Porosity Metal Foam Research Articles

Influence of Pore Density and Porosity on the Melting Process of Bio-Based Nano-Phase Change Materials Inside Open-Cell Metal Foam

In this paper, experimental investigations were carried out to observe the melting process of a bio-based nano-phase change materials (PCM) inside open-cell metal foams. Copper oxide nanoparticles with five different weight fractions (i.e., 0.00%, 0.08%, 0.10%, 0.12%, and 0.30%) were dispersed into bio-based PCM (i.e., coconut oil) to synthesize nano-PCMs. Open-cell aluminum foams of different porosities (i.e., 0.96, 0.92, and 0.88) and pore densities (i.e., 5, 10, and 20 pores per inch (PPI)) were considered. An experimental setup was constructed to monitor the progression of the melting process and to measure transient temperatures variations at different selected locations. Average thermal energy storage rate (TESR) was calculated, alongside the melting time was recorded. The effects of various nanoparticles concentration, metal foam pore densities, porosities, and isothermal surface temperature on the melting time, TESR, thermal energy distribution, and the melting behavior were studied. It was observed that the melting time significantly reduced by using metal foam and increasing the isothermal surface temperature. It was concluded that the effect of adding nanoparticles on the TESR depends on the characteristics of metal foam, as well as, the weight fractions of nanoparticles. The change in TESR varied from −1% to 8.6% upon addition of 0.10 wt % nanoparticles compared to pure PCM, whereas the increase in the nanoparticles concentration from 0.10% to 0.30% changed TESR by −10.6% to 4.5%. The results provide an insight into the interdependencies of parameters such as pore density and porosity of metal foam and nanoparticles concentration on the melting process of nano-PCM in metal foam.

A hydrodynamic analogy based modelling approach for zero-gravity distillation with metal foams

Zero-gravity distillation (ZGD) is one of the few ways to establish a small-scale distillation process. In contrast to conventional distillation columns, capillary forces, e.g. induced by metal foams, are exploited to ensure liquid flow in ZGD units. In order to strengthen the knowledge basis necessary for the ZGD equipment design, understanding of the relevant transport phenomena is necessary. In this work, a model for the description of ZGD processes was developed. It includes momentum, heat and species transport in both liquid and vapour phases. Evaporation and condensation influence on momentum transfer is captured in a simplified manner, allowing an approximate local flow velocity determination. The developed model was implemented in the OpenFOAM® software and used to numerically simulate methanol/ethanol distillation processes in 2D approximation. In particular, the model was applied to investigate the influence of the metal foam porosity and thickness as well as the length of the foam-free compartment on the velocity, temperature and mass fraction distributions.

Numerical Simulations of Flow-Assisted Mixed Convection in a Vertical Channel Filled with High Porosity Metal Foams

In this work, two-dimensional numerical simulations of flow-assisted mixed convection in a vertical channel filled with high porosity metal foams have been carried out by using the commercial ANSYS FLUENT. In order to enhance heat transfer, the vertical channel is filled with aluminum metal foams of different pores per inch (PPI). Four different metal foams PPI 10, 20, 30, and 45, with porosity values varying from 0.90 to 0.95 are considered in this study. The geometry under consideration consists of metal foam attached to the aluminum plate in the vertical channel and the resulting problem becomes conjugate heat transfer. The metal foam region is considered as a homogeneous porous medium with the Darcy Extended Forchheirmer model to evaluate the flow characteristics while the local thermal non-equilibrium heat transfer model is considered for the heat transfer analysis. Initially, numerical results are compared with the experimental results available in literature and the agreement was found to be good. Parametric studies show that as the metal foam PPI increases, the pressure drop increases, while the heat transfer is seen to increase with an increase in the pore density of the metal foam.

Role of porous metal foam on the heat transfer enhancement for a thermal energy storage tube

Thermal energy storage technology has attracted extensive attentions due to its remarkable energy-saving benefits. However, the low thermal conductivity of phase change materials seriously limits the energy storage efficiency, which put forward more stringent requirements for heat transfer enhancement. In this study, a two-dimensional axisymmetric simulation model with natural convection was established for the shell-and-tube thermal energy storage unit. Open-cell metal foam with a porosity of 0.94 and pore density of 15 pore per inch was employed to be arranged in either heat transfer fluid or phase change materials domains. The effects of the metal foam location and the metal foam porosity on the heat storage performance were studied. The numerical method was verified by experimental measurement, achieving good agreement. Results demonstrated that metal foam can significantly enhance heat transfer due mainly to the reduction of thermal resistance in heat transfer fluid. The case that both domains for heat transfer fluid and phase change materials were embedded in porous media can provide the best heat transfer enhancement. Compared with smooth tube without metal foam, the full melting time for this case was reduced by 88.548%; meanwhile, temperature response rate, heat flux and j-factor was increased by 834.27%, 774.90%, 5186.91% respectively. Besides, embedding metal foam into phase change materials can improve the temperature uniformity of phase change materials.

Experimental evaluation of metal foam for sand control

Metal foam, a metal material with a porous structure, is applied as sand control screens. The porosity and pore size of metal foam can be varied to meet sand control requirements. Five types of metal foam screens are designed and tested to evaluate the sand control capability of metal foam. Based on the weakly consolidated reservoir conditions in Bohai Bay, the effects of metal foam screen structure and formation properties on sand control are investigated. The results show that sand control capability of metal foam screens is a function of their thickness and pore size. The anti-plugging ability of the screens is very sensitive to clay content. Using standard sands for sand control experiments, the nominal precision of different metal foam screens can be obtained. The experimental results in this paper provide preliminary but useful implications for design and field application of metal foam as sand control screens. The study also shows that metal foam screen has unique advantages in sand control capacity and ease of field implementation compared with conventional high-quality independent screen and gravel pack, implying it is a promising new solution for sand control.

Experimental investigation of heat transfer of flowing liquid film with inserted metal foam layer subjected to air jet impingement

In this paper, coupling the air jet impingement and the copper metal foam above flowing liquid film were employed to enhance the heat transfer. The thickness of flowing liquid film can be controlled owing to the application of the metal foam above the film, and its solid matrix extends the air-liquid-solid interface of heating surface. The evaporated water can be supplied by the capillary force in the porous layer. The experiments were conducted to investigate the performances of the flowing liquid film with inserted porous layer subjected to impinging jet air. The air jet velocity, the flow rate and thicknesses of the liquid film as well as the porosity of metal foam influence the surface temperature of heated wall and the corresponding local heat transfer coefficient greatly. The change ratios of heat transfer coefficient due to the above factors were presented. More cooling can be obtained on the heated wall in the flowing liquid film with inserted porous layer subjected to impinging jet air while the higher liquid film velocity and air jet velocity, the thinner liquid film and the lower porosity of metal foam occur.

The effect of metal foam fins on the thermo-hydraulic performance of a solar air heater

The metal foam porosity helps the air to penetrate through the fins and extracted more heat gain from the absorber plate. In this experimental study, the effect of metallic foam fins on the thermohydraulic efficiency is investigated through a test rig built for this purpose. Fins with different metal foam pore density (PPI), and three different configurations (longitudinal, corrugated, and staggered) are attached to the back surface of the absorber plate. The experiments are conducted under Baghdad climatic conditions for February, March and April 2018. The results showed that the presence of metal foam fins provided a large surface area for convective heat transfer so that, the air temperature difference and thermal efficiency of the solar collector are increased. The maximum temperature difference for corrugated, staggered, longitudinal metallic foam, and solid longitudinal fins at an air flow rate of 0.01 m 3 /s is 31, 27, 23, and 17 ℃, respectively. Metal foam fins with higher PPI exhibited higher air temperature difference due to higher heat transfer surface area. The highest value of the thermal and effectiveness ei¬ƒciencies for corrugated metal foam fins are 86 %, and 79 %, respectively.

Combining High Porosity with High Surface Area in Flexible Interconnected Nanowire Meshes for Hydrogen Generation and Beyond.

Nanostructured metals with large surface area have a great potential for multiple device applications. Although various metal architectures based on metal nanoligaments and nanowires are well known, they typically show a tradeoff between mechanical robustness, high surface area, and high (macro)porosity, which, when combined, could significantly improve the performance of devices such as batteries, electrolyzers, or sensors. In this work, we rationally designed templated networks of interconnected metal nanowires, combining for the first time high porosity of metal foams, narrowly distributed macropores, and a very high surface area of nanoporous dealloyed metals. Thanks to their structural uniformity, the few-micron thick nanowire meshes are also remarkably flexible and durable. We show how the textural properties of the material can be precisely tuned to optimize the nanowire networks for applications in different devices. In an exemplary application in electrolytic production of hydrogen, thanks to its high surface area, a few-micron thick nanomesh outperformed a 300 times thicker nickel foam. Furthermore, thanks to its high porosity, the Pt-doped nanomesh surpassed a microporous Pt/C cloth, demonstrating benefits of the optimally designed nanowire structure for a simultaneous improvement and miniaturization of electrochemical devices. This work extends the potential of interconnected nanowires to multiple new research and industrial applications requiring highly porous and flexible conductive materials with a high surface-to-volume ratio.

Heat transfer in PEM cooling flow field with high porosity metal foam insert

Conventional cooling channel flow fields of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) introduce some challenges that would reduce the cell total performance. So presenting novel ideas to improve the cooling flow fields is fully appreciable. The more common conventional flow fields include the serpentine, parallel and multichannel would be precisely studied in this paper. In order to see the effect of porous materials in heat transfer, metal foams were introduced to the channels. Unlike continuous long flow passages in conventional channels, metal foams provide randomly interrupted flow passages. Re-circulation of fluid, due to randomly distributed tortuous ligaments, enhances the heat transfer in these new channels. Moreover, to assess the features of utilizing metal foams in cooling channels, different parameters like metal type, porosity percentage and also the cooling media were investigated. Since both thermal and hydraulic points of view are important in cooling engineering, the heat transfer and pressure drop for all three channel types were verified. The results showed that enhancing the porosity of the metal foam would decrease both heat transfer and pressure drop. Also the multi-channel type revealed the best heat transfer behavior in presence of metal foams.

Thermal and economic analysis of charging and discharging characteristics of composite phase change materials for cold storage

This study conducted both experimental and numerical investigations on the solidification behavior in a metal foam composite phase change material (PCM) for cold storage. Volume-average-method was adopted with the help of Forchheimer-Darcy equation to model the fluid flow through porous media. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. Local thermal equilibrium and non-equilibrium states were justified numerically and experimentally. Effect of pore morphological parameters (porosity and pore density) upon the solidification features of composite PCM were investigated. For the appliance of composite PCM to cold storage, techno-economic characteristics was also assessed. Results demonstrated that the full solidification time for metal foams with a porosity of 0.93 and 0.97 can be saved 87.5% and 76.7% respectively compared with pure water. It indicated that porosity of metal foam played a dominant role in heat transfer enhancement; while pore density seemed to have little influence on phase change behavior according to the results. Local natural convection in the unsolidified phase caused a remarkable promotion of the interface evolution, and the full solidification time with natural convection considered can be saved by 14.3% compared with pure conduction for the case with the same porosity of 0.97. The economic analyses indicated that using composite PCM was profitable with a short payback period less than 2 years.

Experimental study on heat transfer enhancement of gas tube partially filled with metal foam

This paper proposes partially filling a gas tube with metal foam to further enhance the gas heat transfer capability with smaller pressure loss. A wind-tunnel-type gas heat transfer test system was built to investigate the features and effects of this heat transfer enhancement method. The effects of pore density and filling thickness of the metal foam on the gas heat transfer in the tube were studied experimentally and analyzed by determining the performance evaluation criteria (PEC), a comprehensive evaluation index. The results show that for the same porosity and filling rate, a high heat transfer coefficient can be obtained at high pore density; however, the comprehensive evaluation index of metal foam with a lower porosity is higher. Thus, lower porosity metal foam inserted at a higher filling rate, together with a low Reynolds number, leads to more efficient heat transfer.

Effects of Metal Foam Porosity, Pore Size, and Ligament Geometry on Fluid Flow

This paper explores the effects of porosity, pore size, and ligament geometry in metal foams on its fluid flow capability. The motivation to understand this phenomenon stems from exploring the use of metal foams for thermal energy dissipation applications where both thermal convection and fluid flow are desired. The goal of this research is to identify the optimum configuration of metal foam design parameters for maximum flow. To study the impacts of said parameters, an experimental study of air flow through open cell metal foams is performed. Seven foam blocks were used in this partial factorial study, representing varying materials, pore size, and porosity. Wind tunnel tests are performed to measure the velocity of air flowing through the foam as a function of the free stream air velocity. Multinomial logit regression was performed to analyze the effects of the design parameters on velocity loss through the foam. Results indicate that effect of porosity on velocity loss is significant while that of pore size is insignificant. However, one test result did not fit this trend and further investigation revealed that this was due to varying ligament geometry in outlier metal foam. The cross section shape of the ligaments varied from a convex triangular shape to a triangle shape with concave surfaces, increasing the amount of drag in the airflow through the sample.

A comparative study of PCM melting process in a heat pipe-assisted LHTES unit enhanced with nanoparticles and metal foams by immersed boundary-lattice Boltzmann method at pore-scale

Latent heat thermal energy storage (LHTES) has attracted lots of attention due to its nearly constant working temperature and large thermal energy storage density. However, the thermal conductivity of phase change materials (PCMs) is usually low which impedes the heat transfer efficiency in the LHTES system. Adding high thermal conductivity nanoparticles or metal foams are the two common approaches to enhance the thermal performance of the PCMs. In the current work, the PCM melting performance in a heat pipe-assisted LHTES unit enhanced by nanoparticle-metal foam combination is numerically investigated by immersed boundary-lattice Boltzmann method (IB-LBM) at pore scale. The microstructure of metal foam is reconstructed using the quartet structure generation set (QSGS). The PCM melting performance in LHTES is studied in terms of porosity and pore size of metal foams, volume fraction of nanoparticles, and radius of heat pipe. A comparative study is carried out to illustrate the effectiveness of enhancing PCM melting performance with different combinations of nanoparticles and metal foams. The results indicate that there exist the optimum metal foam porosity and heat pipe radius for the energy storage efficiency in the LHTES unit. Besides, it is found that using metal foams is more effective than adding nanoparticles for the improvement of PCM heat transfer capability.

Physical and Mechanical Properties of W-Ni-Fe-Co Metal Foam Modified by Titanium Tungsten Carbide Alloying

The paper studies physical and mechanical properties of tungsten-nickel-iron-cobalt metal foam alloyed with titanium tungsten carbide. Test specimens are obtained by the liquid phase sintering of powder materials, including those containing tungsten nanopowders. High porosity metal foams are prepared through varying the porosity of powder specimens and the content of filling material. The penetration capability of cylinder projectiles made of new alloys is explored in this paper. It is shown that their penetration depth exceeds that of the prototype with relevant weight and size, made of tungsten-nickel-iron alloy, other factors being equal.

Experimentally validated analytical expressions for the thermal resistance of a novel composite fin-foam annular array

Novel expressions are developed for the thermal resistance associated with an array consisting of periodic layers of metal fins and open-cell, high porosity metal foam attached annularly to a base cylinder. Predictions generated with the new expressions are verified by comparison with experimental measurements involving such an array and a cylindrical heat pipe. Parametric simulations are performed to assess the performance of the array over a range of geometric configurations, thermal contact resistances, and air velocities. Analytically predicted heat rates for an annular fin array, a foam-only annular array, and the new combined fin-foam array are compared, illustrating the improved thermal performance made possible by combining metal fins and foam into a composite array.

Investigation of the effect of metal foam characteristics on the PCM melting performance in a latent heat thermal energy storage unit by pore-scale lattice Boltzmann modeling

ABSTRACTLatent heat thermal energy storage (LHTES) has many advantages such as high energy density and phase change at a nearly constant temperature compared with sensible thermal energy storage or chemical energy storage techniques. However, one of its major drawbacks is the low thermal conductivity of phase change materials (PCMs) which impedes the heat transfer efficiency. High thermal conductivity metal foams could be added into the LHTES to enhance the heat transfer speed. Under this case, the investigation of the effects of metal foam porosity and pore size on the melting process is essential for improving the heat storage capability of LHTES. In this article, a pore-scale modeling of melting process in a LHTES unit filled with metal foams is carried out by enthalpy-based multiple-relaxation-time lattice Boltzmann method. The quartet structure generation set is used to generate the morphology of metal foams. In addition, a Compute Unified Device Architecture (CUDA) Fortran code is developed in this work for executing highly parallel computation through graphics processing units. The melting process in the PCMs is investigated in terms of porosity, pore size, nonuniform metal foam, hot wall temperature, and initial subcooled temperature to optimize the design of LHTES filled with metal foams.

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.

Enhanced Thermal Performance of Internal Y-Shaped Bifurcation Microchannel Heat Sinks With Metal Foams

Internal Y-shaped bifurcation has been proved to be an advantageous way on improving thermal performance of microchannel heat sinks according to the previous research. Metal foams are known due to their predominate performance such as low-density, large surface area, and high thermal conductivity. In this paper, different parameters of metal foams in Y-shaped bifurcation microchannel heat sinks are designed and investigated numerically. The effects of Reynolds number, porosity of metal foam, and the pore density (PPI) of the metal foam on the microchannel heat sinks are analyzed in detail. It is found that the internal Y-shaped bifurcation microchannel heat sinks with metal foam exhibit better heat transfer enhancement and overall thermal performance. This research provides broad application prospects for heat sinks with metal foam in the thermal management of high power density electronic devices.

Cooling capacity of high porosity open-cell metal foams as passive cryogenic radiators

This work presents an innovative avenue for employment of high porosity open-cell metal foams as extended heat transfer surfaces in passive cryogenic radiators. Metal foams are known for being light in weight and possess high surface area density. In contrast to a solid surface, porosity of metal foams makes it feasible for penetration of radiation thereby resulting in higher radiatively interactive surface area. Two 20 PPI metal foams made of copper and aluminum with 94.9% and 90.3% porosity respectively have been chosen for this study. A laboratory-scale test rig measures the radiative cooling capacity of metal foams in vacuum (10−6mbar) subjected to liquid nitrogen environment. Heat load to the foam has been provided by means of convective fluid loop. Simultaneously, a theoretical model based on radiation-conduction fin analysis has been developed to predict the foam cooling capacity at a specified temperature. The required radiation heat transfer coefficient has been obtained from a previous experiment wherein the foam samples are freely suspended in similar conditions but with no heat load. Lastly, performance of the foams under study has been expressed in terms of a commonly used performance parameter (surface area/cooling capacity) for passive cryogenic radiators.

Solidification enhancement in a triplex-tube latent heat energy storage system using nanoparticles-metal foam combination

Thermal storage systems utilizing Phase Change Materials (PCMs) are known to exhibit slow thermal response. This is mainly due to the relatively low thermal conductivity of most PCMs used in the systems. Thus packing the PCMs in better performing containment vessels and/or employing heat transfer enhancement additives is required for improved performance of these systems. Nanoparticle-metal foam combination as a compound enhancement approach along with triplex-tube heat exchanger as a modified exchanger design were used in this study to improve the PCM solidification rate. A mathematical model based on the thermal equilibrium assumption which takes into account the non-Darcy effects of porous foam and the Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile over the whole solidification process was studied. Results show that dispersing nanoparticles in the presence of metal foams results in total time saving up to 96% depending on foam structure and volumetric nanoparticle concentration.