Research Article Pressure Loss and Transfer Rates in Microstructured Devices with Chemical Reactions Enhanced transport phenomena are essential for chemical reactions in con- tinuous flow microstructured equipment. Flow regimes and heat transfer are governed by laminar and transitional conditions to turbulence. 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. The geometry and cross-section of the smallest channel determine the pressure loss and energy dissipation of the entire system. Heat and mass transfer is greatly influenced by the flow regime, which leads to transport enhancement conjointly with miniaturization. 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 depends on the pressure loss in the microchannel, where the time scales are important. Dimensionless numbers assist the appropriate and successful design of microreactors concerning mixing, residence time, and heat transfer. Keywords: Chemical reactions, Microstructured devices, Pressure loss Received: February 1, 2008; accepted: May 19, 2008 DOI: 10.1002/ceat.200800065 1 Introduction Continuous flow processing offers many advantages ranging from controlled process conditions to high flow rates and mass throughput. In bulk chemistry, nearly all chemical processes benefit from continuous operation. Fluid dynamics determine the characteristics of continuous flow equipment, the pressure loss, residence time, heat transfer, and mixing time (see [1–3]). Yield and selectivity of chemical reactions are greatly influ- enced by flow situation, if their kinetics possesses a typical time scale in the range of the flow processes. In contrast, batch processes prevail in operation and pro- duction in specialty chemistry, fine chemistry, or pharmaceuti- cal production. Batch vessels are versatile for many kinds of re- actions and can handle multiphase systems in multipurpose plants [4]. Vessels can be arranged in various constellations to perform different reaction routes and can also handle certain work-up steps like distillation or extraction. On the other hand, heat transfer and mixing is often limited in stirred ves- sels, which need high dissolution or long operation times or even does not permit highly exothermic reaction [5]. Due to short diffusion length in their tiny channels, micro- structured devices offer high transfer rates for heat and mass, allow short residence times, and small hold-up. However, straight laminar flow is associated with diffusion, a relatively slow process especially in liquids. In microfluidics, much effort is spent to circumvent straight laminar flow and to increase the transfer rates. Many strategies have been developed to shorten the diffusion length, such as split and recombine the flow, chaotic advection by irregular surface grooves or convec- tive flow in bends and curves besides active measures like elec- trokinetic fields, or mechanical actuation by peristaltic pumps, membranes, or ultrasonic fields. An overview can be found in two recent reviews from Nguyen and Wu [6] and Hessel et al. [7]. For chemical production with high flow rates, only few measures of these are suited for mixing in microchannels. In most cases, passive mixers are used for mixing purposes. Multichannel devices with many channels in parallel allow high flow rates and a high surface ratio but are prone to maldistribution between the channels and uncontrolled condi- tions in the single channels. A single channel device has clearly defined flow conditions and is more robust for varying fluid properties and potentially precipitating flow. This paper describes some fundamental characteristics of microstructured single channel devices in fluid dynamics, heat transfer, and mixing as well as its impact on the performance © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Norbert Kockmann 1 1 Lonza AG, R&D Exclusive Synthesis, Visp, Switzerland. – Correspondence: Dr.-Ing. N. Kockmann (norbert.kockmann@lonza.- com), Lonza AG, R&D Exclusive Synthesis, CH-3930 Visp, Switzerland. 1188 Chem. Eng. Technol. 2008, 31, No. 8, 1188–1195