Energy–efficient mixing generated by prescribed crosswise oscillations of a square prism in highly confined flows

Valeije, A.; Sastre, F.; Martín, Elena; Velázquez, A.

doi:10.1016/j.ces.2019.115456

Cited by 4 publications

(6 citation statements)

References 27 publications

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“…Discrepancies in the computed wake frequencies past the prism were less than 4% for Re = 350 and pulsating frequencies truef^A = 1.5. In Valeije et al (2020) the implementation of the solver for the prescribed sinusoidal prism motion was validated with the numerical work of Singh et al (2009). The computed numerical spectral density functions for the prism lift and drag coefficients were in good agreement with their counterpart obtained in Singh et al (2009) for Re = 150 and truef^B equal to 1.2 and 1.5.…”

Section: Description Of the Numerical Methodsmentioning

confidence: 53%

“…For example, regarding pulsating flows, the following references, among others, could be referred to Ji et al (2008), Mulcahey et al (2013), Yu et al (2014), Krishnan et al (2016) and Martin et al (2018). Regarding prism motion, some relevant references are: Celik and Beskok (2009), Singh et al (2009), Reyes et al (2015), Kumar Chauhan et al (2016), Sastre and Velazquez (2017), Ortega-Casanova and Lai (2018), Clemente et al (2019) and Valeije et al (2020).…”

Section: Problem Descriptionmentioning

confidence: 99%

“…Mixing downstream of the prism was quantified using a measure defined in previous studies: Phelps and Tucker (2006), Hsiao et al (2014), Ortega-Casanova (2016), Ortega-Casanova (2017) and Valeije et al (2020). This requires the seeding of “virtual” (massless) particles of different colors a and b .…”

Section: Quantification Of Mixingmentioning

confidence: 99%

“…As in Valeije et al (2020), the selected spatial discretization schemes of each term of the model were: Gauss cubic corrected (fourth-order unbounded scheme) for the diffusive terms, fourth (fourth-order, least-squares scheme) for the gradient and surface normal gradient terms and cubicCorrected (fourth-order, unbounded) interpolation schemes for the convective terms. The number of loops needed for a proper estimate for the PISO method was set up to 3, with 2 nonorthogonal corrections.…”

Section: Discretization Scheme and Iterative Solvermentioning

confidence: 99%

See 3 more Smart Citations

Comparison of three-dimensional flow mixing via pulsation and dynamical stirring: application to the mixing of parallel streams at different temperatures

Sastre

Martín

Velázquez

et al. 2021

HFF

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Purpose This paper aims to compare the performance of flow pulsation versus flow stirring in the context of mixing of a passive scalar at moderate Reynolds numbers in confined flows. This comparison has been undertaken in two limits: diffusion can be neglected as compared to convection (very large Peclet) and diffusion and convection effects are comparable. The comparison was performed both in terms of global parameters: pumping power and mixing efficiency and local flow topology. Design/methodology/approach The study has been addressed by setting up a common conceptual three-dimensional problem that consisted of the mixing of two parallel streams in a square section channel past a square section prism. Stirring and pulsation frequencies and amplitudes were changed and combined at an inlet Reynolds number of 200. The numerical model was solved using a finite volume formulation by adapting a series of open-source OpenFOAM computational fluid dynamic (CFD) libraries. For cases with flow pulsation, the icoFoam solver for laminar incompressible transient flows was used. For cases with stirring, the icoDyMFoam solver, which uses the arbitrary Lagrangian–Eulerian method for the description of the moving dynamical mesh, was used to model the prism motion. At the local flow topology level, a new method was proposed to analyze mixing. Time evolution of folding and wrinkling of sheets made up of virtual particles that travel along streak lines was quantified by generating lower rank projections of the sheets onto the spaces spanned by the main eigenvectors of an appropriate space-temporal data decomposition. Findings In the limit when convection is dominant, the results showed the superior performance of stirring versus flow pulsation both in terms of mixing and required pumping power. In the cases with finite Peclet, the mixing parameters by stirring and flow pulsation were comparable, but pulsation required larger pumping power than stirring. For some precise synchronization of stirring and pulsation, the mixing parameter reached its maximum, although at the expense of higher pumping power. At the local flow topology level, the new method proposed to quantify mixing has been found to correlate well with the global mixing parameter. Originality/value A new systematic comparative study of two methods, stirring and pulsation, to achieve mixing of passive scalars in the mini scale for confined flows has been presented. The main value, apart from the conclusions, is that both methods have been tested against the same flow configuration, which allows for a self-consistent comparison. Of particular interest is the fact that it has been found that accurate synchronization of both methods yields mixing parameters higher than those associated to both methods taken separately. This suggests that it is possible to synchronize mixing methods of a different nature to achieve optimum designs. The new theoretical method that has been proposed to understand the mixing performance at the local level has shown promising results, and it is the intention of the authors to test its validity in a broader range of flow parameters. All these findings could be taken as potential guidelines for the design of mixing processes in the mini scale in the process industry.

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Section: Description Of the Numerical Methodsmentioning

confidence: 53%

Section: Problem Descriptionmentioning

confidence: 99%

Section: Quantification Of Mixingmentioning

confidence: 99%

Section: Discretization Scheme and Iterative Solvermentioning

confidence: 99%

See 2 more Smart Citations

Comparison of three-dimensional flow mixing via pulsation and dynamical stirring: application to the mixing of parallel streams at different temperatures

Sastre

Martín

Velázquez

et al. 2021

HFF

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show abstract

“…They also reported that beyond some threshold, it is of no use to keep increasing motion frequency. Valeije et al (2020) dealt with the effect that the prism motion frequency had on mixing. They found that optimum mixing combined with minimum pumping power took place at the same specific frequency.…”

Section: Introductionmentioning

confidence: 99%

3D active mixing of confined power law aqueous polymer solutions: a comparative numerical study

Martín

Sastre²,

Velázquez³

et al. 2022

HFF

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Purpose This paper aims to study the influence that the second invariant of the rate-of-strain tensor of a power law polymeric fluid (aqueous solution of hydroxyethyl cellulose [HEC]) has on convective mixing performance downstream of a 3D confined oscillating prism. Newtonian and non-Newtonian Reynolds numbers, the mass concentration of HEC and prism oscillation frequency were varied. Design/methodology/approach A conceptual problem was designed. Its objective was to analyze the convective mixing of two adjacent flow streams when they pass around a moving confined prism. The rectangular prism had a square section, and its sinusoidal motion was prescribed inside a channel with a square section too. OpenFOAM libraries were used to simulate the flow field. Regarding prism motion, the icoDyMFoam solver was used. The problem was analyzed both at the global level (mixing parameter) and local level (detailed flow topology). Findings For constant Reynolds number, increasing mass concentrations of HEC (in the range from 0.2% to 0.5%) led to better mixing parameters. The improvement was linked to the effect that the second invariant of the rate-of-strain tensor had on flow topology. It was found that mixing is maximum when the prism motion and its wake (the frequency of the first instability) are synchronized. In practical terms, this means that the optimum stirring frequency does not need to be very high; it suffices that it ensures that synchronization occurs. The dominant vorticity shedding pattern found was the so-called 2P mode. However, a significant difference was found when compared to the free-stream situation. While in the former, the two vorticity regions that make up the 2P pair come from the prism, in the present confined case, one came from the prism, and the other came from the wall. Another difference was that in the present case, the 2P pairs were much more elongated than in the free stream case, and this had a significant influence on the stretching and bending of streak lines and, therefore, on mixing. Practical implications The study that has been presented has a practical industrial implication for the processes industry because it provides guidelines to design active mixers that deal with aqueous power law polymeric solutions. In parallel, it opens up some new research lines in the direction of studying whether the mixing concept might be modified so as to develop a fully passive system that could be far simpler and, possibly, more attractive to industry. Originality/value The originality and value of the study are associated to the systematic approach that has been followed. It has allowed to establish a clear pattern regarding the active mixing behavior of HEC solutions in confined flows. To the best of authors’ knowledge, this could be the first study of this type in the literature. Also, the study has contributed to understand the vorticity shedding patterns that appear in these types of problems and how they shape wake topology and, consequently, mixing performance. The finding that optimum mixing requires synchronization of stirring motion frequency and wake first natural frequency of instability may help to improve the design and operation of industrial mixers dealing with polymeric aqueous solutions.

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Intensification of mixing-pumping process in a novel active micropump-mixer with maximum efficiency and minimum energy cost: A LBM-RSM approach

Khozeymeh-Nezhad

Kharmiani

Niazmand

2021

Chemical Engineering and Processing - Process Intensification

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Energy–efficient mixing generated by prescribed crosswise oscillations of a square prism in highly confined flows

Cited by 4 publications

References 27 publications

Comparison of three-dimensional flow mixing via pulsation and dynamical stirring: application to the mixing of parallel streams at different temperatures

Comparison of three-dimensional flow mixing via pulsation and dynamical stirring: application to the mixing of parallel streams at different temperatures

3D active mixing of confined power law aqueous polymer solutions: a comparative numerical study

Intensification of mixing-pumping process in a novel active micropump-mixer with maximum efficiency and minimum energy cost: A LBM-RSM approach

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