Foam Porosity Research Articles

Energy absorption of discretely assembled composite self-locked systems

Impact accidents cause great damage to lives and devices due to strong destructiveness and weak predictability, and accordingly, flexibility and modifiability are essential in the design of novel impact-resistant structures. To achieve this goal, two newly-designed energy absorption systems were proposed in this paper, which could be discretely assembled without boundary constraints. Quasi-static experiments and finite element method (FEM) simulations were carried out to reveal the deformation mechanism and test the usability, based on which the analytical solutions of the crushing force of the models were established adopting plastic hinge analysis and energy method. Parametric study of multiple-tube systems was conducted to reveal the effects of foam porosity and inner tube parameters on dynamic response, and the optimal design was summarized, achieving the energy absorption efficiency of 39%. The functionally graded design of composite self-locked (CSL) systems was explored, and it was proven that the system with positive stiffness gradient was optimal.

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.

Macroporosity-based prediction models for mechanical properties of foamed concrete

Foamed concrete is a versatile lightweight material that has attracted considerable research attention during the last few years. Various researchers have proposed strength prediction models based on the porosity of the material. However, these models give significantly different values of strength for the same foam porosity. Although the Balshin-type power functions have been found to adequately fit the experimental data, the power exponents reported by various researchers have had wide variations, ranging from 2.7 to 4.9. A fairly similar situation prevails with regards to models for predicting the elastic modulus of foamed concrete. In this research, through an experimental study and also re-examination of previous works, a general expression is derived for quantifying the effect of foam content on the strength of foamed concrete. Using the concept of paste fraction porosity, the discrepancy between power exponents reported by various researchers was resolved. It was found that a Balshin-type function with a power exponent of 3 can be used for the prediction of the strength of foamed concretes, provided the porosity is considered as the paste fraction porosity Pf′. With regards to elastic modulus, by providing new experimental data, more insight is provided on the effect of foam porosity on this parameter.

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.

Utilization of a phase change material with metal foam for the performance improvement of the photovoltaic cells

This study presents a novel configuration for improving the photovoltaic (PV) panel's thermal management system, which includes a phase change material (PCM) with the metal foam layer. During the energy-absorbing mode, the arrangement allows for quicker heat dissipation from the system, resulting in the cooling of the PV panels. The effects of the foam-layer material, PCM thickness, and foam porosity are numerically simulated and analyzed. The results demonstrated that the higher PCM layer thickness leads to a lower PV surface temperature. The extracted curves indicated that lower porosity causes higher maximum PV temperature. Furthermore, it was found that average electrical efficiency for the model with a porosity of 0.9, 0.8, 0.4, and no-foam state are 13.805%, 13.794%, 13.761%, and 13.714%, respectively. All data are almost similar for both copper and aluminum foams, and there are negligible differences between the results. The results for the four chosen months describe that for June, March, and September, the PCM layer absorbs heat and causes a considerable reduction in the PV maximum temperature, but for December, this process is not valid. Accordingly, superior PCM-based thermal management is achieved through the proposed system.

Fabrication of Al/SiC composite foams with TiH2 foaming agent by laser melting deposition

In this work, SiC reinforced aluminum composite foams were successfully fabricated by laser melting deposition (LMD). The microstructure, energy absorption capacity, and compressive properties of Al/SiC composite foams were investigated systematically, and the results indicated that with increasing the content of SiC nanoparticles, the porosity and average pore size of aluminum foams decreased. Compared with the pure aluminum foams, the compressive strength and energy absorption of the Al/SiC composite foams increased by 43.8% and 16.0%, from 28.5 MPa and 55.5 × 106 J m−3 to 41.0 MPa and 64.4 × 106 J m−3, respectively. The research indicates that SiC nanoparticles are effective additives to homogenize the pore size and enhance the mechanical performance of aluminum foams by the LMD method.

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.

Numerical simulation and experimental investigation of foam-mat drying for producing banana powder as influenced by foam thickness

The high surface-to-volume ratio and porosity of foam during foam-mat drying shorten the drying process and improve dried powder quality. Therefore, foam-mat drying has caught the attention of researchers as an effective method in sticky, heat sensitive, and viscous food biomaterials that are not easy to dry with other techniques. This research sought to explore the impact of different foam thicknesses, i.e., 3, 5, and 7 mm, on quantitative and qualitative features of unripe banana powder both experimentally and numerically. An increase in foam thickness enhanced the effective moisture diffusion coefficient by 64.69% and decreased the drying rate by 52.63%. The increase also lowered powder flowability, browning index, and total color difference. According to field-emission scanning electron microscopy, an increase in the foam thickness increased the shrinkage and stickiness of the powders. The thermal response of the powders examined by differential scanning calorimetry demonstrated maximizing the glass transition temperature at 59.75 ˚C with foam thickness of 5 mm. Comparing simulated and experimental data showed a 0.880 correlation coefficient, which confirmed the consistency between experiments and simulations. Results of this study may be used in industrial applications to design a foam-mat drying process for producing quality powder biomaterials.

Pore-scale study on Rayleigh-Bénard convection formed in the melting process of metal foam composite phase change material

Rayleigh-Bénard convection significantly affects the melting process of phase change material (PCM). It has been verified to exist in the model with bottom heating. Nevertheless, researchers rarely focus on the Rayleigh-Bénard convection in the metal foam composite PCMs (MFCPCMs). This paper took numerical investigations to study the melting behavior of the MFCPCMs when Rayleigh-Bénard convection was involved, and a visualized experiment was used to verify their accuracy. By analyzing the number of Bénard cells, dimensionless parameters of Rayleigh number and Nusselt number, we found three regimes, including the conductive regime, linear regime, and coarsening regime, forming in the models. The liquid fraction contour captured the evolution of the melting front, and the state of convective heat transfer was characterized by Bénard cells. Results show that the intensity of Rayleigh-Bénard convection in the MFCPCM is obviously weaker than that in the pure PCM. Moreover, the porosity of metal foam has a significant influence on the development of Rayleigh-Bénard convection. With the increase of the porosity, the suppression of liquid PCM flow is weakened, so the convection is more developed. The inhomogeneous evolution of the melting front is more pronounced. Besides, to study the effect of model size on the melting behavior, we built three groups of models with width-height ratios (γ) of 2, 1, and 0.5, respectively. Results show that the model with large γ has more significant inhibition on the development of Rayleigh-Bénard convection. The solid/liquid interface is flat or with a slight fluctuation. On the contrary, the model with small γ has more developed Rayleigh-Bénard convection. The interface of it has a violent fluctuation, which shows as a humped arch. This work interprets the internal heat-transfer characteristics of the MFCPCM model with Rayleigh-Bénard convection. It paves the way for the structural optimization of the metal skeleton to gain efficient heat storage.

Biomedical Ti-Nb-Zr Foams Prepared by Means of Thermal Dealloying Process and Electrochemical Modification.

The paper presents results of preparation and modification of Ti20Nb5Zr foams by a thermal dealloying method followed by electrochemical modification. The first step of this study was the preparation of Ti20Nb5Zr30Mg nanopowder using mechanical alloying (MA). The second was forming green compacts by cold pressing and then sintering with magnesium dealloyed from the structure, which resulted in pores formation. The next step was surface modification by electrochemical etching and silver nanoparticle deposition. Porosity, morphology, mechanical properties as well as biocompatibility and antibacterial behavior were investigated. Titanium foam porosity up to approximately 60% and wide pore size distribution were successfully prepared. The new materials have shown positive behavior in the MTT assay as well as antibacterial properties. These results confirmed great potential for thermal dealloying in preparation of porous structures.

Encapsulation of coffee silverskin extracts by foam mat drying and comparison with powders obtained by spray drying and freeze-drying.

Coffee silverskin is a coproduct that has a rich composition in bioactive compounds. However, most of these compounds are susceptible to the conditions used during food processing and storage. Encapsulation is a process of great interest to increase the stability of these bioactive compounds, and different methods can influence the final characteristics of the product. Therefore, this study aimed to evaluate the encapsulation methods by foam mat drying, spray drying and freeze-drying for producing powder from coffee silverskin extracts. Density, porosity, overrun, and stability foam were evaluated and the physicochemical properties of powders, such as water activity, moisture, wettability, hygroscopicity, solubility, color, antioxidant activity, and total phenolic were determined. The optimal condition required for the feed mixture for foam formation was 7.6% gum arabic, 2% maltodextrin, and 10.4% egg albumin. All methods presented powders with desirable values of water activity, moisture content, and hygroscopicity, being considered stable for storage, and high content of bioactive compounds. Higher temperatures for foam mat drying produced powders with higher encapsulation efficiency (>77%) and longer wettability than lower temperatures (50 and 60°C). Therefore, this study verified that foam mat drying can be considered an efficient and promising method for encapsulating bioactive compounds from coffee silverskin extract. PRACTICAL APPLICATION: Foam mat drying can be considered an alternative method to conventional encapsulation by spray drying and freeze-drying. This method is simple, inexpensive, and generates high-quality products. Optimization of foam properties is necessary to ensure successful drying.

Analysis of poly(dioxanone) foam prepared using salt leaching method

AbstractThis study aims at preparing and analyzing porous biodegradable polymer foam. Poly(dioxanone) (PDO) foams with a three‐dimensional structure and high porosity were fabricated by using sodium chloride (NaCl) particulate leaching method. The influence of the size composition of PDO and NaCl was investigated to understand the relationship between polymer matrix and salt during the manufacturing process. The physical characteristics of the prepared foam, such as moldability, leaching state, porosity, permeability, swelling ratio, pore density, and mechanical property were analyzed. The PDO foams with high dimensional stability were prepared when the PDO particles were smaller than the NaCl particles, and the porosity of the PDO foam increased with decreasing the particle size of PDO. In addition, the compression modulus of the foam was analyzed to estimate a possibility for application in tissue engineering.

Preparation of lignin-based carbon foam monoliths with high strength and developed micrometer-sized cell/nano-sized porous structures using a self-bubbling method

Lignin is an attractive renewable feedstock used for the production of carbon materials because of its abundance and high carbon content. This work aims to explore a scalable technology to produce carbon foams from lignin. A lignin self-bubbling method has been developed in this study using zinc chloride as the catalyst for the thermal decomposition of lignin, resole as a cross-linking agent and a surfactant as the foaming assistant agent. The effects of dosage of zinc chloride and resole, type and dosage of surfactant, foaming temperature, heat treatment on the structure and properties of the materials have been investigated. The results show that the structure and properties of the resultant lignin-based carbon foams without any fractures is highly tunable depending on the amount of zinc chloride, resole and surfactants used, the foaming temperature in the self-bubbling process and post-heat treatment step. It is found that the non-ionic surfactant Tween-80 can significantly improve the mechanical strength and porosity of monolithic lignin-based carbon foams. The lignin-based carbon foams prepared using a self-bubbling method under ambient pressure not only exhibit a compressive strength of ˃4 MPa and an electric conductivity of 0.79 S cm−1, but also bear a developed structure of micrometer-sized cells with a low density of 0.3 g cm−3 and nanometer-sized pores with surface area of ˃175 m2 g−1. Furthermore, the lignin-based carbon foams have high thermal and structural stability to resist burning for various applications and exhibit excellent performance in oil/water separation, which retain 91% of the adsorption capacity toward oils even after being recycled 20 times.

Laser forming of difficult-to form Al-SiC composite foam – Experimental and numerical analyses

Despite being cheap and having shown high crashworthiness, composite aluminium foam reinforced with silicon carbide (SiC) lacks utilization because of its limited ductility which hinders its shaping by mechanical means. This study established laser forming as a robust method to form this material. Unlike existing literature, the current study takes into account the relative density of the foam along with laser parameters (power, scan speed and beam spot diameter) to develop a statistically significant model for predicting the bending angles. Previously, no studies had been conducted on laser forming of Al-SiC composite foams. Further, three different approaches for numerical simulation of laser forming of metal foams viz. equivalent model, cellular model and voxel model were probably compared for the first time in terms of their accuracy to predict bending and computational time requirement. The cellular model could predict the bending most accurately, yet consumed the least computational time. The complete thermo-mechanical analysis of the voxel model of metal foam had been rarely reported before this. In this paper, a new simpler cellular model was used for simulation that could incorporate higher foam porosity (73%).

Using Cu as a Spacer to Fabricate and Control the Porosity of Titanium Zirconium Based Bulk Metallic Glass Foams for Orthopedic Implant Applications.

In this study, a porous titanium zirconium (TiZr)-based bulk metallic foam was successfully fabricated using the Cu spacer by employing the hot press method. TiZr-based bulk metallic foams with porosities ranging from 0% to 50% were fabricated and analyzed. The results indicate that thermal conductivity increased with the addition of Cu spacer; the increased thermal conductivity reduced the holding time in the hot press method. Moreover, the compressive strength decreased from 1261 to 76 MPa when the porosity of the TiZr-based bulk metallic foam increased to 50%, and the compressive strength was predictable. In addition, the foam demonstrated favorable biocompatibility in cell viability, cell migration capacity, and calcium deposition tests. Moreover, the pore size of the porous TiZr-based bulk metallic foam was around 120 µm. In conclusion, TiZr-based bulk metallic foam has favorable biocompatibility, mechanical property controllability, and porous structure for bone ingrowth and subsequent enhanced osteointegration. This porous TiZr-based bulk metallic foam has great potential as an orthopedic implant to enhance bone healing and decrease healing time.

Analysis of copper foam/low melting point alloy composite phase change material

• Copper foam has a more significant improvement in n-tricosane. • Copper foam/47 alloy is still better in temperature management performance. • Copper foam limits the temperature rise of 47 alloy during the phase transformation. • The low ratio of copper foam greatly improves 47 alloy. • The higher the porosity, the better the temperature management performance. In the current paper, we present the influence of adding high thermal conductivity materials on the thermal management performance of low-melting-point alloys in different aspects. We analyze the phase change process of 47 alloy and n-tricosane before and after compounding with copper foam based on numerical simulation. Moreover, we calculate the temperature management curve of low-melting-point alloy composite materials with different foam porosity. Our results indicate that the addition of copper foam significantly improves the thermal management performance of n-tricosane. Due to the difference in latent heat, the thermal management time of copper foam/47 alloy is 1.21 times higher than the former. The addition of copper foam mainly improves its thermal response and inhibits the temperature rise in the phase transition stage. Just 5% of copper foam has a significant effect. For copper foam/47 alloy, the higher the porosity, the stronger the temperature management ability. This feature is more prominent when the upper limit is the temperature below the melting point.

Hierarchical Structure of Cellulose Nanofibril-Based Foams Explored by Multimodal X-ray Scattering.

Structural characterization techniques are fundamental to correlate the material macro-, nano-, and molecular-scale structures to their macroscopic properties and to engineer hierarchical materials. Here, we combine X-ray transmission with scanning small- and wide-angle X-ray scattering (sSWAXS) to investigate ultraporous and lightweight biopolymer-based foams using cellulose nanofibrils (CNFs) as building blocks. The power of multimodal sSWAXS for multiscale structural characterization of self-assembled CNFs is demonstrated by spatially resolved maps at the macroscale (foam density and porosity), at the nanoscale (foam structural compactness, CNF orientation in the foam walls, and CNF packing state), and at the molecular scale (cellulose crystallite dimensions). Specifically, we compare the impact of freeze–thawing–drying (FTD) fabrication steps, such as static/stirred freezing and thawing in ethanol/water, on foam structural hierarchy spanning from the molecular to the millimeter scale. As such, we demonstrate the potential of X-ray scattering imaging for hierarchical characterization of biopolymers.

Simulating Solid-Liquid Phase-Change Heat Transfer in Metal Foams via a Cascaded Lattice Boltzmann Model.

A cascaded lattice Boltzmann (CLB) model is constructed for simulating heat transfer in metal-foam-based solid-liquid phase change materials (PCMs). The present model captures the phase interface implicitly via the enthalpy methodology, and to avoid iterations in simulations, the CLB equation of the PCM employs the enthalpy as the basic evolution variable through modifying the cascaded collision process. Numerical results demonstrate the effectiveness and practicability of the CLB model for investigating heat transfer in solid-liquid PCMs with metal foams. The effects of the inertial coefficient, permeability and porosity on the melting process are investigated. The results indicate that the empirical correlations of inertial coefficient and permeability based on packed beds overestimate the melting rate at high porosities. Moreover, the porosity has significant impact on phase-change processes. The melting rate increases as the porosity of the metal foam decreases since heat conduction through high thermal conductive metal foam dominates the total heat transfer.

Effect of porosity of aluminum foam on welding between aluminum foam and polycarbonate plate during friction welding

Effect of porosity of aluminum foam on welding between aluminum foam and polycarbonate plate during friction welding