A Study on the Flow Patterns of a Second Grade Viscoe-Lastic Fluid Past a Cavity in a Horizontal Channel

2012 ◽  
Vol 29 (2) ◽  
pp. 207-215 ◽  
Author(s):  
C. H. Hsu ◽  
S. Y. Hu ◽  
K. Y. Kung ◽  
C. C. Kuo ◽  
C. C. Chang
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Field ◽  
Flow Pattern ◽  
Newtonian Fluid ◽  
Viscoelastic Fluids ◽  
Flow Patterns ◽  
Horizontal Channel ◽  
Second Grade ◽  
Fluid Elasticity

AbstractThis paper studies the behavior of second grade viscoelastic fluid past a cavity in a horizontal channel. The effects of Reynolds number, fluid elasticity and the aspect ratio of the cavity on the flow field are simulated numerically. The equations are converted into the vorticity and stream function equations. The solution is obtained by the finite difference method.The behavior of viscoelastic fluids is quite different from the Newtonian fluid, due to the effects of fluid elasticity. Only one flow pattern appears when the Newtonian fluid past the cavity. However, three kinds of flow patterns appear while the viscoelastic fluids past the cavity by increasing Reynolds number from 20 to 300. The flow field is affected by the fluid elasticity as well as the aspect ratio of the cavity. The transitional flow pattern appears at lower Reynolds number as the higher elasticity fluid past the cavity with larger aspect ratio.

Liquid-Liquid Flow Patterns in Microchannels

2017 ◽  
Author(s):  
Zhen Cao ◽  
Zan Wu ◽  
Mehdi Sattari Najafabadi ◽  
Bengt Sunden
Keyword(s):  
Aspect Ratio ◽  
Flow Pattern ◽  
Liquid Flow ◽  
Flow Patterns ◽  
Continuous Phase ◽  
Hydraulic Diameter ◽  
Intermittent Flow ◽  
Dimensionless Number ◽  
Dispersed Phase ◽  
Flow Pattern Map

In the present work, liquid-liquid flow patterns positioned 40 mm downstream the inlet of microchannels were experimentally investigated, including the effect of hydraulic diameter (Dh), liquid properties, aspect ratio of cross section (a) and inlet configuration. Deionized water, butanol, toluene and hexane were selected as probe fluids with water as the continuous phase. Cross-inlet microchannels of 200 μm * 200 μm (Dh = 200 μm), 400 μm * 400 μm (Dh = 400 μm), 600 μm * 600 μm (Dh = 600 μm) and 600 μm * 300 μm (Dh = 400 μm) as well as a T-inlet microchannel of 600 μm * 300 μm (Dh = 400 μm) were tested. For the tests in the microchannels of Dh = 600 μm and 400 μm, the superficial velocities of the dispersed phase and continuous phase varied between 0.3 mm/s and 12 mm/s and between 0.2 mm/s and 50 mm/s, while in the microchannel of Dh = 200 μm the superficial velocities of the dispersed phase and continuous phase ranged from 0.3 mm/s to 21 mm/s and from 0.2 mm/s to 150 mm/s. Annular flow, deformed interface flow, slug flow, intermittent flow, droplet and slug train flow and droplet flow were detected in the experiment. It shows that flow patterns depend on the hydraulic diameter, liquid properties, inlet configuration and aspect ratio significantly. Dimensionless analysis was employed to develop universal flow pattern maps regardless of the hydraulic diameter and liquid properties. It is indicated that an acceptable universal flow pattern map was derived based on the redefined dimensionless number Rei0.2 *Wei0.4, especially for the boundaries of the slug-droplet transitions, which are independent on the hydraulic diameter to some extent. The other dimensionless number Wei*Ohi worked rather effectively to develop a universal flow pattern map independent on liquid properties. The boundaries of the flow pattern transitions in different liquid-liquid flow almost overlap with each other.

Experimental Investigation of Flow Field Past a Spherical Particle Settling in Viscoelastic Fluids Using Particle Image Velocimetry Technique

2018 ◽  
Author(s):  
Sumanth Kumar Arnipally ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Flow Field ◽  
Shear Viscosity ◽  
Particle Image ◽  
Settling Velocity ◽  
Viscoelastic Fluids ◽  
Particle Settling ◽  
Settling Particle ◽  
Fluid Elasticity ◽  
Piv Technique ◽  
Direction Opposite

Experimental investigation of flow field past a spherical particle settling in viscoelastic fluids using particle image shadowgraphy techniques studies have shown that the settling velocity of particles in viscoelastic fluids decreased significantly with the increasing elasticity of the fluids. However, our understanding of how and why the change in fluid elasticity influences the particle settling velocity are not yet fully developed. An experimental study, therefore, has been conducted to understand the reasons behind why the settling velocity of the particles decrease with the increasing fluid elasticity. The main objectives were: (i) to investigate the fluid flow field behind the settling particle by using particle image velocity (PIV) technique; (ii) to understand the changes caused by the elasticity of the fluid on the flow field past the settling particle; (iii) more specifically, to determine how the fluid velocity profile and the resultant drag forces acting on the settling particle change with the increasing fluid elasticity. Two different viscoelastic fluids were formulated by mixing 3 grades of HPAM polymer (MWs: 500,000; 8,000,000; 20,000,000; concentrations: 0.09% and 0.1%wt). The fluids were designed to have almost identical shear viscosity but significantly different elastic properties. The shear viscosity and elasticity of the fluids were determined by performing shear viscosity and frequency sweep oscillatory measurements, respectively. The settling velocities of the spherical particles in viscoelastic polymer fluids were measured by using particle image shadowgraph technique. The fluid flow field behind the settling particle was determined by using the PIV technique. Results of the PIV measurements demonstrated that negative wakes were present in viscoelastic fluids. The stagnation point (i.e. the point where the velocity becomes zero and above that the fluid starts moving in the direction opposite to the particle movement) was closer to the particle settling in the higher elasticity fluid than that in the lower elasticity fluid. The velocity of the fluid in the recirculation region was higher for the flow of the fluid with higher elasticity. The presence of negative wakes having fast moving fluid in the reverse direction near the settling particle possibly creates an additional drag force (acting on the particle in the direction opposite the particle movement), which would eventually slow down the settling particle. Knowledge of the settling behavior of particles is indispensable to design and optimize numerous industrial operations such as cuttings transport in oil and gas well drilling and proppant transport in hydraulic fracturing. In this study, by conducting experiments under controlled conditions, we were able to show how the change in fluid elasticity influenced the particle settling velocity. The results from this fundamental study can be used for development of optimum drilling and fracturing fluid formulations for effective transport of cuttings and proppants.

scholarly journals On the Steady Flow of a Second-Grade Fluid between Two Coaxial Porous Cylinders

2007 ◽  
Vol 2007 ◽  
pp. 1-11 ◽  
Author(s):  
M. Emin Erdoğan ◽  
C. Erdem İmrak
Keyword(s):  
Exact Solution ◽  
Reynolds Number ◽  
Steady Flow ◽  
Newtonian Fluid ◽  
Velocity Variation ◽  
Second Grade ◽  
Second Grade Fluid ◽  
Grade Fluid ◽  
The Cross ◽  
Porous Cylinders

An exact solution of an incompressible second-grade fluid for flow between two coaxial porous cylinders is given. The velocity profiles for various values of the cross-Reynolds number and the elastic number are plotted. It is found that for large values of the cross-Reynolds number, the velocity variation near boundaries shows a different behaviour than that of the Newtonian fluid.

Flow Behavior of FENE-P Fluids in Grooved Parallel Plates With Transverse Cavities

2016 ◽  
Author(s):  
Abdelkader Filali ◽  
Lyes Khezzar ◽  
Mohamed Alshehhi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Parallel Plate ◽  
Flow Behavior ◽  
Rheological Parameters ◽  
Two Dimensional ◽  
Parallel Plates ◽  
Fluid Elasticity ◽  
Newtonian Case ◽  
Plate Channel

Numerical investigation of the flow behavior for Newtonian and viscoelastic FENE-P fluids in a parallel-plate channel with transverse rectangular cavities is carried out using ANSYS-POLYFLOW code. A two-dimensional, laminar and steady flow is considered and the flow behavior influenced by the generated vortices at the transverse rectangular cavities has been studied. The effect of Reynolds number, fluid elasticity and the rheological parameters of the FENE-P model L2, on the flow field is examined. In all non-Newtonian considered cases, different flow field were observed which shows different behavior compared to the Newtonian case.

Visualizations of Viscoelastic Fluid Flow in Microchannels

2008 ◽  
Author(s):  
F.-C. Li ◽  
H. Kinoshita ◽  
M. Oishi ◽  
T. Fujii ◽  
M. Oshima
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Newtonian Fluid ◽  
Viscoelastic Fluid ◽  
Flow Instability ◽  
Viscoelastic Fluids ◽  
Special Kind ◽  
Reynolds Numbers ◽  
Vortical Flow ◽  
Flow Phenomena

Solutions of flexible high-molecular-weight polymers or some kinds of surfactant can be viscoelastic fluids. The elastic stress is induced in such viscoelastic fluids and grow nonlinearly with the flow rate and results in many special flow phenomena, including purely elastic instability in the viscoelastic fluid flow. The elastic flow instability can even result in a special kind of turbulent motion, the so-called elastic turbulence, which is a newly discovered flow phenomenon and arises at arbitrary small Reynolds number. In this study, we experimentally investigated the peculiar flow phenomena of viscoelastic fluids in several different microchannels with curvilinear geometry by visualization technique. The viscoelastic working fluids were aqueous solutions of surfactant, CTAC/NaSal (cetyltrimethyl ammonium chloride/Sodium Salysilate). CTAC solutions with weight concentration of 200 ppm (part per million) and 1000 ppm, respectively, at room temperature were tested. For comparison, water flow in the same microchannels was also visualized. The Reynolds numbers for all the microchannel flows were quite small (for solution flows, the Reynolds numbers were smaller than 1) and the flow should be definitely laminar for Newtonian fluid. It was found that the regular laminar flow patterns for low-Reynolds number Newtonian fluid flow in different microchannels were strongly deformed in solution flows: either asymmetrical flow structures or time-dependent vortical flow motions appeared. These phenomena were considered to be induced by the viscoelasticity of the CTAC solutions.

Hydrodynamically Developing Dual-Wall-Driven Microchannel Flow

2003 ◽  
Author(s):  
J. Tenny ◽  
D. Maynes ◽  
B. W. Webb
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Field ◽  
Wall Motion ◽  
Centerline Velocity ◽  
Channel Inlet ◽  
Wall Velocity ◽  
Developing Flow ◽  
Developing Region ◽  
Channel Aspect Ratio

The developing flow field in a parallel plate microchannel, induced by wall motion, has been modeled numerically. The flow is driven in this scenario not by an applied pressure gradient, but by the movement of the walls in the axial direction at a constant speed. This type of flow simulates the physical driving mechanism that exists in electro-osmotically generated flow with large channel diameter-to-Debye length ratios. The results are general, however, for any microscale flow induced by wall motion and resulting viscous pumping. The dynamics of the developing flow field were explored for channel length-to-hydraulic diameter ratios (aspect ratio) of 5, 10, and 20 at ten Reynolds numbers, Re (based on the wall velocity), below Re < 2000. The results show that far from the inlet the maximum fluid velocity occurs at the walls, as is expected, and the minimum velocity occurs at the channel center. Near the channel inlet, however, the centerline velocity is not a minimum but reaches a local maximum due to a resulting pressure imbalance generated by the wall motion. The ratio of the centerline velocity to wall velocity depends on the axial distance from the channel inlet, the Reynolds number and the channel aspect ratio. As the aspect ratio increases, the centerline velocity tends to approach the wall velocity far downstream from the inlet. Increases in the Reynolds number have the opposite effect on the centerline velocity. The hydrodynamic developing region, defined by that section of the channel where the wall shear stress is changing, also depends on the channel aspect ratio and Re. In general it is found that the developing region is significantly shorter than for pressure-driven flow at the same Re.

CFD Study on the Flow Field and Power Characteristics in a Rushton Turbine Stirred Tank in Laminar Regime

2019 ◽  
Vol 17 (11) ◽  
Author(s):  
Li Liangchao ◽  
Chen Ning ◽  
Xiang Kefeng ◽  
Xiang Beiping
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flow Pattern ◽  
Scale Up ◽  
Stirred Tank ◽  
Turbulent Regime ◽  
Laminar Regime ◽  
Power Number ◽  
Rushton Turbine ◽  
Working Medium

Abstract A computational fluid dynamics (CFD) simulation was performed to study the hydrodynamics characteristics in a Rushton turbine stirred tank in laminar regime. The effects of operating condition, working medium and geometrical parameter on the flow field and power number characteristics were investigated. It is found that the two-loop flow pattern is formed in laminar regime when the impeller is not very close to tank bottom, while its shape and size vary with Reynolds number and impeller diameter. For a given geometrical configuration, the flow pattern, power number and dimensionless velocity profile are mainly depended on Reynolds number, and do not change with working medium and scale-up for a constant Reynolds number. When impeller off-bottom clearance is too low and Reynolds number is relatively high, the fluid flow would transit from two-loop flow pattern to sing-loop flow pattern as that occurs in turbulent regime. Power number falls for larger impeller in laminar regime. Surprisingly, in laminar regime, power number in the baffled tank with small impeller is almost identical to that in the unbaffled tank.

scholarly journals Experimental Flow Field Investigation of the Bio-Inspired Corrugated Wing for MAV Applications

2021 ◽  
Vol 13 (2) ◽  
pp. 37-50
Author(s):  
Y. D. DWIVEDI ◽  
ABHISHEK MOHAPATRA ◽  
T. BLESSINGTON ◽  
Md IRFAN
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Field ◽  
Flow Pattern ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Lower Surface ◽  
Field Investigation ◽  
Low Reynolds ◽  
Air Vehicles

This is an experimental flow field study of a bio-inspired corrugated finite wing from the dragonfly intended to assess the flow behavior over the wing and compare it with a wing of the same geometry with filled corrugation, at low Reynolds numbers 46000 and 67000. The work purpose is to explore the potential application of such types of wings for Micro Air Vehicles (MAVs) or micro sized Unmanned Air Vehicles (UAVs). Two types of wings are taken into account: first wing was a bio-inspired corrugated wing which was obtained from the mid span of the dragonfly, and the second wing was the same geometry with filled corrugation. Both wings were fabricated by using 3-D printing machine. The tufts were glued at three different locations i.e. at center, 30%, and 60% of the semi-span towards the right side of the wing at the trailing edge. The boundary layers were measured by using boundary layer rakes inside the open-end low speed wing tunnel with varied angles of attack. The results of the tuft flow visualization showed that the flow pattern at different span locations was different at different angles of attack and different wing velocities (Reynolds number). The fluctuations of the two different wings at the same angle of attack and Reynolds number were found different. Also, the directions of the flow for both wings were found to be different at different span locations. The boundary layer measurement results for both wings were found to be different at the same angles of attack and Reynolds numbers. The flow pattern also showed that the wing’s upper as well as lower surface behaved differently on the same wing under the same measurement conditions. The results showed that the corrugated wing outperformed the conventional wing at low Reynolds number and the stall angle of the corrugated wing was more than the conventional wing.

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