Mass transfer in a viscous bubble column with forced oscillations

Previously, it was shown that low-amplitude (0.5-2.5 mm) oscillations at moderate frequencies (0-25 Hz) can be used to improve bubble column performance. Literature on pulsed-flow bubble columns has mainly focused on air-water systems. In the present work, the effects of oscillations on mass transfer in a pulsed-flow bubble column were studied for various carboxymethylcellulose solutions giving an effective viscosity range of 1-62 cP. As in our previous work on air-water systems, the viscous system exhibits an initial increase in mass-transfer coefficient as a function of frequency and then leveled to a plateau. This asymptotic behavior can be attributed to the Bjerknes force acting on a bubble, which slows the bubble rise as frequency is increased. The shape of the curve for mass-transfer coefficient vs frequency was unchanged for viscous systems, but the absolute value of the mass-transfer coefficient decreased as a function of increasing viscosity. A theory was developed from first principles to show how the volumetric mass-transfer coefficient changes as a function of operating parameters, such as the frequency and amplitude of vibrations, gas superficial velocity, and viscosity of the fluid. The comparison with experiments was quite good for a large range of velocities and viscosities.