scholarly journals Numerical Investigation of Liquid–Liquid Mixing in Modified T Mixer with 3D Obstacles

2021 ◽  
pp. 25-32
Author(s):  
Md. Readul Mahmud
Keyword(s):  
Numerical Investigation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Mixing Performance ◽  
Wide Range

The fluids inside passive micromixers are laminar in nature and mixing depends primarily on diffusion. Hence mixing efficiency is generally low, and requires a long channel length and longtime compare to active mixers. Various designs of complex channel structures with/without obstacles and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. This work presents a design of a modified T mixer. To enhance the mixing performance, circular and hexagonal obstacles are introduced inside the modified T mixer. Numerical investigation on mixing and flow characteristics in microchannels is carried out using the computational fluid dynamics (CFD) software ANSYS 15. Mixing in the channels has been analyzed by using Navier–Stokes equations with water-water for a wide range of the Reynolds numbers from 1 to 500. The results show that the modified T mixer with circular obstacles has far better mixing performance than the modified T mixer without obstacles. The reason is that fluids' path length becomes longer due to the presence of obstacles which gives fluids more time to diffuse. For all cases, the modified T mixer with circular obstacle yields the best mixing efficiency (more than 60%) at all examined Reynolds numbers. It is also clear that efficiency increase with axial length. Efficiency can be simply improved by adding extra mixing units to provide adequate mixing. The value of the pressure drop is the lowest for the modified T mixer because there is no obstacle inside the channel. Modified T mixer and modified T mixer with circular obstacle have the lowest and highest mixing cost, respectively. Therefore, the current design of modified T with circular obstacles can act as an effective and simple passive mixing device for various micromixing applications.

scholarly journals Turbulent 2.5-dimensional dynamos

2016 ◽  
Vol 799 ◽  
pp. 246-264 ◽  
Author(s):  
K. Seshasayanan ◽  
A. Alexakis
Keyword(s):  
Turbulent Flows ◽  
Large Scale ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Navier Stokes Equations ◽  
Wide Range ◽  
Two Dimensional Flow

We study the linear stage of the dynamo instability of a turbulent two-dimensional flow with three components $(u(x,y,t),v(x,y,t),w(x,y,t))$ that is sometimes referred to as a 2.5-dimensional (2.5-D) flow. The flow evolves based on the two-dimensional Navier–Stokes equations in the presence of a large-scale drag force that leads to the steady state of a turbulent inverse cascade. These flows provide an approximation to very fast rotating flows often observed in nature. The low dimensionality of the system allows for the realization of a large number of numerical simulations and thus the investigation of a wide range of fluid Reynolds numbers $Re$, magnetic Reynolds numbers $Rm$ and forcing length scales. This allows for the examination of dynamo properties at different limits that cannot be achieved with three-dimensional simulations. We examine dynamos for both large and small magnetic Prandtl-number turbulent flows $Pm=Rm/Re$, close to and away from the dynamo onset, as well as dynamos in the presence of scale separation. In particular, we determine the properties of the dynamo onset as a function of $Re$ and the asymptotic behaviour in the large $Rm$ limit. We are thus able to give a complete description of the dynamo properties of these turbulent 2.5-D flows.

Numerical Investigation of Liquids Mixing in Pin-Finned Microchannels

2012 ◽  
Author(s):  
Haleh Shafeie ◽  
Omid Abouali ◽  
Khosrow Jafarpur ◽  
Goodarz Ahmadi
Keyword(s):  
Differential Equation ◽  
Mass Transport ◽  
Computational Model ◽  
Numerical Investigation ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Navier Stokes Equations ◽  
Pin Fins

In the present work, the performance of pin-finned microchannels as the micromixers is investigated. Different patterns for distribution of pin-fins were examined (staggered and oblique distribution of fins). A 3-D computational model was developed and the Navier-Stokes equations were solved and the corresponding flow fields were evaluated. The mass transport differential equation was also solved and the concentration of liquids in the mixture was evaluated. The results for the mixing efficiency were compared between the simple and pin-finned microchannels. The results suggest that the finned microchannels with staggered distribution of pins perform very well in mixing of liquids. The mixing efficiency reaches to 100 percent for the Reynolds numbers in which the mixing efficiency is less than 10 percent for the simple microchannels.

3D Simulation of Vortex Shedding Past Tapered Circular Cylinders in Subcritical Reynolds Numbers

2012 ◽  
Author(s):  
V. Tamimi ◽  
M. Zeinoddini ◽  
A. Bakhtiari ◽  
M. Golestani
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
High Reynolds

In this paper results from simulating the vortex shedding phenomena behind a fixed tapered circular cylinder, at relatively high Reynolds numbers, are reported. Ansys-CFX computational fluid dynamics model, based on solving three-dimensional (3D) incompressible transient Navier Stokes equations, is employed for this purpose. The geometries applied in the models resemble those used in wind tunnel experiments by other researchers. The taper slope along the cylinder span is uniform with a tangent of 24:1. The diameter at mid-span of the cylinder equals to 0.0389 m. The Reynolds number (based on the mid-span diameter) is around 29,000. The computational model has first been calibrated against experiments for uniform 3D cylinders as well as results from a Direct Numerical Simulation of turbulent wake with vortex shedding past a uniform circular cylinder, as obtained by other researchers. The main flow characteristics for tapered cylinders such as vortex dislocations and splitting, cellular vortex shedding, oblique vortex shedding and the variation of the vorticity patterns along the tapered cylinder could be obtained from the simulations.

Analysis of Mixing and Flow Structure in Different Passive Micromixers

2009 ◽  
Author(s):  
Shakhawat Hossain ◽  
Mubashshir Ahmad Ansari ◽  
Kwang-Yong Kim
Keyword(s):  
Pressure Drop ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Channel Height ◽  
Navier Stokes Equations ◽  
Pressure Drops ◽  
Square Wave ◽  
Mixing Performance ◽  
Wide Range

This work presents a numerical investigation on mixing and flow structures in microchannels with different geometries: zig-zag; square-wave; and curved. To conduct the investigation, geometric parameters, such as the area of the cross-section of channel, height of the channel, axial length of the channel, and number of pitches, are kept constant for all three cases. Analyses of mixing and flow fields have been carried out for a wide range 0.267 to 267 of the Reynolds number. Mixing in the channels has been analyzed by using Navier-Stokes equations with two working fluids, water and ethanol. The results show that the square-wave microchannel yields the best mixing performance, and the curved and the zig-zag microchannels show nearly the same performance for most Reynolds numbers. For all three cases, the pressure drop has been calculated for channels with equal streamwise-lengths. The curved channel exhibits the smallest pressure drop among the microchannels, while the pressure drops in the square-wave and zigzag channels are approximately the same.

Stability of Hagen-Poiseuille flow with superimposed rigid rotation

1976 ◽  
Vol 73 (1) ◽  
pp. 153-164 ◽  
Author(s):  
P.-A. Mackrodt
Keyword(s):  
Poiseuille Flow ◽  
Pipe Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Neutral Curve ◽  
Rigid Rotation ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Navier Stokes Equations

The linear stability of Hagen-Poiseuille flow (Poiseuille pipe flow) with superimposed rigid rotation against small three-dimensional disturbances is examined at finite and infinite axial Reynolds numbers. The neutral curve, which is obtained by numerical solution of the system of perturbation equations (derived from the Navier-Stokes equations), has been confirmed for finite axial Reynolds numbers by a few simple experiments. The results suggest that, at high axial Reynolds numbers, the amount of rotation required for destabilization could be small enough to have escaped notice in experiments on the transition to turbulence in (nominally) non-rotating pipe flow.

scholarly journals Nonlinear amplification in hydrodynamic turbulence

2021 ◽  
Vol 930 ◽  
Author(s):  
Kartik P. Iyer ◽  
Katepalli R. Sreenivasan ◽  
P.K. Yeung
Keyword(s):  
Reynolds Number ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Developed Turbulence ◽  
Advection Term ◽  
Nonlinear Amplification

Using direct numerical simulations performed on periodic cubes of various sizes, the largest being $8192^3$ , we examine the nonlinear advection term in the Navier–Stokes equations generating fully developed turbulence. We find significant dissipation even in flow regions where nonlinearity is locally absent. With increasing Reynolds number, the Navier–Stokes dynamics amplifies the nonlinearity in a global sense. This nonlinear amplification with increasing Reynolds number renders the vortex stretching mechanism more intermittent, with the global suppression of nonlinearity, reported previously, restricted to low Reynolds numbers. In regions where vortex stretching is absent, the angle and the ratio between the convective vorticity and solenoidal advection in three-dimensional isotropic turbulence are statistically similar to those in the two-dimensional case, despite the fundamental differences between them.

scholarly journals A 3D Printed Jet Mixer for Centrifugal Microfluidic Platforms

Micromachines ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 695 ◽  
Author(s):  
Yunxia Wang ◽  
Yong Zhang ◽  
Zheng Qiao ◽  
Wanjun Wang
Keyword(s):  
3D Printing ◽  
Three Dimensional ◽  
Mixing Efficiency ◽  
Medical Applications ◽  
Microfluidic Platforms ◽  
Mixing Performance ◽  
Wide Range ◽  
3D Printed ◽  
Miscible Liquids ◽  
Biological And Medical Applications

Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology for applications in centrifugal microfluidic platforms. The contact surface of miscible liquids was enhanced significantly by impinging plumes from two opposite arrays of micronozzles to improve mixing performance. The mixing efficiency was evaluated and compared with the commonly used Y-shaped micromixer. Effective mixing in the jet mixer was achieved within a very short timescale (3s). This 3D printed jet mixer has great potential to be implemented in applications by being incorporated into multifarious 3D printing devices in microfluidic platforms.

Analysis of a Novel Y-Y Micromixer for Mixing at a Wide Range of Reynolds Numbers

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Vladimir Viktorov ◽  
Carmen Visconte ◽  
Md Readul Mahmud
Keyword(s):  
Three Dimensional ◽  
Interfacial Area ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Change Of Direction ◽  
Analysis Technique ◽  
Wide Range ◽  
Passive Micromixer ◽  
In Series ◽  
Flow Through

A novel passive micromixer, denoted as the Y-Y mixer, based on split-and-recombine (SAR) principle is proposed and studied both experimentally and numerically over Reynolds numbers ranging from 1 to 100. Two species are supplied to a prototype via a Y inlet, and flow through four identical elements repeated in series; the width of the mixing channel varies from 0.4 to 0.6 mm, while depth is 0.4 mm. An image analysis technique was used to evaluate mixture homogeneity at four target areas along the mixer. Numerical simulations were found to be a useful support for observing the complex three-dimensional flow inside the channels. Comparison with a known mixer, the tear-drop one, based on the same SAR principle, was also performed, to have a point of reference for evaluating performances. A good agreement was found between numerical and experimental results. Over the examined range of Reynolds numbers Re, the Y-Y micromixer showed at its exit an almost flat mixing characteristic, with a mixing efficiency higher than 0.9; conversely, the tear-drop mixer showed a relevant decrease of efficiency at the midrange. The good performance of the Y-Y micromixer is due to the three-dimensional 90 deg change of direction that occurs in its channel geometry, which causes a fluid swirling already at the midrange of Reynolds numbers. Consequently, the fluid path is lengthened and the interfacial area of species is increased, compensating for the residence time reduction.

Lift, drag and added mass of a hemispherical bubble sliding and growing on a wall in a viscous linear shear flow

2008 ◽  
Vol 366 (1873) ◽  
pp. 2233-2248 ◽  
Author(s):  
Dominique Legendre ◽  
Catherine Colin ◽  
Typhaine Coquard
Keyword(s):  
Shear Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Added Mass ◽  
Unsteady Motion ◽  
Navier Stokes ◽  
Mass Force ◽  
Navier Stokes Equations ◽  
Wide Range ◽  
Linear Shear

The three-dimensional flow around a hemispherical bubble sliding and growing on a wall in a viscous linear shear flow is studied numerically by solving the full Navier–Stokes equations in a boundary-fitted domain. The main goal of the present study is to provide a complete description of the forces experienced by the bubble (drag, lift and added mass) over a wide range of sliding and shear Reynolds numbers (0.01≤ Re b , Re α ≤2000) and shear rate (0≤ Sr ≤5). The drag and lift forces are computed successively for the following situations: an immobile bubble in a linear shear flow; a bubble sliding on the wall in a fluid at rest; and a bubble sliding in a linear shear flow. The added-mass force is studied by considering an unsteady motion relative to the wall or a time-dependent radius.

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