Metal Foam Research Articles

Modeling non-uniform aluminum foams as sacrificial layers for blast mitigation of protected structures — A theoretical approach

Aluminum Foams (AFs) are cellular materials that exhibit energy absorption capabilities, making them desirable to use as sacrificial protective cladding applied on structural members. Thereby, the structural resistance to blast loads is increased. During the foam compaction, inner and local buckling of the material walls occur. The described phenomenon reduces the peak overpressure of the blast load and increases its positive duration while maintaining the impulse and transmitting the plateau stress of the foam to the Protected Structure (PS). The plateau stress is commonly significantly lower than the peak overpressure of the blast load. Available analysis approaches typically neglect the coupling between AF and PS and mostly consider uniform-density foams. Moreover, the efficiency of adding AF has been commonly evaluated by comparing the structural response with and without AF. However, such a comparison may not be adequate for studying energy absorption due to the role that the added mass affects the behavior of the structural system due to inertia forces. In this study, using the shock front theory, a numerical solution to a non-uniform density foam as protective cladding is developed, considering both the foam densification and the PS response. A parametric study is performed using this approach to investigate the efficiency of non-uniform density foam compared to a uniform density foam. Calculation and discussion of the efficiency of uniform and non-uniform foams are presented using a more adequate proposed approach, mainly concluding that under loads considered to be impulsive, the non-uniform AF with certain specimens considerably reduce the Peak Displacement (PD) of the PS significantly more than uniform AF.

Optimizing of a metal foam-assisted solar air heater performance: a thermo-hydraulic analysis of porous insert placement.

A numerical assessment of the heat transfer efficacy of a solar air heater (SAH) was carried out. The SAH is supplied with a porous metal foam layer to improve thermal mixing. Both the local thermal non-equilibrium (LTNE) and Darcy-extended Forchheimer (DEF) models were employed to forecast fluid and thermal transport within the partly filled SAH channel. The analysis was performed for various values of dimensionless foam layer lengths ( ), pore densities ( ), and Reynolds numbers ( ) at a fixed value of layer thickness ( ). Based on the position of the porous layer, three distinct arrangements, marked as Case 1, Case 2, and Case 3, were explored. Regarding the parameters examined, the findings indicate a definite improvement in the average Nusselt number ( ), but unfortunately, the friction factor also increases unfavorably. By reducing the length of the porous layer, a reasonable reduction in heat transfer rate and a significant decrease in pressure drop were noticed. The results showed about 26.64%, 48.73%, and 70.74% reductions in pressure drop by reducing the dimensionless foam length from 1 to 0.25, 0.5, and 0.75 respectively for at . On the other side, there are only about 11.05%, 23.11%, and 40.78% reductions in . The exhaustive analysis of the thermal performance of SAH was conducted using the thermal performance factor (TPF), which considers the trade-off between the SAH channel's potential for improved heat transmission and its cost for pressure loss. The TPF may reach a maximum of 2.82 compared to the empty channel when the metal foam layer is inserted with , for , and .

Heat transfer study of metal foam with partial filling method to strengthen phase change material

The advancement of ice-ball thermal energy storage systems is limited by the poor thermal conductivity of phase change materials(PCM). This paper presents a numerical investigation into enhancing heat transfer in ice balls by partially filling them with metal foam. Dynamic temperature changes, solid phase fraction, and cold storage capacity are analyzed for various filling radius ratios (2/13, 4/13, 6/13, 8/13, and 13/13). We quantitatively assess the specific impact of metal foam filling on heat transfer by calculating changes in the comprehensive thermal conductivity coefficient. Our findings reveal that the comprehensive thermal conductivity coefficient increases nonlinearly with the growing metal foam filling radius ratio, indicating that full filling may not the most optimal configuration. Furthermore, the energy storage capacity per unit time, per unit weight and per unit cost of the ice ball filled with metal foam under different radius ratios was evaluated by comprehensive evaluation criteria, and the optimal filling radius ratio was determined to be 6/13. Contrary to prior findings, this research highlights the efficacy of partial filling strategies, offering valuable insights for optimizing ice ball performance in thermal energy storage applications.

Exploring the impact of inner and middle channel geometries on the melting rate of PCM-metal foam composition in a triplex tube heat exchanger

Triplex tube heat exchangers (TTHXs) are devices suitable for storing thermal energy with PCM because they shorten the melting and solidification periods. Studies in literature have revealed that pipe geometries significantly affect the melting performance of PCM in thermal energy storage with TTHX. In the pipe designs carried out in these studies, convection in the heat transfer fluid (HTF) and the heat transfer surface areas of the pipes were considered. However, in addition to convection in the HTF, heat transfer by conduction and convection within the PCM also significantly affects the melting performance. The novelty of this study was to investigate the effects of inner and middle channel combinations with different geometries in TTHX on conduction and natural convection mechanisms in PCM combined with metal foam. Numerical analyses were carried out for nine inner-middle channel combinations with three different metal foam porosity values (ε = 0.85, 0.90 and 0.95). At porosity values of 0.85 and 0.90, the highest melting rate was achieved with the triangle-triangle inner-middle channel combination within a certain period, and the charging time was shortened by 16.67 % and 14.44 %, respectively, compared to the base case (circle-circle). For the porosity value of 0.95, it was observed that the most suitable channel combination for melting performance was circle-circle, as natural convection flow became more dominant in heat transfer in liquid PCM. At the porosity value of 0.95, the charging time with TTHX containing the circle-circle combination decreased by values ​​ranging from 29.75 % to 59.86 % compared to other combinations.

From bulky Si to porous medium entropy alloy: Enabling highly efficient Li storage via the simultaneous reconstruction of microstructure and component

We show here that the Li-storage performance of Si anode can be substantially improved by engineering a multilevel nanoporous SiGeTiZnCuAl medium entropy alloy (NP-MEA). The NP-MEA is directly engineered through a corrosion-driven phase and structure simultaneous reconstruction by partially etching Al and Zn from the multi-element master alloy. The unique multi-elemental interactions can revolutionize the chemical microenvironment, and thus stabilize the structure and impel the transportation of the electrons and ions. The metallic sponge offers multilevel pore channels for electrolyte permeation and ample space for volume change accommodation, abundant accessible active sites for lithiation/delithiation, as well as the rigid skeleton for expediting the electron transportation and stabilizing the structure. Benefiting from the synergy of component and structure, the NP-MEA delivers a high reversible capacity of 646.1 mAh g−1 after 500 cycles at a current density of 2 A g−1.

Effect of cell diameter variations on the mechanical behavior of aluminum foams: Experiments and modeling

Aluminum foams can be manufactured in a variety of cell sizes; however, existing models focus primarily on density and neglect the effect of cell size. Furthermore, aluminum foams with different cell diameters exhibit diverse mechanical properties. In this study, a quasi-static/dynamic compression test was performed to investigate the mechanical behavior, damage patterns, and damage mechanisms of aluminum foams with different cell diameters. The results demonstrate that the compressive properties of aluminum foams undergo significant changes. As the cell diameter increases, normalized initial damage stress and Young's modulus also increase, leading to enhanced energy absorption. However, this increase in cell diameter negatively affects the energy absorption efficiency, resulting in increased instabilities. A finite element analysis was conducted using the LS-DYNA finite element software to investigate the behavior of aluminum foils under all the experimentally tested loading regimes. The simulation results reveal that the deformation zone formed due to collapse diminishes with increasing cell diameter. More importantly, a new damage mechanism named central cell cleavage was reported, which increased the energy absorption capacity and amplified the instability during deformation. This study offers novel insights into the mechanical behaviors exhibited by aluminum foams, thereby facilitating their application in structural engineering.

High temperature and mesostructure effect on aluminum foam compression responses

Closed-cell Al foam is widely utilized in high-temperature environments due to its high strength-to-weight ratio and considerable energy absorption capability. However, the mechanical properties depend on temperature and mesostructure. In this paper, the compressive responses of Al foams at temperatures ranging from 25 ℃ to 600 ℃ are investigated by experimental tests and two types of high-fidelity finite element simulations, including the X-ray computed tomography (CT) reconstructed model and Voronoi model. A deep learning approach is employed to remove tiny pores of CT slices, simplifying geometry features and improving the computational efficiency of the CT reconstructed model. A novel improved Voronoi model with high accuracy is proposed, considering the nonuniform distribution of cell wall thickness in actual closed-cell Al foams. A temperature-depend macro constitutive model is established and validated through the experimental and numerical results. This work reveals the influence mechanism of temperature and mesostructure on the mechanical responses of Al foams, and exhibits significant potential for the application of Al foams in high temperature environment.

Pore-scale study of melting characteristic of phase change material embedded with novel open-celled metal foam

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.

Al and A356 Alloy Foam Castings Modified with Low Concentrations of Nano-Sized Particles: Structural Study and Compressive Strength Tests

Aluminum and A356 alloy foam castings are produced using a melt-foaming method. Prior to foaming, the melt is modified with nano-sized particles (SiC, TiN, or Al2O3). The nano-sized particles are mixed with micro-sized Al particles, which are ultrasonically treated and hot-extruded. Thus, the so-called “modifying nano-composition” is obtained. The resulting compositions are introduced into the melt of the Al foam at the following mass concentrations of nanoparticles: SiC: 0.038 wt. %; TiN: 0.045 wt. %; and Al2O3: 0.046 wt. %. For the A356 foam, we use the following concentrations: SiC: 0.039 wt. %; TiN: 0.052 wt. %; and Al2O3: 0.086 wt. %. The macrostructure of the foam castings is investigated by CT scanning and 3D analysis. The pore size distributions and accumulative fraction dependencies are determined for all samples. The microstructure of the foam castings is investigated by SEM-EDS analysis. The results confirmed the presence of individual nano-sized particles, as well as clusters of particles in foam walls. The conducted compression tests show a significant increase in the plateau stress (up to 237%) of the modified aluminum foam castings compared to non-modified castings. However, a similar effect of the nano-compositions on A356 alloy foam castings is not observed. The obtained results show that the above-indicated concentrations of nanoparticles can positively influence the mechanical properties of aluminum foam castings. The novelty of the current study is two-fold: (1) such low concentrations of added nanoparticles have never been used before to alter Al foam’s properties, and (2) an original method of introducing the nanoparticles into the melt is applied in the form of nano-compositions.

Experimental investigation of phase change material (PCM) thermal energy storages with and without metal foam at different temperatures

This paper presents an experimental investigation of phase change materials (PCM) thermal energy storage. The experimental unit consists of a square channel with a single flow stream having distilled water as a heat exchange fluid. RT-42 is used as a thermal energy storage and the overall system is designed in two configurations i.e. with and without aluminium metal foam having a porosity of 95%. Each configuration is analysed and compared for two temperature variations i.e. at 55 °C and 65 °C, respectively. The study reveals that the heat storage rate in metal foam (MF) integrated PCM thermal energy storage is enhanced to ~3-4 times as compared to the setup without metal foam. In metal foam PCM energy storage, the temperature distribution is uniform and heat transfer is due to conduction as well as convection, while in case of pure PCM, there exist a temperature gradient within the thermal storage and the heat transfer is slower due to convection phenomenon. It is also observed that the heat transfer rate for 65 °C is comparatively greater than that of 55 °C for both systems as the higher operating temperatures lead to higher heat flux. However, operating at high temperatures is less feasible as the setup is more prone to PCM leakages.

Experimental investigation of effects of convective heat transfer and thermal performance of impinging jet on a metal plate with porous media

This experimental investigation is aimed to evaluate the effects of convective heat transfer phenomena in an aluminium metal flat disc/plate placed below metal foam using a single round jet of air impinging in a confined region. The Jet impingement technique contains pressurized air, which is configured for certain specific application. It is designed to spray the fluid with the help of a nozzle on the surface of the disc or plate which is being heated or is being cooled. To understand the heat transfer phenomena in a metal plate with metal foams facing round air jet impingement; three metal foams of similar geometries but of different porosities and permeabilities are taken for study. Each experiment is performed with seven different flow rates and at two different heights with two different heat flux values. The recorded measurements are temperatures, pressure differences, flow rates, resistance voltages and currents, and time. The outcomes of the experimental data are analysed and compared results of all four distinct kinds of metal foams with different jet to plate height and at different heat fluxes. It is concluded that heat transfer efficiency may or may not increase depending upon the metal foam used. Overall, the conclusions are extremely useful in engineering.

Investigation of the unsteady thermal storage performance of metal foam dual-phase change unit thermal storage tanks in solar thermal utilization systems

The adoption of metal foam thermal energy storage (TES) tanks in solar thermal utilization systems is crucial for enhancing energy supply stability. In this study, to investigate the transient thermal storage performance of TES tanks, a model of a solar thermal utilization system integrated with solar collectors and TES tanks was established. The model was validated through a literature review and experiments. The effects of initial temperature variation of solar collectors and the addition of metal foam on the transient heat transfer characteristics and thermal efficiency of TES tanks were analyzed. The results indicate that the porous structure of metal foam restricts natural convection, thereby improving temperature drift caused by displacement due to phase change material density variation. Maintaining the same initial temperature of solar collectors, filling metal foam can avoid the occurrence of melting dead zones at the bottom of pure paraffin phase change units, leading to an enhancement in the thermal efficiency of TES tanks and a reduction of 48.44% in phase change completion time. Additionally, a low initial temperature of the solar thermal collection system contributes to improving the thermal efficiency of metal foam composite TES tanks.

Simulation of Effect a Variable Height of Porous Absorber on Ventilation Solar Chimney Performance

The improvement in solar chimneys' thermal performance and thermal behavior that can be achieved by adding metal foam has been tested in computational work. The flow and heat transfer governing equations for solar chimney models were solved using computational fluid dynamics (CFD). It was solved using the control volume numerical method in ANSYS FLUENT 14.5. It is used to construct a finite volume modeling technique for solving the governing equations and the radiation heat transfer equations. With standard flat absorber plates, the results showed that heat transmission was increased by the inclusion of metal foam (10 PPI), leading to an increase in air velocity at the solar chimney of around 13.3%. The highest average air velocity with 10 PPI drops by 54.4% as the height of the absorber plate changes from 5 cm to 25 cm respectively.

Comparison between Stiffened Plate and Steel Aluminum Foam Sandwich Panels

Comparison between Stiffened Plate and Steel Aluminum Foam Sandwich Panels

Enhancing the degrees of freedom of topology optimization via variable-porosity metal foams: Design of heat conduction paths in a volume-to-point problem

Multi-material topology optimization determines the optimal distribution of different materials within a design domain in order to achieve specific performance goals. This work takes advantage of such technique to enhance the thermal performance of a benchmark heat conduction problem. The aim is to investigate the impact of enhancing the degrees of freedom introducing different materials, i.e., variable-porosity metal foams in addition to the high-conductivity solid, in the design of heat conduction paths under a constant weight constraint. The study leverages a well-established case study – volume-to-point problem – in the field of thermal management, ensuring a consistent basis for comparison. It consists of a square domain with a uniform heat source and a Dirichlet condition at a point on the boundary. Interpolation functions – ordered solid isotropic material with penalization (SIMP) type – allow the properties – in this case thermal conductivity – of materials to be correctly assigned. The distinction between materials is made by means of different thresholds on the projection function. By varying the foam porosity, we investigate the trade-offs between weight and heat dissipation efficiency. The objective is to find the ideal combination of materials that maximizes heat transfer – minimizing the average domain temperature – while conforming to weight constraints. Findings reveal that multi-material topology optimization – when applied to heat conduction problems – can outperform other design approaches, such as the growth-based algorithm, the evolved constructal tree, and the classical topology optimization (with one solid material), thereby paving the ground to innovative heat sink designs in weight-constrained environments.

Plateau stress estimation of aluminum foam by machine learning using X-ray computed tomography images

Plateau stress estimation of aluminum foam by machine learning using X-ray computed tomography images

Chebyshev polynomial-based Ritz method for thermal buckling and free vibration behaviors of metal foam beams

Chebyshev polynomial-based Ritz method for thermal buckling and free vibration behaviors of metal foam beams

Strength Increase of Alumina Foams by a Sodium Aluminosilicate Glass Coating with Subsequent Na+ ↔ K+ Ion Exchange (Gorilla Glass Coating)

Reticulated alumina ceramic foams manufactured by the Schwartzwalder technique are coated with a sodium aluminosilicate glass using an aqueous precursor containing alumina particles and sodium silicate. After a heat treatment, a well‐adhering glass layer with a thickness between 10 and 120 μm is obtained. Besides the strut surface, the glass phase also penetrates the hollow strut cavities as well as strut cracks. The total porosity of the glass‐coated foams is between 88% and 90%, and the open cellular structure is not negatively affected by the glass coating. The compressive strength increases by a factor of two under consideration of the decrease in total porosity; a compressive strength in the order of magnitude of 2 MPa is feasible. An ion exchange of Na+ by K+ into the glass coating layer (chemical strengthening) is successfully demonstrated, but does not result in an additional improvement of the compressive strength.

Performance improvement of photovoltaic-thermal collector equipped with copper metal foam air channel

ABSTRACT Avoiding high temperatures in photovoltaic cells with appropriate cooling is necessary to increase their conversion efficiency. Passive cooling systems using metal foam in the air channel were investigated, but an overall assessment is necessary for its viable application. In this numerical study, the thermal, electrical, and exergy efficiencies, as well as the entropy generation of a PVT are analyzed in the presence of copper metal foam in the air channel. The investigation is performed using a CFD code based on the pressure-based finite volume method. The non-Darcy effects of the porous foam are taken into account. Validation of the numerical model is made by comparison of the numerical predictions with experimental results of the literature. The outcomes indicate that varying the porosity from 1 to 0.89 increases the thermal energy, electrical energy, and exergy efficiency from 44.50% to 67.01%, 10.64% to 11.54%, and 12.01% to 13.19%, respectively, while the entropy generation decreases from 1.3116 W/K to 1.2942 W/K. Furthermore, the optimum thickness of the cooling channel is determined (30 cm for 0.93 copper foam porosity).

Durable Nano-Flower Structured Foam Coupled with Electrically-Driven in Situ Aeration Enable High-Flux Oil/Water Emulsion Separation with Dynamic Antifouling Ability.

The conventional membranes used for separating oil/water emulsions are typically limited by the properties of the membrane materials and the impact of membrane fouling, making continuous long-term usage unachievable. In this study, a filtering electrode with synchronous self-cleaning functionality is devised, exhibiting notable antifouling ability and an extended operational lifespan, suitable for the continuous separation of oil/water emulsions. Compared with the original Ti foam, the in situ growth of NiTi-LDH (Layered double hydroxide) nano-flowers endows the modified Ti foam (NiTi-LDH/TF) with exceptional superhydrophilicity and underwater superoleophobicity. Driven by gravity, a rejection rate of over 99% is achieved for various emulsions containing oil content ranging from 1% to 50%, as well as oil/seawater emulsions. The flux recovery rate exceeds 90% after one hundred cycles and a 4-h filtration period. The enhanced separation performance is realized through the "gas bridge" effect during in situ aeration and electrochemical anodic oxidation. The internal aeration within the membrane pores contributes to the removal of oil foulants. This study underscores the potential of coupling foam metal filtration materials with electrochemical technology, providing a paradigm for the exploration of novel oil/water separation membranes.