The maximum heat flux of two-phase thermal management systems is controlled by a capillary flow limit through wick structures to the heated surface, i.e., wickability, and a poor capillary flow limit result in the failure of desired thermal management in heat pipe, vapor chamber, other two-phase thermal management systems. Thin sintered particle wick structures have proven effective from numerous studies by simultaneously achieving enhanced liquid supply and reduced thermal resistance. Recent experimental work also shows an improved wickability using thin sintered particle wicks with non-uniform particle sizes. However, there is no a universally-accepted pore-scale computational method to fundamentally understand the wickability enhancement mechanisms. In this study, a free-energy-based, single-component, two-phase Lattice Boltzmann method (LBM) is used to examine the enhanced capillary flow mechanism within the thin sintered particle wick. The present LBM minimizes so-called parasitic currents to round-off by using the potential form of the intermolecular force. It is important to consider a low flow velocity associated with capillary flow in thin wick structures. The accuracy of the wetting boundary treatment which is based on inclusion of linear wall free energy is validated by simulation of equilibrium contact angle (10 \< θ \< 150) as a function of dimensionless wetting potential Ω. The proposed boundary treatment for convex/concave corners of square particles can be extended to more complicated geometries with curved boundaries (e.g. circular particles) represented by a staircase approximation. Furthermore, the LBM simulation results for the rate of rise between two-parallel plates with different spacing (2R = 25, 35, and 45) are shown to agree well with analytical predictions using Bosanquet equation with the RMS error below 6%. The LBM model also provides pore-level simulations for the permeability of both uniform-particle and non-uniform particle-size thin wick structures, and the simulation results of the uniform-particle wick are also validated with Kozeny-Carman equation. In addition, various parameter sets in terms of particle size, surface wettability, particle size ratio, Bond number and number of particle layers are investigated over a wide range of porosity (0.2 \< *ϕ* \< 0.8) and the results for the rate-of-rise, liquid film pressure and permeability have been analyzed systematically. The LBM simulation shows that the enhanced wickability of the non-uniform particle-size wick is related to the selective flow pathway through pore networks formed in the smaller pores between the small/large particles. 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 sizes.


Enhanced Wickability of Thin Non-Uniform Sintered Particle Wicks Using Lattice Boltzmann Method

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Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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