Bubble entrapment and displacement through packed-bed reactors

Understanding the physics of gas-liquid flows through porous media, such as packed-bed reactors (PBRs), in microgravity is essential for air and water recovery in advanced life support systems. Recently, experiments at the International Space Station showed that only bubble and pulse flow regimes are to be expected under microgravity conditions. Toward understanding the bubble flow regime physics in the latter experiments, we develop a computational fluid dynamics framework based on interface-resolved simulations of the flow through representative volume elements. Using this framework, we simulate bubble dynamics through PBRs with different packing-diameter-dependent Weber numbers and under different gravity conditions. The simulations uncover various pore-scale hydrodynamic mechanisms in this bubble flow regime, such as capillary entrapment of a bubble, buoyancy entrapment of a bubble, and inertia-induced displacement of a bubble. We rationalize the results by introducing a dynamic length scale, based on the gas-liquid interfacial area computed from the simulations and the initial bubble diameter. Using this length scale, we quantify the dynamic trade-offs between the inertia, capillary, and buoyancy forces on a bubble passing through a PBR. In doing so, our pore-scale resolved simulations and modeling reveal the conditions for and mechanisms behind bubble entrapment and displacement in porous media.