Mixing Phenomena in Gas Stirred Liquid Systems

Abstract

Extensive investigations were carried out to determine the mixing time (tm) in bubble columns with diameter of 0.2, 0.3, 0.4 and 0.8 m equipped with different type of spargers for different aspect ratios (H/D) of 0.8–8. The superficial gas velocity (Ug) varied from 0.01 to 0.25 m/s. The effect of temperature variations in the range of 20–90°C and surface tension variations (50–70 N·m) on tm was investigated. Experiments proved that as Ug increased, tm decreased in the homogenous regime and leveled off in the heterogeneous regime in tap water systems at ambient and elevated temperatures. There existed a critical aspect ratio (H/D)cri = 2 where tm varied with H/D reversely. The sparger configuration had a weak effect on tm. By placing the gas distributor pipe at the off centered position, tm could be decreased. In acetic acid solution, there existed a “jump point” in the tm vs. Ug curve at Ucri = 0.1 m/s, and tm was 2–3 times that in the tap water system at this point under otherwise identical conditions. The effect of temperature was determined by distinguishing the test temperature into a far from the boiling point stage and a near the boiling point stage. tm decreased marginally in the former stage and drastically in the latter. The surface tension had no notable effect on the liquid phase mixing behavior. Empirical tm correlations were proposed for various pipe distributors by considering the effect of (H/D)cri.