Micro-Scale Velocity Measurements Using Molecular Tagging Velocimetry: Methodology and Uncertainty

Micro-scale fluidic devices are now being designed and manufactured for a host of new applications, and it is certain that new applications will emerge. There is, therefore, a need for increased understanding of the momentum transport phenomena at this scale to aid in the understanding, and design and optimization of such devices. This need is behind the development of new techniques for making flow measurements at the micro-scale. Molecular Tagging Velocimetry (MTV) is a laser-based non-intrusive technique for obtaining detailed measurements of velocity profiles. This paper reports on the extension of the method to microtubes of inside diameter of order 100 µm. Fully developed velocity profile measurements are reported here for a Reynolds number of about 140 in a capillary of inside diameter 148 µm. Two image analysis techniques were compared—the line center method, and the correlation method. It was found that the correlation method produced better results and smaller overall uncertainty. Volumetric flow rate determined from integration of the measured velocity profiles agree with accumulation measurements made over a specified time interval to within 3%; the agreement was usually 1–2%. This work reports on the difficulties encountered in applying MTV at these physical scales, the influence of measurement and analysis parameters on results, and the uncertainty associated with measurements.