Measurement of the Dynamical Mass Transfer of a Single CO₂ Bubble Using LIF/HPTS Visualization and a Photoelectric Optical Fiber Probe

Gas-liquid two-phase flows are widely encountered in industrial plants such as chemical reactors, power plants, environmental plants and so on. It is essential to clarify the dissolution process of the bubbles and the structure of the gas-liquid two-phase flows for realizing the efficient operation of these industrial reactors. However, it is very difficult to clarify them because of their complexity. We made a challenge of clarifying them in detail. First, we discuss the dynamical processes of the mass transfer from a zigzagging CO₂ bubble of 2.9 mm in equivalent diameter by using three measurement methods (i.e. LIF (laser induced fluorescence)/HPTS (8-hydroxypyrene-1, 3, 6-trislfonic acid), PIV and a newly developed photoelectric optical fiber probe: POFP) effectively and mutually-complementarily. We directly visualized the dynamical mass transfer process from a zigzagging CO₂ bubble to the surrounding liquid by using LIF/HPTS. We measured the surrounding liquid motion induced by the bubble buoyancy using PIV. We visualized a high-CO₂-concentration thin layer around the bubble was transported to the bubble rear and accumulated into the horseshoe-like vortices. The clear horse-shoe-like vortices were observed just after the launch of the bubble from a needle. Then, the wreckage of the bubble wake was transported widely into the surrounding liquid by the buoyancy driven flows. We measured directly the CO₂ concentration profile inside the bubble wake by using POFP. We succeeded in clarifying the profile of the CO₂ concentration inside the bubble wake, which is difficult to obtain from only the LIF/HPTS method. From this result, we obtained that the CO₂ concentration takes the maximum at the center region of the bubble wake and sharply decreases toward the outer edge of the bubble wake. Second, we simultaneously measured the diameters and velocities of the bubble by using POFP. We confirmed the performance of the POFP; the results via POFP were compared with those obtained from the visualization of the bubbles by using a high-speed video camera. We demonstrated mutually-complementary use of three measurement methods is very effective to experimentally understand the dynamical processes of the mass transfer from a zigzagging CO₂ bubble to the surrounding liquid.