Porosity Metal Foam Research Articles

Production of Open-Cell Metal Foams by Recycling of Aluminum Alloy Chips.

In this paper, an innovative sustainable method of producing metal foams was presented. The base material was aluminum alloy waste in the form of chips obtained by machining process. The leachable agent, used to create pores in the metal foams, was natrium chloride, which was later removed by leaching, resulting in metal foams with open cells. Open-cell metal foams were produced with three different input parameters: volume percentage of natrium chloride, compaction temperature, and force. The obtained samples were subjected to compression tests during which displacements and compression forces were measured to obtain the necessary data for further analysis. To determine the influence of the input factors on the selected response values such as relative density, stress and energy absorption at 50% deformation, an analysis of variance was performed. As expected, the volume percentage of natrium chloride was shown to be the most influential input factor because it has a direct impact on the obtained metal foam porosity and thus on the density. The optimal values of the input parameters with which the metal foams will have the "most desirable" performances are a 61.44% volume percentage of natrium chloride, a compaction temperature of 300 °C and a compaction force of 495 kN.

Performance Evaluation Based on Exergy Analysis Through Partially Filled Metal Foams in Forced Convection

Abstract The intention of this paper is to present the numerical analysis of thermal performance and exergy transfer through high porosity metal foams filled partially in a horizontal pipe. The heater is embedded in the pipe's circumference and is assigned with known heat input. To enhance heat transfer, aluminum metal foam of pore density 10 with porosity 0.95 is inserted adjacent to the pipe's inner wall. To determine the optimal thickness of metal foam for enhancing its performance thermodynamically, metal foams with five different thicknesses (10, 20, 40, 60, and 80 mm) are examined in this research for a fluid velocity ranging from 0.7 to 7 m/s under forced convection heat transfer condition. The Darcy– Brinkman–Forchheimer and local thermal nonequilibrium (LTNE) models are used for forecasting the flow features and heat transfer through the metal foams, respectively. The numerical methodology implemented in this research is confirmed by comparing the present outcomes with the experimental outcomes accessible in the literature and found a fairly good agreement between them. The thermal performance is assessed in terms of heat transfer enhancement ratio and performance factor, and the thermodynamic performance is evaluated based on exergy analysis. In the exergy analysis, the parameters like mean exergy-based Nusselt number (Nue), merit function (MF), and nondimensional exergy destruction (I*) are considered for the evaluation. The result shows a better performance from partially filled metal foams than from completely filled metal foams.

Numerical study of a hybrid thermal lattice Boltzmann method for pool boiling heat transfer on a modeled hydrophilic metal foam surface

In this paper, a numerical study is conducted to investigate pool boiling heat transfer on a modeled hydrophilic metal foam surface. A pseudopotential multiple-relaxation-time (MRT) lattice Boltzmann (LB) method is employed to solve the flow field, and a finite-difference (FD) scheme is applied to solve phase change. Thermodynamic nonuniformity is largely avoided by adjusting the forcing term’s corresponding parameters. The metal foam structure is simplified as a staggered square array. Both the bottom wall and solid squares are set as constant temperature boundary. Three kinds of boiling stages on smooth and metal foam surfaces are observed at different wall superheats. The effect of the metal foam porosity and pore size on pool boiling heat transfer is studied. Then boiling curves are obtained to analyze heat transfer performance and bubble behavior under several wall superheats. Finally, numerical simulations of pool boiling under microgravity conditions were performed. The bubble behavior shows great agreement with that of related experimental results, with qualitative proof of the correctness of the model.

Experimental investigation of thermal performance of single pass solar collector using high porosity metal foams

The previous literature showed that there have been many studies focusing on some specific aspects of single-pass solar air collectors, such as the effects of the number of passes, the shape of fins, and their effects on thermal performance. Also, the effect of thermal efficiency accompanied by the existence of these fins has been the interest of many studies. A few research types are dealing with using porous materials (Metal foam) to improve thermal performance. Therefore, an experimental apparatus was designed and fabricated to study the effect of Metal Foam (MF) on the performance of solar air collectors. The experiments were held in Iraq, Al Ramadi climate conditions. A comparison of three configurations of absorber plates of solar air heaters with and without MF is presented and evaluated. The results showed that by including MF fins in the absorber plate, the absorber plate's surface area was increased, increasing heat transmission compared to a flat plate (without MF). Moreover, utilizing MF at the tilted angle of 45° (MFθ=45o) increased turbulence intensity, which improved the mixing of cold and hot air. The MFθ=45o layout had the best thermal efficiency of the three employed configurations (94.8%), followed by the MFθ=0o configuration (62.6%) and the flat plate configuration (33.8%), all with the same mass flow rate. Finally, when using MF fins with a tilted angle of 45°, the air temperature differential is bigger compared to MF fins with a tilted angle of 0° or a flat plate collector.

Investigation of optimization methods for metal foam with two-dimensional porosity gradient in shell-and-tube latent heat storage

The latent heat thermal energy storage (LTES) strengthened by metal foam can promote the development of renewable energy and waste heat recovery. In this study, superposition method and 2D iterative method are established to optimize the 2D porosity gradient of metal foam, which is infiltrated in phase change material (PCM) for heat transfer enhancement in LTES with shell-and-tube configuration. The optimization process in these new methods takes the interaction between horizontal and vertical porosity gradient into account and the evolution of two-dimensional metal foam porosity is numerically investigated. Melting behaviors of optimal cases with different methods are compared and analyzed. The numerical results demonstrated that the optimal case obtained by 2D iterative method has best heat transfer performance. Compared with the uniform distribution, a 11.32 % reduction in full melting time can be achieved by the 2D iterative optimal case due to its better temperature uniformity and stronger natural convection.

Determination of porosity and microstructure studies of wax-based Aluminium metal foam

Aluminium metal foams nowadays are popularly used because of their unique feature of high stiffness concerning low density in the order of 10-15% of the bulk Aluminium material. In this paper, Aluminium metal foam is developed using the powder metallurgy technique. The elements used in the composition are Aluminium metal powder and a foaming agent as a wax powder (3-9%). The porosity is calculated using the Archimedes principle and achieved a good percentage of porosity in the specimen with a blowing agent as wax powder and achieved maximum porosity of 60.41%. The Microstructure study has been done on the prepared specimens to check the uniform distribution of porosity on the entire specimen and to check if any foreign chemical factor is incorporated. It is found that there is no adequate result in the prepared specimen.

Numerical investigation and optimization of melting performance for thermal energy storage system partially filled with metal foam layer: New design configurations

Low thermal performance of storage systems represents a barrier to their industrial/engineering application and commercialization. Among all the proposed methods, combination of phase change material with metal foams appears more promising due to the high thermal conductivity of metal foams. However, the insertion of metal foams reduces the PCM volume; hence, a lower amount of stored energy. The present numerical study thoroughly addresses this issue with a focus on the optimization of melting performance for thermal energy storage system partially filled with metal foam layer. A finite volume method based on the enthalpy–porosity technique has been adopted for the numerical simulations. The metal foam location, porosity, and nanoparticle volume fraction were optimized to explore their effects on the melting performance. The results showed that inserting the foam layer diagonally from the top left to the right bottom leads to the lowest melting time. Compared to pure PCM, the melting time increases by 77.7%, while the stored energy decreases by 6.7%. The optimum porosity was found to be 0.88 as it gives approximately the same amount of stored energy as that of pure PCM with a deviation of 4%. Adding nanoparticles to pure PCM increases the melting rate by approximately 8%, while it decreases the stored energy by almost 3%. It is concluded that hybrid systems, i.e., metal foam at an optimum porosity and nanoparticles is more efficient than using each technique separately.

Experimental and numerical study of zero-gravity distillation units with infinite and finite reflux

Zero-gravity distillation (ZGD) is a small-scale distillation process, which offers high separation efficiencies and can be used as a part of modular production plants. Instead of gravity, capillary forces are utilized to realise the fluid flow. In this study, two experimental ZGD setups with different dimensions and materials were built. Furthermore, a modified ZGD unit with dual side heating and cooling was developed. Experiments were carried out with ethanol/water mixtures, both in the infinite reflux mode and with feed and product streams, while the temperature and concentration profiles were recorded under varied feed concentrations and volumetric flow rates. The experimental data was used to validate the process model comprising coupled momentum, heat and mass transfer equations for the liquid and vapour phases as well as heat conduction equations for the unit walls. The fluid dynamics was described using the hydrodynamic analogy concept. A good agreement between simulated and measured ethanol concentrations and temperatures was found. With the validated model, sensitivity studies on the influence of the feed flow rate and the metal foam porosity on the ZGD process were performed. It was found that the separation efficiency decreases with increasing flow rate and increases with lower porosity.

Performance prediction of a fin–metal foam–cold thermal energy storage device: Solidification

Latent heat storage technology is a valuable research direction to alleviate the imbalance of energy supply and demand, but its application is limited by the low thermal conductivity of phase change material. In recent years, the fin–foam structure is proven to alleviate this problem. The solidification behavior of the phase change material in this structure should be predicted to promote its engineering application. In this study, a cold thermal energy storage unit with metal foam and straight fins was constructed. On the basis of dimensionless analysis, experimental and numerical methods were used to investigate the structural parameters of straight fin and metal foam on the liquid fraction and effective Nusselt number (Nu*). Results showed that the height and spacing of fin are the main factors affecting the solidification rate of phase change material, compared with the porosity, pore density and material of metal foam. When fin height increases from 17 to 57 mm and spacing reduces from 120 to 3 mm, the Nu* of the phase change material increases by 1.5 and 12.61 times, respectively. The transient correlation between liquid fraction and Nu* of phase change materials is obtained to guide related design.

Effect of metal foam thickness on the conduction and convection heat transfer for a flat plate with metal foam impinged by multiple jets

ABSTRACT The influence of metal foam thickness on the convection and conduction heat transfer is studied by measuring the local heat transfer of a smooth flat plate, attached and detached metal foamed flat plate under multiple jet impingement conditions. 27 jets of 3 mm diameter are introduced from a jet plate. These jets impinge on a thin stainless steel foil that serves as a targeted plate. The pitch of the jets is 4d in both the spanwise and streamwise directions. The spent fluid is exiting in all directions. The influence of metal foam thickness is investigated for an open-cell aluminum foam with 4, 8, and 12 mm thickness. The porosity of aluminum metal foam is 0.92. The pore density (pores per inch) is 20 PPI. The local heat transfer is measured using infrared thermography and a thin metal foil technique. A smooth flat plate impinged by multiple jets serves as a reference case. The evaluation of the convection and conduction heat transfer offered by the metal foamed flat plate is obtained with the help of the detached foam configuration. The jet diameter-based Reynolds number ranges from 2500 to 15000. The range of the jet to plate spacing covered is 3d to 6d. Depending on the metal foam thickness, the metal foamed flat plate offers additional hydraulic resistance to the jet flow and conduction effect. The additional hydraulic resistance attenuates the convective heat transfer and is represented by attenuation factor (α). For metal foam having 4, 8, and 12 mm thickness, the attenuation factor is around 1.11, 0.99, and 0.64, respectively. The conduction effect offered by metal foam is responsible for the enhancement of the heat transfer. The conduction effect is represented as an enhancement factor (E). For metal foam having 4, 8, and 12 mm thickness, the enhancement factor is around 1.51, 1.58, and 2.32, respectively. The conduction effect presented in the metal foamed flat plate dominates over the attenuation in the convective heat transfer. The overall enhancement offered by 4, 8, and 12 mm metal foamed flat plate is around 1.67, 1.56, and 1.48, respectively.

Comparison on the heat transfer performance and entropy analysis on miniature loop thermosyphon with screen mesh wick and metal foam

Comparison on the heat transfer performance (HTP) of copper screen mesh wick and metal foam inserted evaporator section of miniature loop thermosyphon is experimentally investigated. Porosity of both screen mesh wick and metal foams are fixed to be 63%. Experiments are conducted using DI water under vertical orientation for different heat loads (40 W–280 W) and filling ratios (FR = 20%, 30% and 40%). Results showed a decrease of 12.8% and 5.2% in thermal resistance and wall temperature respectively for the metal foam inserted evaporator. In addition 10.6% enhancement is noted for heat transfer coefficient at the evaporator region for 30% FR. Reduction of 4.6% in heat transfer irreversibility is also noted for metal foam inserted thermosyphon compared to screen mesh wick condition. Increase in interstitial heat transfer between the fibers of metal foam and larger pore size of metal foams resulted in higher permeability compared to screen mesh wick are responsible for the enhancement in the overall HTP of metal foam inserted thermosyphon. Based on the observed results, the use of metal foams inserted thermosyphon will be a better substitute for thermal management applications of electronic devices.

Natural convection melting of phase change material in corrugated porous cavities

In this paper, a numerical study is carried out to examine the melting inside a wavy cavity under partial heating. A wide range of numerical computations have been performed to understand the effect of porosity, pore density, wall waviness, and heater location and intensity on the melting process. The results revealed that lower metal foam porosity resulted in higher melting rate and lower thermal storage capacity. However, pore density indicated no effect on melting performance for porosity in the range 80–96 %. When considering heater location at various porosities, its impact on melting performance is small at low porosity but becomes significant at higher porosity. Top–bottom partial heating can save almost 10 % of the melting time at ɛ = 0.96. Moreover, the PCM can store more energy, i. e. 11.36 %, when the heater location was changed from center or top–bottom position to top or bottom position at ɛ = 0.96. The results further showed that increasing the number of undulations can save 27.4 % of the melting time at ε = 0.96. Therefore, it can be concluded that higher energy storage and melting rate can be achieved by increasing the number of undulations.

Multi-variable optimization of metal hydride hydrogen storage reactor with gradient porosity metal foam and evaluation of comprehensive performance

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

Inverse estimation of heat flux under forced convection conjugate heat transfer in a vertical channel fully filled with metal foam

In this work, for the first time, a heat flux at the boundary is estimated for a conjugate heat transfer under forced convection in the presence of high porosity metal foams. For the forward problem a vertical channel experimental set up reported in the literature is considered. The metal foam placed in the vertical channel is subjected to constant heat flux through aluminum plate and airflow of various velocities is passed through vertical channel for removal of heat from the high porosity metal foam placed in the vertical channel. Six different velocities are considered and the required temperature distribution of the aluminum plate is obtained by solving Darcy extended Forchheimer and Local Thermal non-equilibrium models for metal foams. The forward problem, created using computational fluid dynamics in ANSYS-FLUENT, is substituted with Neural Network for faster computation of the forward problem. The maximum errors between the computational fluid dynamics and Artificial Neural Network models for the heat flux values of 466.66, 666.66 and 1133.3 W/m 2 are found to be 0.086, 0.043, 0.092 respectively. The heat flux to the forward problem is treated as unknown and the same is estimated using an inverse method that couples Particle Swarm Optimization with Bayesian framework. The result of inverse estimation of exact temperature data shows that for a heat flux of 1266.64 W/m 2 the error is found to be 1.6e−4%. Similarly, for the noise added temperature data, the absolute % error in heat flux of 599.985, 733.315 and 1266.635 W/m 2 is 4.80e−2%, 2.20e−2%, 2.30e−2% respectively. • Inverse estimation of boundary heat flux using particle swarm optimization method. • Forward problem is a conjugate heat transfer problem in a vertical channel. • Darcy–Forchheimer, Local Thermal Non-equilibrium models for modelling porous medium. • Different Artificial Neural Network models to facilitate faster computations. • Particle Swarm Optimization combined Bayesian framework to quantify modeling error.

Effect of metal foam on improving solid–liquid phase change in a multi-channel thermal storage tank

Latent heat thermal storage (LHTS) system is a vital way to recover waste heat for energy saving. However, phase change materials (PCMs) with low thermal conductivity severely limit the energy storage efficiency. A novel LHTS tank with multi-channels filled with metal foams is designed to improve the overall heat storage efficiency. Further, a three-dimensional phase transition model is developed, with particular concerns paid on the filling pattern of metal foam in HTF, PCM, and both. The numerical model can better reveal the synergistically enhanced heat transfer and conduction mechanism of heat transfer fluid (HTF) and PCM with metal foam. The numerical model is verified with the existing experimental data, and a satisfactory agreement is obtained. Four filling methods are designed, in which the porosity and pore density of metal foam is 0.93 and 15 pore per inch, respectively. Compared with the non porous tank, the phase transition time can be reduced by 23.7% for PCM filled with metal foam; while filling HTF with metal foam reduces the melting time by 58.3%. The synergized effect of filling both reduces melting time by 77.6%. The heat flow into PCM is increased when metal foam is in HTF. Further, when metal foam is in PCM, the temperature uniformity of PCM is augmented and its phase transition isothermal duration is prolonged. The assessment options can provide scientific design guidance for improving the thermal storage efficiency of LHTS tank.

Numerical investigation on melting behaviour of phase change materials/metal foam composites under hypergravity conditions

The integration of electronic devices in aerospace vehicles leads to a significant increase in the heat dissipation, which makes thermal management a severe challenge. Due to the high thermal energy storage capacity and the excellent thermal diffusivity, phase change materials (PCM)/metal foam composite is a potential thermal management material. In order to deepen the understanding of melting behaviour of PCM/metal foam under hypergravity, the numerical model considering natural convection, flow resistance of metal foam, and non-equilibrium heat transfer is proposed, and the effects of inclination angle, hypergravity value, metal foam porosity, and pore density on the melting are analyzed. It shows that the inclination angle has a great influence on the morphology of the melting interface, while has limited influence on the variation of PCM liquid fraction. As the inclination angle changes from 0° to 180°, the heated wall temperature first decreases, and then increases after reaching the lowest value at 45°, which is the optimal inclination angle. With the rise of hypergravity value, natural convection is enhanced, the heated wall temperature is reduced, while the hypergravity value has limited effect on the PCM liquid fraction. Furthermore, with the increase of metal foam porosity, natural convection is enhanced, while the heated wall temperature and the melting time become larger. When the porosity is larger than 0.95, the effect of metal foam on natural convection suppression is greater than that of heat conductivity enhancement, leading to that the performance of PCM/metal foam is worse than that of the pure PCM. Besides, with the decrease of pore density, natural convection is enhanced, the heated wall temperature becomes lower. Therefore, metal foam with lower pore density is preferred. This paper provides guidance to the optimal design of PCM-based heat sink for aerospace applications.

Analysis of the effects of porous media parameters and inclination angle on the thermal storage and efficiency improvement of a photovoltaic-phase change material system

The heat generation in the photovoltaic (PV) panels leads to the rise in temperature, which subsequently deteriorates the electrical efficiency of PV panels. The application of phase change materials (PCM) can reduce the operating temperature and perform as a cooling mechanism. However, the cooling performance and energy storage capacity of PCM are drastically affected by its poor thermal conductivity. Therefore, in this paper, the impact of the insertion of metal foam on the heat transfer through PCM and the electrical efficiency of PV-PCM systems has been numerically investigate. A comparative study on the impact of the porosity of metal foam ranging from 0.7 to 0.9 has been carried out. Furthermore, different inclination angles, 0° to 90°, have been considered to evaluate the impact of inclination angle on the natural convection enhancement through liquid PCM. Results indicated that increasing the inclination angle results in better natural convection of molten PCM and better heat transfer through PCM. Moreover, results represented that compared with the PV-PCM system, 6.8% and 9.8% enhancement in the average temperature and electrical efficiency, in the case of insertion of metal foam with porosity of 0.9, is achieved.

Parametric optimization of a cesaro fins employed latent heat storage system for melting performance enhancement

The large-scale use of sustainable energy necessitates the use of latent heat storage (LHS). This study aims to increase the melting performance of an LHS system by designing and optimizing the cesaro fins. To examine the melting behaviours of PCM (i.e., RT-82) in a finned LHS system, a 2-D melting heat transfer model is developed and numerically solved. As per literature, there is very literature including the NC (Natural Convection) and represents the coordination in fins, nanoparticles and metal foam. So, the impacts of natural convection, fin arrangement, nanoparticles and metal foam are explored for the Fourier number variations from 0.014 to 0.158 at a constant Stefan number of 0.20. The dynamic temperature distribution, as well as the natural convection and fin arrangement, are investigated to determine how phase change material melts over time by considering the non-thermal equilibrium between metal foam and PCM/nanoPCM. The findings illustrate that natural convection has a significant effect on melting behaviours in the LHTES (Latent Heat Thermal Energy Storage) system, with a 26.8% increase in melting/charging rate as compared to the situation without NC. The LHTES system with improved fin structure (i.e., Type-3) and increased number of fins (i.e., Type-5) configurations have more uniform temperature distribution and a higher melting rate by increasing the heat transfer cooperation between NC and thermal conduction. Low thermal conductivity causes poor performance in PCM (Phase Change Material) energy storage devices. The melting/charging of PCM in an LHTES system is greatly improved in this study by employing a porous metal foam (i.e., copper metal foam) or nanoparticle (i.e., Cu, CuO and Al2O3). The impact of nanoparticle volume fraction and metal foam porosity on the LHTES system's melting/charging performance is also investigated using the enthalpy-porosity technique. According to the results, PCM's melting/charging time is lowered by 63.4% when nanoparticles are mixed in and incorporated with metal foam for the Fourier number varies from 0.014 to 0.158 at a constant Stefan number of 0.20. PCM melting/charging time decreased when the metal foam porosity decreased or increased in the volume fraction of nanoparticles. High porosity metal foams with low volume fractions of nanoparticles can increase melting performance since it assures minimum PCM volume and increases natural convection.

Numerical investigation on non-Newtonian melting heat transfer of phase change material composited with nanoparticles and metal foam in an inner heated cubic cavity

In this paper, the non-Newtonian melting heat transfer of a latent heat thermal energy storage (LHTES) system composited with phase change material (PCM), nanoparticles and metal foam is numerically investigated inside an internal heated cubic cavity. The enthalpy-porosity method and power-law fluid model are adopted to model melting process for nano-enhanced PCM, and the Darcy-Forchheimer law and local thermal non-equilibrium model are assumed for metal foam. The effects of Rayleigh number (Ra), nanoparticle fraction (Φ), metal foam porosity (ε) and heater size on evolvement of solid-liquid interface, temperature of liquid PCM (θnf) and metal foam (θs), and full melting are addressed. The results reveal that with the increase of Ra, the convective heat transfer of PCM dominates the melting characteristic of the composite LHTES unit and accelerates the melting rate. With the increase in Φ, the non-Newtonian rheological behavior of liquid PCM is more pronounced with erratic convection flow due to increase of consistency parameter. Moreover, the convective heat transfer enhancement of θnf with addition of nanoparticles compensates for the conductive heat transfer enhancement of θs with increased ε. The internal heater size also plays an important role in the melting performance of composited PCM.

A new simple method to conveniently measure the open porosity of porous metal foams with reticular structure

Purpose The purpose of this paper is to introduce different methods for measuring the porosity of metal foams, and especially present a new method for conveniently measuring the open porosity that has a stronger impact on a number of physical properties of the porous product.Design/methodology/approach Metal foam is a kind of material that utilizes the function of pores inside the porous body. For such materials, the porosity is an important factor or even a key factor to determine a number of the practical parameters, such as the conductivity, acoustic properties and mechanical performances. Especially, the open porosity has a stronger impact on the sound absorption, electromagnetic shielding, heat transfer of the porous product, as well as the performances of using the internal pore surface. Therefore, it would be meaningful to find the simple and convenient to well measure the open porosity of metal foams.Findings In the present new method, the open porosity can be obtained directly by different volume parameters of the porous sample, while it can only by some weight indexes of the porous sample in other measuring methods.Originality/valueThe characteristic of this new method makes the measurement simpler and more convenient in this new method than in the other methods.