The role of slender beam motion on fluid mixing in a microchannel

Microfluidic devices are used in the biomedical field to enhance biological processes and increase the efficiency in the detection or capture of target molecules or cellular material. The objective of this study is to analyze the fluid and solid interactions between a fluid and a moving flap to determine if the mechanical motion of the flap results in fluid mixing that might be relevant for enhancing biological processes such as DNA hybridization at the micro scale.;The microactuator or moving flap considered in the study is a bilayer flap made of gold and polypyrrole (PPy). Actuation of the bilayer flap occurs when an electro-potential is applied across the flap bilayer. Analytical and numerical methods are used to study the flow field generated by flap rotation and bending motion in a microchannel. In the first part of the study, the flap is treated as a forced oscillator with a prescribed angular velocity. The effects of the hydrodynamic forces on the resulting motion of the solid are not considered. In the second part of the study, the role of flexible flap motion that includes two-way coupling between the fluid and the solid is implemented. The fictitious domain method with distributed Lagrange multipliers (DLM method) is used to model the coupled fluid and solid interactions.;The results of the study show that single flap motion can be as effective as multiple flap motion in enhancing bulk mass transport and surface reactions. In the single flap analysis, factors that effect the efficiency of mixing include the forcing frequency, the wall endpoint condition, the flap length to channel height aspect ratio, and the flap rigidity. The motion of flexible flaps are more effective in enhancing mixing than rigid flaps over a broad range in the applied load. The effectiveness of the flexible flaps can be attributed to a bending motion that opposes the direction of motion. When compared to diffusion only mass transport, the added convection due to the moving flap results in a significant increase in mass transport within a short time interval.