A computational study of extinguishment and enhancement of propane cup-burner flames by halon and alternative agents

Computations of cup-burner flames in normal gravity have been performed using propane as the fuel to reveal the combustion inhibition and enhancement by the CF₃Br (halon 1301) and potential alternative fire-extinguishing agents (C₂HF₅, C₂HF₃Cl₂, and C₃H₂F₃Br). The time-dependent, two-dimensional numerical code used includes a detailed kinetic model (up to 241 species and 3918 reactions), diffusive transport, and a gray-gas radiation model. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of agent in the coflow increases gradually, the premixed-like reaction kernel weakens, thus inducing the flame base detachment from the burner rim and blowoff-type extinguishment eventually. The two-zone flame structure (with two heat-release-rate peaks) is formed in the trailing diffusion flame. The H₂O formed in the inner zone is converted further, primarily in the outer zone, to HF and CF₂O through exothermic reactions most significantly with the C₂HF₅ addition. The total heat release of the entire flame decreases (inhibiting) for CF₃Br but increases (enhancing) for the halon alternative agents, particularly C₂HF₅ and C₂HF₃Cl₂. Addition of C₂HF₅ results in unusual (non-chain branching) reactions.     

Inert hydrocarbon-based refrigerants

This paper determines the flammability properties of two hydrocarbon blends, natural gas and propane–butane refrigerant, mixed with CF₃I and C₃F₇ H inerting agents. Four flammability envelopes are obtained allowing the determination of the minimum inerting concentrations and the maximum hydrocarbon to suppressant weight ratios for formulating non-flammable hydrocarbon refrigerants. These ratios are calculated from the slopes of lines drawn from the origin and tangent to the lower branches of the flammability envelopes. The flammability measurements are conducted using a tubular flow burner. The apparatus is convenient to operate, yields reproducible results without repetitive testing necessitated by explosion vessels. More importantly, the tubular flow burner applies a clear criterion for extinction avoiding the innate problems of the explosion vessels, which relate to the strength of the ignition source and the vessel size. The results indicate that it is not possible, using CF₃I or C₃F₇ H, to formulate a refrigerant mixture with a substantial hydrocarbon content. Specifically, inertion of the propane–butane blend considered in this study demands 87.7% and 94.2% by weight of CF₃I and C₃F₇ H, respectively. CF₃I displays similar inerting properties to those of CF₃Br. The higher inerting requirement for C₃F₇ H stems from the nature of this agent to decrease the lower flammability limit of the hydrocarbon blends.     

Production of H2O2 in hydrocarbon-O2-CF3Br systems

Hydrogen peroxide is produced when CF₃Br is added to flowing hydrocarbon-oxygen mixtures at approximately 350 °C. The H₂O₂ concentration is dependent on the amount of CF₃Br added to the hydrocarbon-oxygen mixture and maximizes at approximately 40 mole% CF₃Br.     

Influence of CF<Subscript>3</Subscript>I and CBrF<Subscript>3</Subscript> on Methanol–Air and Methane–Air Premixed Flames

The suppression of CH₄ and CH₃OH premixed flames with CBrF₃ and CF₃I is examined, using computational techniques. By combining sensitivity analysis, reaction pathway analysis (based on carbon, hydrogen, bromine and iodine atom fluxes) and heat release estimation, we develop an explanation for the difference of suppression efficiencies which is qualitatively consistent with experimental cup burner data. The key reaction steps and channels responsible for the (apparent) higher inhibition efficiency of CF₃I compared to CBrF₃ in CH₃OH premixed flames are disclosed, by combining reaction pathway and heat release contribution analysis. The reaction of bromine atom dominates the decomposition channel for CH₃OH but plays a relatively minor role in the activation of CH₄, while I atom plays a minor role in CH₃OH or CH₄ activation. Accordingly, the rate of production of flame propagating radicals CH₂O and OH is higher in a CH₃OH–air–CBrF₃ system than in a CH₃OH–air–CF₃I system. The overall conclusion is that CBrF₃ contributes significantly to flame propagation for CH₃OH fuel reactions and consequently more CBrF₃ is required to extinguish a CH₃OH flame than CF₃I. Finally the explanation is validated by applying the reaction “switching-off” test.     

Flame heat transfer in storage geometries

This paper presents measurements of the heat flux distribution to the surface of four square towers exposed to buoyant turbulent flames.The steel towers represent an idealisation of a rack storage configuration at reduced scale. Each tower was 1.8 m high and 0.3 m×0.3 m wide. The fuel was supplied from a circular gas burner at the floor. Three different gaseous fuels were used: carbon monoxide (CO), propane (C₃H₈), and propylene (C₃H₆). These fuels cover a wide range of flame sootiness resulting in distinctly different flame heat fluxes. At the same overall heat release rates the peak heat fluxes from C₃H₈ flames were twice those from CO flames, whereas the peak heat fluxes from C₃H₈ flames were 2.8 times those from CO flames. Heat fluxes were measured by thermocouples spot-welded to the back of the steel sheets. They were measured at 52 different locations. This measurement method turns out to be simple, accurate and robust in addition to being inexpensive. Formulas are provided for the flame heat flux distribution in terms of the overall fire heat release rate, fuel sootiness and separation distance between the towers. The formulas are suitable for direct use by engineering models of fire growth in storage geometries. The paper also provides additional data needed for the development of more general CFD models capable of predicting fire growth of other geometries.     

Modeling of dust air flames

This study analyzes a premixed dust–air flame, under conditions where a homogeneous gas-phase reaction front can exist. Discussion on four possible flame types is provided. A solution is obtained for the burning velocity of a flammable dust–air flame in both fuel and oxygen limiting cases. A sensitivity analysis is used to analyze the features controlling the dust burning. It is shown that vaporization is significant for fuel limiting conditions; however, does not play a major role in oxygen limiting cases. The calculated burning velocity shows good agreement with available experimental data for coal–dust–air flames.     

The inhibition of photochemical smog V. Products of the diethylhydroxylamine inhibited reaction

Mixtures of 1.6–26 mTorr C₂H₄ and about half as much NO and either O or $\text{1}\text{4}$ as much diethylhydroxylamine (DEHA) in 10 Torr N₂, ～ 160 Torr O₂ and 0 or 10 Torr H₂O were irradiated to determine the products of reaction. With DEHA present an initial product was HONO. After a short induction period, CH₃CHO, N₂O, and C₂H₅OH were produced. C₂H₅NO₂, NO₂, and some CO₂ were produced after a longer induction period. The CH₃CHO, HONO, N₂O, C₂H₅NO₂, C₂H₅ONO₂, and C₂H₅OH were not produced in the absence of DEHA. The relative maximum concentrations of CH₃CHO, N₂O, C₂H₅NO₂, C₂H₅ONO₂, and C₂H₅OH were 81, 27, 88, 15, and 1.1%, respectively, compared to the initial DEHA concentration.The reaction of NO₂ with DEHA in the absence of O₂ produced CH₃CHO and HONO as major products and C₂H₅OH and C₂H₅ONO₂ as minor products. In the presence of O₂, C₂H₅NO₂ was also produced.A mechanism for the reaction is suggested. Since the presence of DEHA markedly inhibits the reaction (initial rate of C₂H₄ removal reduced by a factor of 5 and initial rate of conversion of NO to NO₂ reduced by a factor of 20), and the only products of reaction not now found in urban atmospheres are the harmless compounds C₂H₅OH and C₂H₅NO₂, it is recommended that DEHA be considered for addition to urban atmospheres to inhibit photochemical smog production.     

Laminar smoke points of coflowing flames in microgravity

Laminar smoke points were measured in nonbuoyant laminar jet diffusion flames in coflowing air. Microgravity was obtained on board the International Space Station. A total of 55 smoke points were found for ethylene, propane, propylene, and propylene/nitrogen mixtures. Burner diameters were 0.41, 0.76, and 1.6 mm, and coflow velocities varied from 5.4 to 65 cm/s. These flames allow extensive control over residence time via variations in dilution, burner diameter, and coflow velocity. The measured smoke-point lengths scaled with d^−0.91u_air^0.41, where d is burner diameter and u_air is coflow velocity. The measurements yielded estimates of sooting propensities of the present fuels in microgravity diffusion flames. Analytical models of residence times in gas jet flames are presented, and although residence time helps explain many of the observed trends it does not correlate the measured smoke points.     

Experimental study of suppressing effect of fine water droplets on propane/air premixed flames stabilized in the stagnation flowfield

Effect of fine water droplets on the laminar burning velocity of propane/air premixed flame was investigated by using a single jet-plate configuration. For the case without water droplets, the measured laminar burning velocities are in reasonably good agreement with previously reported data and the numerical simulation. The dependence of the burning velocity on the stretch rate for the case without water droplets is positive for all mixtures tested, resulting in the negative Markstein length, which coincides with previous experimental and theoretical studies. Water droplets lower significantly the laminar burning velocity and change its dependence on the stretch rate to negative. This leads to apparent positive Markstein lengths. The positive Markstein length was discussed on the basis of the droplets behavior in the stagnation flow field adopted in the present study. Even if the droplet mass loading was kept constant, the water droplets do not follow the diverting flow field when the stretch rate is high and the droplets accumulation occurs in the stagnation region where the burning velocities were measured. This fact results in the lower burning velocity as compared to that measured for uniformly dispersed water droplets.     

Synergism between chemical and physical fire-suppressant agents

A pronounced synergism is reported for mixtures of physical and chemical agents used in flame extinguishment. Mixtures containing approximately 90% (by volume) of either carbon dioxide or nitrogen and 10% of CF₃Br or CF₂ClBr are much more effective in suppressing fires (in cup-burner tests) than would be predicted by an additivity of effects. A method is proposed for delivering solutions of chemical agents dissolved in liquid CO₂ to obtain cooperative fire-suppression effects, while simultaneously reducing the danger to humans and the environment. A simple model has been developed to give very good predictions of the extinguishment concentrations of mixtures of physical and chemical agents.     

Comparative assessment of isophtalic and orthophtalic polyester polymer concrete: Different costs,similar mechanical properties and durability

This study aims to investigate the effect of different concentrations of fly ash on the mechanical properties and durability of polymer concrete compounds prepared with low concentrations of resins. Two different binders were used: orthophtalic and isophtalic polyester. The properties of the resulting materials were studied through compressive strength, flexural strength and chemical attack by acetic acid (CH₃COOH), citric acid (C₆H₈O₇), formic acid (CH₂O₂), lactic acid (C₃H₆O₃), sulfuric acid (H₂SO₄), a cola soft drink and distilled water (H₂O). Sample microstructure after chemical attack was studied using SEM. Results show that both isophtalic and orthophtalic polyester polymer concrete display good mechanical and chemical behavior. It was seen that orthophtalic polyester polymer concrete, when prepared with sand and fly ash, behaves similarly to isophtalic polyester polymer concrete, despite the properties of the isophtalic resin being superior to the orthophtalic variety.     

Experimental investigation of the impact of oxygen flux on the burning dynamics of forest fuel beds

To characterize the burning dynamics of porous wildland fuels it is fundamental to understand the heat and mass transfer mechanisms. These are significantly different compared to solid fuels and less well documented. Radiation feedback from flames and convective heat transfer from forced airflow have been found to influence the pyrolysis and combustion processes. Smoldering combustion and resulting heat feedback is also shown to have significant impact. The link between burning dynamics and the oxygen availability is also explored. Combustion experiments are carried out using the FM Global Fire Propagation Apparatus in order to investigate changes in the burning behavior of porous fuel beds as a function of the oxygen availability. The oxygen flux into the combustion zone was varied by three mechanisms, (1) varying natural entrainment, (2) changing forced flow magnitude and (3) oxygen concentration. Results investigated from the combustion tests were the duration of flaming (from which the average burning rate was deduced), CO and CO₂ generation rates, combustion efficiency and heat release rate. For both test series, the duration of flaming decreased and peak heat release rate increased with increasing oxygen flux. For tests with varying flow magnitude the combustion efficiency stayed constant with a CO/CO₂ ratio below 1.5%. For tests with varying flow oxygen concentration the ratio was much higher, between 12% and 26%, indicating high levels of incomplete combustion. At a given oxygen flux, changes in heat flux feedback from the flames, convection cooling, and combustion efficiency were found to be the reason for differences on the order of 30–50% in burning rate and thus heat release rate. The intensity of smoldering increased with increasing oxygen flux equally for both tests series. The study explored herein provides insight into importance of several heat and mass transfer mechanisms that govern the burning dynamics of porous wildland fuel beds. Furthermore, it also highlights the necessity of understanding incomplete combustion (flaming) in the wildfire context.     

An estimate of the correction applied to radiant flame measurements due to attenuation by atmospheric CO2 and H2O

A narrow band statistical model has been used to estimate the uncertainty introduced into radiative heat flux measurements from fires which is attributable to attenuation by atmospheric H₂O and CO₂. The flames were assumed to be soot-dominated with blackbody emission characteristics. The ambient surroundings near the flames were assumed to be homogeneous with the total pressure being fixed at one atmosphere. Atmospheric CO₂ concentrations were held constant at 0.04 kPa and the water vapor concentrations varied between 0.55–5.63 kPa based on temperature and relative humidity. The remaining partial pressures were accounted for by O₂ and N₂. Correlations to estimate atmospheric attenuation are given over a range of conditions that include path length (10–200 m), ambient temperature (19–35°C), source temperature (1000–1600°C) and relative humidity (0.25–1.0) as parameters. The results of these calculations indicate that, over this range of conditions, the radiant flux can be attenuated by as much as 42%.     

Investigation of flow properties in natural streams using the entropy concept

This paper examines the discharge and velocity distributions in natural open channel flows using the entropy theory. Flow measurements were carried out at four different cross‐sections in central Turkey. The mean and maximum velocities at these stations exhibited a linear distribution and the entropy parameter was calculated to be M=1.31. Using this value, discharges for all flow conditions were calculated as a function of the measured maximum velocities (u_max). It was observed that the u_max/H and z_max/H ratios remained relatively constant when 0.2≤y/T≤0.8, especially for the wider channels. Using these constant values for each station, u_max and z_max could be determined solely as a function of the water depth H. Although the calculated velocities were higher than those measured at some verticals, the entropy‐based approach presents an attractive alternative to the traditional flow‐measurement techniques for the determination of flow properties because of its simplicity and quick application.     

Reactions entre granulats calcaires et pate de ciment alumineux

As it has been pointed out about Portland cement, the aluminous cement reactsd with calcite. This reaction has been studied by X-ray diffraction with two types of specimen: the interfacial zone between cement paste and aggregate is investigated with a “double-specimen” model, the contact zone and the bulk are studied with mortars. The hydration reactions of the aluminous cement largely changed in the interfacial zone by the calcareous nature of the aggreagate. Calcite reacts with the two calcium aluminate hydrates CAH₁₀ et C₂AH₈ to form calcium hydrocarboaluminate. This reaction occurs in two steps: firstly C₄A.1/2 \(\bar C\) .12H₂O and secondly C₃A.CaCO₂.11H₂O. As we know, this reaction retards the conversion of the hexagonal aluminates in the cubic form C₃AH₆, which is responsible for damages on aluminous concretes. This retard of the conversion is studied for calcareous and siliceous concretes. The rate of the conversions depends on the nature of the hydrates; it decreases in the following order: C₂AH₈?CAH₁₀?C₃A.CaCO₃.11H₂O The physico-chemical study of the interfacial zone between aggregate and aluminous cement paste is a step in explaining the mechanical comportment of concretes made with aluminous binders.     

Photo-reductive defluorination of perfluorooctanoic acid in water

Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-reduction method is developed and evaluated for the decomposition of perfluorooctanoic acid (PFOA) in aqueous phase with potassium iodide (KI) as a mediator. The experiment was conducted under 254 nm irradiation at room temperature and pH 9 under anaerobic conditions. Ultraviolet photolysis of iodide solutions led to the generation of hydrated electrons (e_aq⁻, E_aq/e°= −2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic analysis indicated that the PFOA decomposition fit the first-order model with a rate constant of 7.3 × 10⁻³ min⁻¹. Besides fluoride ions, additional intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amounts of CF₃H and C₂F₆ were also detected as reaction products by using GC/MS. With observation of the degradation products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF₂ by UV irradiation and hydrolysis. This method was applied to the decomposition of PFOA in wastewater issued from a fluorochemical plant and proved to be effective.     

Improved parameterization of dust emission (PM10) fluxes by the gradient method using the Naiman tower data at the Horqin desert in China

Dust emission/deposition flux has been estimated using the gradient method with the two-level (3 and 15 m high) measured PM₁₀ concentrations and the sonic anemometer measured momentum and kinematic heat fluxes at 8 m high from a 20-m monitoring tower located at Naiman (Horqin desert) in the Asian dust source region in China for the winter of November 2007 to March 2008. The time series of measured PM₁₀ concentration at 3 m high is used to identify the dust event and the non-dust event periods. It is found that the dust emission/deposition flux (F_C) shows a significant diurnal variation with the maximum emission flux of 5.8 kg km^? 2 h^? 1 at noon and the minimum of ? 1.6 kg km^? 2 h^? 1 in the afternoon for the non-dust event cases. Whereas for the dust event cases, the dust emission flux is found to occur when the prevailing winds are westerlies to northerlies with the maximum flux of 1275 kg km^? 2 d^? 1, while the maximum dust deposition flux of 148 kg km^? 2 d^? 1 occurs with the prevailing winds of southerlies to easterlies without any diurnal variation. The optimal regression equation between F_C and the friction velocity (u_*) for the dust emission cases is found to be F_C = 9.55 u_*^3.13 with the R² value of 0.73. However, this regression equation can be improved by taking into account the convective velocity (w_*). The resulting optimal regression equation is found to be F_C = 9.3(u_* ? 0.1w_*)^3.19 for the stable stratification (w_* < 0) with the R² value of 0.77 and F_C = 10.5(u_* + 0.34w_*)^4.11 for the unstable stratification (w_* > 0) with the R² value of 0.78, suggesting the importance of the convective velocity on the dust emission flux.     

Availability of dissolved iron from Tjeukemeer,The Netherlands,for iron-limited growing Scenedesmus quadricauda

Ultrafiltration of water from eutrophic, alkaline and humic lake Tjeukemeer, The Netherlands, revealed that most dissolved Fe (< 0.2 μm) is found in colloids between 350 and 2000 Å. All dissolved Fe from NH₄Fe(SO₄)₂·12H₂O in the growth medium occurred in particles $\text{< 350}\text{A}\text{?}$, half of which did not exceed 100 Å. The half-saturation growth constant (K_s) of Fe-limited growth of Scenedesmus quadricauda in the presence of EDTA at pH 8.0 and using the natural Fe colloids was almost 3 times that using NH₄Fe(SO₄)₂·12H₂O. The maximum growth rate (μ_max) was not affected by the particle size of the limiting Fe substrate. It is concluded that Fe from the natural colloids is approx. one-third as much available as from NH₄Fe(SO₄)₂·12H₂O.The implications of the effect of the particle size of the growth rate limiting substrate to our understanding of species succession in natural phytoplankton communities are briefly discussed.     

Removal of Cu(II), Ni(II), and Co(II) from aqueous solutions using layered double hydroxide intercalated with EDTA

A sample of a layered double hydroxide intercalated by EDTA has been synthesized and its chemical formula [Zn₄Al₂(OH)₁₂](EDTA) · 8H₂O was determined. The possibility of applying such sorbent for the extraction of Cu(II), Ni(II), and Co(II) from aqueous solutions was investigated. Comparative investigation of the sorption capacity of carbonate and chelate forms of layered double hydroxides was performed. It is shown that the degree of extraction of metals on sorbent [Zn₄Al₂(OH)₁₂](EDTA) · 8H₂O completely correlates with the stability of complex compounds of these metals in the solution.     

Fire Test of Profile Plank for Transformer Pit Fire Protection

In general it is recommended to fill a transformer pit with rock ballast to extinguish the fire if there is a leakage of burning transformer oil. There is a lack of technology-neutral performance requirements for the design of solutions for fire extinguishment in transformer pit fires. This hampers the introduction of alternatives to the traditional method of filling the pit with rocks. Therefore we have conducted quantitative tests where temperatures and concentrations of CO, CO₂, and O₂ were measured at different position in a transformer pit subjected to burning oil simulating an accidental rupture and leakage. The tests were conducted to investigate the extinguishing capacity of one specific alternative solution, i.e. a profile plank layer over the pit. Three tests were performed with 90°C and 140°C pre-heated transformer oil. In the second test, a 19 cm water bed was used to examine the impact of rain water in the pit. The result showed that the profile plank extinguished the flames in a few seconds and that the water level did not have any significant effect on the result. The measurements showed that the temperatures peaked at 600–800°C 50 cm above the profile plank in all tests but dropped to under 100°C in 14–16 s. Furthermore the O₂-concentration dropped to 3–5 vol% below the plank, which contributed to the rapid extinction of the burning oil.