Solid Flame Research Articles

An LBM-FDM coupled numerical model for ignition and transient downward flame spread over solid fuel

The ignition and subsequent transition to steady-state flame spread behaviors over a vertical solid fuel in normal gravity and static environment were numerically studied in this work. Unlike the general approach based on the NS equation for buoyancy flow, the lattice Boltzmann method (LBM) was employed to solve the velocity field in the gas phase. Elliptic equations of temperature and concentration in gas and solid phases were solved by the finite difference method (FDM). An LBM-FDM coupling model for investigating the downward flame spread over solid fuel was developed. The ignition and the flame propagation behavior can be predicted quantitatively. The results show that a point flame with the shape of a disk appears first at the sheet surface when the vertical solid fuel is ignited. The instantaneous temperature response of ignition lags behind the chemical reaction. The point flame gradually develops into an asymmetric arch-shaped flame with two flame fronts near the sample surface. And then, the flame in the downstream zone is separated from the upstream flame source under the effect of the induced buoyant flow, and eventually disappears at the downstream boundary. Finally, the flame on the upstream gradually develops into a steady downward flame spread. The developed model in this work is validated by comparing the gas-phase temperature and flame spread rate between the predicted results and previous experimental data. This paper provides another method to predict the development of solid flame spread.

Theoretical and numerical investigation of heat transfer characteristics of an integrated cookstove under different atmospheric pressures based on theoretical models of solid flame and impingement heat transfer

At present, the problems of the efficient use of energy and heat transfer characteristics of the stoves on plateaus have attracted much attention. In this work, a three-dimensional numerical calculation and theoretical analysis model of impact flame heat transfer was established for the integrated cookstoves widely used in China and verified with the experimental thermal efficiency value. It was found that, with decreased atmospheric pressure, the combustion intensity in the furnace decreases, the flame combustion temperature significantly decreases, the heat transfer rate of the stove decreases, and the total thermal efficiency decreases by 7.5% under pressure of 0.05 MPa compared with normal pressure. By using jet impinged and solid flame models, a heat transfer mathematical model suitable for the inner wok and water jacket of the integrated stove was established. The heat transfer error between theoretical calculation and three-dimensional numerical calculation was no more than 6%. In addition, some methods are proposed to improve the thermal efficiency of integrated stoves under a high-altitude and low-pressure environment. This study not only theoretically reveals the change law of heat transfer characteristics of convective shock and flame radiation heat transfer under low pressure but also has constructive theoretical guiding significance for the improvement of thermal efficiency of highland stoves.

The effect of barriers on reducing thermal heat fluxes from a hydrocarbon pool fire

The radiant heat flux from a pool fire is frequently calculated using the solid flame model, where the flame envelope is approximated as a stationary cylinder whose surface emits thermal radiation at a constant rate. Radiant heat flux calculations using the solid flame model assume the target to be at a given elevation, typically at ground level, and to have an unobstructed view of the fire. The presence of obstacles (e.g., walls, buildings, etc.) or terrain features that would create shaded areas and provide shielding of a target from the fire is typically neglected in these calculations: this is a conservative approach, but it is not accurate. This paper presents a methodology to utilize the solid flame model to calculate the heat flux to a target while taking into account the presence of an obstruction between the target and the fire. The shielded solid flame method can quantitatively account for the presence of obstacles as a passive mitigation measure and allows project developers or designers to optimize their facility layout to meet safety requirements. The methodology presented in this paper uses the same correlations found in currently used solid flame models (e.g., LNGFIRE3), therefore, it remains consistent with current regulatory requirements for LNG facilities in the U.S.

Near-Field Radiant Heat Flux from Open-Air Gasoline and Diesel Pool Fires: Modified Point Source and Discretized Solid Flame Models

This paper proposes novel modifications to existing solid flame and point source models to better predict the spatial contour of near-field, steady-state radiant heat flux from large circular pool fires (with diameters ranging from 1 m to 20 m) with gasoline and diesel fuel. The proposed models account for partial smoke obscuration of the flames, and the emissive power of the visible flame layer is calculated via a radiative fraction of the fire’s heat release rate as a function of the pool size. The modified discretized solid flame model uses a cylinder + cone shape combination whose surfaces are discretized to enable a flexible summation of total radiative energy emission. The modified point source model places its radiating point at the mid-height of the visible flame layer to capture the location of maximum radiation intensity. Predictions from both proposed models are benchmarked against available data from pool fire experiments, calibrated against computational fluid dynamic simulations, and compared with existing analytical solutions for a range of pool fire diameters at varying standoffs and gauge heights. The results demonstrate that the proposed models can effectively predict the spatial contour and peak value of radiant heat flux on nearby targets (i.e., at distances less than 2.5 times the pool diameter) with low computational effort.

Thermomechanical performance of offshore topside steel structure exposed to localised fire conditions

This work reports the results of a numerical investigation aiming at assessing the structural safety of an actual offshore topside steel structure exposed to accidental localised fire conditions. Particularly, the paper explores the nonlinear thermomechanical and ultimate strength behaviours obtained by means of two fire approaches: sophisticated CFD (Computational Fluid Dynamics) and “LF-ESF” (Localised Fire with Ellipsoidal Solid Flame), previously developed and validated by the authors. CFD-based approaches, which typically solve nearly compressible flow with input energy given by a combustion model, allow accurate evaluation of a fluid-thermo response for the entire duration of the simulated accident. However, the analysis complexity, massive amount of produced data, excessive computational and time-consuming make CFD approaches unsuitable for the current applied design usage. On the other hand, the proposed LF-ESF approach displays quite accurate estimates in comparison to CFD counterparts. Moreover, the LF-ESF can be directly modelled in FE-based commercial software and used to obtain the steel temperature variation and thermomechanical behaviour. The obtained results indicate that the LF-ESF approach combined with FE-based models can provide reliable fire-safety analyses, ensuring that the main safety (load-bearing) functions of the offshore steel structures are not impaired during accidental fire conditions.

Development of a framework for dynamic risk assessment of environmental impacts in chemicals warehouse using CFD-BN

Chemical warehouses are one of the high-risk areas in the process industries due to the high diversity and quantity of stored chemicals. Risk assessment is a useful tool for developing appropriate strategies to prevent and control the risks. In this study, computational fluid dynamics (CFD) and Bayesian network (BN) approaches were proposed for dynamic risk assessment. Initially, bow tie (BT) method was used for identifying basic events and modeling the consequences. In order to determine the consequences intensity (heat flux and CO and CO2 concentration), fire dynamics simulator (FDS) and solid flame model were used. A total of 21 causes or failures were identified in the chemical spills, 13 cases of which were related to basic events. Out of the identified causes, the forklift and drum strike basic event had the most contribution of the chemical spills in the warehouse, and the probability of the major spill event scenario 1.25495E−11 was estimated by Bayesian networks. The estimated risk by CFD in combination with BN, after updating, is unacceptable compared to the UK risk criterion. Bayesian networks and CFD approach for dynamic assessment of environmental impact risk in chemical warehouses provide the capability to quantitatively and dynamically assess the consequences of chemical spills by modeling its cause and effect in the warehouse. Based on the results of this method, effective preventive measures can be taken to control the consequences of chemical spills in the warehouse.

Thermal post-buckling behavior of oil storage tanks under a nearby fire

This paper reports research on the thermal buckling and post-buckling of vertical steel tanks under heat induced by a nearby burning tank. A two-layer solid flame model is adopted and a heat transfer analysis is carried out to compute temperatures in the target tank. The temperatures are used as input in the structural analysis based on a geometrically nonlinear analysis and temperature-dependent properties of steel. The structural problem is solved by a finite element analysis to trace the pre- and post-critical equilibrium path. The lower critical temperature is detected and subsequent instabilities are identified until the temperature reaches the maximum value that can be transferred for the specific fuel burning. The post-buckling response is investigated to account for wind effects, separation between tanks, and fluid stored in the target tank. The ratio between first critical temperature and the final temperature at which the process reaches a thermal steady state, is computed in each case.

Evaluation of localized pool fire models to predict the thermal field in offshore topside structures

This article presents a comparative study to predict the thermal behavior of an offshore topside structure under localized fire using different fire models. Thermal fields are estimated using models with different approaches. Sophisticated fire models based on computational fluid dynamics (CFD) are often used in the analysis of this type of accident. However, their high complexity and calculation time make it difficult to use in the design stage of the structure. Simple models usually offer lower temperatures than those estimated by the CFD-FEM model, with limited use in structures with complex geometries. Localized fire with ellipsoidal solid flame (LF-ESF) model was developed as an alternative to previous models that are excessively complex (CFD based) or estimate lower temperatures (Simple). LF-ESF model can evaluate in the design stage the thermal behavior of steel structures under localized fires with the appropriate accuracy in acceptable computation time. The thermal analysis is developed with the aid of commercial software of finite elements. Three case studies are analyzed considering localized fire due to the burning of hydrocarbons. The first two develop the thermal analysis in simple structures and show the main differences between each fire model considered. The last case study evaluated the thermal behavior of an offshore topside structure. The results obtained allow to conclude that the LF-ESF model realistically represents the temperature fields generated by the fire with a relatively low computational cost as compared to the CFD models.

Experimental and theoretical research on flame emissivity and radiative heat flux from heptane pool fires

This paper presents an experimental investigation on the flame radiation characteristics of pool fire, including the flame emissivity, diameter and temperature. A series of experiments of heptane pool fires with diameters of 0.1–0.4 m were carried out. The flame height, mass loss rate, temperature distribution, flame emissivity and radiative heat flux were measured. A four regions function was used to correlate the centerline temperature rise above the pool surface with the flame height. The variations of the flame diameter against the flame height were formulated for D>0.2 m and D ≤ 0.2 m respectively. The highest flame emissivity is found at the flame base, which decreases with increasing height. Furthermore, a new model predicting the radiative heat flux based on classical solid flame model is developed taking into account the flame emissivity, diameter and temperature variations along the flame height. The comparisons between the new model and other models show that the new model can better predict the thermal radiation from heptane pool fires.

The role of two-stage phase formation for the solid-state runaway reaction in Al/Ni reactive multilayers

While extensively studied for heating rates below 1.7 K/s and above 1000 K/s, the solid-state phase transformations in Al/Ni reactive multilayers have not been examined at intermediate heating rates between 100 K/s and 1000 K/s. Combined nanocalorimetry and time-resolved synchrotron x-ray diffraction studies are utilized to address this range of heating rates for multilayers with an overall composition of 10 at. % Ni and a bilayer thickness of 220 nm. It was found that a two-stage phase formation of Al3Ni proceeds up to a heating rate of 1000 K/s. The two growth stages occur in the solid-state and are kinetically separated. The activation energy of the first growth stage is determined to be 137 kJ/mol, which agrees well with the literature data at low heating rates. At 1000 K/s, a transition to a runaway reaction is observed. Unusual for metallic multilayers, the reaction proceeds completely in the solid-state which is also known as “solid flame.” Using nanocalorimetry, a critical input power density for ignition of 5.8 × 104 W/cm3 was determined. The rapid succession of the two Al3Ni formation stages was identified as the underlying mechanism for the self-sustaining reaction.

A standardized nomenclature for spectrogram EEG patterns: Inter-rater agreement and correspondence with common intensive care unit EEG patterns

ObjectiveTo determine the inter-rater agreement (IRA) of a standardized nomenclature for EEG spectrogram patterns, and to estimate the probability distribution of ictal-interictal continuum (IIC) patterns vs. other EEG patterns within each category in this nomenclature. MethodsWe defined seven spectrogram categories: “Solid Flames”, “Irregular Flames”, “Broadband-monotonous”, “Narrowband-monotonous”, “Stripes”, “Low power”, and “Artifact”. Ten electroencephalographers scored 115 spectrograms and the corresponding raw EEG samples. Gwet's agreement coefficient was used to calculate IRA. ResultsSolid Flames represented seizures or IIC patterns 69.4% of the time. Irregular Flames represented seizures or IIC patterns 38.7% of the time. Broadband-monotonous primarily corresponded with seizures or IIC (54.3%) and Narrowband-monotonous with focal or generalized slowing (43.8%). Stripes were associated with burst-suppression (37.2%) and generalized suppression (34.4%). Low Power category was associated with generalized suppression (94%). There was “near perfect” agreement for Solid Flames (κ = 94.36), Low power (κ = 92.61), and Artifact (κ = 93.72). There was “substantial agreement” for all other categories (κ = 74.65–79.49). ConclusionsThis EEG spectrogram nomenclature has high IRA among electroencephalographers. SignificanceThe nomenclature can be a useful tool for EEG screening. Future studies are needed to determine if using this nomenclature shortens time to IIC identification, and how best to use it in practice to reduce time to intervention.

Could pool fire alone cause a domino effect?

The chain of accidents, also known as the domino effect, is responsible for several severe accidents in the chemical and process industries. The pool fire is often blamed as one of the primary accidents triggering a domino event. The present study is devoted to analyzing whether the pool fire alone can cause a domino event in processing and storage facilities. Two models, including a solid flame model and computational fluid dynamic model, are applied to simulate the escalation vector caused by a pool fire. The escalation vector probability is calculated using a probit model for a potential domino effect. This study also investigates the possible factors that can cause a domino effect and determine credible accident scenarios. The proposed concept of escalation vector and numerical models are tested using two past accidents. The study estimates the possibility of pool fires alone causing a domino effect. The results of this study show that although the pool fire alone has the ability to cause a domino event, it is unlikely to occur if a safe distance separates the equipment and proper mitigation measures are employed.

Configuration predictions of large liquefied petroleum gas (LPG) pool fires using CFD method

Liquefied petroleum gas (LPG) has potential pool fire risks due to its flammability. The configuration of pool fires plays a significant role when applying the solid flame model or point source model to assess the risks from heat radiation. However, no existing correlations can precisely predict the configuration of large LPG (100% propane) pool fires. To enhance the fundamental understanding on how pool diameter and wind velocity can influence the configuration of large LPG pool fires, an experimentally validated Computational Fluid Dynamics (CFD) model is employed to simulate fires using different burning rate models. Fire temperature profiles, flame heights, and flame tilts predicted by the CFD model were compared with empirical models and experimental data. Accordingly, new correlations for flame height and flame tilt as functions of pool diameter D and wind velocity uw have been developed. The comparisons demonstrate that the new correlations have the best overall accuracy in the prediction of flame height and tilt for large LPG pool fires under different conditions (10 m ≤ D ≤ 20 m, 0 ≤ uw ≤ 3 m·s−1).

The effect of manufacturing technologies on the flame retardancy of carbon fibre reinforced epoxy resin composites

We prepared reference and flame-retarded carbon fibre reinforced composites both by liquid composite moulding, in particular vacuum infusion, and by hand lamination followed by hot pressing (wet compression moulding) in order to study the effect of carbon fibre reinforcement and particle distribution of solid flame retardants (FRs) on fire performance. The flame-retarded matrix had 3% total phosphorus (P) content from ammonium polyphosphate (APP). When the infusion site of the composite produced by vacuum infusion faced the conical heater during the mass loss type cone calorimeter tests, the peak of heat release rate (pHRR) was lower, the time of pHRR became longer and the intumescence increased in comparison to the laminated sample, which supported our hypothesis about the filtration of solid APP during the vacuum infusion process. In order to model the suspected filtration, we prepared a laminated composite sample with an increasing amount of APP equivalent to 1%, 2%, 3%, 4%, 5% P content in each subsequent layer.The HRR curve of the composite produced by vacuum infusion with the infusion site facing the conical heater was basically identical with the curve of the model composite with the 5% P layer facing the conical heater in the early phase of the degradation, while in the main degradation phase, the lower burnable ratio of the composite prepared by vacuum infusion led to a further decrease in pHRR (184 kW/m2) and THR (15.5 MJ/m2), and the consequent best overall fire performance of the composite produced by vacuum infusion. The suspected accumulation of APP in the first layers of the composite caused by the carbon fibre reinforcement was proven by SEM-EDS elemental maps of the whole cross-section of the composite.

Оценка максимального поперечного размера многослойных биметаллических пленок для протекания в них самораспространяющегося высокотемпературного синтеза на примере структуры Ni/Al

To simulate self-propagating high-temperature synthesis (solid flame combustion), a layered model is taken as the basis in which the product is formed between the layers of the starting reagents due to solid-phase diffusion in non-isothermal conditions, while the combustion wave propagates along these layers.It turned out that the cords from layers of aluminum and nickel with a thickness of up to 50µmv will completely turn into a high-temperature melt The calculation results will optimize the processes welding-soldering of heat-sensitive materials and parts of electronic components of various devices.

Thermal effects of fire on a nearby fuel storage tank

This work presents numerical modeling and quantitative results of the heat transfer process from a burning tank to an adjacent tank. The flame is represented by a solid flame model in which two zones are identified: a lower clear flame layer with high temperatures and a darker upper layer in which the flame carries soot and smoke. Semi-empirical models are used to estimate the geometry of the flame; other models were also adopted to account for wind effects. The emissive power of each layer of the flame was locally evaluated as a function of temperature. A heat transfer process was followed from the flame to the target tank, at which an energy balance is carried out to include radiation from the flame, radiation from target tank surfaces, and convection to air and to fuel stored in the target tank. The results are presented in the form of temperature distributions on the target tank, which are an ingredient to perform structural analysis. Parametric studies are carried out to investigate the influence of the vertical location of the flame, wind speed, level and temperature of the fuel stored in the target tank, size and distance between tanks. Flame location at ground level, wind speed, higher temperatures of stored fluids, and short separation between tanks are identified as crucial elements increasing thermal effects on the target tank, but the results are not so much influenced by tank size.

Effect of aluminum diethylphosphinate on flame retardant and thermal properties of rigid polyurethane foam composites

Rigid polyurethane foam/aluminum diethylphosphinate (RUPF/ADP) composites were prepared by one-step water-blown method. Furthermore, scanning electron microscope (SEM), thermal conductivity meter, thermogravimetric analysis (TGA), limiting oxygen index, Underwriters Laboratories vertical burning test (UL-94) and microsacle combustion calorimetry were applied to investigate thermal conductivity, thermal stability, flame retardancy and combustion behavior of RPUF/ADP composites. Thermogravimetric analysis–Fourier transform infrared spectroscopy (TG–FTIR) was introduced to investigate gaseous products in degradation process of RPUF/ADP composites, while SEM and X-ray photoelectron spectroscopy were used to research char residue of the composites. It was confirmed that RPUF/ADP composites presented well cell structure with density of 53.1–59.0 kg m−3 and thermal conductivity of 0.0425–0.0468 W m−1 K−1, indicating excellent insulation performance of the composites. Flame retardant test showed that ADP significantly enhanced flame retardancy of RPUF/ADP composites, RPUF/ADP30 passed UL-94 V-1 rating with LOI of 23.0 vol%. MCC test showed that ADP could significantly decrease peak of heat release rate (PHPR) of RPUF/ADP composites. PHPR value of RPUF/ADP20 was decreased to 158 W g−1, which was 21.8% reduced compared with that of pure RPUF. TG–FTIR test revealed that the addition of ADP promoted the release of CO2, hydrocarbons and isocyanate compound in first-step degradation of RPUF matrix while inhibited the release of CO in second step degradation. Char residue analysis showed that the addition of ADP promoted polyurethane molecular chain to form aromatic and aromatic heterocyclic structure, enhancing strength and compactness of the char. This work associated a gas–solid flame retardancy mechanism with the incorporation of ADP, which presented an effective strategy for preparation of flame retardant RPUF composites.

Framework for rapid prediction of fire-induced heat flux on concrete tunnel liners with curved ceilings

Recent vehicular fires in concrete-lined tunnels have demonstrated the vulnerability of the liner to heat-induced spalling and cracking damage. To evaluate the structural fire resistance of either existing or newly designed tunnel structures, there is a need for fast-running tools that can accurately predict the distribution and severity of fire-induced heat exposure over the interior surface of the liner. This study proposes an analytical prediction framework which is more realistic than current design fire curves and yet less computationally intensive than high-fidelity numerical solutions. The Confined Discretized Solid Flame (CDSF) model is proposed for calculating the spatial contour of total heat flux imparted to the tunnel liner due to an enclosed fire. The CDSF computation includes both radiation heat transfer via a 3D discretized solid flame and a convective region representing the ceiling jet of smoke and hot gas. CDSF heat flux results show strong agreement with experimentally validated computational models at a fraction of the computational cost over a matrix of four large vehicle fire sizes and three tunnel prototypes with curved ceilings (i.e. horseshoe or circular cross-sections). The fast-running CDSF approach is conducive to parametric thermal analysis and stochastic damage evaluation for concrete tunnel liners exposed to fire.

Static and dynamic flame model effects on thermal buckling: Fixed-roof tanks adjacent to an ethanol pool-fire

Storage tank fires (such as pool-fires) often occur in the petrochemical tank farms. Flame pulsation is an important characteristic of the turbulent flames observed in pool-fires. Current cylindrical solid flame models inadequately predict the thermal radiation of pool-fires because of the ignorance of the flame pulsation effect. In this study, the thermal buckling behavior and fire resistance of a fixed-roof Q345 steel tank with a stepped thickness exposed to a neighboring ethanol pool-fire based on the flame pulsation model is numerically investigated. The influence of smoke generated by the combustion process which can reduce thermal radiation fluxes is taken into account. Geometric and material nonlinearity which considers nonlinear strain-displacement and stress-strain relation respectively is used on finite element analysis. Results show that the thermal buckling mode of the cylindrical tank wall is elastic buckling, and the thermal buckling behavior is non-linear. The fire resistance of the fixed-roof steel tank increases significantly as the vertical fire location increases, and the fire resistance decreases with the burning tank diameter increasing. Moreover, the fire resistance of the fixed-roof steel tank for a cylinder-cone combined flame based on the flame pulsation model is larger than that for a cylindrical flame. The study can be used to optimize the steel structure design of oil tanks for resisting pool-fires, and thus reduce the loss caused by fire accidents in tank farms.

Electrospun Nylon-66/5-(4-dimethylaminobenzyliden) rhodanine composite nanofibres for solid phase extraction of palladium ions from wastewater samples

ABSTRACTIn the present work, a simple procedure is presented for the extraction and determination of pre-concentrated trace amounts of palladium ions through solid phase extraction (SPE) and flame atomic absorption spectrophotometry. This process was performed using Nylon-66/5-(4-dimethylaminobenzylidene) rhodanine composite nanofibres. These nanofibres were produced under optimised conditions via two-axial electrospinning technique and characterised by scanning electron microscopy and Fourier-transform infrared spectroscopy. The effect of experimental parameters including solution pH, the type and volume of eluent and contact time was investigated in extraction and desorption process. Under the optimised conditions, good linearity in the range of 0.07–8 μg L−1 and low detection limit of 0.015 μg L−1 were obtained. High enrichment factor of 187.5 and good relative standard deviation of ±2.2% at 5 μg L−1 of palladium had been achieved. The sorbent capacity for palladium adsorption was obtained 27 mg palladium per gram of nanofibres. So, the SPE was successfully applied to pre-concentrate and determine Pd(II) ions with flame atomic absorption spectrophotometer in real samples.