International Journal of Multiphase Flow, Vol.112, 63-82, 2019
Impact of heat exchanging internals configurations on the gas holdup and bubble properties in a bubble column
The effect of the vertical heat-exchanging tube bundle configurations on local gas holdup and bubble dynamics, including specific gas-liquid interfacial area, bubble chord length, bubble rise velocity, and bubble passage frequency have been studied using the 4-point optical fiber probe technique. Two different tube bundle configurations were investigated, circular tube bundle and hexagonal tube bundle. 30 internal tubes, each with a diameter of 0.5 inches (0.013m), were used in each configuration occupying 25% of the column cross-section area to represent the heat exchanging tubes utilized in the Fischer-Tropsch process. The experimental work was performed in a 0.14m inner diameter Plexiglas bubble column using an air-water system. The applied superficial gas velocities were based on the free cross-sectional area of the column available for fluid flow and were in the range of 0.02 to 0.45 m/s covering bubbly, transition, and churn turbulent flow regimes. Although the size and the number of the tubes in both configurations were similar, their effects on the hydrodynamics were found to be different. When compared to bubble column without internals, the circular tube bundle showed a significant increase in the local gas holdup in the core region and a decrease in the wall regions. Simultaneously, a substantial increase in the bubble chord length and bubble velocity was seen. Another important observation was the decrease in the interfacial area while using circular tube bundle. A distinct asymmetrical effect on the radial profiles of gas holdup and the specific interfacial area was observed when the hexagonal configuration was used. The gas holdup and interfacial area significantly increased on one side of the column and decreased on the other side. The bubble chord length and bubble rise velocity decreased, exhibiting a narrower distribution with smaller values, in comparison to the bubble column without internals. Published by Elsevier Ltd.