Porous Metal Foam Research Articles

Modelling and Simulation of the Coating Process on Open Porous Metal Foams

AbstractBased on an increasing demand of energy and raw materials, resources should be used more efficiently. Therefore, multifunctional materials and lighter constructions, which can endure higher payloads, are needed. Cellular materials like metal foams are bionic, multifunctional materials, which can be optimised by a coating of the foam structure. Due to this coating via electrodeposition, the material properties per unit mass can be optimised. In consequence of the mass transport limitation inside the foam during the electrodeposition process, there occurs an inhomogeneous coating thickness distribution. To obtain a homogeneous coating thickness, in this project the factors are studied and simulated, which influence the electrochemical coating process. The electrodeposition process can be described by an ion source at the anode, the mass transport from anode to cathode and an ion sink at the cathode. The mass transport and the deposition process are characterised by the continuity equation with convection, diffusion, migration, a source term and a sink term. In this contribution, the factors influencing the coating thickness are investigated by numerical simulation to provide a homogeneous coating thickness. A material model is developed coupling mass transport with electrodeposition. A finite difference approach is used to simulate the ion concentration distribution inside the foam.

Highly stable tungsten disulfide supported on a self-standing nickel phosphide foam as a hybrid electrocatalyst for efficient electrolytic hydrogen evolution

The detrimental impacts on environment brought by the combustion of fossil fuel have urged scientists to search for various green substituents. In particular, molecular hydrogen is proposed as one of the competitive candidates among the wide spectrum of different energy sources due to the high gravimetric energy density, cleanliness and renewability. However, the batch production of H2 via electrolytic route requires the cost-effective and high-performance electrocatalysts to minimize the energy loss during conversion. Tungsten disulfides (2H-WS2) is an earth-abundant HER electrocatalyst which possesses high intrinsic catalytic activity and chemical stability. Nonetheless, the HER performance of WS2 is limited by the sparse catalytic edge sites and the unsatisfactory on-plane electrical conductivity. On the other hand, the self-standing nickel phosphide (Ni5P4-Ni2P) grown directly on the Ni foam is a compelling structure for water splitting due to its macroporosity and the metallic nature of 3D networks. Here, we report the hybridization of WS2 and the 3D porous metallic Ni5P4-Ni2P foam induced through a thermal process in a CVD furnace. The resultant hybridized WS2/Ni5P4-Ni2P electrode demonstrated intriguing synergistic effects that improve the overall electrode performances considerably. Experimentally, it was found that the surface of WS2/Ni5P4-Ni2P electrode contains a ternary WS2 (1-x)P2x constituent, bringing the advent of desired electronic perturbations. Notably, the 3D porous metallic WS2/Ni5P4-Ni2P electrode only requires 94 mV (vs. RHE) to drive a geometric current density of − 10 mA cm−2 with a relatively small Tafel slope of 74 mV dec−1. Such enhancements are correlated to the rational designs of WS2/Ni5P4-Ni2P electrode which (i) optimize the hydrogen adsorption Gibbs free energy; (ii) increase of the number of active sites of overall electrode; (iii) facilitate the electron transport from higher Fermi-level Ni5P4-Ni2P foam to the lower Fermi-level WS2; (iV) promote the access of electrolyte and the escape of hydrogen molecules. Additionally, such catalytic performances of the WS2/Ni5P4-Ni2P electrode can last for 22 h without significant degradations, clearly demonstrating the superior long-term operation stability in the acid environment (0.5 M H2SO4). This work provides a versatile platform for fabricating the 3D porous hybridized electrocatalysts for modulating the intrinsic catalytic activity of various transition metal dichalcogenides (TMDs) on nickel phosphide.

Effect of microstructure on melting in metal-foam/paraffin composite phase change materials

The performance of phase change materials (PCM) as energy storage units are often limited by their low thermal conductivities that constrain the rates of melting or solidification. Highly porous metal foam composite PCMs are increasingly being used to abate this limitation and enable greater control over the thermal and phase change characteristics of the system. In the present study, a pore-scale computational analysis is carried out to characterize the performance of an n-eicosane-aluminium-foam composite PCM with a porosity of 0.94, over varying microstructural properties including strut, pore and cell sizes, and specific surface area. The simulations are carried out using OpenFOAM by employing the enthalpy-porosity formulation for modeling phase change during melting. The foam geometries are generated computationally using tools developed by the authors, published recently (Abishek et al., 2017, Ref. [1]). The statistics of the pore-scale structures of the virtual foam geometries and the numerical methodology employed for the modeling were validated against theoretical and empirical data from the literature. The simulations reveal that the presence of metal foam significantly enhances the melting rate as compared to pure PCM. It is also found that the melting rates are strongly correlated to the specific surface of the foam – highlighting a vital parameter that can be used to optimize the performance of the composite PCM for a given application. An empirical relationship correlating the dimensionless melt fraction with the Fourier number, Stefan number and dimensionless specific surface area is also presented for the range of parameters considered in this study.

Melting and solidification of PCM embedded in porous metal foam in horizontal multi-tube heat storage system

In this paper, melting and solidification processes of phase change material embedded in metallic porous foam in a multi-tube heat exchanger are investigated numerically under local non-equilibrium thermal condition. RT 35 is used as phase change material in middle shell of 3D multi-tube heat exchanger. Also, water flows across inner tube/tubes and outer tube as a heat transfer fluid (HTF). The effects of number of inner tubes, their arrangement as well as porosity of metallic foam on thermal characteristics of heat storage unit are studied. Results show that increasing number of inner tubes and adding metallic foam enhance melting and solidification rates significantly. A composite of phase change material/metallic foam with porosity of ε=0.7 engenders shorter melting and solidification time comparing to pure PCM. Arrangement of inner tubes has no effect on melting rate of metal foam/PCM composite. By inserting metallic foam with porosities ε=0.9and ε=0.7, melting time is decreased by 14% and 55%, respectively. Highest melting rate is for case with four inner tubes for all porosities of metallic foam. Regarding solidification process in pure PCM, case with four tubes shows shorter solidification time. Also, highest solidification rate amid composites of phase change material/metallic foam is seen for case with three tubes. Consequently, inserting metallic foam is more efficient in solidification process rather than the melting one. Moreover, increasing number of inner tubes has more influence on phase change rates in metal foam/PCM composites compared to pure PCM.

Performances and Limitations of Metal Supported Cells with Strontium Titanate based Fuel Electrode

AbstractIn this contribution, we report investigation of metal supported cells with a La0.1Sr0.9TiO3–α (LST) based fuel electrode. The cells are prepared on a substrate made of a porous NiCrAl metal foam infiltrated with NiO and LST materials. The functional anode layer, consisting of LST mixed with a Gd0.1Ce0.9O2–α (GDC), is produced by screen printing. Nickel metal is infiltrated in the backbone to enhance electronic and catalytic properties. The electrolyte made of an 1 μm + 0.5µm thick Zr0.84Y0.16O2–α (YSZ) layer followed by a 2 μm thick GDC layer, is fabricated by wet ceramic processing and electron beam physical vapor deposition (EB‐PVD), respectively. La0.6Sr0.4Co0.2Fe0.8O3–α (LSCF) is employed as a cathode material. All cells are electrochemically characterized. At 750 °C and at a cell voltage of 0.7 V, the typically achieved power density value is up to 0.40 W cm−2. With less than 2% variation for 50 cycles, the OCV showed an excellent stability as a function of redox cycles, demonstrating that an electrolyte as thin as 3 µm maintains its integrity, despite the harsh operating conditions. This highlights the potential of perovskite based fuel electrodes in metal supported cells, and paves the way to the next generation of cells' design.

A Porous Microbeam Model for Bending and Vibration Analysis Based on the Sinusoidal Beam Theory and Modified Strain Gradient Theory

In this research, we analyze size-dependent bending and vibration of microbeams made of porous metal foams. The porous microbeam model is developed based on the sinusoidal beam theory and the modified strain gradient theory. Hamilton’s principle is employed to obtain the governing equations and boundary conditions of the porous microbeam. Analytical solutions are presented for deflections and natural frequencies of the porous microbeam by using Navier’s method. The influences of the porosity distribution, the porosity coefficient, the slenderness ratio, and the microbeam thickness are clarified on the static bending and free vibration of porous microbeams. These findings can be applied to the design of metal foam microstructures in engineering.

Morphology Matters: Additive-Assisted Metal Foam Deposition for the Electrochemical CO2 Conversion

High-surface area metal foam catalysts for the electrochemical CO2 reduction reaction (ec-CO2RR) are deposited on planar model substrates and technical supports (e.g. 2D mesh or 3D sponges). The metal deposition is typically carried from acidified plating baths at particularly high current densities (e.g. -3 A/cm2) where the metal deposition is superimposed on the hydrogen evolution reaction (HER). Gas bubbles formed on the support surface serve as geometrical template for the metal deposition leaving highly porous metal foams behind.1,2 Pore density and the particular side-wall morphology of these foams can be fine-tuned not only by the current density, metal ion concentration in solution but also by the use of particular polymeric plating additives (e.g. polyethylene-imines, PVPs, polymerizates of imidazole and epichlorohydrin). The activity and product selectivity of the electrochemical reduction of CO2 on Cu foam catalysts strongly depend on the resulting pore size distribution of the Cu catalyst. The maximum in the C-C coupling efficiency (FEC2 = 55%) observed for pore size dimensions in the range of 50 to 100 µm. Such morphology dependence of the ec-CO2RR product distribution will be discussed not only on the basis of the availability of certain reactive surface sites and facets but also on the basis of a temporal trapping of gaseous intermediates (in particular CO and C2H4) inside the mesoporous catalyst material. Mild thermal annealing (300°C, 1h) of the Cu metal foams activates them for the production of C2 and C3 alcohols (ethanol, n-propanol). Identical location (IL) HR-SEM, HR-TEM, white-light interferometry and 3D optical microscopy are applied to probe morphological changes on different length scales that are induced by the foam activation (e.g. by thermal annealing) and the ec-CO2RR itself. This study indicates that the catalyst morphology might undergo drastic changes under operando conditions. [1] Shin, H. C.; Liu, M. L., Chem. Mater. 2004, 16 (25), 5460-5464. [2] Shin, H. C.; Dong, J.; Liu, M. L., Adv. Mater. 2004, 16 (3), 237-240.

Simulation intricacies of open-cell metal foam fin subjected to convective flow

An exact 3D digital image of 10 PPI open-cell metal foam matrix used in this study has been generated through X-ray micro-computed tomography. The precise foam geometrical model, in combination with the commercial computational software, facilitates synthesizing typical thermal applications of metal foam subjected to convective fluid flow and creates unique opportunity of probing some of the finer fluid flow aspects usually beyond the scope of most of the experimental investigations. Simulation of fluid flow through 10 PPI open porous metal foam subjected to constant terminal temperature has been carried out and validated a priori with the experimental data. The convective flow simulation, being computationally intensive, has been carried out in a small piece of metal foam to eventually extrapolate the data over the original length. The practical limitations of foam modelling leading to the deviations between experimental data and the predicted results have been explained in details. Subsequently, the temperature and flow fields have been probed to understand the complicated flow physics around the metal foam strut. This study gives a better insight of the state of the art research and development in the field of high porosity open-cell metal foam. The computational predictions have also been compared at length with the analytical outcomes based on the simple cubic model of metal foam. This work, in all, provides the end-user an overview of the associated intricacies while considering the computational, experimental and simplified models for open-cell metal foams when used as extended heat transfer surfaces or fins.

Application of Metal Foam as a Flow Field for PEM Fuel Cell Stack

AbstractThe channel/rib structure, commonly used in proton‐exchange membrane fuel cells (PEMFC), has disadvantages of uneven pressure distribution, gas supply, and produced‐water management under “rib” portion. In recent years, porous metal foam has been studied as an alternative flow field. We determined that the application of porous metal foams improved the PEMFC performance by compensating for the drawback of the channel/rib‐type flow field owing to the unique properties of metal foams (e.g., high conductivity, high porosity, and ease‐of‐deformation). Thus, this study confirmed the difference in the PEMFC performance with metal foams depending on cell configurations. Furthermore, the actual 500 W class PEMFC stack was fabricated to confirm the possibility of the metal foam application in the stack scale.

Experimental analysis and dynamic modeling of a photovoltaic module with porous fins

Abstract In this study, experimental analysis and performance predictions of solar photovoltaic (PV) module equipped with porous fins were performed. The experimental setup was tested in Technology Faculty of Firat University, Elazig of Turkey which is located at 36° and 42° North latitudes. The PV module was oriented facing south and tilted to an angle of 36° with respect to the horizontal in order to maximize the solar radiation incident on the glass cover. Experimental analysis was conducted for configurations where PV module is equipped with porous metal foams. A multi-input multi-output dynamic system based on artificial neural networks was obtained for the PV configuration with and without fin by using the measured data (ambient temperature, PV panels back surface temperatures, current, voltage, radiation and wind velocity) from the experimental test rig. It was observed that adding porous fins to the PV module results in performance enhancements. The developed mathematical model based on dynamic neural networks can be used for further development and performance predictions of these systems.

Numerical study on applicability of metal foam as flow distributor in polymer electrolyte fuel cells (PEFCs)

In this paper, the effects of using porous metal foam based bipolar plates (BPs) are investigated under practical automotive fuel cell operations with low humidification reaction gases. Particular emphasis is placed on evaluating water management capabilities of metal foam based BP designs, compared to the traditional serpentine flow field BP designs. A three-dimensional, two-phase fuel cell model developed in a previous study is applied to 25cm2 real-scale fuel cell geometries with metal foam and serpentine flow modes, and then successfully validated against the experimental data measured under different operating pressures and current densities. The detailed simulation results clearly elucidate advantages of using metal foam as flow distributor through extensive multidimensional contours of flow velocity, species, and current density.

Thermal conductivity of highly porous metal foams: Experimental and image based finite element analysis

X-ray tomography is used to produce three-dimensional images of an aluminium alloy foam with a high porosity (>93%). These data allow describing the foam structure from which a finite element model is derived to predict the thermal conductivity of the foam. The results are compared with experimental values measured by a new guarded hot plate apparatus adapted for the range of thermal conductivity values of interest. Good agreement is observed which validated the finite element model used to evaluate the thermal properties of any porous metallic foam with stochastic cell size and configuration. Furthermore, the thermal conductivity of the foam has also been predicted using previous analytical models. The differences with previous values show that it is important to account for the real geometry of the foam to get an accurate value of the thermal conductivity.

Fabrication, Structural Characterization and Uniaxial Tensile Properties of Novel Sintered Multi-Layer Wire Mesh Porous Plates.

There is an increasing interest in developing porous metals or metallic foams for functional and structural applications. The study of the physical and mechanical properties of porous metals is very important and helpful for their application. In this paper, a novel sintered multilayer wire mesh porous plate material (WMPPs) with a thickness of 0.5 mm–3 mm and a porosity of 10–35% was prepared by winding, pressing, rolling, and subsequently vacuum sintering them. The pore size and total size distribution in the as-prepared samples were investigated using the bubble point method. The uniaxial tensile behavior of the WMPPs was investigated in terms of the sintering temperature, porosity, wire diameter, and manufacturing technology. The deformation process and the failure mechanism under the tensile press was also discussed based on the appearance of the fractures (SEM figures). The results indicated that the pore size and total size distribution were closely related to the raw material used and the sintering temperature. For the WMPPs prepared by the wire mesh, the pore structures were inerratic and the vast majority of pore size was less than 10 μm. On the other hand, for the WMPPs that were prepared by wire mesh and powder, the pore structures were irregular and the pore size ranged from 0 μm–50 μm. The experimental data showed that the tensile strength of WMPPs is much higher than any other porous metals or metallic foams. Higher sintering temperatures led to coarser joints between wires and resulted in higher tensile strength. The sintering temperature decreased from 1330 °C to 1130 °C and the tensile strength decreased from 296 MPa to 164 MPa. Lower porosity means that there are more metallurgical joints and metallic frameworks resisting deformation per unit volume. Therefore, lower porosities exhibit higher tensile strength. An increase of porosity from 17.14% to 32.5% led to the decrease of the tensile strength by 90 MPa. The coarser wires led to a bigger contact area between the interconnecting wires, resulting in a stronger sintering neck that exhibited higher tensile strength. The wire diameter increased from 81 μm to 122 μm and the tensile strength increased from 296 MPa to 362 MPa. The fracture morphology showed that the wires experience necking deformation and ductile fracture.

On the Mechanical Properties of Aluminum Matrix Syntactic Foams

Metal matrix syntactic foams (MMSFs, often referred as composite metal foams (CMFs)) are lightweight materials with high specific strength. MMSFs are on the borderline between metal matrix composites and metal foams. On one hand MMSFs are composites, because they are filled by hollow particles and the particles may add strength to the material. On the other hand, they are foams, because the hollow particles ensure porosity to the material. Among metallic foams, MMSFs exhibit outstanding specific mechanical properties due to the hollow inclusions that are typically made from ceramics or high strength alloys, therefore they can be applied as structural materials. The goal of this paper is to summarize the available data on the mechanical properties of MMSFs with aluminum matrix in order to give a strong support to the design engineers. Since the foams are most frequently loaded in compression, the main part of this paper is organized around the available standard related to the compressive properties of porous materials and metallic foams. The quasi‐static results are complemented by properties measured at higher strain rates. Besides this, some insight into the basic fatigue properties as well as into the toughness of MMSFs is also provided.

Coupled CFD-DEM simulation of oscillatory particle-laden fluid flow through a porous metal foam heat exchanger: Mitigation of particulate fouling

A coupled finite volume-discrete element (FVM-DEM) numerical method is developed to investigate oscillating multiphase foulant-laden air (solid-gas) flow and particulate fouling in a porous heat exchanger channel comprising an array of circular cylinders. Oscillatory fluids serve as a steppingstone to advance existing conventional anti-fouling techniques and to yield optimum energy consumption. A performance evaluation criteria based on various amplitudes of pulsation and foulant injection rates is established. The fouling characteristics and pressure drop is compared against a non-oscillating steady flow. For the solid foulant particles considered in this study, the results show that the time-averaged deposition fraction is sensibly invariant with increasing foulant injection rate; however, the same observation is not realized for steady-flow cases. The 1 Hz case showed no significant disparity in terms of deposition fraction at high injection rates compared with the non-oscillating steady flow case. In addition, the 1 Hz case showed miniscule reduction of low-density foulants. The higher-frequency spectrum has superior fouling mitigation capabilities although comparatively higher pressure drop is generated. The 6-pore configuration outperforms the 3-pore under certain oscillatory flow conditions. An optimum frequency of 5 Hz exhibits superior fouling mitigation performance while achieving a low time-averaged pressure drop.

Experimental study on heat transfer and flow characteristics of two kinds of porous metal foam tubes filled with water

This paper presents an experimental study on the flow structures in turbulent Rayleigh-Benard convection with surfactant solutions. The shadowgraph visualization was used to obtain the plumes and the velocity field was measured using particle image velocimetry. The results show that the size of plumes in surfactant solution case is larger than that in Newtonian fluid case and it needs more time for surfactant solution case to start convection. The large-scale circulation fails to form in surfactant solution case and the convection velocity is smaller. A decrease of the measured Nusselt number is observed in surfactant solution case. The phenomena are caused by the shear-shinning and elastic characteristics of surfactant solution.

Editorial: Metallic Foams Special Section

Porous metals and metallic foams have been, for the last 25 years, the focus of very active research and development activities around the world, both at the academic and industrial levels. These materials are used when the combination of metal properties with the characteristics of a properly designed cellular structure provides advantages over other types of materials. They possess a spectrum of unique properties that can be tailored as a function of the final application, such as high impact energy absorption under mechanical load, high specific stiffness and strength, high fire resistance, air and water permeability, unusual acoustic properties for a metallic component, and low relative thermal conductivity. Porous metals and metallic foams are now produced by various companies and used in numerous applications such as light-weight structures, biomedical implants, dust and fluid filters, engine exhaust mufflers, porous electrodes, heat exchangers, sound absorbers, mechanical damping devices, sensors and catalyst substrates. This is currently a wide topic in which several research areas (physics, chemistry, materials science, engineering) merge together to develop improved materials that could be used in a clever way to solve particular engineering problems. By holding the 9th International Conference on Porous Metals and Metallic Foams in Barcelona, Spain (MetFoam) in September 2015, we provided a state-of-the-art review forum for scientists working in this field that hopefully enriched discussions and networking, continuing a nice “tradition” of the eight previous conferences on the same topic. These eight international conferences have already contributed to the success of those materials. Previous conferences were held in Bremen (1999, 2001) and Berlin (2003), both in Germany, Kyoto (2005) in Japan, Montreal (2007) in Canada and Bratislava (2009) in Slovakia as well as Busan, Korea (2011), and Rayleigh, USA (2013). Now MetFoam 2017 is approaching and will be celebrated in Nanjing, China. This special issue of Advanced Engineering Materials mainly contains a selection of the papers presented during MetFoam 2015. The conference encompasses papers dealing with basic fundamentals, fabrication, morphological, and microstructural characterization, property profiles, secondary operations, and various applications of porous metals and metallic foams. More than 200 papers were presented by a broad group of researchers from 36 countries. Scientists and engineers representing universities, federal laboratories, and industries attended. It is our hope that this selection of papers will provide a representative insight into the developments presented at MetFoam 2015. Prof. Miguel Angel Rodríguez-Pérez & Dr. Eusebio Solórzano (Chairpersons MetFoam 2015)

Performance evaluation of a flat-plate solar collector filled with porous metal foam: Experimental and numerical analysis

Experimental and numerical investigations on the effect of porous metal foam on the performance of a flat-plate solar collector have been carried out in this study. The numerical solution is based on the control-volume approach and local thermal equilibrium assumption between the fluid-porous material phase to get the optimum thickness of the porous medium and also evaluate the thermal performance and pressure drop in the porous channel collector. The numerical results exhibit that the maximum thermal performance is obtained in a porous layer dimensionless thickness greater than 0.8, which the fully filled channel is selected in the present study. In the experimental section, an ASHRAE standard is used to examine the effects of metal foam on the solar collector performance at different flow rates. The numerical solution results have been validated against the experimental results, and a reasonable agreement has been achieved. The numerical and experimental results have shown that using the porous medium enhances the maximum thermal efficiency and Nusselt number up to 18.5% and 82%, respectively.

발포금속을 활용한 막가습기의 특성에 관한 연구

발포금속을 활용한 막가습기의 특성에 관한 연구

The control of ultrasonic transmission by the metamaterials structure of electrorheological fluid and metal foam

A metamaterial structure formed by foamed metal and starch and oil-based electrorheological (ER) fluid is designed in this paper. Experiments show that the metamaterial structure exhibits a regulation effect on the amplitude and phase of the transmitted waves of 35–80 kHz ultra-wideband ultrasonic waves in water. With the increase of the electric field, the transmission amplitude and phase of the ultrasonic wave increases, whereas the control ability of the same gradient electric field decreases. The amplitude of the transmission controlled by the metamaterial structure and electric field increases at first, and then decreases with the increase in volume fraction of the ER fluid. Thus, it is thought that the interaction between the microstructure produced by the rheological properties of the ER fluid and the porous foam metal affects the propagation of the acoustic wave.