Characterization of Gas-Liquid Flows in Rectangular Bubble Columns Using Conductivity Probes VIVEK V. BUWA AND VIVEK V. RANADE Industrial Flow Modeling Group, National Chemical Laboratory, Pune, India Unsteady gas-liquid flows in bubble columns are comprised of various flow processes occurring with varying length and time scales and govern mixing and transport pro- cesses. In the present work, we have characterized dynamic and time-averaged properties of gas-liquid flows in rectangular bubble columns using conductivity probes. The development of a single-tip conductivity probe, data processing method- ology, and photographic validation procedure is discussed in detail. The effect of superficial gas velocity and aerated liquid height-to-width (H=W) ratio on voidage fluctuations and time-averaged gas holdup was investigated. The experimental data presented here can help in understanding the dynamics of various flow processes and validating computational fluid dynamics based models. Keywords Bubble column; Gas-liquid flows; Gas holdup; Voidage fluctuations Introduction Bubble columns are widely used in the chemical process industry. Dispersed gas- liquid flow in a bubble column is quite complex and comprised of a variety of flow processes occurring with different length and time scales. Macroscopic low- frequency oscillations (with typical characteristic frequencies less than 1 Hz) are gen- erated by the meandering motion of bubble plume and are comprised of ascending and descending vortical structures with dimensions of the order of the reactor diam- eter. On the other hand, bubble-scale flow processes (vortices shed by bubbles, flow around individual bubbles, bubble-bubble interaction) have very different character- istic length and time scales. The overall dynamics is a result of interactions between these flow processes. The unsteady fluid dynamics govern mixing and other trans- port processes occurring in bubble column reactors and is interrelated in a complex way with design and operating parameters like reactor configuration, sparger, and gas flow rate. In the past several years, attempts have been made to develop computational models for a priori prediction of the dynamic and subsequently the time-averaged flow properties of gas-liquid flows in bubble columns. In the past, most of the mod- eling efforts were focused on simulating the low-frequency oscillations by solving the Reynolds-averaged Navier–Stokes equations (Buwa and Ranade, 2002 and refer- ences cited therein). The model predictions were validated using the measured characteristic frequency of low-frequency oscillations ( <1.0 Hz) and time-averaged Address correspondence to Vivek V. Ranade, Industrial Flow Modeling Group, National Chemical Laboratory, Pune 411 008, India. E-mail: vvranade@ifmg.ncl.res.in Chem. Eng. Comm., 192:1129–1150, 2005 Copyright # Taylor & Francis Inc. ISSN: 0098-6445 print/1563-5201 online DOI: 10.1080/009864490522704 1129