Microparticle image velocimetry (μPIV) study of microcavity flow at low Reynolds number

Fluid flows in microchannels with microcavities at low Reynolds number are increasingly used in microfluidic applications such as trapping and sorting of cells and particles. For optimizing the microcavity configuration and better controlling the microenvironment in the microcavities, it is important to thoroughly understand the flow behaviors in the microcavities. Hence, using microparticle image velocimetry (mu PIV), we investigated quantitatively the flow characteristics of rectangular microcavities with a wide range of aspect ratio (lambda = 0.25-3) and Reynolds numbers (Re = 0-100). Depending on the control parameters (Re and lambda), a flow regime map in microcavities has been constructed, including three different flow patterns: attached flow, separated flow, and transitional flow. The critical parameters for the transform of flow patterns were determined. Only a single central microvortex appears in the microcavities, and the evolution and characteristics of the microvortex were investigated in detail. The results revealing the flow mechanism of different flow patterns in the rectangular microcavities can provide useful design guidelines of microfluidic-based devices, as well as a map to help microfluidic users in their design of application-driven microcavities.