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Efficient fire extinguishing is a safety prerequisite for protecting the environment from fire damage. Understanding the effect of fire extinguishing agent on flame in complex environment is basic work for efficient fire extinguishing. We investigate the impact of HFC-125 on the extinguishment of propane-air highly stretched diffusion flames. Flame thickness is measured using the proportional method. Parameters such as dimensionless flame stand-off distance and flame stretch rate are calculated. Low concentrations of HFC-125 initially increase the flame thickness, but as the concentration increases further, the flame thickness decreases and the flame suppression effect of HFC-125 intensifies. HFC-125 reduces the amount of carbon soot generated and accelerates the transition from yellow to blue flame. Within a specific concentration range, N 2 has a minimal effect on flame structural parameters compared to HFC-125. High concentration of N 2 forms a high bright blue flame, while HFC-125 reacts with the flame to form a blue-violet flame. Compared to HFC-125, HFC-227ea can significantly reduce flame thickness and increase dimensionless flame stand-off distance, exhibiting a notable suppression effect. Furthermore, high concentrations of HFC-125 substantially reduce the critical flame stretch rate and provide a lower extinguishing concentration in counterflow diffusion flames than in the cup burner. [ABSTRACT FROM AUTHOR]

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Due to the greenhouse effect of SF6, the research on alternative insulation gases is currently a hot topic in high voltage engineering. The refrigerant gas such as HFC-227ea with low GWP has stable chemical properties, and high dielectric strength because of a large number of fluorine atoms. However, it is necessary to add buffer gases for relatively high liquefaction temperature(-16.7°C) of HFC-227ea. In this article, the dielectric strengths of HFC-227ea and its gas mixtures under different gas pressure, mixture composition and ratio are investigated under DC and AC electric fields. At atmospheric pressure, the results show that the breakdown voltage of HFC-227ea mixed with N2 or CO2 could only account for 60% of SF6 gas. When HFC-227ea is mixed with HFC-125, which has similar chemical composition and structure, their dielectric strength can reach at least 80% of SF6 gas and the gas mixture shows good synergistic effect. At higher gas pressure, the HFC-227ea/HFC-125 gas mixture at pressure of 0.8 MPa and low HFC-227ea content has the best insulating performance and it is suitable for a lower operating temperature, demonstrating the potential of substituting SF6 for gas insulated electrical equipment.

Oxidation of C 2 HF 5 (pentafluoroethane, R125) that has been extensively used as a refrigerant and fire suppressant agent was examined by weak flames in a micro flow reactor with a controlled temperature profile (MFR) for safety reasons. To investigate the oxidation process of a stoichiometric C 2 HF 5 /air mixture, species measurements for a stoichiometric C 2 HF 5 /air weak flame at the maximum wall temperatures of the reactor from 750 to 1400 K were conducted using a Fourier Transform Infrared Spectroscopy (FTIR). Measurement results showed that two-stage oxidation which consist of the consumption of C 2 HF 5 and formation of C 2 F 6 at the first stage and the reactions of C 2 F 6 at the second stage. Computational results reproduced the observed two-stage oxidation of C 2 HF 5 /air mixture. Since CO remained at the exit of MFR even in the case of a maximum wall temperature at 1400 K, incomplete oxidation of the C 2 HF 5 /air mixture was suggested. Therefore, the weak flame structure at a much higher maximum wall temperature of 2000 K was investigated computationally. The results showed that three-staged complete oxidation of a C 2 HF 5 /air mixture. The three-stage oxidation consisted of the two-stage oxidation similar to that observed in the case of the maximum wall temperature of 1400 K and additional oxidation from CO to CO 2. The latter slowly proceeded because H atom in the fuel was mostly and already consumed by HF formation in the first stage. [ABSTRACT FROM AUTHOR]

This article investigates the toxicology of gaseous products of pentafluoroethane (HFC-125) after the interaction of thermal decomposition with B-class flame together with hexafluoropropane (HFC-236fa) for comparison. For necessary analysis, gas chromatography, ion chromatography, and gas chromatography-mass spectrometry were employed during the interaction between the fire extinguishing agents (FEAs) andn-heptane flame in experiments. The results show that hydrogen fluoride (HF) output was proportional to the pool fire size and interaction time for the two FEAs. Moreover, further toxicology evaluations show that the thermolysis gaseous products of HFC-236fa withn-heptane flame interaction inflict much more harm on the lungs of laboratory mice than that of HFC-125 in pathology tests, thus indicating that besides the HF, other organic traces of gases, such as CF3CH=CF2, CF3CH2CF3, and so on, might have serious impacts on their toxicology. It is expected that these investigative results would be of great help to the further study of FEAs on the toxicology evaluation not only the fire suppression of HFC-125. [ABSTRACT FROM PUBLISHER]

This paper investigates the thermal decomposition properties of pentafluoroethane (HFC-125) fire extinguishing agent, which is regard as the ideal replacement of HCFC and PFC, due to its good environmental performance and low-toxicity, on the pyrolysis properties within 600–850 °C, although the physical-chemical properties and extinguishing characteristics of HFC-125 have been widely reported, its decomposition mechanism is still unclear. With the help of analysis methods of gas chromatography (GC), ion chromatography (IC), gas chromatography–mass spectrometry (GC–MS) together with theoretical calculation, thermal decomposition details of HFC-125 is investigated, as well as possible thermal decomposition mechanism. The results show that the pyrolysis of HFC-125 occurs above 700 °C, the exhaust of HFC-125 pyrolysis products mainly contains CF 2 = CFCF 3 , CHF 3 , CF 2 = CF 2 , CF 3 CHCF 2 , HF, CF 2 = C(CF 3 ) 2 and the component concentrations vary with pyrolysis temperature and residence time. What’s more, a possible decomposition mechanism is also proposed, according to the activation energy of being calculated by using the first order reaction kinetics model and the detail dissociation pathways and gaseous products are deduced using the density functional theory. By combining the experimental results and theoretical calculation, characteristics involved in the decomposition of HFC-125 are given for the first time. It is expected that these investigation results would be of great help to the further study of the fire suppression of HFC-125. [ABSTRACT FROM AUTHOR]

This study is the first to examine the inhibition effectiveness of C 2 HF 3 Cl 2 (HFC-123) on premixed hydrocarbon–air flames and is motivated by the eventual phase-out of CF 3 Br (Halon 1301) used in civilian aircraft cargo compartments. To study the inhibition effectiveness, we measured the laminar burning velocity of CH 4 –air flames with added C 2 HF 3 Cl 2 in a spherical, constant-volume combustion vessel, over a range of inhibitor concentration and fuel–air equivalence ratio. Burning velocities at ambient ( T = 298 K; P = 1.01 bar) and elevated ( T = 400 K; P = 3 bar) conditions were compared to numerical predictions obtained using a newly-developed kinetic mechanism describing the decomposition of hydrochlorofluorocarbons (HCFCs) in hydrocarbon–air systems. The agreement was very good, considering the model parameters were not adjusted, and the present study was the first to test the mechanism against experimental data of a two-carbon HCFC. In addition to providing model validation, the effectiveness of C 2 HF 3 Cl 2 was compared to the analogous HFC compound C 2 HF 5 to explore the advantages of Cl substitution for F. Experimental measurements of agent influence on burning velocity, as well as numerical modeling of premixed flame structures, demonstrated that C 2 F 3 Cl 2 H is a more effective flame inhibitor than C 2 F 5 H, particularly for very lean CH 4 –air mixtures. The reaction pathways and sensitivities were analyzed to interpret the differences in the inhibition mechanisms of C 2 F 5 H and C 2 HF 3 Cl 2 and to prioritize elementary reactions for further study. [ABSTRACT FROM AUTHOR]

Numerical simulations of cup-burner flames in normal Earth gravity have been performed to study the combustion inhibition and unwanted enhancement by fire-extinguishing agents CF 3 Br (Halon 1301) and some potential replacements (C 2 HF 5 , C 2 HF 3 Cl 2 , and C 3 H 2 F 3 Br). A propane–ethanol–water mixture, prescribed for a Federal Aviation Administration (FAA) aerosol can explosion simulator test, was used as the fuel. The time-dependent, two-dimensional numerical code, which includes a detailed kinetic model (up to 241 species and 3918 reactions), diffusive transport, and a gray-gas radiation model, revealed unique two-zone flame structure and predicted the minimum extinguishing concentration of agent when added to the air stream. Despite striking differences in the flame shape, the agent effects were similar to, but stronger than, those in microgravity flames studied previously (for two of the agents). The peak reactivity spot (i.e., reaction kernel) at the flame base stabilized a trailing flame, which was inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of agent in the coflow ( X a ) increased gradually: (1) the premixed-like reaction kernel weakened; (2) the flame base detached from the burner rim, oscillated (particularly for CF 3 Br), until finally, blowoff-type extinguishment occurred; (3) the calculated maximum flame temperature remained nearly constant (≈1800 K) or mildly increased; and (4) the total heat release of the entire flame decreased (inhibited) for CF 3 Br but increased (enhanced) for the halon replacements. In the trailing flame with C 2 HF 5 , a two-zone flame structure (with two heat-release-rate peaks) developed: in the inner zone, H 2 O (a product of hydrocarbon–O 2 combustion and a fuel component) was converted further to HF and CF 2 O through exothermic reactions occurring in the outer zone, where exothermic reactions of the inhibitor also released heat; CO 2 was formed in-between. Thus, addition of C 2 HF 5 resulted in unusual (non-chain branching) reactions and increased total heat release (combustion enhancement) primarily in the trailing diffusion flame. [ABSTRACT FROM AUTHOR]

Highlights: [•] Promoter M (M=Y, Co, La, Zn) can change the catalytic performance of Cr2O3 catalyst. [•] La-Cr2O3(F) catalyst exhibited the highest activity and selectivity and it showed a good reaction stability. [•] Surface acid sites density of M-Cr2O3 catalysts have a larger impact on the activity of the catalyst. [ABSTRACT FROM AUTHOR]

Hydrofluorocarbons (HFCs) are greenhouse gases with high global warming potentials that are mainly used in refrigeration and air conditioning. Historically, they were emitted only slowly from such systems and long term containment remains an important engineering and environmental issue. As part of their commitment under the Rio convention, nations are required to report annual calculated production and emissions of all greenhouse gases and the reports submitted by the European countries have been examined to determine the extent to which containment of HFCs (expressed as the rate of emission from the bank remaining in equipment) has changed with time. Although there is wide variation between countries, the annual emission rates of HFCs have improved significantly over the past 10 years and now represent between 5 and 10% of the bank still contained in equipment. This implies that, at the present state of technology, it would take at least 10-20 years for the original mass of refrigerant charged into a system to be released into the atmosphere. [ABSTRACT FROM AUTHOR]

This paper reports experimental results for the viscosity of gaseous mixtures of HFC-125 (pentafluoroethane)+HFC-32 (difluoromethane). The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15K. The viscosity was measured for three mixtures (mole fraction of HFC-125 is 0.7498, 0.4998, or 0.2475). The viscosity at normal pressure was analyzed with the extended law of corresponding states developed by Kestin et al. and the scaling parameters were obtained for unlike-pair interactions between HFC-125 and HFC-32. The modified Enskog theory developed by Vesovic and Wakeham was applied to predict the viscosity for the binary gaseous mixtures under pressure. For the calculation of the pseudo-radial distribution function in mixtures, a method based on the Carnahan–Starling equation for the radial distribution function of hard sphere mixtures is proposed. [ABSTRACT FROM AUTHOR]

This paper reports measurements of the static relative permittivity of HFC-125 in the liquid phase, performed by using the direct capacitance method at 10 kHz, for temperatures from 214 to 304 K and pressures up to 16 MPa. The repeatability of the measurements was found to be of the order of ±0.7×10−3and the uncertainty is estimated to be better than ±0.72×10−2. We provide a complete set of tables of experimental data as a function of temperature, pressure, and density, which cover the dielectric property needs for most engineering applications. The data obtained were used to establish dielectric equations of state as a function of density and temperature and as a function of pressure and temperature. To study the dependence of the relative permittivity on temperature, pressure and density, we have applied various molecular theories of polar liquids. The apparent dipole moment obtained was μ*=2.482 D. [ABSTRACT FROM AUTHOR]

Isothermal vapor–liquid equilibria for three binary mixtures of CFC alternative refrigerants were determined in an equilibrium apparatus in which both phases were continuously recirculated. The pressures and vapor and liquid compositions were measured for the binary systems trifluoromethane (HFC-23)+difluoromethane (HFC-32) and trifluoromethane (HFC-23)+pentafluoroethane (HFC-125) at 283.15 and 293.15 K and pentafluoroethane (HFC-125)+1,1-difluoroethane (HFC-152a) at 293.15 K. The experimental data were correlated with the Peng–Robinson–Stryjek–Vera equation of state using the Huron–Vidal original mixing rule. Calculated results with this equation showed good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A recently developed scheme, based on considerations of hard-sphere theory, is used for the simultaneous prediction of the thermal conductivity and the viscosity of binary and ternary HFC refrigerant mixtures, consisting of HFC-32, HFC-125, and HFC-134a. In this prediction scheme, the hypothetical molecular parameters of HFC refrigerant mixtures were assumed to be the molar average of the pure component values. The close agreement between the predicted values and the experimental results of thermal conductivity and viscosity demonstrate the predictive power of this scheme. [ABSTRACT FROM AUTHOR]

There are two promising candidates as alternative refrigerants for air-conditioners and heat pumps. The first is R407C, which is composed of HFC-32 (23 mass%), HFC-125 (25 mass%), and HFC-134a (52 mass%). The second is R410A, which is composed of HFC-32 (50 mass%) and HFC-125 (50 mass%). In this study, formation conditions of clathrate compounds between water and HFC alternative refrigerants such as HFC-32, HFC-125, HFC-134a, and their mixtures, R407C and R410A, were investigated. Phase diagrams of clathrates of these HFC alternative refrigerants and their mixtures were determined. From the phase diagrams, the critical decomposition temperature and the critical decomposition pressure were determined. The relationship between the critical decomposition points for the clathrates of HFC-32, HFC-125, HFC-134a, R410A, and R407C were studied. It is found that R407C and R410A form clathrate compounds with water under the evaporating temperature condition in the refrigeration cycle of air-conditioners and heat pumps. [ABSTRACT FROM AUTHOR]

This paper reports experimental results lor the viscosity of gaseous HFC-125 (pentafluoroethane) under high pressures. The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K and at pressures up to the saturated vapor pressures at each temperature at subcritical conditions or up to 9 MPa at supercritical temperatures. Intermolecular scaling parameters of HFC-125 for the extended corresponding states were determined from the viscosity data at 0.1 MPa. An empirical viscosity equation is proposed to interpolate the present experimental results as a function of temperature and density. [ABSTRACT FROM AUTHOR]

Measurements of the thermal conductivity of HFC-125 that have been made by a coaxial cylinder cell operating in steady state are reported. The measurements of the thermal conductivity of HFC-125 were performed along several quasi-isotherms between 300 and 515 K in the gas phase and the liquid phase. The pressure range covered varies from 0.1 to 53 MPa. Based on the measurement of more than 600 points, an empirical equation is provided to describe the thermal conductivity outside the critical region as a function of temperature and density. A careful analysis of the various sources of error leads to an estimated uncertainty of approximately ± 1.5%. [ABSTRACT FROM AUTHOR]

Measurements of the thermal conductivity of HFC-32, HFC-125, and HFC-134a were carried out for the first time in both solid and liquid phases at the saturation pressure at room temperature and in the temperature ranges from 120 to 263, from 140 to 213, and from 130 to 295 K, respectively. A transient hot-wire instrument using one bare platinum wire was employed for measurements, with an uncertainty of less than ±2%. The experimental results demonstrated that the thermal conductivity of HFC-32, HFC-125, and HFC-134a in the solid phase showed a positive temperature dependence. For HFC-32 and HFC-125, there were big jumps between the solid and the liquid thermal conductivity at the melting point. But for HFC-134a, the solid and liquid thermal conductivity at the melting point is almost-continuous. [ABSTRACT FROM AUTHOR]

To provide guidance towards reducing the weight of the HFC-125 storage vessel by reducing the release pressure and to reveal the effects of release pressure on the extinguishing efficiency of HFC-125, we investigated the flow and diffusion characteristics of HFC-125 under six release pressures in the present study. The influence of release pressure on the degree of superheat, injection duration, pressure loss, jet angle, and concentration distribution were analyzed. Results show that the degree of superheat and the injection duration both decreased with the release pressure. The bubble expansion in the HFC-125 could slow down the pressure decrease in the storage vessel. The flow process in the pipeline can be divided into three phases: pipeline filling, stable flow, and mixed gases release. Both of the maximum and mean values of the pipeline pressure loss increased with the release pressure. The maximum concentration value decreased with the increase of the distance from the nozzle. The maximum concentration value in the near field from the nozzle increased with the release pressure. The concentration and holding time (duration above 17.6% volume concentration) of HFC-125 in the near field from the nozzle met the requirements of minimum performance standards (MPS) for HFC-125. [ABSTRACT FROM AUTHOR]