# Experimental Investigation on the Dynamic Characteristics of Bubble-in-Chain Near a Vertical Wall
###### Abstract  
The motion of near-wall bubble-in-chain, which is a crucial aspect of the study of near-wall bubble flows, involves not only the wall effect but also the interactions between bubbles. However, there have been few studies on this topic. In this study, we investigated the motion of near-wall bubble-in-chain using a dual-camera orthogonal shadow method and tracked bubbles using image processing and feature matching techniques. Considering both the wall effect and bubble generation frequency, we discussed the statistical characteristics, motion modes, dynamic characteristics, and energy evolution of bubbles. The results demonstrate that an increase in bubble generation frequency leads to a greater deviation of bubble trajectories from the wall and an increase in trajectory amplitude while weakening the suppression of bubble speed by the wall. Furthermore, changes in both bubble equivalent diameter and drag coefficient reveal how bubble generation frequency affects their shape stability during motion as well as regulation by the wall effect. The drag coefficient decreases with increasing Reynolds number for bubbles; however, an increase in bubble generation frequency broadens its distribution range. Additionally, it is evident that the wall effect significantly impacts drag characteristics for bubbles: uncollided bubbles experience increased drag coefficients with greater distance from the wall while collided bubbles exhibit decreased drag coefficients. In cases of high generation frequency, the conversion of kinetic energy to surface energy during bubble collisions, especially the enhancement of the peak of surface energy, indicates an increase in the bubble's energy storage capacity and energy conversion efficiency. The findings not only enhance comprehension of behavior exhibited by near-wall bubbles but also offer a novel perspective for regulating near-wall bubble flows in industrial applications. s 2024 2024 14 6076 10  
bubble and the wall have minimal impact on migration behavior when there is no direct contact with the wall [5]. Under the traditional condition of a non-slip wall, the influence of the wall is typically manifested as energy dissipation. In comparison to free rising bubbles, both the amplitude and wavelength of the bubble decrease. This phenomenon is commonly attributed to wall interference, resulting in additional energy dissipation during transfer. Near a porous wall, the energy loss remains independent of the initial distance between bubbles. However, for hydrophobic walls, energy loss is directly related to the bubble-wall distance and causes upward sliding along the wall [1]. Furthermore, the bubble profile can be significantly influenced by wall hydrophobicity, subsequently affecting bubble dynamics during ascent [10]. [PERSON] et al. [11] investigated bubble motion near a screen wall and observed minimal impact on bubble motion type with varying initial distances from the wall. The presence of a wall influences the distribution of the flow field around a bubble, resulting in an asymmetric flow pattern. This asymmetry induces a gradient change in the pressure distribution surrounding the bubble, thereby generating a pressure differential on either side of it. This pressure difference serves as the direct driving force for the lateral migration of the bubble. Simultaneously, the existence of a wall also introduces additional resistance to the bubble, augmenting the opposing force during its ascent. The direction of lift force experienced by the bubble is not fixed but varies with both Reynolds number (_Re_) and distance between the bubble and wall [12; 13]. The movement of bubbles is influenced by dimensionless numbers, particularly the Reynolds number (_Re_) and Weber number (_We_). The force exerted on a single spherical bubble near a wall is correlated with _Re_. At low (_Re_ < 100), the bubble predominantly experiences an inward-directed lifting force towards the wall.