Experimental study on 3D bubble shape evolution in swirl flow

Abstract

Evolution of bubble shapes has been a topic that never fades with time due to its close relation with physical processes such as fluid dynamics, heat and mass transfer, which are of fundamental and practical interest. Bubbles in swirl flow, especially, deform severely and take on a wide variety of irregular shapes resulting in great difficulties to obtain their morphological changes. Aiming to solve this problem in a reliable way, a virtual binocular stereo vision (VBSV) platform is set up, in which one camera is able to function as two cameras with the help of four mirrors. Corresponding reconstruction algorithm that assumes each cross section along the height of bubble to be an ellipse is established to compute 3D bubble shape. The unique bubble morphological evolution laws in complex swirl flow are obtained for the first time and the effects of swirl number (S), bubble diameter (d), Reynolds number (Re) and Morton number (Mo) on bubble shapes are investigated separately. Experimental results indicate that an ellipsoid bubble will be squashed and elongated gradually, and it tends to evolve into cap-shaped and cashew-shaped when approaching separator axial centre zone. Moreover, bubbles can undergo more severe deformation with greater S, d, and Re, whereas bigger Mo on the other hand weakens the deformation effect.