Using classical backlighting techniques and often a telecentric configuration, a direct visualisation of bubbles or droplets is possible.
A compilation of several images showing an ascending bubble. An experimental set-up and a data post-treatment method were developed in order to analyze the dynamics and the morphology of bubbles rising freely in liquids. The set-up was used to generate single ellipsoidal bubbles in a water–glycerol mixture and to analyze their dynamics and their morphology for Eötvös numbers between 0.8 and 8 and Morton numbers between 10−11 and 10−7. For instance, it was rigorously shown that the minor axis and the mass center velocity vector of a bubble are aligned in the cases of a zigzag and a helical motion of the bubble. More information can be found here: http://bit.ly/2aZwdY2.
A dense bubble cloud generated by a porous medium used for water ozonation. Advanced ellipse recognition algorithms have been develop that allow an extraction of the relevant size and ellipticity distributions from such images. More information can be found here: http://bit.ly/2b0MpCv