Velocimetry with simultaneously ultrahigh spatial and temporal resolution

(a) (b)

(a) Principle and our setup of LIFPA; (b) LIFPA setup.

Laser induced fluorescence photobleaching anemometer, multiphoton absorption

In many cases, such as micro/nanofluidics, biofluids and fluid dynamics there is a need of measurement of fluid velocity with simultaneously ultrahigh spatial and temporal resolution. For instance, the flows in nanochannels, porous media in shell oil or biological tissues, where the porous diameter can be from a few micrometer down to tens of nanometers, are poorly understood. Current velocimetries primarily rely on particles as tracers, such as micro Particle Image Velocimetry (µPIV). However, for many popular microflows, such as electrokinetics (EK) and near wall flow, magnetophoresis, acoustophoresis, photophoresis and thermophoresis, particles have different velocity from their surrounding fluids. To overcome this issue, we develop a molecular and neutral fluorescent tracer to measure flow velocity with simultaneously ultrahigh spatial (~70 nm) and temporal (~ 5 µs) resolution. The novel technique is laser induced fluorescence photobleaching anemometer. Recently LIFPA has enabled us to discover several new phenomena: µ-electrokinetic turbulence at low Reynolds number; large discrepancies between theory and experiment for rise time of DC electroosmotic flows with a temporal resolution of 5-10 µs; and flow velocity oscillating at high frequency of AC electrokinetic flows; and new route to chaotic electrokinetic flows.

Wei, Zhao, Fang Yang, Jamil Khan, Ken Reifsnider, G.R Wang. Measurement of Velocity Fluctuations in Microuidics with Simultaneously Ultrahigh Spatial and Temporal Resolution. Experiments in Fluids. 56:11, 2016.
G.R. Wang, Fang Yang, Wei Zhao There can be turbulence in microfluidics at low Reynolds number. LabChip, 2014. 14. 1452–1458.
Kuang, G. Wang Far-field nanoscopic velocimeter for nanofluidics. Lab-on-a-Chip. 10, 240–245, (2010).