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An experimental investigation was carried out on high porosity metal foams subjected to array jet impingement with an objective to develop enhanced heat transfer configurations. In this study, we propose an integrated thermal management system (TMS) aimed toward leveraging the conjugate heat transfer capabilities of target plate, metal foam, and the jet plate--all made from aluminum and assembled such that a proper contact between them can be established. Steady-state heat transfer experiments were carried out for 10 and 20 pores per inch (PPI) aluminum foams of 0.93 porosity. Both metal foams were 12.7-mm thick. The normalized jet-to-jet spacing was varied from 2 to 12 times the jet diameter, while the jet diameter was fixed. The ratio of the jet plate thickness and jet diameter (nozzle aspect ratio) was 6.35, which ensured proper development of jets inside the nozzles. Experiments were conducted over a wide range of Reynolds number (based on jet diameter) varied from 100 to 5000. The obtained convective heat transfer coefficient for different configuration was evaluated in context with pressure drop. The analysis of experimental results reveal that large open area ratio jets combined with high porosity metal foams provide highly efficient and high-performance cooling for the investigated range of Reynolds numbers. [ABSTRACT FROM AUTHOR]

An enhanced flow field significantly improves reactant transfer and proton exchange membrane fuel cells (PEMFCs) performance. Metal foams with high porosity and electrical conductivity are promising flow field structures. This study aims to investigate the effect of metal foam porosity and pore density on PEMFC performance. A three-dimensional multi-physics PEMFC model with holomorphic microscopic metal foam (HMMF) as a cathode flow field was established using computational fluid dynamics (CFD). The HMMF with high porosity as a cathode flow field can enhance reactant transfer and accelerate the electrochemical reaction process. It is also observed that increasing the porosity of HMMF can significantly improve the peak power and current density of PEMFC. The simulation results show that the current density gains an increase of 15.3% by raising the porosity from 0.8 to 0.96. Besides, the current density increases by 4.3% when the pore density is 95 PPI compared to 21 PPI. Moreover, the effects of cathode stoichiometry ratios on oxygen molar fraction and polarization curves were studied to obtain better operating conditions for the HMMF flow field. The results indicate that increasing the cathode stoichiometry ratio can effectively enhance oxygen concentration. And the increase of the cathode stoichiometry ratio from 1.5 to 4.0 results in a 45.5% increment of current density. [ABSTRACT FROM AUTHOR]

The present study investigates the aeroelastic flutter characteristics of the graphene platelets (GPL) reinforced metal foam beam. Closed-cell metal foam beams having graded distribution of pores and functionally graded reinforcement of GPLs are considered in this study. The closed-cell metal foam model has been used for deriving the mechanical properties of the foam matrix, which makes provision for determining the relation between the co-efficient of porosity and the co-efficient of density. Modified Halpin-Tsai micromechanics is used to obtain the effective Young's modulus of the GPLs reinforced composite beam, Density and Poisson's ratio are calculated with the help of the rule of mixture. The Hamilton's principle together with the Ritz method, employing the first-order piston theory gives the governing equations of motion for aeroelastic flutter characteristics of the beam for different end conditions. Juxtaposition of dimensionless natural frequencies with the results previously published by others is executed for validating the correctness of the approach followed in the present model. A study of various parameters has been executed, and the results in tables and graphs present the influence of porosity as well as GPLs reinforcement, different boundary conditions and thermal loading on aeroelastic flutter characteristics of the FG-GPL reinforced metal foam beam. [ABSTRACT FROM AUTHOR]

In this research, free vibration characteristics of functionally graded metal foam doubly curved panels reinforced with graphene platelets and with porosities have been surveyed. Halpin Tsai's approach is utilized for extracting the effective Young modulus of porous metal foam nanocomposite and also the effective density of nanocomposite porous doubly curved shell panel is estimated by using an extended rule of mixture. The FSDT hypothesis is utilized for determining the displacement field and the Finite element and Hamilton principle are utilized for deriving the mass and stiffness matrices of the structure. Finally, the influences of several variables such as porosity distribution, porosity coefficient, GPL dispersion pattern, the weight fraction of Nanofillers, and span angles on the free vibrations characteristics of doubly curved shell panels with FG porosities and reinforced by graphene platelet have been reported in detail. [ABSTRACT FROM AUTHOR]

The purpose of present investigation is to study propagation of flexural wave in porous metal foam beams resting on Winkler–Pasternak foundation based upon refined higher-order shear deformable beam theory. Moreover, different types of porosity distribution through the thickness direction are probed namely; uniform, symmetric and asymmetric. The Hamiltonian approach is implemented to catch motion equations of porous metal foam beams. Then, the obtained governing equations of porous metal foam are solved analytically. The influences of different parameters such as various types of porosity distribution, porosity coefficient, slenderness ratio, wave number and elastic foundation coefficients on the variation of wave frequency, escape frequency and phase velocity are covered and presented within the framework of a group of figures which can be observed in detail. [ABSTRACT FROM AUTHOR]

Metal foam flow field shows great potential for next‐generation proton exchange membrane (PEM) fuel cell of high power density due to its well‐connected pore structure, high thermal and electrical conductivity. However, the complicated pore structure makes it a challenge for water management. To tackle this issue, a novel design of metal foam flow field with hierarchical pore structure was proposed. Based on lattice Boltzmann method (LBM), the structure‐performance relationship between hierarchical pore structure and water discharge capability of flow field was explored by using breakthrough time. Furthermore, an optimal hierarchical pore structure for metal foam flow field that shows superior water discharge capability was obtained. Compared with metal foam with uniform coarse pore structure, breakthrough time can be reduced roughly by 17.6% in the one with optimal hierarchical pore structures. This finding provides a theoretical foundation and technical guidance for developing metal foam flow field. [ABSTRACT FROM AUTHOR]

Purpose: This paper assumes that the performance of the porous gradient beam varies with temperature and humidity, while the environmental field varies continuously with the height of the beam section. The thermoelastic dynamic responses of porous beams with non-conservative gradients near buckling are discussed on this basis. Procedure First, the exact vibration model of the porous gradient beam with two porosity distribution types under three thermal and wet conditions is established. Considering that the beam is subjected to the follower load, the thermal coupling relationship and nonlinear dynamic equation of the porous gradient beam composed of porous metal foam material are given. In addition, according to the shooting method, the small amplitude vibration frequency response of the beam near the buckling is calculated. Results: The static and dynamic responses of different parameters (temperature, humidity, porosity, slenderness ratio, etc.) to gradient porous materials are discussed through the numerical results calculated by the shooting method. Conclusions: The results show that the material parameters, external load, and other factors will affect the beam's natural frequency to a certain extent. Therefore, this study can provide the necessary theoretical basis and reference for the safety design of structures under complex working conditions. [ABSTRACT FROM AUTHOR]

This research study performs a numerical assessment of the inward solidification of phase change material (PCM) integrated with metal foam (MF) encapsulated in a horizontal cylindrical geometry. The cylinder is not at melting temperature at the beginning, and its outer surface is subjected to convection boundary conditions. The 1D phase change model is resolved by applying the temperature transforming technique using an in‐house computer program written in C++. Four different MF materials, aluminum, copper, nickel, and stainless steel, with various porosities, are used to examine the thermal behavior of the storage system. It is found that the use of copper as a MF with higher effective thermal conductivity remarkably enhances the elapsed time for complete solidification. Additionally, for a porosity value of 0.92, the time for total solidification of copper is diminished by 94%, while the complete solidification time for Stainless Steel is decreased by 65% in comparison to the situation where no MF is used. [ABSTRACT FROM AUTHOR]

There is a wide range of processes to fabricate porous materials made of ceramics, polymers, and metals with an extensive range of applications. The Gasar method is one of the molten state methods of producing porous structures. Compared to other common commercial methods, the Gasar method allows effective control of the porosity, size, and orientation of the pores. One of the disadvantages of making gaseous foam is the creation of unwanted compounds in the structure of the produced foam limiting its application. Here, the fabrication of magnesium Gasar foam is studied using the thermal decomposition of polypropylene fibers (PPFs) as an additive foaming agent to produce hydrogen gas at atmospheric pressure. In this method, pores are formed due to the dissolution of hydrogen resulting from the thermal decomposition of PPFs in molten magnesium. The optimum amounts of fibers, working conditions of PPFs, preparation of the foaming agent, and the soaking method into the molten are explored and the parameters are optimized. TG, DTA, SEM, FTIR, EDS, and XRD are performed to analysis the foam structure. Also, the porosity amount and its diameter are calculated by CLEMEX software. The results show that by changing the amount of foaming agent from 0.4 to 10.2 wt%, the porosity rate changed from 0 to 23%. The highest porosity of 23% is attributed to 10.2 wt% of the foaming agent. Also, the average pore diameter at different levels of produced foams is investigated as a function of %PPFs. It is proposed that PPFs may be used to fabricate magnesium foams for load-bearing, weight-saving, and impact-absorbing applications. [ABSTRACT FROM AUTHOR]

Using metal foams mitigates the low thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES). However, the heat transfer within PCMs is not uniform due to natural convection. In the present study, the effect of the porosity distribution on the heat transfer performance of shell-and-tube thermal energy storage (TES) was analyzed. The results demonstrated that the melting rate and average heat transfer rate both were improved as the porosity gradient increased along positive y-direction. Compared with the uniform porosity (ε = 0.94), the average heat transfer rate was enhanced by 21.6% for ε = 0.94 + 0.267y during the melting process. For the porosity gradient increasing along outer radius direction, the heat transfer rate near the heating wall was improved, while the phase change process of PCM near the outer wall slowed down. The maximum of average heat transfer rate existed for ε = 0.88 + 0.6r. [ABSTRACT FROM AUTHOR]

Closed-cell aluminium foams with different compositions have been manufactured starting from powders and also characterized from a morphological point of view and by means of compressive tests in order to determine mechanical properties. Circularity, equivalent diameter, and average porosity area of such foams have been calculated from the analysis of cross-sections as well specific energy absorption in compression tests. Samples with a higher amount of blowing agent (TiH2) have the highest energy absorption while samples with a higher amount of stabilizing agent (SiC) exhibit good foam properties overall (best compromise between morphology and energy absorption). The analysis of morphological properties, such as area, circularity, and equivalent diameter, can provide a better understanding of the foam's structure and porosity––parameters which can be manipulated to enhance the foam's properties for specific applications, both structural and functional. [ABSTRACT FROM AUTHOR]

Metal foams and alloy foams are a novel class of engineering materials and have numerous applications because of their properties such as high energy absorption, light weight and high compressive strength. In the present study, the methodology adopted to develop a Ni-Cr alloy foam is discussed. Polyurethane (PU) foam of 40PPI (parts per inch) pore density was used as the precursor and coating techniques such as electroless nickel plating (ELN), ultrasonic-assisted electroplating of nickel (UAEPN), and pack cementation or chromizing were used to develop the Ni-Cr alloy foam. The surface morphology, strut thickness and minimum weight gain after each coating stage were evaluated. It was observed from the results that the adopted coating techniques did not damage the original ligament cross-section of the PU precursor. The minimum weight gain and the coating thickness after the UAEPN process were observed to be 42 g and 40–60 μm, respectively. The properties such as porosity percentage, permeability and compressive strength were evaluated. Finally, the pressure drop through the developed foam was estimated and verified to determine whether the developed foam can be used for filtering applications. [ABSTRACT FROM AUTHOR]

The stress jump coefficient at the fluid/porous interface is a fundamental parameter to study the velocity distribution in a porous composite system. In this paper, a substantial work is carried out to investigate the characteristics of the stress jump coefficient. To this end, the real pore structure of metal foam is constructed using the Weaire–Phelan model, and the macro model and the pore-scale model are presented to simulate a complex three-dimensional porous composite system. Furthermore, a novel method to determine the stress jump coefficient is proposed. The influences of the inlet velocity, the rotation number, the porosity, the free fluid layer thickness, and the flow pattern (the Poiseuille flow, the free boundary flow, and the rotating channel flow) on the stress jump coefficient are studied. The results show that the stress jump coefficient varies with the porosity, which shows that it is dependent on the porous structure. It also found that the stress jump coefficient is independent of the inlet velocity, the rotation number, and the flow pattern. When the thickness of the free fluid layer is large, the stress jump coefficient is also independent of the thickness of the fluid layer. [ABSTRACT FROM AUTHOR]

One of the most promising and heavily researched energy storage systems due to their high energy density, rate capability and extended cycle life are lithium-ion batteries. Their performance and efficiency are nonetheless strongly dependent on their constituent materials and design, including the current collectors. One attractive approach in this respect is the use of metal foams as an alternative to the conventional current collectors. This concept is therefore intended to increase the current collectors' specific surface area and therefore load more active material by nominal area while keeping the cell architectures simple and less costly. In the present work, nickel is chosen as a model system for a proof of concept of a novel manufacturing method for nickel foams using a combination of 3D printing, coating and electroplating. The purpose is to create geometrically well-defined hollow structures with high porosity and specific surface area density that can rival and partially outperform the commercially available nickel foams. To this end, a 3D printer is used to create geometrically flexible and well-defined open-pored disks of HIPS (high-impact polystyrene), which are then spray coated with a graphite-based conducting layer and subsequently electroplated with a 5–30 µm thin layer of nickel from an additive-free nickel sulfamate electrolyte. Following the coating process, the support structure is dissolved with toluene, resulting in structures with a unique combination of porosity in the range of 92.3–99.1% and an ultra-high specific surface area density up to 46 m2/kg. Morphological characterization by light and scanning electron microscopy has proven that the temporarily required polymer substrate can be mildly and completely removed by the suggested room temperature dissolution process. [ABSTRACT FROM AUTHOR]

The "excess salt replication process" is a new simple method of fabrication of open-cell metal foam based on the commonly known salt replication method. Porous materials with porosity between 46% and 66% result when the employed alloy is 25% antimonial lead alloy and when it is 58% to 65% zamak 5. These foams are proposed as structured catalysts instead of packed beds in the treatment of wastewater. The local regimes influencing macroscopic air flow behaviour through these foams are delimited and boundaries are analysed in terms of sample length. Most of the experimental tests in this work exhibited a general trend of air flow in ESR foams dominated by the "strong inertia regime". It was established that the law governing the unidirectional air flow through these foams was the full cubic law. The permeability and inertia coefficient of five samples with a cell diameter between 2.5 and 4.5 mm were calculated, and an empirical correlation was fitted. The irregular cuboid shape of salt grains used in the ESR foam was the origin of the special cell form of ESR foams leading to an anisotropic ordered porous media. This can explain the macroscopic turbulence of air flow because there were many dead zones present in the corner of each cubic cell, thus causing kinetic energy loss starting at earlier regimes. [ABSTRACT FROM AUTHOR]

Constitutive description of the plastic flow in metallic foams has been rarely explored in the literature. Even though the material is of great interest to researchers, its plasticity remains a topic that has a much room for exploration. With the help of the rich literature that explored the material deformation mechanism, it is possible to introduce a connection between the results of the atomistic simulations and the well-established continuum constitutive models that were developed for various loading scenarios. In this work, we perform large-scale atomistic simulations of metallic gold foams of two different sizes at a wide range of strain rates ( 10 7 − 10 9   s − 1 ) under uniaxial compression. By utilizing the results of those simulations, as well as the results we reported in our previous works, a physical atomistic-continuum dislocations-based constitutive modeling connection is proposed to capture the compressive plastic flow in gold foams for a wide range of sizes, strain rates, temperatures, and porosities. The results reported in this work present curated datasets that can be of extreme usefulness for the data-driven AI design of metallic foams with tunable nanoscale properties. Eventually, we aim to produce an optimal physical description to improve integrated physics-based and AI-enabled design, manufacture, and validation of hierarchical architected metallic foams that deliver tailored mechanical responses and precision failure patterns at different scales. [ABSTRACT FROM AUTHOR]

Metal foams are interesting as sound absorbers because of their strength, low mass, high hardness, and damping. To foam fabricationmore accurate and achieve higher sound absorption coefficient (SAC), the effective parameters should be optimized. In earlier study (DOI: 10.32604/sv.2021.09729), the parameters of porosity percentage, pore size (D) and pore opening size (d) were optimized by the authors. In this study, we intend to investigate the effect of optimized percentage, D size and d size on the SAC of aluminum foam in the frequency 0 to 8000 Hz with the thicknesses of 5, 10, 20, and 30 mm. The genetic algorithm was performed employing the Lu model, using MATLAB software. According to the results, the optimum values of, D, and d at different frequencies and thicknesses are not constant. That is, at any given thickness and frequency, there are specific optimum amounts. This study provides a way to improve the SAC performance of porous metal materials for various and targeted applications. [ABSTRACT FROM AUTHOR]

In this paper, the free vibration and mechanical buckling analyses of the metal foam plates with porosities via a moving Kriging meshfree method based on the higher-order shear deformation theory are studied. The displacement fields are approximated by the moving Kriging shape functions, which satisfy Kronecker's delta property. Thanks to that property, the essential boundary conditions can be directly imposed the same with finite element method. In this study, the porosities are distributed by uniform, symmetric, and asymmetric distributions along the thickness direction. The natural frequency and critical buckling load of the metal foam plate are determined by solving the explicit governing equations, which are derived through the variational formulation. The influence of the porosity distribution, porous coefficient, width-to-thickness ratio and boundary condition on the natural frequency and critical buckling load of the porous metal foam plate is investigated and discussed in detail. Numerical examples indicate that the present approach is stable and well accurate predictions for investigating vibration and buckling behaviors of the porous metal foam plate. Moreover, an increase of the porous coefficient makes a decline of the natural frequencies and critical buckling loads of the plate. [ABSTRACT FROM AUTHOR]

Analysis of nonlinear vibration properties of stiffened toroidal convex/concave shells made of porous metal foam material in elastic medium has been performed in the present research. Metal foam is considered as porous material with uniform and nonuniform models. The governing equations of motion of eccentrically stiffened porous toroidal shell segments are derived based on the classical shell theory with the geometrical nonlinear in von Karman–Donnell sense and the smeared stiffeners technique. The nonlinear governing equations are solved with the use of Jacobi elliptic functions to obtain the exact frequency–amplitude curves of the geometrically nonlinear metal foam toroidal shell. Presented results demonstrate the significance of porosity distribution, geometric nonlinearity, foundation factors, stiffeners and curvature radius on vibration characteristics of porous toroidal convex/concave shells. [ABSTRACT FROM AUTHOR]

Aluminium foams possess multi-functional properties and a low specific weight, making them one of the most suitable choices in the application domain of the automobile and aviation sectors, vibrating machining, and structural parts. Compared to traditional fabrication routes, friction stir processing (FSP) is gaining acceptance as it is a cost-effective, highly efficient, and innocuous process to fabricate the foam precursors from the bulk substrate. In the current study, FSP was utilized to develop a precursor with MgCO3 powder acting as the blowing agent. The FSP experiments were performed as per Taguchi's L8 orthogonal array. The precursor was heat treated in an electric furnace at a holding temperature of 650 °C for 10 min. After the post-heat treatments, this precursor resulted in a porous structure due to the evolution of CO2 gas from the composite. The simultaneous effect of tool rotation speed, traverse speed, and shoulder diameter was investigated on the pore size and porosity of the foam produced. The composite parameter "unit stirring" is found to be closely related to the processed zone (PZ) and volume processing rate of the processed zone, pore size, and the degree of porosity. The highest porosity of 16.67% was obtained with an average pore size of 10.5 µm. The largest pore size, 17.8 µm, was observed to be associated with a porosity of 14.40%. The analysis of the Kiviat plot revealed that the values of the PZ area and volume processing rate possess a polar symmetry with unit stirring. The pore size and pore density were both found to be symmetrically distributed about the unit stirring. [ABSTRACT FROM AUTHOR]

A two-dimensional rectangular domain is considered with a discrete arrangement at equal distances from copper metal foam in a solar air heater (SAH). The local thermal non-equilibrium model is used for the analysis of heat transfer in a single-pass rectangular channel of SAH for different mass flow rates ranging from 0.03 to 0.05 kg/s at 850 W/m2 heat flux. Three different pores per inch (PPI) and porosities of copper metal foam with three different discrete thicknesses at equal distances are studied numerically. This paper evaluates the performance of SAH with 10 PPI 0.8769 porosity, 20 PPI 0.8567 porosity, and 30 PPI 0.92 porosity at 22 mm, 44 mm, and 88 mm thicknesses. The Nusselt number for 22 mm, 44 mm, and 88 mm thicknesses is 157.64%, 183.31%, and 218.60%, respectively, higher than the empty channel. The performance factor for 22 mm thick metal foam is 5.02% and 16.61% higher than for 44 mm and 88 mm thick metal foam, respectively. Hence, it is found that metal foam can be an excellent option for heat transfer enhancement in SAH, if it is designed properly. [ABSTRACT FROM AUTHOR]

Metallic foams are classified into two groups based on their pore structure: closed and open pores. The variability of cell structures directly depends on the production method and the variability of parameters. Open – cell metallic foams are used as heat exchangers due to their large surface area, in filters and separators due to their properties such as high liquid/gas permeability and corrosion resistance, and in water purifiers to reduce the concentration of unwanted ions dissolved in water because they can provide liquid flow, and in silencers due to their sound absorbing feature. Due to their thermal conductivity, they are generally used in functional applications such as catalyst supports and flame arresters. In this study, open cell aluminum foams with different pore sizes were produced using the powder metallurgy method and polyurethane foam (PUF) replica technique. After the PUF model material of the foams was removed at 500 °C for 6 h, they were sintered at different temperatures such as 850, 900 and 950 °C for 6 h. Density measurement, XRD analysis, microstructure examination and compression testing were applied to the sintered open-cell foams. The highest pore ratio and compressive strength were determined in foams with a 20 ppi (porosity per inch) pore ratio sintered at 950 °C. [ABSTRACT FROM AUTHOR]

Metallic foams are unique engineering materials with large pore volumes and an interconnected solid-metal structures. Lightweight, high-energy absorbing capacity and low thermal conductivities are some of the distinctive characteristics of metal foam that make them the preferred choice for many structural and functional applications. Although prevalent since 1940, the commercialization of metal foams has not achieved their full potential owing to large-scale production and near-net shaping limitations. In addition to technical challenges, mass production is hindered by to high manufacturing costs compared to those of ceramic and polymer foams. Depending on the pore structure, viz. open or closed, metal foams can be multifunctional, making them suitable for several conventional and niche applications. This review details the prevailing methods for fabricating closed metal foams, as well as their advantages and limitations. Apart from established methods such as gas injection and powder compaction, other emerging unconventional techniques for making metals, alloys and intermetallic foams are also discussed. The parameters that control the physical characteristics, such as the pore size and cell structure of the foam, are also explained. The standard characterization methods used to estimate various physical, mechanical, and thermal properties were reviewed. Applications and recent developments in closed foam research are presented here. [ABSTRACT FROM AUTHOR]

Thermal bifurcation studies are conducted on piezoelectric humid thermal piezoelectric foam nanobeam with voids. Various porosity designs are considered for the proposed structure. By synthesis the piezoelectric and humid thermal parameters with field component and displacement variables, the fundamental equations that governs the present study have been equipped. The finite element technique with developed beam model is applied to obtain the solution of the nanobeam. The authentication of this analytical model is tested with exiting literature. The strength of the nanobeam is improved by performing a detailed parametric study on physical variables and highlighted with plots and tables. [ABSTRACT FROM AUTHOR]

Hydrogen storage performance for metal hydride (MH) reactor is restricted by the poor thermal conductivity of MH. In this study, the gradient porosity metal foam was added into MH reactor for enhancing heat transportation (GMF reactor), and its hydrogen absorption performance was investigated numerically in detail. Then, thermal resistance analysis was conducted to analyze the heat transportation in GMF reactor, and Genetic Algorithm was applied for optimizing metal foam distribution under different conditions. It was indicated that the hydrogenation performance for optimized two-layer GMF reactor was increased by 11.5% compared with uniform metal foam reactor (UMF reactor). The optimization results indicated that the optimal volumetric fractions of metal foam (VFMF) are about 0.08 for both optimized GMF reactor and UMF reactor with the trade-off of hydrogen storage capacity and hydrogen absorption rate. Then, a new indicator of comprehensive hydrogen storage performance (CHSP) for MH reactor was proposed, which includes the influence of hydrogen storage rate, hydrogen storage capacity, volumetric storage density and gravimetric storage density. Besides, the hydrogenation performance for optimized GMF reactor was improved with metal foam layer increasing, and the optimal porosity distribution was gradually approaching a specific power exponent trend. It was showed that the hydrogenation performance for power-exponent GMF reactor was increased by 2.8% and 18.2% compared with that of optimized four-layer GMF reactor and UMF reactor, respectively. • Gradient porosity metal foam (GMF) was added into MH bed to improve heat transfer. • Genetic algorithm was used to optimize the distribution of metal foam. • Performance of two-layer GMF reactor increases by 11.5% compared with UMF reactor. • The optimal volumetric fraction of metal foam (VFMF) for reactors equal about 0.08. • A new indicator of comprehensive hydrogen storage performance (CHSP) was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] Hierarchically porous ceramics possess tailored porosity across multiple length scales, giving rise to materials with low density, high specific properties, and multifunctionality. Here, we report a method that combines self-assembly and 3D printing to create ceramic architectures with hierarchical porosity spanning from the nano- to microscale. To programmably define their microscale porosity, an additive manufacturing method, known as direct ink writing, is used to create 3D lattices composed of cylindrical struts. Nanoscale porosity is generated within each strut by block copolymer templating followed by photopolymerization and pyrolysis in a non-oxidative environment, which transforms the preceramic polymer, polycarbosilane, into silicon oxycarbide with a "nanocoral" morphology. The resulting hierarchically porous ceramic lattices exhibit excellent mechanical energy absorption (0.31 MJ/m3), comparable to metal alloy foams. They also possess an order of magnitude lower thermal conductivity (0.087–0.16 W/m⋅K) compared to bulk preceramic polymer-derived ceramics. Prior to pyrolysis, the printed architectures can be manipulated to produce more complex shapes, including lattices with twisted, helical, and overhang features as well as repeated folding to create an origami airplane. By combining self- and directed assembly, our approach opens new avenues for creating hierarchically porous ceramics. [ABSTRACT FROM AUTHOR]

Metallic foams are engineering materials. Metallic foams are used for various applications such as crashworthiness, heat exchangers, fuel cells, implants, water, and air purifiers because of their low density, high heat dissipation capacity, and high sound and vibration damping ability. Currently, mostly low-density metal foams like aluminum, magnesium, and titanium are produced largely because low-density metal foams are easy. For high-density metals, the flux of matter in the pores is generated during foaming due to its high weight. Therefore, significant porosity is achieved. On the other hand, the cost of the foams of aluminum, titanium, magnesium, and other low-density metals is relatively high. Also, the strength and thermal resistance of foams of aluminum and magnesium are low. Due to the problems above, researchers have developed inexpensive material foams such as iron and steel. Still, the foaming of these materials is relatively complex because of their very high density. Various iron and steel foam fabrication techniques have been developed to produce low-cost foams. Some of them are reviewed in detail in the present work. Casting and powder metallurgy was found to be the two most common techniques to produce iron and steel foams. Foams produced by powder metallurgy had more uniform porosity and mechanical properties than the porosity and mechanical properties of foams produced by casting. [ABSTRACT FROM AUTHOR]

Closed-cell aluminium foams with different compositions have been manufactured starting from powders and also characterized from a morphological point of view and by means of compressive tests in order to determine mechanical properties. Circularity, equivalent diameter, and average porosity area of such foams have been calculated from the analysis of cross-sections as well specific energy absorption in compression tests. Samples with a higher amount of blowing agent (TiH2) have the highest energy absorption while samples with a higher amount of stabilizing agent (SiC) exhibit good foam properties overall (best compromise between morphology and energy absorption). The analysis of morphological properties, such as area, circularity, and equivalent diameter, can provide a better understanding of the foam’s structure and porosity––parameters which can be manipulated to enhance the foam’s properties for specific applications, both structural and functional.

Metal-organic frameworks (MOFs) have emerged as efficient electrocatalysts due to the features of high specific surface area, rich pore structure and diversified composition. It is still challenging to synthesize self-supporting MOF-based catalysts using simple and low-cost fabrication methods. Herein, we successfully fabricated Ni-doped MIL-53(Fe) supported on nickel-iron foam (Ni-MIL-53(Fe)/NFF) as efficient electrocatalyst. A facile two-step solvothermal method without adding any metal salts was used, which can simplify the fabrication process and reduce the experimental cost. In the fabrication process, the bimetallic Ni-MIL-53(Fe)/NFF was in situ converted from an intermediate NiFe 2 O 4 /NFF. The obtained material exhibits outstanding electrocatalytic oxygen evolution performance with a low overpotential of 248 mV at 50 mA cm−2, and a small Tafel slope of 46.4 mV dec−1. This work sheds light on the simple and efficient preparation of bimetallic MOF-based material, which is promising in electrocatalysts. [Display omitted] • Ni-MIL-53(Fe)/NFF is fabricated by a facile two-step hydrothermal process. • No metal salt was used in the fabrication process. • The metal foam not only provides metal sources, but also facilitates electron and mass transportation. • The Ni-MIL-53(Fe)/NFF exhibits remarkable electrocatalytic OER performance. [ABSTRACT FROM AUTHOR]

The fabrication of porous copper with ultrahigh porosity by adding 90% spacer content was an unsolved technical problem in the field. In this study, the green compacts placed on a layer wire mesh during the decomposition process of needlelike carbamide as space holder with volume content up to 90% was successfully conducted to fabricate nondestructive porous copper. Compared with the green compacts directly placed on an alumina plate, the use of this support was crucial for manufacturing highly-porous copper. Characterization of macro- and microscopic morphologies as well as quasi-static compressive test for the obtained porous copper samples was carried out. The results show that the porosity of porous copper samples with 87.3% was slightly smaller than the spacer content. The SEM observation indicates that the internal pores of porous copper formed an open-cell structure and its skeleton was very dense. The compressive tests show that the stress–strain curve of a porous copper sample exhibits the typical characteristics of elastic-plastic metal foam. The energy absorption properties of porous copper samples were also comparable. This study provides a possibility for the preparation of porous copper and other metals with ultrahigh porosity by the well-known space holder method. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal foam flow field with hierarchical pore structure for PEMFC is proposed. • 3D printing technology is applied to precisely manufacture metal foam flow fields. • A liquid water collection system is built to analyze water discharge capability. • Novel metal foam flow field shows superior performance and low pressure drop. Compressing metal foam flow field usually causes a higher pressure drop and uncontrollable pore structure while enhancing the water discharge capability of proton exchange membrane fuel cell (PEMFC). To further enhance the water discharge capability of metal foam flow field at a low cost of pressure drop, a novel metal foam flow field exhibiting hierarchical pore structure (d coarse / d fine =2; V coarse / V fine =1; d fine =0.5 mm) is first introduced. This work numerically investigates water management characteristics and output performance of novel metal foam flow field. Subsequently, 3D printing technology is employed to precisely manufacture metal foam flow fields, which are compared with several flow fields in the cathode side experimentally. Experimental results demonstrate that at 1.5 A / c m 2 during 3 h, the amount of water discharge in metal foam flow field with hierarchical pore structure is close to parallel flow field, which is 1.12 times and 1.30 times that in metal foam flow field with uniform coarse pore and uniform fine pore, respectively. Moreover, compared with the previous optimized strategy, namely metal foam flow field with 75 PPI and a compression rate of 0.75, metal foam flow field with hierarchical pore structure can not only improve the maximum net power density by 9.5 % and water discharge amount by 14.1 %, but also decrease two-thirds of the pressure drop in the cathode side. This research lays the theoretical groundwork and offers technical insight for the implementation of metal foam flow fields in PEMFCs. [ABSTRACT FROM AUTHOR]

• A novel porous structure based on truncated cuboctahedron is proposed. • The novel porous structure better enhances PCM melting near the porous cell corners. • A critical porosity exists to determine the enhancement advantages of two different porous structures. • The critical porosity is decreased with the increase of pore density. Metallic porous structure is a prevailing heat transfer enhancer for the melting of phase change material (PCM), while the effect of the structure on the enhancement performance is yet to be understood. In this work, a pore-scale numerical study on PCM melting embedded in a truncated cuboctahedron porous structure, referred as TCD metal foam, was performed. The solid–liquid interface, temperature and the variation of liquid fraction were analyzed and compared with those with the tetrakaidecahedron porous structure, referred as TKD metal foam. The effects of natural convection, porosity, pore density and heating temperature are explored. It is found the natural convection shortens the PCM melting time by about 7 % with the considered porosity range and thus cannot be ignored. Results also show that the TCD metal foam better enhances PCM melting near the porous cell corners compared to the TKD metal foam. Further analysis shows the TCD metal foam can better enhance melting at the former stage due to the larger surface area, while the TKD metal foam can better enhance melting at the later stage due to the thicker metallic ligaments. With essentially the same melting time at ɛ = 0.941, the half-melting takes 17.2 % of the complete melting time for TCD metal foam and 20.3 % of the complete melting time for TKD metal foam. A critical porosity value exists when comparing the enhancement performance of these two metal foams, below which the better melting enhancement is shifted from the case with TCD metal foam to the case with TKD one. The critical porosities are 0.941, 0.923 and 0.899 at the pore densities of 10, 20 and 30 PPI respectively. [ABSTRACT FROM AUTHOR]

The proton exchange membrane fuel cell components experience severe stresses and deformations during assembly, and in service. The gas diffusion layer (GDL), which is made up of a macroporous substrate (MPS) and a microporous layer (MPL), must withstand such harsh operating conditions. This study reports the mechanical degradation of the MPS exposed to compression cycles owing to service loads and the expected performance variation. Fifty compression cycles with various pressure ranges were carried out on a GDL substrate with an open-cell nickel foam. The surface morphology of the compressed MPS displayed ruptured fibres due to intrusion of nickel foam struts and reduced porosity by 10 per cent due to fibre blockage and the power generated by 15 per cent. Further, the impact of strut intrusion into the MPL at high service loads is reported using extrapolation and analytical methods. The intrusion of struts into the MPL creates macropores, leading to water droplets obstructing oxygen diffusion paths. Besides, under severe loads and repeated compression cycles, the struts puncher MPL and substantially degrade the catalyst layer. At 8MPa contact pressure, the platinum load decreased by approximately by a factor ∼3.6. Unlike conventional graphite plates, the compression effect due to metal foam struts is localized. • Cyclic compression at foam/GDL interface due to service loads is investigated. • Compared to channeled plates damage caused by foam struts to GDL is localize. • Fibre breakage and porosity reduction observed due to struts intrusion into MPS. • Degradation of catalyst layer occurs when struts penetrate into MPL. [ABSTRACT FROM AUTHOR]

[Display omitted] • Naphthalene-based M 2 (dondc) series with open metal sites is prepared. • Ni 2 (dondc) achieves a second-highest volumetric H 2 storage capacity of 10.74 g/L. • The strong affinity of the open metal site to H 2 is confirmed in Ni 2 (dondc). • The long-term durability of Ni 2 (dondc) in H 2 storage is demonstrated. Adsorbent-based hydrogen storage systems offer a potential solution to current challenges in hydrogen storage, particularly those requiring high pressures or cryogenic temperatures. Specifically, the use of metal–organic frameworks (MOFs) featuring open metal sites that strongly adsorb hydrogen represents a promising strategy for near-ambient-temperature hydrogen storage. This study investigates the hydrogen storage properties of M 2 (dondc) (M = Mg2+, Co2+, and Ni2+), an extended version of MOF-74. Among this series, Ni 2 (dondc) exhibits the second-highest volumetric hydrogen capacity of 10.74 g L−1 at 298 K under pressure swing adsorption conditions (100 to 5 bar) at ambient temperatures. The superior hydrogen storage performance of Ni 2 (dondc) is attributed to its highly polarizable Ni open metal sites and a significant heat of adsorption of 12.2 kJ mol−1. These findings are corroborated by temperature-programmed desorption spectroscopy and van der Waals-corrected density functional theory calculations. In addition to its exceptional hydrogen capacity, Ni 2 (dondc) exhibits robust structural stability and long-term durability, positioning it as a promising candidate for near-ambient-temperature hydrogen storage applications. [ABSTRACT FROM AUTHOR]

Metal foams have gained attention due to their heat transfer augmenting capabilities. In the literature, correlations describing relations among their morphological characteristics have successfully been established and well discussed. However, collective expressions that categorize stacked wire mesh based on their morphology and thermo-hydraulic expressions required for numerical modeling are less explored in the literature. In the present study, cross relations among the morphological characteristics of stacked wire-mesh were arrived at based on mesh-size, wire diameter and stacking type, which are essential for describing the medium and determining key input parameters required for numerical modeling. Furthermore, correlation for specific surface area, a vital parameter that plays a major role in interstitial heat transfer, is provided. With the arrived correlations, properties of stacked wire-mesh samples of orderly varied mesh-size and porosity are obtained for various stacking scenarios, and corresponding thermo-hydraulic parameters appearing in the governing equations are evaluated. A vertical channel housing the categorized wire-mesh porous media is numerically modeled to analyze thermal and flow characteristics of such a medium. The proposed correlations can be used in confidence to evaluate thermo-hydraulic parameters appearing in governing equations in order to numerically model various samples of stacked wire-mesh types of porous media in a variety of heat transfer applications. [ABSTRACT FROM AUTHOR]

This investigation deals with wave propagation analysis of porous metal foam resting on the Kerr substrate in the thermal environment within the framework of the refined higher-order plate theory. Different types of temperature rise are studied namely; uniform, linear and sinusoidal temperature rise. The pores are distributed through the thickness symmetrically and asymmetrically. The principle of Hamilton is employed in order to reach motion equations of porous metal foam plates. Next, governing equations of porous metal foam are derived for a refined inverse cotangential shear deformation plate and then solved analytically. The effects of various parameters including porosity coefficient, various types of porosity distribution, different types of temperature rise, length to thickness ratio, shape function, wave number and linear and shear layers of Kerr substrate on the variation of wave frequency and phase velocity of metal foam plate are covered and presented within the framework of a group of figures which can be observed in detail. [ABSTRACT FROM AUTHOR]

The study aims to estimate metal foam microstructure parameters for the maximum sound absorption coefficient (SAC) in the specified frequency band to obtain optimum metal foam fabrication. Lu's theory model is utilised to calculate the SAC of metallic foams that refers to three morphological parameters: porosity, pore size, and pore opening. After Lu model validation, particle swarm optimisation (PSO) is used to optimise the parameters. The optimum values are obtained at frequencies 250 to 8000 Hz, porosity of 50 to 95%, a pore size of 0.1 to 4.5 mm, and pore opening of 0.07 to 0.98 mm. The results revealed that at frequencies above 1000 Hz, the absorption efficiency increases due to changes in the porosity, pore size, and pore opening values rather than the thickness. However, for frequencies below 2000 Hz, increasing the absorption efficiency is strongly correlated with an increase in foam thickness. The PSO is successfully used to find optimum absorption conditions, the reference for absorbent fabrication, on a frequency band 250 to 8000 Hz. The outcomes will provide an efficient tool and guideline for optimum estimation of acoustic absorbents. [ABSTRACT FROM AUTHOR]

Copyright of Erzincan University Journal of Science & Technology is the property of Erzincan Binali Yildirim Universitesi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Over the recent years metallic foams have become a popular material due to their unique characteristics like low density coupled with beneficial mechanical properties such as good energy absorption, heat resistance, flame resistance, etc. However, their production processes (foaming) is highly stochastic which results in an inhomogeneous foam structure. Hybrid aluminum foam with closed-cell has been manufactured using direct foaming method coupled with the Taguchi Design of Experiments (DOE). Image analysis has been carried out to determine the average porous area and pore size. The influence of the production parameters (amount of foaming agent added, mixing speed and temperature) on the pore size and the porous area has been analyzed using the statistical Taguchi technique. From the experiments it was seen that the most important control factor for both the pore size and the porous area is the amount of the foaming agent added, followed by temperature and stirring speed. Furthermore, the statistical significance of these manufacturing parameters on the response was also investigated by performing analysis of variance (ANOVA) statistical method. [ABSTRACT FROM AUTHOR]

The thermal performance of the latent heat thermal energy storage unit (LHTESU) can be effectively promoted by metal foam. In the present work, a new structure of metal foam with a two-dimensional porosity gradient (MFTDPG) is proposed to further accelerate the melting process inside the rectangular cavity. The MFTDPG is obtained by placing the metal foam with small porosity near the left wall and the bottom wall. With consideration of natural convection, the melting behavior under different parameters is numerically analyzed, including the direction of the porosity gradient, the temperature of the left wall, and the aspect ratio of the rectangular cavity. The results show that the structure of metal foam with vertical porosity gradient (MFVPG) and horizontal porosity gradient (MFHPG) can reduce the total melting time by 7.65% and 3.37% respectively. The MFTDPG can shorten the total melting time by 12.07% compared with the structure with uniform porosity. Furthermore, the MFTDPG can achieve the shortest melting time and the maximum thermal energy storage rate (TESR) with different wall temperatures and aspect ratios. For example, when the aspect ratio is 2.5, the total melting time of MFTDPG is reduced by 24.35%, and TESR is increased by 25.88%. • The effects of different porosity gradient directions are numerically analyzed. • The metal foam with a two-dimensional porosity gradient (MFTDPG) is proposed. • Different cases of MFTDPG are designed by the orthogonal experiment table. • The MFTDPG combines the advantages of horizontal and vertical porosity gradient. • The MFTDPG achieves the best performance under different temperature and aspect ratio. [ABSTRACT FROM AUTHOR]

Effects of porosity play a key role in ductile fracture and many modern metals are less than fully dense with a finite porosity created either unintentionally (as in additively manufactured or powder processed materials) or intentionally (as in metallic meta-materials and foams). This study compares the Gurson and Cocks–Ashby models' predictions of porosity evolution (kinetics) and material degradation against unit cell simulations of a strain-rate dependent material under varying triaxiality. Previous comparisons do not address varying triaxiality and direct comparisons between the Gurson and Cocks–Ashby models are limited. This study also uses triaxiality, flow stress, strain rate, and strain-rate sensitivity from unit cell simulations as inputs to each model to give an accurate depiction of the models' performance under complex evolving loading and material states. A fitting procedure for porosity evolution is also shown. This study shows the overall predictive power of the Gurson model over the Cocks–Ashby model. It also highlights the accuracy of the Cocks–Ashby porosity evolution model and Cocks–Ashby degradation function when each model is calibrated independently. [ABSTRACT FROM AUTHOR]

This study investigates the impact of metal foam embedding into evacuated tube collector solar air heaters with inserted baffle (IBMF-ETC-SAH) on the device thermal performance using a computational fluid dynamics (CFD) approach. A three-dimensional model is employed to analyze the system under steady-state conditions. The key finding of this study is that the utilization of metal foam leads to a substantial increase in thermal performance, with an average improvement of approximately 300 %. The investigation examines the influence of metal foam porosity and pores per inch (PPI) on the performance of the IBMF-ETC-SAH across Reynolds numbers ranging from 6000 to 18,000. The results indicate that increasing the PPI from 20 to 40 at a constant porosity of 0.93 has negligible effects on device performance. However, the pressure drop increases by 48 % for a PPI of 40 compared to a PPI of 20. Furthermore, reducing the porosity from 0.95 to 0.9 leads to a 7 % enhancement in thermal performance. The IBMF-ETC-SAH exhibits a significant decrease in the total global entropy generation rate (EGR) compared to the device without metal foam. The maximum value of total EGR for the IB-ETC-SAH case is 2.32 times higher than the corresponding values for the IBMF-ETC-SAH case. [ABSTRACT FROM AUTHOR]

Internal structure of metal foams is one of the most important factors that determine its mechanical properties. There exists a number of methods for studying the nature of the inner porous structure. Unfortunately most of these processes is destructive and therefore it is not possible to reuse the sample. From this point of view, as a suitable method seems to be the ability of using the so-called X-ray microtomography (also micro-CT). This is a non-destructive methodology used in a number of fields (industry, science, archaeology, medicine) for a description of the material distribution in the space (e.g. pores, fillers, defects, etc.). In principle, this technology works on different absorption of X-ray radiation by materials with changing proton number. The contribution was worked out in collaboration with experts from the Faculty of Electrical Engineering and Computer Science of the VŠB-Technical University of Ostrava and it is focused on the analysis of internal structure of the metal foam casting with irregular arrangement of internal pores by using micro-CT. The obtained data were evaluated in the commercial software VGStudio MAX 2.2 and in the FOTOMNG system. For the evaluation of these data a new specialized module was introduced in this system. Several methods of pre-processing the image was prepared for the measurement. This preliminary processing consists, for example, from a binary image thresholding for better diversity between the internal porosity and the material itself or functions for colour inversion.

The pursuit of more representative numerical models for open-cell metallic foams requires the computation of volume and percentage porosity of geometries containing randomly distributed interconnected pores, which is one of the main characteristics that determines its mechanical properties. From a mathematical standpoint, the analytical definition of foam geometries forms a three-dimensional non-convex set. It is known that the volume computation of n-dimensional polytopes and sets is a P-hard problem. A common way to approach this problem is using the Monte Carlo techniques; however, efforts are oriented toward the treatment of convex polytopes and polyhedrons. In this article, the Direct Monte Carlo Simulation (DMCS) is used to compute the percentage porosity of three-dimensional non-convex sets. A single-thread Python code was implemented, and tests were run to estimate the percentage porosity of three-dimensional open-cell porous geometries. Measurements of percentage porosity and runtime requirements over cubical and cylindrical geometries containing from 100 to 4000 overlapping spherical pores showed high accuracy and consistency in non-convex three-dimensional sets, while the proposed algorithm achieved a significant reduction in computing time with respect to the currently available method. In the same manner, results from the proposed algorithm were compared with a similar software available, showing a gain in both performance time and accuracy. [ABSTRACT FROM AUTHOR]

Copyright of Theoretical & Applied Mechanics is the property of Theoretical & Applied Mechanics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The long standing issue of increased heat transfer, always accompanied by increased pressure drop using metal foams, is addressed in the present work. Heat transfer and pressure drop, both of various magnitudes, can be observed in respect to various flow and heat transfer influencing aspects of considered metal foams. In this regard, for the first time, orderly varying pore density (characterized by visible pores per inch, i.e., PPI) and porosity (characterized by ratio of void volume to total volume) along with varied thickness are considered to comprehensively analyze variation in the trade-off scenario between flow resistance minimization and heat transfer augmentation behavior of metal foams with the help of numerical simulations and TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) which is a multi-criteria decision-making tool to address the considered multi-objective problem. A numerical domain of vertical channel is modelled with zone of metal foam porous media at the channel center by invoking LTNE and Darcy–Forchheimer models. Metal foams of four thickness ratios are considered (1, 0.75, 0.5 and 0.25), along with varied pore density (5, 10, 15, 20 and 25 PPI), each at various porosity conditions of 0.8, 0.85, 0.9 and 0.95 porosity. Numerically obtained pressure and temperature field data are critically analyzed for various trade-off scenarios exhibited under the abovementioned variable conditions. A type of metal foam based on its morphological (pore density and porosity) and configurational (thickness) aspects, which can participate in a desired trade-off scenario between flow resistance and heat transfer, is illustrated.

A new sintering method is developed for fabricating large, 3-dimensional, open-cell metal foam parts using milling or friction stir welding machines. Temperature and pressure required for sintering are achieved by plunging and moving a rotating tool against a sacrificial top sheet in the setup. Predefined tool paths are used to compress and sinter the powder mixture in a die cavity. In this paper, the method was used to fabricate open-cell copper foam plates using sintering and dissolution process (SDP). Samples with different porosities were fabricated. Produced foams have uniform mechanical properties, pore morphology, and porosity. Further, their mechanical properties are seen to be on par with that for copper foams fabricated using other sintering methods reported in literature. Except for top sheet, the setup can be reused any number of times. The developed process is robust, cost-effective, operator friendly, and easy to use. [ABSTRACT FROM AUTHOR]

It is significant to have locally non-uniform designs in the flow fields since distributions of the current density, temperature, gas, and water concentration are usually non-uniform along the flow path in the polymer electrolyte membrane fuel cell. In this study, we introduce and use several different metal foam flow fields with different porosity gradients as flow distributors in the fuel cell. By evaluating and analyzing polarization curve, power curve, and electrochemical impedance spectroscopy test results, we verify that the tailored porosity gradient in the metal foam flow field has positive impacts the performance of the fuel cell. Maximum power density of the fuel cell with proper porosity gradient in the metal foam flow field increased by 8.23% compared with the conventional metal foam flow field without porosity gradient. In conclusion, we not only explain why proper porosity gradient in the metal foam flow field makes the performance of the fuel cell improve, but also investigate the performance enhancement in the system net power aspect. • It is significant to have locally non-uniform designs in the flow fields. • Performance of the fuel cell with proper porosity gradient in the metal foam flow field improved. • Reasons of the performance enhancement with proper porosity gradient were examined. • The performance enhancement was investigated in system net power aspect. [ABSTRACT FROM AUTHOR]