scholarly journals A Continuum Model for Complex Flows of Shear Thickening Colloidal Solutions

Fluids ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 21
Author(s):  
Joseph Green ◽  
Daniel Ryckman ◽  
Michael Cromer
Keyword(s):  
Continuum Model ◽  
Full Range ◽  
Shear Thickening ◽  
Free Path Length ◽  
Mean Free Path ◽  
Colloidal Solutions ◽  
Complex Flow ◽  
Complex Flows ◽  
Theoretical Understanding ◽  
Simple Flows

Colloidal shear thickening fluids (STFs) have applications ranging from commercial use to those of interest to the army and law enforcement, and the oil industry. The theoretical understanding of the flow of these particulate suspensions has predominantly been focused through detailed particle simulations. While these simulations are able to accurately capture and predict the behavior of suspensions in simple flows, they are not tractable for more complex flows such as those occurring in applications. The model presented in this work, a modification of an earlier constitutive model by Stickel et al. J. Rheol. 2006, 50, 379–413, describes the evolution of a structure tensor, which is related to the particle mean free-path length. The model contains few adjustable parameters, includes nonlinear terms in the structure, and is able to predict the full range of rheological behavior including shear and extensional thickening (continuous and discontinuous). In order to demonstrate its capability for complex flow simulations, we compare the results of simulations of the model in a simple one-dimensional channel flow versus a full two-dimensional simulation. Ultimately, the model presented is a continuum model shown to predict shear and extensional thickening, as observed in experiment, with a connection to the physical microstructure, and has the capability of helping understand the behavior of STFs in complex flows.

Quality 4.0 conceptualisation and theoretical understanding: a global exploratory qualitative study

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Jiju Antony ◽  
Olivia McDermott ◽  
Michael Sony
Keyword(s):  
Critical Success Factors ◽  
Success Factors ◽  
Full Range ◽  
Senior Management ◽  
Successful Implementation ◽  
Motivating Factors ◽  
Theoretical Understanding ◽  
Content Type ◽  
Critical Success ◽  
Management Professionals

PurposeQuality 4.0 has a unique potential to create a competitive advantage for organisations by improving customer experience and enhancing profitability. The purpose of this study is to examine Quality 4.0, the9; benefits, motivating factors, critical success factors and the skills required by quality professionals in the successful implementation of Quality 4.0. The study also investigates the organisational readiness factors9 and challenges that need to be addressed before Quality 4.0 adoption and assess their importance.Design/methodology/approachA qualitative interview approach was utilised by interviewing a panel of senior management, engineering and continuous improvement (CI); professionals working in leading companies in Asia, Europe and America who are currently deploying Quality 4.0.FindingsThis study provides a theoretical base for the Quality 4.0 body of knowledge in terms of an organisation’s adoption and overcoming implementation challenges and providing examples of Quality 4.0 application. Organisations can use this study to understand what Quality 4.0 means to industry, the benefits and motivating factors for implementing, the Critical Success Factors, challenges, the organisational readiness factors and the role of leadership in a Quality 4.0 deployment. In addition, the study looks at the skills required by future Quality 4.0 professionals in terms of hard skills, soft skills and a curriculum for educating future quality management professionals. The respondents cited that predictive analytics, sensors and tracking, and electronic feedback loops are the most critical technologies for driving Quality 4.0.Research limitations/implicationsOne of the limitations of this research was that as this area is a nascent area the researchers were limited in their literature review. The second limitation was that the study was based on 12 interviews. A more comprehensive longitudinal study would yield more data so that better and robust conclusions can be derived from the study.Originality/valueThis is the first empirical study on Quality 4.0, which captures the viewpoints of senior management professionals on a full range of topics related to Quality 4.0 motivation for deployment, implementation and readiness for its adoption.

Lattice Boltzmann Simulation of Rarefied Gas Flow Along Moving Rigid Objects in Micro-Cavities

2015 ◽  
Author(s):  
Weilin Yang ◽  
Hongxia Li ◽  
TieJun Zhang ◽  
Ibrahim M. Elfadel
Keyword(s):  
Free Path ◽  
Lattice Boltzmann ◽  
Path Length ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Free Path Length ◽  
Mean Free Path ◽  
Fluid Simulation ◽  
Transition Flow ◽  
Rarefied Gas Flow

Rarefied gas flow plays an important role in the design and performance analysis of micro-electro-mechanical systems (MEMS) under high-vacuum conditions. The rarefaction can be evaluated by the Knudsen number (Kn), which is the ratio of the molecular mean free path length and the characteristic length. In micro systems, the rarefied gas flow usually stays in the slip- and transition-flow regions (10−3 < Kn < 10), and may even go into the free molecular flow region (Kn > 10). As a result, conventional design tools based on continuum Navier-Stokes equation solvers are not applicable to analyzing rarefaction phenomena in MEMS under vacuum conditions. In this paper, we investigate the rarefied gas flow by using the lattice Boltzmann method (LBM), which is suitable for mesoscopic fluid simulation. The gas pressure determines the mean free path length and Kn, which further influences the relaxation time in the collision procedure of LBM. Here, we focus on the problem of squeezed film damping caused by an oscillating rigid object in a cavity. We propose an improved LBM with an immersed boundary approach, where an adjustable force term is used to quantify the interaction between the moving object and adjacent fluid, and further determines the slip velocity. With the proposed approach, the rarefied gas flow in MEMS with squeezed film damping is characterized. Different factors that affect the damping coefficient, such as pressure of gas and frequency of oscillation, are investigated in our simulation studies.

On the Discretization of the Power-Law Hemolysis Model

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Mohammad M. Faghih ◽  
Ahmed Islam ◽  
M. Keith Sharp
Keyword(s):  
Fluid Dynamics ◽  
Power Law ◽  
Velocity Fields ◽  
Radial Expansion ◽  
Complex Flows ◽  
Cfd Simulations ◽  
Large Exponent ◽  
Computer Based ◽  
Computational Fluid Dynamics Cfd ◽  
Simple Flows

Abstract Flow-induced hemolysis remains a concern for blood-contacting devices, and computer-based prediction of hemolysis could facilitate faster and more economical refinement of such devices. While evaluation of convergence of velocity fields obtained by computational fluid dynamics (CFD) simulations has become conventional, convergence of hemolysis calculations is also essential. In this paper, convergence of the power-law hemolysis model is compared for simple flows, including pathlines with exponentially increasing and decreasing stress, in gradually expanding and contracting Couette flows, in a sudden radial expansion and in the Food and Drug Administration (FDA) channel. In the exponential cases, convergence along a pathline required from one to tens of thousands of timesteps, depending on the exponent. Greater timesteps were required for rapidly increasing (large exponent) stress and for rapidly decreasing (small exponent) stress. Example pathlines in the Couette flows could be fit with exponential curves, and convergence behavior followed the trends identified from the exponential cases. More complex flows, such as in the radial expansion and the FDA channel, increase the likelihood of encountering problematic pathlines. For the exponential cases, comparison of converged hemolysis values with analytical solutions demonstrated that the error of the converged solution may exceed 10% for both rapidly decreasing and rapidly increasing stress.

scholarly journals Boundary Effects in Solution of Boltzmann's Equation for Electron Swarms

1981 ◽  
Vol 34 (3) ◽  
pp. 223 ◽  
Author(s):  
RE Robson
Keyword(s):  
Steady State ◽  
Analytic Solution ◽  
Full Range ◽  
Mean Free Path ◽  
Path Model ◽  
Zero Field ◽  
Frequency Model ◽  
Molecule Interactions ◽  
Boltzmann's Equation ◽  
Boltzmann’S Equation

The combined effect of interaction of electrons with walls, neutral molecules and an electrostatic field is considered through analytic solution of Boltzmann's equation. In the first instance, we discuss a half-range decomposition in velocity space, corresponding to electrons moving to and from the walls, which is valid for all types of electron-molecule interactions. The half-range equations are solved in the steady state for zero field and the constant mean free path model, and it is shown that the familiar full-range 'two-term' approximation equations are adequate in this case, as far as estimating bulk properties of the electrons is concerned. For the nonzero field, again in the steady state, the full-range equations are solved for the constant collision frequency model.

Imaging of Metal/Semiconductor Interface by Ballistic-Electron-Emission Microscopy (Beem)

1992 ◽  
Vol 295 ◽  
Author(s):  
E. Y. Lee ◽  
B. R. Turnew ◽  
J. R. Jimenez ◽  
L. J. Schowalter
Keyword(s):  
Free Path ◽  
Spatial Resolution ◽  
Electron Emission ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Ballistic Electron Emission Microscopy ◽  
Semiconductor Interface ◽  
Ballistic Electron ◽  
Emission Microscopy

AbstractStudies in ballistic-electron-emission spectroscopy (BEES) have enabled precise energy measurements of Schottky barrier heights with excellent spatial resolution and, more recently, it was shown that even scattering at the metal/semiconductor interface affects the BEES spectrum [1]. Monte Carlo simulations have been done to predict the spatial resolution of ballistic-electron-emission microscopy (BEEM) [2]. In this paper, we will discuss the experimental spatial resolution of BEEM, and we will also give some of our BEES results for Au/Si and for Au/PtSi/Si. Our experimental BEEM studies indicate that, for Au/Si, hot electron transport is diffusive rather than ballistic, because the inelastic mean free path length (∼100 nm) is much larger than the elastic mean free path length (∼10 nm). This is in agreement with existing theories and with the literature on the internal photoemission method of studying the transport. Even in this diffusive regime, the spatial resolution of BEEM is still expected to be very good, being on the order of 10 nm [2]. Our preliminary work on PtSi shows that it has an attenuation length of 4 nm, which differs significantly from that of Au.

Recent Progress in Rheology

1983 ◽  
Vol 50 (4b) ◽  
pp. 1181-1190 ◽  
Author(s):  
R. I. Tanner
Keyword(s):  
Recent Progress ◽  
Numerical Solutions ◽  
Constitutive Relations ◽  
Complex Flows ◽  
Stress Measurements ◽  
Simple Flows ◽  
Fluid Rheology

Progress in fluid rheology is surveyed, including simple flows useful for stress measurements. The question of how to describe more complex flows is discussed in the light of knowledge of fluid microstructure, and several constitutive relations are exhibited. Finally, the need for numerical solutions to problems is emphasized.

A STUDY ON PENETRATION DEPTH OF POLARIZATION IMAGING

2010 ◽  
Vol 03 (03) ◽  
pp. 177-181 ◽  
Author(s):  
RAN LIAO ◽  
NAN ZENG ◽  
DONGZHI LI ◽  
TIANLIANG YUN ◽  
YONGHONG HE ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Optical Measurements ◽  
Degree Of Polarization ◽  
Polarization Imaging ◽  
Optical Clearing ◽  
Different Response

Optical clearing improves the penetration depth of optical measurements in turbid tissues. Polarization imaging has been demonstrated as a potentially promising tool for detecting cancers in superficial tissues, but its limited depth of detection is a major obstacle to the effective application in clinical diagnosis. In the present paper, detection depths of two polarization imaging methods, i.e., rotating linear polarization imaging (RLPI) and degree of polarization imaging (DOPI), are examined quantitatively using both experiments and Monte Carlo simulations. The results show that the contrast curves of RLPI and DOPI are different. The characteristic depth of DOPI scales with transport mean free path length, and that of RLPI increases slightly with g. Both characteristic depths of RLPI and DOPI are on the order of transport mean free path length and the former is almost twice as large as the latter. It is expected that they should have different response to optical clearing process in tissues.

scholarly journals Bidirectional permeability measurements of polar firn

2002 ◽  
Vol 35 ◽  
pp. 63-66 ◽  
Author(s):  
Gina L. Luciano ◽  
Mary R. Albert
Keyword(s):  
Ice Core ◽  
Ice Cores ◽  
Free Path Length ◽  
Mean Free Path ◽  
Transport Processes ◽  
Climate History ◽  
Chemical Modeling ◽  
Vertical Permeability ◽  
Ice Core Record ◽  
Sphere Radius

AbstractIce cores provide a valuable archive of climate history. for a complete understanding of this archive, it is important to understand air–snow exchange processes through the snow and firn in order to fully decode the ice-core record. Transport processes through the snow and firn are dependent upon their physical properties. In this paper, bidirectional permeabilities from selected sections of a 13 mcore from Summit, Greenland, are presented. Differences between lateral and vertical permeabilities are evident throughout the core in permeameter data and in microstructure statistics. Both lateral and vertical permeabilities are consistent with overall patterns of previous polar permeability data with depth. the differences between lateral and vertical permeability measurements for some samples can be attributed to equivalent sphere radius. Further studies examining mean free-path length may be helpful in chemical modeling and in deriving an equation relating permeability to microstructure.

Evaluating Rigid and Semiflexible Fiber Orientation Evolution Models in Simple Flows

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Gregory M. Lambert ◽  
Donald G. Baird
Keyword(s):  
Simple Shear ◽  
Fiber Orientation ◽  
Squeeze Flow ◽  
Model Parameters ◽  
Mold Design ◽  
Random Initial Condition ◽  
Complex Flow ◽  
Planar Extension ◽  
Rod Model ◽  
Simple Flows

As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to fiber reinforced polymer composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injection-molded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiber–polymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to isolate and compare the effects of shear and extension on two orientation models. To this end, simple shear and planar extension are employed, and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house. A novel rheometer tool was developed and fabricated in-house to impart planar extension using a lubricated squeeze flow technique, where a low-viscosity Newtonian lubricant is applied to the solid boundaries to minimize the effect of shearing due to the no-slip boundary condition. The Folgar–Tucker model with a strain reduction factor is used as a rigid fiber model and compared against a bead–rod model (a semiflexible model) proposed by Ortman. Both models are capable of predicting the data, with the bead–rod model performing slightly better. Orientation occurs at a much faster rate under startup of planar extension and also attains a much higher degree of flow alignment when compared with startup of steady shear.

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