Particle Image Velocimetry techniques coupled with advanced Image Processingtools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas-liquid contactors.In this work, an effective experimental technique for measuring local gas hold-up andinterfacial area, as well as bubble size distribution, is discussed. The technique, hereafter referred to as Laser Induced Fluorescence with Shadow Analysis for Bubble Sizing (LIF-SABS) is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipmenttypically available within PIV set-ups. The liquid phase is made fluorescent by a suitable dye, andan optical filter is placed in front of the camera optics, in order to allow only fluoresced light to reach the camera CCD. In this way bubbles intercepted by the laser sheet are clearly identified thanks to the neat shade resulting in the images. This allows excluding from subsequent analysis allbubbles visible in the images but not actually intercepted by the laser sheet, so resulting in better spatial resolution and data reliability.When trying to analyze image information the problem arises that bubble sizes are generally underestimated, due to the fact that the laser sheet randomly cuts bubbles over non-diametrical planes, leading to an apparent bubble size distribution even in the ideal case of single sized bubbles.Clearly in the case of bubbles with a size distribution the experimental information obtained is affected by the superposition of effects. A statistical correction for estimating local gas hold-up andspecific interfacial area from relevant apparent data as obtained by laser sheet illumination and image analysis is discussed and applied to preliminary experimental data obtained in a gas-liquid stirred vessel.
|Numero di pagine||15|
|Stato di pubblicazione||Published - 2010|