Experimental and numerical study of a micromixer
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Poster Session (EPIC - Poster) - P2
Keywords: micromixer, CFD, microfluidics
The purpose of this work is the experimental and numerical investigation of the flow field encountered in micromixing devices. The understanding of the flow processes in micromixers is essential for the design of microfluidic devices like microreactors (Gavriilidis et al., 2002) and can be considered an essential step towards process intensification. Due to the fact that laminar flow is encountered within these microdevices, mixing can be accomplished only through diffusion. A means of augmenting diffusive transport is to lead the flow through alternating bends and thus produce mixing by generating secondary flow that directs fluid from one cross sectional region to the other. Since in this case the inertia driven flow decays very fast due to viscous action, several consecutive bends must be used to repeatedly produce these secondary flows.
Experimental as well as computational studies have been performed the last decade to determine the rate of mixing in various curved ducts at Reynolds numbers of interest to microfluidic applications (e.g. Jiang et al., 2004). In the present study, the experiments are conducted using a prototype of a micromixer comprising of a microchannel (i.d.=100μm) with consecutive curves .
The fast reaction, between the aqueous solutions of KSCN (colourless) and Fe(NO3)3 (yellow) that produces Fe(SCN)3 (red), is used to monitor the rate of mixing. The two miscible liquid streams are introduced through the two branches of a Y-junction, before entering a series of specially designed meanders to produce a continuous swirling flow. The flow rates of the input liquid streams are controlled by piston pumps, while the mixing efficiency is determined by monitoring the colour of the resulting stream using a digital camera mounted to an optical microscope. Experiments are conducted for a range of Reynolds and Dean numbers.
A commercial CFD code (i.e. ANSYS CFX® 10.0) is used to simulate the micromixing process and to obtain results concerning the flow pattern and the mixing efficiency inside the conduit. The CFD simulation is validated using experimental data on mixing length acquired for various flow rates, corresponding to the laminar regime. For the needs of the present study a parallel computing cluster is available, which consists of eight AMD64 processors and a total of 8GB RAM. To efficiently describe the complexity of the narrow passage the grid used for the simulation is an unstructured mesh consisting of tetrahedral and prism elements. The ultimate goal of the CFD simulation is the study of the effect of the various design parameters (i.e. curvature, number of bends) and of fluid physical properties on the overall performance of such type of equipment (i.e. the mixing length).
Information provided by this study, which is still in progress, is expected to be helpful in the efforts to optimize the design of micromixing equipment which turn to be of increasing commercial interest.
References
Gavriilidis, A., Angeli, P., Cao, E., Yeong, K.K. and Wan, Y.S.S. 2002 Technology and applications of microengineered reactors Trans IChemE, 80, Part A.3-30.
Hessel, V., Hardt, S. and Löwe, H. 2004 Chemical Micro Process Engineering- Fundamentals, Modelling and Reactions, Wiley-VCH Verlag, Weinheim, 2004.
Jiang, F., Drese, K.S., Hardt, S., Küpper, M., Schönfeld, F. 2004 Helical flows and chaotic mixing in curved micro channels, AIChE J. 50, 9, 2297-2305.
Presented Thursday 20, 13:30 to 14:40, in session EPIC-1: Poster Session (EPIC - Poster) - P2.
