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Stanford University

Stanford Microfluidics Laboratory

Micron-Resolution Particle Image Velocimetry for Microfluidics

The goal of this project is to measure fluid flow velocities in complex microchannel geometries. Particle-based flow diagnostics provide temporally resolved, high resolution measurements which are applicable to three dimensional flow fields. The motivation behind this project is to establish a robust particle-based measurement diagnostic for microfluidic systems, encompassing pressure-driven and electrokinetically-driven fluid flows.

Project Description
We have developed a micron-resolution particle image velocimetry (mPIV) system to measure instantaneous and ensemble-averaged flow fields in micron-scale fluidic devices. This PIV system measures the total velocity of submicron seed particles; which includes electrophoretic, electroosmotic, and Brownian components. The PIV system uses 300 to 500 nm diameter fluorescent seed particles, an epifluorescent microscope, and an interline-transfer CCD camera to record high-resolution particle-image fields. A double-pulsed, frequency-doubled Nd:YAG laser illuminates the flow and imaging of the fluorescence images of the particles (with an excitation peak at 530 nm and an emission peak at 560 nm) is accomplished using a specially-designed set of filters and a dichroic mirror onto a 12 bit interline-transfer CCD camera. A schematic of the PIV setup is shown in Figure 1.

Figure 1. Schematic of mPIV experimental setup.

Similarity between the electric field and velocity field exists for steady electroosmotic flow in arbitrary shaped microchannels, with uniform fluid properties and a channel system with uniform zeta potential and electrically insulated walls. This condition is expressed as, u(x,y) = -ezE(x,y)/m, and holds throughout the fluid volume for systems with thin Debye layers. The velocity may, in this simple case, be determined from the Laplace equation for the electric potential and the Navier-Stokes equations for the fluid motion need not be solved. Experimental validation of the similarity condition is demonstrated in Figure 2 where electric field lines are superposed on particle pathlines (streamlines for this steady flow).

Figure 2. Visualization of fluorescent particle pathlines for electrokinetic flow through an intersection. The particles are fluorescent polystyrene microspheres.

Figure 3. Mouseover figure to see typical seeded image pair for mPIV


Micron-Resolution Particle Image Velocimetry (mPIV) Flow Examples:

mPIV measurements of pressure-driven flow 



mPIV measurements of electrokinetic flow




mPIV measurements of field amplified sample stacking (FASS) velocity field



Click for Micro-PIV Reference Source Page

1.) Devasenathipathy, S. and Santiago, J.G., "Electrokinetic Flow Diagnostics",in Microscale Diagnostic Techniques Breuer, Kenneth S. (Ed.), pp 113 - 154, 2005, Springer Verlag

2.) Devasenathipathy, S., Santiago, J.G., Meinhart, C.D., and Wereley, S.T., and Takehara, K., "Particle Tracking Techniques for Microfabricated Fluidic Systems," Experiments in Fluids; April 2003; vol.34, no.4, p.504-14

3.)Devasenathipathy, S., Santiago, J.G., and Takehara, K.,"Particle Tracking Techniques for Electrokinetic Microchannel Flows," Analytical Chemistry; AUG 1 2002; v.74, no.15, p.3704-3713