Fluoromax red

Quantitative and spatially resolved two-dimensional (2D) flow fields were obtained using micro-particle image velocimetry (mPIV, TSI Inc.). 74, 75 The fluid was seeded with a low concentration of 2 mm-diameter fluorescent tracer microparticles (Fluoromax red, Thermo Scientific Inc.). The mPIV measurements were recorded at the mid-plane (z = 0) of the channel using an inverted microscope (Nikon Ti) with a 4 Plan Fluor, NA = 0.13 numerical aperture objective lens and a high speed camera (Phantom Miro) working in frame-straddling mode. With this camera and microscope objective, the field of view was 2.56 mm  1.60 mm with a measurement depth of 159 mm, approximately 8% of the height of the channel. At each imposed flow rate, the flow was held for at least 60 seconds, i.e., \30l, before recording the mPIV data. For time-steady flows, mPIV frame pairs were recorded at 25 pairs per second for 10 seconds. For time-dependent flows, mPIV frame pairs were recorded at 50 pairs per second for 30 seconds. Frame pairs were processed both individually and by ensembleaveraging. The velocity field u = [u, v], where u is the x-component of the velocity and v is the y-component of the velocity, was determined via cross-correlation between frame pairs using OpenPIV, an open-source Python package. 76 (link) 3 Results