SIZE NUCLEI MEASUREMENT IN A CAVITATION TUNNEL BY DIGITAL IN-LINE HOLOGRAPHY
Résumé
Digital in-line Holography (DIH) is used to measure size and concentration of small bubbles (6-100 µm) in hydrodynamic facilities. The forward diffraction pattern produced by small objects (bubbles, droplets, particles) illuminated by a laser diode is directly recorded by a camera without objective lens. From this pattern, each image plane can be reconstructed by applying back-propagation formalism (Huygens-Fresnel Integral). Then, after having reconstructed the whole volume, the 3-D location and size of each particle can be measured. Here the wavelet transform is used for the implementation of Fresnel Integral. In the present case, nuclei are measured by a sampling probe specially designed for DIH measurements and equipped with transparent sections. A diverging beam coming from a fiber coupled laser diode (lambda=635 nm, P=12 mW) illuminates the sample volume and the hologram is recorded by a 1024 1280 CMOS camera. From each hologram the volume can be reconstructed slice by slice. We present here the method used for obtaining the size nuclei distribution extracted from hologram analysis. Statistical results (5000 holograms are recorded and processed) obtained under different pressures (P= 567, 927 and 1287 mbars) are compared and discussed.
Domaines
Sciences de l'ingénieur [physics]
Origine : Fichiers produits par l'(les) auteur(s)
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