  Gas-liquid flows through packed bed reactors (PBRs) are challenging to
predict due to the tortuous flow paths that fluid interfaces must traverse.
Experiments at the International Space Station showed that bubble and pulse
flows are predominately observed under microgravity conditions, while the
trickle and spray flows observed under terrestrial conditions are not present
in microgravity. To understand the physics behind the former experiments, we
simulate bubble flow through a PBR for different
packing-particle-diameter-based Weber numbers and under different gravity
conditions. We demonstrate different pore-scale mechanisms, such as capillary
entrapment, buoyancy entrapment, and inertia-induced bubble displacement. Then,
we perform a quantitative analysis by introducing new dynamic scales, dependent
upon the evolving gas-liquid interfacial area, to understand the dynamic
trade-offs between the inertia, capillary, and buoyancy forces on a bubble
passing through a PBR. This analysis leads us to define new dimensionless
Weber-like numbers that delineate bubble entrapment from bubble displacement.
