Abstract:
The effects of varying flow rate ratio and Reynolds number on the momentum
diffusion and flow development of two co-flowing, laminar streams in a rectangular
microchannel are presented. The microchannel has an aspect ratio of approximately 16
with a width of 1006 μm and a height of 63 μm. A long, thin splitter plate initially
separates the two streams such that fully developed flow in each of the two channels is
obtained prior to merging. Fluorescent dye imaging and Particle Image Velocimetry
(PIV) were utilized to observe the interaction between the streams for a range of flow rate
ratios ranging from one to nine while maintaining a chamber Reynolds number of one.
Additionally, PIV data was collected for the same flow rate ratios with a chamber
Reynolds number of ten. It was found that when there is a velocity difference between
the two streams, there is a cross-stream pressure gradient immediately downstream of the
splitter plate that causes the faster moving fluid to expand into the slower moving fluid.
Despite this rapid expansion, the fluids in two streams do not mix and continue to travel
parallel to each other. As expected, the expansion of the faster moving fluid is diminished
by the viscous effects present in the flow, although only at higher flow rate ratios. The
merged streams eventually recover their fully developed profile although it is shown that
existing entrance length relationships do not adequately predict the development length.
In addition, the velocity flow characteristics between the streams is illustrated near the
end of the splitter plate. As the streams travel past the splitter plate, the flow-wise
momentum of the faster moving fluid is converted into a lateral, cross-stream velocity.
The presence of an optimum flow rate ratio for obtaining a maximum cross-stream
velocity magnitude is suggested. The effect of varying Reynolds number on these
observations is also discussed.
