Simultaneous measurements of bubble deformation and breakup with surrounding liquid-phase flow

The tomographic particle image velocimetry (PIV) method and the pulsed shadow technique (PST) are combined to measure the three components of velocity and the 3-D bubble morphology simultaneously within a volumetric space. The innovative experimental setup is made up of 3 cameras, optical splitters, LED arrays and volumetric laser illumination. Multiplicative algebraic reconstruction technique (MART) is adopted to reconstruct particle positions in the volume space. And the 3-D bubble morphologies are reconstructed by both the visual hull method and the binocular stereo vision method. The reconstructed bubbles are then used to remove the ghost particles induced from refraction interference in the transparent bubble. The techniques are demonstrated in two cases: a) rising bubbles in a stagnant water tank; b) bubble breakup in the complex flow such as venturi bubble generator (air bubble breakup in water; Mo = 2.5 × 10 –11 ). Results indicate that the visual hull method always overestimates the bubble volume due to the restriction of the camera setup. And the binocular stereo vision with ellipse fitting on each slicing can obtain relatively reasonable reconstruction results for both ellipsoidal and plicate bubbles. Both methods cannot get the detailed information on the surface of larger bubbles. Although the present methods cannot track the interface and the velocity around the vectors around the bubble accurately, the proposed method in the paper is capable of estimating the bubble shape evolution and the turbulent stress on the bubble simultaneously. Based on the method, the critical Weber number for bubble breakup is estimated at about 3. Graphical Abstract