| Abstract: | The overall gas hold up, EG, and bubble size distribution were separated into the particular gas hold up, EGK, and Sauter diameter. dSG. due to “small bubbles” as well as EGG and dSG, due to “intermediate to large bubbles.” Bubbles are defined to be “small” if they remain in the bubbling layer 15 seconds after the gas flow is turned off. The bubbles which leave the layer during this time are considered to be “intermediate to large bubbles.” The time dependences of EG EGK and EGG, as well as of bubble size distribution after initiating the aeration of the liquid, is investigated. The steady state EG, EGK and EGG, Sauter diameter and specific geometrical surface area of “small” and “intermediate to large” bubbles as well as of the entire bubble population were determined in bubble columns employing 50, 70, 90 and 95% glycerol solutions and perforated plates with different hole diameters (dH = 0.5. 1.0 and 3.0 mm) respectively. In highly viscous media the “small” and “very large” bubble fractions are high. A comparison of the specific geometrical bubble surface areas with the corresponding volumetric mass transfer coefficients, kLa's, measured earlier indicate that the “small” bubbles do not contribute to kLa. The influence of the “small” bubbles on the fluiddynamics of the two phase system is discussed. |
