Open-cell Foams Research Articles

Heat Transfer in 3D Laguerre–Voronoi Open-Cell Foams under Pulsating Flow

Open-cell foams are attractive for heat transfer enhancement in many engineering applications. Forced pulsations can lead to additional heat transfer enhancement in porous media. Studies of heat transfer in open-cell foams under forced pulsation conditions are limited. Therefore, in this work, the possibility of heat transfer enhancement in porous media with flow pulsations is studied by a numerical simulation. To generate the 3D open-cell foams, the Laguerre–Voronoi tessellation method was used. The foam porosity was 0.743, 0.864, and 0.954. The Reynolds numbers ranged from 10 to 55, and the products of the relative amplitude and the Strouhal numbers ranged from 0.114 to 0.344. Heat transfer was studied under the conditions of symmetric and asymmetric pulsations. The results of numerical simulation showed that an increase in the amplitude of pulsations led to an augmentation of heat transfer for all studied porosities. The maximum intensification of heat transfer was 43%. Symmetric pulsations were more efficient than asymmetric pulsations, with Reynolds numbers less than 25. The Thermal Performance Factor was always higher for asymmetric pulsations, due to the friction factor for symmetrical pulsations being much higher than for asymmetric pulsations. Based on the results of a numerical simulation, empirical correlations were obtained to predict the heat transfer intensification in porous media for a steady and pulsating flow.

Numerical Modeling of Pure and Metal-Foam Loaded PCMs

Despite many desirable properties, most phase change materials (PCMs) undergo timing issues during the phase change process due to a low thermal conductivity, which limits their application in heat storages. Thus, many techniques have been pointed out to overcome these disadvantages and improve heat transfer, such as coupling PCMs with metal inserts, like high porosity open-cell metal foams. Indeed, the presence of a metal foam increases the effective thermal conductivity of the composite medium and speeds up the charging and discharging phases. In the present paper, a numerical model developed in COMSOL ambient has been calibrated by comparison with experimental results on the melting of pure and metal-foam loaded PCMs, placed in a small case and heated from the top by an electric resistance. The numerical model considers the metal foam as a static solid, filled with a phase changing fluid and employs a literature correlation to evaluate the effective thermal conductivity of the composite medium. The performance of two different paraffinic PCMs (RT35 and RT35HC byRubitherm GmbH,D), loaded either with a copper foam (20 PPI, 95% porosity, byPorometal,China) or with an aluminum one (10 PPI, 96% porosity, byRecemat,NL) has been investigated in terms of speed rate of the phase change front, time required to complete the melting process, temperature distribution and effect of foam porosity. The obtained results clearly evidence the significant heat transfer improvement yielded by metal foams, whose presence increases the effective thermal conductivity of the composite medium (from 0.2 to 7.03 W/mK for copper foam and to 3.52 W/mK for aluminum one), leading to a significant decrease of the charging time and to a lower temperature gradient within the PCM (from about 16 to 3 K).

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

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

Quasistatic deformation analysis of melt-based molded die-cast open-cell aluminum alloy foam

Quasistatic deformation analysis of melt-based molded die-cast open-cell aluminum alloy foam

Sound Absorption Improvement in Porous Ferroelectret Polyethylene with Effective Piezoelectric Mechanism.

Airborne sound absorption in porous materials involves complex mechanisms of converting mechanical acoustic energy into heat. In this work, the effective piezoelectric properties of polyethylene ferroelectret foams on sound absorption were investigated by comparable samples with and without the piezoelectric response. Corona poling and thermal annealing treatments were applied to the samples in order to enable and remove the piezoelectric property, respectively, while the microstructure and the mechanical properties remained substantially unchanged. The effective piezoelectric properties and airborne sound absorption coefficients of the polyethylene foam samples before and after material treatments were measured and analyzed. Our experimental results and theoretical analysis showed that the open-cell ferroelectret polymer foam with an effective piezoelectric property provides an additional electromechanical energy conversion mechanism to enhance the airborne acoustic absorption performance.

A Hybrid Syntactic Foam-Based Open-Cell Foam with Reversible Actuation.

Herein, we report the first hybrid open-cell foam with revisable actuation. Open-cell foams with revisable actuation are favoable for many applications. However, it is challenging to fabricate such open-cell foams with very low density. This study presents a novel concept of creating hybrid two-way (2W) shape memory open-cell foams using two-way shape-memory-polymer-based syntactic foams as the matrix. Previously, a syntactic foam prepared by incorporating hollow glass microbubbles in the cross-linked semicrystalline cis-poly(1,4-butadiene) (cPBD) was proved to have enhanced strength and specific energy output compared to the neat cPBD. Here, the same syntactic foam was used as the matrix, and the open-cell structure was produced by the salt-leaching method. The hybrid foam exhibits very attractive properties, including reversible actuation strain up to 50%, density as low as 0.07 g/cm3, energy output up to 0.23 J/g, tensile strength up to 0.84 MPa, elongation at break as high as 339%, high thermal stability with peak decomposition temperature at 450 °C, and Joule heating and strain sensing capabilities. The tensile strength and stiffness are shown to follow the well-known Gibson-Ashby model for porous materials. Combining the open-cell structure with the reversible actuation and other functionalities enables numerous potential applications for the prepared hybrid foam, including adjustable filters, insulators, sealers, and smart scaffolds.

Experimental Studies of the Effective Thermal Conductivity of Polyurethane Foams with Different Morphologies

Polyurethane foam (PUF) is actively used for thermal insulation. The main characteristic of thermal insulation is effective thermal conductivity. We studied the effective thermal conductivity of six samples of PUF with different types and sizes of cells. In the course of the research, heat was supplied to the foam using an induction heater in three different positions: above, below, or from the side of the foam. The studies were carried out in the temperature range from 30 to 100 °C. The research results showed that for all positions of the heater, the parameter that makes the greatest contribution to the change in thermal conductivity is the cell size. Two open-cell foam samples of different sizes (d = 3.1 mm and d = 0.725 mm) have thermal conductivity values of 0.0452 and 0.0287 W/m⸱K, respectively, at 50 °C. In the case of similar cell sizes for any position of the heater, the determining factor is the type of cells. Mixed-cell foam (d = 3.28 mm) at 50 °C has a thermal conductivity value of 0.0377 W/m⸱K, and open-cell foam (d = 3.1 mm) at the same temperature has a thermal conductivity value of 0.0452 W/m⸱K. The same foam sample shows different values of effective thermal conductivity when changing the position of the heater. When the heater is located from below the foam, for example, mixed-cell foam (d = 3.4 mm) has higher values of thermal conductivity (0.0446 W/m⸱K), than if the heater is located from above (0.0390 W/m⸱K). There are different values of the effective thermal conductivity in the upper and lower parts of the samples when the heater is located from the side of the foam. At 80 °C the difference is 40% for the open-cell foam (d = 3.1 mm).

Prediction of high-temperature infrared radiative properties of nickel foam ligaments

High-temperature radiative properties of open-cell foam ligaments are rather sparse due to measurement limitation. This study aims to numerically predict the infrared radiative properties of nickel foam ligaments at high temperatures. In this work, rough surfaces of ligaments are modeled with SEM scanning pictures, and optical properties of nickel components are simulated using ab initio molecular dynamics method at 298 K, 673 K, 873 K, 1073 K and 1273 K. The reflectivity of smooth surface is determined with empirical formulas at high temperatures. Moreover, the spectral radiative properties of nickel foam ligaments are predicted with finite difference time domain method at the waveband of 0.8–8.5 μm based on the modeled surfaces and high-temperature optical properties of components. It is found high temperature can marginally strengthen radiation scattering of the ligament surfaces, while having little effect on the distribution of radiation scattering. For instance, the directional-hemispherical reflectivity increases approximately linearly with temperature. As the incident wavelength grows, the directional-hemispherical reflectivity and proportion of specular reflection both show a rapid increase in the studied waveband, while the value of reflection main peak of directional-hemispherical reflectivity declines. With the growth of incident angle, the center position of main reflection peak is moving to the direction of increasing angles. Polynomial fit is applied to anticipate the relationship between proportion of specular reflection and incident wavelength with a RSME less than 0.02. This work demonstrates a practical method for obtaining the infrared radiative properties of open-cell metal foam ligaments at high temperatures.

Washcoated open-cell foam cobalt spinel catalysts for N2O decomposition

The Co3O4 modified with 1 wt.% Cs was deposited on α-Al2O3 open-cell foam covered with different washcoats (MgO, MnO2, SiO2, TiO2), investigated by XRD, Raman microspectroscopy, nitrogen physisorption, XPS, SEM and TPR-H2 in order to elucidate interactions between Cs-Co3O4 and the washcoat and their effect on surface area, reducibility, dispersion, and low temperature decomposition of N2O. The samples with SiO2 and TiO2 washcoats had the largest surface areas. Only SiO2 did not interact with the active phase and did not change the reducibility of the catalyst. Although the same Cs concentration was adjusted during preparation of all catalysts, differences in the Cs/Co surface molar ratio were observed due to a different level of Co3O4 particles aggregation and cesium dispersion. Catalytic activity correlated with the surface Cs/Co molar ratio closely interconnected with the surface Co3+/Co2+ molar ratio while there were no direct relationships to the redox properties and surface area. The highest activity was achieved for the MgO washcoat prepared from carbonate with the highest Co3+/Co2+ molar ratio corresponding to the optimal Cs/Co surface molar ratio around 0.1.

Unconventional and Dynamically Anisotropic Thermal Conductivity in Compressed Flexible Graphene Foams.

Although a variety of methods to predict the effective thermal conductivity of porous foams have been proposed, the response of such materials under dynamic compressive loading has generally not been considered. Understanding the dynamic thermal behavior will widen the potential applications of porous foams and provide insights into methods of modifying material properties to achieve desired performance. Previous experimental work on the thermal conductivity of a flexible graphene composite under compression showed intriguing behavior: the cross-plane thermal conductivity remained approximately constant with increasing compression, despite the increasing mass density. In this work, we use molecular dynamics (MD) simulations and finite element analysis to study the variation in both the cross-plane and in-plane thermal conductivities by compressing isotropic graphene foams. We have found that, interestingly, the cross-plane thermal conductivity decreases with compression while the in-plane thermal conductivity increases; hence, the dynamic thermal transport of the graphene foam becomes anisotropic with a significant anisotropy ratio. Such observations cannot be explained by the conventional effective medium theory, which describes the increase of thermal conductivity to be proportional to mass density. Thus, we propose a model that can describe such anisotropic effective thermal conductivity of highly porous open-cell media during compression. The model is validated against the MD simulations as well as a larger-scale finite element simulation of an open-cell foam geometry.

Elastic Properties of Open Cell Metallic Foams-Modeling of Pore Size Variation Effect.

Elastic properties of open-cell metallic foams are investigated in correlation with relative density and pore size variation. A variety of foam architectures, with open porosity above 70% (relative density below 0.30) and various pore size distributions, were modeled using Laguerre–Voronoi tessellations (LVT). The coefficient of pore volume variation, CV(V), was introduced to quantify the uniformity of designed structures and ranged between 0.5 to 2.1. Elastic behavior of the modeled foams to uniaxial compression along three orthogonal directions was analyzed using the finite element (FE) method. It is shown that Young’s modulus and Poisson’s ratio of open-cell metals is not solely a function of relative density (porosity) but the pore size variation as well. For similar porosity (approx. 74–98%), Young’s modulus and Poisson’s ratio may be reduced by approx. 25–30% and 10–25%, respectively, when CV(V) increases from 0.5 to 2.1. Furthermore, the incorporation of a relationship between Young’s modulus and the coefficient of pore volume variation to the Gibson–Ashby model is proposed.

Forced convection heat transfer: A comparison between open-cell metal foams and additive manufactured kelvin cells

The Kelvin cells are normally applied to represent the open-cell metal foams for simulation due to the similar pore structure. However, the experimental comparison between Kelvin cells and open-cell metal foams is rarely reported. This study compares the forced convective heat transfer properties of four Ni70Cr30 metal foams and one GH4169 Kevin cells manufactured from additive manufacturing. The results indicate that the pressure drop and overall heat transfer coefficient (HTC) increase with the increase of PPI, while decreasing with the increase of porosity. Moreover, the comparisons between present data and data from the literature prove the reasonability of the experiments. The pressure drop and overall HTC of Kelvin cells are 64.4% and 12.3% higher than open-cell metal foams, while showing 26.2% lower overall heat transfer performance at 6 m/s. The pore structure, thicker skeleton, higher porosity, and surface roughness of Kelvin cells contribute to the higher pressure drop than open-cell metal foams. The comparison among experimental correlations and present data indicates that the correlations for predicting the behavior of open-cell metal foams could not be used directly to predict Kelvin cells.

Experimental Study of a Compact Microwave Applicator for Evaporation of Airflow-Entrained Droplets.

In many energy and process engineering systems where fluids are processed, droplet-laden gas flows may occur. As droplets are often detrimental to the system’s operation, they need to be removed. Compact engineering solutions for the removal of entrained droplets are difficult to achieve with conventional flow control and heat transfer approaches and thus droplet removal devices are hence often costly and bulky. In this study, we analyzed the potential of a compact technology based on droplet capture and in situ evaporation by microwave heating. For that, we designed a microwave applicator containing a porous droplet separator for capturing and evaporating droplets. The application of open-cell ceramic foams as filter medium reduced 99.9% of the volumetric flow of droplets, while additional microwave exposure increases reduction to 99.99%. In addition, microwave-heated foams prevent droplet re-entrainment and structure-borne liquid accumulation within foams, thus avoiding water clogging and flooding.

Morphological Features of PUR-Wood Particle Composite Foams.

The aim of this study was to apply waste wood particles (WP) with different sizes from primary wood processing as a filler for open-cell PUR foams. For this purpose, various wood particle sizes were added as a filler for polyurethane foams (PUR). The effects of the addition of of 0.05–<0.125 mm, 0.125–<0.315 mm, 0.315–1.25 mm, and >1.25–2.0 of WP to the polyurethane matrix on the density, the kinetics of PUR foaming, the cell structure, and the morphology were investigated. Scanning electron microscope (SEM) and X-ray computer tomography were used. Based on the results, it was found that the addition of WP in the amount of 10% leads to an increase in density with an increase in particle size. The research shows that the morphology of the PUR-WP foam is influenced by its particle size. The difference in the number and size of cells in PUR-WP composites depends on the wood particle size. The addition of dust causes the formation of cells of much smaller sizes; confirmed by SEM images. Moreover, computer tomography clearly demonstrates that the WP are well-dispersed within the foams’ structures.

Facile coating of Co3O4 on open-cell metallic foam for N2O catalytic decomposition

Co3O4 coated on open-cell metallic foams, which can merge the catalytic activity of Co3O4 and advantages derived from the geometry of the support, are promising for environmental applications such as the decomposition of N2O (deN2O). This study demonstrates how it is possible to easily and reproducibly prepare a well-adhered layer of Co3O4 with a similar specific surface area as the materials prepared with the precipitation method (∼ 23 m2 g−1coating) and controlled thickness on FeCrAlloy open-cell foams of different porosity and dimension by the electrosynthesis of Co(OH)2 followed by thermal treatment (600 °C). The obtained structured catalysts show stable performance after three cycles of catalytic decomposition of N2O between 250 and 550 °C, with a similar T50 of approximately 460 °C, which is comparable to the combustion or precipitated catalysts but provides a lower pressure drop. Under the operating conditions with a sequential test, the presence of NO and/or O2 in the feed gas inhibits partially the catalytic activity of the structured catalysts while the presence of H2O shows a slight enhancement in the N2O conversion at a temperature above 450 °C.

Influence of bubble departure control on nucleate pool boiling heat transfer of electrodeposited copper foam: Experiments and correlation

Pool boiling is highly suitable for cooling in various industries due to its high heat transfer capability. Among pool boiling enhancement methods, embedding open-cell metal foams to the heater surface are particularly beneficial as they increase the effective heat transfer area. In this study, by analyzing 30 samples, the effect of pore density, thickness, and channels with different diameters on copper metal foams were investigated. In addition, the electrodeposition method was used to deposit a porous layer on the edges of copper metal foam to increase boiling efficiency in atmospheric conditions with deionized water as a working fluid. As an innovation, holes with different diameters were created inside the specimens using machining to construct a suitable exit path for the bubbles. According to the results, creating a channel with a diameter of 3 mm inside foams with thicknesses of 8 mm and 10 mm, both in the untreated and electrodeposited modes, improved the heat transfer coefficient (HTC) compared to foam without the channel. On the other hand, a 5 mm diameter channel decreased boiling efficiency due to a substantial reduction in effective surface area compared to a 3 mm channel. At low heat fluxes, the electrodeposited sample with a pore density of 20 ppi, a thickness of 10 mm, and a channel diameter of 5 mm achieved an HTC of 13.56 W/cm2. K that was approximately 3.5 times higher than the plain copper sample. A high-speed camera was utilized to observe the bubble departure from the channels during changing the heat flux. Finally, by considering the dimensionless parameters of the problem, an experimental correlation was derived to predict the HTC values.

An easy-to-implement self-healing smart design for increasing impact strength and crashworthiness resistance of honeycomb sandwich structures

In this paper, the dynamic compression impact response of an aluminum honeycomb core filled with open-cell foams impregnated with self-healing liquid agents was investigated experimentally. Samples were subjected to a variety of impacts in order to determine healing time and self-healing performance. Three different sandwich specimens were developed to evaluate the effectiveness of self-healing. The sandwich specimens are designated as B (empty honeycomb core cells), S (only open-cell soft polyurethane foam-filled honeycomb core cells), and self-healing agent (SHA) (open-cell soft polyurethane foams impregnated with liquid self-healing agents). The test results were presented by considering the crashworthiness and healing efficiency criteria, and the impact characteristics of the samples were compared related to these criteria. After testing, the results demonstrated that the self-healing agent specimens had much fewer buckling deformation and displacement than their counterparts. Significant improvements were achieved in healing efficiencies and crashworthiness evaluation criteria. The peak load and the energy needed to attain peak load are considered healing efficiency criteria. Self-healing agent specimens reached 29.7% and 12.9% more peak loads, and in the energy absorbed up to peak loads 140% and 34.9% higher values than the B and S sandwiches. In the same samples, crushing strain features were acquired as 50% versus 66%, indicating less displacement in self-healing agent specimens than counterparts. The results indicated that an aluminum honeycomb sandwich structure that can heal itself after damage and recover impact characteristics remarkably could be produced practically.

Significance of SWCNTs and MWCNTs on the dynamics of hybrid nanofluid flow over a stretching surface

In this article, the hybrid nanofluid flow across the hot substrate of a heated sink coated with an open-cell metallic foam is explored to increase the rate of heat transfer. Two sorts of nanoparticles are considered to be specific MWCNT and SWCNT taking water as the base liquid. Tiny particles are examined because of their remarkable properties, such as exceptional thermal conductance, which is important in modern nano-technology, cooling systems, material sciences, and electronic parts. The primary goal of this extensive study is to improve heat transportation. The mathematical equations for the considered flow are the Navier–Stokes equations in the form of the Darcy–Brinkman–Forchheirmer model. Using similarity variables, a system of PDEs is converted into a system of dimensionless ODEs. The subsequent ODEs are settled by utilizing the numerical technique bvp4c in MATLAB. The significant results are presented with the guide of figures and tables. From this analysis, it is observed that the Xue model has a larger heat transport rate than the Yamada–Ota and Tiwari–Das models. Furthermore, the Xue model achieves a higher skin friction coefficient and Nusselt number values than the Yamada–Ota and Tiwari–Das models.

Free Vibration Analysis of a Graphene-Platelet-Reinforced, Porous, Two-Cylindrical-Panel System

In this study, a novel, dynamic model of a graphene-platelet-reinforced, porous (GPLRP) double-cylindrical-panel system is proposed. The material properties of a graphene-platelet-reinforced, porous, double-cylindrical-panel system were determined by the Halpin–Tsai micromechanics model and the typical mechanical properties of open-cell metal foams. Different types of porosity distribution and graphene platelet (GPL) distribution patterns were considered. Love’s shell theory was utilized to derive the theoretical formulation, and the Rayleigh–Ritz method was used to calculate the natural frequencies of the system. The proposed model was validated by several comparison studies with the natural frequencies in the existing literature. Finally, the effects of stiffness of Winkler springs, boundary condition, porosity coefficient, porosity distribution, GPL distribution pattern, and GPL weight fraction on the free vibration characteristics of the system were evaluated.

Random vibration study of functionally graded porous curved beams with elastically restrained ends

Firstly, the random vibration characteristics of functionally graded porous (FGP) curved beams with elastically restrained ends are studied. An efficient model is presented by the Timoshenko beam theory and spectral-Chebyshev method. In this paper, three different types of porous distribution are considered, and the relationship between porosity coefficient and material parameters is determined according to the typical mechanical properties of open cell foam metal. Four types of curved beams with different curvatures are selected for the study, which are elliptical beam, parabolic beam, hyperbolic beam and circular beam. The one-dimensional admissible displacement functions of the FGP curved beam are constructed by Chebyshev polynomials of the first kind with Gauss-Lobatto sampling points discretization. Three artificial boundary springs are used to impose elastic boundary constraints at the ends of the curved beam. The pseudo excitation method is used to apply stationary and non-stationary random excitations, including point excitation and base acceleration excitation. The stationary random vibration responses of the FGP curved beam with different boundary conditions, involving the power spectral density (PSD) and root mean square (RMS) values of displacement, velocity and acceleration, are calculated and agreed well with the finite element method (FEM). At last, the RMS values of the non-stationary random vibration response of the FGP curved beam are given.