In this work, an electroosmotic flow micropump is proposed and investigated using theoretical analysis and numerical simulations. The micropump comprises an array of interdigitated electrodes on the top and the bottom surfaces of a rectangular microchannel. Theoretical analysis and extensive numerical simulations are performed to predict the pressure-flow characteristics of the micropump. The results of the model and simulations are compared which show good agreement with each other. The effects of various geometrical parameters including spacing between a pair of electrodes, gap between adjacent pairs of electrodes, width and height of the electrodes, and width of the microchannel and operating parameter including applied voltage on the performance of the micropump in terms of flow and pressure capacity is investigated. © 2013 Springer-Verlag Berlin Heidelberg.

Ashis Kumar Sen

Department of Mechanical Engineering

Applied voltages

Electroosmotic flow

INTER-DIGITATED ELECTRODES

Model and simulation

Numerical investigations

Operating parameters

PRESSURE-FLOW CHARACTERISTICS

Rectangular microchannels

Electrodes

Electroosmosis

Microchannels

Numerical models

Computer simulation

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Microsystem Technologies

This paper reports experimental and numerical studies of a passive microfluidic device that stabilizes a pulsating incoming flow and delivers a steady flow at the outlet. The device employs a series of chambers along the flow direction with a thin polymeric membrane (of thickness 75-250 μm) serving as the compliant boundary. The deformation of the membrane allows accumulation of fluid during an overflow and discharge of fluid during an underflow for flow stabilization. Coupled fluid-structure simulations are performed using Mooney-Rivlin formulations to account for a thin hyperelastic membrane material undergoing large deformations to accurately predict the device performance. The device was fabricated with PDMS as the substrate material and thin PDMS membrane as the compliant boundary. The performance of the device is defined in terms of a parameter called 'Attenuation Factor (AF)'. The effect of various design parameters including membrane thickness, elastic modulus, chamber size and number of chambers in series as well as operating conditions including the outlet pressure, mean input flow rate, fluctuation amplitude and frequency on the device performance were studied using experiments and simulations. The simulation results successfully confront the experimental data (within 10%) which validates the numerical simulations. The device was used at the exit of a PZT actuated valveless micropump to take pulsating flow at the upstream and deliver steady flow downstream. The amplitude of the pulsating flow delivered by the micropump was significantly reduced (AF = 0.05 for a device with three 4 mm chambers) but at the expense of a reduction in the pressure capability (<20%). The proposed device could potentially be used for reducing flow pulsations in practical microfluidic circuits. © 2015 IOP Publishing Ltd.

Fulltext

Journal of Micromechanics and Microengineering

Experimental and numerical studies of a microfluidic device with compliant chambers for flow stabilization

This work presents theoretical, numerical and experimental investigations of electrokinetic transport and separation of droplets in a microchannel. A theoretical model is used to predict that, in case of micron-sized droplets transported by electro-osmotic flow, the drag force is dominant as compared to the dielectrophoretic force. Numerical simulations were performed to capture the transient electrokinetic motion of the droplets using a two-dimensional multi-physics model. The numerical model employs Navier-Stokes equations for the fluid flow and Laplace equation for the electric potential in an Arbitrary Lagrangian-Eulerian framework. A microfluidic chip was fabricated using micromilling followed by solvent-assisted bonding. Experiments were performed with oil-in-water droplets produced using a cross-junction structure and applying electric fields using two cylindrical electrodes located at both ends of a straight microchannel. Droplets of different sizes were produced by controlling the relative flow rates of the discrete and continuous phases and separated along the channel due to the competition between the hydrodynamic and electrical forces. The numerical predictions of the particle transport are in quantitative agreement with the experimental results. The work reported here can be useful for separation and probing of individual biological cells for lab-on-chip applications. © 2013 Springer-Verlag Berlin Heidelberg.

Microfluidics and Nanofluidics

Electrokinetic transport and separation of droplets in a microchannel

This paper reports theoretical and numerical analysis of fluid flow and heat transfer in a cascade electro-osmotic flow (EOF) micropump for chip cooling. A simple analytical model is developed to determine the temperature distribution in a two-dimensional (2D) single channel EOF micropump with forced convection due to a voltage difference between both ends. Numerical simulations are performed to determine the temperature distribution in the domain which is compared with that predicted by the model. A novel cascade EOF micropump with multiple microchannels in series and parallel and with an array of interdigitated electrodes along the flow direction is proposed. The simulations predict the maximum flow rate and pressure capability of one single stage of the micropump and the analytical model employs equivalent circuit theory to predict the total flow rate and back pressure. Each stage of the proposed micropump comprises sump and pump regions having opposing electric field directions. The various design parameters of the micropump includes the height of the pump and sump (h), number of stages (n), channel width (w), thickness of the channel wall or fin (r), and width ratio of the pump and sump (s:p) regions. Numerical simulations are performed to predict the effects of these design parameters on the pump performance which is compared with that predicted by the analytical model. The micropump is used for cooling cooling of an Intel® Core™ i5 chip which produces a maximum heat of 95W over an area of 3.75×3.75 cm. Based on the parametric studies a design for the cascade EOF micropump is proposed which provides a maximum flow rate of 14.16 ml/min and a maximum back pressure of 572.5 Pa to maintain a maximum chip temperature of 310.63 K. Copyright © 2014 by ASME.

Journal of Electronic Packaging, Transactions of the ASME

Flow and heat transfer analysis of an electro-osmotic flow micropump for chip cooling

This work presents a study of a passive micromixer with lateral obstructions along a microchannel. The mixing process is simulated by solving the continuity, momentum and diffusion equations. The mixing performance is quantified in terms of a parameter called 'mixing efficiency'. A comparison of mixing efficiencies with and without obstructions clearly indicates the benefit of having obstructions along the microchannel. The numerical model was validated by comparing simulation results with experimental results for a micromixer. An extensive parametric study was carried out to investigate the influence of the geometrical and operational parameters in terms of the mixing efficiency and pressure drop, which are two important criteria for the design of micromixers. A very interesting observation reveals that there exists a critical Reynolds number (Re cr ~ 100) below which the mixing process is diffusion dominated and thus the mixing efficiency is reduced with increase in Re and above which the mixing process is advection dominated and mixing efficiency increases with increase in Re. Microchannels with symmetric and staggered protrusion arrangements were studied and compared. The mixing performance of the staggered arrangement was comparable with that of symmetric arrangement but the pressure drop was lower in the case of staggered arrangements making it more suitable. © 2012 Springer-Verlag.

Investigations into mixing of fluids in microchannels with lateral obstructions

This work presents theoretical analysis, numerical simulation, fabrication and test of a micromixer chip for mixing fluids in microchannel. A threedimensional analytical model is developed using a different mathematical approach to study passive laminar mixing phenomena and predict concentration distribution in a microchannel. The analytical model is validated by comparing with experimental and simulation results. The process of mixing fluids in a microchannel is simulated by solving the continuity, momentum and mass diffusionequations. The simulation results are validated and thenparametric studies are performed to investigate the effects of channel aspect ratio, Reynolds number and diffusion coefficient on the mixing performance. The micromixer chip is fabricated with patterned SU-8 photoresist as the microchannel layer on a PMMA substrate using a combination of photolithography and micro-milling. Experiments are performed with different mixing fluids and the results were compared with that obtained from the theoretical model and simulation results. © 2012 Springer-Verlag.

Analytical, numerical and experimental investigations of mixing fluids in microchannel

This paper presents a three-dimensional simulation of a micro hydrocyclone for the separation of micron sized particles from liquid in a particulated sample. A theoretical analysis is performed to demonstrate the working principle of the micro hydrocyclone and develop design models. The geometry of the proposed device is designed based on the Bradley model, since it offers a lower cut-size, thus making it suitable for microfluidics applications. The operational parameters of the hydrocyclone are derived from a dimensional group model. The particle separation process inside the micro hydrocyclone is simulated by solving fluid flows using Navier-Stokes equations and particle dynamics using the Lagrangian approach in a Eulerean fluid. First, the numerical model is validated by comparing the simulation results with the experimental results for a macroscale hydrocyclone reported in the literature. Then, the micro hydrocyclone is simulated and the simulation results are presented and discussed in the context of the functioning of the micro hydrocyclone. Finally, the effects of inlet velocity, vortex finder diameter, particle size, and density on the separation efficiency are investigated. The proposed device can be easily integrated with micro-environments; thus, is suitable for lab-on-chip and microsystems development. © 2012 American Society of Mechanical Engineers.

Journal of Fluids Engineering, Transactions of the ASME

Analysis and simulation of a micro hydrocyclone device for particle liquid separation

Mixing of fluids in microchannels is challenging due to the inherent laminar nature of the fluid flows. This work presents numerical investigations of an active micromixer with an array of lateral electrode pattern along the microchannel. The proposed micromixer is simulated using a numerical model that solves the coupled flow, electric field and diffusion equations with appropriate boundary conditions. The geometry of the micromixer is illustrated and the numerical model is described. The simulation model is validated by comparing the model predictions with experimental results. The performance of the active micromixer is compared with that of an equivalent passive micromixer indicating the advantage. An extensive parametric study is carried out to investigate mixing performance of the proposed micromixer with respect to various geometrical and operational parameters. The layout of the electrodes parallel and staggered electrode arrangements are studied and compared. Effects of electric potential, Reynolds number, Peclet number, Zeta potential, electrode arrangements, gap between electrodes, and number electrode pairs on the mixing performance is studied and discussed. © 2012 Bentham Science Publishers.

Journal	Microsystem Technologies
ISSN	09467076
Open Access	No