Chapter 8 - Characterization techniques

Abstract

This chaper summarizes key diagnostics techniques for characterization of micromixers. Since both velocity field and concentration field are important for good mixing, diagnostics techniques for these fields are the focus of this chapter. The quantification of the extent of mixing is important for the evaluation of performance as well as the design optimization of micromixers. Optical microscopy is the key tool for characterizing micromixers. It offers a noninvasive means of measurement in microscale. Together with digital cameras and digital image processing, a number of measurements in micromixers can be carried out with optical microscopy. Optical microscopy works with the electromagnetic spectrum, which is visible to the human eye. A typical human eye responds to wavelengths in air from 400 to 700 nm. The corresponding wavelengths in other media are reduced by a factor of the refractive index. One of the main challenges in characterizing of micromixers is the two-dimensional nature of fluorescent measurement with a camera/microscope system. The use of mixing index and probability distribution function (PDF) is based on statistical evaluation of tracing fluorescent dyes. These methods are suitable for micromixers with flat channels, where the concentration distribution along the view direction is negligible. Thus, the use of a two-dimensional camera/microscope system is justified. For cases with concentration distribution along the view direction, measurement would only be possible with the more expensive laser scanning confocal microscope system.