Numerical modelling of heat generated by electroosmotic flows in micro-channels

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In this paper, numerical modeling of Joule heating in electroosmotic flows is described in some detail. The finite element method is used for the spatial discretization along with the characteristic based split (CBS) time discretization. A new non-dimensional scaling is also introduced. In addition to standard problems of micro channel flows, flow and heat generation in a T-mixer are also discussed in this paper

Numerical characterization of silicon DC electro-osmotic pumps: the role of the micro channel geometry

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.A numerical analysis of silicon DC open channel EOPs is presented to show which parameters should be taken into account in the design of these devices. Particular attention is paid to the influence of the channel cross-section geometry on pump behavior, especially in relation to the electrical properties of the fluid. Rectangular and trapezoidal, micro and nano channels chemically etched on silicon wafers are considered and a broad range of operative conditions are analyzed. In order to make all the results available, two user-friendly correlations that predict the characteristic curves of the pumps are given as functions of the relevant parameters. The EOP model used to obtain the results is explained extensively, as well as the method used to solve it. A brief discussion on the domain in which it applies is also presented

Design of a lab-on-a-chip for clinical tests of human physiological fluids

Labs-on-a-chip are useful to perform in situ clinical tests with instantaneous results. In this work, the design phase of the development of a lab-on-a-chip is presented. The device will be used to perform tests on physiological fluids. It will be able to test 8 components: calcium, chloride, creatinine, glucose, magnesium, total protein, urea and uric acid. A sample of the physiological fluid reacts with several reagents and the device measures the absorbance of the reaction products. The lab-on-a-chip is composed of a microfluidic system and an optical detection system. The first contains microchannels and micro-reactors fabricated using SU-8 techniques. The second includes CMOS photodetectors and readout electronics, as well as optical filters fabricated using CMOS-compatible post-processing on top of the photodetectors. Careful design of the microfluidic system of a lab-on-a-chip requires knowledge of the transport phenomena in the microchannels. Numerical methods are used to simulate the electroosmotic flow, reaction and mixture in the system. Velocitypressure formulation of the Navier-Stokes equations is solved by a finite difference method. Mass transport equation is solved by a second order finite difference method. For enzymatic reactions, biochemical reaction kinetics is considered. Design choices are presented and explained. The final design of the microfluidic system complies with layout restriction and kinetic, mass transport and other physical limitations. The dimensions of the micro-reactors are optimized to maximize mixing. The design of the optical detection system involves selection of the dielectric layers available in the CMOS process for the photodetectors and selection of the dielectric thin-films layers for the optical filters. An array of 8 selective optical filters is designed for parallel testing of the 8 reported components. They are structurally optimized for an optical response at the absorption peak of each reaction product. The lab-on-a-chip output provides a digital signal for computer interfacing.R&D Centre Algoritmi.Escola de Engenharia da Universidade do Minho - Program IN2TEC.Fundação para a Ciência e a Tecnologia (FCT) - Grant SFRH/BPD/17689/2004

Design and realization of an electrophoretron cycler

Polymerase Chain Reaction (PCR) is a powerful enzymatic reaction commonly used to amplify specific sequences of Deoxyribo Nucleic Acid (DNA). Since the introduction of the lab on a chip concept, numerous Continuous Flow PCR cyclers were realized with success at the micro scale. As reducing the reactor size and improving thermal management led to reduced sample volumes, results could be achieved much faster with these CF-PCR cyclers than with common commercial cycler. Furthermore, most of these demonstrated CF-PCRs are nowadays evolving towards high-throughput systems. However, most CF-PCR cyclers require complex manipulations and are not flexible (e.g. fixed number of cycles, and/or only usable for PCR …). The concept of the electrophoretron cycler was introduced and demonstrated at the macro scale in 2001. The present work aims at using this electrokinetic cycler combining electroosmosis and electrophoresis in order to achieve cycling of the DNA species in a micro scale on-chip device, while applying only one potential difference. Even limited by polymers properties, appropriate design of the closed-loop microchannel allows the hydrodynamic effect resulting from mass conservation to drastically improve cycling time and species profile. This result has been justified by appropriate theoretical analysis combined with numerical simulations, while polymers properties have been carefully characterized using experiments, resulting in the first micro scale electrophoretron prototype which has been tested in PCR like conditions

Experimental Characterization Of Electrical Current Leakage In Poly(Dimethylsiloxane) Microfluidic Devices

Poly(dimethylsiloxane) (PDMS) is usually considered as a dielectric material and the PDMS microchannel wall can be treated as an electrically insulated boundary in an applied electric field. However, in certain layouts of microfluidic networks, electrical leakage through the PDMS microfluidic channel walls may not be negligible, which must be carefully considered in the microfluidic circuit design. In this paper, we report on the experimental characterization of the electrical leakage current through PDMS microfluidic channel walls of different configurations. Our numerical and experimental studies indicate that for tens of microns thick PDMS channel walls, electrical leakage through the PDMS wall could significantly alter the electrical field in the main channel. We further show that we can use the electrical leakage through the PDMS microfluidic channel wall to control the electrolyte flow inside the microfluidic channel and manipulate the particle motion inside the microfluidic channel. More specifically, we can trap individual particles at different locations inside the microfluidic channel by balancing the electroosmotic flow and the electrophoretic migration of the particle

Fast nonlinear ion transport via field-induced hydrodynamic slip in sub-20-nm hydrophilic nanofluidic transistors

Electrolyte transport through an array of 20 nm wide, 20 μm long SiO_2 nanofluidic transistors is described. At sufficiently low ionic strength, the Debye screening length exceeds the channel width, and ion transport is limited by the negatively charged channel surfaces. At source−drain biases >5 V, the current exhibits a sharp, nonlinear increase, with a 20−50-fold conductance enhancement. This behavior is attributed to a breakdown of the zero-slip condition. Implications for energy conversion devices are discussed

Electroosmotic Flow in Microchannel with Black Silicon Nanostructures

Although electroosmotic flow (EOF) has been applied to drive fluid flow in microfluidic chips, some of the phenomena associated with it can adversely affect the performance of certain applications such as electrophoresis and ion preconcentration. To minimize the undesirable effects, EOF can be suppressed by polymer coatings or introduction of nanostructures. In this work, we presented a novel technique that employs the Dry Etching, Electroplating and Molding (DEEMO) process along with reactive ion etching (RIE), to fabricate microchannel with black silicon nanostructures (prolate hemispheroid-like structures). The effect of black silicon nanostructures on EOF was examined experimentally by current monitoring method, and numerically by finite element simulations. The experimental results showed that the EOF velocity was reduced by 13 ± 7%, which is reasonably close to the simulation results that predict a reduction of approximately 8%. EOF reduction is caused by the distortion of local electric field at the nanostructured surface. Numerical simulations show that the EOF velocity decreases with increasing nanostructure height or decreasing diameter. This reveals the potential of tuning the etching process parameters to generate nanostructures for better EOF suppression. The outcome of this investigation enhances the fundamental understanding of EOF behavior, with implications on the precise EOF control in devices utilizing nanostructured surfaces for chemical and biological analyses