Residence time distribution in coil and plate micro-reactors

Micro-reactors, enabling continuous processes at small scales, have been of growing interest due to their advantages over batch. These advantages include better scaling, as well as improved mass and heat transfer, though many new challenges arise due to the small scales involved such as non-negligible entrance effects and significant pressure losses. The flow in coils, rectangular channel serpentine plates, mix-and-reside plates, and liquid–liquid (LL) mixing plates was investigated and characterized using residence time distribution (RTD) tests. A pulse test was used to determine the RTD curve of these reactors at flowrates ranging from 15 to 100 g/min of water. A semi-empirical, multi-parameter model was used to describe the asymmetrical curves, while the axial dispersion model was used to describe the symmetrical ones. The Peclet number is given in function of the Reynolds number for the LL plates that were found to be near-plug flow ( Pe  > 100). In a plate with continuous LL micro-mixers, the Pe ranged from 193 to 467 with Pe increasing as Re increased. Importantly, the effect of straight channel segments interspaced between mixers is also evaluated as a method of volume gain for scale-up of micro-reactors. For a given average energy dissipation rate, the Pe number was maintained for the shorter channel segments between LL micro-mixers whereas longer spacing lengths likely lead to the development of unidirectional laminar flow and resulting in the observed increased axial dispersion and tailing in the RTD.