Mixing in microfluidic system using curved microchannels
Mixing is a critical issue in microfluidic systems since at the small scale turbulent mixing is normally prevented. The two main phenomena occurring within micromixers, are diffusion and convective transport. Passive micromixers employ particular designs to enhance the convective mixing using lamination or chaotic-advection of the flow. Chaotic advection micromixers induce flow perturbations to the fluid mainstream through by means of grooves, ridges, obstacles or similar elements in the microchannel. Another way of inducing perturbation is the use of curved channels, where two transversal counter-rotating vortices, known as Dean Vortices, are generated by the imbalance between centrifugal and viscous forces . We apply different experimental methods to experimentally characterize the behavior of different micromixers designs, provided by the cooperation partners. These methods include LIF techniques and surface reconstruction approaches based on the APTV. Results are compare with analytical prediction and numerical simulations of the flow.
Partner: Politecnico di Torino, Karlsruhe Institute of Technology, TU Eindhoven
Contacts: Dr. Massimiliano Rossi
Mixing in electrochemical cells
In the case of electrochemical deposition of metals an electric field is present in the electrochemical cell. By the superposition of a magnetic field a Lorentz force is generated if the field lines are not perfectly parallel. This volume force acts only in a small region close to the electrodes surfaces but will generate a flow that extends far in the electrochemical cell. The deposition rate is enhanced since fresh bulk solution is brougth to the electrode. If small gradient in the magnetic field are imposed, the deposited metal layer can even be structured as shown by the IFW Dresden. The characterization of the truely three-dimensional and transient flow is crucial to understand the mechanisms. Using the astigmatism particle tracking method in connection with a long-range microscope enabled highly temporal and spatial resolved measurements of the three dimensional velocity field in a fluid volume by a single camera. Thus, the complex interplay of magnetic field gradient force and the Lorentz force induced convective effects could be analyzed experimentally for the first time.
Funded by the Deutsche Forschungsgemeinschaft (DFG).
Partner: IFW Dresden
Contacts: Dr. Christian Cierpka