Preferential Paths of Air-water Two-phase Flow in Porous Structures with Special Consideration of Channel Thickness Effects.

Accurate understanding and predicting the flow paths of immiscible two-phase flow in rocky porous structures are of critical importance for the evaluation of oil or gas recovery and prediction of rock slides caused by gas-liquid flow. A 2D phase field model was established for compressible air-water two-phase flow in heterogenous porous structures. The dynamic characteristics of air-water two-phase interface and preferential paths in porous structures were simulated. The factors affecting the path selection of two-phase flow in porous structures were analyzed. Transparent physical models of complex porous structures were prepared using 3D printing technology. Tracer dye was used to visually observe the flow characteristics and path selection in air-water two-phase displacement experiments. The experimental observations agree with the numerical results used to validate the accuracy of phase field model. The effects of channel thickness on the air-water two-phase flow behavior and paths in porous structures were also analyzed. The results indicate that thick channels can induce secondary air flow paths due to the increase in flow resistance; consequently, the flow distribution is different from that in narrow channels. This study provides a new reference for quantitatively analyzing multi-phase flow and predicting the preferential paths of immiscible fluids in porous structures

Hydrodynamics of Gas-Liquid Bubble Columns and Air-Lift Loop Reactors: Experiments and Numerical Simulations

International audienceIt is generally accepted that a key to improvements in the modeling of gas-liquid reactors is a realistic description of two-phase flow. One of the main unresolved problems is the modeling of turbulence in the continuous phase. In the majority of publications on numerical simulations of stationary two-phase flows, the standard k-epsilon model developed for single-phase flows has been used. The general applicability of this model to instationary two-phase flows is however disputed. In our last contribution on the ISCRE-15, we discussed the above question with the example of a locally aerated, flat bubble column. The results showed that it is possible to obtain a realistic dynamic solution with the k-epsilon turbulence model. It was however obvious that the general applicability of the 3D k-epsilon turbulence model to the dynamic simulation of bubbly flows needed further validation for a large spectrum of test cases of turbulent gas-liquid flows. A series of new test cases for symmetrically aerated, empty bubble column with different aspect ratios will be presented in this contribution. The comparison of detailed experiments and flow simulation results will be given. Another important unresolved problem is the modeling of the turbulence induced by the gas phase. In the test cases of locally aerated, flat bubble colums mentioned above, the gas phase occupied only a very small part of the reactor, and the influence of the bubble-induced turbulence could be fully neglected. In this contribution some new simulation results for air-lift loop reactors of different geometries will be presented. In this new test cases, the gas phase occupies the whole cross-section of the riser, so that the bubble-induced turbulence is of the same order of magnitude as the shear-induced one. The neglection of this effect in the model leads to very poor agreement between the simulation results and experiments. The most popular modifications of the standard k-epsilon model, which try to describe the influence of the rising gas bubbles on the turbulence in liquid phase will be discussed. Unfortunately, in some test cases, none of them can lead to a better agreement with experiments, so that further investigations in this area are necessary

Hydrodynamics of Gas-Liquid Bubble Columns and Air-Lift Loop Reactors: Experiments and Numerical Simulations

It is generally accepted that a key to improvements in the modeling of gas-liquid reactors is a realistic description of two-phase flow. One of the main unresolved problems is the modeling of turbulence in the continuous phase. In the majority of publications on numerical simulations of stationary two-phase flows, the standard k-epsilon model developed for single-phase flows has been used. The general applicability of this model to instationary two-phase flows is however disputed. In our last contribution on the ISCRE-15, we discussed the above question with the example of a locally aerated, flat bubble column. The results showed that it is possible to obtain a realistic dynamic solution with the k-epsilon turbulence model. It was however obvious that the general applicability of the 3D k-epsilon turbulence model to the dynamic simulation of bubbly flows needed further validation for a large spectrum of test cases of turbulent gas-liquid flows. A series of new test cases for symmetrically aerated, empty bubble column with different aspect ratios will be presented in this contribution. The comparison of detailed experiments and flow simulation results will be given. Another important unresolved problem is the modeling of the turbulence induced by the gas phase. In the test cases of locally aerated, flat bubble colums mentioned above, the gas phase occupied only a very small part of the reactor, and the influence of the bubble-induced turbulence could be fully neglected. In this contribution some new simulation results for air-lift loop reactors of different geometries will be presented. In this new test cases, the gas phase occupies the whole cross-section of the riser, so that the bubble-induced turbulence is of the same order of magnitude as the shear-induced one. The neglection of this effect in the model leads to very poor agreement between the simulation results and experiments. The most popular modifications of the standard k-epsilon model, which try to describe the influence of the rising gas bubbles on the turbulence in liquid phase will be discussed. Unfortunately, in some test cases, none of them can lead to a better agreement with experiments, so that further investigations in this area are necessary