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Thin non-uniform particle size wicks are essential to improve the maximum heat flux of two-phase thermal management systems by improving the wickability. To understand the enhanced wickability, we examine a pore-scale capillary flow within the thin sintered particle wick using a free-energy-based, single-component, two-phase Lattice Boltzmann Method (LBM) with a minimal parasitic current. The developed LBM approach is validated through the rate-of-rise in the two-parallel plates with parallel plates spacing of W = 48 against analytical Bosanquet equation, achieving the RMS error below 10%. The LBM predicts the rate-of-rise through the uniform and non-uniform particle-size wicks between two-parallel plate, including the capillary meniscus front and dynamic capillary filling. At the same plate spacing and porosity, i.e., W = 48 lu and ε = 0.75, the non-uniform particle size wick achieves enhanced wickability by providing the selective flow pathway through pore networks formed in the smaller pores between the small/large particles, which is in qualitative agreement with previous experimental results. The enhancement of the maximum and minimum dimensionless liquid height and the liquid-filled pore ratio of non-uniform particle size wick is found to be up to 11.1, 27.47, and 26.11%, respectively. The simulation results provide insights into the optimal wick structures for high heat flux two-phase thermal management system by enhancing the wickability through the non-uniform particle (or pore) sizes.

The upper heat flux limit of nucleate pool-boiling heat transfer (NPHT), i.e., Critical Heat Flux (CHF), results in system burnouts in various energy and industrial applications, and the understandings of the tailored CHF mechanisms are crucial to develop robust thermal management systems. In various applications, the understandings of the tailored CHF mechanisms are essential for design flexibility and operation sustainability, but previous CHF tailoring studies focused on upward-facing heater orientation. This study examines the tailored hydrodynamic-instability using columnar post wick array to enhance CHF on tilted heater surfaces (with surface orientation θ = 60°–130°). Liquid supply enhances via the capillary flow through the post wicks, while the produced vapor efficiently escapes through pore space among the post wicks. The enhanced CHF are predicted using a modified interfacial lift-off CHF hydrodynamic model that relies on classical two-dimensional interfacial instability theory. On the tilted plain surface with the surface orientation from 60° to 130°, the model predicts the CHF, qCHF = 126.5 to 92.5 W/cm2 at the critical hydrodynamic instability wavelength, λcr = 9.2 to 12.7 mm, respectively, using water as a working fluid. The enhanced CHF is predicted at the surface orientations of θ = 90° and 120°, showing a maximum of 185% and 250% increase, respectively. The maximum enhancement occurs at the smallest columnar-post pitch distances, lp = 2.5 mm, where qCHF increases from 104 to 295 W/cm2 for θ = 90°, and from 89 to 313 W/cm2 for θ = 120°. The developed model will provide insights into the tailored hydrodynamic instability wavelength at tilted angle via engineered surface.