Yu Yan’s research while affiliated with University of Shanghai for Science and Technology and other places

In this paper, a three-dimensional numerical simulation of the motion behavior of bubbles in complex porous medium channels in a large density ratio gas-liquid system is conducted based on the lattice Boltzmann method. The Eötvös number (Eo), contact angle (θ) and Reynolds number (Re) are systematically discussed with emphasis on the law of their coupling effect affecting bubble velocity, morphological evolution and stagnation phenomenon. The results show that the increase of contact angle will reduce the bubble velocity but intensify the velocity fluctuations, making the bubbles tend flat, while the increase of Eo number significantly suppresses the influence of the contact angle, stabilizes the bubble velocity, and makes its shape close to a bullet head shape. When the contact angle is large (θ>90°) and the Eo number is small (Eo<10), the adhesion force is significantly enhanced and the bubbles will stagnate inside the porous medium. Re number and contact angle compete in the generation of resistance, and have mutually reinforcing effects on the average velocity of bubbles and interface evolution. The larger contact angle makes the deformation of the bubble tail intensify and becomes unstable, and as the Re number further increases, the tail tentacles are more likely to break, forming residual bubbles. It is also found in this work that the coupling between Eo number and Re number significantly affects bubble behavior in motion and morphological evolution. Under the conditions of high Eo number (Eo≥25) and high Re number (Re≥14), the bubble velocity increases with the Eo number rising, and the trend becomes more significant as the Re number increases; while under the conditions of low Eo number (Eo<25) and low Re number (Re<14), the speed change pattern is completely opposite. This phenomenon is due to the high instability of bubble morphology under the conditions of high Eo number and high Re number, which affects the buoyancy and speed performance. The research results provide important guidance for optimizing the flow behavior of bubbles in porous medium.

Rising bubble systems in porous media exist in a variety of industrial processes. However, the flow characteristics of the issue are not well understood. In this work, the rising of bubble/bubbles through two types of porous structures, namely, in-line structured pore and staggered structured pore, are studied using a large density ratio lattice Boltzmann model. The effects of Eötvös number, pore shape, viscosity ratio, initial bubble number, and arrangement manner of the initial bubbles on the bubble deformation, bubble rising velocity, residual bubble mass, bubble perimeter, and the number of bubble breakups are investigated. It is found that as the Eötvös number increases, the bubbles are more easily broken during the process of passing through the porous media, the shapes of the sub-bubbles deviate from the original ones more and more, the bubble perimeter increases, and the difference between the bubble dynamics obtained by the in-line and staggered porous media decreases. Compared to the results of circular and rectangular pores, the bubble rising through the diamondoid pore has a more considerable deformation, which causes a slower rising speed. Furthermore, in the case that two bubbles are originally placed under the porous medium, the bubble deformation is greater and the bubble fracture times increase if the initial bubbles are aligned vertically. The findings of this work can contribute to the understanding of gas–liquid two-phase flow in porous media.