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Helically coiled tubes offer improved residence and thermal time distributions due to the formation of Dean vortices via centrifugal forces. Design and fabrication of several milli/microstructured helically coiled tube reactors are described for processes requiring a narrow residence time distribution (RTD) and efficient heat transfer at laminar flow regime. The performance of microstructured reactor capillaries, which provide a high specific surface area, is combined with a type of helically coiled tube, namely, a coiled flow inverter allowing for the narrowest RTD in laminar flow regimes. Axial dispersion is characterized by obtaining the RTD curves from different reactor setups. Overall heat transfer coefficients of a new reactor setup are measured in order to determine the heat transfer efficiency.

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A multiphase flow profile inside a helically coiled tubular device (HCTD) was observed by using a high-speed camera. Gas−liquid slug flow observations revealed that the Taylor vortices are influenced by secondary flow due to the centrifugal force acting perpendicular to the flow direction. Hence, mixing inside the liquid slug is enhanced by the combination of Dean and Taylor vortices in HCTD. The modular design of a specific type of HCTD, that is, the coiled flow inverter (CFI) is elucidated by the representation of a new design space diagram. Continuous precipitation of calcium carbonate (CaCO 3 ) was investigated for modular CFI made of polyvinyl chloride (PVC) tubes (d i = 3.2 mm) with slug flow patterns. CaCO 3 was continuously precipitated along CFI with a conversion of ca. 90%. CFI provided a narrower particle size distribution with median particle diameters around 28 μm and more uniform morphology in comparison to a batch reactor.

For complete chemical processes, downstream operation steps are essential, but on a miniaturized scale, they are not so far developed as the microreactors. This contribution presents three different unit operations for phase and component separation. Liquid-liquid extraction is often performed in columns, which were miniaturized for higher separation efficiency and flow rates suitable for processes in flow chemistry. Two-phase mass transfer processes in capillaries benefit from rapid final phase separation, which can be performed in an in-line phase splitter based on different surface wetting behavior. Crystallization is often a final purification step, which is performed in a continuously operated helical tube setup with narrow residence time distribution. For all unit operations, design criteria are shown with typical applications. The methodology of downscaling of known equipment and employing typical microscale phenomena such as good flow control, laminar flow, or dominant surface forces leads to successful equipment design.

A micro-structured tubular reactor and a milli-structured tubular cooling crystallizer were equipped with thermocouples to observe the axial temperature profiles along the tubes. In order to avoid interactions of the temperature sensors with the fluid inside the channel, the sensors were fixed on the outside of the tube wall. By attaching polymeric foam insulation on the temperature sensors, the influences of surrounding heating/cooling agents on the measurement were dampened. The remaining error on the measurement was characterized experimentally. Simplified 1D simulation models were subsequently used to estimate the overall heat transfer coefficients in the devices. The influences on the remaining error in the temperature measurement on the estimated heat transfer coefficient was discussed.