Transport Phenomena in Chaotic Laminar Flows

Sundararajan, Pavithra; Stroock, Abraham D.

doi:10.1146/annurev-chembioeng-062011-081000

Cited by 31 publications

(22 citation statements)

References 62 publications

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“…Microscale chaotic advection has been previously explored as a means to enhance bulk mixing in steadystate axial flows involving continuous transport of species from inlet to outlet (24). In contrast to our observations, results of these studies suggest that enhanced mixing in the bulk does not necessarily augment transport to the sidewall surfaces because chaotic and nonchaotic flow states act similarly to inhibit growth of nearwall species depletion zones over the timescale of residence within the microchannel (25), leading to a generally accepted conclusion that chaotic advection does not appreciably enhance interfacial transport in these scenarios (26). This regime is evident at residence times below t* ∼ 10 in our pore-mimicking system, where the data in Fig.…”

Section: Significancecontrasting

confidence: 99%

Synchronized chaotic targeting and acceleration of surface chemistry in prebiotic hydrothermal microenvironments

Priye

Hassan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Porous mineral formations near subsea alkaline hydrothermal vents embed microenvironments that make them potential hot spots for prebiotic biochemistry. But, synthesis of long-chain macromolecules needed to support higher-order functions in living systems (e.g., polypeptides, proteins, and nucleic acids) cannot occur without enrichment of chemical precursors before initiating polymerization, and identifying a suitable mechanism has become a key unanswered question in the origin of life. Here, we apply simulations and in situ experiments to show how 3D chaotic thermal convection-flows that naturally permeate hydrothermal pore networks-supplies a robust mechanism for focused accumulation at discrete targeted surface sites. This interfacial enrichment is synchronized with bulk homogenization of chemical species, yielding two distinct processes that are seemingly opposed yet synergistically combine to accelerate surface reaction kinetics by several orders of magnitude. Our results suggest that chaotic thermal convection may play a previously unappreciated role in mediating surface-catalyzed synthesis in the prebiotic milieu.thermal convection | prebiotic biochemistry | hydrothermal vents | chaos S ubsea hydrothermal microenvironments uniquely embed catalytically active mineral surfaces in the presence of thermal and chemical gradients, establishing disequilibrium pathways essential for emergence of biochemical complexity (1-3). Synthesis of organic monomers, for example, can be supported in these systems via pH conditions that favor hydrogen-dependent redox processes similar to the CO 2 reducing acetyl-CoA biochemical pathway (4). The recent discovery of alkaline vent systems [e.g., Lost City vent, mid-Atlantic ridge (5, 6)] has generated particular excitement because geochemical serpentinization yields surroundings abundant in hydrogen at moderate temperatures (150-200°C) (Fig. 1A). These attributes, combined with the excess hydrogen's ability to exothermically reduce carbon dioxide into methane, have fueled interest in elucidating the role of alkaline vents in orchestrating synthesis of prebiotic chemical precursors critical to the origin of life (4, 7).But, a favorable chemical environment alone is not sufficient to drive macromolecular synthesis owing to the extremely dilute concentrations of precursor compounds in the prebiotic ocean (8-11). Recent studies have explored the combined action of laminar (2D) thermal convection and thermophoresis as a physical enrichment mechanism, albeit in hairline-sized fissures (diameter d ≤ 100 μm) under steep thermal gradients (100-1,000°C/mm) (12-15). In contrast, surprisingly complex 3D flows characterized by chaotic thermal convection (16, 17) emerge over a broader pore size range [millimeters to centimeters, consistent with porosities in young active carbonate chimneys (18)] and under moderate temperature gradients (0.1-10°C/mm) (19,20) (Fig. 1A and SI Appendix). Here we apply simulations and in situ experiments to show how chaotic thermal convection under conditions mimi...

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Section: Significancecontrasting

confidence: 99%

Synchronized chaotic targeting and acceleration of surface chemistry in prebiotic hydrothermal microenvironments

Priye

Hassan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Fortunately, a large body of experimental, analytical, and computational work, on passive straight channel micromixers, has been dedicated to their geometry optimization [32][33][34][35]. The strength of these flow patterns is determined by the longitudinal pressure gradient between the inlet and outlet and by the geometrical parameters defining the ridge/groove structures that include: the angle q with respect to the channel axis; the groove's depth h, width w, and length l; and the spatial periodicity s. Thus, the search space for the optimal geometrical parameters is quite large.…”

Section: Discussionmentioning

confidence: 99%

“…The strength of these flow patterns is determined by the longitudinal pressure gradient between the inlet and outlet and by the geometrical parameters defining the ridge/groove structures that include: the angle q with respect to the channel axis; the groove's depth h, width w, and length l; and the spatial periodicity s. Thus, the search space for the optimal geometrical parameters is quite large. Fortunately, a large body of experimental, analytical, and computational work, on passive straight channel micromixers, has been dedicated to their geometry optimization [32][33][34][35]. Some of the determined geometrical dimensions that ensure maximization of the transversal flow components and vorticity include: ridge orientation q = 45°with respect to the fluid flow direction [25]; ridge depth as a function of the main channel height h = 0.25H [32,33]; ratio of groove width w to pitch s 0.5 to 0.7 [26,36].…”

Section: Discussionmentioning

confidence: 99%

Use of Grooved Microchannels to Improve the Performance of Membrane‐Less Fuel Cells

D’Alessandro

Fodor

2014

Fuel Cells

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In this work, the fluid dynamics within a membrane‐less microchannel fuel cell is analyzed computationally. The membrane‐less design is a result of the laminar nature of the fluid flow at small Reynolds numbers, restricting the fuel and oxidant to the vicinity of the corresponding electrodes, without the need of a proton exchange membrane (PEM). However, the performance of such cells is limited by the slow diffusive mass transport near the electrodes, with a large fraction of the reactants leaving the channel without coming in contact with the catalytic surfaces, and thus not being used. We mitigate this problem through the introduction of channel surface modification consisting of angled grooves designed to create convective flows that direct the reactants toward the active surfaces. The grooved structures are optimized for maximum fuel utilization. Operation of this type of cells at Péclet numbers close to 2,500 leads to a performance doubling compared with unmodified cells. Moreover, this increase in efficiency is accompanied by a more uniform distribution of the current across the electrodes, reducing the possibility of hot spots being developed.

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“…1B, can dramatically reduce mixing length for low viscosity fluids (e.g., aqueous solutions). More sophisticated analyses (26)(27)(28) show that in the final stages of the homogenization process ℓ=d J Pe 1=4 due to wall effects, but because our subsequent analysis is intended to be only of leading order, the use of the Ranz model in deriving the mixing timescale is appropriate (29). In both cases, chaotic advection yields a sublinear scaling between channel length and flow rate.…”

Section: Active and Passive Mixing In Microfluidic Devicesmentioning

confidence: 99%

Active mixing of complex fluids at the microscale

Ober

Foresti

Lewis

2015

Proc. Natl. Acad. Sci. U.S.A.

242

165

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Mixing of complex fluids at low Reynolds number is fundamental for a broad range of applications, including materials assembly, microfluidics, and biomedical devices. Of these materials, yield stress fluids (and gels) pose the most significant challenges, especially when they must be mixed in low volumes over short timescales. New scaling relationships between mixer dimensions and operating conditions are derived and experimentally verified to create a framework for designing active microfluidic mixers that can efficiently homogenize a wide range of complex fluids. Active mixing printheads are then designed and implemented for multimaterial 3D printing of viscoelastic inks with programmable control of local composition. microfluidic mixing | yield stress fluids | 3D printing | graded materials M ixing at low Reynolds number is important for many processes (1, 2) from bioassays (3) and medical analysis (4), to materials synthesis (5) and patterning (6). Microfluidic devices that passively mix small fluid volumes (7-9) via chaotic advection or secondary flows have been implemented for many targeted applications (10-12). Passive mixers are simple and operate with no moving parts, but their mixing efficiency is strongly coupled to flow rate and geometry. Moreover, they are typically suited only for low-viscosity fluids containing diffusive species, such as colloidal particles (13). Whereas elastic instabilities have been shown to drive mixing of weakly viscoelastic polymer solutions in microfluidic devices (14), there is growing interest in continuous mixing of strongly viscoelastic materials, i.e., yield stress fluids, in microchannels, which until now has only been demonstrated at the macroscale (15, 16). The ability to uniformly and rapidly mix such liquids at the microscale would open new avenues for myriad applications, including additive manufacturing (17, 18). For example, concentrated viscoelastic inks are patterned by direct ink writing, an extrusion-based 3D printing method (19). To date, this flexible printing method has been used to create ceramic (20, 21), polymeric (22), metallic (23), and composite (24) architectures as well as vascularized tissues (25). In each case, the ink composition remains constant during the printing process. The ability to create more complex architectures with local compositional gradients is cumbersome at best, requiring a coordinated printpath between multiple individually addressable printheads--each of which contains a different ink (25).To overcome this challenge, we design, characterize, and exploit the mixing efficiency of an active mixer that homogenizes multiple materials at the microscale. To understand the relative advantages of active mixing, we derive and experimentally validate scaling relationships that are consistent with existing theory for passive mixers (10). To our knowledge, this is the first quantitative explanation of the mechanism by which an active microfluidic mixer decouples the intensity of the chaotic advection from the flow rate. This unique feat...

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Transport Phenomena in Chaotic Laminar Flows

Cited by 31 publications

References 62 publications

Synchronized chaotic targeting and acceleration of surface chemistry in prebiotic hydrothermal microenvironments

Synchronized chaotic targeting and acceleration of surface chemistry in prebiotic hydrothermal microenvironments

Use of Grooved Microchannels to Improve the Performance of Membrane‐Less Fuel Cells

Active mixing of complex fluids at the microscale

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