DC-biased AC-electroosmotic and AC-electrothermal flow mixing in microchannels.
ABSTRACT This paper presents a novel approach of mixing two laminar flowing streams in microchannels. The mixer consists of a pair of electrodes disposed along a fluidic channel. By energizing the electrodes with a DC-biased (2.5 V) AC voltage (20 Vpp), an electrokinetic flow is induced with a flow profile perpendicular to that of the incoming laminar streams of liquids to be mixed. As a result, the flow lines of the incoming streams and the induced flow are forced to crossover and very efficient stirring and mixing at short mixing length can be achieved. The mixer can be operated from the AC-electroosmotic (ACEO) (sigma=1 mS/m, f=100 kHz) to the AC-electrothermal (ACET) (sigma=500 mS/m, f=500 kHz) flow regimes. The mixing efficiency in the ACEO regime was 92%, with a mixing length of 600 microm (Q=2 microL/min), an estimated mixing time of 69 ms and an induced ACEO flow velocity of approximately 725 microm/s. The mixing efficiency in the ACET regime was 65% for a mixing length of approximately 1200 microm. The mixer is efficient and suitable for mixing reagents in a fluid media from low to high conductivity as required in diverse microfluidic applications.
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ABSTRACT: Oscillating sharp edges have been employed to achieve rapid and homogeneous mixing in microchannels using acoustic streaming. Here we use a perturbation approach to study the flow around oscillating sharp edges in a microchannel. This work extends prior experimental studies to numerically characterize the effect of various parameters on the acoustically induced flow. Our numerical results match well with the experimental results. We investigated multiple device parameters such as the tip angle, oscillation amplitude, and channel dimensions. Our results indicate that, due to the inherent nonlinearity of acoustic streaming, the channel dimensions could significantly impact the flow patterns and device performance.Lab on a Chip 02/2014; · 5.70 Impact Factor
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ABSTRACT: A quartz crystal microbalance (QCM) serving as a biosensor to detect the target biomolecules (analytes) often suffers from the time consuming process, especially in the case of diffusion-limited reaction. In this experimental work, we modify the reaction chamber of a conventional QCM by integrating into the multi-microelectrodes to produce electrothermal vortex flow which can efficiently drive the analytes moving toward the sensor surface, where the analytes were captured by the immobilized ligands. The microelectrodes are placed on the top surface of the chamber opposite to the sensor, which is located on the bottom of the chamber. Besides, the height of reaction chamber is reduced to assure that the suspended analytes in the fluid can be effectively drived to the sensor surface by induced electrothermal vortex flow, and also the sample costs are saved. A series of frequency shift measurements associated with the adding mass due to the specific binding of the analytes in the fluid flow and the immobilized ligands on the QCM sensor surface are performed with or without applying electrothermal effect (ETE). The experimental results show that electrothermal vortex flow does effectively accelerate the specific binding and make the frequency shift measurement more sensible. In addition, the images of the binding surfaces of the sensors with or without applying electrothermal effect are taken through the scanning electron microscopy. By comparing the images, it also clearly indicates that ETE does raise the specific binding of the analytes and ligands and efficiently improves the performance of the QCM sensor.Biomicrofluidics 09/2014; 8(5):054116. · 3.77 Impact Factor
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ABSTRACT: Recently, ac electro-osmosis (ACEO) has attracted intensive attention due to its capabilities of pumping and mixing enhancement with relatively low voltages. In this paper, we report the effects of electrode arrangement on the performance of a micromixer using dc-biased ACEO with respect to flow rate and ac frequency. The mixer consists of two inlet channels and a straight main microchannel with gold electrode pairs deposited on its bottom, and utilizes asymmetric vortex flows generated by dc-biased ACEO for mixing. The results indicate that there is significant dependence of mixing performance on the number of electrode pairs, especially for different flow rates. For example, the single electrode pair resulted in the best mixing performance at the highest flow rate of 9 µL min−1 (average velocity of 2.5 cm s−1) while three or four electrode pairs provided the maximum mixing performance for the flow rate lower than 4 µL min−1 (4.11 cm s−1). Also, we found that a mixing index of 95% can be achieved by using three electrode pairs while a single electrode pair leads to a mixing index of 85% for a given condition.Journal of Micromechanics and Microengineering 10/2012; 22(11):115034. · 1.73 Impact Factor