Open-cell Foams Research Articles

Melting characteristics of phase change material inside graded aluminum foam based on tetrakaidecahedron model: Pore-scale simulations

Metallic ligaments in open-cell metal foams have effectively improved the heat conduction of phase change materials (PCMs). However, when the gradient direction of porosity is perpendicular to the direction of heat conduction, the mechanism by which graded foam (GF) influences the phase transition of PCM remains elusive. To address this issue, this study employs the pore-scale numerical simulation and develops a numerical model to study the impact of GF on the charging of PCM-foam composites. The analysis identifies the local convection and heat conduction as the most crucial factors influencing heat transfer during phase transition. To effectively examine the role of metallic ligaments in the phase transition, simplified tetrakaidecahedron cells are adopted. The results demonstrate that the GF delays the charging of PCM. Specifically, compared to the homogeneous foam, the full melting time (FMT) of PCM in the GF increases by over 29%. Additionally, the integral-mean temperature response rate (ITRR) of PCM in the GF decreases by 20.2% to 22.1%. Within the GF, the PCM requires more time to melt completely in the tetrakaidecahedron cells with high porosity. Moreover, local convection plays a pivotal role, considerably reducing the FMTs of PCMs by over 85% and increasing the ITRRs of these structures by 588.1% to 599.0%.

Impact response of composite energy absorbers based on foam-filled metallic and polymeric auxetic frames

In this paper, an innovative concept is proposed, based on the hexachiral auxetic frames filled with foams with enhanced energy absorption capabilities. Numerical assessments of the composite foam-filled auxetic absorbers, of pure foam blocks and unfilled auxetic frames for metallic and polymeric material combinations were accomplished considering a case of localized impact. The energy absorbed by the composite absorbers are found superior to the sum of the energies absorbed by constituent elements tested separately with clear advantages also at the level of the specific energy absorbed per unit mass. The interactions between the two constituents are analyzed and discussed. An experiment considering a 3D-printed polymeric hexachiral frame filled with open-cell soft polyurethane foam under localized impact is conducted to validate the numerical approach. Eventually, a parametric sensitivity study is conducted numerically to illustrate the effects of geometrical parameters on the energy absorption capacity. Overall, the results confirm the potential and the great design flexibility of the concept, provides the guidelines to design advanced energy absorbing system, underlies the importance of the combination between the frame and foam properties and the effect of the main geometrical parameters on the performance.

Investigating the potential of dihydroxystearic acid as feedstock for rigid polyurethane foam

Rigid polyurethane (PU) foam has been widely used for a multitude of applications, primarily as thermal insulation materials. With the exhortation of “green chemistry” and sustainable development, bio-based polyols are being introduced to replace the conventional petrochemical-based polyols. Hence, the use of 9, 10-dihydroxystearic acid (DHSA), derived from palm oil-based oleic acid, as a feedstock for rigid PU foam production was explored. In this study, the effects of the weight ratio percentage of DHSA on the characteristics of the resulting PU foams were investigated. The DHSA was utilized as a co-polyol to synthesize rigid PU foams by reacting with the diisocyanate compound, blowing agent and additives. In general, the effects of DHSA in the formulations on the quality of the foams were relatively similar to PU formulation without the addition of DHSA, particularly in terms of density, compressive strength, thermal conductivity, cell structure and dimensional stability. The remarkable effect of DHSA addition in the PU formulations was observed through the open PU cell content using a pycnometer and scanning electron microscopy (SEM). The addition of DHSA has the ability to open the cell structure of the resulting rigid PU foams. The open cell content increased notably from 6.83% to 90.99% when the DHSA content was increased from 0% to 50%. The ability of DHSA to produce open-cell rigid PU foam widens up the potential applications of rigid PU foams as sound absorption materials.

The effect of the foam structure and distribution on the thermomechanical vibration behavior of sandwich nanoplates with magneto-electro-elastic face layers

This study examined the thermal vibration of a foam core nanoplate composed of ceramic silicon nitride (Si3N4) and metal biomaterial (Ti-6Al-4V) in the core layer, and cobalt-ferrite (CoFe2O4) and barium-titanate (BaTiO3) in the face layers. The constitutive equation is influenced by various factors, including nonlocal elasticity, thermal expansion, strain gradient elasticity, magnetostrictive, and electroelastic properties, as well as sinusoidal higher-order shear deformation theory (SHSDT) with stretching effect. The study found that the thermomechanical vibration behavior of nanoplates was influenced by the ratio of open cell foam to solid, nonlocal factors, thermal load, electrical and magnetic potentials, and different foam distribution.

A bioengineering investigation of cervical collar design and fit: Implications on skin health

BackgroundCervical collars restrict cervical spine movement to minimise the risk of spinal cord injury. Collars apply mechanical loading to the skin putting it at risk of skin damage. Indeed, cervical collar-related pressure ulcers are unacceptably prevalent, especially at the occiput, mandibles, and chin. Collar design and fit are often key considerations for prevention. MethodsThis comprehensive study evaluated four commercial prehospital and acute care cervical collars. Pressure, microclimate, transepidermal water loss and skin hydration were measured at the interface between the device and the skin. Range of motion restriction was measured to evaluate effective immobilisation. Head, neck, and shoulder morphology was evaluated using three-dimensional scans. FindingsThe occiput experienced significantly higher interface pressures than the chin and mandibles for most collar designs. Interface pressure at the occiput was significantly higher for the Stiffneck extrication collar compared to the other collar designs. The Stiffneck collar also provided the most movement restriction, though not significantly more than other designs. Relative humidity at the device skin interface was significantly higher for the Stiffneck and Philadelphia collars corresponding to closed cell foam padding, in contrast to the open cell foams lined with permeable fabric used in the other collars. Collar discomfort correlated with both occipital pressure and skin humidity. InterpretationThe occiput is at increased risk of cervical collar-related pressure ulcers during supine immobilisation, especially for Stiffneck extrication collars. Lined open-cell foams could be used to minimise skin humidity and increase comfort.

Ultrasonic spot welding of open-cell Cu foam and Al plate: A study on the quality of joints

As a type of novel material, open-cell copper (Cu) foam has been widely applied in electrode production of batteries, due to its functional and structural properties. The use of ultrasonic welding technique to join Cu foam and aluminium (Al) plate has been proven to be feasible, but quality evaluation of the joints remains a blank to be filled in. In this study, orthogonal test design is used to investigate the effects of welding pressure, welding amplitude, welding energy and the interaction among the three parameters on the shear-tensile strength of ultrasonically welded joints of Cu foam/Al plate, and it is influenced by the three parameters in the following order: welding pressure > welding energy > welding amplitude. Based on the results of the orthogonal test, a Cu foam/Al plate ultrasonic welding joint evaluation system is established, based on which, qualitative and quantitative analysis on the quality of the joints classified the joints into three grades. The optimal parameter combination of the welding joint of Cu foam/Al plate is obtained as follows: 0.5 MPa, 65 %, 130 J, under which the porous structure of the joint is complete while its tensile strength is equal to or even better than the base material.

A new modelling method for open cell foam structure based on centroidal and capacity constraint power diagram

To efficiently establish a finite element model that is highly compatible with the intricate microstructure of foam materials, this study carries out simulation and experimental investigations into open cell foams and explores their compression behavior assuming isotropy. Using an in-house algorithm, we optimize the traditional power diagram model, which is widely used in foam finite element simulation. Specifically, a parameterized geometric foam model is developed based on the centroidal and capacity constrained power diagram (CCCPD), which accurately reflects the internal meso-structure of foam materials. The optimized foam model can restore the typical deformation process of foams under compressive load, thus addressing the limitations of existing foam models. The accuracy of the optimized model is validated by conducting uniaxial Quasi-static compression experiments on foamed thermoplastic polyurethane (TPU) material and comparing the experimental results of the 3D printing model with the simulation results of the optimized model. The improved foam model serves as a basis for future research on open cell foam materials.

Experimental study of the low-velocity impact behavior of open-cell aluminum foam made by the infiltration method

This study examined the behavior and energy absorption of open-cell aluminum foam under different loading conditions. The foam was made by infiltration, a low-cost method that produced a uniform pore distribution. The foam was compressed using two machines with varying impact velocities and weights. The stress–strain and energy absorption curves of the foam were measured and analyzed. The results showed that the strain rate and the impact weight affected the compressive properties and energy absorption of the foam. The strain rate up to 264 s−1 with constant mass did not affect the plateau stress, which was the constant stress in the plastic region. However, at 264 s−1, increasing the impact weight increased the plateau stress and the energy absorption of the foam, which showed that the strain rate sensitivity depended on the impact inertia. The study revealed the dynamic characteristics of open-cell aluminum foam made by infiltration and provided insights for its use in impact protection. The study also showed that infiltration was a reliable and consistent method for making open-cell aluminum foam. The study highlighted the important roles of plateau stress and hardening effect in influencing the energy absorption of the foam under dynamic loading. The study suggested that future studies should consider the impact inertia as a parameter that affects the strain rate sensitivity of the foam.

Interface characterization of Mg-7Al-1Ca alloy reinforced by integrated 3D[sbnd]Cu open-cell foam

In this study, a 3DCu open-cell metal foam has produced through investment casting, then molten Mg-7Al-1Ca has penetrated through the 3DCu open-cell foam to produce the composite. The composites were heat treated at 290 °C and 480 °C for 1 h to find the adhesion mechanism at the interface of Mg-7Al-1Ca/3D-Cu open-cell foam. Then, the microstructural and mechanical properties of the Mg-7Al-1Ca/3D-Cu open-cell foam interface were investigated by metallography, micro-hardness, and punch-out test. The results indicate that the shear strength of the Mg-7Al-1Ca/3D-Cu interface is a function of the diffusion bond thickness and types of intermetallic phases. The as-cast sample tolerated 98.5 MPa shear stress. However, the 480 °C heat-treated sample has the most fracture toughness compared to the 290 °C heat-treated and the as-cast samples, 84.7, 75.6, and 35.1 J/mm3, respectively. Therefore, the heat-treatment cycle, T = 480 °C, t = 1 h, with decreasing 9.5% (98.5 to 89 MPa) of the shear strength led to an 140% (35.1 to 84.7 J/mm3) increase in energy absorption density of the interface of the composite.

Structure-property relationships of polydisperse open-cell foams: Application to melamine foams

Melamine foam, categorized as an open-cell foam structure, absorbs sound through its three-dimensional network of thin struts. The pore size polydispersity within the open-cell melamine microstructure is evidenced from a top-down approach and confirmed by scanning electron microscope (SEM)-image analysis. The remarkable ability of melamine foams to mitigate sound energy is attributed to the pore size distribution, which encompasses co-existing pores of distinct characteristic sizes. Consequently, low-frequency and high-frequency fluid flows will follow different paths within the pore structure. A poly-sized model, which provides a connection between microstructure polydispersity and macroscopic properties, is successfully applied to three different melamine foams. This work highlights the significance and implications of polydispersity effects on the acoustic behavior of open-cell foams.

Ultra-high porosity of open-cell alumina ceramic foams prepared by adding tiny amounts of γ-AlO(OH) sol

A creative and environmentally friendly preparation of high-porosity open-cell ceramic foams was investigated. The samples were prepared from the ?-Al2O3 slurry with 25 wt.% solid loading in which a tiny amount of boehmite (?-AlO(OH)) sol was added for the formation of particle-stabilized foams without introducing any sacrificial phases. The volumetric shrinking of ?-AlO(OH) enables the formation of open-cell while avoiding the generation of polluting gases. The resulting alumina ceramic foams have a synergistic increase in porosity and compressive strength, reaching a compressive strength of 1.17MPa and an ultra-high porosity of 94.8%. This is due to the fact that the pore struts (connecting neighbouring cells) are almost defect-free, while the high sintering activity of ?-AlO(OH) promotes the sintering of ceramic phase and formation of alumina with small grains which has the strengthening effect on the obtained structures. By achieving open-cell, the heat conduction path increased, which reduces the thermal conductivity of the ceramic foam. This work provides an alternative and environmentally friendly new strategy for open-cell ceramics processing.

РОЛЬ ТЕХНОЛОГИЧЕСКИХ ФАКТОРОВ В ФОРМИРОВАНИИ СТРУКТУРЫ ОТКРЫТОПОРИСТЫХ ВСПЕНЕННЫХ МАТЕРИАЛОВ НА ОСНОВЕ ЭТИЛЕН-ПРОПИЛЕН-ДИЕНОВЫХ СОПОЛИМЕРОВ ПУТЕМ КОМПРЕССИОННОГО ФОРМОВАНИЯ

Ethylene-propylene copolymers (EPDM) are known for a wide range of useful properties. EPDM-based rubbers have weather resistance, resistance to aggressive environments and wide operating temperatures. EPDM-based blends allow to create composite materials such as open-cell polymer foam. Due to their unique composition, open-cell elastomeric foam based on EPDM can have different structures, densities and properties. This paper presents a study of the possibilities of technologies of first-stage and second-stage foaming in vulcanization presses in order to regulate the pore structure of open-cell material based on ethylene-propylene-diene copolymer.

Explicit Topology Optimization of Voronoi Foams.

Topology optimization can maximally leverage the high DOFs and mechanical potentiality of porous foams but faces challenges in adapting to free-form outer shapes, maintaining full connectivity between adjacent foam cells, and achieving high simulation accuracy. Utilizing the concept of Voronoi tessellation may help overcome the challenges owing to its distinguished properties on highly flexible topology, natural edge connectivity, and easy shape conforming. However, a variational optimization of the so-called Voronoi foams has not yet been fully explored. In addressing the issue, a concept of explicit topology optimization of open-cell Voronoi foams is proposed that can efficiently and reliably guide the foam's topology and geometry variations under critical physical and geometric requirements. Taking the site (or seed) positions and beam radii as the DOFs, we explore the differentiability of the open-cell Voronoi foams w.r.t. its seed locations, and propose a highly efficient local finite difference method to estimate the derivatives. During the gradient-based optimization, the foam topology can change freely, and some seeds may even be pushed out of shape, which greatly alleviates the challenges of prescribing a fixed underlying grid. The foam's mechanical property is also computed with a much-improved efficiency by an order of magnitude, in comparison with benchmark FEM, via a new material-aware numerical coarsening method on its highly heterogeneous density field counterpart. We show the improved performance of our Voronoi foam in comparison with classical topology optimization approaches and demonstrate its advantages in various settings.

Microstructure-based modeling to characterize low pore density open-cell foams and its experimental validation.

Microlattices with large pore sizes are involved in many multifunctional applications, so it is essential to understand their acoustic properties. However, for these low pore density microlattice foams, the classical homogenization or "equivalent fluid" methods fail abruptly. This paper proposes and discusses a microstructure-based direct fluid model (DFM) that would help to predict the acoustic performance of low pore density periodic open-cell foams with spherical pores. The DFM is simulated directly, including the microscale geometric features inherent in the unit cell. A comparative study is performed for designed three-dimensional (3D) body-centered-cubic (BCC) porous foams having pores per inch (PPI) ranging from 1 to 12 over the frequency range of 500-4100 Hz with equivalent fluid models and experiments. The study shows the extent of deviation in homogenization-based methods from the experiment for PPI < 5. On the other hand, the acoustic performance parameters predicted with the DFM agree well with experiments on 3D-printed samples fabricated by additive manufacturing of varying PPI starting from 1. This study shows that the DFM is a valid method to predict the acoustics of low PPI microlattices. Furthermore, the gradual transition from dissipative to the reactive regime with a decrease in PPI is also brought out.

Rational design of a polypropylene composite foam with open-cell structure via graphite conductive network for sound absorption.

An exciting result is reported in this study where a polypropylene (PP) foam with a high open-cell content was achieved by constructing a thermally conductive network for the first time. PP and nano-graphite particles were used as substrate and filler, respectively, to prepare the PP-graphite (PP-G) composite foam by twin-screw blending, hot pressing, and supercritical CO2 foaming. The nano-graphite particles can effectively adjust the microstructure of the PP-G foam and achieve a high porosity. When the amount of nano-graphite is 10.0 wt%, the PP-G foam exhibits optimal sound absorption performance, compression resistance, heat insulation, and hydrophobic properties. In the human-sensitive frequency range of 1000-6000 Hz, the corresponding average SAC is above 0.9, and the internal tortuosity is 5.27. After 50 cycles of compression, the compressive stress is 980 kPa and the SAC loss is only 7.8%. This study also innovatively proposed a new strategy to achieve the simple and rapid preparation of open-cell PP foams by increasing the thermal conductivity of the foaming substrate.

INVESTIGATIONS ON OPEN-CELL METAL FOAM–FITTED TUBES FOR HEAT TRANSFER ENHANCEMENT – A DISCUSSION ON ENHANCEMENT MECHANISMS

Metal foams are drawing increasing attention due to their high surface area-to-volume ratio, high thermal conductivity, and low density. Heat exchanger manufacturers are constantly looking for innovative methods toward building highly efficient and compact heat exchangers. To enhance heat transfer, the effective thermal conductivity, fitment of foam on pipe, influence of working fluids, and effect of the bonding method are major areas of investigation. This paper aims to present a review of various investigations conducted on open-cell metal foam for enhancing heat transfer. The pore size distribution of metal foam directly influences the effective thermal conductivity. Recent progress toward bimodal pore size distribution has been reviewed and discussed. There exists a tradeoff between enhancing heat transfer and the corresponding pressure drop. Different configurations of fitting metal foam on pipes, such as fully filled, partially filled, and tubes wrapped with metal foam, are critically reviewed, and their performance is compared. The working fluid and its conditions used with metal foam has tremendous potential toward enhancing heat transfer. The influence of nonrefrigerants, refrigerants, and nanofluids has been presented in this regard. Different bonding methods and their influence on thermal resistance are also reviewed. To date, there is hardly any literature that addresses the performance of metal foam–fitted tubes in condensers and evaporators for vapor compression refrigeration systems. Metal foam-fitted tubes have shown promising results in terms of heat transfer enhancement. The outcome of this review provides insights into further research on the use of metal foam–fitted tubes for refrigeration applications.

Geometric models for incorporating solid accumulation at the nodes of open-cell foams

Geometric models for incorporating solid accumulation at the nodes of open-cell foams

Heat transfer intensification in compact tubular reactors with cellular internals: A pilot-scale assessment of highly conductive packed-POCS with skin applied to the Fischer-Tropsch synthesis

Heat management poses severe constraints when designing non-adiabatic multi-tubular packed-bed reactors for strongly exothermic or endothermic catalytic processes. The exploitation of conduction in the solid matrix of engineered continuous internals (e.g., honeycomb monoliths, open-cell foams, periodic open-cell structures) as a heat transfer mechanism alternative, or possibly additional, to fluid-phase convection, is a promising strategy to relax some of these constraints, offering new opportunities for the intensification of catalytic reactors. Preliminary experimental data and modelling studies show that this is particularly true for compact-scale applications, when conductive internals are packed with catalyst micro-pellets. In this work, through pilot-scale testing, we show that overall heat transfer coefficients as high as 1300 W/m2/K can be achieved in periodic open-cell structures (POCS) made of a highly conductive aluminium alloy, 3D printed with an external continuous skin and packed with 300–400 μm catalyst micro-pellets. To this aim, a Fischer-Tropsch experimental campaign has been carried out in a pilot-scale rig, using an established 20 wt% Co/Al2O3 catalyst formulation and a tubular reactor (28.80 mm I.D., 20 cm catalyst bed length) externally cooled with an isothermal diathermic oil. Thanks to the outstanding heat transfer properties of the packed-POCS reactor, by progressively increasing the oil temperature from 180 °C to 225 °C, once-through CO conversions as high as 70 % have been measured at gas hourly space velocities exceeding 4000 cm3(STP)/h/gcat, resulting in C5+ yields in excess of 0.35 g/h/gcat, with a CH4 selectivity always below 15 %. Such performances, made possible by the intensified heat management granted by the adopted reactor internals, are among the best ever reported for a compact-scale Fischer-Tropsch tubular reactor.

Optimization of an Open-Cell Foam-Based Ni-Mg-Al Catalyst for Enhanced CO2 Hydrogenation to Methane

In the presented work, the catalytic performance of a nickel catalyst, in CO2 hydrogenation to methane, within a ZrO2 open-cell foam (OCF)-based catalyst was studied. Two series of analogous samples were prepared and coated with 100–150 mg of a Mg-Al oxide interface to stabilize the formation of well-dispersed Ni crystallites, with 10–15 wt% of nickel as an active phase, based on 30 ppi foam or 45 ppi foam. The main factor influencing catalytic performance was the geometric parameters of the applied foams. The series of catalysts based on 30 ppi OCF showed CO2 conversion in the range of 30–50% at 300 °C, while those based on 45 ppi OCF resulted in a significantly enhancement of the catalytic activity: 90–92% CO2 conversion under the same experimental conditions. Calculations of the internal and external mass transfer limitations were performed. The observed difference in the catalytic activity was primarily related to the radial transport inside the pores, confirmed with the explicitly higher conversions.

CO2 methanation over open cell foams prepared via chemical conversion coating

In the framework of the CO2 utilization, and of the integration of renewable energy sources into the power generation scenario, the methanation reaction plays a key role, being the core of the power-to-gas, or power-to-X, processes. Structured catalysts are widely recognized for being particularly promising in exothermic processes, as they ensure a better thermal management of the heat generated within the system. In recent years, the application of metallic structures has spread. Nevertheless, the functionalization of these structures via washcoating procedure has several disadvantages. Herein, it is highlighted the potential of ceria chemical-conversion coating (CCC) as technique for the preparation of methanation catalysts, and optimize the Ni deposition procedure on such structures. In this work, the suitability of the obtained catalysts for CO2 methanation was evaluated in several operating conditions, obtaining CO2 conversion as high as 70 % below 400 °C with the most promising sample. In a first analysis, it was demonstrated that the catalysts prepared through the CCC technique can be applied in the CO2 methanation systems. In addition, through a kinetic analysis it was highlighted that the preparation method could be a key parameter for the selectivity of the process, driving the system towards a direct CO2 methanation or to the CO-path mechanism, therefore further studies should be performed to better explore this aspect.