Open-cell Foams Research Articles

Transient non-Fourier behavior of large surface bodies

The variety and complexity of heterogeneous materials in the engineering practice are continuously increasing, open-cell metal foams filled with phase change materials are typical examples. These are also having an impact on the recent developments in the energy industry. Earlier room temperature heat pulse experiments on macroscale foam samples showed non-Fourier over-diffusive behavior on a particular time scale. Since there is a need to investigate such complex structures on larger spatial scales and extend the one-dimensional analysis on two-, and three-dimensional settings, here we develop a two-dimensional analytical solution for the Guyer-Krumhansl and Jeffreys-type heat equations in cylindrical coordinates to investigate the transient thermal behavior of large bodies. We provide the steady-state and transient temperature and heat flux distributions for a space-dependent heat source. The solutions presented here will be helpful for the thermal characterization of complex materials and for the validation of numerical methods.

Nonlinear transient thermo-mechanical responses of porous graphene platelet-reinforced cylindrical panels under moving distributed loads

This paper is the first attempt, to the best of the authors’ knowledge, to explore the nonlinear temperature-dependent dynamic responses of a porous functionally graded graphene nanoplatelet-reinforced composite (FG-GPLRC) cylindrical panel subjected to a moving distributed load. The desired porous FG-GPLRC structure can be achieved by reasonably designing the inner pore size and GPL dispersion patterns. A temperature-dependent dynamic model is proposed by introducing the equivalent thermo-mechanical parameters of the porous FG-GPLRCs with the help of the Halpin–Tsai micromechanics model, extended rule of mixtures, and open-cell metal foam model. The nonlinear governing equations of motion of nanocomposite cylindrical panels are derived based on the first-order shear deformation theory and the standard Lagrange equation with the aid of von Kármán geometric nonlinearity. Additionally, a closed-form Navier-type solution is implemented to model the simply-supported edges of the structures. Finally, the nonlinear dynamic response is determined using the Newmark direct integration technique combined with the Newton–Raphson iterative scheme. A parametric analysis is conducted, and the results indicate that the present model can predicate the temperature-dependent buckling behaviors and transient dynamic responses of the porous FG-GPLRC cylindrical panel. It is also found that dispersing more GPLs and fabricating more internal pores near the mid-surface of the panel can greatly reduce the response amplitudes induced by the moving loads, and the moving distributed load with a shorter length can result in a higher response.

From Bioresources to Thermal Insulation Materials: Synthesis and Properties of Two-Component Open-Cell Spray Polyurethane Foams Based on Bio-Polyols from Used Cooking Oil.

Open-cell spray polyurethane foams are widely used as highly efficient thermal insulation materials with vapor permeability and soundproofing properties. Unfortunately, for the production of commercial foams, mainly non-renewable petrochemical raw materials are used. The aim of this study was to determine the possibility of completely replacing petrochemical polyols (the main raw material used in the synthesis of polyurethanes, alongside isocyanates) with bio-polyols obtained from used cooking oils, classified as waste materials. The research consisted of three stages: the synthesis of bio-polyols, the development of polyurethane foam systems under laboratory conditions, and the testing of developed polyurethane spray systems under industrial conditions. The synthesis of the bio-polyols was carried out by using two different methods: a one-step transesterification process using triethanolamine and a two-step process of epoxidation and opening oxirane rings with diethylene glycol. The obtained bio-polyols were analyzed using gel chromatography and nuclear magnetic resonance spectroscopy. The developed polyurethane foam formulations included two types of fire retardants: halogenated tris(1-chloro-2-propyl) phosphate (TCPP) and halogen-free triethyl phosphate (TEP). In the formulations of polyurethane systems, reactive amine catalysts were employed, which become incorporated into the polymer matrix during foaming, significantly reducing their emission after application. The foams were manufactured on both a laboratory and industrial scale using high-pressure spray machines under conditions recommended by commercial system manufacturers: spray pressure 80-100 bar, component temperature 45-52 °C, and component volumetric ratio 1:1. The open-cell foams had apparent densities 14-21.5 kg/m3, thermal conductivity coefficients 35-38 mW/m∙K, closed-cell contents <5%, water vapor diffusion resistance factors (μ) <6, and limiting oxygen indexes 21.3-21.5%. The properties of the obtained foams were comparable to commercial materials. The developed polyurethane spray systems can be used as thermal insulation materials for insulating interior walls, attics, and ceilings.

Analytical Fractal Model for Effective Thermal Conductivity of Open-Cell Metallic Foams With Coated Hollow Ligaments

Abstract Coating the hollow ligaments of open-cell (fluid-through) metallic foams (MFs) fabricated via the sintering route with a thin layer of graphene can improve the effective thermal conductivity (ETC) of the foam without significantly increasing its flow resistance, potentially important for thermal storage applications. However, the Euclidean geometry cannot accurately depict the random distribution of pores within MFs. To this end, the present study aims to analyze how such thin coatings affect the ETC of MF by employing the fractal theory to depict the random distribution of its open pores. Subsequently, a cubic representative structure is chosen for self-similar pores in the fractal to establish a correlation between the geometric parameters of MF and its fractal dimension. Upon determining the thermal resistance provided a representative structure of the foam having coated hollow ligaments, its ETC is derived as a function of fractal dimension, dimensionless parameters of pore size, porosity, and thermal conductivity of relevant materials (e.g., ligaments, coatings, and filling medium). For validation, existing experimental data are used to compare with analytical predictions, with good agreement achieved. It is demonstrated that the ligament hollowness weakens the thermal conduction of MFs. In addition, when the coating has a thermal conductivity greater than that of ligament, the coating enhances the ability of the foam to conduct heat. Although the ligament hollowness and coating thickness are imperative factors affecting the ETC, the material makes of ligament and coating plays a decisive role in the ETC.

Micromotion measurement at the interfaces of cemented tibial endoprosthetic replacements: A new standardized in vitro model using open-cell rigid foam.

Early aseptic loosening following primary total knee arthroplasty related to several factors might appear at the interface implant-cement or cement-bone. A standardized in vitro model might provide information on the relevance of single variable parameter of cementation including technique and cement respectively bone structure on fixation strength. Micromotion measurement using different directions of load should detect the primary stability of the interfaces. An open-cell rigid foam model was used for cementation of PFC-Sigma tibial trays with Palacos®. Pins were applied to the model for continuous non-destructive measurement. Relative micromotions for rotation, valgus-varus and extension flexion stress were detected at the interfaces as well as cement penetration was measured. The reproducibility of the measurement could be shown for all interfaces in extension-flexion movements. For rotation a negative trend was shown for the interface cement-prosthesis and cement-bone concerning varus-valgus stress reflecting varying surgical cementation technique. More micromotion related to extension-flexion force might reflect the design of the implant. Measurement of relative micromotion and cement distribution appear accurate to detect small differences of movement at different interfaces of cemented tibial implants and the results are reproducible for most parameter. An increased number of specimens should achieve statistical relevance for all measurements.

Improving volume-averaged simulations of matrix-stabilized combustion through direct X-ray µCT characterization: Application to NH3/H2-air combustion

Porous media combustion (PMC) relies on internal heat recirculation in an open-cell ceramic foam matrix to enhance the flame speed of fuels with poor combustion properties. Volume-averaged simulations are often used to study the combustion performance and pollutant emissions of such systems. However, due to the varying complexity of matrix geometries found in practical burners, as well as the wide range of closure models for the constitutive relations of the solid phase, contradicting statements about the predictive accuracy of these volume-averaged models can be found in the literature. In this work, we propose an open-source modeling framework for accurate volume-averaged PMC simulations by using first-principles methods to determine effective properties used in closure models. This framework relies on adequately characterizing the topology of the solid matrix, using commonly available X-ray computed microtomography. With this approach, significant improvements in accuracy are reported compared to empirical models from the literature. The framework based on first-principle evaluations of constitutive relations is compared against experimental measurements conducted on an interface-stabilized burner operated with premixed NH3/H2-air. The model shows good agreement for exhaust gas composition and stability limits. The proposed simulation framework performs significantly better than state-of-the-art techniques that employ commonly used empirical correlations for effective matrix properties. Statement of SignificanceWe present a new open-source simulation framework for improved characterization of porous media combustion. By utilizing µCT techniques, accurate effective matrix properties can be determined from first-principle simulations. These effective properties are used in closure models for 1D volume-averaged reacting flow simulations using appropriate sub-models for heat recirculation. This modeling framework is able to reliably predict stability limits while conventional closure models yield erroneous trends. Assessment of the resulting modeling framework is performed using experiments with exhaust gas characterization performed on a NH3/H2-air porous media burner.

Investigation of CO2 sequestration performance and statistical analysis of dye removal efficiency of liquefied hornbeam based carbon foams: Effects of biomass/solvent weight ratio, tar contribution, and chemical activation

The preparation of carbon foams from bio-based polyols was a preferable alternative for the development of new materials from waste resources. The research described the usage of wood processing factory waste for the production of open-cell carbon foams with a high application potential. Bio-based carbon foams were developed by hornbeam tree sawdust, a low-cost and renewable material for dye removal via adsorption and CO2 uptake performance. In this work, the influences of the solvent type, and solvent/biomass weight ratio on the characteristics of carbon foams were investigated in the solvolytic liquefaction process. A chemical activation process with KOH was applied to the foams and this provided high porosity and surface area (up to 1454 m2/g). Carbon foams were found to have comparable compressive strengths; up to 1.080 MPa. As a result of the statistical analysis, according to the variance analysis performed with a confidence level limit of 95%, it was specified that pH had a negative coefficient and was the most significant factor in NH dye removal. According to the experiments carried out within the scope of investigating the usability of carbon foams in the removal of pollutants from gas and liquid systems, HCFTA-3 carbon foam exhibited a maximum removal efficiency of 55.2% for NH dye when pH was 2, and HCFA-3 carbon foam had the highest CO2 holding capacity at 0 °C as measured by 6.53 mmol/g CO2. This study provided an understanding of the sustainable bio-based carbon foams from industrial waste biomass for practical application of green chemistry.

Evaluation of the Effect of Waste from Agricultural Production on the Properties of Flexible Polyurethane Foams.

The management of by-products and waste from agriculture and the agri-food industry is a challenge for the plastics industry. Flexible polyurethane foams (EPPUR) containing ground corncake from corn oil production were obtained. The influence of the bio-filler on the physico-mechanical and thermal properties of synthesized flexible polyurethane foams was investigated. The content of corncake ranged from 0 php (part per 100 parts of polyol) to 10 php. Open-cell flexible polyurethane foams with a favorable comfort factor were obtained. The lower reactivity of the developed polyurethane systems was conducive to the formation of cells of slightly smaller sizes but of a more regular shape in comparison with the foam not modified with the bio-filler. Measurements of the mechanical properties indicated that the modified foams held had similar or even better properties than the reference sample without bio-filler.

3D-Printed Graphene Nanoplatelets/Polymer Foams for Low/Medium-Pressure Sensors.

The increasing interest in wearable devices for health monitoring, illness prevention, and human motion detection has driven research towards developing novel and cost-effective solutions for highly sensitive flexible sensors. The objective of this work is to develop innovative piezoresistive pressure sensors utilizing two types of 3D porous flexible open-cell foams: Grid and triply periodic minimal surface structures. These foams will be produced through a procedure involving the 3D printing of sacrificial templates, followed by infiltration with various low-viscosity polymers, leaching, and ultimately coating the pores with graphene nanoplatelets (GNPs). Additive manufacturing enables precise control over the shape and dimensions of the structure by manipulating geometric parameters during the design phase. This control extends to the piezoresistive response of the sensors, which is achieved by infiltrating the foams with varying concentrations of a colloidal suspension of GNPs. To examine the morphology of the produced materials, field emission scanning electron microscopy (FE-SEM) is employed, while mechanical and piezoresistive behavior are investigated through quasi-static uniaxial compression tests. The results obtained indicate that the optimized grid-based structure sensors, manufactured using the commercial polymer Solaris, exhibit the highest sensitivity compared to other tested samples. These sensors demonstrate a maximum sensitivity of 0.088 kPa-1 for pressures below 10 kPa, increasing to 0.24 kPa-1 for pressures of 80 kPa. Furthermore, the developed sensors are successfully applied to measure heartbeats both before and after aerobic activity, showcasing their excellent sensitivity within the typical pressure range exerted by the heartbeat, which typically falls between 10 and 20 kPa.

Dynamics of functionally graded beams carrying a moving load with influence of porosities and partial foundation support

The novelty of the present work is to study the simultaneous influence of porosities and partial Pasternak foundation support on dynamics of functionally graded (FG) beams carrying a moving load. The beams are made from an open-cell steel foam with symmetric and asymmetric porosity distributions in the thickness direction. Based on a refined third-order shear deformation theory, a two-node beam element with ten degrees of freedom is derived and employed to construct the discretized equation of motion for the beams. Dynamic characteristics, including the time histories for mid-span deflection, dynamic magnification factor (DMF) and the stress distribution, are computed with the aid of the Newmark method. The numerical result reveals that the foundation supporting length has an important role on the dynamics of the beams, and the dependence of the DMF upon the porosity coefficient is governed by the foundation supporting length. It is also found that the asymmetric porosity distribution has more impact on the dynamic response of the beams than the symmetric one does, and the difference between the DMFs obtained from the two porosity distributions is more significant for the beam with a higher porosity coefficient. The effects of the porosities, the foundation support and the moving load velocity on the dynamic behavior of the beams are examined in detail and highlighted

Thermally induced vibration analysis of sandwich beam with metal foam core subjected to blast loading by a framework of two-unknown higher-order beam theory

Vibrational characteristics of a sandwich beam in thermal environments subjected to blast pressure are investigated in this paper. The sandwich beam is composed of two isotropic skins and an open-cell metal foam core with either uniform or symmetric distribution of internal pores. The pressure of blast loading is modelled by Friedlander’s equation. A two-unknown higher-order beam theory combined with Hamilton’s principle is used to establish the governing equations. Navier-type solution and Newmark-beta method are applied to deal with the governing equation and obtain the dynamic responses. The efficiency and accuracy of the present study are examined through numerical examples. Effects of temperature-dependent material properties, porosity coefficient, core-to-skin thickness ratio, length-to-height ratio, and structural damping on the natural frequencies and dynamic deflection of the sandwich beam are investigated in detail.

Investigating mass transfer coefficients in lean methane combustion reaction through the morphological and geometric analysis of structured open cell foam catalysts

In this work, we characterized ceramic open cell foams made of zirconia, silicon carbide and alumina of different nominal pore densities (30–45 ppi) using X-ray computed microtomography. This technique allowed the comprehensive and quantitative extraction of morphological and geometrical characteristics of the structures (pore size, strut diameter and length, node diameter, open porosity and specific geometrical surface area). An empirical model was proposed to determine the specific surface area from parameters easily accessible with standard laboratory equipment. Moreover, lean CH4 combustion tests were performed on ceramic foams coated with PdO/Co3O4 at 3 wt%. Mass transfer coefficients of the foams were measured by monitoring the oxidation reaction under diffusional control conditions. We derived a dimensionless correlation of the type Sh = A∙Rem∙Sc1/3. Finally, the pressure drop across the foams as a function of surface velocity was evaluated and compared with various experimental data and models available in the literature.

Design of sound absorbers based on open-cell foams via microstructure-based modeling

Design of sound absorbers based on open-cell foams via microstructure-based modeling

Numerical study of heat transfer and load-bearing performances of corrugated sandwich structure with open-cell metal foam

Critical engineering applications require lightweight components that can effectively dissipate heat and provide sufficient load-bearing capacity. Examples of such applications include the jet blast deflector (JBD) on an aircraft carrier and engine combustion chambers in supersonic vehicles. While lightweight corrugated sandwich structures (CSSs) exhibit excellent load-bearing capacity, their heat transfer capacity falls short. To overcome this limitation, a strategy of filling the CSS with an open-cell metal foam (MF) is proposed to create a sandwich structure with ultralight load bearing and heat transfer capabilities. Numerical simulations were conducted to study the heat transfer and load-bearing performance of this new structure. The findings indicate that the use of a MF significantly improves the heat transfer capabilities of the CSS. Compared to the CSS, the Nusselt number of MF and CSS-foam composite at a Reynolds number of 240 were enhanced by 51.3% and 102.3%, respectively. The overall thermal performance of CSS-foam composites was optimized under the same pumping power constraints. In turbulent conditions, the overall thermal performance of CSS-foam composites was 5.9% to 55.4% higher than that of CSS in turbulent conditions. Furthermore, the simulations showed that when the CSS was subjected to static and quasi-static compression, the maximum von Mises stress occurred at the connection between the panel and the web.

Comparative full-field velocimetry of liquid flow within monolithic catalyst carriers via CFD simulations and MRV measurements

In reaction engineering, reactor performance can be improved in many cases by overcoming transport limitations. This requires detailed analyses of transport phenomena in the catalytic beds. Nuclear magnetic resonance (NMR) velocimetry measurements have been utilized for analyzing mass transport of gas flows within opaque monoliths. Comparisons to full-field computational fluid dynamics (CFD) simulations, however, show significant deviations. In this study, polyethylene glycol (PEG) and 3D-printed monoliths including one open-cell foam (OCF) and one honeycomb were used to demonstrate that both operating fluid and monolith morphology influence the achievable signal-to-noise ratio and resolution of NMR data. The velocity profiles measured by NMR in OCF agreed well with full-field CFD simulations with ± 5% deviation. In addition, the similarity between the simulated and experimental velocity fields was quantified by the similarity index, which is 1 for identical images. A mean value of 0.83 was determined for a 10 PPI OCF. Thus, using PEG as the operating fluid and a 10 PPI OCF allows to improve both spatial resolution by 34% and the quality of agreement by 13 percentage points compared to the published results of gas velocimetry within 20 PPI OCF. We further identified and quantified possible sources of deviation between CFD and MRV velocity fields. By limiting our analysis to velocities higher than 45% of the maximum velocity, we could achieve similarity indices of 0.95–0.99.

Design of Aerospace Vehicles’ Thermal Protection Based on Heat-Insulating Materials with Optimal Structure

Highly porous open-cell carbon materials have great potential for use as high-temperature thermal insulation for space vehicles due to a unique combination of properties: low density, high rigidity, sufficient compressive strength, and low thermal conductivity. The physical properties of these materials essentially depend on their microstructure. This implies the possibility of constructing a new advanced technique for the optimal design of multilayer thermal protection systems for aerospace vehicles, taking into account the dependence of materials’ thermal properties on microstructure. The formulation of the optimization problem traditional to thermal design implies the determination of the layer thicknesses that provide a minimum specific mass of the thermal protection, subject to the specified constraints on the maximum temperatures in the layers. The novelty of this work lies in the fact that, along with the thickness of the layers, the design parameters include the cell diameter and porosity, which characterize the structure of highly porous cellular materials. The innovative part of the presented paper lies in the determination of cell diameter and the porosity of open-cell carbon foam together with the thickness of the layers for multilayer thermal insulation, ensuring the required operational temperature on the boundaries of the layers and a minimum of the total mass of the system. This article reveals new possibilities for using the numerical optimization method to determine the geometric parameters of the thermal protection system and the morphology of the materials used. A new methodology for designing heat-loaded structures based on the simultaneous selection of macro- and micro-parameters of the system is proposed. The basic principles of constructing an algorithm for designing a multilayer thermal protection system are outlined, taking into account the possibility of choosing the parameters of the highly porous materials’ structure. The reliability of the developed optimization method was verified by comparing the results of mathematical modeling with experimental data obtained for highly porous cellular materials with known microstructure parameters.

Magnetic Resonance Velocimetry for porous media: sources and reduction of measurement errors for improved accuracy

Nuclear Magnetic Resonance (NMR) is a powerful tool for noninvasively investigating static and dynamic properties of fluids inside complex and opaque structures. Thus, Magnetic Resonance Velocimetry (MRV) allows for the in situ analysis of the local flow velocity of fluids. Such an analysis characterises mass transport properties and helps to validate or improve numerical predictions for porous media. The benefit of such validations is lowered by several problems worsening the measurement accuracy. This publication addresses systematic errors and the influence of noise, which may reduce the accuracy of MRV measurements. Techniques are described to minimise or correct displacement and phase errors. A new multi-echo MRV-sequence is proposed as a compromise between Velocity-to-Noise Ratio (VNR), total measurement time, spatial resolution and displacement errors. For improved VNR, a dual-VENC encoding scheme was used and repetition time T_{text{R}} was optimised. As an example, the proposed MRV sequence was used to measure the three-directional flow velocity of water in an Open Cell Foam (OCF) with 10 pores per inch with three-dimensional isotropic spatial resolution.

Study on sound absorption properties of closed cell aluminum foam with different microporous structures

With the rapid development of modern society, environmental pollution is increasingly serious, among which noise pollution has become the world’s three major. At present, the methods to solve the noise problem are becoming more and more diverse. Among them, the use of porous materials for sound absorption and noise reduction is still one of the most important ways. Open-cell aluminum foam has high manufacturing costs and limited application scenarios. Therefore, some scholars have studied low-cost closed-cell aluminum foam, hoping to improve its sound absorption coefficient. Closed-cell aluminum foam is mainly used in sound insulation and has little sound absorption ability. For improving closed-cell aluminum foam sound absorption property, some scholars have researched the influence of mechanical perforation on the acoustic property of aluminum foam, but the sound absorption potential of small holes cannot be played due to the large aperture made during the process. Therefore, this paper designs and processes different aluminum foam sound absorption structures based on high-speed EDM technology and studies the effect of perforation aperture, perforation depth, and perforation rate on sound absorption peak value and sound absorption coefficient in low and middle-frequency bands (250HZ-2000Hz).

Cytotoxic Properties of Polyurethane Foams for Biomedical Applications as a Function of Isocyanate Index.

Polyurethane foams are widely used in biomedical applications due to their desirable mechanical properties and biocompatibility. However, the cytotoxicity of its raw materials can limit their use in certain applications. In this study, a group of open-cell polyurethane foams were investigated for their cytotoxic properties as a function of the isocyanate index, a critical parameter in the synthesis of polyurethanes. The foams were synthesized using a variety of isocyanate indices and characterized for their chemical structure and cytotoxicity. This study indicates that the isocyanate index highly influences the chemical structure of polyurethane foams, also causing changes in cytotoxicity. These findings have important implications for designing and using polyurethane foams as composite matrices in biomedical applications, as careful consideration of the isocyanate index is necessary to ensure biocompatibility.

Compressive mechanical properties of open-cell cubic and rhombic dodecahedron lattice structures of variable cross section fabricated by fused deposition modeling

Foams are known as structures with a high percentage of empty spaces and pores within them. Foams are classified into two categories, open-cell, and closed-cell, depending on their geometry and structure. Investigation of open-cell foams with non-uniform cross sections has been among the topics of recent studies. This research investigates the static analysis of cell foams fabricated through the additive manufacturing method. For this purpose, two structures with rhombic dodecahedron and cubic unit cells were placed under static loads using experimental, analytical, and numerical approaches. Thus, both unit cells with different relative density samples, were made with non-uniform cross-sections and validated with numerical values. Furthermore, the mechanical properties from analytical relationships were obtained for a uniform cross-section and further validated with numerical values. The open-cell porous structure built by additive manufacturing for Polylactic acid was investigated. The samples were tested under uniaxial compression with a constant strain rate, and the data obtained from the test was used to assess the structure's mechanical properties. For the analytical section, Timoshenko beam theory was utilized. Timoshenko beam theory was used in analytical solutions close to numerical results regarding yield stress, elastic modulus, and Poisson's ratio. In both unit cells, yield stress and elastic modulus were found to be increased proportionately with increasing relative density, in uniform and non-uniform conditions. By comparing the unit cells' yield stress, the impact of non-uniformity used for rhombic dodecahedron was found to be greater than cubic.