hartofilakidis type. Structural support was necessary in 10 hips. No structural support was necessary in Hartofilakidis type 1, dysplasia cases. However, 27-30% of cases with type 2 or type 3 dysplasia required structural support. All cases with templated cup coverage of 65% or less required structural support. Templated coverage within 65-75% and over 75% resulted in 20% and 10% of patients receiving structural augmentation, respectively. Conclusions Pre-Operative planning for THA in the setting of hip dysplasia is crucial and can provide valuable insight to the need for column augmentation. However, the 3-D severity of the deformity may be underestimated in the 2-D radiographs.

scholarly journals Influence of Water Temperature on Results of Current Meter Calibration and Measurement

2013 ◽  
Vol 61 (3) ◽  
pp. 208-213 ◽  
Author(s):  
Daniel Mattas ◽  
Libuše Ramešová
Keyword(s):  
Water Temperature ◽  
Rotational Velocity ◽  
Rotational Frequency ◽  
Water Velocity ◽  
Uncertainty Of Measurements ◽  
Influence Of Water ◽  
Type 3 ◽  
Measured Water ◽  
Term Data

Abstract On the basis of the results of calibration of current meters at water of varying temperatures, a hypothesis that water temperature influences measured water velocities was formulated. The analysis of our long-term data showed that the water temperature does have an influence on measured water velocity. This influence can be taken into account for practical purposes as a contribution to the uncertainty of measurements. The influence depends on the type of current meter propeller. This paper presents results obtained for the Ott C-2 current meter with propellers of the types 1, 2, 3, 5 and 6. Our analysis showed that the uncertainty is equal or less than 5% for measurements carried out in water with temperatures above 8°C. The differences between measured water velocities for water temperatures 5°C and 20°C reached maximum 6% (depending on the propeller) in a slowly flowing water (rotational frequency n = 1 s-1). For rotational velocity n ≥ 2 s-1 the differences between velocities measured at water temperatures 5 and 20°C were mostly under 3%. The less influenced propeller is of type 3 for which the uncertainty of measurement does not reach 5% even for water temperature 1°C if the rotational frequency is bigger than 0.7 s-1.

The granular column collapse as a continuum: validity of a two-dimensional Navier–Stokes model with a μ(I)-rheology

2011 ◽  
Vol 686 ◽  
pp. 378-408 ◽  
Author(s):  
P.-Y. Lagrée ◽  
L. Staron ◽  
S. Popinet
Keyword(s):  
Analytical Solutions ◽  
Granular Layer ◽  
Contact Dynamics ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Numerical Work ◽  
Aspect Ratios ◽  
Column Collapse ◽  
Wide Range ◽  
Granular Column

AbstractThere is a large amount of experimental and numerical work dealing with dry granular flows (such as sand, glass beads, etc.) that supports the so-called $\ensuremath{\mu} (I)$-rheology. The reliability of the $\ensuremath{\mu} (I)$-rheology in the case of complex transient flows is not fully ascertained, however. From this perspective, the granular column collapse experiment provides an interesting benchmark. In this paper we implement the $\ensuremath{\mu} (I)$-rheology in a Navier–Stokes solver (Gerris) and compare the resulting solutions with both analytical solutions and two-dimensional contact dynamics discrete simulations. In a first series of simulations, we check the numerical model in the case of a steady infinite two-dimensional granular layer avalanching on an inclined plane. A second layer of Newtonian fluid is then added over the granular layer in order to recover a close approximation of a free-surface condition. Comparisons with analytical and semi-analytical solutions provide conclusive validation of the numerical implementation of the $\ensuremath{\mu} (I)$-rheology. In a second part, we simulate the unsteady two-dimensional collapse of granular columns over a wide range of aspect ratios. Systematic comparisons with discrete two-dimensional contact dynamics simulations show good agreement between the two methods for the inner deformations and the time evolution of the shape during most of the flow, while a systematic underestimation of the final run-out is observed. The experimental scalings of spreading of the column as a function of the aspect ratio available from the literature are also recovered. A discussion follows on the performances of other rheologies, and on the sensitivity of the simulations to the parameters of the $\ensuremath{\mu} (I)$-rheology.

scholarly journals Novel 3-D T-Shaped Passive Micromixer Design with Helicoidal Flows

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 637 ◽  
Author(s):  
Mahmut Burak Okuducu ◽  
Mustafa M. Aral
Keyword(s):  
Fluid Flow ◽  
Fluid Mixing ◽  
Mixing Efficiency ◽  
Flow Profile ◽  
Complex Flow ◽  
Mixing Index ◽  
Micro Channels ◽  
Mixing Dynamics ◽  
Passive Micromixer ◽  
Novel Design

Laminar fluid flow and advection-dominant transport produce ineffective mixing conditions in micromixers. In these systems, a desirable fluid mixing over a short distance may be achieved using special geometries in which complex flow paths are generated. In this paper, a novel design, utilizing semi-circular ridges, is proposed to improve mixing in micro channels. Fluid flow and scalar transport are investigated employing Computational Fluid Dynamics (CFD) tool. Mixing dynamics are investigated in detail for alternative designs, injection, and diffusivity conditions. Results indicate that the convex alignment of semi-circular elements yields a specific, helicoidal-shaped fluid flow along the mixing channel which in turn enhances fluid mixing. In all cases examined, homogenous concentration distributions with mixing index values over 80% are obtained. When it is compared to the classical T-shaped micromixer, the novel design increases mixing index and mixing performance values by the factors of 8.7 and 3.3, respectively. It is also shown that different orientations of ridges adversely affect the mixing efficiency by disturbing the formation of helicoidal-shaped flow profile.

A Numerical Study on the Flow Characteristics of Opposed Impinging Jets

2012 ◽  
Vol 516-517 ◽  
pp. 854-857
Author(s):  
Shu Xia Qiu ◽  
Ning Pang
Keyword(s):  
Unsteady Flow ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Impinging Jets ◽  
Mixing Efficiency ◽  
Fluid Temperature ◽  
Mixing Rate ◽  
Numerical Work ◽  
Mixing Performance ◽  
Flow Pulsations

Inspired by the increasing interests on mixing effectiveness of opposed impinging jets, a numerical work is carried out to study the flow characteristics. The fluid temperature is used as a passive tracer to evaluate the mixing rate in the current mathematical models. The effect of Reynolds number on the mixing performance is discussed. Furthermore, in order to enhance the mixing efficiency and reduce the energy cost, unsteady flow pulsations are induced at the jet inlets. The numerical results indicate that the mixing efficiency can be improved by the unsteady flow pulsations via adjusting the hydrodynamics characteristics in the opposed jets.

scholarly journals Discrete element modeling of boulder and cliff morphologies on comet 67P/Churyumov-Gerasimenko

2020 ◽  
Vol 641 ◽  
pp. A19 ◽  
Author(s):  
D. Kappel ◽  
M. Sachse ◽  
D. Haack ◽  
K. A. Otto
Keyword(s):  
Discrete Element ◽  
Morphological Features ◽  
Spherical Particles ◽  
Structural Defects ◽  
Mechanical Parameters ◽  
Surface Material ◽  
Numerical Work ◽  
Sample Return ◽  
Comet 67P ◽  
Cometary Activity

Context. Even after the Rosetta mission, some of the mechanical parameters of comet 67P/Churyumov-Gerasimenko’s surface material are not yet well constrained. These parameters are needed to improve our understanding of cometary activity or for planning sample return missions. Aims. We study some of the physical processes involved in the formation of selected surface features and investigate the mechanical and geometrical parameters involved. Methods. Applying the discrete element method (DEM) in a low-gravity environment, we numerically simulated the surface layer particle dynamics involved in the formation of selected morphological features. The material considered is a mixture of polydisperse ice and dust spheres with inter-particle forces given by the Hertz contact model, translational friction, rolling friction, cohesion from unsintered contacts, and optionally due to bonds from ice sintering. We determined a working set of parameters that enables the simulations to be reasonably realistic and investigated morphological changes due to modifications thereof. Results. The selected morphological features are reasonably well reproduced using model materials with a tensile strength on the order of 1–10 Pa. Increasing the diameters of the spherical particles decreases the material strength, and increasing the friction leads to a more brittle but somewhat stronger material. High friction is required to make the material sufficiently brittle to match observations, which points to the presence of very rough, even angular particles. Reasonable seismic activity does not suffice to trigger the collapses of cliffs without material heterogeneities or structural defects. Conclusions. DEM modeling can be a powerful tool to investigate mechanical parameters of cometary surface material. However, many uncertainties arise from our limited understanding of particle shapes, spatial configurations, and size distributions, all on multiple length scales. Further numerical work, in situ measurements, and sample return missions are needed to better understand the mechanics of cometary material and cometary activity.

scholarly journals Turbulent Mixing and Exchange with Interior Waters on Sloping Boundaries

2012 ◽  
Vol 42 (6) ◽  
pp. 910-927 ◽  
Author(s):  
Eric Kunze ◽  
Chris MacKay ◽  
Erika E. McPhee-Shaw ◽  
Katie Morrice ◽  
James B. Girton ◽  
...  
Keyword(s):  
Turbulent Mixing ◽  
World Ocean ◽  
Mixing Efficiency ◽  
Turbulent Layer ◽  
Turbulent Dissipation ◽  
Eddy Diffusivities ◽  
Dissipation Rates ◽  
Mixing Dynamics ◽  
Order Of Magnitude ◽  
Internal Wave Generation

Abstract Microstructure measurements along the axes of Monterey and Soquel Submarine Canyons reveal 200–300-m-thick well-stratified turbulent near-bottom layers with average turbulent kinetic energy dissipation rates 〈ɛ〉 = 4 × 10−8 W kg−1 and eddy diffusivities K = 16 × 10−4 m2 s−1 (assuming mixing efficiency γ = 0.2) to at least thalweg depths of 1200 m. Turbulent dissipation rates are an order of magnitude lower in overlying waters, whereas buoyancy frequencies are only 25% higher. Well-mixed bottom boundary layer thicknesses hN are an order of magnitude thinner than the stratified turbulent layer (hN ≪ hɛ). Because well-stratified turbulent layers are commonly observed above slopes, arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal-wave generation or interaction with topography. An advective–diffusive balance is used to infer velocities and transports, predicting horizontal upslope flows of 10–50 m day−1. Extrapolating this estimate globally suggests that canyon turbulence may contribute 2–3 times as much diapycnal transport to the World Ocean as interior mixing. The upcanyon turbulence-driven transports are not uniform, and the resulting upslope convergences will drive exchange between the turbulent layer and more quiescent interior. Predicted density surfaces of detrainment and entrainment are consistent with observed isopycnals of intermediate nepheloid and clear layers. These data demonstrate that turbulent mixing dynamics on sloping topography are fundamentally 2D or 3D in the ocean, so they cannot be accurately described by 1D models.

scholarly journals On the hydrodynamics of ‘slip–stick’ spheres

2008 ◽  
Vol 606 ◽  
pp. 115-132 ◽  
Author(s):  
JAMES W. SWAN ◽  
ADITYA S. KHAIR
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Spherical Particle ◽  
Stokes Flow ◽  
Velocity Gradient ◽  
Slip Length ◽  
Rotational Velocity ◽  
Spherical Particles ◽  
Force Density ◽  
Translational Velocity

The breakdown of the no-slip condition at fluid–solid interfaces generates a host of interesting fluid-dynamical phenomena. In this paper, we consider such a scenario by investigating the low-Reynolds-number hydrodynamics of a novel ‘slip–stick’ spherical particle whose surface is partitioned into slip and no-slip regions. In the limit where the slip length is small compared to the size of the particle, we first compute the translational velocity of such a particle due to the force density on its surface. Subsequently, we compute the rotational velocity and the response to an ambient straining field of a slip–stick particle. These three Faxén-type formulae are rich in detail about the dynamics of the particles: chiefly, we find that the translational velocity of a slip–stick sphere is coupled to all of the moments of the force density on its surface; furthermore, such a particle can migrate parallel to the velocity gradient in a shear flow. Perhaps most important is the coupling we predict between torque and translation (and force and rotation), which is uncharacteristic of spherical particles in unbounded Stokes flow and originates purely from the slip–stick asymmetry.

Scanning Electron Microscopy of the Red Pulp of the Spleen

1971 ◽  
Vol 29 ◽  
pp. 496-497
Author(s):  
Masayuki Miyoshi
Keyword(s):  
Electron Microscope ◽  
Ringer Solution ◽  
Conclusive Evidence ◽  
Sinus Wall ◽  
Transmission Electron ◽  
Type 3 ◽  
Cytoplasmic Processes ◽  
Splenic Red Pulp ◽  
Scanning Electron ◽  
Red Pulp

In spite of various attempts, conclusive evidence to explain blood passage in the splenic red pulp does not seem to have been presented. Scanning electron microscope (SEM) observations on the rabbit spleen, originally performed by us, revealed that the sinus was lined by a perforated lattice composed of longitudinally extended rod cells and transverse cytoplasmic processes, and that perforations in the lattice were continuous to the spaces among the stellate reticulum cells of the cord. In the present study the observation was extended to the dog and rat spleens, in which the cord is more developed than in the rabbit in order to clarify the possible differences in the fine structure of the sinus wall. An attempt was also made to examine the development and distribution of macrophage in the blood passage of the red pulp.Spleens were washed and fixed by perfusion with Ringer solution and then with buffered glutaraldehyde. Small tissue cubes were dehydrated with acetone, dried in air and heated with gold. Observations were made by a JEOL SEM Type-3. One air dried tissue cube was cut into small pieces and post fixed with buffered OsO4 for examination under the transmission electron microscope (TEM).

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