Application of micro particle shadow velocimetry μPSV to two-phase flows in microchannels

Micro particle shadow velocimetry (μPSV) is performed in the present study for simultaneous velocity measurement and interface tracking in both liquid-liquid and gas-liquid two-phase flows through circular microchannels of 500 μm diameter. The back-lit illumination using a non-coherent LED light source, combined with full refractive index matching of the liquid phases, the tube wall material and the channel exterior medium, allowed velocimetry to be done both within and around the liquid droplets, and even close to the interfaces and boundaries. Moreover, post-processing methods are proposed and implemented in order to resolve motion of isolated gas bubbles and immiscible liquid droplets in laminar flows quantitatively. In particular, simultaneous measurements of local instantaneous phase velocities and flow rates, liquid film dynamics and its thickness, shape and volume of the dispersed phase, and development length in front and at the back of the bubbles are obtained using one single sequence of gray scale shadowgraphy images. Such results are valuable for validation of corresponding numerical simulation codes. It is believed that this approach significantly reduces the size and cost of the experimental setup while increasing the accuracy and reliability of the measurements.