Measurement And Simulation Of Gas-liquid Two-phase Bubbly Flow In Structured Porous Medium

The hydrodynamic behavior of bubbly flow in bubble columns packed with structured packing is different from that in empty bubble columns. In order to investigate the hydrodynamic properties of bubbly flow in structured packing, three-dimensional Laser Doppler Velocimetry (LDV) was used to measure the liquid velocity distribution. Besides, the computational fluid dynamic (CFD) method was used to simulate the bubbly flow in structured packing.The experimental object was bubbly flow in Mellapak 350Y structured packing. The influence of gas flow rate and packing geometry on time-averaged velocity distribution was investigated. Three-dimensional Laser Doppler Velocimetry (LDV) was used to measure the liquid velocity surrounding the bubbles with different gas inlet flow rate. The experimental results show that the bubbles were disintegrated and dispersed by structured packing. Influenced by forces near interface, in vertical direction, the smaller the distance between liquid and bubbles, the larger the velocity of liquid was observed. As the gas flow rate increased, the region of liquid influenced by gas phase was enlarged, and this region tended to expand where the flow passage was becoming larger. The motion of bubbles also accelerated the horizontal flow of the liquid. The velocity at a fixed point near the bubble showed frequent fluctuation when time changed. The scale-wise power distribution was obtained after wavelet transform analysis of velocity time series. It was indicated that the motion of bubbles caused high frequency fluctuation in the liquid.For the complex geometry of structured packing and limitation of computational power, it is too difficult to simulate the bubbly flow in the whole structured packing. Simplified two-dimensional and three-dimensional physical models were constructed, whose geometries were similar to structured packing. The volume of fluid (VOF) method was used for unsteady simulation. In the proposed model, two source terms were added into the momentum transport equation to describe the effects of surface tension and interface interaction. The results of 2D model indicated that the bubbles rising in a chain oscillated and coalesced with increasing of gas inlet rate. The velocity of liquid surrounding the bubble increased and vortexes of different scale were observed. The velocity at a fixed point in liquid fluctuated more and more frequently as the gas inlet velocity increased. In three-dimensional unsteady simulation, the break-up of bubbles at criss-crossing section of the packing could be clearly observed in the animation of the bubbly flow. The velocity of the liquid surrounding bubbles was larger than other regions in the horizontal cross-section. Besides, the bubble trajectory changed when it passed through the criss-crossing section of the packing and liquid recirculation cells appeared in upper and lower locations. Both flow characteristics allowed for excellent transverse mixing and alleviated fluid back mixing.