(102d) Characterization of Flow Regimes and Transport Phenomena in Complex Microchannels

Enhanced transport phenomena are essential for chemical reactions in continuous flow microstructured equipment. Flow regimes and heat transfer are governed by laminar conditions, especially in liquid phase systems. To achieve high mass flow rates, typical dimensions of channels in microstructured equipment are in the range from 50 to 1000 µm, while flow velocities are ranging from cm/s to few m/s. In channel curves and meandering channels, secondary flow structures appear, starting from Dean flow with a vortex pair to more chaotic flow structures at higher Re numbers. In complex channel arrangements, the narrowest cross section mainly determines the pressure loss and energy dissipation of the entire system. Nevertheless, a detailed analysis of the flow regimes is essential for the understanding of transport phenomena in these channel structures.

Heat and mass transfer is greatly influenced by the convective flow regime, which leads to further enhancement conjointly with miniaturization. Typical examples of curved flow and mixing in T-shaped micromixers are given. It is shown that the pressure loss and energy dissipation can be used to determine heat transfer coefficients and mixing characteristics.

Chemical reactions are characterized by their kinetics and stoichiometry. Rapid mixing, short residence time within the device, and narrow residence time distribution are important parameters for to design microstructured devices for process development and chemical production. Dimensionless numbers assist the appropriate and successful design of microreactors concerning mixing, residence time, and heat transfer.