470 research outputs found
Theoretical and Numerical Investigation of Liquid-Gas Interface Location of Capillary Driven Flow During the Time Throughout Circular Microchannels
The main aim of this study is to find the best, most rapid, and the most
accurate numerical method to find the liquid-gas interface of capillary driven
flow during the time in circular Microchannels by using COMSOL Multiphysics
software. Capillary driven flow by eliminating micropumps or any physical
pressure gradient generators can make the microfluidic devices cheaper and more
usable. Hence, by using this two-phase flow, the final costs of lots of
microfluidic devices and lab-on-a-chip can significantly be decreased and help
them to be commercialized. The first step to employing the capillary flow in
these devices is the simulation of this flow inside the microchannels. One of
the most common and valid software for this work is COMSOL Multiphysics; this
fact reveals the importance of this study. In this research study, simulation
results obtained by using two possible numerical methods in this software, for
capillary flows of water and ethanol in two different circular microchannels,
verified and compared with four other methods, which verified experimentally
before. Finally, the most accurate and time-saving numerical method of this
software will be specified. This appropriate technique can contribute to
simulate microfluidic and lab-on-a-chip devices, which are made of different
mechanical and electrical parts, in COMSOL Multiphysics software by choosing
the best method.Comment: 7 pages, 13 figures, 7 tables, 2017 5th International Conference on
Robotics and Mechatronics (ICROM
Numerical and experimental analysis on microbubble generation and multiphase mixing in novel microfluidic devices
In this study, a novel K-junction microfluidic junction and a conventional cross-junction were investigated numerically and experimentally for microbubble generation and multiple fluids mixing. In the K-junction, liquid solutions were injected into the junction via three liquid inlet channels, along with inert nitrogen gas supplied via the gas inlet channel, to periodically generate microbubbles in a controlled manner at the outlet channel. Numerical simulations based on Finite Volume method and Volume of Fluid (VOF) technique and experiments of both the K-junction and the cross-junction were conducted. The effect of parameters such as contact angle, surface tension, viscosity, gas pressure and gas-liquid flow ratios on the microbubble size distribution was investigated. The process of microbubble generation, obtained through high speed camera imaging and the numerical simulation, has shown good agreement in both junctions as well as the influence of viscosity and gas-liquid flow ratios for the K-junction and cross-junction. It was indicated that parameters like solution viscosities, gas-to-liquid flow ratios, gas inlet pressure, and their combination have a significant influence on the microbubble diameter, which was found to be in the range of 70-240 µm when using micro capillaries of 100 µm inner diameter. The multiple fluids mixing study was investigated by using two or three different polymer solutions for the cross-junction and the K-junction respectively in simulations and experiments. It can be seen that the mixing process obtained from simulations agrees well with experimental results and chaotic mixing was found in the mixing area of the K-junction, with higher mixing efficiency than the cross junction. Fluorescent images of microbubbles generated by using polymer solutions with dyes inside have shown the devices’ potential of encapsulating fluorescent dyes and polymers on the shell of bubbles and could be adopted as a method to encapsulate active pharmaceutical ingredients for potential applications in drug delivery
Laminar flow and heat transfer characteristics of interrupted microchannel heat sink with ribs in the transverse microchambers
publisher: Elsevier articletitle: Laminar flow and heat transfer characteristics of interrupted microchannel heat sink with ribs in the transverse microchambers journaltitle: International Journal of Thermal Sciences articlelink: http://dx.doi.org/10.1016/j.ijthermalsci.2016.06.029 content_type: article copyright: © 2016 Elsevier Masson SAS. All rights reserved.The work was supported by the Engineering and Physical Sciences Research Council (EPSRC) of the UK through research grant (EP/L001233/1) and the National Natural Science Foundation of China (51576005)
Investigation of chaotic advection regime and its effect on thermal performance of wavy walled microchannels
Ph.DDOCTOR OF PHILOSOPH
An experimental and theoretical investigation of particle–wall impacts in a T-junction
Understanding the behaviour of particles entrained in a fluid flow upon changes in flow direction is crucial in problems where particle inertia is important, such as the erosion process in pipe bends.We present results on the impact of particles in a T-shaped channel in the laminar-turbulent transitional regime. The impacting event for a given system is described in terms of the Reynolds number and the particle Stokes number. Experimental results for the impact are compared with the trajectories predicted by theoretical particle tracing models for a range of configurations to determine the role of the viscous boundary layer in retarding the particles and reducing the rate of collision with the substrate. In particular a 2D model based on a stagnation point flow is used together with 3D numerical simulations. We show how the simple 2D model provides a tractable way of understanding the general collision behaviour, while more advanced 3D simulation can be helpful in understanding the details of the flow
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Thermohydraulic performance of microchannel heat sinks with triangular ribs on sidewalls – Part 1: Local fluid flow and heat transfer characteristics
Engineering and Physical Sciences Research Council (EPSRC) of the U
Experimental study of fluid flow and heat transfer in tortuous microchannels
Tortuous microchannels have attracted increasing interest due to great potential to enhance fluid mixing and heat transfer. While the fluid flow and heat transfer in wavy microchannels have been studied extensively in a numerical fashion, experimental studies are very limited due to the technical difficulties of making accurate measurements in micro-scale flows. This thesis provides insights into thermohydraulics of tortuous microchannels by developing experimental techniques and performing systematic visualisation and heat transfer experiments. The detailed flow patterns (including Dean vortices) and transition behaviours in wavy channels are successfully identified using Micro-Particle Image Velocimetry (micro-PIV) and 3D reconstruction techniques. Conjugate heat transfer simulations are carried out to understand the complex thermal behaviour present in the current experimental design and to validate and compare with experimental results. The impact of tortuous geometry on flow and heat transfer in microchannels is studied systematically. The high quality experimental data provide a new perspective on flow behaviour and heat transfer performance in wavy microchannels. In addition, the stackability of channels on a plate is considered. The zigzag pathways are found to provide the greatest heat transfer intensification based on a plate structure. A significant component of the research in this thesis has been the development of experimental techniques to measure local heat transfer rates in microchannels. A two-dye laser induced fluorescence (LIF) technique using temperature sensitive particles (TSPs) is developed with promising characteristics for local temperature measurement and the capability for simultaneous measurement of temperature and velocity fields in microscale systems. The advanced experimental techniques developed in this thesis provide important tools for the investigation of thermohydraulics of various micro-devices in the field of engineering
Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents
Chaotic micromixers such as the staggered herringbone mixer developed by
Stroock et al. allow efficient mixing of fluids even at low Reynolds number by
repeated stretching and folding of the fluid interfaces. The ability of the
fluid to mix well depends on the rate at which "chaotic advection" occurs in
the mixer. An optimization of mixer geometries is a non trivial task which is
often performed by time consuming and expensive trial and error experiments. In
this paper an algorithm is presented that applies the concept of finite-time
Lyapunov exponents to obtain a quantitative measure of the chaotic advection of
the flow and hence the performance of micromixers. By performing lattice
Boltzmann simulations of the flow inside a mixer geometry, introducing massless
and non-interacting tracer particles and following their trajectories the
finite time Lyapunov exponents can be calculated. The applicability of the
method is demonstrated by a comparison of the improved geometrical structure of
the staggered herringbone mixer with available literature data.Comment: 9 pages, 8 figure
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