Parametric Study of Obstacle Geometry Effect on Mixing Performance in a Convergent-Divergent Micromixer with Sinusoidal Walls

2017 ◽  
Vol 12 (1) ◽  
Author(s):  
Fazlollah Heshmatnezhad ◽  
Halimeh Aghaei ◽  
Ali Reza Solaimany Nazar
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Molecular Diffusion ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Mixing Efficiency ◽  
Main Concept ◽  
Mixing Index ◽  
Operational Parameter

Abstract This study presents a numerical simulation through computational fluid dynamics on mixing and flow structures in convergent-divergent micromixer with a triangular obstacle. The main concept in this design is to enhance the interfacial area between the two fluids by creating a transverse flow and split, and recombination of fluids flow due to the presence of obstacles. The effect of triangular obstacle size, the number of units, changing the position of an obstacle in the mixing channel and operational parameter like the Reynolds number on the mixing efficiency and pressure drop are assessed. The results indicate that at inlet Reynolds numbers below 5, the molecular diffusion is the most important mechanism of mixing, and the mixing index is almost the same for all cases. By increasing the inlet Reynolds number above 5, mixing index increases dramatically, due to the secondary flows. Based on the simulation results, due to increasing the effect of dean and separation vortices as well as more recirculation of flow in the side branches and behind the triangular obstacle, the highest mixing index is obtained at the aspect ratio of 2 for the triangular obstacle and its position at the front of the mixing unit. Also the highest value of mixing index is obtained by six unit of mixing chamber. The effect of changing the position of the obstacle in the channel and changing the aspect ratio of the obstacle is evident in high Reynolds numbers. An increase in the Reynolds number in both cases (changing the aspect ratio and position of the obstacle) leads to pressure drop increases.

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

Numerical and Experimental Investigation of the Effect of Geometrical Parameters on the Performance of a Contraction-Expansion Helical Mixer

2014 ◽  
Vol 12 (1) ◽  
pp. 465-475 ◽  
Author(s):  
Liang Dong ◽  
Zhang Shufen
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Coupling Reaction ◽  
Secondary Flows ◽  
Sudden Expansion ◽  
Mixing Efficiency ◽  
Radius Of Curvature ◽  
Geometrical Parameters ◽  
Diazo Coupling ◽  
Diazo Coupling Reaction

Abstract In this study, the mixing efficiency of a passive contraction-expansion helical mixer, which combines several features, such as helical pipes for induction of secondary flows and sudden expansion and contraction array for expansion vortices, was numerically and experimentally studied. We employed the method of Box–Behnken to select the appropriate design points. Then, various configurations were investigated via computational fluid dynamics (CFD) simulations. The extent of mixing was evaluated by monitoring the residence time distribution (RTD) and observing the shape of the RTD curves. A fast competitive-consecutive diazo coupling reaction is carried out to validate the RTD results. The influences of radius of curvature of the helical mixer, ratio of the length of the contraction part to expansion part, pitch of helical mixer, and the Reynolds number (Re) on mixing efficiency, and pressure drop were also investigated. As expected, the radius of curvature of the helical mixer, ratio of the length of the contraction part to expansion part, and the Reynolds number affected significantly the mixing efficiency, while the pitch of helical mixer had little influence on mixing efficiency. Quadratic models for mixing efficiency and pressure drop were then proposed and could be used for designing the optimal contraction-expansion helical mixer for the required pumping power.

scholarly journals Design of a Novel μ-Mixer

2017 ◽  
Author(s):  
Athanasios G. Kanaris ◽  
Aikaterini A. Mouza
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Swirling Flow ◽  
Numerical Data ◽  
Secondary Flows ◽  
Design Parameters ◽  
Mixing Efficiency ◽  
Geometrical Parameters ◽  
Straight Tube ◽  
Propeller Blades

In this work the efficiency of a new μ-mixer design is investigated. As in this type of devices the Reynolds number is low, mixing is diffusion dominated and it can be enhanced by creating secondary flows. In this study we propose the introduction of helical inserts into a straight tube to create swirling flow. The influence of the insert’s geometrical parameters (pitch and length of the propeller blades) and of the Reynolds number on the mixing efficiency and on the pressure drop are numerically investigated. The mixing efficiency of the device is assessed by calculating a number, i.e. the Index of Mixing Efficiency that quantifies the uniformity of concentration at the outlet of the device. The influence of the design parameters on the mixing efficiency is assessed by performing a series of “computational” experiments, in which the values of the parameter are selected using DOE methodology. Finally using the numerical data, appropriate design equations are formulated, which, for given values ​​of the design parameters, can estimate with reasonable accuracy both the mixing efficiency and the pressure drop of the proposed mixing device.

Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV

2015 ◽  
Author(s):  
Charles P. Brown ◽  
Lesley M. Wright ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Spanwise Direction ◽  
Reduced Pressure ◽  
Line Array

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).

Analysis of mixing performances in microchannel with obstacles of different aspect ratios

2019 ◽  
Vol 233 (5) ◽  
pp. 1045-1051 ◽  
Author(s):  
Bappa Mondal ◽  
Sukumar Pati ◽  
PK Patowari
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Flow Condition ◽  
Schmidt Number ◽  
Mixing Efficiency ◽  
Rectangular Microchannel ◽  
Mixing Performance ◽  
Aspect Ratios ◽  
Flow Through

In this study, the mixing performance and pressure drop characteristics have been numerically analyzed for flow through rectangular microchannel with obstacles in the walls arranged in a staggered manner. Three different aspect ratios (AR) of the obstacles are considered, namely 4:1, 1:1, and 1:4. The effects of aspect ratio of the obstacles on the mixing efficiency and the pressure drop are analyzed and compared with that of the channel without obstacle. The results are presented in terms of Reynolds number (Re) and Schmidt number (Sc) in the following range: 0.2 ≤ Re ≤ 1 and 500 ≤ Sc ≤ 1500. Enhanced mixing efficiency is achieved for the case of microchannel with obstacles and the corresponding pressure drop is also found to be higher. The mixing efficiency as well as the pressure drop is maximum for AR = 1:4 among all the geometries considered in the analysis in same flow condition. Furthermore, for a given configuration of the microchannel the mixing efficiency is governed by the mass Peclet number and, accordingly, the mixing efficiency increases with the decrease in Schmidt number for a given Reynolds number.

scholarly journals A stretchable micromixer with enhanced performance for intermediate Reynolds numbers

2021 ◽  
Author(s):  
Hedieh Fallahi ◽  
Jun Zhang ◽  
Jordan Nicholls ◽  
Pradip Singha ◽  
Nhat-Khuong Nguyen ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Molecular Diffusion ◽  
Inertial Force ◽  
Reynolds Numbers ◽  
Chaotic Advection ◽  
Low Flow ◽  
Viscous Force ◽  
Mixing Efficiency ◽  
Potential Candidate ◽  
Low Reynolds

Abstract Chemical reactions in microscale require good mixing at a relatively low flowrate. However, mixing in microscale faces the major challenge of stable laminar flow associated with the low Reynolds number, the relative ratio between inertial force and viscous force. For low Reynolds numbers of less than unity, mixing occurs due to molecular diffusion. For high Reynolds number of more than several tens, chaotic advection enhances mixing. However, in the intermediate regime, mixing is not efficient. This paper reports a stretchable micromixer with dynamically tuneable channel dimensions. Periodically stretching the device changes the channel geometry and the curvature induced secondary Dean flows. The dynamically evolving secondary and main flows in the mixing channel result in chaotic advection and enhance mixing. The concept was demonstrated in a stretchable micromixer with a serpentine channel. We evaluated the performance of this stretchable micromixer both experimentally and numerically. At the intermediate range of Reynolds numbers from 4 to 17, the periodically stretched micromixer showed a better mixing efficiency than the non-stretched counterpart. Therefore, our stretchable micromixer is a potential candidate for applications where precious reagents need to be mixed at relatively low flow rate conditions.

scholarly journals A stretchable micrometer with enhanced performance for intermediate Reynolds numbers

2021 ◽  
Author(s):  
Hedieh Fallahi ◽  
Jun Zhang ◽  
Jordan Nicholls ◽  
Pradip Singha ◽  
Nhat-Khuong Nguyen ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Molecular Diffusion ◽  
Inertial Force ◽  
Reynolds Numbers ◽  
Chaotic Advection ◽  
Low Flow ◽  
Viscous Force ◽  
Mixing Efficiency ◽  
Potential Candidate ◽  
Low Reynolds

Abstract Chemical reactions in microscale require good mixing at a relatively low flowrate. However, mixing in microscale faces the major challenge of stable laminar flow associated with the low Reynolds number, the relative ratio between inertial force and viscous force. For low Reynolds numbers of less than unity, mixing occurs due to molecular diffusion. For high Reynolds number of more than several tens, chaotic advection enhances mixing. However, in the intermediate regime, mixing is not efficient. This paper reports a stretchable micromixer with dynamically tuneable channel dimensions. Periodically stretching the device changes the channel geometry and the curvature induced secondary Dean flows. The dynamically evolving secondary and main flows in the mixing channel result in chaotic advection and enhance mixing. The concept was demonstrated in a stretchable micromixer with a serpentine channel. We evaluated the performance of this stretchable micromixer both experimentally and numerically. At the intermediate range of Reynolds numbers from 4 to 17, the periodically stretched micromixer showed a better mixing efficiency than the non-stretched counterpart. Therefore, our stretchable micromixer is a potential candidate for applications where precious reagents need to be mixed at relatively low flow rate conditions.

Numerical Simulation of Fluid Mixing in Micro-Mixers

2015 ◽  
Vol 659 ◽  
pp. 671-675
Author(s):  
Supasit Prasertlarp ◽  
Sompong Putivisutisak
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Ultrasound Imaging ◽  
Vortex Structure ◽  
Flow Dynamics ◽  
Fluid Mixing ◽  
Mixing Efficiency ◽  
Inlet Velocity

A 3-D numerical simulation is performed to study the flow dynamics and mixing characteristics between two different kinds of fluid within T-shaped micro-mixers. Water and ethanol are selected as the mixing fluids due to its application in calibrating the ultrasound imaging equipment. The present work focuses on the effects of inlet velocity and aspect ratio of the mixing channel. The Reynolds number is varied from 0.1 to 300 and the aspect ratio in the range between 0.2 and 1. The flow of interest is laminar, steady and without chemical reaction. It is found that at low Reynolds number, the stratified flow character is presented. As the velocity inlet increases, the mixing efficiency is decreased. However, for the Reynolds number greater than 100 the mixing efficiency is increased due to the buildup vortex structure. Furthermore, when increasing the Reynolds number, the pressure drop significantly increases. Thus, it is seen that both the inlet velocity and aspect ratio significantly affect the mixing efficiency and pressure drop.

Effects of Obstacles on the Mixing Performance in Microchannels

2007 ◽  
Author(s):  
Tae-An Kim ◽  
Youn-Jea Kim
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Lower Layer ◽  
Flow Direction ◽  
Diffusion Path ◽  
Mixing Efficiency ◽  
Convection Flow ◽  
Rectangular Microchannel ◽  
Mixing Performance

The mixing of two or more fluid streams in microchannels needs quite long channel lengths. Therefore, in order to improve the mixing performance, obstacles have been placed in the channel to disrupt flow and to reduce the diffusion path. The disruption to flow velocity field alters the flow direction from one fluid to another. Properly designed geometric parameters, such as layout, angle with main flow direction and aspect ratio of obstacles, will be resulted in improving the mixing performance with only little increase of the pressure drop. In this study, T-type rectangular microchannel is used, which has two inlets with W×H×L = 100×100×100 μm3 and one outlet with W×H×L = 200×100×6950 μm3. Furthermore, the mixing channel has obstacles which are placed with an angle of inclination and with dimensions W×H×L = 10×100×h μm3 on the lower layer. In order to estimate the performance of the mixing, numerical analyses are carried out with water and ethanol. Especially, the diffusion coefficient, D, is set to 10−10 m2/s for simulating two-fluid diffusion-convection flow, the mixing efficiency and the pressure drop of microchannel are investigated with various values of the angle of inclination, aspect ratio (h = αH) of obstacle and Reynolds number. When the flow passes through on the obstacles, rotation flow is observed. This flow pattern is repeated at each cycle. Besides, in each case that obstacles are turned to the center of channel and to the side walls, rotational direction is changed reversely. In case of pressure drop, as the Reynolds number, the angle of obstacle (θ) and the aspect ratio (α) are increased, the pressure drop is also increased. Results show that the ratio between the maximum and minimum of pressure drop is the order-of-magnitude of 1 at Re = 1.667. Results also show that the angle of inclination of obstacles has more influence on the mixing performance than the height of obstacles and Reynolds number.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

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