Foam Fraction Research Articles

An inverse method for estimating air volume fraction of sea foam from emissivity data

ABSTRACTThe air volume fraction (AVF) of a sea foam layer is a key parameter that affects the microwave emissivity and brightness temperature of the sea surface. To extract AVF of a sea foam layer from the measured emissivity data at microwave frequencies, a novel retrieval method is developed based on the spectral representation of effective dielectric constant of sea foam composites media, with the volume fraction of constituents and the geometry of foam microstructure included in the spectral function. In the retrieval method, the cost function of emissivity is constructed with two constraints: one is the first two moments of the spectral function and the other is derived from the spectral representation of coated spherical composites. We tested the inverse method using the simulation data of a known emissivity model with Gaussian noise. Good agreement is obtained between the inverse results and the known AVF of sea foam from the simulated emissivity data with varying sea surface temperature, salinity, and incident angle. Finally, the proposed method was used to estimate the AVF of the sea foam layer from the measured emissivity data at frequencies 1.4, 6.8, 10.8, 35, and 36.5 GHz. Generally, the retrieved values of the AVF fall in the range of 0.85–0.98. This study implies that our method can be extended to retrieve the volume fraction of constituents of other composites media from the passive microwave remote-sensing data.

Mechanical properties of non-autoclaved foam concrete: analytical models vs. experimental data

In this paper, we focus on the mechanical characterisation of non-autoclaved foam concrete according to its macro porosity (foam volume fraction). Firstly, five densities of foam concrete ranging between 600 and 1400 kg/m3 have been designed and then made by varying the volume fraction of a pre-formed organic foam within the same mortar matrix. Secondly, this range of foam concrete has been characterised experimentally by measuring their Young’s moduli and their compressive and flexural tensile strengths. Based on these experimental results, it has been confirmed that foam concrete mechanical properties decrease with the increase of its macro porosity. Besides, analytical models have been identified to predict foam concrete mechanical properties according to its macro porosity. In fact, it has been found that the Young’s modulus and the compressive strength of foam concrete can be well predicted according to its macro porosity by Balshin type power laws. Moreover, it has been shown that a Shiller type exponential law gives a good prediction for the foam concrete flexural tensile strength. Finally, it has been observed that foam concrete tensile failure becomes less brittle when its macro porosity increases.

A simple and environment-friendly approach for synthesizing macroporous polymers from aqueous foams

We propose a facile and environment-friendly approach for the preparation of macroporous polyacrylamide (PAM) via thermal-initiated polymerization of aqueous foams that are stabilized by surface-modified silica nanoparticles. Cetyltrimethylammonium bromide (CTAB) is used to delicately adjust the surface amphiphilicity of silica to stabilize aqueous foams. The air bubble size and size distribution is affected by the wettability of silica particles, solid content and air volume fraction in the foams. The morphology of macroporous polymers is observed by a scanning electron microscope (SEM). The pore and pore throat size can be tailored effectively by varying the silica content and air volume fraction. A high porosity of 83% is achieved when the air volume fraction of the aqueous foam is 65%. PAM hydrogels obtained via polymerizing aqueous foams show pronounced advantage over the ones prepared from oil-in-water (O/W) emulsions in wastewater treatment because of their unique pore structure. This strategy would also be extended to prepare other macroporous polymers with well-defined pore structures.

Low-density and structure-tunable microcellular PMMA foams with improved thermal-insulation and compressive mechanical properties

Polymer foams play an increasingly significant role in the field of thermal insulation due to their low thermal conductivities. As thermal insulation materials, their performances are primarily determined by the cellular structure. However, the correlation between the foam’s properties and its cellular structure is still not fully understood. This greatly limits the development of high-performance polymer foams with optimal cellular structures. Hereby, we report the fabrication of poly (methyl methacrylate) (PMMA) foams with widely tunable cellular structures by using CO2 as the blowing agent. In particular, the microcellular PMMA foam with a void fraction of 0.956 and with an average cell size of 4.7μm was obtained, which, to the best of knowledge, is by far the largest void fraction of polymer foam with a cell size of less than 5μm. The PMMA foam presents an excellent thermal-insulation behaviour with a thermal conductivity of as low as 29.9mW/mK. Meanwhile, the PMMA foam exhibits excellent mechanical properties due to its extremely small cell sizes. Moreover, the dependences of thermal and mechanical properties on cellular structure are obtained by independently analyzing the effects of cell size and void fraction. All these results demonstrate a promising method to fabricate environmentally friendly and economical thermal insulation materials with improved thermal-insulation and compressive mechanical properties.

Foam fractionation as a tool to study the air-water interface structure-function relationship of wheat gluten hydrolysates

Enzymatic hydrolysis of wheat gluten protein improves its solubility and produces hydrolysates with foaming properties which may find applications in food products. First, we here investigated whether foam-liquid fractionation can concentrate wheat gluten peptides with foaming properties. Foam and liquid fractions had high and very low foam stability (FS), respectively. In addition, foam fractions were able to decrease surface tension more pronouncedly than un-fractionated samples and liquid fractions, suggesting they are able to arrange themselves more efficiently at an interface. As a second objective, foam fractionation served as a tool to study the structural properties of the peptides, causing these differences in air-water interfacial behavior. Zeta potential and surface hydrophobicity measurements did not fully explain these differences but suggested that hydrophobic interactions at the air-water interface are more important than electrostatic interactions. RP-HPLC showed a large overlap between foam and liquid fractions. However, a small fraction of very hydrophobic peptides with relatively high average molecular mass was clearly enriched in the foam fraction. These peptides were also more concentrated in un-fractionated DH 2 hydrolysates, which had high FS, than in DH 6 hydrolysates, which had low FS. These peptides most likely play a key role in stabilizing the air-water interface.

Observations and parameterizations of surfzone albedo

Incident shortwave solar radiation entering the ocean depends on albedo α and plays an important role in the temperature variability and pathogen mortality of the nearshore region. As foam has an elevated albedo, open-ocean albedo parameterizations include whitecapping effects through a wind-based foam fraction. However, surfzone depth-limited wave breaking does not require wind. Surfzone albedo observations are very rare, the variability of surfzone albedo is not known, and parameterizations are not available. New, year-long upwelling and downwelling shortwave radiation observations were made from the Scripps Institution of Oceanography pier spanning the surfzone and inner-shelf. Surfzone albedo was elevated due to foam with mean observed albedo of α=0.15 and one-minute average albedo as high as α=0.45, far exceeding expected albedo (0.06) from standard parameterizations. Using a pier-mounted GoPro camera, an image-based albedo parameterization is developed that estimates the fractional foam area to derive albedo. This parameterization has high skill (r2=0.90) on time scales as short as a wave period (9 s). A second wave-model based parameterization for (hourly) averaged albedo is developed relating the non-dimensional roller energy dissipation to the mean foam fraction and thus albedo. The parameterization has good skill (r2=0.68) and resolves cross-shore albedo variations. These new parameterizations can be used where imagery is available or wave models are applicable, and can be used to constrain local heat budgets and pathogen mortality.

Foam Flow Experiments. I. Estimation of the Bubble generation-Coalescence Function

Gas injection leads to foam formation in porous media in the presence of surfactant solutions, which is used for flow diversion and enhanced oil recovery. We present here laboratory experiments of co-injecting nitrogen and sodium C14?16 alpha olefin sulfonate with two concentrations: 20× the critical micelle concentration (CMC) in an unconsolidated sandpack of 1860 Darcy and at the CMC for a Bentheimer sandstone of 3 Darcy. The steady state profile for the unconsolidated sandpack is achieved after 1.3 pore volumes, whereas for Bentheimer sandstone, steady state is obtained after injection of 12–15 pore volume. A model that leads to four equations, viz., a pressure equation, a water saturation equation, a bubble density equation and a surfactant transport–adsorption equation, is used to explain the experimental pressure drop. It is asserted that the experimental pressure drop across the measurement points can be used to obtain a first estimate of the average bubble density, which can be further used to obtain part of the source term in the bubble density equation. If we consider flowing fraction of foam, the rate of change of bubble density during transient state can be equated to the bubble density generation-coalescence function plus the terms accounted for bubble transport by convection and diffusion divided by porosity and saturation.

Sucrose substitution by polyols in sponge cake and their effects on the foaming and thermal properties of egg protein

Three polyols (maltitol, xylitol, and erythritol) were used to replace sucrose in sponge cake formulation and their effects on the foaming and thermal properties of egg protein in liquid whole egg (LWE) and the qualities of resulted sponge cake were investigated. It turned out that, the presence of maltitol acted closest to sucrose in sponge cake system. LWE with both sucrose and maltitol had relatively higher apparent viscosity and temperature of protein denaturation, while the substitution by xylitol and erythritol increased these parameters to a smaller extent. Surface tension and pH values of LWE solution with different sweeteners presented no significant difference. The replacement of sucrose by polyols increased %overrun and air phase fraction of LWE foam, indicating an increase in foaming ability, while the replacement by xylitol and erythritol reduced the foaming stability significantly (P < 0.05). The observation of microstructure of LWE foam also confirmed the effects of sucrose and polyols on the foaming properties of LWE. When compared to sucrose, the treatment with maltitol resulted in similar specific volume of sponge cake, while xylitol and erythritol significantly (P < 0.05) decreased this parameter. Positive linear relationship was observed between foam stability and specific volume of resulted sponge cake in this study.

Production and characterization of microbial biosurfactants for potential use in oil-spill remediation

Two biosurfactants, surfactin and fatty acyl-glutamate, were produced from genetically-modified strains of Bacillus subtilis on 2% glucose and mineral salts media in shake-flasks and bioreactors. Biosurfactant synthesis ceased when the main carbohydrate source was completely depleted. Surfactin titers were ∼30-fold higher than fatty acyl-glutamate in the same medium. When bacteria were grown in large aerated bioreactors, biosurfactants mostly partitioned to the foam fraction, which was recovered. Dispersion effectiveness of surfactin and fatty acyl-glutamate was evaluated by measuring the critical micelle concentration (CMC) and dispersant-to-oil ratio (DOR). The CMC values for surfactin and fatty acyl-glutamate in double deionized distilled water were 0.015 and 0.10g/L, respectively. However, CMC values were higher, 0.02 and 0.4g/L for surfactin and fatty acyl-glutamate, respectively, in 12 parts per trillion (ppt) Instant Ocean® sea salt, which has been partly attributed to saline-induced conformational changes in the solvated ionic species of the biosurfactants. The DORs for surfactin and fatty acyl-glutamate were 1:96 and 1:12, respectively, in water. In Instant Ocean® solutions containing 12ppt sea salt, these decreased to 1:30 and 1:4, respectively, suggesting reduction in oil dispersing efficiency of both surfactants in saline. Surfactant toxicities were assessed using the Gulf killifish, Fundulus grandis, which is common in estuarine habitats of the Gulf of Mexico. Surfactin was 10-fold more toxic than fatty acyl-glutamate. A commercial surfactant, sodium laurel sulfate, had intermediate toxicity. Raising the salinity from 5 to 25ppt increased the toxicity of all three surfactants; however, the increase was the lowest for fatty acyl-glutamate.

Experimental investigation of liquid foams by polarised light scattering technique via the Mueller matrix

Experiments were conducted using well-controlled bubble size-distributed foam stabilised by Sodium Dodecyl Sulphate (SDS) solution to investigate the individual effect of liquid fraction of foam on the six independent normalised Mueller matrix elements via polarised light scattering technique. The liquid fraction, bubble size distribution and the Mueller matrix elements were measured individually during a foam free drainage process. It was found that the effect of foam properties on the Mueller matrix was more obvious when the foam was in a static state. Under the circumstance that the bubble size distribution was kept almost constant during the drainage process, the six independent normalised Mueller matrix elements showed dependence on the liquid fraction except N34, whereas N22 and N33 showed the highest sensitivity. In addition, N12 and N44 exhibited reflection symmetry in the static stage during foam draining. This suggests that only five independent Mueller matrix elements are sufficient to represent the current foam because of its axisymmetry.

A Theoretical Comparative Study Between Open Cell Foam and Conventional Packed Bed in Externally Cooled Multitubular Fixed-Bed Reactors for the C1 Chemistry

The open cell foams are likely to be the next generation of catalyst supports due to their interesting specific properties (large exchange area, easy control of external porosity, etc.). In multitubular packed-bed reactors used for the C1 chemistry which constitute the focus of this work, it is well known that the removal of the reaction heat and the pressure drop are the most critical aspects for planning and designing chemical engineering processes. In this context, the objective of the present work is to compare the 'conventional' SiC spherical particles bed and SiC open cell foam bed for the C1 chemistry. From simulations, this work allows observing and quantifying the influences of the fluid velocity and the type of catalyst used (foam or packed bed) on the properties of transport. The observed responses are the total effective thermal conductivity and the pressure drop. The results indicate that it will be necessary to tune the void fraction and morphological parameters of the open cell foam in order to obtain the best compromise between pressure drop and a good thermal behavior.

Use of a voith flotation cell for removal of lipophilic extractives and Mn ions from spruce thermomechanical pulping process waters

The effects of a chelating surfactant and different foaming agents on the efficiency of cleaning process waters from a thermomechanical pulp (TMP) mill were studied in a Voith flotation cell. Turbidity measurements and gas chromatography were used to determine the removal extent and characteristics of dissolved and colloidal substances (DisCo). The metal ion content in the process waters before flotation and the metal chelate removal after flotation were determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). FiberLab™ equipment was used to characterize changes in the size of fibers present in the process waters. The results indicate that a decrease in turbidity of up to 91% and the removal of 80% of lipophilic extractives in the TMP water could be obtained using a single-stage flotation unit. Furthermore, the foam fraction was within 5% of the initial volume, and 100% of the Mn2+/chelating surfactant complex added to the TMP water was removed.

Dielectric and Radiative Properties of Sea Foam at Microwave Frequencies: Conceptual Understanding of Foam Emissivity

Foam fraction can be retrieved from space-based microwave radiometric data at frequencies from 1 to 37 GHz. The retrievals require modeling of ocean surface emissivity fully covered with sea foam. To model foam emissivity well, knowledge of foam properties, both mechanical and dielectric, is necessary because these control the radiative processes in foam. We present a physical description of foam dielectric properties obtained from the foam dielectric constant including foam skin depth; foam impedance; wavelength variations in foam thickness, roughness of foam layer interfaces with air and seawater; and foam scattering parameters such as size parameter, and refraction index. Using these, we analyze the scattering, absorption, reflection and transmission in foam and gain insights into why volume scattering in foam is weak; why the main absorption losses are confined to the wet portion of the foam; how the foam impedance matching provides the transmission of electromagnetic radiation in foam and maximizes the absorption; and what is the potential for surface scattering at the foam layers boundaries. We put all these elements together and offer a conceptual understanding for the high, black-body-like emissivity of foam floating on the sea surface. We also consider possible scattering regimes in foam.

Aerial Radiometric and Video Measurements of Whitecap Coverage

This paper presents the results of high-altitude microwave radiometric and video measurements in the presence of breaking waves made during the passage of Hurricane Dean on August 21, 2007, over the Gulf of Mexico. Previous measurements of foam fraction and radiometric brightness temperature have focused on the small scale, in which individual foam patches were of the same scale as the radiometer footprint. To work with data from spaceborne microwave radiometers, which have footprints on the scale of tens of kilometers, the knowledge of how the foam fraction sensitivity of brightness temperature scales when footprints increase from meters to kilometers is necessary. Video images of the sea surface recorded with a high-resolution monochrome digital camera were used to determine the foam fraction. Ocean-surface brightness temperature was measured with the Airborne Polarimetric Microwave Imaging Radiometer (APMIR) of the Naval Research Laboratory at frequencies of 6.6 [vertical and horizontal (VH) polarizations], 6.8 (VH), 7.2 (VH), and 10.7 GHz (V), with full polarimetric brightness temperatures measured at 19.35 and 37.0 GHz. Collocated nearly contemporaneous brightness temperatures were available from WindSat, Special Sensor Microwave Imager/Sounder, and Special Sensor Microwave/Imager satellite radiometer overpasses. Oceanographic and meteorological data were taken from buoys located along the flight track. There was good correlation between brightness temperatures measured with APMIR and satellite-borne radiometers with absolute differences largely within the expected uncertainty of the data. An analysis of the video imagery provided the fractional area coverage of the actively breaking waves on the ocean surface. The increase in brightness temperature from each of the microwave sensors was correlated with the whitecap coverage measured by the camera. The experiment not only serves as an important bridge between measurements made with spatial scales on the order of tens of meters and data collected from satellites with spatial scales of tens of kilometers but also provides guidance for improving future field measurements on this topic.

Modification of aqueous enzymatic oil extraction to increase the yield of corn oil from dry fractionated corn germ

In previous aqueous enzymatic oil extraction (AEOE) experiments we reported a best free oil yield of 49% of the hexane extracted yield of dry fractionated corn germ. In the current experiments, a dispersion of 10% cooked, dry-fractionated germ in water was treated with α-amylase, glucoamylase and a cellulase complex. Free oil was collected by centrifuging a foam fraction of the dispersion. Several dispersion treatments were tried to evaluate their release of free oil and effect on the production of foam. The foam contained up to 8% free oil (dispersed from germ containing 26% oil) and fines oil (not centrifugally separable), protein and germ particles. Treatment with α-amylase and glucoamylase prior to treatment with the commercial cellulase used in previous AEOE studies increased the free oil yields about 25–61% of the hexane-extractable yield. A preliminary cost analysis indicates that oil separation with the amylase enhanced AEOE appears to be preferable to AEOE alone and profitable if crude corn oil cost exceeds $1.1/kg ($0.50/lb).

Effect of gas type on foam film permeability and its implications for foam flow in porous media

The aim of this paper is to provide a perspective on the effect of gas type on the permeability of foam films stabilized by different types of surfactant and to present a critical overview of the tracer gas experiments, which is the common approach to determine the trapped fraction of foam in porous media. In these experiments some part of the gas is replaced by a “ tracer gas” during the steady-state stage of the experiments and trapped fraction of foam is determined by fitting the effluent data to a capacitance mass-transfer model. We present the experimental results on the measurement of the gas permeability of foam films stabilized with five surfactants (non-ionic, anionic and cationic) and different salt concentrations. The salt concentrations assure formation of either common black (CBF) or Newton black films (NBF). The experiments are performed with different single gasses. The permeability of the CBF is in general higher than that of the NBF. This behavior is explained by the higher density of the surfactant molecules in the NBF compared to that of CBF. It is also observed that the permeability coefficient, K(cm/s), of CBF and NBF for non-ionic and cationic surfactants are similar and K is insensitive to film thickness. Compared to anionic surfactants, the films made by the non-ionic surfactant have much lower permeability while the films made by the cationic surfactant have larger permeability. This conclusion is valid for all gasses. For all types of surfactant the gas permeability of foam film is largely dependent on the dissolution of gas in the surfactant solution and increases with increasing gas solubility in the bulk liquid. The measured values of K are consistent with rapid diffusion of tracer gasses through trapped gas adjacent to flowing gas in porous media, and difficulties in interpreting the results of tracer-foam experiments with conventional capacitance models. The implications of the results for foam flow in porous media and factors leading to difficulties in the modeling of trapped fraction of foam are discussed in detail. To avoid complications in the interpretation of the results, the best tracer would be one with a permeability close to the permeability of the gas in the foam. This puts a lower limit on the effective diffusion coefficient for tracer in an experiment.

Empirical Relationship between Relative Electrical Conductivity and Relative Density of the Al-Foam Fabricated through Pressure Assisted Sintering/Dissolution Process

The viability of electrical conductivity as a tool for evaluating variations in morphology of pressure assisted sintering/dissolution Al-foam compacts was investigated. In the preparation of foam specimens, the Al powder and the NaCl (leaching agent) were dry-mixed together in order to prepare homogenously mixture. The blended mixture was then subjected to pressure assisted sintering in which a pressure beyond atmospheric level is externally applied to the specimen during high-frequency induction heated sintering. The embedded leaching agent was then dissolved in order to leave behind an open-celled Al with the same chemical composition as that of the original Al powder. The final material is highly porous and has an interconnected porosity network. The structure of the resulting material has three levels of porosity (i.e. main cells, windows and microporosity). The cell morphology and the size of Al foam closely match those of the leaching particles used. The influence of processing parameters: volume fraction of leaching agent, compaction pressure at elevated temperature, sintering temperature, sintering time and heating rate on the electrical conductivity of the final foams were studied. It was found that all the chosen factors have significant effects on the physical and mechanical properties of the foam and Al volume fraction is the most important parameter affecting the relative electrical conductivity and relative density of the resultant foam. The findings also suggests that the relationship between relative electrical conductivity and density of the specimen does not follow the mathematical description given by Skrohod and Solinin, instead the power law seems to be a good characterization of the relationship between experimental data of electrical conductivity and density of the resultant foams.

The Effect of Air Foam Inclusion on the Permeability and Absorption Properties of Light Weight Soil

Cement-treated clay with air foam, which is called Super Geo-Material (SGM), was developed to utilize dredged clay in an effective way. As SGM is mainly used at levels below the ground water table, water permeability and absorption properties of SGM will affect the durability of the material. In this research, the changes in SGM permeability and absorption as functions of the air foam fraction were investigated. First, permeability tests with triaxial apparatus and constant rate of consolidation tests were conducted on samples containing less than 10% of air foam by volume. From the results, air foam was found to be an impermeable medium in SGM. Secondly, a series of permeability tests and absorption tests were conducted for the SGM with different fractions of air foam while observing the specimen with a micro focus X-ray Computed Tomography (CT) scanner. The results showed that the permeability of SGM increased dramatically due to the appearance of interior water channels when the air foam fraction exceeded 30% by volume. The density distribution change and water absorbed zones of the specimens during absorption tests were estimated using the X-ray CT data. From these results, the air in the SGM was found to be progressively substituted with water from the surface to the inside of the specimen and the substituted zone expanded as it made its way to the specimen interior. The expansion velocity of the substituted zone was not affected by the coefficient of permeability but by the fraction of the air in the specimen.

G040034 発泡アルミニウムの型成形における自重の影響([G04003]機械材料・材料加工部門一般セッション(3))

Moulding of aluminium foams from a solid bar including a foaming agent is examined. Aluminium powder mixed with a foaming agent is formed to a solid bar by hot extrusion. The solid bar is extruded into a mould by using the heated die for foaming of aluminium, and then the mould is filled with the aluminium foam from the heated die. The experiments using cylindrical moulds of different aspect ratio of height to diameter for different moulding directions are conducted. In moulding horizontally, the aluminium foam extruded from the heated die tends to go down in the mould due to self-weight when the mould diameter is large. In the case of small diameter, the aluminium does not expand enough in the mould due to friction by increasing contacting force. The volume fraction of aluminium foam to the mould inside becomes large under appropriate conditions of the aspect ratio of mould shape and the moulding direction.

Can oceanic foams limit global warming?

When the diverse methods proposed for solar radiation management are surveyed, a relatively simple, environmentally acceptable, double-acting mechanism for increasing the earth's albedo emerges. It is a low-level environmental intervention that enhances a mechanism already active in nature by increasing the foam fraction of the ocean surface. Bubble rafts increase the optical reflectivity of the ocean and when bubbles burst, they launch seasalt particles that loft and increase the number concentration of cloud droplets in the marine boundary layer, thus increasing the reflectivity of stratocumulus. A strategy based on recent research for producing microbubbles appears to be the best option for large-scale use.