Foam Spread Research Articles

Enhanced rheology and firefighting performance of fluorine-free soft foams through the assembly of cellulose nanofibres and cellulose nanocrystals at the air–liquid interface

In this work, we developed soft and highly stable perfluorocarbon-free foams based on cellulose nanofibres (CNFs), cellulose nanocrystals (CNCs) and alkyl polyglycoside (APG). Neither the CNCs nor the CNFs can effectively stabilise the APG foam, which is reflected in the spontaneous degradation of the foam. Interestingly, blending these two nanocelluloses and foaming resulted in an ultrastable foam. The reflective optical interference technique was used to visualise liquid flow in the liquid film, and the results showed that the foam film with a thickness of only a few tens of nanometres gained excellent mechanical stability by tuning the assembly of CNCs and CNFs at the air–liquid interface. Moreover, the interfibril interactions at the Plateau borders reduce the bubble coarsening rate and drainage rate. In pool fire extinguishing tests, increasing the total concentration of CNCs and CNFs improved the foam stability, but increasing the viscosity led to a decrease in the foam spreading rate. Thus, a formulation with 0.4 % nanocellulose has poorer firefighting performance than a formulation with 0.15 % nanocellulose. When the ratios of CNCs and CNFs are properly controlled, the burnback performance of perfluorocarbon-free foam is better than that of state-of-the-art fluorinated AFFFs for n-heptane pool fires. The sustainability of the firefighting process is considerably improved by switching to the nonperfluorinated liquid foam developed in this work.

Experimental Study on Foam Spreading on Fuel Layers with Different Thicknesses

Experimental Study on Foam Spreading on Fuel Layers with Different Thicknesses

Experimental study on upward fire spread of polyurethane foam under double fire source conditions with different restricted facade Structures

This paper examines the impact of insulation material (PU) fire spread characteristics under dual fire source conditions considering various restricted facade Structures. It is found that the merging tendency is affected by the flame inclination angle θ1 and mapping length L. Additionally, the flame merging behavior is determined by the combined effects of the chimney effect, inter-flame air entrainment, and heat transfer changes caused by the restricted angle. The Inter-flame air entrainment λ was introduced to confirm that there is a positive correlation between flame height and Inter-flame air entrainment in the large-angle restricted facade Structures (θ=120°,150°，180°). By introducing the hydraulic diameter Deff* to compare the experimental data with the previous flame pulsation frequency model, the proposed f=0.5g/Deff* model can further improve the accuracy of the prediction results. During the flame merging stage, the axial temperature field distribution on the PU board surface was compared. The study found that the restricted facade Structures resulting in a cooling effect due to fresh air entrainment at the bottom with the chimney effect. As a result, the small-angle restricted facade Structures (θ=30°，60°，90°) led to an upper-high and lower-low distribution of axial temperature.

Experimental Research on the Effectiveness of Different Types of Foam of Extinguishing Methanol / Diesel Pool Fires

ABSTRACT Storage tank fire can pose great threats to life and environment as it can cause strong radiant heat, fast-spreading flame, and destructive explosion. In this research, a 1.5 m-diameter circular steel pan is used to simulate the full surface fire of a storage tank in an industrial park. A self-built fire-extinguishing system gently releasing foam at the rate of 11.4 L/min was applied for the evaluation of the effectiveness of different types of foam of extinguishing diesel/methanol pool fires. Experiments were conducted to analyze the temperature increases of fires after releasing different types of foam. In this research, the nondimensional average temperature 0.85 and 0.71 regard as the fire extinguishing temperatures of methanol and diesel fuel, respectively. Over the spreading process, the increase in foam spreading length over time still follows the power law. The fastest flow velocity of 6% FP/AR in methanol pool fire and 6% Synthetic foams in diesel pool fire was 0.0136 m s −1and 0.044 m s −1, respectively, with a foam application rate of 11.4 L/min. The results show that, in the methanol pool fire, the cooling effect of the foam is ranked as FP/AR > AFFF > AFFF/AR > S > FP > S/AR. And the cooling effect of foam for diesel is ranked as S > S/AR > AFFF > AFFF/AR > FP > FP/AR. Foam’s cooling impact is especially notable in diesel pool fires. As for methanol pool fires, the foam extinguishing mechanism is mainly based on the “anti-soluble film” effect, which quickly forms a covering layer on the surface of the flammable liquid, seperating the flame from heat feedback and inhibiting the generation of flammable vapors, insulating itself against the air and ultimately asphyxiating the fire.

Spread of Mesalazine Rectal Foam after Single Dose in Mild Ulcer Patients

Background: The rectal foam enemas were used for ulcerative colitis of distal regions due to its desired efficacy and less side effects. The spread and persistence of the drug plays a key role in the treatment. Therefore, the objective of the present study is to study the spread and persistence of Salofalk (Mesalazine foam Enema), manufactured by Dr. Falk Pharma GmbH (mesalazine) rectal foam in mild ulcerative colitis patients.
 Methods: This is an open label, uncontrolled prospective study in ulcerative colitis patients. The patients received 2 g of mesalazine rectal foam (labelled with Tcm99) in two actuations (30 mL). The spread of the radiolabeled formulation was assessed over a period of 4 h by gamma scintigraphy.
 Results: The formulation was retained by the patients till 4 h imaging period. The foam spread in rectum, sigmoid colon and descending colon. The percentage radioactive dose exposed is more in sigmoid colon compared to rectum and descending colon in 4 h imaging period. The spread of the foam extended till descending colon for two out of 4 patients.
 Conclusion: The study results are consistent with the previous studies, and it supports the label indication. The obtained data of the present study provides in vivo evidence of the spread of formulation in the desired site of action.

Direct foam writing in microgravity

Herein we report 2D printing in microgravity of aqueous-based foams containing metal oxide nanoparticles. Such hierarchical foams have potential space applications, for example for in situ habitat repair work, or for UV shielding. Foam line patterns of a TiO2-containing foam have been printed onto glass substrates via Direct Foam Writing (DFW) under microgravity conditions through a parabolic aircraft flight. Initial characterization of the foam properties (printed foam line width, bubble size, etc.) are presented. It has been found that gravity plays a significant role in the process of direct foam writing. The foam spread less over the substrate when deposited in microgravity as compared to Earth gravity. This had a direct impact on the cross-sectional area and surface roughness of the printed lines. Additionally, the contact angle of deionized water on a film exposed to microgravity was higher than that of a film not exposed to microgravity, due to the increased surface roughness of films exposed to microgravity.

Research on the influence of foaming gas in compressed air/nitrogen foam on extinguishing the n-heptane tank fire

Tank fires threaten the lives of people and pollute the environment for their intense radiant heat, rapid fire spread and explosion hazard. Compressed air/nitrogen foam (CAF/CNF), a cleaner fire extinguishing technique used for the tank fire suppression because halogen-based agents were prohibited for environmental reasons. In this work, the influence of foaming gas in CAF/CNF on extinguishing the n-heptane tank fire was firstly investigated. Firstly, it was found that CNF spreads faster with rapid increase in foam thickness, mainly due to its better stability and less evaporation. Secondly, after foam was discharged, there existed a short increase of the combustion intensity, associated with three monotonous regions and two time delays in the whole extinguishing time. The two time delays were caused by Rayleigh–Taylor instability and flame sheet shift, respectively, and the shift distance was larger for CNF. Finally, the influential factors contributing to flame extinction were exhibited to be mainly related to the decrease in liquid burning rate and gas-phase Damkohler number. Among these factors, foam spreading rate and thickness dominated due to coupled chemical and physical extinguishing effects. Resulted from some competitive effects, CNF was slightly more efficient at extinguishing tank fires than CAF.

Environmentally Friendly Firefighting Foams Used to Fight Flammable Liquid Fire

The application of conventional aqueous film-forming foam (AFFF) has been restricted due to the environmental hazards caused by long-chain fluorocarbon surfactants. Environmentally friendly firefighting foams are urgently needed. In this study, AFFFs based on a long-chain fluorocarbon surfactant and a short-chain fluorocarbon surfactant, and fluorine-free foams based on a silicone surfactant and a mixture of foam stabilizers are prepared. The critical properties, including film-forming ability, foam stability, and foam spreading property, of foams and a commercial AFFF are investigated systematically. The fire extinguishing and burn-back performances are evaluated by a small-scale test method. Results indicate that the removal of fluorocarbon surfactants from AFFF leads to an apparent decrease in film-forming ability, foam stability, foam spreading property, and corresponding fire extinguishing performance. AFFF based on short-chain fluorocarbon surfactant shows excellent extinguishing and burn-back performances even if its film-forming ability, foam stability, and foam spreading are slightly worse than those of conventional AFFF. Although FfreeF cannot form an aqueous film and exhibits poor foam spreading, it demonstrates satisfactory fire extinguishing performance and optimal burn-back performance depending on its superhigh stability. This study can provide guidance in the development of environmentally friendly firefighting foams.

Fuel effects on aqueous film formation and foam degradation and their impact on fire suppression by foams containing fluorosurfactants

SummarySpreading coefficient, foam degradation, fuel transport through a foam layer, foam spread, and fire extinction time were collected by varying fuels for a given fluorosurfactant formulation. Varying fuel structure systematically enabled variation of foam‐fuel interactions, and spreading coefficients, which affected aqueous film formation. A wide range of spreading coefficients were studied using two foam formulations. Surfactant formulations with near‐zero or negative spreading coefficients (−1.2, −0.12 mN/m) suppressed the fires within the same time or faster than those with positive spreading coefficients (1.77, 3.28 mN/m). Both foams extinguished an iso‐octane and methylcyclohexane pool fire despite negative spreading coefficients on iso‐octane and positive spreading coefficients on methylcyclohexane. The fire extinction times collected relate more closely to foam degradation than to film formation. Foam degradation results showed a roughly 20% variation in lifetime between the two foams and the three fuels, consistent with fire extinction times. To understand the relationship between foam degradation and solution properties, a single lamella experiment was designed that monitors lamella thickness and lifetime. This experiment, relating solution to foam properties, will aid in the development of environmentally friendly surfactant replacements in firefighting foams.

Experimental investigation on the spread of aqueous foam over ethanol surface

Abstract The presence of ethanol has an adverse effect on foam spreading, and ethanol fire is difficult to extinguish with aqueous fire-fighting foams. Thus, it is necessary to explore the foam formulation suitable for ethanol fuels and study the spreading behavior of foam over ethanol surface. In the current work, stable foams based on hydrocarbon surfactant (SDS), fluorocarbon surfactant (FC1157), and polymers (XG) were prepared by using the compressed-air foam system. The spreading behaviors of foam on polar ethanol and non-polar heptane surface were observed and compared. Furthermore, the effects of stabilizer concentrations, foam flow rates and expansion ratios on foam spreading performance were investigated, respectively. The results indicate that aqueous SDS foam can spread on the heptane layer continuously, but it is difficult to cover the ethanol surface. The addition of XG and FC1157 can synergistically improve the spreading performance of aqueous foam over ethanol. Depending on stabilizer concentrations, there are remarkable differences in foam spreading behaviors. Besides, different foam application parameters including expansion ratios and foam flow rates significantly affect the foam spreading rate, despite the same foam formulation. The research methods and results guide the optimal design of foam formulations as well as the practical application of aqueous foam for ethanol fire extinguishment.

A theoretical and experimental study of extinguishing compressed air foam on an n-heptane storage tank fire with variable fuel thickness

Compressed air foam (CAF) is an environment friendly fire extinguishing technique being used around the world since the ban of halogen-based agents. In this work, its extinguishing behavior on a radiation-controlled storage tank fire was firstly investigated based on the controlling mechanism of burning rate. A formula of burning rate after foam discharge is deduced. It was found that the oleophobic effect of fluorocarbon surfactants, the increased foam layer thickness and lower diffusion coefficient had coupled chemical and physical effects on extinguishing, which outweighed the cooling effect of foam evaporation. Due to the properties of CAF, a special phenomenon of the sudden increase in the flame temperature and radiation after foam discharge was analyzed. The increase in foam spreading length with time was found to still abide by a power law under fire conditions. A concept of effective and total extinguishing time was suggested, both of which reduce with a rising foam flow rate, but the reduction rate decreases at higher flow rate. In addition, the foam dosage with flow rate had a U-shaped curve at total extinction. For the case of lower fuel thickness, its burning rate was lower and the extinguishing time was longer.

Ultrasound- and fluoroscopy-guided foam sclerotherapy for lower extremity venous ulcers

ObjectiveIn foam sclerotherapy for varicose veins, ultrasound can track the spread of foam in only one direction. We hypothesized that using fluoroscopy in combination with ultrasound can reveal the spread of foam to deep veins through perforator veins and to other varicose veins in different directions. In this study, we examined the safety and effectiveness of ultrasound- and fluoroscopy-guided foam sclerotherapy for lower extremity venous ulcers. MethodsThis retrospective study included all patients receiving ultrasound- and fluoroscopy-guided foam sclerotherapy for varicose ulcers (Clinical, Etiology, Anatomy, and Pathophysiology class 6) of the lower extremities at the Fourth Affiliated Hospital of Jiangsu University (Zhenjiang, China) between May 1, 2016, and April 30, 2018. Polidocanol foam sclerosant was injected through indwelling needles (placed every 20 cm for saphenous veins and every 5-10 cm for others) into the varicose veins. When the contrast medium in the target vessels was replaced by the hypointense foam sclerosant or on signs of foam entry into the perforator veins under fluoroscopy, the injection was stopped and the site was manually pressed. All patients received postprocedure compression with elastic bandages until ulcer healing and compression stockings (30-40 mm Hg) thereafter. ResultsA total of 35 patients (42 limbs) were included. The maximal ulcer diameter was 3.6 ± 1.4 cm (range, 1.1-5.8 cm). The number of injection sites ranged from 3 to 10; total foam amount ranged from 4.5 to 35 mL. All 35 patients completed 12-month follow-up. Ulcer healing rate was 100%, and 1-year recurrence rate was 2.9%. The Venous Clinical Severity Score was 12.98 ± 3.91 before treatment, decreasing to 3.02 ± 2.39 at 12 months (P < .01). Superficial thrombophlebitis developed in 21 (50%) limbs. No deep venous thrombosis or pulmonary embolism was observed during follow-up. Among the 33 limbs (27 patients) with ultrasound examination at 12 months, 28 (84.8%) limbs had complete occlusion and the remaining 5 (15.2%) had recanalization. ConclusionsUltrasound- and fluoroscopy-guided foam sclerotherapy is safe and effective for the treatment of venous ulcers of the lower extremities.

Characterizing the Role of Fluorocarbon and Hydrocarbon Surfactants in Firefighting-Foam Formulations for Fire-Suppression

Fluorosurfactants used in current firefighting foams must be replaced with environmentally-friendly surfactants; however, current fluorine-free surfactants have subpar fire performance. Understanding how a surfactant affects fire performance of a foam is essential for developing new fluorine-free replacement surfactants. Surfactants can affect foam’s ability to form a barrier between a fuel-pool surface and the fire, thereby suppressing the fuel feeding the fire and extinguishing it. Fire extinction performance, fuel transport through a foam layer, foam degradation by fuel, and foam spread rate were measured for solutions containing a mixture of fluorocarbon and hydrocarbon surfactants as well as the individual surfactants to understand the roles of different surfactants in a formulation. The measurements show that surfactants that reduce foam degradation and fuel transport rates through a foam covering a hot pool result in faster fire extinction. Small synergistic effects for the mixture of fluorocarbon surfactant (Cap) and a hydrocarbon surfactant (Gluc215) were found in foam degradation rate and fuel transport rate through a foam layer. The surfactant mixture had 30% longer foam lifetime and two times smaller fuel flux through a foam layer than the fluorosurfactant solution (Cap) and differed with the hydrocarbon surfactant solution (Gluc215) by more than a factor of ten. However, when a different hydrocarbon surfactant (TX100) was used in a mixture with the fluorocarbon surfactant, synergism was not observed. The small synergistic effects resulted in a small reduction in fire extinction times at high foam application rates (> 500 mL/min) at which foams can cover the pool surface quickly. At small foam application rates (< 500 mL/min), effects of foam spread rates become significant; the fluorocarbon surfactant (Cap) formed wetter foam that spread quicker and led to smaller fire extinction times than those for the surfactant mixture (Cap + Gluc215). Thus, the foam spread, foam degradation, and fuel transport rate measurements performed in the presence of a hot fuel but in the absence of a fire can explain the surfactant’s effects on fire extinction times for the six formulations. Traditionally, aqueous film formation was thought to be the key for fire suppression of AFFF rather than the foam dynamics described in this work. Additional properties such as static and dynamic surface tensions, foam bubble diameter distribution, bubble coarsening, liquid drainage from the foam, and expansion ratio were also measured in the absence of a fuel, but did not explain the trends in extinction performance among the surfactants.

Study of Environmental-Friendly Firefighting Foam Based on the Mixture of Hydrocarbon and Silicone Surfactants

The application of conventional aqueous film-forming foam (AFFF) has been severely restricted due to the serious environmental hazard caused by the key component, fluorocarbon surfactants. Environmental-friendly fluorine-free firefighting foams need to be developed urgently. In this study, five silicone surfactants are chosen as key component to prepare fluorine-free firefighting foams. The aqueous solution properties of the fluorine-free firefighting foams are studied in details, including surface tension, interfacial tension, spreading property, viscosity and foaming ability. Foam drainage and foam spread on heptane surface are analyzed. Fire extinguishing and burn-back performance of fluorine-free foams is evaluated based on a small-scale standard method. Particularly, fire extinguishing and burn-back performance of a commercial AFFF is also evaluated as a comparison. Results show that fluorine-free foams cannot form aqueous film on cyclohexane surface, no matter whether spreading coefficient is greater than zero or not. Fluorine-free foams exhibit much better foam stability but worse foam spread property than commercial AFFF. Not all the fluorine-free foams containing silicone surfactant performed as well as AFFF containing fluorocarbon surfactant. Only fluorine-free foam containing silicone surfactant of OFX-5211 shows better fire extinguishing and burn-back performance than AFFF. The higher efficiency of fluorine-free foam in fire extinguishing and burn-back should be attributed to the stronger foam stability.

Modulation of fluorocarbon surfactant diffusion with diethylene glycol butyl ether for improved foam characteristics and fire suppression

Analysis of aqueous solutions comprised of a fluorocarbon-betaine surfactant with and without diethylene glycol butyl ether (DGBE) have provided insight into the effect of DGBE on fire suppression and foam quality. Incorporation of DGBE decreased the Sauter mean bubble size and liquid drainage that resulted in faster foam spread, which lead to improved fire suppression performance at slow foam application rates. The DGBE effects were found to be relatively small at fast foam application rates. Dynamic surface tension characterization showed that diffusion of the surfactant was more rapid in the water-DGBE solvent system such that the air-liquid interface could have stabilized faster thus resulting in a smaller bubble size. The faster surfactant diffusion in the presence of DGBE is consistent with the measurements of larger micelle diffusion coefficients and smaller micelle sizes when DGBE is included with the fluorocarbon surfactant. Smaller observed micelle size provides evidence of the incorporation of DGBE into the fluorocarbon surfactant micelle within the palisade layer thus altering the micelle composition and size. Measurements of bubble size, dynamic surface tension and micelle size support altered fluorocarbon surfactant behavior in solution which resulted in the generation of a more stable foam capable of faster foam spread and fire suppression as a result of the presence of DGBE in solution.

Experimental study on thermal structure inside flame front with a melting layer for downward flame spread of XPS foam.

Thermal structure inside flame front during downward flame spread was experimentally measured for XPS foam with thicknesses of 1.6, 2.4, 3.4, and 4.4 cm. The temperature distribution and temperature gradient in the condensed phase, as well as the shape of the molten liquid, were obtained by 2-D heat transfer equations and experimental measurement. The results show that both the temperature and its temperature gradient decrease from the sample surface to the inside of the condensed phase, which results in the inclination of the melting interface. The molten layer is the thinnest near the sample surface and thicker inside the condensed phase. The adhering of the molten liquid to the wall greatly increases the thickness of the molten layer near the back wall, and the higher the thickness, the more molten material adheres to the wall. Finally, there is a relatively flat solid-liquid interface near the sample surface and a large inclined solid-liquid interface near the back of the sample, especially for the thicker samples of 3.4cm and 4.4cm. It is indicated that the distribution of the molten layer in the direction perpendicular to the plane of the XPS sheet is a significant factor for dripping and collapsing.

AFFF spread over liquid surface under external radiation conditions

Aqueous film forming foam (AFFF) is effective in extinguishing oil fires. The extinguishing effect generally depends on the foam spread process and its coverage area. In this study, the foam spread process under external thermal radiation is investigated. Firstly, based on the axisymmetric foam spread model, the relationship of radiation and foam thickness is discussed. Then foam spreading experiments under pool fire condition were carried out, to simulate the actual extinguishing process of AFFF. Finally, the foam spread model considering the external radiation flux is developed which may provide theoretical guidance for fire suppression using AFFF.

Orientation effect on upward flame propagation over rigid polyurethane foam

Inclined upward (concurrent) flame spread over rigid polyurethane (RPU) foam which can exhibit great fire hazard in real high-rise building fire disasters has attracted more and more attentions in the previous studies. In this work, a series of bench-scale experiments and theoretical analyses were conducted to explore the orientation effect on upward flame spread of RPU foam with sample inclination ranging from 10° to 85°. Results show that the fitted correlations between flame length and pyrolysis length are different due to the increasing inclinations, and can be categorized by a modified Rayleigh number. Meanwhile, the power exponents of the fitted expressions between flame length and heat release rate per unit width can also be classified: the power exponent n = 1, n<1 and n>1, when 10° ≤ θ ≤ 40°, 50° ≤ θ ≤ 70°, and θ ≥ 80°, respectively. Furthermore, the dimensionless mass loss rate is approximately proportional to the quarter power of the modified Rayleigh number. The relationship between upward flame spread rate and sine of inclined angle is approximately exponential, and a critical modified Rayleigh number at which no flame spread can be sustained is proposed. The results of this study can provide a reference to high-rise building fire risk assessment and energy conservation system design.

Influence of total head of foam on optimum intensity and minimum particular expense solution size of foamer

The issues addressed included questions and prospects for use of the hydrocarbonic and fluorinated film-forming foamers for fire suppression of emergency passages and the fires of oil products in tanks at supply of foam from long distance. The results of the experiment show that hydrocarbonic foams with increase in falling height cause strong decrease in efficiency of fire suppression. The blow of foam about a surface conducts to partial immersions in oil product that leads to foam pollution by fuel. It is shown that using hydrocarbonic foamers with growth of total head from 5 to 15 cm a particular expense size and optimum intensity 2 times increase. While the fluorinated foams show increase inefficiency of fire suppression by increase in total head which is explained by superficial activity - aqueous solutions of film-forming foamers have positive value of spreading coefficient. The higher the drainage is, the stronger the foam and hydrocarbon surface hit that leads to the accelerated release of solution from foamy films more strongly and promotes fast foam spreading. Experiments confirm expert's opinion about low efficiency of the foams, received their hydrocarbonic foamers when giving with compact streams on long distance. Therefore, replacing of fluorinated film-forming foamers with hydrocarbonic ones, which decay after application well, is premature.

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.