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Despite the importance of droplet monodispersity, a universal methodology for high monodispersity droplet generation does not exist yet. We have recently demonstrated that unlike the conventional method of droplet generation, applying an identical pressure from a single source makes the microfluidic droplet system immune to the external fluctuations that originate from the imperfection of the flow source. In this work, we show that our method is universal and applicable to other common microfluidic devices and flow sources. We applied this method to flow-focusing and coflow devices that are commonly used for high-frequency microdroplet generation. In addition to the pressure pump, we used a syringe pump to show that our method is applicable to flow rate controllable systems as well. We compared the monodispersity of droplets formed by the conventional methods and the novel method explained in this work. © 2022 The Authors

In this article, we report a method to damp microfluidic hydrodynamic fluctuations caused by flow sources. We demonstrate that compliance of elastomeric off-chip tubings can be used to damp fluctuations and lead to steady flow rates. We analyze the whole microfluidic system using electrical circuit analogies, and demonstrate that off-chip compliances are significant, especially for displacement pump driven systems. We apply this hydrodynamic damping method to microfluidic droplet generation. Our results show that highly monodisperse microdroplets can be obtained by syringe pump driven systems utilizing this damping effect. We reached a coefficient of variation of 0.39% for the microdroplet area using a standard T-junction geometry. Additionally, we demonstrated that pressure pumps inherently use this effect, and have so far led the high performances reported in the literature in terms of droplet monodispersity. The presented off-chip hydrodynamic damping method is not only low-cost and practical, but can also be used in elastomeric and rigid microchannels without need to introduce additional components to the fluidic circuit. This project was supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK, Project No. 215E086 ). Dr. Elnaz Alizadeh Haghighi is thankful to the support of TÜBİTAK BİDEB-2216 Postdoctoral Research Fellowship . The authors also thank Dr. Amar S. Basu for providing DMV software.

Droplet microfluidic systems are becoming routine in advanced biochemical studies such as single cell gene expression, immuno profiling, precise nucleic acid quantification (dPCR) and particle synthesis. For all these applications, ensuring droplet monodispersity is critical to minimize the uncertainty due to droplet volume variation. Despite the wide usage of droplet-based microfluidic systems, the limit of monodispersity for droplet generation systems is still unknown. Here, we present an analytical approach that takes into account all the system dynamics and internal/external factors that disturb monodisper-sity. Interestingly, we are able to model the dynamics of a segmented two-phase flow system using a single-phase flow analogy, electron flow, in electrical circuits. We offer a unique solution and design guidelines to ensure ultra-monodisperse droplet generation. Our analytical conclusions are experimentally verified using a T-junction droplet generator. Equally importantly, we show the limiting experimental factors for reaching the theoretical maximum of monodispersity. (C) 2020 Elsevier Ltd. All rights reserved.

In this paper, a magnetohydrodynamic micropump with side-walled electrodes has been studied. Micropump was fabricated using MEMS technology and applied Lorentz force induced as a result of interaction between an applied electric field and a perpendicular magnetic field to pump the continuous steady, incompressible and fully developed laminar conducting fluid. Since the micro-pump dimensions are comparable to that of the fluid molecules, the assumption of the continuum fluid theory is no longer justified. Hence, micropolar fluid theory is considered in this study. Application of the theory of fluid dynamics and electromagnetic led to derivation of governing equations of the corresponding momentum and angular momentum. The governing equations and their associated boundary conditions were first cast into dimensionless form. The resulting partial differential equations were solved numerically using finite difference technique and the profiles of the velocity and microrotations are obtained. The results for a special case were compared with the experimental ones and they showed a good agreement with each other. Furthermore, the effects of coupling number, Hartmann number and micropolar parameter on the velocity, microrotation and flow rate are discussed.