Transient flow structure in the entrance region of a bubble column using particle image velocimetry

The transient flow phenomena in the entrance region of a three-dimensional bubble column system were investigated over the dispersed bubble and coalesced bubble regimes. Two different gas distributors (porous plate and perforated plate) were studied to elucidate their effects on the overall hydrodynamic behavior of the system and on the hydrodynamic behavior of the entrance region. The instantaneous and averaged How information was obtained through the use of a Particle Image Velocimetry (PIV) system. The PIV system is a non-intrusive technique capable of simultaneously providing the full-field flow information of both the gas and liquid phases. The overall gas holdup of the bubble column system was used to demarcate the flow conditions, in order of increasing gas velocity, into the dispersed bubble regime and the coalesced bubble regime which consisted of the vortical-spiral and turbulent flow conditions. The instantaneous flow fields and averaged liquid velocity and gas holdup profiles obtained through the PIV system provide a better understanding of the mechanisms responsible for the development of the flow in each regime. The averaged results were also used to determine the length required for the flow to become fully developed. The results show that the entrance effects are significant in the dispersed bubble regime but diminish with increasing velocity in the coalesced bubble regime, represented by the vortical-spiral and turbulent flow conditions.