Hydrodynamic Characteristics of Two-Phase Systems in Tapered Bubble Columns

Abstract

A tapered bubble column (TBC) features a cross-section that gradually expands along its height, forming a distinct type of bubble column reactor. Such geometry promotes intensive mixing and broader particle size dispersion compared with conventional cylindrical columns. This work experimentally investigates the hydrodynamic characteristics of gas bubbles in a tapered column. The reactor, 1.8 m in height, has a diameter expanding from 0.07 m at the base to 0.17 m at the top. Underneath the mixing chamber, there is a perforated sinter element with an average pore size of 1 mm. The test program maintained consistent temperatures for both the air and the liquid. Two tips on a modified electroconductivity probe (to improve reading accuracy) and a high-speed digital camera formed the basis of the bubble monitoring and analysis method (BMAS). Three axial sites, Z/D = 4, 15, and 25 m, with radial velocity ranges of 0.002-0.016 m/s, 0.001-0.01 m/s, and 0.001-0.008 m/s, respectively, were studied under the following conditions: air-water and air-0.5M NaCl solutions with a liquid flow rate of 200 l/hr and superficial gas velocity. All other factors remained the same. Bubble coalescence rate, bubble rise velocity, gas hold-up, and bubble diameter were enhanced when the surface gas velocity was increased. Increases in salt content caused a reduction in bubble diameter from 3 to 2 mm in the air-water and air-brine systems studied.