scholarly journals Impact of Modified Spacer on Flow Pattern in Narrow Spacer-Filled Channels for Spiral-Wound Membrane Modules

Environments ◽  
2018 ◽  
Vol 5 (11) ◽  
pp. 116
Author(s):  
Zhiming Han ◽  
Mitsuharu Terashima ◽  
Bing Liu ◽  
Hidenari Yasui
Keyword(s):  
Shear Stress ◽  
Flow Pattern ◽  
Friction Factor ◽  
Flow Direction ◽  
Dead Zone ◽  
Three Dimensional ◽  
Stress Contour ◽  
Directional Change ◽  
Low Shear Stress ◽  
Membrane Modules

A modified spacer, which was constructed with arched filaments and zigzag filaments, was designed to improve vortex shedding and generate a directional change in flow patterns of membrane modules, especially in the vicinity of the feed spacer filament, which is most affected by fouling. A unit cell was investigated by using a three-dimensional computational fluid dynamics (CFD) model for hydrodynamic simulation. The results of CFD simulations were carried out for the fluid flow in order to understand the effect of the modified spacer on vortices to the performance of arched filaments at different distances. From 2D velocity vectors and shear stress contour mixing, the flow pattern and dead zone flushing were depicted. The ratio of low shear stress area to the total area increased with the inlet velocity closed to 20%. The energy consumption with respect to flow direction for the arched filament was 80% lower than that in the zigzag filament. Compared with previous commercial spacers’ simulation, the friction factor was lower when the main flow was normal to the arched filament and the modified friction factor was close to the commercial spacers. The homogenization was realized through the flow pattern created by the modified spacer.

scholarly journals CFD Investigation of the Effect of the Feed Spacer on Hydrodynamics in Spiral Wound Membrane Modules

2018 ◽  
Vol 23 (4) ◽  
pp. 80 ◽  
Author(s):  
Zhiming Han ◽  
Mitsuharu Terashima ◽  
Bing Liu ◽  
Hidenari Yasui
Keyword(s):  
Shear Stress ◽  
Friction Factor ◽  
Dead Zone ◽  
Three Dimensional ◽  
Flow Profile ◽  
Power Number ◽  
Contour Plots ◽  
Computational Fluid Dynamics Cfd ◽  
Membrane Modules ◽  
Spiral Wound

Spacers are designed to create a feed channel, but they are also obstacles to the flow in spiral wound membrane modules. The geometry of the feed spacer influences the flow pattern, which was investigated by using a three-dimensional Computational Fluid Dynamics (CFD) model. For the conventional feed spacer, unavoidable disadvantages were caused by its line contact with the membrane. The pillar-like feed spacer was designed to achieve area contact, which made it possible to enhance the porosity and minimize the adverse effects from the dead zone caused by the transverse filament. Through reductions in the connecting filament’s diameter, the channel porosity reached 0.979. Regarding the maximum porosity, the dimensionless power number was reduced by 47.31% at Reynolds number 150 in comparison with a previously studied commercial spacer. Furthermore, a modified friction factor, as a dimensionless parameter, was employed to investigate the shear stress at the membrane’s surface. At dimensionless power number 106, the enhancement of the modified friction factor increased by approximately 22.27% in comparison with the results of a previous study. Based on the numerical prediction, the homogenization of shear stress distribution, which changed the flow profile near the membrane, was featured through contour plots.

Numerical Studies of Three-Dimensional Arterial Flows in Reverse Curvature Geometry: Part I—Peak Flow

1993 ◽  
Vol 115 (3) ◽  
pp. 316-326 ◽  
Author(s):  
R. K. Banerjee ◽  
Y. I. Cho ◽  
L. H. Back
Keyword(s):  
Shear Stress ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Outer Wall ◽  
Momentum Effect ◽  
Centrifugal Effect ◽  
Stress Region ◽  
Secondary Motion ◽  
Low Shear Stress ◽  
Experimental Values

A three-dimensional flow simulation at Repeak = 192 and 580 was made in a smooth reverse curvature model that conformed to the gentle “S” shape from a human left femoral artery angiogram. The objective of this numerical investigation was to find the changes in pressure, shear stress, velocity profile, and particle path occurring in the double-curved arterial vessel. Due to the impingement of blood at the outer wall in the first bend region, the wall shear stress approached 40 dyne/cm2—a value over twice as large as in the straight upstream segment. Conversely, at the inner wall in the first bend, a low shear stress region was found where the value of the shear stress was consistently smaller than that in the straight section. The initiation of centrifugal effects caused by the first bend could clearly be seen at Repeak = 580, but due to the close proximity of the reverse curvature segment, the momentum effect due to the second bend overshadowed the centrifugal effect. Hence, only near the end of the second bend did the centrifugal effect due to the second bend result in a double-spiral-secondary motion. In addition, the numerically calculated pressure drop data were in agreement with prior experimental values.

scholarly journals Investigation of shear-induced rearrangement of carbon nanotube bundles using Taylor–Couette flow

RSC Advances ◽  
2021 ◽  
Vol 11 (60) ◽  
pp. 38152-38160
Author(s):  
Haemin Lee ◽  
Jinhwan Park ◽  
Hyunjung Cho ◽  
Jaegeun Lee ◽  
Kun-Hong Lee
Keyword(s):  
Shear Stress ◽  
Carbon Nanotube ◽  
Flow Pattern ◽  
Couette Flow ◽  
Nanotube Bundles ◽  
Low Shear Stress ◽  
Taylor Couette ◽  
Low Shear ◽  
Taylor Couette Flow

The rearrangement of CNT bundles depends on the flow pattern and flow-induced shear stress. When the Taylor–Couette flow is stable and laminar, and has sufficiently low shear stress, CNT assemblies assume a highly aligned and densified structure.

scholarly journals Computer Simulation of Flow Dynamics in an Intracranial Aneurysm

2004 ◽  
Vol 10 (1_suppl) ◽  
pp. 155-160 ◽  
Author(s):  
N. Kobayashi ◽  
S. Miyachi ◽  
T. Okamoto ◽  
K. Hattori ◽  
T. Kojima ◽  
...  
Keyword(s):  
Shear Stress ◽  
Flow Pattern ◽  
Vessel Wall ◽  
Arterial Wall ◽  
Three Dimensional ◽  
Flow Dynamics ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Pressure Peak ◽  
Aneurysm Model

Using a supercomputer, the authors studied the effect of vessel wall pulsation on flow dynamics with a three-dimensional model simulating both a rigid and pulsatile style. The design of the aneurysm models was set with a 5 mm dome diameter and a 1 or 3 mm orifice size to simulate a carotid-ophthalmic aneurysm. Flow dynamics were analyzed according to flow pattern, wall pressure and wall shear stress. The flow pattern in the aneurysm sac showed the great difference between rigid and pulsatile models particularly in the small-neck aneurysm model. The arterial wall tended to be exposed to a higher pressure peak in the pulsatile model than in the rigid one, especially at its bifurcation and curved regions. Sites of shear stress peak were found on the aneurysmal dome as well as at the distal end of the orifice in both rigid and pulsatile models. The effects of vessel-wall pulsation should be considered whenever evaluating conditions in and around an aneurysm.

Tectonic relaxation and the development of cross fold in the Singhbhum Proterozoic mobile belt: Insights from physical and numerical model experiments

2020 ◽  
Author(s):  
Puspendu Saha ◽  
Atin Kumar Mitra ◽  
Nibir Mandal
Keyword(s):  
Shear Stress ◽  
Large Scale ◽  
Flow Direction ◽  
Regional Scale ◽  
Three Dimensional ◽  
Mobile Belt ◽  
Horizontal Shear ◽  
Eastern Flank ◽  
Analogue Models ◽  
Gravity Driven Flow

<p>Mobile belts are generally characterized by deformational structures of multiple generations, indicating complex spatial and temporal evolution of the strain fields. These deformed terrains show interference patterns indicating superposition of structures striking transverse to the orogenic trend which leads to the development of cross folds in mobile belts. Despite significant work on cross-folding, it is still not well understood how horizontal shortening can develop regionally along the trend of an orthogonal convergent belts. Our present work deals with the spectacular cross-folds in the eastern flank of the Singhbhum Proterozoic mobile belt.</p><p>This study uses three-dimensional continuum models to address the long-standing question: what is the tectonics of regional scale cross-folds with axial planes transecting the orogenic trend? Physical experiments were conducted with PDMS (Poly dimethyl siloxane), a Newtonian viscous material under lower strain rate of deformation. We propose that the belt underwent orogen-parallel flow during tectonic relaxation, developing orogen-parallel shortening, as observed in analogue models. This gravity-driven flow appears to be potential factor for cross folding in orogenic belts. In order to substantiate the deformation of analogue models, the horizontal shear stress was mapped in FE models. This reveals a distinct zone of shear stress localization in the eastern flank. Model results suggest that the arcuate belt is likely to show deformations by large horizontal shear at the flank of the model. This prediction agrees to the observations from analogue models. In order to study the large scale three-dimensional flow pattern, velocity vectors are plotted in the model. The vector diagram shows that the material flow does not take place orthogonally to the orogenic trend, while at the NE margin the flow direction is parallel to orogenic trend, resulting in the development of cross folds in Singhbhum mobile belts.</p>

scholarly journals Three-Dimensional Numerical Simulations and Antifouling Mechanism of Microorganisms on Microstructured Surfaces

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 319
Author(s):  
Hongyue Yang ◽  
Songling Wang ◽  
Chunxi Li ◽  
Hengfan Li
Keyword(s):  
Shear Stress ◽  
Flow Velocity ◽  
Vortex Flow ◽  
Flow Direction ◽  
Stress Gradient ◽  
Three Dimensional ◽  
Low Flow ◽  
Shear Stresses ◽  
Wall Area ◽  
Microstructured Surface

As marine biofouling seriously affects the development and utilization of oceans, the antifouling technology of microstructured surface has become a research hotspot due to its green and environmentally friendly advantages. In the present research, the motion models of microorganisms on the surfaces of five rectangular micropits, in co-current and counter-current flow direction, were established. Dynamic mesh technology was used to simulate the movements of microorganisms with different radii in the near-wall area, and the fluid kinematics and shear stress distributions in different-sized micropits were compared. Furthermore, moving microorganisms were included in the three-dimensional microstructure model to achieve the real situation of biofouling. Simulation results revealed that the vortex flow velocity in the micropits increased with the increase of the inlet flow velocity and the existence of the vortex flow effectively reduced the formation of conditioning layers in the micropits. In the downstream and countercurrent directions, the average shear stresses on the wall decreased with the increase of the micropit depth and width, and the shear stress on the inner wall of the Mp1 micropit (a patterned surface arranged with cubes of 2 µm × 2 µm × 2 µm) was found to be the largest. A low shear stress region with a low flow velocity was formed around microorganisms in the process of approaching the microstructured surface. The shear stress gradient of micro-ridge steps increased with the approach of microorganisms, indicating that microridge edges had a better effect on reducing microbial attachment.

scholarly journals Significance of Slippage and Electric Field in Mucociliary Transport of Biomagnetic Fluid

Lubricants ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 48
Author(s):  
Sufian Munawar
Keyword(s):  
Shear Stress ◽  
Flow Direction ◽  
Pressure Rise ◽  
Physical Parameters ◽  
Slippage Effect ◽  
Channel Surface ◽  
Electro Osmosis ◽  
Biomagnetic Fluid ◽  
Velocity Pressure ◽  
Metachronal Waves

Shear stress at the cilia wall is considered as an imperative factor that affects the efficiency of cilia beatings as it describes the momentum transfer between the fluid and the cilia. We consider a visco-inelastic Prandtl fluid in a ciliated channel under electro-osmotic pumping and the slippage effect at cilia surface. Cilia beating is responsible for the stimulation of the flow in the channel. Evenly distributed cilia tend to move in a coordinated rhythm to mobilize propulsive metachronal waves along the channel surface by achieving elliptic trajectory movements in the flow direction. After using lubrication approximations, the governing equations are solved by the perturbation method. The pressure rise per metachronal wavelength is obtained by numerically integrating the expression. The effects of the physical parameters of interest on various flow quantities, such as velocity, pressure gradient, pressure rise, stream function, and shear stress at the ciliated wall, are discussed through graphs. The analysis reveals that the axial velocity is enhanced by escalating the Helmholtz–Smoluchowski velocity and the electro-osmosis effects near the elastic wall. The shear stress at the ciliated boundary elevates with an increase in the cilia length and the eccentricity of the cilia structure.

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