Experimental investigation on the influence of surfactant concentration on the bubble shape and mass transfer in a small channel


Experimental investigation on the influence of surfactant concentration on the bubble shape and mass transfer in a small channel

Haghnegahdar, M.; Boden, S.; Hampel, U.

In the work presented in this paper, the shape and absorption rate of an individual elongated Taylor bubble of CO2 through contaminated water was measured in millimeter-size channel. The influence of concentration of surfactant on dissolution rate of an individual elongated Taylor bubble of carbon dioxide in water was investigated using high resolution X-ray radiography technique in vertical channels. The bubbles were held stationary in the down-flowing liquid and the liquid-side mass transfer coefficient was determined from microfocus X-ray images.
The experiments cover a range of initial bubble equivalent diameter (deq: sphere-volume equivalent bubble diameter) varying from 6 to 10 mm. The pipe is a glass pipe with 6 mm inside diameter (D). The bubble is unceasingly monitored by holding the bubble stationary using downward flow of liquid. The X-ray method was chosen since it is not dependent on the refractive index; therefore it is the most accurate method in comparison with other conventional optical techniques. This technique was qualified to disclose the three-dimensional shape of Taylor bubbles in capillary and enabled the acquisition of a series of high-resolution radiographic images of nearly stationary Taylor bubbles (Haghnegahdar et al., 2015). The processed images which give volume (and also the interfacial area) of the bubble with high accuracy as a function of time, are used to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation. The liquid phase is milli-pore water contaminated by conventional surfactants and the gas phase is CO2.
The results confirmed the accumulation of surfactants on the tail of the bubbles. Furthermore, applying different concentrations of surfactant reveals that in our case, where surface coverage ratio of surfactant on the bubbles is high, increase of contamination does not have a noticeable influence on the mass transfer coefficient of bubbles.

Keywords: Surfactant concentration; Taylor bubble; Mass transfer coefficient

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    14th Multiphase Flow Conference and Short Course:Simulation, Experiment and Application, 08.-10.11.2016, HZDR, Dresden, Germany

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Publ.-Id: 24441