Solid Foam Research Articles

Effect of bed configuration and fluid properties on dispersion in solid foams

Effect of bed configuration and fluid properties on dispersion in solid foams

A Study on a Polymeric Foam Based on Pulse Proteins and Cellulose Fibrils.

Biofoams are a challenge for scientists in terms of innovation. Incorporation of cellulose fibrils (CF), might help improve the microstructure of foams, thus this study focuses on studying the impact of CF on the foaming properties and rheology of lentil protein (LP) foams at various pH and CF concentrations. Additionally, LP-CF mixtures were transformed into solid foams, and their microstructure, physical properties, and morphology were evaluated. CF concentration significantly impacted on LP-CF foam properties, primarily due to high viscosity values. Increased CF concentration resulted in improved FS values (up to 77 min) at all pH values. This is likely attributed to associative interactions and coacervates formation. Also, foam microstructure could be related to apparent viscosity, suggesting the role of viscosity in preserving the integrity of the wet foam structure during freezing and lyophilization processes. However, elevated viscosity values might negatively impact properties such as foaming capacity and produce denser microstructures. The microstructure and morphology analysis revealed that certain foams exhibited a sponge-like structure with open pores and semi-spherical shapes, supported by CF fibers extending and forming layers. However, the structure itself was irregular. While others exhibited non-uniform, irregular pore size, and shape, along with a denser structure. These findings contribute to understanding the behavior of LP-CF mixtures, although additional investigations on mechanical properties, biodegradability, and hydrophobicity are necessary to reach their full potential for various applications.

Data-driven modelling of the multiaxial yield behaviour of nanoporous metals

Nanoporous metals, built out of complex ligament networks, can be produced with an additional level of hierarchy. The resulting complexity of the structure makes modelling of the mechanical behaviour computationally expensive and time consuming. In addition, multiaxial stresses occur in the higher hierarchy ligaments. Therefore, knowledge of the multiaxial material behaviour, including the 6D yield surface, is required. Surrogate models, predicting the mechanical behaviour of the lower level of hierarchy, represented by finite element beam models, are a promising approach to overcome such challenges, when existing analytical models are not able to describe the material behaviour. Therefore, as a first step, we studied the elastic behaviour and the yield surfaces of representative volume elements with idealised diamond and Kelvin structure in finite element simulations. The yield surfaces showed pronounced anisotropy and could not be described by the Deshpande-Fleck model for isotropic solid foams. Instead, we used data-driven and hybrid artificial neural networks, as well as data-driven support vector machines and compared them regarding their potential for the prediction of yield surfaces. All considered methods were well suited and resulted in relative errors <4.5%. Support vector machines showed the best generalisation and accuracy in 6D stress space and are suitable for extrapolation outside the range of training data.

Effective thermal diffusivity and conductivity of a fluid-saturated solid foam

The thermal properties of composite materials, such as fluid-saturated solid foams, can be estimated in two ways: using equivalent models based on both the thermal properties of the liquid and solid phases or by direct measurements, which, however, are not always straightforward. In this paper, we provide a new experimental device based on the four-layer (4L) method to measure the effective thermal diffusivity of a solid foam filled with different fluids (glycerol and water). The specific heat of the solid part is measured using differential scanning calorimetry, and the volumetric heat capacity of the composite system is estimated using an additive law. The effective thermal conductivity deduced from experiments is then compared with the maximum and minimum values obtained from the parallel and series equivalent models. The proposed 4L method is first validated by measuring the thermal diffusivity of pure water and then used afterward to measure the effective thermal diffusivity of the fluid-saturated foam. Experimental results converge with those obtained from equivalent models in the case where the different components of the system have similar thermal conductivities (e.g., glycerol-saturated foam). On the other hand, when the liquid and solid phases have very different thermal properties (e.g., water-saturated foam), the experimental results differ from what equivalent models predict. This highlights the need to make appropriate experimental measurements to estimate the overall thermal properties of these latter multicomponent systems or to consider more realistic equivalent models.

Formulation and Evaluation of Polyherbal-Spirulina Based Conditioning and Antioxidant Shampoo

Herbal shampoos are cosmetics made up of traditional ayurvedic herbs used for cleaning the hair, and scalp as that regular shampoo. The aim of the present study is to formulate a polyherbal-spirulina based conditioning and antioxidant shampoo and to assess its physiochemical function that emphasizes safety, efficacy, elimination of harmful chemical ingredients, and substitution with safe natural ingredients in different proportions. Evaluation of physicochemical properties, antioxidant activity, and toxicity analysis of herbal and spirulina based shampoo done based on parameters of physicochemical properties such as visual inspection, pH, wetting time, % of solid contents, foam volume, and stability, dirt dispersion, and conditioning performance was performed. The formulated shampoo was clear, attractive, and appealing. It showed good cleansing and detergency, good foam stability, and excellent conditioning performance.

Bone density and proximal support effects on dental implant stability – Finite element analysis and in vitro experiments

ObjectivesThe application of dental implants presents the occurrence of implant failures associated with bone proximal support. This study aims to assess implant behavior, in particular implant stability and strain distribution in the bone at different bone densities, and the effect of proximal bone support. Material and methodsThree bone densities (D20, D15, and D10) were considered in the experimental in vitro study, represented by solid rigid polyurethane foam and two conditions of bone support in the proximal region. A finite element model was developed and validated experimentally and a Branemark model at a 3:1 scale was implanted in the experiments; the model was loaded and extracted. ResultsThe results of the experimental models validate the finite element models with a correlation R2 equal to 0.899 and NMSE of 7%. The implant extraction tests for the effect of bone properties in the maximum load were 2832 N for D20 and 792 N for D10. The effect of proximal bone support changes the implant stability was observed experimentally; at 1 mm less bone support decreases by 20% of stability and at 2 mm by 58% for D15 density. ConclusionsBone properties and bone quantity are important for the initial stability of the implant. A bone volume fraction of less than 24 g/cm3 exhibits poor behavior and is not indicated for implantation. Proximal bone support reduces the primary stability of the implant and the effect is critical in lower bone density.

Experimental study on seismic behavior of fabricated lightweight steel solid waste High-strength foam concrete composite wall

In order to actively implement the “dual carbon” goal and promote the popularization and application of green energy-saving prefabricated buildings in low-rise and multi-storey residential structures in villages and towns, a prefabricated light steel solid waste high-strength foam concrete composite wall was proposed. The wall is composed of high-strength foam concrete, cold-drawn steel wire mesh and cold-formed steel, which can realize the integration of load-bearing and energy-saving of wall components. The failure characteristics, hysteresis characteristics, bearing capacity and deformation performance, stiffness degradation and energy dissipation capacity of the wall specimens with different structures were analyzed through monotonic load and in-plane lateral cyclic loading test on three different wall specimens. The results show that under the action of cyclic load, the wall specimens with three different structures all have shear failure, and the wall specimens without cold-formed steel at the ends have low bearing capacity and poor seismic behavior. The bearing capacity and seismic behavior of the wall specimens with cold-formed steel at the ends were significantly improved, and the cold-formed steel, cold-drawn steel mesh, and high-strength foam concrete had good coordination performance. Considering the inherent characteristics of foam concrete, based on the existing specifications, the formula for calculating the shear bearing capacity of the prefabricated light steel solid waste high-strength foam concrete composite wall is given. The shear bearing capacity of wall members with different structures, different loading methods and different axial compression ratios are tested and calculated, and the calculated results of shear bearing capacity are in good agreement with the test results.

Green Preparation of Lightweight, High-Strength Cellulose-Based Foam and Evaluation of Its Adsorption Properties.

In recent years, the application scope of most cellulose-based foams is limited due to their low adsorbability and poor recyclability. In this study, a green solvent is used to extract and dissolve cellulose, and the structural stability of the solid foam is enhanced by adding a secondary liquid via the capillary foam technology, and the strength of the solid foam is improved. In addition, the effects of the addition of different gelatin concentrations on the micro-morphology, crystal structure, mechanical properties, adsorption, and recyclability of the cellulose-based foam are investigated. The results show that the cellulose-based foam structure becomes compact, the crystallinity is decreased, the disorder is increased, and the mechanical properties are improved, but its circulation capacity is decreased. When the volume fraction of gelatin is 2.4%, the mechanical properties of foam are the best. The stress of the foam is 55.746 kPa at 60% deformation, and the adsorption capacity reaches 57.061 g/g. The results can serve as a reference for the preparation of highly stable cellulose-based solid foams with excellent adsorption properties.

Thermal gelation of cellulose based suspensions

A more sustainable future calls for bio-based alternatives to replace plastic foams for various applications, such as packaging, insulation and cushioning. Some bio-based foams emerging in scientific publications are fabricated using liquid foam templating and methyl cellulose as well as fibers as main constituents. Scaling up of the production, however, requires a comprehensive understanding of the rheology of the foam during the shaping and drying processes. In this article, we report rheological studies of cellulose based systems in the context of thermal gelation. In more precise terms, we study how the presence of cellulose fibers and other additive materials influences the thermal gelation properties of methyl cellulose. We observe that the rheological properties, while heavily dependent on the material composition, are reasonably adjustable by appropriate material choices. The fibers are seen to decrease the temperature required for methyl cellulose to undergo a viscoelastic transition which is useful in the solid foam fabrication process. We anticipate that in the present application, the fibers increase the stability of the desired structure during the drying stage of the foam.

Versatile Assembly of Metal-Phenolic Network Foams Enabled by Tannin-Cellulose Nanofibers.

Metal-phenolic network (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNFs) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesivemetal-phenolic layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe(III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application.

Experimental investigation on the leakage plugging and fire extinguishment characteristics of industrial solid waste-based composite foam slurry materials

For understanding the leakage plugging and fire extinguishment characteristics of industrial solid waste-based composite foam slurry material (CFSM), the plugging effectiveness, thermal stability, and fire extinguishing and cooling process were analyzed systematically. The experimental device was designed to test the plugging effect of CFSM, when the thermal stability performance monitoring system and fire-extinguishing experimental platform were built to analyze the thermal stability, heat insulation properties, and extinguishment of CFSM, respectively. The results revealed that the surface temperature of CFSM with thickness more than 60 mm would not exceed the critical self-heating temperature of coal (60 °C) before reaching the equilibrium state of condensation heat, thus showing the good thermal insulation effect. The thermal conductivity of CFSM did not exceed 0.098 W/(m·k), indicating the excellent thermal insulation properties. The plugging experiments exhibited that the macroscopic plugging effect of CFSM with thickness more than 40 mm was less different from that of the completely sealed state, and the closed porosity of CFSM reached 74.5%, thus showing the well plugging performance. Moreover, the fire-extinguishing experiments indicated that CFSM could quickly flow and diffuse in burning coal, and exhibiting the well fire-extinguishing properties by covering the fire source, bonding-coating and lasting oxygen insulation. The study would provide an effective basis for the application of fire extinguishment technology using CFSM.

Gas-liquid flow regimes and effective interfacial area in a solid foam block stirred tank

Recently, a solid foam block (SFB) stirred tank has attracted wide attention owing to its excellent mass transfer efficiency. However, more fundamental information is needed to deepen the understanding of the strengthening mechanism and application of this novel stirrer. Therefore, in this work, the flow regimes and the effective interfacial area as the crucial information for the mass transfer process in the SFB stirred tank are investigated by high-speed imaging and the Danckwerts-plot technique. Four typical flow regimes are revealed in the SFB stirred tank, which corresponds to the three changes in the effective interfacial area from 30 to 1490 m − 1 when adjusting the operating conditions. Correlations are respectively developed with the deviation of ±10% and ±15% to distinguish the flow regimes and predict the effective interfacial area in SFB stirred tank. Compared with the Rushton stirred tank, the SFB stirred tank is able to generate two times effective interfacial areas at fixed power input, showing superior performance and the promising prospect in some certain multiphase application fields.

Effects of hollow skeleton on melting process in copper foam

The compositing of porous medium and phase change material is an effective way to improve the heat transfer performance of solid-liquid phase change energy storage system. In this paper, we reconstruct the three-dimensional numerical structure of the copper foam by using the micro computed tomography, and then conduct the pore-scale numerical simulation of the melting process in a cubic cavity filled with the phase change material comprised of the copper foam via the lattice Boltzmann method. The effects of the hollow skeleton on the melting process are discussed in detail under different Rayleigh numbers and ratios of thermal conductivity of the copper foam to that of the phase change material. The results show that the hollow skeleton copper foam possesses a lower average Nusselt number along the left wall at the early stage of the melting process, a slower melting rate, and a higher energy storage efficiency than the solid skeleton copper foam. Comparing with the skeleton region of the copper foam, the heat transfer rate entering the cubic cavity through the hollow region of the skeleton is almost negligible. Because of the competition between heat conduction and natural convection, the heat transfer enhancement efficiency of copper foam first increases, then decreases, and then increases again with the increase of the Fourier number. When the Rayleigh number decreases, the energy storage efficiency increases, and the natural convection also weakens. Meanwhile, the fluctuation of the heat transfer enhancement efficiency decreases as the Fourier number increases, and the gap of the heat transfer enhancement efficiency between the hollow skeleton copper foam and the solid skeleton copper foam becomes smaller. When the ratio of the thermal conductivity of the copper foam skeleton to that of the phase change material increases, the energy storage efficiency is relatively high at the early stage of the melting process but becomes relatively low when the melting process is completed. With a larger thermal conductivity ratio, the heat transfer rate entering the cubic cavity through the skeleton region of the copper foam becomes dominant, which reduces the effect of the hollow skeleton on heat transfer, and thus the gap of the heat transfer enhancement efficiency between the hollow skeleton copper foam and the solid skeleton copper foam becomes relatively small.

Investigation of flow and heat transfer behavior of integrated pin fin-aluminum foam heat sink

• A novel aluminium foam heat sink (AFHS) consisting of pin fin inserts is proposed. • The developed mathematical model is validated with experimental data. • Thermo-hydraulic characteristics of proposed heat sinks are numerically studied. • Pin fin inserts lead to an enhancement on the heat removal capability of AFHS. • Pressure drop along the flow direction increases with pin fin insertion into AFHS. With the rapid development in the electronics industry, the thermal management of high power density electronic products (HPDEPs) has become very important and requires innovative heat removal technologies. In this study, an integrated heat sink (IHS) fabricated by combining aluminum foam and pin-finned heat sink configurations that are frequently used in the cooling of electronic products has been proposed as an effective solution for the thermal management of HPDEPs. The heat removal and pressure drop characteristics of the IHS were numerically investigated for its various design conditions such as the length/height ratio ( L/H ), fin profile, fin/foam height ratio ( H fin /H foam ), and heat sink/fin volume ratio ( V hs /V f ) over the range of Reynolds ( Re Dh ) number from 500 to 3500 by using the COMSOL Multiphysics v5.4. Before the numerical study was performed, to verify the outcomes of the developed simulation models, some of the IHS subjected to the numerical study were fabricated and their pressure drop and heat removal performances were experimentally examined in the range of Re Dh from 596 to 3551. As a result of the study, it was found that the thermal contact resistance ( TCR ) between the IHS and the heated surface has a greater effect on the Nusselt ( Nu ) number compared to the TCR between the solid fins and aluminum foam. The in-line or staggered arrangement of pin fins inside the aluminum foam did not lead to any significant difference in the overall performance of investigated IHS. For all the IHS examined, an increase in Re Dh results in a similar increase in the Nu and ΔP along the flow direction. In general, the most efficient IHS among the investigated ones in terms of the H fin /H foam ratio is the IHS with half-length fins, H fin /H foam =15/30. Average values of thermal performance factor ( ƞ) of the IHS with H fin /H foam ratio of 15/30 in in-line and staggered arrangement over the Re Dh number studied are 1.3 and 1.25 times higher relative to IHS with H fin /H foam ratio of 30/15. For a fixed number of fins, η of the IHS with fins of 4mm diameter is superior up to Re Dh =2000, after which, the situation varies in favor of the 8mm solid finned aluminum foam heat sink. Increasing the fin diameter from 4mm to 12mm in both fin configurations worsens the average value of ƞ by 10%. For a constant fin diameter, IHSs with 9 fins in in-line and 8 fins in staggered configuration have the highest ƞ when the Re Dh is greater than 2500 and 2000, respectively. Among the fin profiles examined, the IHS with elliptical fins is found to have the highest η , with a value of 1.24, at Re Dh =3500.

Early freezing dynamics of an aqueous foam.

Phase-change is an essential and unavoidable process to obtain solid foam. We study experimentally the solidification dynamics of a model aqueous foam in contact with a cold substrate. The substrate temperature, the foam bubble radius and the liquid fraction are changed. We show that the freezing dynamics always starts by following a self-similar square root of time diffusive dynamics. These early dynamics are then predicted as a function of the control parameters using a 1D diffusion model and by treating our foam as a homogeneous fluid with equivalent thermophysical properties. In particular, we build a new expression for the foam conductivity. Finally, experimental and theoretical results are compared and interpreted. This study paves the way towards the understanding of the complex foam freezing dynamics at longer times, when the freezing is then coupled to water migration in the foam.

Effect of Copper Foam Baffles on Thermal Hydraulic Performance for Staggered Arrangement in a Duct

Metal foam is a novel material recently utilized in baffles as an alternative to solid baffles for reducing flow resistance. However, copper foam baffles have been suggested in this research to overcome this issue. So, the experimental tests were carried out in a manufactured square channel (250 mm x 250 mm) and heated uniformly at the bottom wall of the test section.Its walls are mounted copper foam baffles at a fixed porosity of 95%.Baffles were fixed alternatively on the top and bottom of the walls in staggered mode between two successive baffles (center to center) and were kept constant at 250 mm. The experimental work was done for different grades of the pore density of copper foam (10, 15, and 20 pores per inch (PPI)) with a window cut ratio of 25% and a constant heat flux of 4.4 kW/m2.Reynolds number was varied from 3.8x104 to 5.4x104. The data for conventional copper solid baffles were used to compare the effect of foam metal baffles.The obtained results manifested that relative to the solid-copper baffles, the copper foam baffles have a greatly lower friction factor, whereas the friction factor for the solid baffles and copper foam baffles (10, 15, and 20) PPI is about (460), and (20, 29, and 38) times, respectively above the smooth surface. Moreover, the results of previous work predicted the present experimental work very well.

Formulation and Evaluation of Polyherbal Shampoo Containing Different Herbal extract

The aim of the present study is to formulate and evaluate polyherbal shampoo containing natural ingredients with an emphasis on safety and efficacy. It clears dirt and dandruff, promotes hair growth, luster, strengthens and darkens the hair. The shampoo is prepared by taking the polyherbal extract from Hibiscus Flowers, Pomegranate Peels, Neem Leaves, Curry Leaves, Shikakai and Amla Fruit in different proportions. Several physicochemical tests were performed for visual assessment, wetting time, pH, viscosity, assurance of solid contents, surface tension, dirt dispersion, conditioning performance and foam stability. The formulated polyherbal shampoo is brown in color with demonstrable good froth stability, good cleansing ability, low surface tension, optimum pH and conditioning activity. Dirt dispersion of polyherbal shampoo is light in colour along with 25 ml foam height. All these are the ideal characteristics of good quality polyherbal shampoo to be used in daily life. However, further scientific investigation is required for validation of its overall quality.

Cell walls of extruded pea snacks: Morphological and mechanical characterisation and finite element modelling

Pulses extruded foods can be envisaged asall solid foams with voids and walls, the latter being considered as a dense starch/protein composite. Pea flour (PF) and blends of pea starch and pea protein isolate (PPI) with different protein contents (0.5–88% dry basis) were extruded to obtain models of dense starch-protein composites. Their morphology was revealed by CLSM microscopy, and their mechanical properties were investigated using a three-point bending test complemented by Finite Element Method (FEM) modelling. Composite morphology revealed protein aggregates dispersed in the starch matrix. It was described by a starch-protein interface index Ii computed from the measured total area and perimeter of protein aggregates. The mechanical test showed that the extruded PF and PPI ruptured in the elastic domain, while the extruded starch-PPI (SP) blends ruptured in the plasticity domain. The mechanical properties of pea composites were weakened by increasing the particle volume fractions, including proteins and fibres, probably due to the poor adhesion between starch and the other constituents. The mechanical behaviour of pea composites did not accurately follow simple mixing laws because of their morphological heterogeneity. Modelling results show that the elastoplastic constitutive model using the Voce plasticity model satisfactorily described the hardening behaviour of SP blend composites. Reasonable agreement (2–10%) was found between the experimental and modelling approaches for most materials. The computed Young’s modulus (1.3–2.5 GPa) and saturation flow stress (20–45 MPa) increased with increasing Ii (0.7–3.1), reflecting the increase of interfacial stiffening with the increase of contact area between starch and proteins. FEM modelling allowed to identify the mechanical effect of structural heterogeneities.

Zn-doped titania nanoparticles as building blocks for solid foam filters of water and air via photocatalytic oxidation

Photocatalytic oxidation (PCO) could provide energy-efficient purification of water and air. Its efficacy is constrained mainly by limited photocatalytic activity and active surface. To address both, solid foams with hierarchic porous structures spanning multiple length-scales, stabilized by photocatalytic Zn-doped titania nanoparticles (NP) were synthesized and tested. The NP were characterized by SEM, EDS, DLS, XRD, Raman and UV–Vis spectroscopies. Solid foams were stabilized by NP complexes with cationic surfactants. The foam morphology was characterized and photocatalytic activity was demonstrated in water. The present work paves the way for the development of efficient systems for air and water purification in demanding technological sectors, such as aerospace.

Frontal polymerization-triggered simultaneous ring-opening metathesis polymerization and cross metathesis affords anisotropic macroporous dicyclopentadiene cellulose nanocrystal foam

Multifunctionality and effectiveness of macroporous solid foams in extreme environments have captivated the attention of both academia and industries. The most recent rapid, energy-efficient strategy to manufacture solid foams with directionality is the frontal polymerization (FP) of dicyclopentadiene (DCPD). However, there still remains the need for a time efficient one-pot approach to induce anisotropic macroporosity in DCPD foams. Here we show a rapid production of cellular solids by frontally polymerizing a mixture of DCPD monomer and allyl-functionalized cellulose nanocrystals (ACs). Our results demonstrate a clear correlation between increasing % allylation and AC wt%, and the formed pore architectures. Especially, we show enhanced front velocity (vf) and reduced reaction initiation time (tinit) by introducing an optimal amount of 2 wt% AC. Conclusively, the small- and wide-angle X-ray scattering (SAXS, WAXS) analyses reveal that the incorporation of 2 wt% AC affects the crystal structure of FP-mediated DCPD/AC foams and enhances their oxidation resistance.