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In this study, an innovative thermal energy storage design method was developed by adding the combination of metal foam and fin to phase change materials (PCMs). A numerical model was built and verified based on the comparison among the present model prediction, experimental measurements, and numerical results in open literature. To highlight the novel design method, four cases including fin-PCM, foam-PCM, fin-foam-PCM, and PCM unit were compared by means of solidification features. The temperature distribution, solidification front propagation, and buoyancy-induced convection in the liquid PCM were accounted for. Numerical results demonstrated that metal foam outperformed fin regarding the improvement on solidification phase change. The combination of foam and fin achieved the best performance, leading to a 90.5% reduction in complete energy release time in comparison with the PCM unit. The proposed design method provided reference potentials for advancing energy storage engineering. However, buoyancy-induced convection in the liquid PCM before solidification was harmful to the formation of solidification front and its movement. A maximal 11.5% prolonging time for the complete solidification was found.

Molten salt has been widely used in latent heat thermal energy storage (LHTES) system, which can be incorporated into hybrid photovoltaic/thermal solar system to accommodate the built environment. Solar salt (60 wt.% NaNO3 and 40 wt.% KNO3) was employed as the phase change materials (PCMs) in this study, and both aluminum oxide (Al2O3) nanopowder and metal foam were used to improve the properties of pure solar salt. The synthesis of the salt/metal foam composites seeded with Al2O3 nanopowder were performed with the two-step and impregnation methods, and the composite PCMs were characterized morphologically and thermally. Then pure solar salt, the salt/2 wt.% Al2O3 nanopowder and salt/copper foam composite seeded with 2 wt.% Al2O3 nanopowder were encapsulated in a pilot test rig, respectively, where a heater of 380.0 W was located in the center of the LHTES unit. The charging and discharging processes of the LHTES unit were conducted extensively, whereas the heating temperatures were controlled at 240 °C, 260 °C and 280 °C respectively. Temperature evolutions at radial, angular and axial positions were recorded, and the time-durations and volumetric mean powers during the charging and discharging processes were obtained and calculated subsequently. The results show that physical bonding between Al2O3 nanopowder and nitrate molecule has been formed from the morphological pictures together with XRD and FTIR curves. Slight changes are found between the melting/freezing phase change temperatures of the salt/metal foam composites seeded with Al2O3 nanopowder and those of pure solar salt, and the specific heats of the salt/Al2O3 nanopowder composite slightly increase with the addition of Al2O3 nanopowder. The time-duration of the charging process for the salt/copper foam composite seeded with Al2O3 nanopowder at the heating temperature of 240 °C can be reduced by about 74.0%, compared to that of pure solar salt, indicating that the heat transfer characteristics of the LHTES unit encapsulated with the salt/copper foam composite seeded with Al2O3 nanopowder can be enhanced significantly. Consequently, the mean volumetric powers of the charging process were distinctly enhanced, e.g., the volumetric mean power of heat storage can reach 110.76 kW/m3, compared to 31.94 kW/m3 of pure solar salt. However, the additive has little effect on the volumetric mean power of heat retrieval because of the domination of natural air cooling.

The performance of photovoltaic (PV) modules worsens due to increasing their operating temperature. In the current study, a passive cooling technique comprising an aluminum metal foam (AMF) with PCM for thermal regulation of a PV system is performed. Outdoors experiments are conducted comprising two modules: PV without any modifications and PV with AMF embedded in PCM denoted as PV/PCM/AMF. The temperature distribution on the surface of the PV panels, PCM temperature, open-circuit voltage, and output power produced were recorded during the winter period. The results revealed that the PV surface temperature of the PV-PCM/AFM system was 4 %, 7.4 %, and 13.2 % lower than that of conventional PV, and the power produced from PV-PCM/AFM system was 1.85 %, 3.38 %, and 4.14 % higher than that of conventional PV in December, January, and February, respectively.

In this study, the effect of enhancing the core flow heat transfer with metal foam on the performance of thermoelectric generators with different power generation characteristics is studied experimentally. Filling the core flow area of the gas channel in a thermoelectric generator with metal foam can greatly improve the heat transfer capacity of the gas channel with a small pressure loss, thereby improving the power generation efficiency. The results show that, first, the heat transfer enhancement achieved by partially filling the core area of the gas channel with metal foam can significantly improve the performance of thermoelectric generators, the maximum output power is about 1.5 times higher than that of the unfilled channel. Second, for a thermoelectric generator with different modules, the friction coefficient for different filling ratios increases by about 16 times at most, while the Nu value increases by only three times at most, and according to the PEC of the gas channel, metal foam with high filling rate and low pore density is more suitable for the thermoelectric generator. Third, it is more appropriate to use the thermoelectric module with a high figure of merit as the selection criterion for deciding whether to adopt the technique of enhancing heat exchange through the gas channel. The maximum output power and efficiency of the thermoelectric generator using the high figure of merit module are 300% and 160% higher than those of the thermoelectric generator using the low figure of merit module, respectively.

This paper presents the numerical examination of the effect of spatial porosity variation of aluminum metal foams filled in a vertical channel. The physical domain comprises of a vertical channel in which aluminum plate cum heater assembly is placed at the center of the channel. The heat transfer from the aluminum plate is enhanced by using aluminum metal foams of different pore densities of 10, 20, 30, and 45 with varied porosities are considered in the present examination. A conjugate heat transfer analysis is carried out with the help of ANSYS FLUENT for a fluid inlet velocity of 0.1 – 1.5 m/s. The flow-through metal foam porous medium is predicted with the help of Darcy Extended Forchheimer model while heat transfer is predicted using the local thermal non-equilibrium model. The numerical methodology adopted in the current work is validated by comparing the present results with the literature. The hydrodynamic characteristics such as pressure drop and friction factor and thermal characteristics represented by Nusselt number, Colburn j factor, and overall performance factor are discussed in the present numerical investigation. The results of spatially varied porosity of metal foams are compared with uniform porosity metal foam. It is observed from the results that the spatial variation in porosity for the considered metal foam and the considered thickness of the channel does not significantly improve heat transfer but a slight decrease in pressure drop is observed compared to uniform porosity metal foam.

Three passive cooling configurations of a concentrator photovoltaic (CPV) system have been proposed to dissipate the heat via pure phase change material (PCM), Nano-PCM, and metal Foam-PCM as heat absorbers. A computational fluid dynamic model has been developed to compare the cooling capacity, thermal performance, and electrical efficiency of these configurations at three inclination angles. Evaluation of metal Foam-PCM performance, comparison between Foam- and Nano-PCM at different inclination angles, and exploring the effects on the output efficiencies are the most significant innovations of this study, which is not presented extensively before. In this regard, an experimental setup has been provided to validate the numerical simulations. The results revealed that the Foam-PCM sink could accelerate the melting process so that it mitigates the complete melting time and average PV temperature by 13.6% and 10.7%, respectively, at 150° inclination angle compared to the pure PCM. While the Nano-PCM sink does not make significant improvements. The results also indicate that the amount of absorbed heat and produced electricity till the complete melting time in Foam-PCM are increased by 7.5% and 4.8%, respectively. The superiority of the metal Foam-PCM sink could be improved by increasing the mass of metal through reducing the foam porosity.

The PCM composited with metal foam (PCM-porous system) as heat sink to cool photovoltaic (PV) panel is a potential application. However, there has little attention on the differences in cooling effect of PCM-porous systems when PV panels install with different inclination angles. To fill this research gap, the charging processes of PCM-porous systems with different inclined angles (φ = 0°, 30°, 60°, 90°) have been investigated numerically and experimentally in the current work. Meanwhile, the influences of different Rayleigh numbers (Ra = 1.4568 × 106, 1.8210 × 108, 1.1654 × 1010) have been considered. Results show that the inclined angle has little impact on the PCM-porous system with small porosity (e = 85%, 90%), which is much different from the PCM-porous system with larger porosity (e = 95%). In the discussion, an interesting phenomenon has been found that the weak natural convection of liquid PCM in porous media induced by the inclined cavity plays a negative role in melting process, which is obvious in PCM-porous system with small porosity (e = 85%, 90%). But this negative effect is not necessarily a bad thing due to that it can extend the duration time to cool the PV panel. The maximum duration time of PCM-porous system with e = 85% or 90% is 2 times of system with e = 95% (φ≠0°).

The ultrafast frequency response supercapacitor is a promising candidate for alternating current line filtering. We report the fabrication of a special structured ionic liquid-based supercapacitor with an ultrafast response of only 1.5 ms. The three-dimensional aluminum (Al) foam in situ coated with carbon layer (∼500 nm) serves as the novel, highly efficient electrode-current collector. The high porosity (95%) of Al foam allows the rapid ion diffusion and the as-obtained Al/C interface with atomic-level mixing allows the fast electron transfer, two crucial factors for ultrafast response. Hence, it possesses an excellent specific mass capacitance of 68 mF g-1 at 120 Hz, as well as an ultrahigh rate of up to 3000 V s -1. The supercapacitors exhibit frequency modulation performance in the range of 20 kHz to 16 MHz. They exhibit the similar even better alternating current filtering performance, as compared to the commercial aluminum electrolytic capacitors, detected at 10 Hz, 60 Hz, 100 Hz and 1 M Hz. These results suggest that, although ILs have high viscosity and low ion mobility, the IL-based supercapacitor has a great potential to be used as a device for alternating current line filtering, as well as providing nonvolatile and nonflammability safety.

In this study, the predicting and avoiding method of core fracture in plastic forming for aluminum foam sandwich panel (AFSP) were investigated. By observing the macroscopic core cracks and microscopic morphology of the fracture surfaces, the core fracture occurred in plastic forming of AFSP can be confirmed as ductile fracture. Five ductile fracture criteria were introduced for predicting the fracture initiation and detailed simulations on plastic forming of AFSP were performed with a mesoscopic 3D Voronoi AFSP model; besides, multi-point forming experiments of cylindrical, spherical, and saddle-shaped AFSPs were carried out. Normalized value I distributions on the cores using different fracture criteria and core cracks found experimentally indicate that Ko fracture criterion is the most suitable to predict the core cracking during curved AFSPs forming. Moreover, on the basis of the core value I distributions obtained using Ko criterion and the experimental panels in the case of different forming step numbers and core relative densities, it is found that the risk of core fracture can be reduced by adopting multi-step forming and increasing the core relative density.

In this paper, three different methods (secondary growth method, in situ hydrothermal method and hot pressing with silane method) for synthesizing silicalite-1 molecular sieve anti-corrosive film on open-cell aluminum foam surface were studied, and the silane coupling agent was used as a connecting layer to enhance the bonding force. The surface morphology was observed by scanning electron microscopy, the phase composition was analyzed by x-ray diffraction, and the corrosion resistance was predicted by electrochemical test results. It was shown that the silicalite-1 anti-corrosion film prepared by the secondary growth method has the best surface, crystallinity (more than 98%), anti-corrosion performance, and good hydrophobicity. Finally, through Raman Microscopy test, the film formation mechanism of the secondary growth method was analyzed. The results show that the initial hydrogen bonds between the hydroxyl groups of the molecular sieve particle and the hydroxyl groups of the silane coupling agent change to covalent bonds due to the dehydration condensation reaction, and other free hydroxyl groups react in the same way with the hydroxyl groups on the aluminum foam surface.

Critical size of droplet on metal fiber is an important parameter during the dehumidifying process, as it determines the drainage performance of metal foam heat exchangers. In the present study, the droplet shedding characteristics on metal fibers with various fiber diameters, surface wettability and inclined angles were investigated experimentally. The results show that, the critical size of droplet on metal fibers is increased by 69%-213% as the receding contact angle reduces from 132.8° to 17.2°, and it is increased by 93%-292% as the fiber diameter increases from 0.3 mm to 2.0 mm. As the inclined angle of metal fiber increases from 0° to 90°, the critical droplet size is decreased by 78%-86%. Based on the equilibrium of gravity and capillary force, a predictive correlation for the critical droplet size on metal fibers with different wettability and inclined angles was developed, and it agrees with 90% of the experimental data within a deviation of ±15%.

The magnetron sputtering has been used to prepare metal foam wicks for heat pipes by coating the surface of copper foam with zinc oxide (ZnO) nanoparticles. The main properties, including microscop...

This paper is a numerical study about the catalyst morphology CuO/ZnO/Al2O3 effects on the hydrogen production from methanol steam reforming, for proton exchange membrane fuel cells (PMEFC). The study is focused on the influences of the metal foam insert, catalyst layer segmentation, and metal foam as catalyst support on the reactor performance: hydrogen yield and methanol conversion. According to the carried simulations, it is found that these configurations improve the reformer performances compared to the continuous catalyst layer configuration. The insertion of metal foam increases the efficiency of up to 75.41% at 525 K. Also, at this reaction temperature, the segmentation of the catalyst layer in similar parts increases the reformer efficiency by 2.11%, 4.23%, 6.77%, and 8.6% for 2, 4, 8, and 16 identical parts, respectively. As well as, the metal foam as catalyst support is more efficient compared to the other configurations, the efficiency is equal to 64% at T = 495 k.

In the framework of third-order shear deformation shell theory, this research explores stability behavior of metal foam double-curvature shells under transverse mechanical loading. It is also assumed that the metal foam shell has been reinforced with eccentrical stiffeners. Metal foam has been considered identical to porous materials having uniform or non-uniform pores. The double-curvature foam shell has been exposed to out-of-plane pressure load which leads to post-buckling stability in nonlinear regimes. Employing an analytical procedure and taking into consideration Airy stress function, the established governing equations have been solved to determine the stability load of stiffened double-curvature metal foam shells. Curvature radius, stiffeners, pore volume and shell geometry are shown to have remarkable influences on stability curves.

This work analyzes the free vibration of a spinning functionally graded graphene platelet-reinforced metal foam (FG-GPLRMF) beam. The differential transformation method is extended to analyze flap-wise bending vibration and chordwise bending vibration with Coriolis force effect for the first time. The beam is modeled using the Euler–Bernoulli beam theory. The Halpin–Tsai micromechanics model is utilized to predict effective material properties. Various types of graphene platelet (GPL) and porosity distributions are considered. The governing equations and corresponding boundary conditions of the FG-GPLRMF beam are obtained via Hamilton’s principle. Results show that the vibration characteristics of the FG-GPLRMF beam are affected by the GPL geometry size, types of porosity, and GPL distributions. Among different types of porosity, the Porosity-A causes the highest fundamental natural frequency, while the Porosity-B corresponds to the lowest one of the spinning FG-GPLRMF beam in most cases. Moreover, the GPL pattern and porosity distribution have a coupled effect on the bending vibration of the spinning FG-GPLRMF beam.

We investigate the nonlinear bending behavior of nanoporous metal foam plates within the framework of isogeometric analysis (IGA) and higher-order plate theory. The nonlocal strain gradient theory (NSGT) taking into account the length scale and nonlocal parameters has been adopted to establish a scale dependent model of metal foam nanoscale plates. Von Karman nonlinear strains are then used to take up the geometric nonlinearity. Different pore dispersions, namely uniform, symmetric and asymmetric, are confirmed. By using the principle of virtual work, nonlinear governing equations are derived and then solved by using an isogeometric analysis and iterative Newton-Raphson method. Influences of the length scale parameter, porosity distributions, nonlocal parameter and nanoporous coefficient on the nonlinear deflection of the plate are numerically experimented in detail. Some findings would play an important role for designing metal foam structures.

Cooling technology exploiting the endothermic reaction of fuel has been developed to prevent structural deformation in engines due to air friction and overheating during supersonic flight. Endothermic fuels are liquid hydrocarbon fuels that can absorb heat through endothermic reactions. The initial heat sink capacity of conventional pellet type catalysts for the endothermic reaction cannot be maintained, leading to more rapid deactivation due to coke formation. To maintain the heat sink performance of decomposition catalysts, HZSM-5 catalyst washcoated on metal foam(HZSM-5/metal foam) was used herein. The reactions were carried out in a batch reactor at 673 K at a pressure of 50 bar using methylcyclohexane (MCH) and n-dodecane as reactants. The total MCH conversion achieved with the pellets and HZSM-5/metal foam was same at 93 %. In the case of n-dodecane, the total conversion achieved with the HZSM-5/metal foam (91 %) was superior to that achieved with the pellets (69 %).

This study conducted a simulation and an experimental study on a channel that was partly filled with open-cell metal foam block. Different blockage ratios have been considered, where the foam height could occupy more than half of the channel size. The aim is to investigate the flow behaviours across the complicated structure of the porous medium. Results show that the use of Ergun and Forchheimer models showed a similar stagnant region and recirculation zone in the partially filled channel, which agreed with the experimental results. However, the deviation in pressure drop performance at a high blockage ratio is noticeable.

Poor thermal conductivity of phase change materials (PCMs) is the principal barrier to their widespread application. As such, numerous single or hybrid techniques have been proposed to lower the thermal resistance of PCMs. In the present paper, a hybrid approach, including the dispersing of nano-sized particles and embedding in a porous medium, was employed to augment the rate of heat transfer and melting process of the resulting nano-enhanced PCM (NePCM). Aluminum foam was used as the solid matrix, and phase-change heat transfer of a NePCM comprising n-octadecane as the phase change substance and nano-sized particles of mesoporous silica (MPSiO2) was studied. Previous experimental studies have shown that, although n-octadecane behaves as a Newtonian fluid, the mentioned NePCM behavior deviates from that of Newtonian fluids. Hence, the thermal and hydrodynamic behaviors of the non-Newtonian suspension of the NePCM in porous media were investigated numerically. Governing equations, including mass and momentum conservation for the liquid NePCM and energy equations for both solid and liquid phases, were solved using the Galerkin finite element method. The deformed mesh technique was employed to address the movement of the melting front. The finite element code was validated against several experimental and numerical works and was sufficiently accurate. Results showed that owing to the alteration of the rheological and thermophysical characteristics of the NePCM, increasing concentration of nanoparticles reduced the average Nusselt number and the normalized melt volume fraction (NMVF). It was also found that porosity played an important role in the phase-change rate. Although the steady-state condition was achieved faster in the case of lowest porosity, the maximum NMVF was achieved in the case of the highest porosity after Fourier number = 0.02.

The latent heat thermal energy storage unit (LHTESU) strengthened by metal foam can effectively store solar energy and realize the sustainable utilization of solar energy. In this paper, the metal foam with a two-dimensional (radial and circumferential direction) porosity gradient is proposed for the problem of slow melting rate and non-uniform melting in the horizontal shell-and-tube LHTESU. The non-uniform index and thermal energy storage rate are introduced to evaluate different metal foam structures. Under the same amount of metal foam, the influence of one-dimensional and two-dimensional graded structures is numerically studied. The results show that circumferential graded structure can alleviate the non-uniform melting problem. Compared with the uniform structure, the non-uniformity index decreases by 36.63% and the thermal energy storage rate is increased by 38.60%. In addition, the optimum circumferential porosity gradient also increases with the increase of Ra*. The strengthening effect of the circumferential and radial graded structures is also compared. It can be found that with the increase of porosity gradient, the strengthening effect of the circumferential graded structure increases gradually and that of radial graded structure first increases and then decreases. When the circumferential graded structure is combined with the radial graded structure, the two-dimensional porosity gradient structure can further improve the thermal performance of LHTESU. Compared with the uniform structure, the thermal energy storage rate can be increased by 47.40%.

Closed-cell porous aluminum is expected to be a prominent material in near future because of its light weight, high specific modulus of elasticity, high energy absorption efficiency and high sound-insulating capacity in the automotive and aerospace industries. Recently, a new method of foaming has been developed in which a precursor is formed using friction stir processing. In the friction stir processing route, a precursor is fabricated by embedding a mixture of blowing agent powder and stabilization agent powder into aluminum alloy plates by the significant stirring action of friction stir processing. By applying the friction stir processing route precursor method, the cost-effective Al-foam formation along with high productivity can be accomplished. In this study, titanium hydride powder has been used as the blowing agent as it is reported to be most compatible with aluminum matrix. The effect of percentage of stabilization agent, i.e. alumina powder on porosity of aluminum foams formed using friction stir processing route is analyzed. The porous aluminum formed with three different percentages of alumina is observed and their porosity is calculated. Also, the compressive performance of the obtained samples is observed in order to examine the alumina powder addition on mechanical properties of the obtained metal foam. This study aims at analyzing the significance of addition of the alumina into the blowing agent while developing the metal foam through friction stir processing route.

High-density aluminum foam can provide higher stiffness and absorb more energy during the impact Obtaining the constitutive law of such foam requires tri-axial tests with very high pressure, where difficulty may arise because the hydrostatic pressure can reach more than 30 MPa. In this paper, instead of using tri-axial tests, we proposed three easier tests—tension, compression and shear to obtain the parameters of constitutive model (the Deshpande–Fleck model). To verify the constitutive model both statically and dynamically, we carried out additional triaxial tests and direct impact tests, respectively. Based on the derived model, we performed finite element simulation to study the impact response of the present foam. By dimensional analysis, we proposed an empirical equation for a non-dimensional impact time $${\bar{t}}_{\mathrm {d}}$$ , the impact time divided by the time required for plastic wave travelling from the impact surface to the bottom surface, to determine the deformation characteristic of the aluminum foam after impact. For the case with $${\bar{t}}_{\mathrm {d}}\le 1$$ , the deformation tends to exhibit a shock-type characteristic, while for the case with $${\bar{t}}_{\mathrm {d}}>5$$ , the deformation tends to exhibit an upsetting-type characteristic.

One of the methods for improving the seismic behavior of structures was to use inactive control devices. Recently, in civil engineering applications, a relatively new material named metal foam has been utilized progressively due to its high energy dissipation capability and remarkable axial strain. In this study, several non-linear time-history analyses were conducted for investigating the seismic behavior of steel frames equipped with the composite brace using a three-dimensional (3D) finite element (FE) method. Crushable foam (CF) and elastic-perfectly plastic models were considered for metal foam and steel members. FE results revealed that the maximum drift ratio decreased by 35% and 72% under near-field and far-field records in the steel frames equipped with composite brace compared to the conventional steel brace frames. Employing the composite brace led to prevent global buckling of the brace and consequently decrease in load-bearing capacity. Furthermore, composite brace caused the reduction of bending moment demand in the first-story column by 18%.

Large open-cell copper (Cu) foam plates were fabricated using the sintering and dissolution process with NaCl spacers. A rotating tungsten carbide (WC) tool with a flat shoulder was used to generate the temperature and pressure needed for sintering. Sintering was done on a friction stir welding machine. Tool path and die design control the sintered part shape and size. The process allows for fabrication of large three-dimensional metal foam parts on conventional milling and friction stir welding machines. NaCl volume fraction in metal powder-NaCl filler mixture was kept at 80%. Copper foam obtained in this manner had uniform porosity. Tool traverse speed affected sintering time and temperature and influenced the mechanical properties and microstructure of sintered parts. The microstructure of copper foam was studied using a scanning electron microscope. Compression tests were used to study its mechanical properties. Macro-pores were seen to have NaCl particle morphology. Foam mechanical properties were seen to be on par with that reported in literature. The sintering and dissolution process presented in this work results in open-cell foams with large surface areas. It is an attractive alternative for the fabrication of three-dimensional porous sintered parts.

Adsorption cooling and desalination (ACD) system powered by renewable energy has been considered as a promising solution to solve interconnected global problems such as freshwater scarcity, high-cost air conditioning, CO2 emission, and global warming. In this work, a new nanoporous silica was synthesized through a self-assembly process using a combination of ionic and non-ionic surfactants. The silica has shown unique pore structures, including high surface area and large pore volume, as well as ideal pore size distribution. The new silica was deposited (coated) over the ligaments of aluminum foam for use as a sorption bed. An uncoated aluminum foam packed with conventional silica RD (regular density) particles serves as a baseline sorption bed. The freshwater production rate and cooling power produced using the two sorbents were compared. Silica RD outperforms the new silica for cooling while the new silica is far better for desalination application. Insights for such results are provided.

The model equation method (MEM) is a new method to measure the porosity of porous materials. This paper demonstrates the application value of the MEM in the preparation of titanium foams from an experimental point of view. The results showed that the porosities calculated by the MEM were in the range of 0.533–0.701 with the spacer contents between 0.55 and -0.75. The measured values were highly consistent with those of the mass volume method, which indicates that the MEM was feasible to measure porosity. The correlation equation between porosity and spacer content has a very high prediction accuracy by a linear fitting. The elastic modulus and yield strength of titanium foams were 4.8–29 GPa and 10.2–101.1 MPa, respectively. The relative elastic modulus and relative yield strength were directly proportional to the n-th power of relative density through a nonlinear fitting. The mathematical correlations between relative mechanical properties and spacer content were established. This study not only proves that the new method of porosity measurement has an important application value, but also realizes the source control of mechanical properties of titanium foams.

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%.

Thermal energy storage (TES) has been playing a crucial role in addressing the issue of solving the intermittent and random problems in solar energy utilization. The objective of this study is to squarely address and clarify the contribution of metal fin and foam to enhancing the phase change heat transfer by experiments. A novel hybrid fin-foam tube is proposed and its thermal performance is evaluated by experimentally comparing with other three competing structures including bare, fin, and metal foam tubes. A well-designed test rig is built and the energy storage features for the designed four TES tubes are analyzed by the complete melting time, melting front evolution, temperature variation and uniformity, and the temperature response rate. Results show that the fin-foam hybrid structure outperforms the other competing ones, demonstrating a reduction of 83.35% in complete melting time (compared with the bare tube). The transient temperature response is maximized by 529.1%. As for the single structure, both fins and metal foam can improve conductivity of phase change materials. The metal foam does a good favor to improve the uniformity of the temperature field inside the TES tube, but the fins weakened the uniformity. If the design target is temperature uniformity, adding metal foams other than fins can fulfil the task.

The space holder process (SHP) is a useful and common technique to obtain metal foams. However, an important question remains unsolved: Would the quality of the salt affect the properties of the aluminum foam obtained? In this paper, removable preforms of two types of salt (refined and unrefined) were infiltrated with A356 aluminum alloy to obtain metal foams with different pore sizes. The interaction preform-metal was studied from analyzing the morphological structure of the foams, the metal microstructure, and the corrosion resistance of the Al356 alloy. It was observed that, although the two types of salt exhibited some differences, they did not show variations in relation to the porous structure and metal microstructure in the aluminum foams obtained. Additionally, the electrochemical analyses did not show significant effects on the corrosion behavior of aluminum foams caused by the interaction with the salt preforms.

In this study, the consequence of cell-size, cell-wall-thickness and cell circularity together on the compressive performance of closed-cell aluminum foam was analyzed experimentally and with FEM simultaneously. The closed-cell metal foams (CAFs) with varying cell sizes of 55% porosity were synthesized through stir casting technique. The granular metallic calcium is used as a stabilizing/thickening agent, and TiH2 powder used as a foaming agent. The uniaxial compression tests were performed to investigate the compressive deformation behavior of CAFs. The simulation studies were carried out by taking the assumption similar to experimental constraints. The circular-shaped cells were created in FE half symmetrical model of varying cell sizes (in 2-Dimensional). The cell sizes used in FE models are 1.5 mm, 2.5 mm, 2.8 mm and of 3.5 mm. While in experimental samples, different cell sizes obtained are 1.65 mm, 2.47 mm, 2.88 mm and 3.59 mm. In both of the investigations, it is observed that the energy absorption capacity and plateau strength decrease with an increase in cell sizes or vice versa. A similar effect was also observed with an increase in cell wall thickness. The obtained FE results are acceptable and comparable with the experimental for each cell size model. The deformation mechanism was analyzed using deformed sample images, which were captured during the deformation as well as during the different stages in the FEA models.

In the last decades, Aluminum foam has attracted many researchers and manufacturers due to its unique properties which find a lot of applications, especially in a lightweight structure. The current work aims to study the effect of adding calcined alumina to the melting aluminum on the final mechanical and microstructure of produced aluminum foam. Calcium carbonate was used as a foaming agent. The study reveals that calcination times/temperature have a significant effect on the final foam porosity. with increasing calcination time from 30 min to 90 min the foam density improved from 2.27 to 1.27 g/cm3, which consequently result in increase of samples porosity from 15.9 to 52.7%. also, the results from the compression test show that the variation of calcination time can be used to alter the energy absorption capacity of samples. Tested samples achieved the highest energy absorption of 128 MPa at a calcination time of 90 min. Also, the study reveals that calcination temperature has a significant effect on the final foam porosity. with increasing calcination temperature from 400 to 800°C, the foam density improved from 2.18 to 1.09 g/cm3, which consequently result in increase of samples porosity from 18.94 to 52.79%. Tested samples achieved the highest energy absorption of 325 MPa at a calcination temperature of 800°C. The increase in porosity is measured by ImageJ software, and the energy absorption test was carried out by a quasi-static compression test. These improvements produced material can be used in applications needs high energy absorption like automotive industry.

Open-cell aluminum foams with spherical cells have great potential application due to their reliable structural and functional performance. However, a problem of poor cell connectivity always arises during fabrication. Three precursor designs were explored to optimize the cell structure. The results showed that the lack of the treatment of the space holders caused poor cell connectivity and a lower porosity, which could be resolved by introducing alcohol as a binder or hot-pressing space holders in precursor designs. Nevertheless, a poor fluid of the granules in the former had a negative effect on porosity improvement, whereas the latter created a precursor with strong bonding between the granules with good flow characteristics and led to a significant improvement in cell connectivity and porosity. This work could provide an approach to designing precursor structures in order to tailor the structure of the final open-cell aluminum foam.

The closed-cell aluminum alloy foams were fabricated by the molten body transitional foaming process. In this research, the closed-cell aluminum foams were successfully fabricated with different zinc contents (4, 8, and 12wt%) using the melt-foaming method and blowing agents. Calcium was used to increase the melt viscosity and CaCO3 was used as a foaming agent. Uniaxial compressions tests were performed on the foams to investigate the effects of zinc addition on the mechanical behavior of fabricated Al–Zn foams. The effects of zinc additions on the foam properties such as density, porosity, pore diameter, yield strength, plateau stress, and energy absorption were investigated. According to the X-ray analysis results, the reaction between Al–Ca–Zn leads to the formation of oxide phases in the melt and increases the melt viscosity and also the cell wall thickness. Foam with 4wt% Zn has a good yield strength and longer plateau region than pure aluminum foam due to the uniform cell structure. The foam density and the absorbed energy per unit volume of Al–Zn foams increase with increasing zinc content to foams.

Simultaneous charging and discharging (SCD) of the latent thermal energy storage (LTES) can improve the flexibility of solar thermal systems and ensure the continuity of energy supply. Experiments and numerical simulation are conducted in this study to reveal the SCD thermal behavior of LTES device using flat micro-heat pipe array–metal foam composite structure. The effects of heat transfer fluid (HTF) temperature, volumetric flow, initial phase change material (PCM) state, and metal foam are analyzed. Results show that PCM absorbs heat from hot HTF or releases heat to cold HTF at the beginning depending on the PCM and HTF temperatures. The SCD eventually reaches an approximate steady state, cold HTF exchanges heat directly with hot HTF, power and PCM temperature remain unchanged. Low cold HTF temperature quickly reaches steady state and low final PCM temperature but has no influence on steady state power. PCM initial state and metal foam porosity do not affect the steady state power and final PCM temperature. However, they affect the time to reach steady state. Metal foam pore density has no obvious effect on SCD. SCD has more stable discharging performance than single discharging, especially when the cold HTF temperature is high.

In this study, the vibration and flutter characteristics of the graphene platelets reinforced functionally graded porous cylindrical panels subjected to the supersonic flow are investigated for the first time. The considered panels are constructed of the nanocomposites that made of matrix of open-cell metal foams with graded pore distributions and are reinforced uniformly by the graphene platelets. The typical mechanical properties of porous matrix are determined using open-cell metal foam model, which provides a typical mechanical feature to determine the relationship between coefficients of density and porosity. The effective elasticity modulus of the nanocomposite is determined based on a modified Halpin-Tsai micromechanics model, and the rule of mixture is used to calculate the Poisson's ratio and mass density. A high order shear deformable computational framework is developed with inclusion of the trapezoidal shape factor to eliminate the errors introduced by the curvature of the panels. The standard Lagrange processing in conjunction with the Navier-solution technique, with the help of the first-order piston theory, is applied to derive the equations of motion related to the vibration and flutter characteristics of the cylindrical panel with simple-supported boundary condition. Comparisons of the natural frequencies with the previous works are performed to validate the proposed model. Parameter studies are carried out, and the results in the form of graphs or tables reveal the effects of pore, graphene platelets on the supersonic flutter characteristics of the nanocomposite cylindrical panels subjected to the aerodynamic flow.

In this paper, the Taguchi optimization methodology was utilized for optimizing the production parameters of aluminum foam sandwich panels (AFSP) with different skin layers under low-velocity impact loading. The core material of AFSP was A356 aluminum foam reinforced with SiC particles produced by the CaCO3 foaming agent with 20, 30, and 40 mm thicknesses. The skin layers of plates were made of glass/epoxy with the quasi-isotropic and cross-ply layout as well as the pure aluminum layer. The drop weight impact device was used for the impact test. Three types of impactors (spherical, parabolic, and cone) were used. The evaluated impact parameters are the skin layer layout, impactor shape and core thickness of AFSP. Also, the measured response factors were the specific absorbed energy (SAE), maximum displacement (MD), and maximum impact force (MIF). The Taguchi method was used to check the effect of the production parameters on the response factors by creating the orthogonal array (OA). The results indicated that the best combination of production parameters can be determined by the application of the Taguchi method. These results can provide the optimal impact responses (the largest SAE, the smallest MD, and the smallest value of MIF). For the best SAE and MIF, A1–B1–C1 (pure aluminum/conical/20 mm core) was also investigated. Meanwhile, the optimized combination of levels for all the three production factors was examined to provide the lowest MD (A3–B2–C1, cross-ply/parabolic/20 mm core).

Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and quasi-static shear-compression combined loadings is investigated in this study. First, quasi-static and dynamic compression-shear combined tests at different loading angles are conducted using a universal testing machine and a rotatable Hopkinson bar system, respectively. Shear deformation reduces the plateau stress as the loading angle increases. Subsequently, the yield modes of the metal foam under combined loadings are investigated. Only one yield band occurs under a combined loading with large loading angles (mode I), whereas several yield bands occur under a combined loading with small loading angles (mode II). Finally, the yield surface plot of metal foam indicates significant enhancement in terms of normal stress and shear stress under dynamic loading. Quasi-static and dynamic phenomenological yield criteria for a shear-normal stress space are established to provide a brief and precise prediction of the behavior of metal foam under quasi-static and dynamic combined loadings.

Aluminum foams have recently received special attention due to their peculiar mechanical properties. For example, their energy absorption capacity in crash events and low density are very desirable...

In the present study, the microstructural characteristics, compressive strength, and corrosion behavior of aluminum-cenosphere composite foam (CF) developed by spray forming route (processed with 5 Psi (3.45 × 104 N/m2) and 10 Psi (6.90 × 104 N/m2) hydrogen pressure) has been undertaken. The microstructure of the spray-formed coupon consists of hollow cenosphere particles distributed uniformly in aluminum matrix. Compressive yield strength (YS) of the aluminum-cenosphere foam (CF) is different from commercially pure aluminum (cp-Al). It is found that the YS of the foam processed with 5 Psi is 83.62 MPa and for the foam processed at 10 Psi is 113.32 MPa as compared to 104.42 MPa for cp-Al. A detailed study of corrosion behavior through electrochemical measurements indicates that CF exhibits a reduced corrosion rate from 0.092 (for cp-Al) to 0.056 mm/year and 0.080 mm/year for the samples processed with 10 and 5 Psi, respectively. Through a detailed analysis of Nyquist and Bode plots derived from EIS measurements, it is concluded that mostly localized corrosion occurs in all the samples. The post-corrosion microstructural study confirms that interface of aluminum and cenosphere is the potential area for initiation of corrosion.

The outstanding mechanical properties and lightness of aluminum foam make it attractive as buffering and energy absorption material for spacecraft landing in deep space exploration. In this paper, cell-based model of open-cell aluminum foam has been established by Voronoi tessellation method. Through quantitative comparisons of energy absorption performance between different simulation models, it can be found that the improvement of base material properties can lead to significant enhancement of energy absorption ability, and there is an approximate linear relationship between relative density and relative energy absorption at low speeds. Characteristic deformation mode has been discussed under different compression speeds. The isotropic buffering characteristic of aluminum foam materials has been verified by the simulation of a footpad filled with aluminum foam impacting on a sloping ground.

PurposeThe purpose of this paper is to provide a summarization and review of the present author's main investigations on failure modes of reticular metal foams under different loadings in engineering applications.Design/methodology/approachWith the octahedral structure model proposed by the present authors themselves, the fundamentally mechanical relations have been systematically studied for reticular metal foams with open cells in their previous works. On this basis, such model theory is continually used to investigate the failure mode of this kind of porous materials under compression, bending, torsion and shearing, which are common loading forms in engineering applications.FindingsThe pore-strut of metal foams under different compressive loadings will fail in the tensile breaking mode when it is brittle. While it is ductile, it will tend to the shearing failure mode when the shearing strength is half or nearly half of the tensile strength for the corresponding dense material and to the tensile breaking mode when the shearing strength is higher than half of the tensile strength to a certain value. The failure modes of such porous materials under bending, torsional and shearing loads are also similarly related to their material species.Originality/valueThis paper presents a distinctive method to conveniently analyze and estimate the failure mode of metal foams under different loadings in engineering applications.

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The present numerical investigation examines the performance improvement of thermoelectric generators (TEGs) by using phase change materials (PCM) and porous medium. Due to the high latent heat of PCMs, both sides of the TEG were filled with paraffin RT35 (on the cold-side) and paraffin RT69 (on the hot-side). The PCM in the cold-side of the TEG was used as a heat-sink whereas the PCM in hot-side of the TEG was used to reduce the output voltage fluctuations. Since the system was periodically subjected to heat flux from an external heat source, the paraffin in the hot-side of the TEG was also used to generate a continuous thermal heat when the heat source was cut-off. To increase the thermal conductivity of the phase change material, this investigation studied the effect of using the copper porous medium with different porosities (0.80, 0.90, and 0.95) and three different pores per inches (PPI) as 10, 20, and 40. The results show that the use of porous on the cold-side of the TEG produces more electrical energy and output voltage compared to (i) having porous medium on the hot-side and (ii) using PCM without porous medium on both sides of the thermoelectric generator. Furthermore, the results indicated that the TEG performance enhanced by increasing PPI and reducing porosity. As a result, by increasing the PPI from 10 to 40 (at 0.80 porosity) and by reducing porosity from 0.95 to 0.80 (at PPI 20), the electricity generated increases by 13.57 and 5.36%, respectively.

In this paper, a mathematical model for heat transfer in a heat sink covered by an open-cell metal foam under impinging jet flow is presented. Hydrogen and air were considered as the cooling fluids. The Darcy–Brinkman–Forchheimer relationship for the momentum equation was employed, while the two-equation energy model under the local thermal non-equilibrium (LTNE) condition for the energy equation was used. The mathematical model of similarity solution was first validated with analytical and experimental data from literature, and numerical data from Ansys-Fluent®. Then, the differences between numerical predictions under the local thermal equilibrium (LTE) and LTNE on flow and temperature distributions were presented and analyzed. It was shown that when the effective thermal conductivity of solid is very low, the difference of temperature of solid and gas cannot be neglected and LTNE should be considered. In other words, when effective thermal conductivity ratio, β, declines, the deviation between the LTNE and LTE models increases considerably. Finally, the effects of critical dimensionless parameters on the flow and heat transfer characteristics were investigated. The results indicate that cooling performance of the metal foam can be improved by increasing the Reynolds and Darcy numbers while decreasing the aspect ratio of the heat sink. Besides, the properties of metal foam and gas were studied. Hydrogen, as a cooling gas, has better thermal performance than air.

In the present study, we analyze the nonlinear forced vibration of thin-walled metal foam cylindrical shells reinforced with functionally graded graphene platelets. Attention is focused on the 1:1:1:2 internal resonances, which is detected to exist in this novel nanocomposite structure. Three kinds of porosity distribution and different kinds of graphene platelet distribution are considered. The equations of motion and the compatibility equation are deduced according to the Donnell’s nonlinear shell theory. The stress function is introduced, and then, the four-degree-of-freedom nonlinear ordinary differential equations (ODEs) are obtained via the Galerkin method. The numerical analysis of nonlinear forced vibration responses is presented by using the pseudo-arclength continuation technique. The present results are validated by comparison with those in existing literature for special cases. Results demonstrate that the amplitude–frequency relations of the system are very complex due to the 1:1:1:2 internal resonances. Porosity distribution and graphene platelet (GPL) distribution influence obviously the nonlinear behavior of the shells. We also found that the inclusion of graphene platelets in the shells weakens the nonlinear coupling effect. Moreover, the effects of the porosity coefficient and GPL weight fraction on the nonlinear dynamical response are strongly related to the porosity distribution as well as graphene platelet distribution.