Heat transfer enhancement in a cross-slot micro-geometry

Abed, Waleed M.; Domingues, Allysson F.; Poole, Robert J.; Dennis, David

doi:10.1016/j.ijthermalsci.2017.07.017

Cited by 19 publications

(9 citation statements)

References 34 publications

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“…Yet, if fast acquisition is not required and thus averaging over time is possible, the thermal resolution obtained in this work was as low as 0.03 ºC at room temperature and 0.07 ºC at 85 ºC. This strategy is thus valid for the study of fluids in microchannels and has indeed been applied for different types of structures such as cross-slot microgeometries [45], temperature-jump chips [46], or herringbone structures designed to enhance heat transfer [47], but it also has certain limitations that need to be considered. On one hand, the intensity recorded is affected by fluctuations of the illumination source, photobleaching, or inhomogeneous dye concentration.…”

Section: Organic Dyes Polymers and Proteinsmentioning

confidence: 82%

Guiding Rules for Selecting a Nanothermometer

2018

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Temperature is a basic parameter influencing the behavior of systems in physics, chemistry and biology. From living cells to microcircuits, a wide range of cases require thermometry techniques that can be applied to reduced areas, offering sub-micrometric resolution and high accuracy. Since traditional thermometers cannot be applied in such systems, alternative tools have been specifically designed to measure temperature at the nanoscale; including scanning thermal microscopy, non-contact optical techniques or various types of luminescent nanoparticles. Each option presents interesting advantages, but also limitations that need to be considered and understood. We provide here an overview of the main currently available nanothermometry tools, discussing their pros and cons toward potential applications.

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Section: Organic Dyes Polymers and Proteinsmentioning

confidence: 82%

Guiding Rules for Selecting a Nanothermometer

2018

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“…This includes designs such as cross-slots, T-junctions, and flow-focusing configurations. To date, the use of cross-slot geometries has found great success and has been widely used both in numerical (Poole et al 2007;Afonso et al 2010;Cruz et al 2016;Zografos et al 2018) and experimental (Arratia et al 2006;Dylla-Spears et al 2010;Gossett et al 2012b;Haward et al 2012a;Burshtein et al 2017;Abed et al 2017) studies related to Newtonian flows, viscoelastic flows, and singlemolecule/single-cell responses, due to the fact that they are able to generate strong extensional flows exploiting the presence of the stagnation point (SP). Moreover, improved counterparts have also been proposed employing optimisation techniques as potential platforms for achieving accurate rheological measurements (Alves 2008;Haward et al 2012b;Haward and McKinley 2013;Galindo-Rosales et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Optimised multi-stream microfluidic designs for controlled extensional deformation

Zografos

Haward

Oliveira

2019

Microfluid Nanofluid

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In this study, we optimise two types of multi-stream configurations (a T-junction and a flow-focusing design) to generate a homogeneous extensional flow within a well-defined region. The former is used to generate a stagnation point flow allowing molecules to accumulate significant strain, which has been found very useful for performing elongational studies. The latter relies on the presence of opposing lateral streams to shape a main stream and generate a strong region of extension in which the shearing effects of fluid-wall interactions are reduced near the region of interest. The optimisations are performed in two (2D) and three dimensions (3D) under creeping flow conditions for Newtonian fluid flow. It is demonstrated that in contrast with the classical-shaped geometries, the optimised designs are able to generate a well-defined region of homogeneous extension. The operational limits of the obtained 3D optimised configurations are investigated in terms of Weissenberg number for both constant viscosity and shear-thinning viscoelastic fluids. Additionally, for the 3D optimised flow-focusing device, the operational limits are investigated in terms of increasing Reynolds number and for a range of velocity ratios between the opposing lateral streams and the main stream. For all obtained 3D optimised multi-stream configurations, we perform the experimental validation considering a Newtonian fluid flow. Our results show good agreement with the numerical study, reproducing the desired kinematics for which the designs are optimised.

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“…At higher Re's, an axial vortex appears at the intersection of the channels and extends towards each outlet. In channels with a square cross-section 8,20,23 , the transition between the two regimes occurs for Re c ∼ 40 , while for circular channels 24 it is slightly higher with Re c ∼ 48.…”

Section: Introductionmentioning

confidence: 97%

“…To allow all those operations, a perfect control of the fluids and of their flow is required. Knowing and understanding how vortices are created is, for instance, crucial to combine fluids and to ensure a good mixing between them in order to enhance mass or heat transfer 8 . But, due to the small dimensions of those systems and because of the viscosity of the fluids, vortices cannot be obtained by making the fluid turbulent.…”

Section: Introductionmentioning

confidence: 99%

Influence of aspect ratio on vortex formation in X-junctions: Direct numerical simulations and eigenmode decomposition

et al. 2020

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We study numerically the appearance and number of axial vortices in the outlets of X-shaped junctions of two perpendicular channels of rectangular sections with facing inlets. We explore the effect of the aspect ratio of the cross section, AR, on the number of vortices created at the center of the junction. Direct numerical simulations (DNSs) performed for different values of the Reynolds number Re and AR demonstrate that vortices with their axis parallel to the outlets, referred to as axial vortices, appear above critical Reynolds numbers Rec. As AR increases from 1 to 11, the number of vortices observed increases from 1 to 4, independently of Re. For AR = 1, the single axial vortex induces an interpenetration of the inlet fluids in the whole section; instead, for larger AR’s for which more vortices appear, the two inlet fluids remain largely segregated in bands, except close to the vortices. The linear stability analysis demonstrates that only one leading eigenmode is unstable for a given set of values of AR and Re. This mode provides a simplified model of the flow field, reproducing its key features such as the number of vortices and their distance. Its determination with this method requires a much smaller computational load than the DNS. This approach is shown to allow one to determine quickly and precisely the critical Reynolds number Rec and the sensitivity function S, which characterizes the influence of variations of the base flow on the unstable one.

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Heat transfer enhancement in a cross-slot micro-geometry

Cited by 19 publications

References 34 publications

Guiding Rules for Selecting a Nanothermometer

Guiding Rules for Selecting a Nanothermometer

Optimised multi-stream microfluidic designs for controlled extensional deformation

Influence of aspect ratio on vortex formation in X-junctions: Direct numerical simulations and eigenmode decomposition

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