TMCnet News
Passive Micromixing Solution [Sensors & Transducers (Canada)](Sensors & Transducers (Canada) Via Acquire Media NewsEdge) Abstract: Mixing rate is characterized by the diffusion flux given by the Fick's law. A passive mixing strategy is proposed to enhance mixing of two fluids through perturbed jet flow. A numerical study of passive mixers has been presented. This paper is focused on the modeling of a micro-injection systems composed of passive amplifier without mechanical part. The micro-system modeling is based on geometrical oscillators form. An asymmetric micro-oscillator design based on a monostable fluidic amplifier is proposed [2, 7]. The characteristic size of the channels is generally about a few hundred of microns. The numerical results indicate that the mixing performance can be as high as 92 % within a typical mixing chamber of 2.25 mm diameter and 0.20 mm length when the Reynolds number is Re = 490. In addition, the results confirm that self-rotation in the circular mixer significantly enhances the mixing performance. The novel micro mixing method presented in this study provides a simple solution to mixing problems in micro system. Copyright © 2011 IFSA. Keywords: Modelling, Micro mixture, Diffusion, Size effect. (ProQuest: ... denotes formulae omitted.) 1. Introduction As biochemical reactions that are performed in bio-MEMS require mixing, mixing is an important issue in bio-MEMS. There has been increasing interest among both biologists and researchers at the medicinal laboratories on the study of mixtures on a metric and micro scale. In the context of the MEMS, a numerical study on static micro mixers and the possible prospects for technical adapted solution of microsystems have been presented. Micro mixers can be classified under two categories, passive and active. Whereas external perturbations are introduced in active micro mixers to enhance mixing, the mixing process in passive mixers completely relies on diffusion or chaotic advection. Decreasing the diffusion path between the mixing fluids and increasing the contact surface between them will enhance mixing. The behavioral study of the micro flow mixers can enable the prediction of the state of the mixture and the efficiency of mixing. Within the last decade the world of the "bio" micro technology has growth up, more to many university and private groups which have been developing micro systems for biomedical and chemical applications. Fluidic elements with no moving parts, able to realize logic (yes, no, and, or...) or proportional (signal amplification) functions. Were widely studied in the 1960s [2, 6] the characteristic size of the channels is generally about a few tens of microns. This miniaturization involves series of fundamental problems related to the fluid mechanic. Indeed, at these scales, the fluidic flows are laminar [I]. The working principle of this device consists in disturbing the flow of jets moving along the principal channel by flow oscillations generated by three pairs of lateral canals. The device is called micro injector. In these cases, the oscillators use special designed geometric configurations, identified by the absence of moving parts, to create an environment where self-induced, sustained oscillations will occur [2, 3], they can be used as flow meters. A novel fluidic oscillator has been developed and tested by V. Tesar, make these oscillators attractive as micro reactor injection application. A fast micro mixing is essential in many operations that are employed in biochemical analysis, administration of drugs, and also other biological processes involving handling of cells and enzymatic reactions, which occur in pharmaceutical products. When transverse-sectional dimensions of channel are approximately ten micrometers, the molecular diffusion can facilitate mixing of two fluids in few seconds. However, when dimensions are approximately hundred micrometers, a micro-mixer-based molecular diffusion can facilitate mixing in ten seconds [I]. The literature describes significant number devices that have been designed to improve the mixing on a nanometric scale [3 -6]; these devices are the micro mixers that have been categorized into active and passive based on the pattern of control flow [7-10]. 2. Design and Operation of the Oscillator Description Micro oscillator was obtained from wall attachment micro fluidic amplifiers using a feedback loop from the outputs to the control input, Fig. 1 [2-4]. The principle of oscillators is based on a fluid jet, which injected into the oscillator, bends due to small fluctuations towards one of the attachment walls. Some examples of systems and processes that might employ this technology include inkjet printers, blood-cell-separation equipment, chemical synthesis, genetic analysis, drug delivery, electro chromatography, micro-scaled cooling systems of electronic devices which generate high power. The fluid flow on the bent side of the jet is restricted and a lowpressure regime is created, which causes the jet to attach to the wall (Coanda effect) [5-7]. 2.1. Approximation of the Oscillation Frequency The period of oscillations is determined by the switching time from the attachment wall to another and the transmission time through the feedback channel [3-6]; the frequency is determined by expression (1): ... (1) where/is the frequency (Hz), ts is the switching time (s) and ¿,is the transmission time (s). 2.2. Oscillator Model The oscillators are characterized by their flow evolution versus pressure [I]. Two main advantages of micro-fluidic can be highlighted: very small analysis devices reduce the time of analysis and volume of components needed. The model oscillator is similar to a V. Tesar model with major modification [6]. Its profile is presented in Fig. 2. The geometry of the mixer can be separated into two regions, the mixing and the control region. The secondary flow through the control orifice perturbs the aspired flow and the principal flow. 2.3. Description Geometry We simulate the air flow in an oscillator geometry without feedback, it is a configuration with two injectors only with events for every injector, that dimension is (32.24 ? 10.6) mm. The output orifice size equal 0.50 mm. The pressure applied on the valve supply is supposed to be positive. A jet issuing from a nozzle and expanding between two inclined walls will attach to the less inclined one or to the wall which is closer from the jet axis Figure 2. The jet will oscillate, and the element will behave as a fluidic oscillator. 3. Model Simulation With a plane oscillator of constant depth made with a square tube. Such plane oscillators are simulated by a fully CFD approach. Hypotheses: The simulation of the micro-injection systems is obtained with several hypotheses: * Air and laminar regime; * Incompressible ideal gas flow; * Inlet pressure 2 x 105 Pa. Next results are presented for the Reynolds number at the nozzle is around 300. 4. Hydrodynamic Results On the first results case geometry Figure 1, we present the following results. The next Figure 3 represents the mass flow output mixer (volume VO). The spectral analyses with Fourier transformation FFT describe the frequency oscillation of system (Figure 4). All following results are obtained for monostable oscillator. The relationship / (Ì/V) is linear; the injector form is supposed the Volume layout. This linear relationship for a given supply pressure presented below (Fig. 5). The variation of the alimentation pressure, that allows us to make a note of principal frequencies and second frequencies (Fig. 6). 5. Species Transport Equations The frequency of third case is approximately double of the first injector, Table 1. When you choose to solve conservation equations for chemical species, FLUENT predicts the local mass fraction of each species, Yi, through the solution of a convection-diffusion equation for the ith species. This conservation equation takes the following general form: ... (2) In the first equation, Ji is the diffusion flux of species z, which arises due to concentration grathents. By default, FLUENT uses the dilute approximation, under which the diffusion flux can be written as ... (3) where Di;m is the diffusion coefficient for species i in the mixture. 5.1. Estimation of the Efficiency of Mixing For estimating the mixing of index mixture, the following expression [11-14] is specified: ... (4) ...(5) Mi, and M represent mass fraction of/ pixel and average, respectively. 5.2. Mixing Results The principal objective of our study is oriented to control injection system for mixing applications. In this context we chose the V3 configuration. This geometry constituted by monostable amplifier. The mass flow output mixer system signal and mass fraction distribution in output mixer system for Volume V3 are represented respectively in Figures 7 and 8. The different positions of index mixture are represented in Figure 9, The values on percentage of these different positions are recapitulated in the Table 2. 6. Conclusion In this paper, a global modeling of an injection system has been purposed in order to normalize its behavior. The reversed flow exists at down pressure with oscillation frequency between 0.5 kHz and 1.8 kHz. The performance of oscillating injection system mill metric size was simulated. The first results of theses numerical calculations indicate evaluation oscillating frequency of fluidic monostable oscillator, the next one consist of oscillating controlled injection system with four injectors. The performance of oscillating micromixer with millimetric size was simulated by using CFD Code. The first results of these numerical calculations indicate the evaluation of the fluidic oscillator oscillating frequency; the second one consists of oscillating micromixer frequency and mass fraction with millimetric size. In perspective we propose to undertake an experimental study to estimate a masse fraction mixture. References [1]. P. Tabeling, Introduction à la micro fluidique, Collection Echelles, Berlin, 2003. [2]. K. Foster, C. A. Parker, Fluidic Components &Circuits, 1970, John Wiley & Soon Ltd, pp. 265-273. [3]. U. Gebhard, H. Hein and U. Schmidt., Numerical investigation of fluidic micro-oscillators, J. Micromech, Microeng, 6, 1996, pp. 115-117. [4]. Eliphas Wagner Simôes, Rogerio Furlan, Roerto Eduardo Bruzetti Leminski, Numerical oscillator for gas flow control and measurement, J. Flow Measurement and Instrumentation, 16, 2005, pp. 7-12. [5], V Tesar, J. R. Tippetts, Y. Y. Low, Oscillator mixer for chemical microreactors, in Proceedings of the 9th International Symposium on Flow Visualisation, 2000, pp. 298.1-298.7. [6]. W. Gerhard, Fluidic temperature sensor investigation for high gas temperatures, AGARDograph, 135, 1969. [7]. R. Khelfaoui, S. Colin, R. Caen, S. Orieux, and L. Baldas, Numerical and experimental analysis of monostable mini- and micro-oscillators, Heat Transfer Engineering, 30, 1-2, 2009, pp. 121-129. [8]. J. Beebe, Passive Mixing in a Three-Dimensional Serpentine MicroChannel, J. MEMS, 9, 2, 2000, pp. 190-197. [9]. H. H. Bau, J. Zhong and M. Yi, A minute magneto hydro dynamic (MHD) mixer, Sens. Actuators B, 79, 2-3, 2001, pp. 207-215. [10]. M. Koch, H. Witt, A. G. R. Evans and A. Brunnschweiler, Improved characterization technique for micromixers,/. Micromech. Microeng., 9, 1998, pp. 156-158. [H]. V Hohreiter, J. Chung, E. Cummings, T. Postlethwaite, Effects of system dimension on turbulence and micro fluidic, University of Florida, Dept. of Mechanical Engineering, Gainesville, Florida, USA. [12].Yi-Kuen Lee, Patrick Tableing, Chiang Shih, and Chih-Ming Ho, Characterization of MEMS-Fabricated mixing device, International mechanical engineering Congress et exposition, Orlando, Florida, November 5-10, 2000, pp. 505-511. [13].Che-Hsin Lin, Chien-Hsiung Tsai and Lung-Ming Fu, A rapid three-dimensional vortex micromixer utilizing self-rotation effects under low Reynolds number conditions, J. Micromech. Microeng., 15, 2005, pp. 935-943. [14]. R. Khelfaoui, B. Benyoucef, and S. Colin, Micro mixture: sixe effect of micro mixing, in Technical Proceedings of the 2007 NSTI Nanotechnology Conference and trade Show Nanotech 2007, Santa Clara, USA, Vol. 3, 2007, pp. 201-204. 2011 Copyright ©, International Frequency Sensor Association (IFSA). AU rights reserved. (http://www.sensorsportal.com) 1 Brahim DENNAI, 1RaCMd KHELFAOUI, 2Boumédiène BENYOUCEF and 3Asma ABDENBI 1 Laboratory ENERGARID, University of Bechar, B. P. 417, 08000 Bechar, Algeria Tel: 213 49 81 55 81/91, fax: 213 49 81 52 44 laboratory URMER, University of Abu Bakr Belkaid, Tlemcen, Algeria 3 University of Bechar, B. P. 417, 08000 Bechar, Algeria Received: 16 July 2011 /Accepted: 22 August 2011 /Published: 30 August 2011 (c) 2011 International Frequency Sensor Association |