Porous Metal Foam Research Articles

Investigating post-buckling of geometrically imperfect metal foam nanobeams with symmetric and asymmetric porosity distributions

In this research, analysis of post-buckling behavior of porous metal foam nanobeams is performed based on a nonlocal nonlinear refined shear deformation beam model with geometric nonlinearity and imperfection. In the metal foam nanobeam, porosities are dispersed by uniform, symmetric and asymmetric models. The present nanobeam model satisfies the shear deformation effect needless of any shear correction factor. The post-buckling load-deflection relation is obtained by solving the governing equations having cubic nonlinearity applying Galerkin’s method needless of any iteration process. New results show the importance of porosity coefficient, porosity distribution, geometrical imperfection, nonlocal parameter, foundation parameters and slenderness ratio on nonlinear buckling behavior of porous nanoscale beams. Specially, porosities have a great impact on post-buckling configuration of both ideal and imperfect nanobeams.

Thermal and Fluid Transport in Micro-Open-Cell Metal Foams: Effect of Node Size

Open-cell metal foams exhibit distinctive advantages in fluid control and heat transfer enhancement in thermal and chemical engineering. The thermofluidic transport characteristics at pore scale such as topological microstructure and morphological appearance significantly affect fluid flow and conjugated heat transfer in open-cell metal foams, important for practically designed applications. The present study employed an idealized tetrakaidecahedron unit cell (UC) model to numerically investigate the transport properties and conjugated heat transfer in highly porous open-cell metal foams (porosity—0.95). The effects of foam ligaments and nodes (size and cross-sectional shape) on thermal conduction, fluid flow, and conjugated heat transfer were particularly studied. Good agreement was found between the present predictions and the results in open literature. The effective thermal conductivity was found to decrease with increasing node-size-to-ligament ratio, while the permeability and volume-averaged Nusselt number were increased. This indicated that the effects of node size and shape upon thermofluidic transport need to be considered for open-cell metal foams having high porosities.

A novel design of solar chimney for cooling load reduction and other applications in buildings

Cooling load accounts for more than 70% of the electric energy used in buildings in the Middle East. This paper presents a passive method to reduce the cooling load in buildings. The proposed concept includes adding an external solar shield enclosing an air gap between it and the outer wall of the building. This external solar shield layer would absorb the solar radiation incident on the outer walls of the building and get heated inducing a convective airflow in the gap between the layer and the building. This is an example of solar chimney in a flat geometry with a superficial resemblance to Trombe wall. Conventional Trombe wall channel heats the building external wall and creates a convective flow in-between a transparent glass layer and the heated wall. This hot flow is used either as a warm inlet air to the building in winter or help inducing airflow from inside the building for ventilation in summer. However, in the present work, the solar chimney induced airflow is purely external to the building.The proposed external solar shield starts with a glass layer from outside followed by an opaque porous metallic layer followed by an air channel before the building outer walls. The absorbing porous layer would get heated up quickly and transfer its heat to the air in the gap effectively due to its large surface area. The porous layer thickness is optimized at 15cm while the air gap is optimized at 0.3m. Numerical simulations based on finite volume analysis using ANSYS Fluent were carried out for a wall of 3m height. Comparisons of the performance of buildings with its outer walls shielded by white painted, black painted and glazed walls are presented and discussed with respect to that of buildings with bared outer walls as a control.Putting glazing alone after an air gap, expectedly, increases the heat gained by 47–56% compared to 0.7 emissivity simple bared wall. Single black and white solar shielding walls reduce the heat gain by 30 and 67%, respectively. However, the proposed design of a solar chimney with a glass outer wall followed by a porous foam metal layer on its inner surface, reduced thermal gain by 67–79%. This results in electrical cooling load reduction by about 28%. Furthermore, the heated airflow induced by a solar chimney formed with a 20×3m south wall can be utilized to induce water evaporation of 625–1046kg/day allowing active evaporative cooling and/or water desalination under solar irradiation condition of Dhahran, Saudi Arabia

Thermal performance of nanofluids in metal foam tube: Thermal dispersion model incorporating heterogeneous distribution of nanoparticles

This study presents the application of a modified single-phase method by thermal dispersion model incorporating heterogeneous distribution of nanoparticle concentration for evaluating thermal performance of a nanofluid in a circular porous metal foam tube. Numerical approach was conducted for Re=200–1000, mean concentration of 0.5–2%, and metal foam porosity of 0.7–0.9. It is observed that the predicted data by application of the thermal dispersion approach are in satisfactory agreement with those obtained experimentally, whereas applying the general homogeneous model results in an underestimation. The results reveal that the heterogeneity of the concentration distribution is directly proportional to nanoparticle mean concentration, Reynolds number, and the metal foam porosity. The velocity and temperature profiles at a cross section have been found to be flatter in dispersion model compared to those obtained from the homogeneous model. Furthermore, it is achieved that the Nusselt number varies directly relative to mean concentration and Reynolds number, whereas it inversely alters relative to the porosity. This reduction is found to be more profound at lower porosities.

Analysis of particle-laden fluid flows, tortuosity and particle-fluid behaviour in metal foam heat exchangers

Tortuosity and porosity are critical parameters for characterizing fluid flow in porous media. These parameters are of paramount importance in the design of porous compact heat exchangers, packed bed reactors, and catalysis supports; however, in the context of heat exchangers, these parameters are generally formulated for single-phase fluid flow under steady-state conditions. However, most industrial flows in a porous medium such as metal foams comprise of transient particle-laden fluid flow. A coupled finite volume and discrete element method (FVM-DEM) is developed to examine transient particle-laden Stokesian flow, particulate fouling (deposition), and fluid flow patterns in an idealized porous metal foam. This work presents a comparative analysis of the analytical and numerical pressure drop profiles. The solid-gas suspension in a porous media is discussed. Secondly, a new time-dependent pore-level fluid tortuosity relation is established which is linked with a modified porosity-based Darcy-Forchheimer equation. Fluid disturbance attributable to the inception of particle deposition is quantified by the tortuosity and instantaneous shift in streamline angle ratio. It is shown that the streamline angle ratio and the meandering of fluid flow paths vary with changing porosity and tortuosity. Moreover, the Reynolds number and particle density play a critical role in the alteration of the resistance to fluid flow and permeability which is related to the tortuosity and variation in fluid flow behaviour. The results and numerical method serves as a steppingstone to better optimize various heat exchangers while taking into account complex multiphase flow behaviour and the tortuous flow paths of porous structures.

A coupled finite volume & discrete element method to examine particulate foulant transport in metal foam heat exchangers

The exorbitant costs associated with particulate fouling necessitates the need to formulate advanced methods to comprehend mass transport and fouling in heat exchangers. A coupled finite volume and discrete element method is developed to investigate the mechanisms that govern particle-laden gas flows and particulate fouling in idealized porous metal foam heat exchangers. This meticulous examination will take great precedence in addressing the negative impact particulate fouling has in the industry. The numerical method will permit engineers to better optimize porous metal foams for applications such as air-cooled heat aluminium heat exchangers. The robustness of this numerical method is validated against the original and modified Darcy-Forchheimer analytical equations through a novel modified porosity theory. Good agreement is obtained between the numerical and analytical results. It is shown that both 2D and 3D heat exchanger configurations of identical porosities with different geometric profiles have shown similar deposition fraction and pressure drop magnitudes albeit having a slightly different fouling layer distribution. This is attributable to the particle properties and the variation between the 2D and 3D inlet injection plane surface area. It is found that the commencement of sandstone and sawdust deposition in a 6-pore configuration differs by 0.57s, whereas a three pore configuration completely nullifies particulate fouling irrespective of foulant type. A staggered row configuration has shown significant reduction in pressure drop as compared to the 6-pore heat exchanger configuration. For the case of sandstone particles, the optimum heat exchanger geometry exhibits 78% less pressure drop and 100% less deposition fraction compared with the original 6-pore configuration.

Experimental study on the influence of porous foam metal filled in the core flow region on the performance of thermoelectric generators

Semiconductor thermoelectric generator technology is a new type of power generation technology. The use of semiconductor thermoelectric power generation technology for automobile exhaust heat recovery and utilization can effectively improve energy efficiency. In this study, a test system is set up to simulate the automobile exhaust, and the effect of core flow heat-transfer enhancement on the performance of the thermoelectric generator is investigated using thermoelectric module Bi2Te3 to recover the waste heat from automobile exhaust and convert it into electrical energy. The results show that filling foam metal can significantly improve the performance of the generator. The convective heat-transfer coefficient of the channel increases by four times, and the output power of the thermoelectric generator is doubled when the intake flow rate is 120m3/h, the inlet temperature is 300°C, the pore density of the foam metal is 20 pores per inch, and the filling rate of the foam metal is 75%. In addition, the improvement in the performance of the generator is different under different intake air flows, different foam-metal filling rates, and different pore densities.

Free convection of hybrid Al2O3-Cu water nanofluid in a differentially heated porous cavity

Hybrid nanofluids are a new type of enhanced working fluids, engineered with enhanced thermo-physical properties. The hybrid nanofluids profit from the thermo-physical properties of more than one type of nanoparticles. The present study aims to address the free convective heat transfer of the Al2O3-Cu water hybrid nanofluid in a cavity filled with a porous medium. Two types of important porous media, glass ball and aluminum metal foam, are considered for the porous matrix. The experimental data show dramatic enhancement in the thermal conductivity and dynamic viscosity of the synthesized hybrid nanofluids, and hence, these thermophysical properties could not be modeled using available models of nanofluids. Thus, the actual available experimental data for the thermal conductivity and the dynamic viscosity of hybrid nanofluids are directly utilized in the present theoretical study. Various comparison with results published previously in the literature are performed and the results are found to be in excellent agreement. In most cases, the average Nusselt number Nul is decreasing function of the volume fraction of nanoparticles. The results show the reduction of heat transfer using nanoparticles in porous media. The observed reduction of the heat transfer rate is much higher for hybrid nanofluid compared to the single nanofluid.

Experimental investigation on PEM fuel cell cold start behavior containing porous metal foam as cathode flow distributor

Metal foam has been regarded as one of the most important replacement for the conventional flow distributor of commercial fuel cells in recent years. One critical issue for the commercialization of proton exchange membrane (PEM) fuel cell is the successful startup from subzero temperatures. In this study, experimental tests on a PEM fuel cell using nickel metal foam as the cathode flow distributor are carried out to investigate the cold start performance. The cold start performance is also compared to a PEM fuel cell with parallel flow channels. Both galvanostatic and potentiostatic control are considered. The results show that under normal operating conditions the metal foam PEM fuel cell exhibits higher maximum net power density than the cell with parallel flow channels, whereas the parallel channel case exhibits slightly better performance at lower current densities. For cold start tests, metal foam is superior to the conventional parallel flow channel under galvanostatic control, due to its extremely porous structure, uniform mass and heat distribution. It is more difficult for PEM fuel cell under potentiostatic control to successfully start up due to possible ice blockage at the outlet.

Melting behaviors of PCM in porous metal foam characterized by fractal geometry

The fractal Brownian motion is introduced to describe the pore distribution of porous metal foam. By the fractal description, a model of melting heat transfer for the phase change material (PCM) is developed and applied to investigate the melting behaviors in porous metal foam with a particular focus on the role of pore distribution. The dynamic response of temperature and the evolution of melting front are presented. The effects of porosity and fractal dimension on the melting heat transfer are all examined and investigated. In addition, an experiment of melting heat transfer is performed to verify the present model. The results indicate that the porous metal foam is of significance for the enhancement of melting heat transfer. When compared with PCM alone, the melting process in porous metal foam possesses the larger melting rate, the faster evolution of melting front and the higher liquid fraction. Unlike the PCM alone, the melting front is no longer continuous and many independent solid-liquid interfaces are formed inside pores owing to the interstitial heat transfer. Interestingly, the melting phase change is also affected by the fractal dimension even though the porosity is identical. A porous metal foam with smaller fractal dimension is beneficial for the melting heat transfer.

Cumulative effects of using pin fin heat sink and porous metal foam on thermal management of lithium-ion batteries

Three-dimensional transient thermal analysis of an air-cooled module was carried out to investigate cumulative effects of using pin fin heat sink and porous metal foam on thermal management of a Li-ion (lithium-ion) battery pack. Five different cases were designed as Case 1: flow channel without any pin fin or porous metal foam insertion, Case 2: flow channel with aluminum pin fins, Case 3: flow channel with porous aluminum foam pin fins, Case 4: fully inserted flow channel with porous aluminum foam, and Case 5: fully inserted flow channel with porous aluminum foam and aluminum pin fins. The effects of porous aluminum insertions, pin fin types, air flow inlet temperature, and air flow inlet velocity on the temperature uniformity and maximum temperature inside the battery pack were systematically investigated. The results showed that using pin fin heat sink (Case 2) is appropriate only for low air flow velocities. In addition, the use of porous aluminum pin fins or embedding porous aluminum foam inside the air flow channel (Cases 3 and 4) are not beneficial for thermal management improvement. The combination of aluminum pin fins and porous aluminum foam insertion inside the air flow channel (Case 5) is a proper option that improves both temperature reduction and temperature uniformity inside the battery cell.

The Experimental Study of Convection Heat Transfer Characteristics and Pressure Drop of Magnetite Nanofluid in a Porous Metal Foam Tube

In the present study, the laminar forced convection heat transfer improvement and pressure loss of magnetite $$\hbox {Fe}_{3}\hbox {O}_{4}$$ /water nanofluid flowing through a porous metal foam tube have been studied experimentally. To reach this goal, the magnetite $$\hbox {Fe}_{3}\hbox {O}_{4}$$ nanoparticles with 30 nm diameter are synthesized. The investigation of the effect of nanoparticle weight fraction and Reynolds number on the convection heat transfer and pressure drop characteristics are two objectives of this work. The experimental observations reveal that the increment of nanoparticle weight fraction and Reynolds number improves the Nusselt number. Furthermore, the Nusselt number enhancement is more pronounced for the high Reynolds numbers due to the addition of nanoparticles. By dispersing 1% weight fraction of magnetite nanoparticles inside DI-water, 7.4 and 11.7% heat transfer enhancements are achieved at $$Re = 200$$ and 1000, respectively. A slight increase in magnetite $$\hbox {Fe}_{3}\hbox {O}_{4}$$ nanofluid pressure drop is observed rather than that of DI-water due to the increment of nanofluid viscosity by nanoparticle dispersion inside the water. A performance index is proposed to consider the effects of Nusselt number enhancement and pressure drop simultaneously. It is shown that the performance index is higher than unity at all conditions in this study. Therefore, the convection heat transfer improvement dominates the pressure loss. A novel correlation is derived and presented based on the experiments to predict the Nusselt number.

Investigating the convection heat transfer of Fe3O4 nanofluid in a porous metal foam tube under constant magnetic field

An experimental study is conducted to investigate the convection heat transfer of Fe3O4/water nanofluid through a porous metal foam tube with uniform heat flux under the influence of constant magnetic field. This magnetic field is generated by four identical electromagnets. The electromagnets sequence is one of the most important parameters that has considerable effect on the convection heat transfer in this subject. Therefore, four different configurations of electromagnets are considered and the efficient arrangement is obtained by a numerical simulation using single-phase method in order to reach the higher heat transfer rate. Furthermore, the effects of Reynolds number, nanofluid weight fraction and magnetic field intensity on the forced convection heat transfer in the porous metal foam tube are examined under presence and absence of constant magnetic field. The experimental results show that the application of Fe3O4/water nanofluid enhances the convection heat transfer compared to DI-water. Additionally, implement of constant magnetic field leads to improve the convection heat transfer of nanofluid through the porous metal foam tube. This heat transfer improvement is more intensified in the lower fluid velocities as well as higher nanoparticle weight fractions. The maximum of 23.4% heat transfer enhancement is obtained by dispersion of 2% weight fraction of nanofluid inside the DI-water at Re=200 under applied magnetic field of 200G (0.02 T) intensity. A new correlation has been proposed for the Nusselt number of Fe3O4/water nanofluid in terms of Reynolds number, Prandtl number, nanoparticle weight fraction and magnetic field intensity which predicts the experimental data accurately.

Highly Efficient Hydrogen Evolution from Edge-Oriented WS2(1-x)Se2x Particles on Three-Dimensional Porous NiSe2 Foam.

The large consumption of natural fossil fuels and accompanying environmental problems are driving the exploration of cost-effective and robust catalysts for hydrogen evolution reaction (HER) in water splitting. Tungsten dichalcogenides (WS2, WSe2, etc.) are promising candidates for such purpose, but their HER performances are inherently limited by the sparse catalytic edge sites and poor electrical conductivity. Here we demonstrate a highly active and stable HER catalyst by integrating ternary tungsten sulfoselenide WS2(1-x)Se2x particles with a 3D porous metallic NiSe2 foam, in which good electrical conductivity, good contact, large surface area, and high-density active edge sites are simultaneously obtained, thus contributing to outstanding catalytic performance: large cathode current density (-10 mA/cm2 at -88 mV), low Tafel slope (46.7 mV/dec), large exchange current density (214.7 μA/cm2), and good stability, which is better than most reports on WS2 and NiSe2 catalysts. This work paves an interesting route for boosting HER efficiency of transition metal dichalcogenide catalysts.

Enhancement of phase-change evaporators with zeotropic refrigerant mixture using metal foams

Almost all thermal systems use some kind of heat exchanger. In many cases, evaporators are needed for systems such as organic Rankine cycle (ORC) systems. Evaporators contribute to a big portion of the capital cost, and their price is directly related to their size or transfer area. Highly porous open-cell metal foams are being considered to improve performance while keeping the size of heat exchangers small. This study experimentally investigates the degradation of the heat transfer coefficient of zeotropic mixtures during phase change in a plate heat exchanger with metal-foam-filled channels. The working fluids were pure R245fa and a zeotropic mixture of R245fa/R134a (0.6/0.4 molar ratio). The results show that the metal foams significantly increase the recovered heat, overall heat transfer coefficient, and effectiveness of the heat exchanger for mass flux ranging from 90 to 290kg/m2s, but at the expense of increasing the pressure drop. The same improvement was observed for the mixture of refrigerants. The degraded heat transfer coefficient of the mixture compared to the pure refrigerants was recovered by the introduction of metal foams to the system. New correlations are proposed to predict the two-phase heat transfer coefficient of both pure R245fa and the refrigerant mixture in metal foam evaporators.

The role of porous metal foam on the unidirectional solidification of saturating fluid for cold storage

We conducted analytical, numerical and experimental investigations on solidification of fluid saturated in highly porous metal foams with open cells. Based on pore-scale thermal equilibrium assumption, an analytical extension of the classical Neumann’s solution was made to predict phase change heat transfer in PCM-foam composites. To explore the heat transfer mechanisms underlying the phase change process and clarify the role of foam insertion, three-dimensional direct numerical simulations on periodically distributed tetrakaidecahedron cells were carried out. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. The phase interface was macroscopically flat via experimental visualization but microscopically irregular via pore-scale simulations. Temperature difference between the saturating PCM and metallic ligaments was negligible, so that local thermal equilibrium and one-equation model were applicable especially at low Ste numbers (e.g., 0.22). The present findings provide new insights to cold energy storage design, utilization and economic analysis in HVAC systems.

Thermal Analysis of Cold Storage: The Role of Porous Metal Foam

We conduct both analytical and numerical investigations on the solidification behavior of fluid saturated in highly porous open-cell metallic foams. Based on the pore-scaled thermal equilibrium assumption, an analytical extension is made to the classical Neumann's solution to solidifying fluid as an interstitial into metallic foams. To underlying the heat transfer mechanisms for phase change process and the role of inserted foam, an idealized tetrakaidecahedron unit cell geometric model was reconstructed and direct numerical simulations were conducted. Showing good agreement with experimental results and direct numerical simulations, the developed model is verified, favoring the assumption of local thermal equilibrium. The numerical simulation results at pore scale qualitatively demonstrate that: i) the solidification interface is globally flat within a pore; ii) the local natural convection does exist and it contributes to the evolution of solidification interface (9% promotion).

Thin-Shell Model for Effective Thermal and Electrical Conductivity of Highly Porous Closed-Cell Metal Foams

In this paper, a unit-cell model for determination of the effective thermal and electrical conductivity, respectively, of highly porous, closed-cell metal foams is presented. Hereby, (i) a large contrast between the transport properties of the conducting, solid material phase and the pore space is assumed, and (ii) thin, interconnected spherical shells of the solid material phase in a simple cubic arrangement are considered as a geometrical model. The unit-cell model prediction is compared to (i) literature data and (ii) well-established homogenization schemes from the effective medium theory.

Quantitative x-ray Analysis: Applications in Machining of Porous Metallic Foams

In the present study, surface integrity in the face milling of open-cell aluminum metal foams was studied at full-volume using micro-computed tomography. Morphological damage to the pore-strut network of the foam was characterized as a function of machining parameters. Post-mortem surface integrity characteristics including effective pore size, foam porosity, and depth of the deformation-affected zone were characterized using the voxel-based data. The machined surface exhibits spatially-graded characteristics, featuring distinct regions of foam-strut bending/buckling and fracture. Implications of these observations for understanding effects on performance relative to structural bio-medical applications and integrity optimization strategies are described.

Rheological Study of a Copper Feedstock

MIM technique is described in which allows for the production of highly porous metallic foams with porosity levels up to 90%. It makes use of the pressure built up by the decomposition of a foaming agent which is incorporated in a foamable precursor copper material obtained by powder compaction. A suitable behaviors feedstock that refers to its rheological is one of the key factors to ensure the successful of MIM technique and to predict failure, whether due to the binder component and compositions, powder loading or unsuitable process parameters. Potassium carbonate and polyethylene is added and were mixed homogeneously to form a copper feedstock. The rheological results in term of shear rate, shear stress, viscosity, melting rate and softening temperature which related to pseduoplastic behaviors have been conducted using a capillary rheometer (CFT-500D, Shimadzu) at various temperature and loads. The result has indicated that the viscosity of the feedstock is decreased with increasing shear rate thus proved the feedstock to be pseudoplastic.