Theoretical and numerical investigation on capillary wicking dynamics of liquid hydrogen on micro-structured surfaces

Efficient management of cryogenic propellants in microgravity is critical for long-term on-orbit coasting and deep-space exploration. Surface tension-driven liquid acquisition devices (LADs) are promising solutions for ensuring gas-free delivery of cryogens. However, the pore-scale wicking dynamics on micro-structured surfaces, which dictate the performance of LADs, remain insufficiently understood. In this study, the capillary wicking of liquid hydrogen (LH2) on regular micropillar arrays is investigated using a three-dimensional central-moment pseudopotential lattice Boltzmann model coupled with a modified Benedict–Webb–Rubin (MBWR) equation of state (EOS). The central-moment formulation enables stable computation at the extremely low lattice kinematic viscosity of LH2 (νl = 0.005 035), while the MBWR EOS provides the accurate coexistence densities required to quantify the non-negligible inertial response arising from the extremely low viscosity of LH2. An inertia-inclusive pore-scale model is established by retaining capillary driving, cumulative viscous resistance, and the unsteady momentum of the moving liquid. Dimensionless-number analysis shows that the overall process remains capillary driven, whereas inertia becomes comparable to capillarity during rapid advancement between successive micropillar rows. Two dimensionless transport indices are introduced to distinguish the long-time wicking capability and the microscale local acceleration capability. Over the finite propagation interval considered in the present work, the front motion deviates from the classical Washburn scaling, L ∼ t1/2, because the inertial contribution remains dynamically relevant. A power-law empirical relation, L* = a(t*)b, is used to characterize the influence of inertia on the finite-range wicking behavior, where a represents the overall transport-rate magnitude and b reflects the departure from the viscous-dominated Washburn limit. These findings provide a quantitative pore-scale framework for the geometric design of liquid-hydrogen acquisition structures.