Experimental study and CFD simulation of the multiphase flow conditions encountered in a Novel Down-flow bubble column

Abstract

The present work reports the experimental and CFD investigations of a Novel Down-flow bubble column to understand the flow characteristics. A novel mechanism of gas-liquid injection has been used to generate a high concentration of micro-bubbles with uniform distribution in a column of large cross-section (0.3 m diameter). Gas hold-up is obtained using three different measurement techniques: Phase isolation method, pressure transducer method and Gamma Ray Densitometry. Bubble size is measured using a high-speed camera-borescope assembly. A 3D Euler-Euler CFD model has been employed to simulate the flow behavior inside the column at different operating conditions. Due to the huge disparity in the formulation of the drag laws available for the simulation of bubbly flows in the Euler-Euler framework, a drag modification factor is used to improve the accuracy of the CFD simulations. The experimental results confirmed the bubble size to be in the micro-bubble range (300–800 µm) and also indicated a flat radial gas hold-up profile in the downstream section of the column for all operating conditions. CFD analysis revealed the flow pattern in the downstream section to be pure down-flow with no liquid re-circulations for the majority of operating conditions (VG = 2.5–18 and VL = 58–75 mm/s), and mild circulations were found only at extreme operating conditions with very low/high gas injection rates relative to the liquid injection rate. Both experiments and CFD results demonstrate that the novel gas-liquid injection mechanism is capable of producing a high concentration (up to 54% gas hold-up) of micro-bubbles (300–800 µm) with no liquid recirculation in a column of larger cross-section.