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Abstract: We implement a lattice Boltzmann method (LBM) for decaying homogeneous isotropic turbulence based on an analogous Galerkin filter and focus on the fundamental statistical isotropic property. This regularized method is constructed based on orthogonal Hermite polynomial space. For decaying homogeneous isotropic turbulence, this regularized method can simulate the isotropic property very well. Numerical studies demonstrate that the novel regularized LBM is a promising approximation of turbulent fluid flows, which paves the way for coupling various turbulent models with LBM. [Copyright &y& Elsevier]

Abstract: In this work, an isothermal, steady-state, three-dimensional (3D) multicomponent transport model is developed for proton exchange membrane (PEM) fuel cell with straight gas channels. The model computational domain, includes anode flow channel, membrane electrode assembly (MEA) and cathode flow channel. The catalyst layer within the domain has physical volume without simplification. A comprehensive set of 3D continuity equation, momentum equations and species conservation equations are formulated to describe the flow and species transport of the gas mixture in the coupled gas channels and the electrodes. The electrochemical reaction rate is modified by an agglomerate model to account for the effect of diffusion resistance through catalyst particle. The activation overpotential is predicted locally in the catalyst layer by separately solving electric potential equations of membrane phase and solid phase. The model is validated by comparison of the model prediction with experimental data of Ticianelli et al. The results indicate the detailed distribution characteristics of oxygen concentration, local current density and cathode activation overpotential at different current densities. The distribution patterns are relatively uniform at low average current density and are severely non-uniform at higher current density due to the mass transfer limitation. The local effectiveness factor in the catalyst layer can be obtained with this model, so the mass transport limitation is displayed from another point of view. [Copyright &y& Elsevier]

To determine the thermal properties of eutectic mixture of fatty acids by theoretic calculations, a formula of predicting thermal properties of eutectic mixture was selected and validated, and then the melting temperature and latent heat of eutectic mixture of fatty acids were calculated. From the calculation, the result of the theoretic calculation agrees well with that of the previous experiments. For the 15 eutectic mixtures of fatty acids, the minimum and maximum of the melting temperature are (10.2 and 51.5) °C, respectively. The minimum and maximum of the latent heat are (138.6 and 187.5) J·g–1, respectively. The eutectic mixtures of fatty acids are suitable for heating, a heat water system, phase wallboard, concrete and phase clothes, and other engineering applications. [ABSTRACT FROM AUTHOR]

The interface tends to behave as a circular shape under the effect of surface tension in the two-dimensional two-phase fluid flow. In this study, based on the coupled volume-of-fluid and level set (VOSET) method, an accurate circle-based interface reconstruction (CIR) algorithm for structured meshes is proposed, which features a straightforward implementation procedure. A portion of the standard circle is employed to approximate the curve interface, without the need for complex classification, coordinate transformation, and equation transformation. The radius of this circle is computed simply by the curvature and signed distance at the mixed cell center, and the center of this circle is determined using a straightforward dichotomy method under the mass conservation constraints. Results indicate that the coupled VOSET and CIR (VOSET-CIR) method maintains superior computational accuracy in the signed distance, interface curvature, and dynamic interface reconstruction compared to the coupled VOSET and piecewise linear interface calculation (VOSET-PLIC) method, with accuracy improvements ranging from 34% to 1490% across different test cases. Furthermore, the VOSET-CIR method outperforms the efficient least squares volume-of-fluid interface reconstruction (ELVIRA) and PLIC algorithms in reconstructing random circles and surpasses the quadratic spline based interface reconstruction (QUASI) algorithm in reconstructing random squares. In terms of computational efficiency, except for the initial PLIC algorithm, the time costs of the VOSET-CIR method are substantially lower than those of the ELVIRA and QUASI algorithms, as well as the VOSET-PLIC method. [ABSTRACT FROM AUTHOR]

understanding interactions between multiphase flow and reactive transport processes in catalyst layers (CL) of proton exchange membrane fuel cells is crucial for obtaining better performance and lower cost. In this study, a pore-scale model is developed to simulate coupled processes occurring in CLs, including oxygen diffusion, electrochemical reaction, and air-liquid two phase flow. Simulation conducted in an idealized local CL structures shows that the pore-scale model successfully captures dynamic behaviors of liquid water including generation, growth and subsequent migration, as well as the interaction between multiphase flow and reactive transport. Pore-scale simulation is then conducted in hydrophobic CLs with complicated structures where carbon, platinum, ionomer and pores are resolved. It is found that filling modes of the liquid water in the CLs are different. Before forming the continuous flow paths in CLs, liquid water presents as tiny droplets in pores surrounding relative large pores. After the continuous flow paths are formed, liquid water dynamic behaviors follow the capillary fingering mechanism. The multiphase flow and reactive transport processes are closely coupled with each other, and as liquid water saturation increases the reaction rate decreases. Increasing the hydrophobicity can alleviate the water flooding, accelerate the water breakthrough, and facilitate the water evaporation. • Pore-scale model for multiphase reactive transport in catalyst layer is developed. • Dynamic behaviors of liquid water generated by the reaction are studied. • Interaction between multiphase flow and reactive transport is revealed. • Variations of saturation, reaction rate and interfacial area are discussed. [ABSTRACT FROM AUTHOR]

Dropwise condensation on rough surfaces enhanced with pillars in the presence of non-condensable gas (NCG) including the initial nucleation process is simulated using the multispecies multiphase lattice Boltzmann method, and the effect of mass fraction of NCG, the surface wettability, the bottom wall temperature and the geometrical parameter (the pillar height H) on condensation process are investigated. It's found that these four factors all have an effect on the nucleation position, waiting time, condensate behaviors, and the wetting state of the droplet. With higher values of NCG mass fraction, surface hydrophobicity, pillar height H, and lower bottom wall temperature, the nucleation occurs on top of the pillars and the waiting time before nucleation gets longer. It's also concluded that the wetting state of the droplet tends to be the Cassie state, and the average heat flux gets smaller with higher values of the former three parameters and lower bottom wall temperature. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation was applied to test and evaluate the ability of several models of carbon dioxide on predicting thermodynamics and transport properties. Firstly, we compared the liquid-vapor coexist curves of seven kinds of carbon dioxide models by molecular dynamics simulations. It was found that the Cygan_flex model and EPM2 model were more accurate than the others. Then we investigated the structural properties of carbon dioxide using NPT ensemble molecular dynamics simulation. The fluid became less dense with the increasing temperature. Thirdly, the self-diffusion coefficients were studied at temperature and pressure up to 600 K and 80 MPa, respectively. The results showed that the self-diffusion coefficient decreased with the increasing pressure and increased with increasing temperature. Finally, we calculated the thermal conductivity of carbon dioxide at 250 K using EPM2_flex model, Cygan_flex model and TraPPE_flex model. So, we should pay attention to the selection of appropriate carbon dioxide models to obtain different carbon dioxide properties. • We reproduced the liquid-vapor coexist curve for seven carbon dioxide models. • Self-diffusion coefficient and thermal conductivity of carbon dioxide are obtained. • Choose appropriate carbon dioxide model for different carbon dioxide properties. [ABSTRACT FROM AUTHOR]

Porous structures of agglomerates in cathode catalyst layers (CLs) of proton exchange membrane fuel cells are reconstructed, in which all the four phases are resolved including Platinum, carbon, ionomer and pore. A pore-scale reactive transport model based on the lattice Boltzmann method is developed, in which oxygen dissolution reaction at pore-ionomer interface, oxygen diffusion inside ionomer, and electrochemical reaction at ionomer-Pt interface are considered. Emphasis is put on structural parameters, especially Pt/C mass ratio, on the reactive transport process and the volumetric reaction rate (or current density). Pore-scale results show that while under high Pt loading oxygen is depleted quite close to the surface of the spherical agglomerate, it has to penetrate deep into the porous agglomerate before it is completely consumed under low Pt loading which is not captured by classical agglomerate model based on homogeneous mixture assumption. Pore-scale results also found that effects of transport inside the agglomerate decreases as reaction rate, porosity or ionomer thickness increases. Finally, local transport resistance inside the agglomerate is evaluated, and it increases as the agglomerate size increases or the dissolution reaction rate decreases. • 3D porous agglomerates are reconstructed and pore-scale model is developed. • Pt loading sensitive volumetric reaction rate is predicted. • Effects of agglomerate size, porosity and ionomer thickness are studied. • Local transport resistance is evaluated. [ABSTRACT FROM AUTHOR]

Highlights • Nucleation position rises from the bottom to top of pillar with the increase of gs. • The wetting state changes from the Wenzel state to Cassie with the increase of gs. • The average condensation rate is smaller at higher surface hydrophobicity. • The nucleation waiting time is higher at higher surface hydrophobicity. Abstract Dropwise condensation on rough structures with different wettability are numerically simulated using Lattice Boltzmann method. The latent heat during condensation process together with the energy equation is taken into consideration in this paper by solving the temperature distribution equation with a source term for the phase change. Typical droplet nucleation positions and wetting states are found out at different surface wettability through numerical results. It is concluded that with the increase of strength coefficient of the fluid-solid interaction or surface hydrophobicity, the nucleation position rises from the bottom to top of the pillar, and the wetting state of droplet changes from the wetting Wenzel state to the nonwetting Cassie one. [ABSTRACT FROM AUTHOR]

Collision between particle and wall is common in granular two-phase flow. This study is helpful to optimise flow conveying system, reduce attrition between materials and devices, and improve development of economy. The collision between a single coarse particle (3 mm in diameter) and wall in a viscous media was investigated by Hertz–Mindlin no-slip contact model based on the coupled computational fluid dynamics and discrete element method (CFD-DEM). Effects of impact velocity and viscosity of media on contact processes and contact force are studied in this research. The calculated results from the collision model are consistent with experimental data, and contact velocity and viscosity of media show significant effects on the contact force of particles. With the reduction of the dimensionless number St , the ratio of unloading time to loading time increases significantly. [ABSTRACT FROM AUTHOR]

• Water desalination performances of COFs membranes were studied by molecular dynamics. • Water permeation of CTF-FUM and TPMA monolayer membranes are 3 orders of magnitude higher than TFC. • CTF-FUM and TPMA membranes could exhibit nearly 100% salt rejection. • Membrane thickness should be considered for designing 2D hydrophobic COF membranes. To explore energy-efficient two-dimensional porous materials for water desalination is an urgent demand for rational utilization of water and sustainable development. In addition, how the pore hydrophilicity influencing the desalination performance remains elusive. Basing on molecular dynamics (MD) simulations, we herein proposed ultrathin membranes of 2D covalent organic frameworks (COFs) with triazine units that are competent to reject ions efficiently while giving access to high water permeability. The ordered porous structure of these two COFs membranes (CTF-FUM and TPMA) enable nearly 100% salt rejection and show remarkable higher water permeation (∼57.2 and ∼ 48.1 L cm−2 day−1 MPa−1, respectively) over 3 magnitude compared to commercial TFC membranes (∼0.03 L cm−2 day−1 MPa−1). As a further step, the influence of layer number on membrane desalination performance was discussed to understand the underlying mechanisms. Compared to TPMA multilayer, it was found that CTF-FUM multilayer with hydrophobic pore shows less water permeability and higher transport resistance, and even has no obvious water transport through the 8-layer membrane. This MD simulation work gives a microscopic insight into 2D COF membranes on desalination and suggests that TPMA multilayer might be a promising membrane material for desalination applications. [ABSTRACT FROM AUTHOR]

A three-dimensional double distribution function thermal lattice Boltzmann model has been developed for simulation of thermal compressible flows in the low Mach number limit. Both the flow field and energy conservation equation are solved by LB approach. A higher order density distribution function on standard lattices is used to solve the flow field, while an energy distribution function is employed to compute the temperature field. The equation of state of thermal perfect gas is recovered by higher order Hermite polynomial expansions in Navier–Stokes–Fourier equations. The equilibrium distribution functions of D3Q15, D3Q19 and D3Q27 lattices are obtained from the Hermite expansion. They exhibit slight differences originating in differences in the discrete lattice symmetries. The correction terms in LB models for third order derivation are added using an external force in orthogonal polynomials form. Present models are successfully assessed considering several test cases, namely the thermal Couette flow, Rayleigh–Bénard convection, natural convection in square cavity and a spherical explosion in a 3D enclosed box. The numerical results are in good agreement with both analytical solution and results given by previous authors. [ABSTRACT FROM AUTHOR]

• A comprehensive review on numerical simulations of boiling heat transfer from atomistic to mesoscopic and macroscopic scales is presented. • Critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling are highlighted. • Potential solutions and future research in the field of boiling heat transfer using the MDS, LB and CFD methods are proposed. Boiling is an efficient heat transfer mode with significant potential for thermal management in high-power electronic equipment. However, a comprehensive understanding of the boiling process, which encompasses bubble nucleation, growth, coalescence, slipping, and detachment across various scales, remains challenging. Molecular dynamics simulation, lattice Boltzmann, and computational fluid dynamics methods are popular and powerful tools for investigating boiling heat transfer phenomena at microscopic, mesoscopic, and macroscopic scales. These methods enable researchers to uncover the underlying boiling mechanisms and propose heat transfer enhancement techniques. Therefore, this paper provides a comprehensive review of boiling heat transfer, spanning from atomistic to mesoscopic and macroscopic scales, utilizing these three numerical methods. It addresses critical issues related to nanoscale bubble nucleation mechanisms, pool boiling, and flow boiling, and proposes potential solutions and future researches, supplementing our previous review [Some advances in numerical simulations of multiscale heat transfer problems and particularly for boiling heat transfer, Annu. Rev. Heat Transf., 6 (2022) 217–269]. Besides, by shedding light on the characteristics of these numerical methods in studying boiling heat transfer, this paper aims to foster their development and advance enhanced heat transfer technologies. [ABSTRACT FROM AUTHOR]

The inner doubly iterative efficient algorithm (IDEAL), an advanced fully implicit algorithm for solving the pressure-velocity coupling problem, lacks a comprehensive implementation procedure on commonly used collocated unstructured grids. Therefore, this study provides a thorough demonstration of the fundamental principles, solving procedures, discretizations of momentum and pressure equations, Rhie-Chow interpolation implementation, mass continuity processing, and boundary condition treatment associated with the IDEAL algorithm on a collocated unstructured grid. Additionally, a comparative analysis between the semi-implicit method for pressure-linked equations (SIMPLE) and the IDEAL algorithm is conducted concerning computational efficiency under different grid types and flow conditions. The results indicate a significantly higher computational efficiency achieved by the IDEAL algorithm across all tested cases, attributed to its ability to overcome two fundamental assumptions inherent in the SIMPLE algorithm. The average acceleration ratio for these cases is approximately 3.13 (tSIMPLE/tIDEAL). This study serves as a valuable reference for the further development and application of the IDEAL algorithm in solving flow problems with complex irregular domains discretized by unstructured grids. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) porous flow fields have been utilized to achieve ultrahigh power density for proton exchange membrane fuel cells (PEMFCs). However, issues such as the severe corrosion and high interface contact resistance of 3D porous flow field limit the effective enhancement in power density. In this work, porous flow fields with various pore structures, i.e., Ni foam and Ti felt are employed and further decorated with carbon coating using the chemical vapor deposition (CVD) method to improve the anti-corrosion capacity. Meanwhile, the through-plane electrical conductivity and hydrophobicity are collectively improved for Ni foam and Ti felt by the carbon coating. Single fuel cell (FC) tests show that both the peak power density (PPD) and limiting current density (LCD) are improved for PEMFCs assembled with C@Ni foam and C@Ti felt flow fields in the cathode. The corresponding electrochemical impedance spectroscopy (EIS) confirms that the improved PPD (C@Ti felt) is attributed to the collective improvements in electrical conductivity and anti-corrosion capacity, and the improved LCD (C@Ni foam) is attributed to enhanced water removal capacity. The triple improvements in the intrinsic property of porous flow field materials obtained in this work are expected to offer novel approaches for developing PEMFCs with ultrahigh power density. [Display omitted] • Carbon coating is introduced in porous flow field by chemical vapor deposition (CVD). • Through-plane contact resistance is reduced for C@Ni and C@Ti porous flow field. • Anticorrosion capacity was enhanced for C@Ni and C@Ti porous flow field materials. • Water removal capacity is improved for C@Ni and C@Ti porous flow field materials. • Electrochemical performance is enhanced for fuel cell with C@Ni and C@Ti. [ABSTRACT FROM AUTHOR]

Global warming due to greenhouse gas emissions has continuously threatened the climate and environment. Zirconium-based metal-organic frameworks (Zr-MOFs) with Zr 6 inner cores represent a subfamily of nanoporous materials with good physicochemical stabilities, showing significant prospects for practical applications in gas separation. A molecular simulation study is reported here to investigate the membrane separation of CO 2 /N 2 and CO 2 /CH 4 mixtures in five Zr-MOFs (Zr-fum, UiO-66, DUT-52, Zr-cca, UiO-67) with similar ligand in their structures and different pore-limiting diameter (PLD) ranging from 0.36 nm to 0.59 nm. The gas permeation and separation performance are evaluated with the concentration gradient-driven molecular dynamics (CGD-MD) method. The results show that the separation of both gas mixtures is dominated by the preferential sorption of CO 2 over N 2 and CH 4 , respectively. Meanwhile, the PLD of MOFs is also a significant factor governing permeation. MOFs with a larger PLD have a higher permeability and a lower selectivity for CO 2 /N 2 and CO 2 /CH 4 separation. Free-energy profiles were calculated to describe the insights into CO 2 separation, that the larger PLD can cause a lower energy barrier when gases transport through the pore of MOFs. The results were compared with the grand canonical Monte Carlo and equilibrium molecular dynamics (GCMC + EMD) approach, a traditional method to predict gas adsorption and diffusion in MOFs. As the GCMC+EMD approach neglected the interaction between components and potential mass transfer resistance at the surface of the membranes, the results obtained from the CGD-MD method in this work are more reliable. This study provides microscopic insights into CO 2 separation in Zr-MOF membranes and suggests their potential use for gas separation. [ABSTRACT FROM AUTHOR]

Effectively addressing crude oil spills remains a global challenge due to its high viscosity and limited flow characteristics. In this study, we successfully prepared a modified sponge (PCP@MS) by embedding the photothermal material of Co-HHTP and coating the melamine sponge (MS) with low-surface-energy polydimethylsiloxane (PDMS). The PCP@MS exhibited outstanding hydrophobicity with WCA of 160.2° and high oil absorption capacity of 59–107 g/g. The PCP@MS showed high separation efficiency of 99.2% for various oil-water mixtures, along with notable self-cleaning properties and mechanical stability. The internal micro-nano hierarchical structure on the sponge surface significantly enhanced light absorption, synergizing with the photo-thermal conversion properties of Co-HHTP, enabled PCP@MS to achieve a surface temperature of 109.2 °C under 1.0 solar light within 300 s. With the aid of solar radiation, PCP@MS is able to heat up quickly and successfully lowering the viscosity of the surrounding crude oil, resulting in an oil recovery rate of 8.76 g/min. Density functional theory (DFT) calculation results revealed that Co-HHTP featured a zero-gap band structure, rendering advantageous electronic properties for full-wavelength light absorption. This in situ solar-heated absorbent design is poised to advance the practical application of viscous oil spill cleanup and recovery. [Display omitted] • PCP@MS possesses remarkable self-cleaning, chemical and mechanical stability. • PCP@MS exhibits efficient oil-water separation and high absorption capacities. • Zero-gap band structure of Co-HHTP enhances PCP@MS's photothermal performance. • The recovery rate of PCP@MS exceeds 92% over 10 cycles of crude oil absorption. • PCP@MS is capable of remediating high-viscosity crude oil at a rate of 8.76 g/min. [ABSTRACT FROM AUTHOR]

• A proposed surrogate model can well predict the cathode transport process of PEMFC. • Cathode gas channels with high performance are designed by topology optimization. • A continuity optimized strategy is proposed to increase the inlet velocity to 7 m s−1. • The topology optimized gas channels are superior to the traditional designs. • Topology optimized gas channels are compared with the bio-inspired gas channels. Optimizing the gas channels (GCs) plays an important role on improving the performance of proton exchange membrane fuel cells (PEMFCs). In this study, a topology optimization (TO) model is developed for optimizing the cathode GCs. A reduced two-dimensional (2D) reactive transport model is developed based on the 3D half-cell model, which considers the multiscale oxygen reactive transport processes inside GCs, the gas diffusion layer and the catalyst layer. The reduced 2D surrogate model can predict the polarization curve agreeing well with experimental results. The TO is employed to optimize the GCs with the objectives of reducing flow resistance and increasing the current density. A continuous scheme is developed to conduct the TO under high inlet velocity. GCs with five different inlet/outlet configurations are optimized. As validated by 3D simulations, the TO structures can obtain higher current density with reduced pressure drop compared with parallel GCs. Finally, the TO GCs are compared with existing bio-inspired GCs. The tree-like structure with wider inlet/outlet channels and narrower center channel is considered as a promising design for future investigation. The present study is helpful for the designing of next-generation of GCs for better cell performance. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage have been an effective way to deal with global climate issues. Injecting CO2 into depleted oil reservoirs can reach the dual goal of carbon storage and enhanced oil recovery. To optimize the gas injection strategy, it is necessary to understand the underlying mechanisms of three-phase fluid flow of oil, water, and gas. In this study, a lattice Boltzmann color gradient model is used to investigate the pore-scale three-phase displacement process in porous media. Gas is injected into the porous domain initially occupied by water and oil. Typical microscopic behaviors, including coalescence and split-up, pinch-off, double and multiple displacement, as well as parallel flow, are identified and discussed. Effects of water content (ϕ), capillary number (Ca), wettability and viscosity ratio (M) on the flow pattern, and oil recovery rate are explored. The oil ganglia inhibit the development of gas fingers, causing stronger viscous fingering characteristics with increasing ϕ. The fingering pattern is located in the crossover zone for the Ca from 5 × 10−5 to 5 × 10−4. As ϕ increases, the oil recovery rate reduces. The oil ganglia tend to occupy small pores as oil wettability enhanced, making it more difficult to be drained out. The reduction of oil viscosity is beneficial to improve connectivity, thereby effectively enhancing the oil recovery. Finally, the CO2 storage rate is also evaluated. It is found that the storage rate is very sensitive to the initial oil–water distributions. In general, the storage rate increases as ϕ decreases, Ca increases, and oil wettability enhances. [ABSTRACT FROM AUTHOR]

To develop high-performance non-precious metal-based electrocatalysts for oxygen reduction reaction (ORR) is an urgent demand. We herein report an ingenious strategy to develop highly selective and competitive precious metal-free ORR electrocatalyst Co/CoO/SnO encapsulated in N-rich mesoporous carbon (CCS@NPC) nanocubes, via a simple one-step introduction of all functional components. Atomically mixed composites with significantly enhanced catalytic activity were obtained by adopting amorphous mesoporous ternary metal oxides CoSnO 3 nanocubes as precursor and template. The synergistic effect of the triphase nanohybrids (Co, CoO & SnO) anchored in nitrogen-doped mesoporous carbon nanocubes promoted the catalytic reactions, owning to the anisotropic morphology, great heterojunction interfaces, and structural stability. The large-scale prepared CCS@NPC exhibited excellent electrocatalytic activity toward ORR with an admirable onset potential (1.01 V) and diffusion-limited current density (5.88 mA cm−2). The CCS@NPC showed stronger stability (20 h) and higher methanol tolerance with the concentration up to 8.0 M, compared to that of commercial Pt/C. • Oxygen vacancies-rich CCS@NPC catalyst was synthesized without any solvent. • Introducing porous CoSnO 3 and ZIF-67 increased the specific surface area obviously. • Synergies among Co/Co/SnO and N-doped carbon nanocubes enhanced the ORR kinetics. • CCS@NPC showed super methanol tolerance with high concentration (8.0 M). [ABSTRACT FROM AUTHOR]

Abstract: Fatty acids as phase change materials have attracted much attention for their various applications in building energy efficiency, solar heating systems and air-conditioning systems. After summarizing the basic characteristics of fatty acids, eutectic mixtures of fatty acids and fatty acid esters, as well as the preparation and characteristics of fatty acid composites as phase change materials (PCMs), this paper analyzes the thermal reliability and stability of fatty acids as PCMs and their heat transfer characteristics in a unit which is followed by an introduction to the energy storage systems of three kinds of fatty acids as PCMs. Besides, it also points out the future research direction of fatty acids as PCMs as a solution of the insufficiency and flaws of current researches. [Copyright &y& Elsevier]

Perfluorooctanoic acid (PFOA) poses a threat to the environment and human health due to its persistence, bioaccumulation, and reproductive toxicity. Herein, a lanthanide metal-organic framework (Ln-MOF)-based surface molecularly imprinted polymers (SMIPs) ratiometric fluorescence probe (Eu/Tb-MOF@MIPs) and a smartphone-assisted portable device were developed for the detection of PFOA with high selectivity in real water samples. The integration of Eu/Tb MOFs as carriers not only had highly stable multiple emission signals but also prevented deformation of the imprinting cavity of MIPs. Meanwhile, the MIPs layer preserved the fluorescence of Ln-MOF and provided selective cavities for improved specificity. Molecular dynamics (MD) was employed to simulate the polymerization process of MIPs, revealing that the formation of multiple recognition sites was attributed to the establishment of hydrogen bonds between functional monomers and templates. The probe showed a good linear relationship with PFOA concentration in the range of 0.02–2.8 μM, by giving the limit of detection (LOD) of 0.98 nM. Additionally, The red-green-blue (RGB) values analysis based on the smartphone-assisted portable device demonstrated a linear relationship of 0.1–2.8 μM PFOA with the LOD of 3.26 nM. The developed probe and portable device sensing platform exhibit substantial potential for on-site detecting PFOA in practical applications and provide a reliable strategy for the intelligent identification of important targets in water environmental samples. [ABSTRACT FROM AUTHOR]

Flow boiling stands out as an efficient mode of heat transfer with significant potential for reducing carbon footprint. Based on a coupled Volume-of-Fluid and Level Set (VOSET) method, this numerical study reveals the microlayer and its evaporative heat flux distributions, as well as the effects of microlayer evaporation and depletion on bubble dynamic behavior, flow pattern, wall superheat distribution, and boiling crisis for the flow boiling in a mini-channel. These aspects are firstly comprehensively reported by the numerical method. Results indicate that the rapid evaporation of a thin microlayer positioned beneath elongated bubbles significantly contributes to heat dissipation during flow boiling in a mini-channel. The heat flux through the microlayer surpasses 300 kW/m2, accounting for approximately 42% of heat dissipation at 200 kW/m2. Furthermore, this contribution increases to over 70% as the heat flux exceeds 500 kW/m2. As a result, in comparison to scenarios without microlayers, the presence of microlayers results in an average heat transfer coefficient (HTC) that is 3.97 times larger within the range of 200–500 kW/m2. Additionally, microlayer evaporation delays the happening of flow boiling crisis. Without microlayers, the wall superheat exceeds 180 K at 500 kW/m2, whereas under microlayer influence, the maximum local wall superheat is only 37.09 K at 1000 kW/m2. With further increases in heat flux, the emergence of large dry patches resulting from microlayer depletion induces the beginning of heat transfer deterioration. Finally, the ongoing coalescence of elongated bubbles necessitates a prolonged period for rewetting dry patches at the exit of the mini-channel, triggering the flow boiling crisis at 1300 kW/m2. The study results provide crucial guidance for the development and application of the flow boiling heat transfer technology for the thermal management of data centers. [ABSTRACT FROM AUTHOR]

This article describes an improved paving method of automatic quadrilateral mesh generation. Paving, which was first proposed by Blacker and Stephenson [1], is a kind of direct method for generating a quadrilateral mesh and has been widely used since it was presented. This article aims to improve some weaknesses of the traditional paving method by generating high-quality quadrilateral grids without employment of a background mesh. Through efficient intersection resolution and other optimization measures, the improved paving method can generate well-aligned rows of quadrilateral elements almost parallel to the boundary of the domain, automatically and quickly. [ABSTRACT FROM AUTHOR]

A full-knowledge of the temperature distribution in a data center is crucial for the design and operation to avoid thermal failure. However, it is a great challenge to conduct full-field simulations using the computational fluid dynamics/heat transfer (CFD/HT) method due to the unacceptable computational cost caused by the multi-scale structure of data centers. In this paper, a novel multi-scale model based on POD and CFD coupling is proposed to predict the thermal and fluid characteristics in data centers from room scale to chip scale. The temperature and flow fields in an air-cooled data center are predicted and analyzed under the scales of room, server, IGBT and chip. Based on the CFD results of Room-Server level, 16 sets of design cases' temperature fields for Server-IGBT level are compared using the POD and CFD methods, which shows that the maximum average absolute deviation and average relative deviation are 0.004 °C and 0.59%, respectively. Subsequently, three sets of off-design cases for Server-IGBT level and IGBT-Chip level are predicted using the aforementioned methods, yielding the maximum relative deviation 7.21% and 0.98%, respectively. The salient outcome is the remarkable 175-fold reduction in CPU processing time achieved with the POD model compared to traditional CFD simulations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Double transition metal atoms on GDY break the scaling relationship. • Machine learning speeds up the screening catalysts and reveals the descriptors. • Relations of intermediate adsorption energies aid catalyst selection in deep CO 2 RR. • GDY-based catalysts with strong CO binding exhibit high selectivity towards CH 4. Electrochemical CO 2 reduction reaction (CO 2 RR) has become a promising application in addressing energy challenges and environmental crises. However, the scaling relationship between the reaction intermediates constrains the successful deep reduction of CO 2. Dual-metal-site catalysts (DMSCs) have emerged as potential electrocatalysts for CO 2 RR by breaking the scaling relationship due to their more adaptable active sites. Herein, this study aims to investigate the correlation between the adsorption energies of essential intermediates in CO 2 RR catalysis with double transition metal atoms anchored on graphdiyne monolayer (TM 1 -TM 2 @GDY) through machine-learning (ML) assisted density functional theory (DFT) calculations. The results reveal the important descriptors of CO 2 RR catalyzed by TM 1 -TM 2 @GDY, and demonstrate that the heteronuclear TM 1 -TM 2 @GDY have great potential for deep CO 2 reduction. Especially, Co-Mo@GDY and Co-W@GDY show low limiting potential (-0.60 V and −0.39 V, respectively) and high selectivity on the reaction from CO 2 to CH 4 based on the free energy diagrams. This study indicates that the two TM atoms on GDY act cooperatively for the catalysis of CO 2 RR. Notably, utilizing ML eliminates the need to calculate all transition metal combinations by DFT, which is a great boost in quickly investigating catalytic performance and high screening for excellent catalysts. [ABSTRACT FROM AUTHOR]

Membrane separation technology has been widely used in the separation and capture of CO 2 to reduce carbon emissions. The performances of facilitated hybrid membranes (FHMs) can be improved by properly adding metal-organic framework (MOF)-based nanoparticles (NPs) and modifying polymers to the polymer matrix. Grafting and blending methods are widely used to introduce modifying polymers to improve the compatibility between NPs and the polymer matrix, and the performance of FHMs for CO 2 separation. However, the separation performance of FHMs decreases significantly when the long chains of the polymer infiltrate into the pores of the MOF at the interface between the modifying polymer and MOF. To in-depth understand the nano-scale polymer-NPs interfacial interaction mechanism of the grafting and blending methods, we herein employed molecular dynamic (MD) simulation method combined with experiments to investigate the interface between NPs of Cu-MOF (Cu-BDC) and four commonly used modifying polymers (PEG, polyethylene glycol; PEI, polyethylenimine; PVA, polyvinyl alcohol; PPy, polypyrrole) with PVDF (polyvinylidene difluoride) as the polymer matrix. The results showed that the blending method for modification can effectively avoid the polymer blockage in Cu-BDC pores by using four modifying polymers, while the grafting method caused polymer infiltration for PEG and PEI. The relationship between the polymer diameter and the pore limiting diameter (PLD) of the Cu-BDC was evaluated to analyze the polymer infiltration effect. FHMs of Cu-BDC/PEG@PVDF were synthesized based on the MD simulation results, which showed excellent CO 2 separation performance due to the good compatibility between the Cu-BDC and the modified matrix polymer. This work offers an insight in nano-scale into the interface design between the MOF and the polymer for FHMs separating CO 2. [Display omitted] • The interface interaction between MOF and modifying polymers was studied by molecular dynamics. • Using blending method to avoid the modifying polymer (PEG and PEI) infiltrating into MOF(Cu-BDC) pores. • The compatibility between modified matrix polymer and MOF was improved. • Cu-BDC/PEG@PVDF was synthesized and exhibited good performance for CO 2 separation. [ABSTRACT FROM AUTHOR]

Complex multi-component pollutant-oil-water emulsions have caused serious environmental problems and increased the difficulty of purification treatment in the last few decades. The membrane based on two-dimensional (2D) materials can rationally control the interlayer distance, thus improved the separation performance of the membrane for complex wastewater. We herein reported a composite membrane, in which 2D metal-organic frameworks (MOFs) Co -CAT-1 with super-hydrophilicity cross-linked by polyethylene imine (PEI) was integrated into graphene oxide (GO) and then coated on polyvinylidene fluoride (PVDF) membrane (CPG membrane). The CPG membrane exhibited highly efficient in separating oil-water (including crude oil) emulsions, achieving a flux of 219 L∙m−2∙h−1∙bar−1 and a separation efficiency of 99.2 %. Moreover, the separation efficiency for complex emulsions after several cycles was maintained >99 % for dyes and 76 % for heavy metal ions (Ni2+, Pb2+, Zn2+). The remarkable fouling resistance and reusability of CPG membrane in purifying complex oil-in-water emulsions can be attributed to their internal cross-linking, electrostatic interactions, hydrogen bonding attraction, and π-π stacking. Molecular dynamics simulations were employed for in-depth studies on the separation processes of dye- and heavy metal ions-emulsions, revealing the mechanisms of mass transfer within the membrane. This work aims to construct stable and multifunctional membranes for separating pollutant-oil-water emulsions with multi-component. [Display omitted] • CPG composite membrane was fabricated via a facile self-assembly process. • The membrane showed promising synergistic separation performance and excellent reusability for multi-component emulsions. • CPG composite membrane exhibits excellent underwater oil repellency, anti-fouling, and superior resistance to extreme conditions. • The molecular dynamics simulations were employed to reveal the separation mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The natural convection on metallic foam-sintered plate at different inclination angles was experimentally studied. Seven copper foam samples with different pore densities (10–40 pore per inch), porosities (0.90–0.95), and aspect ratios (the ratio of foam thickness to sample length, 0.1–0.5) were measured at inclination angles of 0° (vertical orientation), 15°, 30°, 45°, 60°, 75°, 90° (horizontal orientation). The heat conduction and natural convection inside the foam both contributed to the total heat transfer. Although, the form and viscous drag, which are influenced by permeability and viscous friction in the thermal boundary layer respectively, tend to suppress the natural convection, the heat transfer was finally enhanced by the foam sintered surface due to large surface area extension. Optimum inclination range 60–75° corresponding to maximum average Nu number was found in the heat flux range of 600–1800W/m2. The sintered foam surface with lower porosity and pore density was recommended for heat transfer enhancement. Particularly, the sample with porosity 0.9, pore density of 10PPI, aspect ratio of 0.5 offered the highest average Nu number among the studied samples. An empirical correlation for modified Nusselt number at isoflux boundary condition considering the foam morphology parameter and inclination angle was proposed within deviation ±15% between the correlation and the experimental data. [Copyright &y& Elsevier]

• The construction of the enhanced plate used in the AHU is proposed. • The highest enhanced effects are obtained for "H12-R10-h4" (PEC=1.45 at Re=5000). • All nine enhanced channels can enhance heat transfer at the same pressure drop. • The DMTD is proposed for the cross-flow AHU heat exchanger design. • The heat exchanger picked up is "H7.5-R10-h3" which has the maximum ratio of the heat exchange rate (40.5 kW) over the flow loss power (3.25 kW). In this paper, the construction process of the enhanced plate, the heat transfer and fluid flow characteristics, and the domain decomposition method for AHU performance estimation are presented. The AHU heat exchanger 3D model is built from plate modeling to heat exchanger assembling. The heat transfer plate modeling starts from a basic flat plate, elliptic cylindrical dimples (ECDs) are firstly added to the fixed location, and then spherical crown dimples (SCDs) are applied to the flat surface among the ECDs. For the enhanced channels, the effect of channel height is weaker than SCD depth on the Nusselt number and friction factors. For all enhanced channels, the PECs are larger than 1.1 within Re from 5000 to 35,355. The performance of a deeper depth of SCD is superior to that of a shallow one when the channel height is the same. Among the nine channels studied, the highest enhanced effects are obtained for "H12-R10-h4" (PEC=1.45 at Re=5000). And all nine enhanced channels can enhance heat transfer at the same pressure drop among the Reynolds number of 5000 to 35,355. The energy saving performance decreases with Re, and the channels with smaller SCD depth can save more energy when channel height is identical at the higher Reynolds number region. A decomposition thermal design method is proposed for the cross-flow AHU heat exchanger design, and the typical AHU design result is picked based on the heat exchange rate and flow loss power. The recommended heat exchanger is "H7.5-R10-h3" whose heat exchange rate is 40.5 kW when flow loss power is 3.25 kW. [ABSTRACT FROM AUTHOR]

The presence of aggregated platinum in a proton exchange membrane (PEM) is inevitable due to the degradation and re-deposition of the platinum catalysts. While few studies focus on the thermal conductivity of PEM containing platinum particles. First of all, recent studies on the thermal conductivity of pure Nafion are reviewed. Subsequently, classical molecular dynamics is used to calculate the thermal conductivity of Nafion containing a platinum particle, with the effects of water content, particle size and particle number taken into consideration. It is found that thermal conductivity increases with the increase of water content. Increasing particle size and particle number both have negative effects on the thermal conductivity. Moreover, the total heat transfer is decomposed into the heat transfer between polymer chain atoms, that between atoms in small molecules, that between platinum atoms, and the coupled heat transfer of the above three parts. Based on the decomposition, the inherent mechanisms of these effects are revealed. • Recent studies on the thermal conductivity of Nafion membrane are reviewed. • Thermal conductivity of after-used Nafion is studied using classic molecular dynamics. • The heat transfer process in after-used Nafion is revealed in details. [ABSTRACT FROM AUTHOR]

Accurate, simple and quick detection methods for Cr(VI) detection are urgently needed for water quality monitoring. Herein, a novel and facile method of detecting Cr(VI) (Cr 2 O 7 2−/CrO 4 2−) ions is developed via the fluorescent detection technology based on metal-organic frameworks (MOFs) doped with sulfur quantum dots (SQDs) (SQDs@UiO-66-NH 2). The blue-light-emitting SQDs@UiO-66-NH 2 composites exhibit excellent fluorescent properties in water environment with high quantum yield (68%) and ideal fluorescent stability, thus demonstrating excellent potential for serving as a chemical sensor. After characterizing the performance and stability of SQDs@UiO-66-NH 2 , qualitative and quantitative detection of Cr 2 O 7 2− and CrO 4 2− ions was successfully conducted. The fluorescence of SQDs@UiO-66-NH 2 composites in aqueous solution was quenched effectively with more than 90% quenching efficiency by Cr(VI) via the inner filter effect. The detection system provides considerable advantages such as rapid response (10 s), high sensitivity with a low detection limit of 0.16 μM in a broad linear range of 0–200 μM (R2 = 0.99) for Cr 2 O 7 2− and 0.17 μM for CrO 4 2− in a broad linear range of 0–220 μM (R2 = 0.99), high selectivity and reproducibility for at least five cycles with simple washing with alcohol. In practical applications, the sensor showed rapid response, high sensitivity and excellent recoveries (96.7%–105.4%) for detecting Cr 2 O 7 2− in real water samples. Furthermore, a SQDs@UiO-66-NH 2 -based fluorescent test paper was successfully developed, providing a simple, reliable and portable method for Cr(VI) (Cr 2 O 7 2−/CrO 4 2−) detection in water environment. Image 1 • A luminescent sensor (SQDs@UiO-66-NH 2) with high quantum yield via PSM method was fabricated. • Qualitative and quantitative detection of Cr(VI) with rapid, sensitive and selective response achieved via IFE effect. • Portable SQDs@UiO-66-NH 2 -based fluorescent test paper was facilely developed for Cr(VI) detection. • Satisfied recoveries obtained with the sensor applied in Cr(VI) detection in real water samples. [ABSTRACT FROM AUTHOR]

A molecularly imprinted polymers (MIPs)-isolated AuNP-enhanced fluorescence sensor, AuNP@MIPs-CdTe QDs, was developed for highly sensitive and selective detection of oxytetracycline (OTC) in aqueous medium. The developed sensor combined the advantages of strong fluorescence signal of metal-enhanced fluorescence (MEF), high selectivity of MIPs, and stability of CdTe QDs. The MIPs shell with specific recognition served as an isolation layer to adjust the distance between AuNP and CdTe QDs to optimize the MEF system. The sensor demonstrated the detection limit as low as 5.22 nM (2.40 μg/L) for a concentration range of 0.1–3.0 μM OTC and good recovery rates of 96.0–103.0% in real water samples. In addition, high specificity recognition for OTC over its analogs was achieved with an imprinting factor of 6.10. Molecular dynamics (MD) simulation was utilized to simulate the polymerization process of MIPs and revealed H-bond formation as the mainly binding sites of APTES and OTC, and finite-difference time-domain (FDTD) analysis was employed to obtain the distribution of electromagnetic field (EM) for AuNP@MIPs-CdTe QDs. The experimental results combined with theoretical analyses not only provided a novel MIP-isolated MEF sensor with excellent detection performance for OTC but also established a theoretical basis for the development of a new generation of sensors. [Display omitted] • The imprinted polymers-isolated AuNP-enhanced fluorescence sensor was synthesized. • Metal-enhanced fluorescence combined with imprinted polymers to improve performance. • Molecular dynamics simulation revealed imprinted sites were identified by H-bonds. • The sensor showed great potential for oxytetracycline detection in water samples. [ABSTRACT FROM AUTHOR]

Facilitated transport mixed matrix membranes (FTMMMs) separation technology has shown advantages in improving CO 2 recycling efficiency and reducing the environmental impacts associated with carbon emission. The design of FTMMMs is highly dependent on the selection of a compatible combination of polymer and filler. Herein, a novel grafted nanoparticles (GNPs) filler UiO-66-NM@PEG with multiple groups prone to hydrogen bond was designed to alleviate the phase separation and performance degradation caused by filler/polymer poor compatibility. In the GNPs configuration, by employing the coexistence strategy of coupling reaction and covalent bonds, maleic anhydride (MAH) was coupled with the amino group on UiO-66-NH 2 without clogging or cracking, and the generated carboxyl groups can be cross-linked with the hydroxyl groups on the poly (ethylene glycol) (PEG) by covalent bonds. The UiO-66-NM@PEG demonstrated excellent interface compatibility between the filler and matrix phase of UiO-66-NM@PEG/PVDF, which was further convinced by molecular modelling. The resultant UiO-66-NM@PEG/PVDF achieved a simultaneous enhancement of gas permeability (537.6 Barrer) and ideal CO 2 /N 2 selectivity (47.8), which surpassed Robenson upper bound. Moreover, the UiO-66-NM@PEG/PVDF has a lasting sustainability over 960 h (40 days), and a valid anti-acid/alkali corrosion resistance in harsh environments. More importantly, UiO-66-NM@PEG can also be well mixed with other mixture matrices such as hydroxy-terminated polydimethylsiloxane (PDMS) and polyether-block-polyamide copolymer (PEBAX) to promote permeability/ideal selectivity up to (724.1 Barrer/21.1) and (307.4 Barrer/31.4). We thus concluded that this rational-design GNPs approach provides a general toolbox for controllable engineering in GNPs whereby enhanced favorable filler/matrix compatibility in FTMMMs with optimized CO 2 /N 2 separation properties. By the means of covalent "bridge-crosslinking", the UiO-66-NM@PEG/PVDF FTMMM with favorable phase compatibility between filler/matrix displayed excellent gas separation performance. [Display omitted] • A novel grafted filler UiO-66-NM@PEG was synthesized via Covalent "Bridge-crosslinking" strategy. • The membrane showed excellent sustainability over 40 days and corrosion resistance. • UiO-66-NM@PEG exhibited favorable filler/matrix compatibility in other two matrices. • The performance of UiO-66-NM@PEG/PVDF surpassed Robenson upper bound. [ABSTRACT FROM AUTHOR]

• A method for studying microlayer effects on flow boiling is proposed. • The availability of combining radius-based and taylor models in describing microlayer formation is verified. • The implementation procedure of the microlayer model is fully demonstrated. • The effects of different microlayer models on flow boiling are illustrated. • The contribution of microlayer evaporation to heat transfer is 75%−83%. The microlayer evaporation below the vapor bubble contributes much to heat dissipation and bubble growth, but it is hard to explore this microcosmic phenomenon. This study proposes a method for investigating the subcooled flow boiling heat transfer in a rectangular channel by considering the microlayer, conjugated heat transfer, a reasonable nucleation site density, and an accurate liquid-vapor interface. The implementation procedure of the microlayer model in the numerical simulation is fully demonstrated. Based on that, the bubble growth, flow pattern, heat transfer, microlayer depletion, evolutions of evaporative heat flux and dry patch during the subcooled flow boiling under different initial microlayer thicknesses are presented. Results indicate that microlayer evaporation contributes much to bubble volume and heat dissipation. The vapor volume generated by the microlayer evaporation exceeds that flows out of the channel because of the condensation effect at the liquid-vapor interface induced by the subcooled liquid, indicating bubble growth and expansion are completely attributed to microlayer evaporation. Simultaneously, much heat dissipates from the heat source due to microlayer evaporation, which contributes over 70% to both local and whole heat transfer. Because of microlayer depletion, some dry patches may appear at the elongated bubble tail. Therefore, liquid slug, elongated bubble, and dry patch circulate in the studied mini-channel, corresponding to heat transfer modes of liquid convection, microlayer evaporation, and vapor convection, supporting the three-zone heat transfer model. In addition, the initial microlayer thickness is related to the thermal resistance and affects the microlayer evaporation rate, leading to different flow patterns and heat transfer characteristics. The initial microlayer thickness is related to the slipping velocity of bubbles based on the Taylor model, which is recommended for the flow boiling study in a mini-channel. [ABSTRACT FROM AUTHOR]

Highlights • The bubble nucleation position changes with increasing wall temperature. • Differences in nucleation process at different wall temperatures were explained. • An optimal area fraction exists for the lowest nucleation temperature. Abstract The bubble nucleation of liquid argon over patterned surfaces with different wettabilities is investigated by using molecular dynamics (MD) simulations. In order to study effects of different wall temperatures on bubble nucleation process, bubble nucleation positions and bubble dynamics behaviors are observed. Simulation results show that at low wall temperatures bubble nucleation tends to occur over the hydrophobic part of the wall. With increasing wall temperature, the bubble nucleus gradually changes its position from the hydrophobic to hydrophilic part. When the wall temperature increases to a certain value, bubble nuclei first appear on both the hydrophobic and hydrophilic parts. By analyzing heat flux and change trend of argon state points, differences in bubble nucleation process at different wall temperatures are explained. Moreover, the effect of area fraction of hydrophobic part on bubble nucleation temperature is investigated. It is found that there exists an optimal area fraction which makes the bubble nucleation temperature the lowest. [ABSTRACT FROM AUTHOR]

Highlights • Relative humidity has little effect on the temperature distribution of the fin. • No condensation occurs near the inlet area. • The maximum condensation mass flux is detected in the second row of pipe. • Relative humidity has little influence on the sensible heat transfer rate. • But manifests profound effects on the latent and total heat transfer rate. Abstract The heat and mass transfer of a five-row fin-and-tube heat exchanger under dehumidifying conditions is numerically studied in this paper, and the distributions of vapor condensation mass rate for both fin and tube surfaces are obtained. The influences of vapor mass percent of humid air and inlet velocity on heat and mass transfer are investigated. Numerical results reveal that relative humidity has little effect on the temperature distribution of the fin under humid conditions. It is also noticed that no condensation occurs near the inlet area, and the maximum condensation mass flux is detected in the second row of pipe; this phenomenon is more obvious at higher inlet velocities. Relative humidity has little influence on the sensible heat transfer rate; however, it manifests profound effects on the latent heat transfer rate and total heat transfer rate. The dimensionless heat and mass transfer factors are also obtained from the numerical study and compared with the correlations in literature. [ABSTRACT FROM AUTHOR]

For applications of reactive transport in porous media, optimal porous structures should possess both high surface area for reactive sites loading and low mass transport resistance. Hierarchical porous media with a combination of pores at different scales are designed for this purpose. Using the lattice Boltzmann method, pore-scale numerical studies are conducted to investigate diffusion-reaction processes in 2D hierarchical porous media generated by self-developed reconstruction scheme. Complex interactions between porous structures and reactive transport are revealed under different conditions. Simulation results show that adding macropores can greatly enhance the mass transport, but at the same time reduce the reactive surface, leading to complex change trend of the total reaction rate. Effects of gradient distribution of macropores within the porous medium are also investigated. It is found that a front-loose, back-tight (FLBT) hierarchical structure is desirable for enhancing mass transport, increasing total reaction rate, and improving catalyst utilization. On the whole, from the viewpoint of reducing cost and improving material performance, hierarchical porous structures, especially gradient structures with the size of macropores gradually decreasing along the transport direction, are desirable for catalyst application. [ABSTRACT FROM AUTHOR]

Solubility trapping is crucial for permanent CO 2 sequestration in deep saline aquifers. For the first time, a pore-scale numerical method is developed to investigate coupled scCO 2 -water two-phase flow, multicomponent (CO 2 (aq), H + , HCO 3 − , CO 3 2− and OH − ) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO 2 (aq) concentration, scCO 2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is required by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The pore-scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Finally, effects of wettability are also studied. The pore-scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO 2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models. [ABSTRACT FROM AUTHOR]

Comprehensive insights into the sludge digestate dewaterability were gained through porous network structure of sludge. We measured the evolution of digestate dewaterability, represented by the solid content of centrifugally dewatered cake, in high-solids sequencing batch digesters with and without thermal hydrolysis pretreatment (THP). The results show that the dewaterability of the sludge after digestion was improved by 3.5% (±0.5%) for unpretreated sludge and 5.1% (±0.4%) for thermally hydrolyzed sludge. Compared to the unpretreated sludge digestate, thermal hydrolysis pretreatment eventually resulted in an improvement of dewaterability by 4.6% (±0.5%). Smaller particle size and larger surface area of sludge were induced by thermal hydrolysis and anaerobic digestion treatments. The structure strength and compactness of sludge, represented by elastic modulus and fractal dimension respectively, decreased with increase of digestion time. The porous network structure was broken up by thermal hydrolysis pretreatment and was further weakened during anaerobic digestion, which correspondingly improved the dewaterability of digestates. The logarithm of elastic modulus increased linearly with fractal dimension regardless of the pretreatment. Both fractal dimension and elastic modulus showed linear relationship with dewaterability. The rheological characterization combined with the analysis of fractal dimension of sewage sludge porous network structure was found applicable in quantitative evaluation of sludge dewaterability, which depended positively on both thermal hydrolysis and anaerobic digestion. [ABSTRACT FROM AUTHOR]

In this paper, a 3-D model of an electrostatic fluid accelerator was simulated using the finite element method (as implemented in COMSOL Multiphysics). To investigate the heat transfer performance of the accelerator, the impinging flow of the accelerator was used to cool down a heating round plate. The heat transfer coefficient and temperature distribution of the plate were numerically investigated with respect to the heat flux and radius of the round plate, and a comparison was made between the impinging flow of the accelerator and a uniform jet flow. To explore this in greater depth, a non-uniform heat flux was applied on the round plate to study the cooling effect of the accelerator on the surface with a hot spot. The effects of the hot spot heat flux and the hot spot size were then investigated. This study provides a reference for the practical cooling process of commercial chips, with and without hot spots, by adopting electrostatic fluid accelerators. [ABSTRACT FROM AUTHOR]

Self-cleaning porous membrane can serve as condensing surface for its capacity of transporting condensate to the back through the pores thus keeping the surface clean during the whole condensing period. However, the three-dimensional (3D) condensate behaviors including the initial nucleation, growth and permeation in the porous structures have seldom been clarified comprehensively. In this work, the 3D pseudopotential LB model with a phase change model are employed, and the condensation process inside the porous membrane with various porosity, wettability, additional external force and section geometric configurations are investigated. It's found that with the increase of porosity, surface hydrophobicity and additional external force, more rapid penetration of condensate in the porous media and correspondingly faster removal rate of liquid can be obtained, and the subsequent vapor condensation is enhanced. But the nucleation time gets longer with high porosity and surface hydrophobicity. The additional external force has little effect on the nucleation time. Larger porosity and lower flow resistance inside the straight channel lead to higher condensation rate at the initial stage of condensation, while the porous structure with distorted pores with the same porosity contributes to improve the total condensation amount. This work helps to select the porous membranes with different porosity, wettability or pore scale geometric characteristic and external field for different condensation conditions in specific applications. [ABSTRACT FROM AUTHOR]

• Density based topology optimization method is used to design microchannel heat sinks. • Five inlet and outlet structures are considered by bi-objective optimization. • Straight line inlet and outlet with extension area presents best overall performance. • Reynolds number, thermal conductivity ratio and fluid heat generation are studied. • 2D optimized results are stretched to 3D geometry and validated by 3D CFD simulation. Topology optimization can generate better structures of microchannel with improved cooling performance. In this paper, microchannel heat sinks with five different inlet and outlet structure combinations are optimized using bi-objective topology optimization based on the density method. The layouts of channels are optimized to minimize the power dissipation and total heat generation at the same time. The results show that the straight line inlet and outlet with extension areas (SE) can reduce 20%-50% power dissipation when realizing the same heat transfer performance compared with traditional one channel inlet and one channel outlet (OC). Effects of Reynolds number, the ratio of solid and fluid thermal conductivity and the dimensionless heat generation coefficient in fluid domains are also investigated. The simple channels can be obtained with higher ratio of solid and fluid thermal conductivity and/or higher dimensionless heat generation coefficient in fluid domains. With optimization further considered in the inlet and outlet regions, better overall performance can be obtained. Finally, the 2D optimized structures are further validated by three-dimensional numerical simulation. It is found that the optimized design can realize 53.28% increment of Nusselt number with 40.89% reduction in pressure drop compared with traditional microchannel heat sinks. [ABSTRACT FROM AUTHOR]

In this study, laboratory tests of both low temperature (60–90 °C) and high temperature (120–180 °C) thermal hydrolysis (LTHP and HTHP) were performed on mechanically dewatered high-solid sludges (at total solid of 14.2 wt% and 18.2 wt%) to evaluate the extent of organic solubilization through rheological measurements. The effects of treatment temperature and duration on organic solubilization and viscoelastic behavior of the sludge were comprehensively investigated. The results indicated that the organic solubilization contents including soluble chemical oxygen demand, soluble protein, and soluble polysaccharides increased logarithmically with the treatment time. Protein solubilized considerably faster than polysaccharides during thermal hydrolysis. The rheological curves exhibited the Payne effect in the amplitude sweep oscillation test. The elastic modulus in linear viscoelastic regime decreased logarithmically with treatment time. The viscoelastic behavior of sludge was well modeled by the Kaye–Bernstein–Kearsly–Zapas (KBKZ) model with paralleled Maxwell elements to describe the frequency dependence of elastic modulus and viscous modulus. With respect to the relaxation spectrum, the relaxation modulus first decreased with relaxation time and then increased. The relaxation modulus in each Maxwell element decreased with the treatment temperature and duration. Furthermore, in the HTHP, the influence of treatment temperature on enhancing organic solubilization and decreasing viscoelasticity exceeded the influence of treatment duration. In contrast, the treatment duration played a more important role than temperature in the LTHP. The content of organic matters was linearly related and logarithmically related to the elastic modulus in the LTHP and in the HTHP, respectively. The rheology analyses demonstrated that viscoelastic properties could be used as indicators to estimate the extent of organic matter solubilization in thermal hydrolysis process. The developed viscoelastic model provided insights for future research in numerically simulating the fluid dynamics of sludge. [ABSTRACT FROM AUTHOR]

In this paper we use the multiphase multispecies Lattice Boltzmann method to investigate the influence of non-condensable gas on condensation. Condensation on a horizontal cold wall as well as that on a vertical wall with droplet movement is investigaged. The presence of non-condensable gas obviously reduces the condensation mass rate as well as the heat flux compared to condensation from pure vapor. The waiting time before nucleation is increased with non-condensable gas, and the wetting characteristics are also changed (the contact angles are increased), which further influences the heat transfer. Correlations of the relationship between droplet diameter and condensing time for different surface wettability, or contact angles, as well as different air mass fraction are obtained. As for condensation on a surface parallel to the gravitational force, it’s demonstrated that the presence of non-condensable gas reduces the droplet departure diameter and increases the period between subsequent droplet formation and departure. [ABSTRACT FROM AUTHOR]

Fundamental understanding of coupled physicochemical processes is crucial for improving the heat storage/release performance of thermochemical heat storage systems. In this study, for the first time a coupled lattice Boltzmann model is developed to simulate the particle-scale physicochemical processes during Ca(OH) 2 dehydration, including fluid flow, heat transfer, vapor mass transport and chemical reaction. The dehydration processes of a single Ca(OH) 2 particle, a single particle with coated ceramic shell and packed particles are studied, and thorough parametric studies are performed. The results show that the dehydration reaction rate of a single particle is mainly determined by the temperature and Ca(OH) 2 concentration. Introducing more micro-pores or meso-pores into the particle is favorable to achieve quicker heat storage, but at the cost of lower energy density. Increasing the Reynolds number from 0.3 to 3 or increasing the inlet temperature by 50 K can shorten the reaction time t c by at least 33.8%. Dedicate design of the shell coated on the particle can enhance the dehydration process with t c decreased by 3.5%. The underlying heterogenous structures greatly affect the reaction rate of packed particles, and local cracks should be prevented to achieve fast and stable heat storage response. • Reactive transport process of Ca(OH) 2 dehydration at particle scale is simulated. • Temperature and solid concentration determine the dehydration of single particle. • Coating ceramic shell would increase the dehydration reaction rate of particle. • Structural heterogeneity strongly affects the dehydration of packed particles. • Effects of structural and operational parameters on the dehydration are studied. [ABSTRACT FROM AUTHOR]

Representative elementary volume (REV)-scale structure of shale matrix is reconstructed based on elementary building block (EBB) model using a stochastic reconstruction method called Quartet Structure Generation Set. In the EBB model, various constituents with different pore morphologies in shale matrix including organic matter and inorganic minerals are considered as different EBBs, and in each EBB, specific structural parameters and transport properties are locally defined. A generalized lattice Boltzmann model for fluid flow through tight porous media with slippage is employed to simulate fluid flow through the reconstructed REV-scale structures. A four-EBB shale matrix including clay, calcite, pyrite and organic matter is studied and its permeability is predicted. Effects of organic content, grain size, interparticle pores on the permeability of the REV-scale matrix are investigated. It is found that smaller grain size and interparticle pores can increase the permeability. The influences of complex physical processes such as slippage and adsorption on the REV-scale permeability are also explored. Slippage effect increases as the pore size decreases. Adsorption has two opposite effects on the permeability, and which one dominates depend on pressure. The present study can help understand gas transport in shale matrix and improve reservoir scale studies. [ABSTRACT FROM AUTHOR]

A thermal conductivity test apparatus based on transient plane source method is built and developed to measure effective thermal conductivity of open porous materials at different gas pressures. The effective thermal conductivity of open nano-porous silica materials with porosity of 88.5% is measured under gas pressures ranging from 0.001 Pa to 1 MPa. The contribution of gaseous heat conduction to the effective thermal conductivity of materials is decomposed by subtracting the effective thermal conductivity at ultimate vacuum from that at different gas pressure. It is found that the contribution of gaseous heat conduction is much different with the gas thermal conductivity in nano-porous materials and that in free space. The result is also demonstrated by theoretical analysis and numerical simulation. [ABSTRACT FROM AUTHOR]

A numerical approach is developed to simulate the formation of pseudomorphs with presence of chemical fluids at the mesoscopic scale. This approach consists of the lattice Boltzmann method (LBM) for transport of chemical species in the pore space, a chemical reaction model including basic kinetics of the coupled dissolution and precipitation reactions, and a mesoscopic model for nucleation and crystal growth. Our study confirms the mechanism of the solution chemistry-driven interface-coupled dissolution-precipitation for the formation of pseudomorphs and identifies several sources for the generation of porosity in the pseudomorphs. We demonstrate that epitaxial precipitation is not necessary and random crystal growth may be more favorable for pseudomorphs. We show that the difference of precipitation barrier on the surface of the primary and secondary minerals should not be too large. Otherwise only the rim of the primary phase is roughly preserved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ca(ClO) 2 promoted sludge disintegration and VFAs production in acidogenic phase. • The functional microbes in methanogenic phase were enriched by Ca(ClO) 2. • Ca(ClO) 2 enhanced methane yield from two-phase anaerobic digestion system. • Ca(ClO) 2 -based method realized the balance between economy and efficacy. This study investigated the effects of calcium hypochlorite (Ca(ClO) 2) on biomethane generation from sludge two-phase anaerobic digestion system. In first (acidogenic) phase, volatile fatty acids (VFAs) were largely generated when pretreated by Ca(ClO) 2 , while the methane yield was severely inhibited. In second (methanogenic) phase, the methane yield was observably enhanced by Ca(ClO) 2. Further calculation showed that the total methane yield from the two phases was firstly promoted from 156.0 ± 4.5 to 269.9 ± 5.2 mL when Ca(ClO) 2 dosage enhanced from 0 to 1.6 g/L, which then reduced to 235.4 ± 5.5 mL when Ca(ClO) 2 content reached 2.0 g/L. Mechanism analysis showed that the suppression of Ca(ClO) 2 on coenzyme F 420 activity was relieved in methanogenic phase, and the abundances of functional microbes in methanogenic phase were enriched when added with Ca(ClO) 2. The Ca(ClO) 2 -based method well realized the balance between efficacy and economy, possessing outstanding potential for large-scale applications. [ABSTRACT FROM AUTHOR]