Investigation of Mixing Performance in Passive Micromixers - Industrial

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Investigation of mixing performance in passive micro-mixers Weipeng Zhang, Xi Wang, Xin Feng, Chao Yang, and Zai-Sha Mao Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01765 • Publication Date (Web): 05 Sep 2016 Downloaded from http://pubs.acs.org on September 12, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Investigation of mixing performance in passive micro-mixers Weipeng Zhang 1, Xi Wang 2 *, Xin Feng 1, Chao Yang 1*, Zai-Sha Mao 1 1

Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China 2

Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

Abstract This work is focused on the mixing performance in passive micro-channels. Experiments are carried out to investigate the effect of inlet mixing angle and surface wettability on the micro-mixing efficiency in micro-mixers. The iodate-iodide testing reaction and a micro-PIV system are adopted to characterize the micro-mixing efficiency. The results demonstrate that the micro-mixing efficiency is enhanced as the inlet mixing angle increases. It is also illustrated that the mixing performance in hydrophobic micro-channels is better compared to hydrophilic ones. To optimize the configuration of micro-channels for better mixing, a novel baffled spiral micro-mixer is developed. The experiments show that the micro-mixing efficiency in the novel micro-mixer is significantly improved compared to conventional ones.

Keywords: passive micro-mixer; mixing performance; spiral channel; inlet angle; surface wettability

1. Introduction Mixing is a fundamental phenomenon in many fields such as pharmaceutical, cosmetic and

*

Corresponding authors. Tel.: +86-10-62554558. Fax: +86-10-82544928. E-mail address: [email protected] (X. Wang), [email protected] (C. Yang). 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

chemical industries1-3. The mixing on molecular scale (namely micro-mixing) plays a key role in reaction processes of material synthesis, polymerization, crystallization and drug delivery, and influences the selectivity and quality of final products4-6. Due to the ongoing progress in Micro-Electro-Mechanical-Systems (MEMS), the micro-mixer where rapid mixing of samples and reagents are required has become an important element in both laboratories and commercial practice and attracts increasing attentions7,8. The well-defined distribution of reactants throughout the micro-device depends on the process of molecule diffusion. The micro-mixing in such reactors is fast enough to make macro-mixing irrelevant9. As a system shrinks in size, the gravitational and inertial effects become insignificant in comparison to interfacial and viscous forces10. Surface interaction refers not only to the interfacial interaction between two fluid phases, but also the interaction of each fluid with channel walls11. More and more attentions have been drawn on the wettability gradient along the solid surface for actuating droplet motion or accelerating liquid flow, which shows potentials in enhancing the process of heat and mass transfer12,13. The effect of the surface properties of micro-channel walls becomes prominent, which influences profoundly both the nature of two-phase flow and flow regime transitions. Barajas and Panton14 reported that in partially non-wetting systems (contact angle θ>90°), the transition boundaries between slug and multiple rivulet flows and between slug and annular flows were significantly affected by the contact angle. Previous investigation by our group15,16 revealed that the effect of surface wettability on micro-fluidics in the surface tension-dominated zone was more apparent compared to the inertia-dominated zone. Zhao et al.17 investigated the influence of surface properties on the flow characteristics and the mass transfer performance of two immiscible liquids in a polymethyl methacrylate (PMMA) micro-channel, and 2


Page 2 of 43

Page 3 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


found that the fluctuation amplitude increased more significantly after the channel surface being modified more hydrophobic. In short, the surface wetting property has been proved to be a non-negligible impact factor for micro-fluidics. However, detailed knowledge of this effect on the micro-mixing characteristics in micro-channels is desired. Micro-mixers can be coarsely classified as active and passive mixers. For an active micro-mixer, external energy supplier such as ultrasound, time-dependent electric and magnetic field etc. is needed. In a passive micro-mixer, there is no external energy input apart from the pressure drop to drive the flow. Mixing occurs as a result of diffusion or chaotic advection. Liu et al.18,19 studied the micro-mixing performance in micro-mixers with various configurations by both experiment and CFD simulation. They concluded that the intensity of mixing had a nearly linear relationship with Reynolds numbers (Re) in the range from 2000 to 10000 while being independent on the width of the mixing channel. Under typical operating conditions, the flow in passive micro-structured devices is laminar and the molecular diffusion across the channels is slow, which makes efficient mixing in micro-fluidic devices rather difficult. To overcome this problem, measures have been taken to enhance the micro-mixing in passive micro-mixers. Chung et al.20 presented a planar micro-mixer with rhombic micro-channels and a converging-diverging element. Nimafar et al.21 compared the mixing process in T-shape, O-shape and H-shape micro-channels, and found that the H-shape micro-mixer had the best mixing efficiency. Ahn et al.22 quantified the secondary flow and pattern of two-liquid mixing inside a meandering square micro-channel. Apart from improvement of the configuration of micro-mixers, operation condition is another important factor for micro-mixing. The micro-mixing performance was associated with the packing length and appropriate packing position23,24. For a passive micro-mixer, more special geometries are 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 43

required to form the chaotic advection or splitting/recombining flows to intensify the mixing process. Moreover, the effect of inlet configuration on mixing performance draws considerable attention. Different mixing geometries have been proposed over the years. Flow focusing, co-flowing and T-junction structures appear as unit operations and are frequently used in the flow of immiscible liquids25. T-junction mixers can be differentiated based on the size of each part of the junction and the position of the continuous phase introduction26. Since the entrance region is very important for transport and mixing characteristics, the effect of geometries at the intersection section of a micro-channel on the micro-mixing performance is investigated in the current work. Glass micro-channels with the intersection angle between inlet channels varying from 60° to 300° are explored. Moreover, the micro-mixing efficiencies in hydrophilic, hydrophobic and partiallyhydrophobic micro-channels are compared. The influence of wettability of channel wall on the mixing performance is analyzed. In addition, a novel baffled spiral micro-mixer is developed so as to intensify the mixing efficiency of fluids in micro-channel mixers.

2. Experimental details 2.1 Chemical probe for mixing performance The Villermaux-Dushman method which was firstly developed for stirred vessels27-29 is adopted to characterize the micro-mixing efficiency. It is based on a parallel competing reaction system including the following two steps: The neutralization of diborohydride ions:

H 2 BO3− + H + → H 3 BO3 4


(1)

Page 5 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The comproportionation reaction of iodate and iodide to iodine (namely Dushman reaction):

5 I − + IO3− + 6 H + → 3I 2 + 3 H 2 O

(2)

The redox reaction (2) is fast, in the same range of the micro-mixing process, but is much slower than the neutralization reaction (1). The kinetics and characteristic time of reaction (2) are30,31 2

2

r = k ( H + ) ( I − ) ( IO3− )

(

tr = 1 min 1 [H + ], 3[I O3− ], 3 [I − ] r 2 5

(3)

)

(4)

The rate constant k is a function of the ionic strength of the mixture, which is denoted as32,33

lg ( k ) = 9.28105 − 3.664 I , for I < 0.166 mol/L lg ( k ) = 8.383 − 1.5115 I + 0.23689 I , for I > 0.166 mol/L

(5) (6)

The iodide-iodate reaction method itself can serve as a preliminary test to test if mixing is sufficiently fast to investigate the kinetics of the Dushman reaction at the respective concentrations. If considerable amounts of iodine are detected, it can be concluded that the rate of the Dushman reaction is faster than the mixing process. Otherwise, if the mixing process is faster than the Dushman reaction, the chemical selectivity is solely governed by the chemical kinetics of reactions (2) and (1), and thus no detectable amounts of iodine (or tri-iodide) would be found. The iodine produced in reaction (2) further reacts with the excess iodide to form tri-iodide according to chemical equilibrium (7):

 → I 3− I 2 + I − ← 

(7)

The temperature dependence of the chemical equilibrium constant is given as follows:

kB =

lg k B =

[I 3− ] [I 2 ][I − ]

555 + 7.355 − 2.575lg T T

(8)

(9)

The tri-iodide in the sample collected from the exit of the mixer was detected by a UV 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 43

spectrophotometer (Lab Tech UV-2000) at the absorbance maxima of 353 nm. Based on the concentration of the reactants and tri-iodide, the segregation index X S can be defined as28,29

XS =

Y=

YST =

Y YST

2 ([I 2 ] + [I3− ]) [H + ]0

6[I O3− ]0 6[I O3− ]0 + [H 2 BO3− ]0

(10)

(11)

(12)

where Y is the ratio of the acid mole number consumed by the oxidation reaction to the total acid mole number injected, and YST is the value of Y in the case of total segregation when micro-mixing process is infinitely slow30,31. Buffer solution (solution A) was prepared with boric acid and iodide-iodate solutions of potassium iodate and potassium iodide. The purity of chemical reagents is 98% (Beijing Chemical Works). The buffer solution was prepared by first adding boric acid and sodium hydroxide into de-ionized water, secondly potassium iodate and potassium iodide were separately dissolved into de-ionized water and then consecutively added to the buffer solution. All solutions were prepared with de-ionized water stripped with nitrogen to remove the dissolved oxygen so as to prevent the possible oxidation of iodide ions. Solution B contained sulphuric acid only. All the experiments were assumed to be isothermally conducted and operated at 25 ºC. Both solutions were fed by precision syringe pumps (Model 22, Harvard Apparatus, USA, with flowrate stability within 0.35% and reproducibility within 0.95%). The concentrations of reactants are listed in Table 1. According to the Lambert-Beer law, there is a linear relationship between the absorbance and the concentration of tri-iodide ions, which is illustrated in Figure 1, which was determined experimentally as 6


Page 7 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A = 26.23[I3− ]

(13)

2.2 Test sections A series of micro-channels with the inlet mixing angle varying from 60° to 300° are tested, as shown in Figure 2. Dimensions and materials of the micro-channels are given in Table 2. All T-shape and Y-shape micro-channels are designed to have two 20 mm-length inlet branches and a straight mixing section. The PDMS (polydimethylsiloxane) chips were supplied by Capital Bio Corporation, Beijing, China, and fabricated by the lithography technology, and bonding the chips was accomplished by pressing oxygen plasma treatment. The hydrophilic glass micro-channels provided by Institute of Microanalytical Systems, Zhejiang University were made through the wet etching technology using hydrofluoric acid. The surface of the glass micro-channel is smooth, and the effect of roughness on the contact angle is negligible. The contact angle of liquid on solid surface measured on a flat sample of the channel material describes the general surface wettability of micro-channel materials. The contact angle is measured by a FTA200 Dynamic Contact Angle Analyzer (USA). Equi-spaced five points on the chip is measured, and the mean value on these points is adopted as the contact angle of the chip. The contact angles of de-ionized water on glass and PDMS used in this work are 37° and 135°, respectively. In addition, the modifications on the surface of glass were carried out. Trimethylchlorosilane (C.P., purity≥98%, Sinopharm Chemical Reagent Co., Beijing) is used as the modifying liquid. The glass chip was immersed in the solution for 2 hours, and then dried at 100 °C in stagnant air. The contact angle of glass chip after surface modification is 94°. The flow in micro-fluidic devices is laminar at low Reynolds numbers and the inertial force is usually negligible. However, inertial focusing represents a passive technique for manipulating 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

and separating cells on micro-scale without an external force or field32. A few curved configurations were developed to enable the secondary flow33-35 in micro-channels. A baffled spiral micro-channel is developed in this work to intensify the micro-mixing process, which is shown in Figure 3a. 52 baffles were arranged on the wall of the spiral micro-channel. The interval distance between two baffles is not constant. Baffles at the entrance section were installed more densely than those at the downstream section. The lateral motion of liquid across the channel is enhanced by imposing centrifugal forces which induce Dean vortices that perturb the stable flow36,37. Along both lateral walls of the channel, baffles are symmetrically arranged as given in Figure 3b.

2.3 Micro-PIV measurement system A micro particle image velocimetry system (MicroVec Inc, China) is adopted to obtain the velocity distribution in micro-channels. The flow field of view is illuminated by a double-pulsed Nd:YAG laser (λ=532 nm). A 12-bit charge coupled device camera (Imperx, Ipxvga 210-L, 2056×2060 px2, USA ) equipped with 10× (NA0.3) microscope objective lens is used to capture the images, and each laser beam is guided to the test field through a florescent filter located in the connector between the microscope lens and CCD camera. The laser and CCD camera are controlled by a synchronizer and the obtained pictures are processed by a commercial software. Tracer (polystyrene particle coated with Rhodamine B) with a diameter of 3 µm (peak absorption spectrum at λ=550 nm, peak emission spectrum at λ=590 nm) is chosen to trace the local fluid flow.

8


Page 8 of 43

Page 9 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fast Fourier Transform (FFT) cross-correlation is carried out to determine the flow field. The captured images are divided into an interrogation area of 16×16 px2 with an overlap of 50% of the area during the correlation. An adaptive window scheme incorporated in the commercial software is adopted to offset the calculation error.

3. Results and discussion 3.1 Effect of inlet configuration Xu et al.38 found that the mass transfer during droplet forming stage at the crossing junction contributed a large fraction of the total mass transfer in micro-channels. Advection at the conjunction is enhanced by the shear effect of the intersecting inlet flows, and it can improve significantly the mass transfer and mixing efficiency. The shear effect at the entrance section is dependent on the mixing angle of inlet junction. The velocity distributions at the intersection for mixing angles of 90°, 150°, 180° and 300° are shown in Figure 4. Each velocity vector map is the mean of 100 consecutive images. Generally speaking for all the mixing angles, Poiseuille flow is formed after the inlet streams merge at the junction of inlet channels. However, the velocity distribution at the intersection varies noticeably. When the streams meet at the junction, one side of boundary layer separates from the channel wall and is mixed with the boundary layer of the other stream under the inertia and shear forces of the fluids. The shear effect is related to the mixing angle at the intersection. As the mixing angle increases, the advection effect is enhanced and the diffusion distance between the molecules of two fluids is reduced. The conclusion and results we obtained are consistent to that presented by Hsieh et al.39. Also, the stagnation zone in Figures 4(a), 4(c), 4(e) and 4(g) at the 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

junction is enlarged as the mixing angle increases. When the mixing angle is above 180°, although the secondary flow advantageous for the mixing process is generated, the extra pressure drop caused by the configuration of intersection is also significantly increased. The significant relationship of mixing angle with mixing efficiency is shown in Figure 5. The segregation index decreases as the mixing angle increases from 60° to 300°, which is a little different from the conclusion presented by Shi et al.40. They studied the mixing efficiency of Y-type micro-mixers by CFD, and found that 120° is the optimal mixing angle. In our work, according to the micro-PIV results mentioned above, the advection effect is more intensified at the intersection of large mixing angle, and the mixing performance is improved as the mixing angle increases. In compromised consideration of mixing efficiency and energy consumption, the optimal mixing angle should be between 90° and 180°.

3.2 Effect of surface wettability The mixing performance of micro-channels with different wetting properties as shown in Figures 6 (a) and 6(b) indicates the same law that at the given superficial velocity of fluids, the mixing efficiency is changed by the wetting conditions. The segregation index increases with the increase of the superficial velocity of solution A. At a given superficial velocity, the segregation index in the hydrophobic micro-channel is lower than that in the hydrophilic ones, meaning a better micromixing effect. On micro-scale, the effect of surface force to fluid flow becomes dominant. Wang et al.15 and Zhao et al.17 found that for the given flow rate, flows were different in the micro-channels with different surface wettabilities. As the mixing performance in this work is concerned, in a hydrophobic micro-channel, the surface energy of channel wall is low, which 10


Page 10 of 43

Page 11 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


weakens the interaction between liquid fluid and solid wall. All of these may contribute to enhance the mixing efficiency in micro-channels. The segregation index of the micro-channel reactor we obtained is smaller compared to conventional reactors41, even much smaller compared to impinging jet reactors42.

3.3 Novel micro-mixer As for the flow of low Reynolds numbers in micro-channels, inertial forces are often neglected as compared with dominant viscous and interface effects43. Spiral micro mixers have drawn little attention, despite their significant contribution to developing a secondary flow and optimizing the mixing efficiency32. A passive spiral micro-mixer with baffles as shown in Figure 3 is proposed in this work to intensify the mixing process. Baffles are set in interval arrangement at both sides of the spiral mixing channel wall, and the local arrangement of the baffles and the SEM picture of the baffle are shown in Figures 7 and 8 respectively. For the spiral geometry of the micro-mixer, the radius of the innermost circle is 3 cm while that of the outermost circle is 8 cm. The cross-section of the spiral mixing channel is rectangular. The baffles in the micro-mixer are arranged more densely at the entrance section than those at the fully developed section. At the entrance section, baffles are arranged every 15° of the central angle, and at the fully developed section, the baffles are arranged every 45° of the central angle. Figure 9 illustrates the velocity profile of the test section measured by a micro-PIV system. Since spiral configuration is adopted and in addition to the baffles incorporated to intensify local mixing, the lateral motion of fluid in the micro-mixer is dramatically enhanced by the baffle-disturbed centrifugal force, which is quite different from those in straight micro-channels. 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The local fluid motion around the baffle is accelerated and the advection effect is significantly enhanced. Moreover, the intensification by baffles in the inner circle is more noticeable compared to outer circles. These observations suggest that the channel inlet should be set in the inner circle and the baffles should be arranged more densely at the entrance section than in the downstream section. Comparison of the micro-mixing efficiency among straight channels, the spiral channels with baffles and the spiral channels without baffles is shown in Figure 10. The design of the spiral channel has a significant enhancing effect on mixing. Therefore, uniform mixing can be achieved at a shorter distance. For the straight channel with a relatively weak mixing effect, a higher flow rate is required to achieve the same mixing effect. The mixing efficiency in the spiral micro-mixer with baffles is much higher compared to straight micro-channels and spiral micro-mixers without baffles.

4. Conclusions Experimental investigation of the enhancement of mixing efficiencies in micro-mixers is performed in this work. The Villermaux-Dushman method is used to characterize the micro-mixing performance. The effect of inlet intersection angle and surface wettability is studied. It has been found that the mixing efficiency increases with the intersection angle. The advection effect becomes more intensive and the mixing performance is improved as the intersection angle increases. In view of both micro-mixing efficiency and energy dissipation, the optimal inlet mixing angles of 90°-180° are recommended. In addition, the mixing performance in hydrophobic micro-channels is better than that in hydrophilic ones. Furthermore, a spiral micro-channel with baffles is proposed, in which the mixing efficiency is significantly improved as compared to the 12


Page 12 of 43

Page 13 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


conventional ones.

Acknowledgement Financial supports from 973 Program (2012CB224806), the National Natural Science Foundation of China (21406236, 21406129, 21490584), the State Key Lab Foundation of China (SKL-ChE-14A01) and Jiangsu National Synergetic Innovation Center for Advanced Materials are gratefully acknowledged.

Nomenclature A = absorbance, g·cm/L I = mole concentration of the liquid, mol/L k = rate constant, mol/s r = reaction rate, s-1 Re = Reynolds number tr = characteristic time of reaction, s T = temperature, K Umax = maximum velocity in the flow direction, m/s Xs = segregation index Y = yield Yst = yield at total segregation

Greek letters θ = contact angle of liquid on solid surface, °

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

References (1) Pashkova, A.; Greiner, L. Enthalpy of mixing for the determination of mixing efficiency of microstructured mixers by isothermal heat balance calorimetry. Chem. Eng. Sci. 2012, 76(28), 45. (2) Cheng, D.; Cheng, J.C.; Li, X.Y.; Wang, X.; Yang, C.; Mao, Z.-S. Experimental study on gas–liquid–liquid macro-mixing in a stirred tank. Chem. Eng. Sci., 2012, 75(25), 256. (3) Zhao, Y.C.; Li, X.Y.; Cheng, J.C.; Yang, C.; Mao, Z.-S. Experimental study on liquid-liquid macromixing in a stirred tank. Ind. Eng. Chem. Res. 2011, 50(75), 5952. (4) Bourne, J.R. Mixing on the molecular scale (micromixing). Chem. Eng. Sci. 1983, 38(1), 5. (5) van Leeuwen, M.L.J.; Bruinsma, O.S.L.; van Rosmalen, G.M. Influence of mixing on the product quality in precipitation. Chem. Eng. Sci. 1996, 51(11), 2595. (6) Ghanem, A.; Lemenand, T.; Valle, D.D.; Peerhossaini, H. Static mixers: Mechanisms, applications, and characterization methods – A review. Chem. Eng. Res. Des. 2014, 92(2), 205. (7) Braune, S.; Pöchlauer, P.; Reintjens, R.; Steinhofer, S.; Winter, M.; Olivier, L.; Guidat, R.; Woehl, P.; Guermeur, C. Selective nitration in a microreactor for pharmaceutical production under cGMP conditions. Chem. Today, 2008, 26(5), 1. (8) Kölbl, A.; Kraut, M.; Schubert, K. On the scalability of microstructured mixing devices. Chem. Eng. J. 2010, 160(3), 865. (9) Petrov, A.P.; Dodgson, B.J.; Cherney, L.T.; Krylov, S.N. Predictive measure of quality of micromixing. Chem. Commun. 2011, 47(27), 767. (10) Tostado, C.P.; Xu, J.H.; Luo, G.S. The effects of hydrophilic surfactant concentration and

14


Page 14 of 43

Page 15 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


flow ratio on dynamic wetting in a T-junction microfluidic device. Chem. Eng. J. 2011, 171(3), 1340. (11) Huh, D.; Kuo, C.-H.; Grotberg, J.B.; Takayama, S. Gas–liquid two-phase flow patterns in rectangular polymeric microchannels: effect of surface wetting properties. New J. Phys. 2009, 11, 75034. (12) Cheng, J.; Zhang, Y.; Pi, P.H.; Lu, L.S.; Tang, Y. Effect of gradient wetting surface on liquid flow in rectangular microchannels driven by capillary force and gravity: An analytical study. Int. Commun. Heat Mass Transfer, 2011, 38(10), 1340. (13) Sun, J.; He, Y.L.; Tao, W.Q.; Rose, J.W.; Wang, H.S. Multi-scale study of liquid flow in micro/nanochannels: Effects of surface wettability and topology. Microfluid. Nanofluid. 2012, 12(6), 991. (14) Barajas, A.M.; Panton, R.L. The effects of contact angle on two-phase flow in capillary tubes. Int. J. Multiphase Flow, 1993, 19(2), 337. (15) Wang, X.; Yong, Y.M.; Fan, P.; Yu, G.Z.; Yang, C.; Mao, Z.-S. Flow regime transition for co-current gas–liquid flow in micro-channels. Chem. Eng. Sci. 2012, 69(1), 578. (16) Wang, X.; Yong, Y.M.; Yang, C.; Mao, Z.-S.; Li, D.D. Investigation on pressure drop characteristic and mass transfer performance of gas-liquid flow in micro-channels. Microfluid. Nanofluid. 2014, 16(1), 413. (17) Zhao, Y.C.; Su, Y.H.; Chen, G.W.; Yuan, Q. Effect of surface properties on the flow characteristics and mass transfer performance in microchannels. Chem. Eng. Sci. 2010, 65(5), 1563. (18) Liu, Z.D.; Lu, Y.C.; Wang, J.W.; Luo, G.S. Mixing characterization and scaling-up analysis of 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

asymmetrical T-shaped micromixer: Experiment and CFD simulation. Chem. Eng. J. 2012, 181-182, 597. (19) Ghanem, A.; Habchi, C.; Lemenand, T.; Valle, D.D.; Peerhossaini, H. Mixing performances of swirl flow and corrugated channel reactors. Chem. Eng. Res. Des. 2014, 92(11), 2213. (20) Chung, C.K.; Shih, T.R. Effect of geometry on fluid mixing of the rhombic micromixers. Microfluid. Nanofluid. 2008, 4(5), 419. (21) Nimafar, M.; Viktorov, V.; Martinelli, M. Experimental comparative mixing performance of passive micromixers with H-shaped sub-channels. Chem. Eng. Sci. 2012, 76(28), 37. (22) Ahn, Y.-C.; Jung, W.; Chen, Z.P. Optical sectioning for microfluidics: secondary flow and mixing in a meandering microchannel. Lab Chip, 2008, 8(1), 125. (23) Su, Y.H.; Chen, G.W.; Yuan, Q. Ideal micromixing performance in packed microchannels. Chem. Eng. Sci. 2011, 66(13), 2912. (24) Ghanem, A.; Lemenand, T.; Valle, D.D.; Peerhossaini, H. Transport Phenomena in Passively Manipulated Chaotic Flows: Split-and-Recombine Reactors. 6th Symposium on Transport Phenomena in Mixing, Proceeding of the ASME 2013 Fluids Engineering Division Summer Meeting, Nevada, USA, July 7-11, 2013. (25) Gregorc, J.; Žun, I. Inlet conditions effect on bubble to slug flow transition in mini-channels. Chem. Eng. Sci. 2013, 102(15), 106. (26) Choi, C.; Yu, D.I.; Kim, M. Surface wettability effect on flow pattern and pressure drop in adiabatic two-phase flows in rectangular microchannels with T-junction mixer. Exp. Therm. Fluid Sci. 2011, 35(6), 1086. (27) Villermaux, J.; Falk, L.; Fournier, M.C.; Detrez, C. Use of parallel competing reactions to 16


Page 16 of 43

Page 17 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


characterize micromixing efficiency. AIChE Symp. Ser. 1991, 88(6), 286. (28) Fournier, M.C.; Falk, L., Villermaux, J. A new parallel competing reaction system for assessing micromixing efficiency—experimental approach. Chem. Eng. Sci. 1996, 51(22), 5053. (29) Fournier, M.C.; Falk, L.; Villermaux, J. A new parallel competing reac-tion system for assessing micromixing efficiency—determination of micromixing by a simple mixing model. Chem. Eng. Sci. 1996, 51(23), 5187. (30) Habchi, C.; Valle, D.D.; Lemenand, T.; Anxionnaz, Z.; Tochon, P.; Cabassud, M.; Gourdon, C.; Peerhossaini, H. A new adaptive procedure for using chemical probes to characterize mixing. Chem. Eng. Sci. 2011, 66(15), 3540. (31) Habchi, C.; Lemenand, T.; Valle, D.D.; Khaled, M; Elmarakbi, A.; Peerhossaini, H. Mixing assessment by chemical probe. J. Ind. Eng. Chem. 2014, 20(4), 1411. (32) Martel, J.M.; Toner, M. Inertial focusing dynamics in spiral microchannels. Phys. Fluids, 2012, 24(3), 32001. (33) Braun, N.P.; Baier, T.; Hardt, S.; Microfluidic centrifuge based on a counterflow configuration. Microfluid. Nanofluid. 2012, 12(1), 317. (34) Olsen, C.K.; Hoyland, J.D.; Rubahn, H.-G. Influence of geometry on hydrodynamic focusing and long-range fluid behavior in PDMS microfluidic chips. Microfluid. Nanofluid. 2012, 12(5), 795. (35) Donaldson, A.A.; Kirpalani, D.M.; Macchi, A. Curvature induced flow pattern transitions in serpentine mini-channels. Int. J. Multiphase Flow, 2011, 37(5), 429. (36) Sollier, E.; Rostaing, H.; Pouteau, P.; Fouillet, Y.; Achard, J.-L. Passive microfluidic devices 17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

for plasma extraction from whole human blood. Sens. Actuator B, 2009, 141(2), 617. (37) Lemenand, T.; Habchi, C.; Valle, D.D.; Bellettre J.; Peerhossaini, H. Mass transfer and emulsification by chaotic advection. Int. J. Heat Mass Tran. 2014, 71, 228. (38) Xu, J.H.; Tan, J.; Li, S.W.; Luo, G.S. Enhancement of mass transfer performance of liquid–liquid system by droplet flow in microchannels. Chem. Eng. J. 2008, 141(1-3), 242. (39) Hsieh, S.S.; Lin, J.W.; Chen, J. Mixing efficiency of Y-type micromixers with different angles. Int. J. Heat Fluid Flow, 2013, 44(12), 130. (40) Shi, X.; Xiang, Y.; Wen, L.X.; Chen, J.F. CFD analysis of flow patterns and micromixing efficiency in a Y-type microchannel reactor. Ind. Eng. Chem. Res. 2012, 51(43), 13944. (41) Li, W.B.; Geng, X.Y.; Bao, Y.Y.; Gao, Z.M.; Micromixing characteristics in a gasliquid-solid stirred tank with settling particles. Chin. J. Chem. Eng. 2015, 23(3), 461. (42) Gao, Z.M.; Han, J.; Bao, Y.Y.; Li, Z.P. Micromixing efficiency in a T-shaped confined impinging jet reactor. Chin. J. Chem. Eng. 2015, 23(2), 350. (43) Wielhorski, Y.; Abdelwahed, M.A.B.; Bizet, L.; Bréard, J. Wetting effect on bubble shapes formed in a cylindrical T-junction. Chem. Eng. Sci. 2012, 84(52), 100.

18


Page 18 of 43

Page 19 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Reactant concentrations

Reactant

Concentration (mol/L)

Solution A: KI

1.16×10-3

KIO3

2.23×10-3

H3BO3

1.818×10-2

NaOH

9.09×10-2

Solution B: H2SO4

0.018-0.036

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 43

Table 2. Dimensions of micro-channels

Micro-channel

Material

Mixing

Channel

Channel

Test length

angle (°)

width (µm)

depth (µm)

(cm)

Shape

I

glass

T

90

200

100

3

II

Modified glass

T

90

200

100

3

III

PDMS

T

90

200

100

3

IV

glass

Y

60

200

100

3

V

glass

Y

150

200

100

3

VI

glass

T

180

200

100

3

VII

glass

Y

240

200

100

3

VIII

glass

Y

300

200

100

3

IX

PDMS

S-without baffles

90

400

200

48

X

PDMS

S-with baffles

90

400

200

48

20


Page 21 of 43

1.0 -

A=26.23[I3 ] 0.8

2

R =0.9993

0.6

A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.4 0.2 0.0 0.00

0.01

0.02

0.03

0.04

-

[I3 ] (mmol/L) Figure 1. Correlation between absorbance and concentration of tri-iodide complex

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. Schematic of micro-channels with different inlet angles

22


Page 22 of 43

Page 23 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) Appearance Figure 3. A spiral micro-channel with baffles

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(b) Sketch of baffle arrangement Figure 3. A spiral micro-channel with baffles

24


Page 24 of 43

Page 25 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a) Vector picture of 90° Figure 4. Velocity maps of different mixing angles at the intersection

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(b) Contour picture of 90° Figure 4. Velocity maps of different mixing angles at the intersection

26


Page 26 of 43

Page 27 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(c) Vector picture of 150° Figure 4. Velocity maps of different mixing angles at the intersection

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(d) Contour picture of 150° Figure 4. Velocity maps of different mixing angles at the intersection

28


Page 28 of 43

Page 29 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(e) Vector picture of 180° Figure 4. Velocity maps of different mixing angles at the intersection

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(f) Contour picture of 180° Figure 4. Velocity maps of different mixing angles at the intersection

30


Page 30 of 43

Page 31 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(g) Vector picture of 300° Figure 4. Velocity maps of different mixing angles at the intersection

31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(h) Contour picture of 300° Figure 4. Velocity maps of different mixing angles at the intersection

32


Page 32 of 43

Page 33 of 43

11

u=0.05m/s u=0.1m/s u=0.2m/s

9

XS (10-3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


7

5

3 50

100

150

200

250

300

Inlet angle (degree) Figure 5. Micro-mixing efficiencies of micro-channels with different inlet angles

33



1.8

channel I (hydropilic) channel II (partially wetted) channel III (hydrophobic)

1.5

Xs (10-3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 43

1.2 0.9 0.6 0.3 0.0 0.3

0.5

0.7

0.9

1.1

1.3

Superficial velocity of solution A (m/s) (a) Volumetric flow ratio of solutions A and B is 0.5 Figure 6. Micro-mixing efficiencies of micro-channels with different wettability

34


Page 35 of 43

channel I(hydropilic) channel II(partially wetted) channel III(hydrophobic)

0.8

XS (10-3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.6

0.4

0.2

0.0 0.3

0.5

0.7

0.9

1.1

1.3

Superficial velocity of solution A (m/s) (b) Volumetric flow ratio of solutions A and B is 1 Figure 6. Micro-mixing efficiencies of micro-channels with different wettability

35



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 7. Image of test section for micro-PIV measurement

36


Page 36 of 43

Page 37 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. SEM image of the baffle arranged on the inner channel wall

37



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) Contour picture Figure 9. Results of micro-PIV measurement

38


Page 38 of 43

Page 39 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(b) Vector picture Figure 9. Results of micro-PIV measurement

39



14

channel III (straight channel without baffles) channel IX (spiral channel without baffles) channel X (spiral channel with baffles)

12

XS (10-3)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 43

10 8

6

4 1.0

1.5

2.0

2.5

3.0

Volume flow rate (mL/min)

Figure 10. Comparison of micro-mixing efficiencies in different micro-mixers

40


Page 41 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


List of Tables and Figures

Table 1. Reactant concentrations

Table 2. Dimensions of micro-channels

Figure 1. Correlation between absorbance and concentration of tri-iodide complex

Figure 2. Schematic of micro-channels with different inlet angles

Figure 3. A spiral micro-channel with baffles (a) Appearance

(b) Sketch of baffle arrangement

Figure 4. Velocity maps of different mixing angles at the intersection (a) Vector picture of 90°;

(b) Contour picture of 90°;

(c) Vector picture of 150°;

(d) Contour picture of 150°;

(e) Vector picture of 180°;

(f) Contour picture of 180°;

(g) Vector picture of 300°;

(h) Contour picture of 300°

Figure 5. Micro-mixing efficiencies of micro-channels with different inlet angles

41



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6. Micro-mixing efficiencies of micro-channels with different wettability (a) Volumetric flow ratio of solutions A and B is 0.5; (b) Volumetric flow ratio of solutions A and B is 1

Figure 7. Image of test section for micro-PIV measurement

Figure 8. SEM image of the baffle arranged on the inner channel wall

Figure 9. Results of micro-PIV measurement (a) Contour picture;

(b) Vector picture

Figure 10. Comparison of micro-mixing efficiencies in different micro-mixers

42


Page 42 of 43

Page 43 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC graphic

SEM

Micro-PIV

Figure A spiral micro-channel with baffles and its micro structures

43


Investigation of Mixing Performance in Passive Micromixers - Industrial

Recommend Documents