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This study aims to enhance the liquid water distribution within electrodes by innovatively designing a microporous layer (MPL) featuring orderly gradient perforations. Utilizing a multi‐component multi‐phase lattice Boltzmann model (LBM), which has been rigorously validated through contact angle measurements, Laplace pressure tests, grid independence checks, and comparisons with experimental data to ensure high predictive accuracy. The research systematically analyzes the governing liquid water transport in orderly gradient perforation MPLs. Leveraging this reliable modeling platform, the study conducts an exhaustive optimization analysis of gradient direction, gradation counts, and perforation geometry under constant porosity conditions. Findings reveal that negative gradient perforation designs significantly outperform positive gradient and conventional straight perforations, enhancing dry pore retention by at least 10.8%. Within the gradation counts, the ternary gradient structure further boosts channel retention by an additional minimum of 14.9% compared to quinary and continuous gradient structures. Moreover, cylindrical perforations demonstrate a substantial decrease surpassing spherical and square designs by at least 13.8% for liquid water saturation. Critically, the optimized model effectively inhibit the formation of saturation‐induced blockages in localized thickness regions. In conclusion, the investigation offers a robust basis for advancing MPL design strategies, targeting improved electrochemical processes and battery performance. [ABSTRACT FROM AUTHOR]

Gas-lubricated journal bearings (GLJBs) are widely utilized in rotating machines and the complex flow in ultra-thin clearances is a hot research topic. In this paper, the micro-clearance between the journal and housing of a GLJB was selected as the research object of a typically curved variable cross-section microchannel. In addition, the multiple-relaxation-time (MRT) model of the lattice Boltzmann method (LBM) was employed to analyze the shear flow characteristics. The generalized form of interpolation supplemented LBM (GILBM) based on the body-fitted grid was utilized due to complex geometry, and the Langmuir slip boundary model was introduced through the non-equilibrium extrapolation (NEE) method to simulate the rarefied airflow from the slip region to transition region. The velocity and pressure fields in the microchannel under different bearing parameters and operating conditions were described by the present model. What's more, the gas backflow phenomenon was captured. Additionally, the effect of velocity slip on the performance characteristics of GLJBs was studied. It was found that with the increase of eccentricity ratio and rotor speed, or a decrease of clearance size, the load-carrying capacity and friction torque of GLJBs rise, and the occurrence of velocity slip weakens the static performances of GLJBs. [ABSTRACT FROM AUTHOR]

A modified lattice Boltzmann model for conjugate heat transfer in a system containing simultaneously a porous medium and other media is proposed. In this model, the volumetric heat capacity and a new parameter are introduced to the equilibrium temperature distribution function for satisfying the temperature and heat flux continuities at the interface between two phases with different thermal properties (thermal conductivity and volumetric heat capacity), as well as avoiding any correction of distribution functions neighboring the interface. The macroscopic temperature equations are correctly recovered from the corresponding lattice Boltzmann equations by the Chapman–Enskog procedure. Detailed numerical tests of the proposed model are carried out for several benchmark problems including steady-state conjugate heat conduction within two-layer solid medium, transient conjugate heat conduction in infinite composite solid, conjugate natural convection in a cavity partially filled with porous medium and conjugate heat transfer in porous media with a conducting wall. The present numerical results are in excellent agreement with analytical and numerical solutions reported in previous studies. Therefore, it is verified that the present model can be served as a feasible tool for conjugate heat transfer problems in porous media. [ABSTRACT FROM AUTHOR]

Gas diffusion in porous media are great importance in many science and engineering fields. In this paper, lattice Boltzmann method is applied to simulate the gas diffusion in the fractal reconstructed porous building materials. The isotropic porous materials are reconstructed by the random midpoint displacement (RMD) algorithm. In addition, the filtering and linear spatial transforms are introduced to reconstructed anisotropic porous materials which conform to the typical characteristics of porous building materials. The two-point correlation function and fractal dimension of anisotropic porous media present uniform with the anisotropic strength varied from 0 to 0.6. Lattice Boltzmann method is developed to study the gas diffusion behaviors in the reconstructed anisotropic porous materials with different fractal dimension. The effective diffusion coefficients along different directions of anisotropic porous materials are analyzed. [ABSTRACT FROM AUTHOR]

A binary mixture lattice Boltzmann model (LBM) is used to simulate the diffusion process in stochastic fractal porous media generated by the fractional Brownian motion model. The isotropic porous media is reconstructed from fractional Brownian rough surface using the random midpoint displacement algorithm and the binary processing. In addition, the 2D and 3D anisotropic porous media is generated by transforming the isotropic fractional Brownian rough surface with a structure filter. LBM is applied to simulate the diffusion processes of reconstructed isotropic and anisotropic porous media for various fractal dimensions. The results indicate that the increasing fractal dimension can lead to the reduction of effective diffusion coefficients at the same porosity. The degrees of anisotropy for diffusion of anisotropic porous media are presented with the different anisotropic strength. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study on the melting behavior of phase change material (PCM) in metal foams has been carried out at the pore scale. Paraffin wax was used as phase change material, in which aluminum foams were embedded to enhance the heat transfer. The temperature field and the melting evolution of the PCM at the pore scale were studied using an infrared camera and an optical microscope, respectively. The experimental results indicated that the metal foam is capable of enhancing the solid–liquid phase-change heat transfer, mainly because of the thermal conduction in the metal matrix. It was observed that the effect of the metal structure on the heat transfer is significant during the melting of PCM. A thermal lattice Boltzmann model with doubled populations was implemented to simulate the two-dimensional melting of the phase change material in metal foams. The numerical results agree well with the experimental observations qualitatively. [Copyright &y& Elsevier]

Abstract: A thermal lattice Boltzmann model for natural convection in porous media under local thermal non-equilibrium conditions is proposed through an appropriate selection of equilibrium distribution functions and discrete source terms. In this model, two new distribution functions are introduced to simulate the temperature fields of the fluid and solid matrix phases in addition to the density distribution function for the velocity field. The macroscopic energy equations are recovered from the corresponding lattice Boltzmann equations by the Chapman–Enskog procedure. Detailed numerical tests of the proposed model are carried out for three different cases under both steady state and transient conditions. The influence of various parameters such as ratio of solid-to-fluid thermal conductivities, interstitial Nusselt number, Rayleigh number, and Darcy number on the thermal and flow fields is investigated. The present numerical results agree well with the solutions reported in previous studies. Therefore, it is verified that the present model can be served as a feasible and efficient tool for non-equilibrium natural convection problems in porous media. [Copyright &y& Elsevier]

Abstract: This paper presents migration of volatile organic compounds (VOC) in porous building materials which are considered as stochastic porous media for the purpose of theoretical study. Desorption and diffusion processes of VOC in porous materials are simulated by three-dimensional lattice Boltzmann method (LBM) which is derived from binary mixture model. Based on this model, the simulated transient concentration distribution of binary gas diffusion in 3D channel which is obtained from simulation agrees well with analytical solution. The stochastic porous materials are constructed with quartet structure generation set (QSGS) method. This model can predict the effective diffusivity of porous materials successfully through comparing with empirical model and experimental data. A boundary condition of solid–pore interfaces is proposed to simulate desorption process of adsorption phase VOC on solid matrix. The coupling relationship between migration characteristics and key parameters of porous materials, such as partition coefficient, core distribution probability and porosity, is analyzed. The significance of desorption in migration process of VOC is observed. [Copyright &y& Elsevier]

Abstract: A thermal lattice Boltzmann model is developed for the melting with natural convection in porous media at the representative elementary volume scale. An evolution equation of the temperature distribution function is constructed through selecting the equilibrium distribution function and non-linear source term properly. Simulations of melting with natural convection in a cavity with and without a porous matrix are performed using the present model. Numerical results show good agreement with previous analytical, experimental and numerical solutions. In addition, the analysis of the melting process over a wider range of dimensionless parameters indicates that for conditions of high Darcy number and high porosity the effect of natural convection on the melting becomes stronger, and the Rayleigh number based on porous media (Ram ) proposed in the previous studies may not be appropriate to correlate the average hot wall Nusselt number independently. The present model is also suitable for simulating freezing and solidification in porous media without modification. [ABSTRACT FROM AUTHOR]

This paper presents an improved lattice Boltzmann (LB) method to simulate solid-liquid phase change with natural convection in porous media under local thermal non-equilibrium (LTNE) conditions. In this method, three distribution functions are respectively adopted for flow field, and temperature field of the PCM and solid matrix. Different from previous models, the present model for temperature field incorporates the total enthalpy and a free parameter in the equilibrium distribution function, and thus could have high computational efficiency by avoiding iteration procedure to deal with phase change. The present model is validated by the melting with natural convection in a square cavity filled with a metal foam. It is found that the numerical results are in good agreement with other numerical results, and the present method could preserve higher accuracy due to numerical diffusion reduction through keeping the relaxation time at around unity as well as tuning the free parameters properly. [ABSTRACT FROM AUTHOR]

• Wetting transition induced by subcooling and droplet return can flood the condensing surface. • The removal mechanism of jumping and sliding droplets at various conditions is analyzed. • Self-jumping dynamics of droplet at the various initial states is simulated by LBM. • HTC is enhanced by 21.1, 49.2 and 72.4% at α = 30°, 60° and 90° compared to α = 0°. • If the energy conversion efficiency is below 2.1%, coalesced droplets are stuck to the surface. Due to the excellent heat transfer efficiency, dynamic behaviors of coalescence-induced droplet jumping on superhydrophobic surfaces have been extensively investigated to facilitate the technological applications in power generation, refrigeration, and water harvesting. Despite numerous experiments and simulations of vapor condensation, the droplet dynamics and heat transfer performance affected by the combination of initial wetting state and inclination during pure vapor condensation are still poorly understood. Combining visual experiments and lattice Boltzmann simulations, the droplet dynamics, size distribution and heat transfer on the nanostructured surface at various condensing conditions are analyzed. As the subcooling increases from 0.5 to 3.5 K, the jumping frequency of droplets at α = 90° decreases significantly from 173 to 36 cm−2 s−1 and the average droplet diameter is increased by ∼300%. Meanwhile, the jumping diameter ranges from 20 to 280 μm, with a ∼60% reduction in maximum jumping height. The critical sliding diameters at α = 30° are 1.5, 1.4 and 1.5 times higher than those at a 90° inclination as the subcoolings are 5.0 K, 6.5 K and 8.0 K, respectively. Heat transfer coefficient is enhanced by 21.1% at α = 30°, 49.2% at α = 60°, and 72.4% at α = 90°. In addition, the LB results demonstrate that if the energy conversion efficiency is below 2.1%, condensate droplets are stuck to the substrate rather than jumping away spontaneously. [ABSTRACT FROM AUTHOR]

Of the composite PCMs that regulate temperature in thermal energy storage, metal foam is a good candidate because of its high conductivity. This paper aims to characterize the behavior of composite PCMs through the dual experimental and numerical approach. The approach takes into consideration the natural convection of PCMs and the porosity character of metal foams which is constructed by quartet structure generation set (QSGS) method. The model uses the two-dimensional lattice Boltzmann method based on the enthalpy method. The effects of foam porosity and characterized numbers on the heat transfer process in porous structures are investigated. The numerical and experimental results exhibit good agreement. The results indicates that for higher porosities of metal foams, the PCMs proves to speed up the melting rate. The significance of heat conduction in melting process of PCM in foam metal is observed. The approach adopted allows to highlight the behavior of the composite PCMs to better characterize its properties of heat-enhancement. [ABSTRACT FROM AUTHOR]

Dropwise condensation heat transfer on the micropillared surfaces is modeled using the 2D multiphase lattice Boltzmann method. Dynamic evolution of condensate droplets and heat transfer performance on the vertical micropillared surfaces with different wettability is investigated. The condensate mass and critical departure radius of droplets decrease as the surface wettability weakens. The superhydrophobic surface with the contact angle of 155° exhibits the highest heat flux. The released latent heat of saturated vapor results in a higher temperature at two-phase interface than elsewhere and a greater temperature gradient near the solid-liquid contact area. When the droplet detaches from the surface, the heat flux is reduced greatly. In addition, we concentrate on droplet jumping dynamics induced by merging on the microspined and microgrooved surfaces, especially considering the coupled phase change heat transfer process. Compared to the microgrooved surface, microspined structure is beneficial to improve the jumping velocity of droplets due to restricting the liquid bridge expansion and increasing the counteraction of substrate towards liquid bridge. Smaller width and height of microgroove can reduce the critical departure size as well as increase the jumping velocity. [ABSTRACT FROM AUTHOR]

In this work, the pseudopotential lattice Boltzmann method is used to simulate the vapor condensation on the asymmetric micropillar-arrayed surface. The impact of surface wettability, structural height and spacing on the dynamic characteristics of droplets and condensation performance are analyzed. Finally, the heat flux and migration velocity of condensate on the micropillar-arrayed substrates with various structures for the same roughness are compared. The results demonstrate that the weaker wettability accelerates the droplet migration and thus enhances the heat transfer performance. By properly designing the spacing and height of the trapezoidal microstructures, both the migration velocity of droplets and heat flux can be enhanced. There exists an optimal microstructure to maximize the migration velocity and heat flux. Compared with the asymmetric trapezoidal structures, the migration velocity of droplets is smaller and the heat transfer efficiency is lower on the asymmetric triangular structures. This work illustrates the mechanism of directional migration of droplets and vapor condensation on the asymmetric micropillared arrays in detail. [ABSTRACT FROM AUTHOR]

• Droplet size distribution is reduced after adding micro- and nano-structures. • Heat transfer coefficient of the S10R30 surface can be enhanced by 26.4%. • Four typically condensate behaviors are analyzed by LBM and experiments. • The microscopic mechanism of droplet dynamics is revealed via LBM and ESEM. Recently, micro- or nano- structured surfaces haven been developed to enhance condensation heat transfer, water harvesting and self-cleaning. However, at large subcoolings, condensate floods the subcooled substrate, thus deteriorating the heat transfer efficiency. Here, the superhydrophobic surfaces with micropillared and nanopillared structures are proposed to enhance heat transfer at large subcoolings. The influence of micropillar spacing and surface subcooling on the droplet dynamics and heat transfer performance is experimentally investigated using microscopic visualization techniques. In addition, the microscopic modeling of condensation heat transfer on the microstructured surfaces is performed using the mesoscopic lattice Boltzmann method. The results demonstrate that the droplet size distribution on the micropillared surface is significantly smaller over that of the nanostructured surface. The heat transfer coefficient decreases with the increase of micropillar spacing. As the subcooling rises, although the condensate floods the substrate, the heat transfer coefficient of the S10R30 (S10R30 represents the micropillar arrays with s = 10 μm and 2 r = 60 μm) surface is enhanced by 26.4% compared to the hydrophobic nanostructured surface. This is because the height of liquid film is the same of order of magnitude as the micropillars, reducing the thermal resistance caused by the liquid layer. Combining environmental scanning electron microscope (ESEM) observations and LB simulation results, it is concluded that the droplets first nucleate at the bottom corner of micropillars. In addition, the condensate droplets merge to form a film, fill the micropillar gaps, and cover the entire micropillars, leading to a sharp decrease in heat flux. These findings provide a theoretical and experimental guidance for the development of condensing surfaces to enhance heat transfer. [ABSTRACT FROM AUTHOR]