Experimental analysis of the effects of liquid phase surface tension on the hydrodynamics and mass transfer in a square bubble column

International audienceThe effects of liquid surface tension were investigated on gas-liquid interfaces in bubbly flows through the analysis of hydrodynamic and mass transfer features. Tap water and aqueous solutions with two types of surfactant (cationic and anionic) are used as aqueous liquid phases. In fact, these surfactants are organic collectors consisting of an amine and ester. The influences of surfactant concentration and superficial gas velocity on the volumetric mass transfer coefficient and the gas holdup were highlighted. The experimental findings revealed that although the two surfactants tested generated a decrease in surface tension, their effects on gas holdup and flow regimes are very different. First, it was observed that the gas holdup in amine aqueous solutions was very close to that in tap water, but it increased once the superficial gas velocity was above 7 cm.s-1. Conversely, the presence of ester decreased the overall gas holdup since bubble net coalescence was enhanced, and the heterogeneous flow regime prevailed above 2.9 cm.s-1. Thus, the homogeneous regime prevailed with superficial gas velocity less than 4.4 cm.s-1 for tap water and amine aqueous solution, which corresponds to the transition point. Experimental findings exhibited also that the power spectral density of pressure fluctuations is a convenient tool to identify the prevailing flow regimes even in surfactant aqueous solutions. Besides that, both organic surfactants strongly reduced the volumetric mass transfer coefficient in comparison to tap water, mainly by inducing an additional resistance to gas-liquid mass transfer through interfacial adsorption for the cationic amine, but by promoting bubble coalescence for the anionic ester aqueous solution