| Many techniques have been developed for measuring convective flow velocities in liquids such as LDV, PIV, molecular tagging velocimetry, etc. A little-used method that is in principle much simpler than the aforementioned techniques is Photobleaching Velocimetry. A particularly attractive feature of this technique is that a single beam may be used for both tagging and probing, though for some applications separate beams may be desirable. A significant weakness of PV is that typically high laser power is needed to obtain sufficient photobleaching that significant contrast between low-velocity (highly-bleached) and high-velocity (less-bleached) regions can be obtained.;Recently, it was discovered that this disabling of fluorescence does not occur in the absence of light and is a kinetically controlled process in the presence of light, and is reversible on a much longer time scale, thus the photobleaching solutions are re-usable. Furthermore, the laser intensity per unit volume of photobleached solution with the laser path is on the order of a few mW/cm3, thus no significant heating of the water occurs.;The circular pipe and Taylor-Couette flows were tested to test the viability of dithionite-sensitized photobleaching as a velocimetry tool. As results of experiment, the relationship between fluorescence intensity and the known local velocity was nearly linear for a circular pipe flow. However, the observed relation was a linear, but not matched well due to wall curvature for the TC flow. To analyze this result, the numerical simulation was studied. According to this numerical analysis, the bleaching rate coefficient, fluoresced light coefficient and Gaussian beam width were found. The bleaching rate coefficient was matched very well with experiment result. So, if we assume the velocity with given coefficients or we know the intensity, the intensity will be estimated or the velocity will be calculated using this velocimetry.;In future studies, the utility of this photobleaching velocimetry will be tested in a turbulent pipe flow, the 4-roll mill and TC flow with a minimized curvature effect. If these studies further confirm the viability of the technique, it may emerge as a simple, easily interpreted alternative to LDV or PIV in many liquid-flow velocimetry applications. |
