Interface mass transfer and properties of bubbly flows in a column with Newtonian and non-Newtonian liquids

The mass transfer of gas–liquid systems is commonly reported through the volumetric mass transfer coefficient, kLa, which is a function of several complex phenomena. To optimize the rate of mass transfer, increased knowledge about the individual effects of the interfacial area, a, and the liquid-side mass transfer coefficient, kL, on kLa is necessary. In this study, kLa was measured by monitoring the dissolved oxygen concentration in a bubble column. The bubble flows were recorded by a photographic method and the images were analyzed by means of artificial neural network to determine the bubble size. The effects of rheology, superficial gas velocity, and gas sparger design were analyzed. kL decreased with an increase in the superficial gas velocity and with an increase in the viscosity. The relative change in a was much larger compared to the relative change in kL, and hence, for the investigated operational conditions and liquid solutions, the change in kLa was mainly attributed to the change in a. Bubble clusters were formed in the non-Newtonian solutions but for the given operating conditions and liquid solutions, the bubble cluster formation did not have a prominent effect on the mass transfer.