Behavior Of Foams Research Articles

Experimental comparison of foam flow and gas flow in municipal solid waste

Foam is found to be a special fluid (i.e., gas divided by liquid film) that exists in municipal solid waste (MSW) landfills. As a disconnected phase, the unsaturated flow behavior of foam is significantly different from that of gas in connected phase. In this study, the difference between foam flow and gas flow was characterized through displacement tests in the MSW columns. Resistance factor, which is defined as the ratio of steady pressure drop between foam displacement and gas displacement, is employed to characterize this difference. The effects of foam quality, void ratio, and particle size on resistance factor were studied. The unsaturated permeability curves of foams generated by leachate samples at different depths were measured. The leachate at the middle layer has low surface tension to produce strong foam, while the leachate at the top and bottom layers has high surface tension to produce weak foam. The unsaturated permeabilities of weak foam and strong foam were about 1 and 2 orders of magnitude smaller than that of gas, respectively. The reduction in waste void ratio decreased the resistance factor as the excessive shearing effect in small pores would cause the foam to collapse.

Investigating the foaming behavior of a soybean derived surfactant for gas well deliquification in a sparger setup

Surfactant injection is one of the common gas-well deliquification techniques to enhance gas productivity. However, most traditional chemical-based surfactants are often nonbiodegradable, toxic, and lead to environmental and potential health risks. There is a need to investigate surfactants of natural origins, soybean derived surfactants (SODS) offer promising eco-friendly alternatives. It is crucial to understand the foaming behavior of the biosurfactant and its effectiveness in the deliquification process. Therefore, the main objective of this study is to carry out a comprehensive analysis of the foaming characteristics of SODS and correlate its dynamic surface tension to the foaming properties of other known surfactant solutions using a sparger setup.The results showed that the SODS can generate stable foams and have the potential to mitigate liquid loading problems in gas wells. The bubble formation at the tip of the sparger is highly dependent on the bubble size and foam drainage, so, the surface tension reduction rate (R1/2) is inversely proportional to the bubble radius (R‾) for all the surfactants under study. Consequently, the total foam weight and foam density of SODS are determined at the top of the production column of the experimental setup, hence the liquid content of the foam (∅l) determines the foam formation for the biosurfactant. Also, the foaming qualities in terms of foamability and foam stability increase with maximum R1/2 for the all the surfactants used. The sparger configuration agrees with the Ross-Miles test for ∅l and R1/2 with the R2 value of 0.91. The study offers a novel strategy for effective gas well deliquification using surfactants with natural origins, furthering sustainable practices in the oil and gas production sector.

Improving phase change heat transfer in an enclosure partially filled by uniform and anisotropic metal foam layers

Anisotropic metal foams exhibit exceptional potential for improving the efficiency of latent heat thermal energy storage (LHTES) units by enhancing heat transfer and thermal energy storage rates. This study explores the largely uncharted area of thermal behavior of anisotropic metal foams in varied configurations and enclosure designs. The research focuses on an LHTES unit with a specific channel configuration, constructed using copper and containing three layers of copper metal foam, one of which is anisotropic and infused with paraffin wax. The finite element method was utilized to manage the complexities emerging from phase change, and the anisotropic angle varied from 0 to 90° in three different placements of the AMFL: top, middle, or bottom of the enclosure. The ideal design was achieved with an AMFL in the middle with a 0°angle, resulting in a 3.7 % reduction in melting time and approximately a 2.3 % reduction in solidification time. However, AMFL designs at the middle placement with a 75° anisotropic angle were less effective, hampering the melting and solidification processes, thus potentially extending charging and discharging times. The study concludes that the placement and angle of the AMFL layer are vital for the heat transfer capabilities of phase change materials. AMFL at the middle with a 0° angle optimally leverages temperature gradients, enhancing heat transfer compared to other investigated cases. An AMFL in the middle with a 0° angle exhibits approximately 7.1 % and 6.3 % improvements for melting fractions of 0.9 and 0.95, respectively, underscoring its potential for efficient thermal energy storage.

Effect of cell diameter variations on the mechanical behavior of aluminum foams: Experiments and modeling

Aluminum foams can be manufactured in a variety of cell sizes; however, existing models focus primarily on density and neglect the effect of cell size. Furthermore, aluminum foams with different cell diameters exhibit diverse mechanical properties. In this study, a quasi-static/dynamic compression test was performed to investigate the mechanical behavior, damage patterns, and damage mechanisms of aluminum foams with different cell diameters. The results demonstrate that the compressive properties of aluminum foams undergo significant changes. As the cell diameter increases, normalized initial damage stress and Young's modulus also increase, leading to enhanced energy absorption. However, this increase in cell diameter negatively affects the energy absorption efficiency, resulting in increased instabilities. A finite element analysis was conducted using the LS-DYNA finite element software to investigate the behavior of aluminum foils under all the experimentally tested loading regimes. The simulation results reveal that the deformation zone formed due to collapse diminishes with increasing cell diameter. More importantly, a new damage mechanism named central cell cleavage was reported, which increased the energy absorption capacity and amplified the instability during deformation. This study offers novel insights into the mechanical behaviors exhibited by aluminum foams, thereby facilitating their application in structural engineering.

Fabrication of lightweight, tough polypropylene composite foams: effects of nucleating agent structure on the foaming behavior and tensile property of polypropylene foams

Fabrication of lightweight, tough polypropylene composite foams: effects of nucleating agent structure on the foaming behavior and tensile property of polypropylene foams

Laboratory Scale Evaluation of the Slag Foaming Behavior

Due to the ambitious climate targets of the European Union, one can expect that the electric arc furnace (EAF) will gain greater importance in the future of steelmaking. Since slag foaming is a decisive factor in an efficient process, understanding this phenomenon is essential when applying hydrogen-based direct reduced iron (DRI). Therefore, a method was developed to check different slag compositions concerning their foaming behavior. Slag samples are melted, and a carbon carrier is added. After a selected reaction time, the crucible is quenched in liquid nitrogen, superficially freezing the state while foaming. Afterward, it is halved, providing metallographic examination and height measurement possibilities. Three slags were tested, MgO-saturated EAF slag, MgO-unsaturated EAF slag, and electrical Smelter-like slag. Digital and scanning electron microscopy with energy dispersive x-ray spectroscopy are used to compare the slags and evaluate the method. The Smelter slag shows no foamability, unaffected by the FeO content. Contrary, good foamability can be observed for EAF slags.

Foam drainage modeling of vertical foam column and validation with experimental results

The understanding of the mechanisms behind foam generation and the structure of foam itself form the basis of foam-related experiments for its application in Enhanced Oil Recovery and overcoming gas injection limitations. Novel insights in this paper towards the theory of foam generation can help explain experimental results and lead to improved formulas of the applied substances and concentrations. This study aims to investigate the mechanisms behind foam generation and the structure of foam by specific laboratory experiments and theoretical analyses. The liquid drainage through interconnected Plateau borders was found to be the most critical foam decay mechanism for this particular research. The justification of the foam drainage equation was demonstrated by comparing the numerical solution with the outcome of a few bulk experiments. The discrepancies were described according to the limitations of both the theory and the experimental settings. Foam modelling gives more profound knowledge in more detail of the different stages in foam drainage than experimental data can deliver, which is because of the lack of continuous measurement of foam conductivity for the foam bulk test. Therefore, a comprehension of foam modelling investigation and comparison is required to gain a deeper understanding of foam behaviour.

Multi-sensor-based process monitoring and quality assessment during laser forming of novel titanium foam to prevent cellular structure damage

Titanium foam finds its application in different fields like battery electrodes, heat exchangers, biological prosthetics, and lightweight structures for aeronautical parts. However, the inherent property of the foam to fail during mechanical loading conditions poses a challenge in providing final shape to these materials for practical applications. The present work investigates forming of Titanium foam (Ti Foam) using inline process monitoring for achieving controlled foam deformation while maintaining its quality without failure. Infrared (IR) pyrometer and laser-based displacement sensor were used to monitor the foam deformation behavior and thermal signature. The monitoring data were used to understand the process mechanism of laser forming. The bending mechanism within the foam was analysed with respect to solid sheet bending process. The correlation of the achieved bending angles, was attempted with the process parameters for surface, microstructural, elemental, and phase transformation. A critical analysis of Ti foam behavior, like surface melting, in situ oxidation, phase transformation, and formation of nano-structures on foam surface was addressed based on process parameter combinations. Micro-computed tomography (μCT) was carried out to investigate the pore deformation mechanism. Metallurgical characterisations for foam surface and phase analysis were carried out using X-ray photoelectron spectroscopy (XPS) and tunneling electron microscopy (TEM) to determine the chemical and crystallographic states of the laser-formed surface.

Biochar as a slag foaming agent in EAF – A novel experimental setup

Slag foaming practice is employed widely in electric arc furnace steelmaking to improve the energy efficiency, protect the furnace structures and reduce noise pollution. Slag foaming is typically launched by injecting fossil-based carbonaceous material (e.g. coke dust) into the melt. In this study, a novel laboratory-scale experimental setup was used for studying the substitution of fossil carbon by biochar as slag foaming agent. The setup was equipped with an injection device for feeding carbon and a camera system for observing the foaming phenomenon and recording the process. A set of experiments was conducted for studying the foaming in slag-carbon systems using two carbonaceous materials: 1) coke dust was used as a reference material and 2) a high-quality biochar was used as a possible replacement. In the experiments, sufficient foaming was achieved with both of the carbonaceous materials. The biochar produced almost equal foaming behavior as coke dust. The results indicate that biochar could be used to substitute carbon for slag foaming in the EAF.

Compressive Mechanical Behavior and Corresponding Failure Mechanism of Polymethacrylimide Foam Induced by Thermo-Mechanical Coupling.

Thermal-mechanical coupling during the molding process can cause compressive yield in the polymer foam core and then affect the molding quality of the sandwich structure. This work investigates the compressive mechanical properties and failure mechanism of polymethacrylimide (PMI) foam in the molding temperature range of 20-120 °C. First, the DMA result indicates that PMI foam has minimal mechanical loss in the 20~120 °C range and can be regarded as an elastoplastic material, and the TGA curve further proves that the PMI foam is thermally stable within 120 °C. Then, the compression results show that compared with 20 °C, the yield stress and elastic modulus of PMI foam decrease by 22.0% and 17.5% at 80 °C and 35.2% and 31.4% at 120 °C, respectively. Meanwhile, the failure mode changes from brittle fracture to plastic yield at about 80 °C. Moreover, a real representative volume element (rRVE) of PMI foam is established by using Micro-CT and Avizo 3D reconstruction methods, and the simulation results indicate that PMI foam mainly shows brittle fractures at 20 °C, while both brittle fractures and plastic yield occur at 80 °C, and most foam cells undergo plastic yield at 120 °C. Finally, the simulation based on a single-cell RVE reveals that the air pressure inside the foam has an obvious influence of about 6.7% on the yield stress of PMI foam at 80 °C (brittle-plastic transition zone).

Synergistic effects of in situ fibrillated polytetrafluoroethylene and polystyrene–butadiene block on the microcellular foaming behaviors of polyphenylene oxide modified by high‐impact polystyrene

AbstractMicrocellular foams of polyphenylene oxide/high‐impact polystyrene (PPO/HIPS) with high strength are prepared using supercritical CO2 foaming technology. The study focuses on examining the influence of polytetrafluoroethylene (PTFE) and polystyrene–butadiene block (SEBS) polymers in PPO/HIPS blends. Compared with the pure PPO/HIPS blend, the PPO/HIPS blend with 1 phr PTFE exhibits higher impact strength (7.62 kJ/m2), and the foam compressive strength is 5% larger. The PPO/HIPS foams with 1 phr PTFE (as a nucleating agent) and 5 phr SEBS (as a toughening agent) display a small cell diameter (13.73 μm) and the highest cell density (2.02 × 109 cells/cm3) compared to the pure PPO/HIPS blend. Moreover, the compressive strength of the PPO/HIPS/PTFE‐1/SEBS‐5 foam (1.63 MPa at a 5% strain) demonstrates a remarkable increase of 92% compared to that of the PPO/HIPS/PTFE‐1 foam.

Effect of foaming behavior of polypropylene foams on flame retardant properties under different weight reduction methods

AbstractIn previous studies, the effect of cell structures of polypropylene (PP) foam materials on flammability behavior had been largely overlooked. In this work, ammonium polyphosphate and pentaerythritol were used as intumescent flame retardants (IFR) for PP, and then the PP‐IFR flame retardant foams were prepared by using injection foaming technology with two different weight reduction methods (same mold volume before foaming and after foaming). The results showed that the average cell size of all the PP‐IFR flame retardant foams in the 10% to 30% weight reduction was less than 100 μm. The PP‐IFR flame retardant foams with an average cell diameter of 26.22 μm and cell density of 7.88 × 106 cells/cm3 had the best limiting oxygen index (LOI) of 27.9%. In addition, the PP‐IFR flame retardant foams with better foaming quality had a higher LOI and a denser foam carbon layer whatever the weight reduction methods, resulting in better flame retardant properties. The escape of gases from the foamed and un‐foamed areas not only reduced the concentration of flammable gases but also led to the collapse and rupture of the foam carbon layer during the combustion process. Hence, it provides guidance for preparing PP foam materials with excellent flame retardancy.

On the efficiency of uniform aluminum foam as energy-absorbing sacrificial cladding for structural blast mitigation

Aluminum foams are porous and recyclable lightweight materials with outstanding mechanical features, such as their energy absorption capabilities, their most noteworthy property. In view of these qualities, this class of material is a great candidate to use as sacrificial layers applied on structures under threat for blast load protection. Few works studied the coupled behavior between the sacrificial layer made of aluminum foams and the protected structure while commonly neglecting the nonlinearity of the protected structure and impact events caused by the foam. Nevertheless, the efficiency of the foam as an energy absorbent was not adequately addressed in all the existing works. The model suggested in the work is formulated using the shock front theory and validated against experimental results. It is designed to address physical aspects that have remained unaddressed in previous numerical models. Moreover, the model is employed to examine the efficiency of the foam as an energy absorbent, along with a novel methodology proposed in the current work, aiming to carry out adequate testing. Finally, the proposed model is used to evaluate the foam behavior against a wide range of pressure and impulse combinations, leading to unprecedented behavior in the reduction of peak displacements and consequently damage mitigation. The finding of the current study shows a new direction in testing the efficiency of sacrificial layers as energy absorbents.

Development of a friction factor correlation applicable to both wet and dry foam flow in circular vertical pipes

BackgroundFoam flow, distinguished by its low density and extensive specific surface area, is employed for the cleaning of plant systems. However, its dual nature as a gas-liquid mixture and a non-Newtonian fluid complicates the prediction of the frictional pressure drop. MethodsThis study constructed a laboratory-scale experimental setup to illustrate the upward flow behavior of aqueous foam in a vertical circular pipe, capturing the foam flow using a high-speed camera. Utilizing the collected data and images, a model was developed for the friction factor to predict the frictional pressure drop of the foam flow, under the assumption that the foam flow is a non-Newtonian, quasi-homogeneous, steady, and fully developed laminar flow. Significant findingsWet foam, characterized by small, uniformly distributed spherical bubbles, is observed at lower foam quality levels. In contrast, dry foam, marked by a larger mean bubble diameter, non-uniform bubble distributions, and slugs, is observed at higher foam quality levels. A notable inflection point in the frictional pressure drop is observed during the transition from wet to dry foam within a vertical pipe. The foam regime and frictional pressure drop characteristics of the foam flow show limited sensitivity to surfactant concentration within the experimental range. A correlation for friction factors, applicable to both wet and dry foam flows in vertical circular pipes, was developed based on the Reynolds number, exhibiting a prediction error of 23.6 %.

Investigation on foam properties of Gemini quaternary ammonium salt containing hydroxyl hydrophilic headgroup

Four Gemini quaternary ammonium salts, tetramethylene-1,4- bis [N, N-bis(hydroxypropyl)-hexa/decyloxypropylammonium] bromide (GC6/10-P) and tetramethylene-1,4-bis [N, N-bis(hydroxyethyl)-hexa/decyloxypropylammonium] bromide (GC6/10-E) were synthesized by two-step reactions. This study analyzes the foam properties, including foamability, foam stability, and foam size distribution, of GC6/10-P and GC6/10-E using the Foamscan method. The influence of surfactant concentration and gas flow rate on the properties of Gemini quaternary ammonium salt foam was also studied. Additionally, the relationship between surfactant structure and foam morphology in aqueous solutions was discussed. The results show that all four types of Gemini quaternary ammonium salt surfactants are low-foaming surfactants. The foam capacity (FC) sequence is as follows: GC10-E > GC10-P > GC6-E > GC6-P. The foamability and foam stability are enhanced with increasing surfactant concentration, which increases the adsorbed quantity of surfactant molecules at the air-water interface. The foam produced by GC6-P/E systems is the most unstable; the foam behaviors show faster Ostwald ripening and drainage process in aqueous system. It seems that 150–200 mL/min is an ideal air intake speed. The presence of hydroxyl in the molecular structure enhances the formation of hydrogen bonding between surfactants and water molecules, leading to greater molecular compactness. The results indicate that the foaming behavior of hydroxyl Gemini quaternary ammonium salts can be correlated with concentration and alkyl chains. Foamscan are proposed to research the foaming and foam stability behavior and provide a useful guide for evaluating the foamability of cationic surfactants-based systems, especially in the development of environmentally friendly foam systems suitable for low-foaming products.

Adsorption Layer Properties and Foam Behavior of Aqueous Solutions of Whey Protein Isolate (WPI) Modified by Vacuum Cold Plasma (VCP)

For years, cold plasma processing has been used as a non-thermal technology in industries such as food. As interfacial properties of protein play a remarkable role in many processes, this study investigates the effect of cold plasma on the foaming and interfacial behavior of WPI. The objective of this study is to evaluate the effect of different gases (air, 1:1 argon–air mixture, and sulfur hexafluoride (SF6)) used in low-pressure cold plasma (VCP) treatments of whey protein isolate (WPI) on the surface and foaming behavior of aqueous WPI solutions. Dynamic surface dilational elasticity, surface tension isotherms, surface layer thickness, and the foamability and foam stability were investigated in this study. VCP treatment did not significantly affect the adsorption layer thickness. However, an increase in induction time, surface pressure equilibrium value, and aggregated size is observed after SF6VCP treatment, which can be attributed to the reaction of WPI with the reactive SF6 species of the cold plasma. The surface dilational elastic modulus increased after VCP treatment, which can be related to the increased mechanical strength of the protein layer via sulfonation and aggregate formation. VCP treatment of WPI increases the foam stability, while the average diameter of foam bubbles and liquid drainage in the foam depends on the gas used for the cold plasma.

Effect of long‐chain branching structures on supercritical CO2 foaming behavior of iPB‐1 with different crystalline form ratios

AbstractTo solve the poor cellular morphology of linear iPB‐1 during supercritical CO2 foaming, the modification and the special crystalline transition behavior of iPB‐1 were used to improve its foaming performance. Based on free radical polymerization, long‐chain branching iPB‐1 is achieved. Long‐chain branching structures not only reduce crystallinity of iPB‐1, but also increase the crystallization temperature. Long‐chain branching structures can accelerate the crystalline transformation rate of iPB‐1. After annealing at room temperature for 24 h, the crystalline transformation of the raw iPB‐1 material is completed by 14%, while long‐chain branching iPB‐1 reaches 33%. The crystalline transformation of the modified iPB‐1 is completed by 85% after annealing for 48 h. Compared with the raw iPB‐1 material with crystalline form I, the introduction of long‐chain branching structures is favorable for broadening the foaming temperature interval from 10 to 20°C, while the foaming temperature interval of the long‐chain branching iPB‐1 with crystalline form II increases to 25°C. The iPB‐1 with high content of crystalline form I and long‐chain branching structures are conductive to the formation of uniform cells. This will broaden the application of iPB‐1 foam in automotive interiors, packaging, and transportation fields.

Melt Rheological and Bead Foaming Behavior of Recycled Polyethylene Terephthalate/Polybutylene Terephthalate Blends Modified with a Joncryl Chain Extender

Melt Rheological and Bead Foaming Behavior of Recycled Polyethylene Terephthalate/Polybutylene Terephthalate Blends Modified with a Joncryl Chain Extender

Enhancing Pb2+ removal efficiency in flow-through systems using flue gas desulfurization gypsum-based porous materials: Experimental and numerical studies

This study addresses the poor permeability of flue gas desulfurization (FGD) gypsum in water remediation and further explores its potential for resource utilization. FGD gypsum-based porous materials (FGPMs) were prepared using different foaming behavior as permeable reactive barrier (PRB) media materials. The dynamic removal performance of Pb2+ was investigated, and a numerical model was developed to validate the results. The findings reveal that the adsorption mechanisms of FGPMs primarily involve ion exchange and surface precipitation. Pb2+ does not alter the structure or functional groups of the materials. By optimizing the foaming behavior to enhance pore connectivity, the adsorption capacity increased from 8.78 mg/g to 13.42 mg/g, thereby extending the service life of the PRB. The presence of closed and capillary pores hinders the dynamic removal performance of Pb2+. Furthermore, the FGPMs exhibit superior removal performance at low flow rates, low concentrations, and high column heights, as confirmed by the numerical model. These results offer valuable insights for designing and optimizing FGD gypsum-based adsorption processes to remove Pb2+ from wastewater efficiently.

Effect of pore size polydispersity on the acoustic properties of high-porosity solid foams

This study investigates the influence of pore size polydispersity on the acoustic behavior of high-porosity solid foams using numerical simulations. The effect of the size of the periodic unit cell (PUC) on the transport parameters is first examined. It is found that the size of the PUC required for properly estimating the acoustic properties of random foams depends on both the analyzed transport parameter(s) and level of polydispersity. Assuming identical and constant aperture ratio of membranes, the results indicate that (i) the viscous permeability is a reliable indicator regarding the size of the PUC (a more constraining property than the other transport parameters), and (ii) high-polydispersity foams require a larger number of pores in the PUC to achieve convergence with respect to morphological characteristics and acoustic properties. The influence of polydispersity on dimensionless transport parameters is then analyzed. It is found that polydispersity has a negligible effect on the high-frequency tortuosity but induces substantial variations in the remaining macroscopic parameters. Simulations further show that the ratio of the dimensionless transport parameters does not depend on membrane aperture ratio. This important result allows us to propose a fast method to estimate the acoustic properties of a random foam from the transport parameters of monodisperse foams with different pore sizes, for each studied transport parameter. The proposed method is finally employed to characterize the pore size and polydispersity in two real foams (with and without membranes), solving an inverse problem.