Effect of superhydrophobic surfaces on bubble column flow dynamics. (March 2023)

• Record Type: Journal Article
• Authors: Rodriguez, Angel F.; Mäkiharju, Simo A.
• Is Part Of: Flow measurement and instrumentation. Volume 89(2023)
• Publication Date: 2023-03
• Subjects: Bubble column -- X-ray Computed Tomography -- Multiphase flow -- Superhydrophobic surfaces; Fluid dynamic measurements -- Periodicals; Flow meters -- Periodicals; Fluides, Dynamique des -- Mesure -- Périodiques; Débitmètres -- Périodiques; 681.2805
• DOI: 10.1016/j.flowmeasinst.2022.102299
• Languages: English
• ISSNs: 0955-5986

Abstract

Abstract: Bubbly flow in bubble column reactors promotes mixing necessary for many chemical processes. We show that if superhydrophobic-coated material is introduced into a bubble column, there can be a substantial difference in gas holdup and earlier initiation of churn-turbulent flow which can alter larger-scale mixing without a need to change the superficial gas velocity. Addition of superhydrophobic surface can also cause bubbles to (directly or indirectly assisted by the surface) escape faster to the free surface resulting in a reduced void fraction (i.e., reduced gas holdup). As the flow becomes optically opaque at few percent gas phase volume fraction, we utilize two dual plane wire mesh sensors to obtain velocity profiles and bubble size distributions, in addition to the traditional pressure and level based gas holdup measurements to calculate average phase fraction. Additionally, a custom build photon-counting dual energy threshold X-ray computed tomography system is employed to get a higher resolution measurement of the time average phase fraction non-intrusively. We report satisfactory agreement between these techniques with differences arising for understood reasons, and use the insight thus yielded to discuss the effect of superhydrophobic surfaces on bubble column flow dynamics. Graphical abstract: Highlights: Five phase fraction measurement techniques are compared to characterize flow in a bubble column. Introduction of superhydrophobic coating is found to significantly reduce the gas hold up. Photon-counting dual energy threshold detector is utilized for X-ray computed tomography.