Foaming Solution Research Articles

Wettability-independent critical heat flux during boiling crisis in foaming solutions

We present the first experimental study of surface wettability-independent critical heat flux (CHF) during boiling crisis with foaming solutions. Foaming solution refers to those aqueous surfactant solutions, which are very effective in avoiding bubble coalescence and form vapor foam. The slowly rising small bubbles in the foam crowd the heater surface to inhibit rewetting and trigger boiling crisis. Similar to the typical relation between the terminal velocity and the bubble size, we observe a power law exponent of half between the CHF and the bubble size. Such a behavior suggests that the ability of buoyancy to remove bubble swarm away from the heater surface dictates the CHF during boiling with foaming solutions. Resulting premature dryout not only reduces CHF significantly in comparison to boiling with pure water but also renders the effect of wettability improvements from micro-/nano- texturing inconsequential to CHF enhancement. Terminal velocity of the rising bubbles is estimated to model the maximum vapor-removal capacity and successfully predict the CHF over a wide range of concentrations. We further show that weakly foaming surfactants, or, the strongly foaming surfactants, but at lower concentrations, behave similar to water wherein they form large bubbles and wettability improvements via surface modifications exhibit CHF enhancements. The physical insights gained in this study can now be used to devise strategies for CHF enhancement with aqueous surfactant solutions.

Fluorinated and fluorine-free firefighting foams spread on heptane surface

The application of fluorinated firefighting foam has been restricted due to its serious environmental hazard. Thus, new fluorine-free firefighting foam formulations must be urgently developed. In this work, fluorinated and fluorine-free firefighting foams are synthesized. The spreading of the two foams on the surface of liquid fuel is achieved by using a circle stainless steel tray. Variation in the instantaneous spreading area of the foams versus time is analyzed. In addition, the effect of foam flow rate and expansion ratio (ER) on foam spreading is studied. Results indicate that an aqueous film on the heptane surface is observed during fluorinated foam spreading but not during fluorine-free foam spreading. At the same foam flow rate and ER, fluorinated foam shows faster spreading than fluorine-free foam. The foam spreading rate (FSR) increases with the increasing foam flow rate and decreases with the increasing ER. The high surface tension and great viscosity of fluorine-free foam solution are significant factors resulting in its slow spreading. Therefore, fluorine-free foam can spread on the heptane surface as fast as fluorinated foam by increasing the foam flow rate and lowering the ER.

Efficient removal of perfluorooctane sulfonate from aqueous film-forming foam solution by aeration-foam collection

Aqueous film-forming foams (AFFFs) used in fire-fighting are one of the main contamination sources of perfluorooctane sulfonate (PFOS) to the subterranean environment, requiring high costs for remediation. In this study, a method that combined aeration and foam collection was presented to remove PFOS from a commercially available AFFF solution. The method utilized the strong surfactant properties of PFOS that cause it to be highly enriched at air-water interfaces. With an aeration flow rate of 75 mL/min, PFOS removal percent reached 96% after 2 h, and the PFOS concentration in the collected foam was up to 6.5 mmol/L, beneficial for PFOS recovery and reuse. Increasing the aeration flow rate, ionic strength and concentration of co-existing surfactant, as well as decreasing the initial PFOS concentration, increased the removal percents of PFOS by increasing the foam volume, but reduced the enrichment of PFOS in the foams. With the assistance of a co-existing hydrocarbon surfactant, PFOS removal percent was above 99.9% after aeration-foam collection for 2 h and the enrichment factor exceeded 8400. Aeration-foam collection was less effective for short-chain perfluoroalkyl substances due to their relatively lower surface activity. Aeration-foam collection was found to be effective for the removal of high concentrations of PFOS from AFFF-contaminated wastewater, and the concentrated PFOS in the collected foam can be reused.

Porous materials based on foaming solutions obtained from industrial waste

This study analyzes foam concrete production efficiency. Research has shown the possibility of using a newly-designed protein-based foaming agent to produce porous materials using gypsum and cement binders. The protein foaming agent is obtained by alkaline hydrolysis of a raw mixture consisting of industrial waste in an electromagnetic field. The mixture consists of spent biomass of the Aspergillus niger fungus and dust from burning furnaces used in cement production. Varying the content of the foaming agent allows obtaining gypsum binder-based foam concretes with the density of 200-500 kg/m3 and compressive strength of 0.1-1.0 MPa, which can be used for thermal and sound insulation of building interiors. Cement binders were used to obtain structural and thermal insulation materials with the density of 300-950 kg/m3 and compressive strength of 0.9-9.0 MPa. The maximum operating temperature of cement-based foam concretes is 500°C because it provides the shrinkage of less than 2%.

Effect of operating parameters and corrosion inhibitors on foaming behavior of aqueous methyldiethanolamine solutions

Corrosion inhibitors are one of the main causes of amine foaming in gas sweetening units. A detailed understanding of amine foaming behavior in the presence of corrosion inhibitors is of great importance if the foaming is to be minimized. In this work, a comparative study was carried out to investigate the foaming tendency and bubbles characteristics of aqueous methyldiethanolamine (MDEA) in the presence of fatty acid-based (Bis(2-Hydroxyehyl)cocoalkylamine; BHCL) and hydrocarbon-based (HCB) corrosion inhibitors. The effect of different operating parameters such as nitrogen flow rate, corrosion inhibitor concentration, foaming time, solution temperature and pore size of the gas diffuser were studied using foam scan instrument. The results showed that on increasing the foaming time, solution temperature and corrosion inhibitor concentrations, the foaming tendency increased. For BHCL, the foam height tends to decrease with a high flow rate and a small pore size of the gas diffuser. Nevertheless, the opposite trend was observed in the presence of the HCB corrosion inhibitor. Depending upon the type of corrosion inhibitors, careful optimization of the operating conditions showed a high potential to minimize amine foaming.

Shear-thinning fluids for gravity and anisotropy mitigation during soil remediation in the vadose zone

Surfactant foam has been proposed as an effective treatment fluid for in situ environmental remediation of soils. In the vadose zone, it could improve treatment homogeneity, but its use remains challenging. To better understand and predict foam formation and propagation in vadose zone, we studied them in 24 soils with wide range of properties (including permeability: 2 10−12 to 3.3 10−9 m2). Foam rheology showed to be complex and mostly influenced by soil permeability and grading. Below 2 10−11 m2, foam propagation velocity was not influenced by permeability. Conversely, slight shear thinning to Newtonian behavior was observed for higher permeabilities. Benefits for remediation in anisotropic vadose zones and the injection strategies (mobility control agent or blocking agent) were discussed. Moreover, different methods of foam injection were compared over the range of soil permeability. It showed that “surfactant alternating gas” method was the most suitable for soil permeability lower than 5 10−10 m2 to avoid soil fracturing. Conversely, in higher permeability soils, pre-generated foam was required to get high viscosity foam. Foam and xanthan polymer solution behaviors were compared across the range of permeability studied. They show similarities, and the benefits of one among the other should be evaluated for each specific case.

Experimental Study on Optimization of Indoor Foaming Agent Concentration

Aiming at the selection of foaming agent in air foam flooding technology, in this paper,Ross-miles static experiment on the seven groups of surfactants at different concentrations of foam bubble height and half-life determination determines two important factors that affect the performance of a frothing agent:foaming volume and foam stability. It is also an important indicator of screening frothing agent in practical application. The experimental results show that the foaming volume and the stability of different foaming agents are different, the bubble volume of all blowing agents increased with increasing concentration, and the optimum concentration of most of the foaming agent solution is 0.5%. However, some foaming agents such as ZJ008 and KHD570A appeared foam hollow and fast defoaming at low concentration. They cannot be used as a practical frothing agent.

Influence of water to solid ratio on mechanical properties of GBFS-based geopolymer foam concrete

The development of sustainable building materials with reduced environmental footprint in both, manufacturing and operational phases of the material lifecycle, is attracting increased interest in the construction industry worldwide. A recent innovation, the geopolymer foam concrete, combines the performance benefits and operational energy savings achievable through the use of lightweight foam concrete, with the cradle-togate emissions reductions obtained through the use of a geopolymer binder derived from granulated blast-furnace slag (GBFS). In this study mechanical properties of GBFS-based foam concrete were investigated for samples of different water to solid ratio (0.252, 0.287 and 0.321). According to ASTM C 796-97 both mass of the foaming solution and water in sodium silicate solution was considered as part of the total amount of mixing water. As a solid part, GBFS and solid part of activators (NaOH and sodium silicate) was accounted. A group of specimens (40x40x160 beams and 100x100x100 cubes) have been prepared and volume density, bending, compressive strength tests have been performed. In a result an optimized lightweight GBFS-based geopolymer foam concrete was obtained, characterized by 1.8 kg/dm3 volume density, 2.6 MPa bending strength and 51.8 MPa compressive strength measured on beams and 44.1 MPa compressive strength on cubes.

Experimental Study on the Extinguishing Efficiency of Compressed Air Foam Sprinkler System on Oil Pool Fire

Abstract In order to evaluate the impact of foam qualities and foam application rates on the extinguishing efficiency of compressed air foam sprinkler system on oil pool fire, a series of large-scale gasoline fire extinguishment experiments have been conducted under different expansion ratios and foam application rates. The consumed foam solution dosages to control and extinguish the pool fire have been calculated out respectively. The result showed that foam qualities significantly affect the extinguishing efficiency and burn back resistance performance of compressed air foam sprinkler system. The optimal expansion ratios of compressed air foam was about 10:1 comprehensive considering the extinguishing performance, re-ignition resistance, burn back protection and economical efficiency. It was found that as the foam application rate increases, the fire extinguishing and burn back protection performances of compressed air foam can be evidently improved. The most economical and efficient foam application rate on gasoline pool fire was 3.48 L/ (min· m2), and the minimum foam solution dosage to 90% control and entirely extinguish the fire were 0.99 L/ m2 and 2.38 L/ m2 respectively. The research results are vital to the engineering application of compressed air foam sprinkler system.

A cooler for dense-array CPV receivers based on metal foam

Open-cell metal foams were experimentally evaluated as heat transfer enhancers in a cold plate suitable for concentrating photovoltaic (CPV) receivers. Aluminum based foams with 20, 30 and 40 pores per inch (PPI) were tested in a compact heat exchanger with forced convection of water over a range of flow rates and heating rates. Heat transfer rate and pressure drop were characterized as a function of water flow rate through the heat exchanger. The results were compared to a commercially available cooling plate solution and to previous studies with different configurations of water-cooled metal foams. The results show a better combination of heat transfer and pressure drop performance with the metal foam solution compared to the commercial cooler. Estimate of the impact on the CPV receiver performance in an example case shows that using the metal foam cooler may increase the electricity production by about 1.5%.

Self-regulation of foam volume and bubble size during foaming via shear mixing

Here we study the factors affecting the foam generation in a planetary mixer with a series of surfactant solutions, having different dynamic surface tensions, surface dilatational moduli and bulk viscosities. The foam generation in this device consists of three well defined periods: (1) Induction period during which very slow increase of the foam volume is observed. The duration of this period depends significantly on the shear rate during foaming and on the volume of the surfactant solution; (2) Fast increase of foam volume; the rate of this process depends primarily on the shear rate and dynamic surface tension of the solutions; (3) Plateau region in which the foam volume remains constant. The experimental results show that the processes of air entrapment ends when a certain critical (dimensionless) shear stress of the foam is reached. Depending on the bulk and surface properties of the surfactant solutions, this critical stress is achieved for foams with different air volume fractions and mean bubble sizes. Thus, when solutions with higher bulk viscosity and/or higher surface modulus are used, the critical stress is reached at lower air volume fraction and with smaller bubbles. Power-law equations are shown to describe very well the effects of the foaming shear rate and solution viscosity on the final foam volume and mean bubble size.

Enhancing foam stability in porous media by applying nanoparticles

ABSTRACTSeveral new foaming agent formulations (surfactants and polymers) in the presence of multi-walled carbon nanotube (MWCNT) were developed in 3% salinity (NaCl, 2.4 wt%, CaCl2, 0.6 wt%). The dispersion stability of the MWCNT and the viscosity of the solutions were examined as a prerequisite for reservoir applications. Foam was generated in situ and one-dimensional flow-through tests were performed by co-injecting air and foaming solution either in the presence of MWCNT or at particle-free condition. The pressure drop (Δp) across the sand-pack and the nanoparticles breakthrough were closely monitored. The fluid injection rate, gas fraction, and the effect of MWCNT on foams in porous media were investigated.Our results reveal that foams stabilized by the selected nanoparticles are capable of generating stronger foams leading to higher apparent Δp. The Δp profile varies with gas fraction, which largely affects the foam texture and quality. Also, the viscosity of foaming agent solutions influences Δp values. Adding MWCNT to the foaming agent solutions appears beneficial to the flooding as surfactants adsorption onto nanoparticle surfaces, which facilitates surfactants partitioning to the G/L interface.Addition of nanoparticles in the developed foam formulations leads to the formation of high-quality stronger foams in porous media, which could potentially improve the sweep efficiency and increase the oil recovery.

PHOTOTOXICITY OF SOIL, POLLUTED BY SODIUM FLOWERS FOR FIRE GASES

Annually among all types of emergencies the number of fire accidents increases, especially it occurs in natural ecological systems. An effective method of locating and extinguishing of fires in the initial stages is the foam extinguishing system appliance. In such situations, there is a problem of environmental pollution by substances that are used for fire extinguishing. During extinction the fire foam breaks up and solutions of foaming agents pollute the soil, migrate into the water. Lack of information about the fire foam impact on the soil ecosystem makes conditions for further research. The article presents the results of investigations of the influence of made in Ukraine general and special foam generators for extinguishing fires on plant growth. For the research the natural grey forest soil pollution by foaming agents was imitated. In laboratory conditions the growth plant tests proved the influence of foaming agents on the growth of the root and sprout Sinapus alba. According to the measurements results the phytotoxic effect was calculated and the level of toxicity of the soil was estimated. Samples of soils from contaminated fields were re-sampled (one and three months after contamination) for studying of dynamics of phytotoxicity changes of the soil polluted by foaming agents. Negative effects of all foaming agents for extinguishing fires on the growth of the root and shoots of plants were demonstrated. A high phytotoxic effect of special purpose foaming agents was determined over against general purpose foaming agents. It was determined that phytotoxicity of the soil contaminated by foaming agents can last for a long time (more than 3 months). The results of research proved that general-purpose foam solutions made of synthetic surfactants are the most safe for plants. To assess the dynamics of phytotoxicity changes in soil contaminated with solutions of foaming agents, soil phytotease was re-tested after 30 and 90 days of contamination. It was found that solutions of foaming agents have different effects on plants and, accordingly, different phytotoxicity of the soil. The most dangerous for plants is fresh soil pollution with solutions of foaming agents based on fluorinated hydrocarbons.

Organic pollutant loading and biodegradability of firefighting foam

Firefighting foam has been widely used as the high-performance extinguishing agent in extinguishing the liquid poor fire. It was concerned for its environmental impacts due to its massive usage. In this study, the organic loading level and the biodegradability of 18 firefighting foams commonly used in China were evaluated and compared. The COD and TOC of firefighting foam concentrates are extremely high. Furthermore, those of foam solutions are also much higher than regular wastewater. The COD/TOC ratio of synthetic foams are higher than protein foams. The 28-day biodegradation rates of 18 firefighting foams are all over 60%, indicating that they are all ready biodegradable. Protein foams (P, FP and FFFP) have the higher organic loading and lower 28-day biodegradation rates compared to the synthetic foams (Class A foam, AFFF and S). The short and long-term impact of protein foams on the environment are larger than synthetic foams.

Investigating the effect of nano-silica on efficiency of the foam in enhanced oil recovery

Due to the vast production of crude oil and consequent pressure drops through the reservoirs, secondary and tertiary oil recovery processes are highly necessary to recover the trapped oil. Among the different tertiary oil recovery processes, foam injection is one of the most newly proposed methods. In this regard, in the current investigation, foam solution is prepared using formation brine, C19TAB surfactant and air concomitant with nano-silica (SiO2) as foam stabilizer and mobility controller. The measurements revealed that using the surfactant-nano SiO2 foam solution not only leads to formation of stable foam, but also can reduce the interfacial tension mostly considered as an effective parameter for higher oil recovery. Finally, the results demonstrate that there is a good chance of reducing the mobility ratio from 1.12 for formation brine and reservoir oil to 0.845 for foam solution prepared by nanoparticles.

Emergency Obstetric Kits: Knowledge, Attitudes and Practices of Health Care Providers

More than half (58.6%) of the staff interviewed were nursing assistants. The EOK for deliveries do not contain non-sterile examination gloves, while those for cesarean sections do not have analgesics. However, most staff (72.8%) declared the delivery kit was complete; just as 74.1% declared the cesarean sections kit was complete. Only 10.0% of the staff knew that the foaming antiseptic solution was useful for simple deliveries, while 25.8% believed that Polyvidone iodine was unnecessary in the delivery kit. A minority of the staff knew that when one of the kit’s components was unavailable, the hospital pharmacist was mandated to provide them and later renew the stock at the supply center. These were 31.4% and 33.3% of the respondents surveyed on delivery and cesareansection kits respectively. Most (52.8%) gave a prescription to the family to purchase the missing component and 48.5% did not take any steps when it came to the cesarean kit.

Model Solution as a Beer Foam Standard Should Contain Fatty Acids

A reliable foam standard is needed for the beer brewing industry owing to the complexity of the beer foam matrix, its changing foaming properties over time, and interbatch variations in the product. Model foam standards proposed so far ignore the presence of foam-negative compounds. Response surface methodologies were applied to delimit the effects of components of foam standards (bovine serum albumin, ethanol, linoleic acid, and iso-α-bitter acids) on foam stability. Statistical analyses of experimental data were used to evaluate the significance of each component and their mutual interactions. The presence of linoleic acid in the foam standard was shown to be statistically important for foam stability and for interactions with individual components. A quadratic model was developed that describes alterations in foam stability as a result of changes in composition of foam standards, and this was validated by multiple measurements. A model beer foam solution can therefore be used as a reference in a brewing laboratory to validate methods of foam quality control and/or as a standard for foam research.

Investigation on stabilization of CO2 foam by ionic and nonionic surfactants in presence of different additives for application in enhanced oil recovery

Application of foam in upstream petroleum industry specifically in enhanced oil recovery (EOR) has gained significant interest in recent years. In view of this, an attempt has been paid to design the suitable foaming agents (foamer) by evaluating the influence of three surfactants, five nanoparticles and several additives. Experimental investigations have been carried out in order to examine the mechanism of foam generation in presence of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and polysorbate 80 (Tween 80) as anionic, cationic and nonionic surfactants by using the CO2 as gaseous component. It has been found that ionic surfactants show the higher foam life compared to nonionic surfactant. Out of different nano particles used, namely alumina (Al2O3) zirconium oxide (ZrO2), calcium carbonate (CaCO3), boron nitride (BN) and silica (SiO2), boron nitride shows the maximum improvement of foam stability. The foam stability of surfactant-nanoparticles foam is further increased by addition of different additives viz. polymer, alcohol and alkali. The results show that, the designed foaming solution have nearly 2.5 times higher half-decay time (t1/2) compared to the simple surfactant system. Finally, it has been found that gas injection rate plays an important role in obtaining a uniform and stabilized foam.

Экспериментальные исследования влияния конструктивных элементов оросителей на кратность воздушно-механической пены

Проведены экспериментальные исследования процесса образования воздушно-механической пены низкой кратности в розеточных оросителях с целью установления влияния отдельных элементов их конструкции на кратность получаемой пены. Проведен анализ полученных экспериментальных данных и определены наиболее перспективные направления повышения эффективности тушения пенными оросителями в автоматических установках пожаротушения.

Highly ordered biobased scaffolds: From liquid to solid foams

We propose here a liquid foam templating route using microfluidic techniques to produce biobased monodisperse chitosan foams from aqueous chitosan solutions which are stabilized with a biobased sugar surfactant. The foaming solution contained 1.5 wt % chitosan and was stabilized by 0.1 wt % surfactant. We show how microfluidics allows for the generation of bubble sizes from 200 μm to 800 μm with the help of microfluidic chips with constrictions of different sizes. Due to the monodispersity of the resulting bubbles, highly ordered liquid foams are formed. We freeze-dried the non-cross-linked chitosan liquid foams to obtain solid chitosan foams. In addition, we also cross-linked the liquid templates by genipin, a natural cross-linker, via heating at 40 °C for 2 h. The aqueous cross-linked foams were dried, either by heating at 60 °C for 18 h or by freeze-drying. We found that the drying method, as well as whether the foams were cross-linked or not, have a tremendous influence on the morphology of the solid foams.