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Purpose: The purpose of this study is to establish an effective numerical simulation method to describe the flow pattern and optimize the strategy of noncontact mixing induced by alternating Gaussian light inside a nanofluid droplet and analyzing the influencing factors and flow mechanism of fluid mixing inside a droplet. Design/methodology/approach: First, the heat converted by the alternating incident Gaussian light acting on the nanoparticles was considered as the bulk heat source distribution, and the equilibrium equation between the surface tension and the viscous force at the upper boundary force was established; then, the numerical simulation methods for multiple-physical-field coupling was established, and the mixing index was used to quantify the mixing degree inside a droplet. The effects of the incident position of alternating Gaussian light and the height of the droplet on the mixing characteristics inside a droplet were studied. Finally, the nondimensional Marangoni number was used to reveal the flow mechanism of the internal mixing of the droplet. Findings: Noncontact alternating Gaussian light can induce asymmetric vortex motion inside a nanofluid droplet. The incident position of alternating Gaussian light is a significant factor affecting the mixing degree in the droplet. In addition, the heat transfer caused by the surface tension gradient promotes the convection effect, which significantly enhances the mixing of the fluid in the droplet. Originality/value: This study demonstrates the possibility of the chaotic mixing phenomenon induced by noncontact Gaussian light that occurs within a tiny droplet and provides a feasible method to achieve efficient mixing inside droplets at the microscale. [ABSTRACT FROM AUTHOR]

Highlights: [•] We evaluate mixing performance of micromixer T-junction with wavy structure. [•] Mixing performance is compared in terms of mixing index performance index (PI). [•] Mixing performance is superior as compared to conventional T-junction. [•] PI improves up to 2 order-of-magnitudes at higher Reynolds numbers. [•] Effect of Dean number is investigated. [Copyright &y& Elsevier]

Abstract: Enhancing and controlling chaotic advection or chaotic mixing within liquid droplets is crucial for a variety of applications including digital microfluidic devices which use microscopic “discrete” fluid volumes (droplets) as microreactors. In this work, we consider the Stokes flow of a translating spherical liquid droplet which we perturb by imposing a time-periodic rigid-body rotation. Using the tools of dynamical systems, we have shown in previous work that the rotation not only leads to one or more three-dimensional chaotic mixing regions, in which mixing occurs through the stretching and folding of material lines, but also offers the possibility of controlling both the size and the location of chaotic mixing within the drop. Such a control was achieved through appropriate tuning of the amplitude and frequency of the rotation in order to use resonances between the natural frequencies of the system and those of the external forcing. In this paper, we study the influence of the orientation of the rotation axis on the chaotic mixing zones as a third parameter, as well as propose an experimental set up to implement the techniques discussed. [Copyright &y& Elsevier]