Visualisation of gas-liquid mass transfer around a rising bubble in a quiescent liquid using an oxygen sensitive dye

Abstract

21An approach for visualizing and measuring the mass transfer around a single bubble rising in a 22 quiescent liquid is reported. A colorimetric technique, developed by using 23 an oxygen sensitive redox dye was implemented. It was based on the reduction of the 24 colorimetric indicator in presence of oxygen, this reduction being catalysed by sodium 25 hydroxide and glucose. In this study, resazurin was selected because it offered various reduced 26 forms with colours ranging from transparent (without oxygen) to pink (in presence of oxygen). 27These advantages made it possible to visualize the spatio-temporal oxygen mass transfer around 28 rising bubbles. Images were recorded by a CCD camera and, after post-processing, the shape, 29 size, and velocity of the bubbles were measured and the colours around the bubbles mapped. A 30 calibration, linking the level of colour with the dissolved oxygen concentration, enabled colour 31 maps to be converted into oxygen concentration fields. A rheoscopic fluid was used to visualize 32 the wake of the bubbles. A calculation method was also developed to determine the transferred 33 oxygen fluxes around bubbles of two sizes (d = 0.82 mm and d = 2.12 mm) and the associated 34 liquid-side mass transfer coefficients. The results compared satisfactorily with classical global 35 measurements made by oxygen micro-sensors or from the classical models. This study thus 36 constitutes a striking example of how this new colorimetric method could become a remarkable 37 tool for exploring gas-liquid mass transfer in fluids. 38 39 40 41

Bubble dynamics and mass transfer characteristics from an immersed orifice plate

“…The bubble waiting time is shortened while the departure time is prolonged with the increasing gas velocity. Similar phenomenon has been reported by Dietrich et al . It is noted that within the scope of the experiment, the waiting time of the bubble changes from 4 to 96 ms, while the bubble departure time is only changed within 5 ms.…”

Hydrodynamics and gas-liquid mass transfer around a confined sliding bubble

“…This dissymmetry between the reaction times makes the method very suitable for high-speed imaging experiments. The physicochemical parameters of the solutions have been thoroughly analyzed [12,36,38].…”

Characterization of Bubble Shapes in Non‐Newtonian Fluids by Parametric Equations

“…1). After testing several functions, the following correlation was proposed to fit the experimental data: b ¼ n À 0:11De 0:19 Eo 0:11 þ 0:80 (16) This equation is correlated to the result depicted in Fig. 10 as b decreases monotonically with high De and Eo numbers and the shear-thinning levels.…”

“…It is generally agreed that non-Newtonian fluids have complex rheological properties (e.g., shear thinning, viscoelasticity, etc.) leading to a variety of bubble shapes, such as teardrop or elongated bubbles [13][14][15][16][17][18].…”