An experimental study of the dynamics and mass transfer of a rising bubble

Abstract

In this work, the rise characteristics of shrinking CO2 and non-shrinking N2 bubbles in distilled water for a wide range of bubble sizes in ellipsoidal and wobbly regime (deq = 1.5 mm to 6.5 mm) have been investigated. For these bubbles, their size, trajectory, and rise velocity have been measured using a moving camera system, while the dissolved CO2 is qualitatively studied using a planar laser-induced fluorescence (P-LIF) technique. We explore the interplay between hydrodynamics and mass transfer using well-studied regimes in bubble behaviour. Our results show that the interrelation between mass transfer and bubble rise dynamics is quasi-steady in nature and strongly dependent on wake-induced effects: shape and path oscillations. Based on an analogy of the two phenomena, we conclude that the behaviour of smaller bubbles (<2 mm) as immobile spheres from a mass transfer perspective is not related to the mobility of the interface, but a lack of surface renewal of dissolved gas at the interface. We propose a mechanistic correlation for calculating the mass transfer coefficient, kL, in this regime of bubble size, using the knowledge of the drag coefficient.