Influence of viscosity and surface tension on bubble aspect ratios in bubble swarms: A new correlation

Bubble columns have been used and widely investigated for many decades because of their numerous advantages in operation and design compared to other multiphase reactor types. Their structure is simple, but the flow generated in the reactor is quite complex, and precise correlations for the prediction of nonadjustable parameters are needed for numerical simulations and modeling. For this reason, experimental bubble aspect ratio data from the literature and our own measurements in bubble swarms were analyzed in this study. The investigated experimental data cover a viscosity range of 0.86–9.29 mPa·s and a surface tension range of 44.8–72.24 mN/m and accordingly, a Morton number range of 1.7×10⁻¹¹–7.0×10⁻⁷. Utilizing bubble aspect ratios, determined for approximately 1 million bubbles in each of the specific operational cases investigated, a new correlation is proposed for the bubble aspect ratio of CO₂ bubbles in liquids without and with surfactant. It is based on the Eötvös and Morton numbers, which determine the rising behavior of bubbles in a column. This correlation is validated with data from the literature (Besagni and Inzoli, 2019; Liu et al., 2021b; Ziegenhein and Lucas, 2017; Ziegenhein et al., 2018). It is shown that for viscosities and surface tensions in the validation range of this study, the correlation performs well and allows the determination of spheroidal bubble aspect ratios as a function of the gas and liquid characteristics of the specific experiment.