Bubble dynamics and mass transfer characteristics from an immersed orifice plate

BACKGROUND: Bubble dynamics plays an important role in performance enhancement of multiphase reactor. The formation of the bubbles at the orifice is critical for the dynamics of bubbles and the mass transfer process during the rising stage. However, few studies have focused on the detailed changing characteristic of bubble formation and its relationship with mass transfer. RESULTS: The evolution of the bubble dynamics from millimeter to micrometer-sized immersed orifice plates is in situ visualized. Bubble inrush is observed from the orifices with diameters below 421 μm, resulting in significant fluctuation on the gas–liquid interface. The base of the leading bubble varies with the orifice diameter. Smaller orifice is preferred to produce more trailing bubbles with smaller size. The inrush time of the trailing bubble is prolonged with decreasing orifice diameter and increasing gas velocity. The inrush time and diameter of the latter trailing bubble are higher than the former at a certain gas velocity. The volumetric mass transfer coefficient (K_La) is obtained by measuring the bubble volume during the rising process using chemical absorption of carbon dioxide (CO₂) with sodium hydroxide (NaOH). Increasing gas velocity, decreasing orifice diameter and bubble inrush make an apparent positive impact on the K_La. CONCLUSIONS: The bubble inrush happens at micrometer orifice. Decreasing orifice diameter and increasing gas velocity are important to intensify oscillation of the leading bubble and increase the frequency of bubbles with high specific interfacial area, which are conducive to the enhancement of the volumetric mass transfer coefficient.