Secondary Flows, Mixing, and Chemical Reaction Analysis of Droplet-Based Flow inside Serpentine Microchannels with Different Cross Sections.

Chemical bioreactions are an important aspect of many recent microfluidic devices, and their applications in biomedical science have been growing worldwide. Droplet-based microreactors are among the attractive types of unit operations, which utilize droplets for enhancement in both mixing and chemical reactions. In the present study, a finite-volume-method (FVM) numerical investigation is conducted based on the volume-of-fluid (VOF) applying for the droplet-based flows. This multiphase computational modeling is used for the study of the chemical reaction and mixing phenomenon inside a serpentine microchannel and explores the effects of the aspect ratio (i.e., AR = height/width) of rectangular cross-sectional geometries as well as three other cross-sectional geometries including trapezoidal, triangular, and circular, on consumption and production rates of chemical species. It is found that in these droplet bioreactors, the reaction begins from the forward section of the droplet. We investigate the secondary flows and chemical reactions inside the droplets in a serpentine microchannel with different cross-sectional geometries. Different transient Dean vortices and secondary flows in the presence and absence of the droplets are studied and explained based on the position of the droplets. It is found that as the droplets pass through the microchannel turns, the patterns and magnitude of the secondary flows change, depending on the cross-sectional geometry. Eventually, the results demonstrate that the AR = 2 rectangular cross-section is the most helpful geometry, whereas the trapezoidal cross-section takes into account the least efficient one between all geometries.