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This paper presents an experimental study on the flame geometric characteristics of large-scale open pool fires under well-controlled wind conditions. Square fuel pools with combustion areas of 50 m2, 100 m2, 200 m2, 380 m2, and 400 m2 were used to burn RP-5 aviation fuel and diesel oil. A large-scale open jet wind tunnel generated a well-controlled and regulated horizontal wind field with wind speed (U) of up to 17 m/s. It was found that the evolution of large-scale pool fires under wind conditions involved four regimes, namely free vertical pool fire, tilted pool fire without flame drag, tilted pool fire with stable flame drag, and tilted pool fire close to the ground. The wind significantly affected the flame shape, the vortex structures, and the smoke layer characteristics around the flame. Five quantities of flame geometry were measured, including the flame base drag (l d), the flame length (L), the vertical flame height (H), and two flame tilt angles of θ 1 (defined by the fuel pool center) and θ 2 (defined by the flame base center). The critical wind speeds for flame base drag were obtained for the first time, and it showed a steady increase with the fuel pool size. With increasing U , the vertical flame height (H) decreased steadily, while the flame length (L) increased slightly, and the flame base drag (l d) and the flame tilt angles (θ 1 , θ 2) increased steadily and leveled off for U >7–8 m/s. By introducing the buoyancy length scale and integrating the mixture fraction equation, the correlations for the five flame geometric characteristics were derived, which agreed well with the data of large-scale pool fires in this work and literature. The correlation for flame base drag also successfully predicted the critical wind speed for the occurrence of the flame drag. [ABSTRACT FROM AUTHOR]

In realistic industrial scenarios, the leakage of aviation kerosene (RP-5) under forced airflow easily leads to fire spread, which seriously threatens the safety of human life and causes enormous economic losses. Therefore, it is necessary to study the characteristic parameters of flame spread over RP-5 aviation kerosene under forced airflow, such as flame tilt angle (θ), flame height (H), and flame spread rate (V). In this paper, the RP-5 flame spread experiments were carried out by varying the speed (u = 0–6 m/s) and direction (concurrent, opposed, and perpendicular airflows) of the forced airflow. The results show that the flame tilt angle increases as the airflow speed increases and finally tends to be stable, while the flame height decreases monotonically with airflow speed. The special behaviors of flame bifurcation and fire spread rate induced by the critical airflow speed are observed. The phenomenon of "flame bifurcation" will occur due to the influence of differential pressure resistance under high concurrent airflow conditions (u > 1 m/s). When the airflow is relatively small (u ≤ 1 m/s), the mean flame spread rate varies slightly with increasing airflow speed. With further increasing the airflow speed (u > 1 m/s), the mean flame spread rate increases with an increase in the concurrent airflow speed while decreasing as the opposed airflow speed increases. By contrast, the mean flame spread rate remains essentially unchanged under all perpendicular airflows. [ABSTRACT FROM AUTHOR]

The extensive use and improper handling of plastics have caused extensive microplastic (MP) pollution in terrestrial environments. Di(2-ethylhexyl) phthalate (DEHP), the main additive used in plastics, is toxic to organisms and may pose risks to human and animal reproductive functions. However, research on the release behavior of DEHP from MPs is scarce. In this study, the effects of particle size and environmental conditions (temperature, pH, ionic strength, and cation type) on DEHP release from polylactide (PLA), polystyrene (PS), and polyvinyl chloride (PVC) MPs were determined by performing leaching experiments. The results showed that when particle size decreased, the content of DEHP in the MPs and the amount of released DEHP increased though increasing specific surface area. An increase in temperature also promoted DEHP release; when the temperature increased from 15 °C to 45 °C, the amount of DEHP released from PLA, PS, and PVC increased by 38.4%, 71.0%, and 109%, respectively. The lower the crystallinity, the greater the increase in the amount of DEHP released. Ionic strength inhibited the release of DEHP from MPs. When Na+ concentration increased from 0 to 200 mM, the amount of DEHP released from PLA, PS, and PVC decreased by 27.4%, 41.6%, and 35.3%, respectively. The effect of Ca2+ on DEHP release from MPs was greater than that of Na+. In addition, the process of DEHP release from MPs fit well with a pseudo-first-order kinetic model. The results of this study provide a theoretical basis for managing and controlling the risks associated with plastic wastes. [Display omitted] • Leaching experiments were conducted on various MPs types under different conditions. • Petroleum-based and biodegradable plastics release DEHP into the environment. • Reducing the particle sizes increased the extractable DEHP content of the MPs. • Higher polymer crystallinity reduced the impact of temperature on DEHP release. [ABSTRACT FROM AUTHOR]

Highlights • One-dimensional analysis is used for UTLTs smoke control design. • Diverse driving forces are combined for smoke control of UTLTs. • Jet fans, axial fans and natural smoke exhaust are well cooperated. • One-dimensional analysis results agree well with CFD simulations. Abstract Urban traffic link tunnels (UTLTs) could become increasingly more complex because they incorporate both looped main tunnels and multiple branch tunnels. In such a complex tunnel structure, smoke control in the event of fire becomes more difficult than that in conventional simple tunnels due to the enhanced flow interactions among various branches. Moreover, there are still no specific smoke control guidelines for such complex tunnels. Furthermore, the use of a single smoke control method could be inapplicable or even unaffordable in UTLTs because the complicity of the configuration and the interaction between the flow of different branches. In this paper, hybrid ventilation modes which combine diverse flow driving forces are proposed for smoke control in UTLTs. The hybrid modes could exploit the advantages of each of the constitutive modes. Three-dimensional numerical simulations are performed to show the benefits of combining diverse driving forces. Then, a one-dimensional flow modelling approach was employed to investigate the efficiency of three hybrid modes. The results demonstrate that proper matching of various driving forces is crucial for effective application of the hybrid modes. This paper provides a new route for UTLT smoke control and also demonstrates the advantages of one-dimensional flow modelling in such designs. [ABSTRACT FROM AUTHOR]

Pool fires caused by leaks of aviation fuels such as RP-5 can result in severe catastrophes. This problem is especially more pronounced in ships and oil tankers. Accordingly, investigation of wind-exposed pool fires is of great significance to the safety of ships. In the present study, an experimental platform was designed and constructed to study the evolutions of flame shape, burning rate, and downstream gas temperature in square aviation fuel pool fires exposed to crosswind. In this regard, different pool side lengths (D = 0.32–0.55 m) and crosswind speeds (V = 0–6.5 m/s) were analyzed. The obtained results show that as the wind speed increased, the flame length and flame tilt angle increased first and then stabilized, and the maximum values almost reached 2.5 m and 90°, respectively. Based on the force analysis, the normalized flame length (L / L V =0) and tangent of flame tilt angle (tanθ) can be expressed by the power function of Forde number (Fr). It is found that the burning rate grew steadily first, followed by a level-off value, and the maximum value is 0.0481kg/(m2.s). Accordingly, a piecewise function based on the boundary theory was proposed to estimate the burning rate. The performed analyses reveal that the downstream gas temperature increased first to a peak value (within 1000 ° C) and then decreased. A modified exponential correlation of the decay of the downstream gas temperature (ΔT/ΔT peak) with the fire distance (x/D') was developed in terms of the heat transfer balance. [ABSTRACT FROM AUTHOR]

Recycling is the primary method to handle electronic waste plastics, however, little attention has been paid to the risk posed by heavy metal migration in waste plastic products. The effect of multistage recycling processes on heavy metal migration and the environmental risk posed by heavy metals during recycling processes were investigated by: (1) Recycling waste plastics and determining the heavy metal contents in secondary products; (2) Using toxic leaching experiments to assess environmental risks of heavy metal migration in secondary products; and (3) Evaluating the effect of recycling processes on the mechanical properties and microstructure of plastics. Results showed that the contents of some harmful heavy metals in processed products exceeded the Safety of Toys Standard. Toxic leaching tests showed that Ni, Cu, Zn, Pb, and Sb migrated outward during secondary products use. With increased recycling times, concentrations of migrated Ni, Cu, Zn, Pb, and Sb increased, and the leached concentrations exceeded the limits stipulated in the Groundwater Quality Standard. Increased recycling times also accelerated waste plastics aging and caused the deterioration of mechanical properties. Furthermore, adhesion between layers decreased, stratification and cracking in polymers appeared, and adhesion of waste plastics to additives decreased. Therefore, the environmental risks of waste plastic recycling should be carefully considered. Image 1 • Recycled waste plastic products may pose environmental and human health risks. • We recycled waste plastics and determined the metal contents in secondary products. • High metal concentrations were present in leachate from recycled products. • Metal concentrations exceeded human safety and groundwater standards. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the development characteristics of multiple fires in tunnels holds significant importance in estimating the thermal safe distance required for both people and facilities. In this paper, a series of numerical and experimental works are performed to examine the ceiling gas temperature, fire merging, and flame length of twin fires in a tunnel. Varied thermal hazard scenarios were simulated by altering the ambient pressure, heat release rate, and pool spacing. The findings indicate that as the ambient pressure reduces, the air entrainment coefficient decreases, resulting in a higher ceiling gas temperature. Large pool spacings demonstrate two peak impact points in ceiling gas temperature. However, as the pool spacings decrease further, only one peak impact point appears above the center of two fire sources. As pressure mounts, the low-oxygen zone at the tunnel ceiling contracts progressively, and it primarily appears in the additional region between two fire sources. The temperature processing method is adopted to determine the fire merging and flame length. The fire merging probability is predicted by introducing a piecewise model. Furthermore, a physical model is proposed based on the air entrainment theory to establish the relationship between flame length and the effects of pool spacing, ambient pressure, and heat release rate, which can be applied to both open spaces and tunnels. • Varied thermal hazard scenarios are simulated by altering the ambient pressure, heat release rate, and pool spacing. • The evolution behaviors of ceiling gas temperature, fire merging, and flame length are analyzed. • The prediction models of fire merging and flame length are established based on the temperature method and air entrainment theory. [ABSTRACT FROM AUTHOR]

• Experiments were performed to explore the flame performance and burning characteristics of two unequal rectangular n-heptane fires. • Various parameters such as flame interaction, mass burning rate, flame height, temperature, and radiation were collected and analyzed. • By incorporating air entrainment theory, models for flame merging and flame height were developed. The production, transportation, and storage of combustible liquid fuel encounter substantial safety challenges, notably pool fires resulting from the seepage of storage vessels and pipelines. In practical fire incidents, multiple fire sources with varying pool dimensions and thermal loads are present, exacerbating the severity and uncontrollability of these disasters. Experiments were performed to explore the flame performance and burning characteristics from two unequal rectangular n-heptane fires with varied pool spacings (0–1 m) and area ratios of two rectangular pools (1–4 times). The results indicate a significant association between the three stages of flame interaction and the ratio of spacing to flame height at zero spacing (S / L f , S= 0). As S increased, the total mass burning rate increased at first and then decreased gradually owing to the competitive nature of heat feedback and air entrainment mechanisms, and the maximum value was reached when S equaled 1.5 times the pool width (S/w = 1.5). In the case of unequal double fire sources, it was observed that as the scale difference between the two fuel pools increased, the impact of interaction on the larger fuel pool became less pronounced. Conversely, the smaller-scale fuel pool experienced a more substantial heat feedback, resulting in a swift escalation in its mass burning rate. Combined with the stage of flame interaction, a piecewise model of flame height was proposed by incorporating the energy conservation principle and the air entrainment theory. The accuracy of the models concerning flame interaction intensity and flame height was validated through comparisons with data from existing literature. These models can also be extended for application to scenarios involving two identical fires and configurations with square arrays of fires. [ABSTRACT FROM AUTHOR]

Flame radiative characteristics, depending on the flame type, flame scale, and fuel type, are key parameters that determine fire spread and thermal hazards. Accurate prediction of flame radiation in large-scale natural fires requires detailed information on radiative characteristics. This paper presented an experimental study on the radiative properties of large-scale fire whirls with RP-5 aviation fuel. The maximum flame height and mean width reached 21.40 m and 3.60 m, respectively. Unlike large-scale free pool fires, the radial stabilization effect of the fire whirl suppressed the unstable toroidal vortex structures and the smoke production significantly. Most of the flame was high-temperature and high-emissive power areas in the large-scale fire whirl, and the emissive power exceeded 100 kW/m2 on about 60 % flame area. The flame temperature and emissive power first increased with height, then stabilized and decreased in the upper part of the fire whirl. The peak flame temperature, mean flame temperature, and mean emissive power all increased with an increase in the flame width. The mean emissive power ranged from 93.06 to 157.47 kW/m2, 2.3–3.9 times the values in free pool fires of the same scale. The solid flame radiation model could effectively predict the instantaneous radiative heat fluxes from large-scale fire whirls to distant external targets with the corrections of atmospheric transmissivity. The semi-empirical correlation of the radiative fraction based on the turbulent dissipation showed that neither the flame size nor heat release rate affects the radiative fraction, consistent with the our and other researchers' experimental data from medium to large-scale fire whirls. [ABSTRACT FROM AUTHOR]

The pyrolysis of woody biomass has received extensive attention due to its importance in the thermal chemical conversion and energy utilization. Due to the complexity of actual reaction scheme, the pyrolysis of wood is generally modeled on the basis of apparent kinetic models. In this paper, six classic lumped kinetic models (Models I-VI) were applied and compared with each other to analyze their sensitivity coupled with Shuffled Complex Evolution method based on the measured thermogravimetric data. The optimized kinetic parameters were used to predict the pyrolysis process, and then verify the validity of different reaction kinetic models. The results show that the existence of second tar reaction for one-component mechanism and the refinement of reactant components for multi-component mechanism can be helpful to improve the reasonability of reaction models. Eventually, the simplest global reaction Model I and second tar reaction involved one-component Models III, IV, as well as three-component parallel reaction Model V can achieve the better compatibility of reaction kinetic models and Shuffled Complex Evolution optimization, with the acceptable efficiency to describe the pyrolysis of woody biomass. • Sensitivity of commonly used TG pyrolysis kinetic models is compared. • Shuffled Complex Evolution method is coupled with all reaction models. • Various sets of optimized reaction kinetic parameters are obtained. • Second tar reaction and reactant component refinement can improve pyrolysis model. [ABSTRACT FROM AUTHOR]

The dynamics of back-layering flow induced by a continuous buoyant release in a naturally ventilated inclined tunnel are investigated. The back-layering length and the density difference between the buoyant back-layering and the ambient flow are investigated using brine water experiments. The back-layering length is independent of buoyancy flux of the releasing source in such a configuration; however, the density difference between the buoyant back-layering and the ambient flow increases with a 0.52 power function of buoyancy flux. The back-layering fluid density is remarkably larger than that of downstream flow. In particular, we focus on the critical condition for preventing back-layering in such a naturally-ventilated tunnel configuration. The longitudinal flow in an inclined naturally-ventilated tunnel is assumed to be induced by the stack effect. We firstly derive a theoretical equation for predicting the critical condition for an inclined tunnel and identify that the critical condition is sensitive to buoyancy source location, but it does not exhibit any significant dependency on buoyancy flux of the source. The experimental results show that, in a wide range of values of buoyancy flux, the conclusions derived from the theoretical analysis are valid, indicating the critical velocity can be achieved in an inclined tunnel without any forced mechanical flow, and the condition for achieving the critical velocity is mainly dependent of buoyant source location. [ABSTRACT FROM AUTHOR]

The multiplicity of smoke flow states may pose a great threat to both human evacuation and emergency rescue in tunnels. A case study is conducted to investigate the multiple steady states of fire smoke transport in a triple-branch tunnel. Both theoretical analysis and numerical simulation are employed in this study. For the case examined in this study, at least three flow regimes are identified under the effects of similar boundary conditions. The results indicate that even for a “well-designed” smoke exhaust system, multiple flow regimes could exist and some flow modes could threaten the human evacuation. The operating point of the mechanical fan system shifts due to the transition between multiple flow regimes. The preliminary results indicate that the inclination angle of the inclined tunnel branches could play an important role in the multiplicity of smoke flow states in such a tunnel system. [ABSTRACT FROM AUTHOR]

• The combined kinetic method is coupled with Particle Swarm Optimization. • The three-parallel reaction model can describe beech pyrolysis well. • Cellulose corresponds to Power law reaction mechanism. • Both hemicellulose and lignin correspond to Order-based reaction mechanism. • The application of the established mechanism is validated for wider heating rates. Kinetic reaction mechanism plays a key role in accurately predicting biomass pyrolysis behavior. However, the order-based reaction mechanism is usually defined as the default in the existing kinetic studies. For the purpose of exploring the exact kinetic reaction mechanism of biomass pyrolysis, the combined kinetic method is tried here by coupling two common kinetic models (one-step global reaction and three-parallel reaction). The decomposition rate expressed by the method is related to three key parameters, whose values are corresponding to the establishment of reaction mechanism. The combined kinetic method is further coupled with a heuristic optimization algorithm to obtain more exact kinetic parameters in order to explore the reaction mechanism. The results show that it is hard to infer the reaction mechanism based on one-step global reaction, while based on three-parallel reaction, the respective reaction mechanism of each component can be established as Power law for cellulose, Order-based for hemicellulose and lignin by comparing with the thermogravimetric data. More importantly, the established mechanism and optimized parameters can be used to accurately predict the micro-scale pyrolysis behavior of biomass (beech) at a wider range of heating rates. [ABSTRACT FROM AUTHOR]

As a graphene-like material, MXene, represented by Ti 3 C 2 T x , has been found to possess promising flame retardant potential in polymers due to their excellent thermal and catalytic actions, as well as lamellar barrier effect. Thus, it is of great significance to explore whether MXene with double transition metal components has a higher flame retardant efficiency. Herein, Ti 3 C 2 T x and bimetallic MXene (Mo 2 Ti 2 C 3 T x) were fabricated by acid-etching method and then introduced into epoxy resin (EP) for the comparative investigation of their flame-retardant effect. The results indicated that MXenes were homogeneously dispersed in EP matrix, which can contribute to the improvements of thermal and flame retardant properties of EP composites. Upon the incorporation of 1 wt% Mo 2 Ti 2 C 3 T x MXene, the EP composites achieved a significantly reduced maximum mass loss rate (R max) by 39.4%, superb over EP/Ti 3 C 2 T x composites. Moreover, Mo 2 Ti 2 C 3 T x MXene endowed EP composites with a notable downward trend in fire risk, reflected by the decreasing PHRR of 34%, PSPR of 32.7%, TSP of 57.7%, PCO of 30.8%, along with significantly reduced SF value by 72.7%, which was superior to EP/Ti 3 C 2 T x composites. The strong catalytic attenuation and charring effect of transition metal Mo–Ti elements for bimetallic Mo 2 Ti 2 C 3 T x MXene, as well as nanosheet structure, imparted excellent fire retardant performance to EP composites. This work provides new insights into the application of bimetallic MXenes in flame retardant polymer composites. [ABSTRACT FROM AUTHOR]

Thermoplastic polymers are versatile for different fields, and their waste is produced largely. Among the waste treatment methods, pyrolysis is an important method to dispose of thermoplastic polymers waste because of potential energy utilization. Furthermore, accurate pyrolysis kinetic parameters can reflect the pyrolysis process. Therein, reaction order n is an essential factor to characterize reaction kinetics, while the difference between different n values is very small, so the accuracy of n should be paid more attention. To obtain the accurate n value of thermoplastic polymers waste in nitrogen, one representative material called extruded polystyrene (XPS) was studied by using thermogravimetric analysis at five heating rates. The kinetic parameters and thermodynamic parameters were calculated simultaneously, and n was estimated by multiple methods (master plots, model-free, Shuffled Complex Evolution (SCE) and model reconstruction) at heating rates of 10, 30 and 40 K/min. The results showed that XPS waste had important energy potentials, and the n was 2, 2.08, 1.99 and 1.64 for four methods, respectively. Moreover, based on fixed kinetic parameters, the accuracy of n obtained by multiple methods was compared at 3 and 80 K/min not used to estimate kinetic parameters. The accuracy of these methods was: SCE > model reconstruction > model-free > master plots. • The kinetics and thermodynamic parameters are analyzed simultaneously. • The accuracy of reaction order estimated by multiple methods is compared. • The Shuffled Complex Evolution (SCE) method has the highest accuracy. • Two biomass materials are used to validate the high accuracy of the SCE method. [ABSTRACT FROM AUTHOR]

Open square fuel pools with areas of 50 m2, 100 m2, 200 m2, 380 m2, and 400 m2 were used to burn RP-5 aviation fuel and diesel oil, under a well-controlled and regulated horizontal wind field with speeds ranging from 0 to 17 m/s by a large-scale open jet wind tunnel. The mean mass burning rate of the fuel in the quasi-steady period was taken as the representative value. Under the calm condition, the burning rates of the two fuels were proportional to the ratios of the ideal heat of combustion to the effective heat of gasification. The burning rates of different size pool fires were little affected by various wind conditions. With the increase of wind speed, all pool fires exhibited a common pattern in the burning rate, a steady growth followed by a level-off constant value. The traditional Froude number (Fr) was unable to predict the behavior of large-scale pool fires under various wind speeds. A modified Froude number (F r * = Fr·Re 0.2) was developed based on the heat transfer correlation for turbulent mixed convection on a horizontal flat plate and successfully correlated a total of nine different large-scale pool fire experimental data under wind conditions. [ABSTRACT FROM AUTHOR]

An open jet wind tunnel with an exit area of 23 ​× ​9 ​m2 has been built to study the behaviors of large-scale pool fires under controlled wind conditions. A series of measurements on the mean and fluctuating wind velocities, using arrays of hot-wire probes and ultrasonic anemometers, were extensively performed in the transverse planes at the leading and trailing edges of the pool (28 ​m and 48 ​m to the exit). The entire pool was located in the potential core of the central jet flow region, and the longitudinal velocity (U) and turbulence intensity (I u) exhibited acceptable uniform distributions within the two vertical planes. The mean turbulence intensities in the two planes were close to those in the flat open grassland and sea (7%–10%). The longitudinal velocity spectra were in good agreement with the Von Kármán spectrum at all levels, and the onset frequency for isotropy was about 1.5–3.0 ​Hz. In the central flow region, the turbulence dissipation rates (ε) were fitted well by ε ​= ​0.067 U 2.69 I u 1.90, and the best-fit line for the turbulent diffusivity (ν t) was ν t ​= ​0.21 U 0.95 I u 0.98. The detailed mean flow and turbulence characteristics provided the necessary information for the pool fire tests and numerical model verification. • An open jet wind tunnel (OJWT) with an exit area of 23 m × 9 m was built for outdoor largescale pool fire research. • Mean and turbulent flow characteristics of OJWT were investigated with hot-wire probes and ultrasonic anemometers. • Mean velocity and turbulence intensity exhibited acceptable uniform distributions in the pool region. • Longitudinal velocity spectra fitted well with the Von Kármán spectrum at all levels. • Turbulence dissipation rate and turbulent diffusivity were correlated with wind speed and turbulence intensity. [ABSTRACT FROM AUTHOR]

This paper investigates the temperature profile of large scale RP – 5 aviation kerosene pool fire in an open space through a series of large scale experiments of 1 m2, 5 m2, 10 m2, 25 m2 pool sizes. The temperature profile is acquired by thermocouple trees positioned in various distances to the pool centerline, while the ambient wind velocity is captured by four transducers in the experimental field. Results show that the large scale pool fire behaves different to the used small to medium scale experiments. The mass loss rate is in good agreement with Blinov and Khudyakov's results, but the vertical temperature is much lower than the McCaffery's results due to the reduced global combustion efficiency as more sooty smoke produced. The three regimes in McCaffery's model is redefined, correlating well with the vertical temperature profile upon the pool centerline. Gaussian Fit is well proposed for the lateral temperature profile at the pool base level, however as the ambient wind inevitable, the fire plume would be tilted to the downstream direction. Finally, the isothermal diagrams of fire plume for various pool sizes are plotted showing the temperature field of plumes, and also the tilt angle of plumes is presented. [ABSTRACT FROM AUTHOR]