Pool Diameter Research Articles

Experimental study on radiative heat flux from annular pool fires under the cross airflow

This paper investigates the radiative heat flux of annular pool fires under cross airflow (0–5 m/s), a configuration that has been underexplored in fire safety research despite its relevance in industrial fire hazards. Results show that radiative heat flux decreases with increasing distance from the fire source but increases with higher cross airflow speeds and larger annular pool diameters (Din/Dout). Existing models overestimate radiative heat flux in annular pool fires due to the underrepresented hollow flame region. A new modified triangular prism radiation model was developed based on the similarity criterion of annular pool fires. An extensive comparative analysis was further conducted, encompassing a wide array of experimental configurations documented in the literature, characterized by varying diameters spanning from 0.1 m to 0.7 m and cross wind velocity ranges extending from 0 m/s up to 5 m/s. The results of this comprehensive examination reveal a good agreement between the newly established model and the empirical data, thereby substantiating the model’s universal applicability and robust reliability. The new model will effectively assist industrial facilities in enhancing fire safety design, strengthening thermal hazard prevention and control, and ensuring a higher level of fire safety design.

Correlations between Bench-Scale and Large-Scale Extinction Metrics for Firefighting Foams

Locally weighted regressions (LWR) were calculated between MIL-PRF-24385 1.8 m diameter pool fire extinction results and various 19 cm pool fire metrics, as compiled in a recent database. The goal: to define correlations between bench and large-scale foam fire extinction experiments to improve bench-scale experiments to more rapidly screen the firefighting potential of environmentally-friendly foams. Bench-scale metrics included the area under the curve (AUC) for extinction time versus foam flow rate profiles, the average extinction times at binned foam flow rate ranges, and CO2-based extinction times, determined through tunable diode laser absorption spectroscopy (TDLAS) measurements above the pool fire. When cross-validation was implemented within the LWR algorithm, the AUC values, CO2-based extinction times, and extinction times for a flow rate-bin > 1500 ml/min showed the best correlations to large-scale data; however, the R2 values were all below 0.6, indicating a low level of correlation. Although differences between active versus passive firefighter and foam generation methods exist between the two scales, data accuracy and limited data are likely contributing the most to low R2 values. The LWR correlations are promising and can be improved with accurate data, providing confidence in bench-scale testing despite diminished radiation intensity and turbulence associated with larger fires.

Experimental investigation at reduced scale of the effect of a ceiling on the burning rate of a pool fire

This study examines the influence of the proximity of a ceiling on the burning rate of a fire in enclosures. The parameters included the pool diameter, distance to the ceiling and fuel type. The analysis focused on the average mass loss rate. The results confirmed the increase in mass loss rate with the elevation for all fuel types. This increase in the mass loss rate appears from a distance to the ceiling that is correlated with the flame height. It is caused by an increase in the heat flux emitted by the flame, which changes shape, and the temperature of the ceiling, which increases with the fire elevation. A correlation is proposed to predict the increase in mass loss rate as a function of the enthalpy ratio Δ H/ Lv and flame height. A comparison of the results with previous experimental studies demonstrated consistency between the different tests.

Experimental investigation of effects of ullage height on the burning rate and heat feedback in pool fires

Pool fire with varying ullage height is a common type of accident that occurs in industrial parks. This paper explores the ullage height effects on the burning rate and heat feedback in pool fires through the experimental and theoretical study. A series of experiments were conducted using heptane with four tray sizes and five ullage heights. The results show that, the burning rate initially decreases, then increases and finally decreases as the ullage height increases. These results are mainly dependent on the change of internal flame behavior and thus heat feedback mechanisms with increasing ullage height. In the small ullage height conditions, the convective heat feedback reduces substantially whereas the radiative one rises slightly. When the ullage height reaches to a certain value, the convective heat feedback suddenly increases because of the flame inside the tray. The radiative heat feedback decreases gradually as the ullage height increase continually, while the convective one becomes nearly constant. Based on these results, three regimes are identified in terms of the burning rate variation with heat feedback: (1) convection controlled, (2) convection-radiation controlled and (3) radiation controlled. The new controlling mechanism of the burning rate variation (with ullage height), as a further extension of the classic scaling model by Blinov and Khudyakov on the burning rate variation (with pool diameter), could lay a solid foundation for future studies of the other key parameters in tank fires.

Large Pool Fires in the Process Industry. A Simple Model for Safety Distances Estimation

In recent years, the global production growth and the complexity of processes operation have increased safety concern, especially during the design project, considering potential accidental events as fires, explosions, and their related domino effects. Pool fire is one of the most frequent accidental events. Some procedures for safety distances estimation from pool fires were reported. However, there is a lack of adequate simple models to directly estimate safety distances covering a wide range of substances and pool diameters, considering a continuous interval of receptor vulnerabilities (from damage to people to domino effect prevention). In this paper, a simple model to estimate safety distances is proposed, suitable to be incorporated into complex models (e.g. safety management systems, layout optimization). A surrogate model is achieved by adopting a reference one. Methodologically, the main variables that play a key role modelling a pool fire were selected and their influence on the safety distance was analyzed to propose simple mathematical expressions. NLP optimization problems were solved to optimize the model parameters. A conservative, accurate and easy-to-use model was achieved with the aim of developing safer plants or for their safe operation by improving the optimal process design, or implementing safe management systems, considering risks.

Modelling flame-to-fuel heat transfer by deep learning and fire images

In numerical fire simulations, the calculation of thermal feedback from the flame to the solid and liquid fuel surface plays a critical role as it connects the fundamental gas-phase flame burning and condensed-phase fuel gasification. However, it is a computationally intensive task in CFD fire modelling methods because of the requirement of a high-resolution grid for calculating the interface heat transfer. This paper proposed a real-time prediction of the flame-to-fuel heat transfer by using simulated flame images and a computer-vision deep learning method. Different methanol pool fires were selected to produce the image database for training the model. As the pool diameters increase from 20 to 40 cm, the dominant flame-to-fuel heat transfer shifts from convection to radiation. Results show that the proposed AI algorithm trained by flame images can predict both the convective and radiative heat flux distributions on the condensed fuel surface with a relative error below 20%, based on the input of real-time flame morphology that can be captured by a larger grid size. Regardless of growing or decaying fires or puffing flames induced by buoyancy, this method can further predict the non-uniform distribution of heat transfer coefficient on the interface rather than using empirical correlations. This work demonstrates the use of AI and computer vision in accelerating numerical fire simulation, which helps simulate complex fire behaviours with simpler models and smaller computational costs. Highlights A total framework between AI model and fire simulation software is designed to further enhance the reliability of AI-based fire simulations. A standard pool fire simulation database is built using numerical model recommend by the IAFSS Computation Group. A deep learning model is developed to predict both the convective and radiative heat flux distributions on the condensed fuel surface using numerical images database. The demonstration showcases the application of AI and computer vision to accelerate numerical fire simulation.

Experimental study of heat loss and heat feedback of pool fire of millimeter to centimeter fuel thickness

The leaked liquid fuel has the potential to form a pool fire due to the boundary. The thickness of the fuel (δ) may transition from the millimeter-level to the centimeter-level over time as it leaks. In cases where the pool fires have a δ at the millimeter-level, it is important not to ignore heat loss from the fuel to the substrate, as this can significantly impact both heat transfer and heat feedback evolution. Experiments were conducted to investigate the heat loss and feedback of n-heptane pool fires with varying δ and pool diameters (D). Results showed that the fuel burning rate remains constant whereas δ will vary if the flame is in the steady burning stage. As δ increases, both convection and radiation losses absorbed by the substrate decrease rapidly before decreasing slowly. Smaller values of δ or larger D can result in a greater percentage of heat loss. The effect of heat loss on heat feedback was revealed, and a dominant control mechanism (DCM) for heat feedback was identified for values of δ ranging from millimeters to centimeters with D. As D increases, when δ≤5.0 mm, DCM transits from convection to radiation; when δ=5.0∼10.0 mm, DCM transits from radiation to convection, then to radiation; when δ≥10.0 mm, DCM transits from conduction to convection, then to radiation again. As δ increases, when D ≤ 5.0 cm, DCM transits from convection to radiation, then to conduction; when D continues to increase, DCM is always convection (D = 5.0∼10.0 cm) or transits from convection to radiation (D = 10.0∼20.0 cm). When D ≥ 20.0 cm, DCM is always radiation.

Mini but Mighty: Oscillations in diffusion flames at sub-atmospheric conditions

The oscillatory behaviour of buoyant diffusion flames plays a vital role in determining how flames evolve. Although previous studies have established an inverse square root relationship between oscillatory frequency and pool diameter, f ∼ D-1/2, few have explored the synergistic effect of diameter and reduced pressure on the pulsation phenomenon. This study mainly investigates the characteristics of convection-controlled pool fires (D < 20 cm) at varying sub-atmospheric pressures, with a particular focus on the influence of eddy effects. Four burner sizes (7 cm, 10 cm, 13 cm, and 16 cm) are selected, and pressure levels are set at 95 kPa, 80 kPa, 60 kPa, and 40 kPa, respectively. A pressure chamber, maintaining a nearly constant pressure during combustion, is employed. The morphology of diffusion flames is recorded and subsequently analysed at different pressures. The study finds that flame shapes change from turbulent to laminar as pressure decreases, which is attributed to the smaller vortex size and corresponds to the varicose and sinuous models. Flame height and oscillatory frequency show a slight increase with decreasing pressure. A new correlation based on the dimensionless Richardson number and Strouhal number is proposed to correlate the oscillation and diameter at different pressures, St=0.58(1/Ri)0.54. This study provides interesting insights into the behaviour of buoyant diffusion flames under sub-atmospheric conditions, highlighting the transition from turbulent to laminar flame shapes, changes in flame height, and pulsation frequency trends. This research could potentially contribute to the comprehension of buoyant diffusion flames at sub-atmospheric conditions in future.

Boiling combustion behaviors and heat feedback of pool fire of diesel fuel–water emulsification

AbstractIn the process of submarine oil exploitation and crude oil shipping, the offshore oil leakage accidents occur frequently. In the process of oil spill weathering on the sea, the oil is potentially mixed with water to form oil–water emulsification. The in situ burning is a low‐pollution and high‐efficiency method to eliminate the spilled oil. Meanwhile, as an alternative fuel, the emulsified diesel fuel has the advantage of energy saving and emission reduction. The combustion behaviors of pool fire of diesel fuel–water emulsifications are experimentally studied using three circular fuel reservoirs (10, 15, 20 cm) and five mass proportions of water (0%, 5%, 10%, 15%, 20%). The unsteady combustion process of emulsified diesel fuel is appreciated based on combustion phenomenon, mass burning rate, and flame length. The effects of pool diameter, ratio of water content, and initial fuel thickness on burning rate and flame length are revealed. The primary heat transfer mode in controlling the combustion behavior is explored according to the coupling factors of physical boundary of fuel reservoir, flame, and wall temperatures. This work is of great significance for understanding the combustion behavior of oil spill on the sea and optimizing the removal scheme of oil spill pollutants.

Continuous boilover behaviors of large-scale kerosene pool fires under sub-atmospheric pressure

Accidental fire is a major safety concern in chemical parks, highlighted by the several major fire accidents involving storage tanks in recent years. Boilover is considered as one of the most destructive tank fire scenarios, which occurs when a liquid fuel burning on a water layer, leading to the explosive evaporation of water and consequently a sudden increase of the heat release rate (HRR) and associated flame height due to the splashing of burning fuel. Previous studies on boilover with large-scale pool fires were mostly conducted under normal atmospheric pressure. However, chemical parks are often located in plateau regions, where the effects of reduced pressure on boilover behaviors were rarely examined. Moreover, following the initial boilover, continuous boilover could occur, and its understanding is particularly important in the thermal hazard and risk analysis and firefighting of tank fires. In this study, thin-layer boilover experiments were conducted under sub-atmospheric pressure using aviation kerosene (RP-3) with various initial fuel thicknesses and pool diameters. The burning process, boilover intensity, temperature in the fuel and water layers and associated thermal hazard were analyzed. Experimental results showed that continuous boilover occurred in all test conditions, characterized by a high intensity initial boilover followed by a series of subsequent ones with gradually reduced intensity. The mass burning rate and flame height varied significantly during boilover. It was found that the boilover intensity increases with the initial fuel thickness but decreases with the pool diameter and approaches a nearly constant value when the pan diameter is sufficiently large. The temperature at the fuel/water interface was found to increase from 93 ℃ to around 108 ℃ during boilover, both of which are lower than those observed under normal atmospheric pressure due to reduced water boiling point. The thermal hazard calculated for the initial boilover is highest as expected, and that of subsequent boilovers gradually decreases but could still be higher than that at the steady burning stage. The findings in this work will contribute to risk assessment of continuous boilover in fire accidents.

Experimental study of the thermal and burning characteristics of 15 cm pool fires fueled by heptane-toluene mixtures

This article presents an experimental investigation of the effects of the fuel sooting propensity on the thermal and burning characteristics of 15 cm diameter pool fires burning in air. Heptane is used as reference fuel and two other heptane/toluene blends with toluene volume concentration of 5% and 10% are considered to vary the fuel sooting propensity. An exhaustive characterization of the pool fires is performed with measurements of the flame geometry, puffing frequency, mass burning rate, combustion efficiency, local temperature statistics from a dual thermocouple technique, local mean soot volume fraction from laser light extinction, radiative loss to the surroundings and total heat flux to the center of the pool surface. This comprehensive dataset can be used to develop and validate models for soot formation and radiative heat transfer. The experimental results show that the increase in fuel sooting propensity, characterized by a smoke point height decreasing from 12.5 cm to 4.9 cm, results in a significant enhancement in soot production, with the peak of mean soot volume fraction increasing from 0.62 ppm to 1.11 ppm. Radiative loss to the surroundings is also affected, as radiant fraction and total heat flux to the center of the fuel surface increase from 0.37 to 0.45 and 18.5 to 22.2 kW/m2 respectively. This is accompanied by a significant reduction in combustion efficiency from 0.95 to 0.83. In an opposite way, the impact on the temperature statistics is minor.

Impact of candle wicks and fuels on burning rate, flame shape, and melt pool diameter

Impact of candle wicks and fuels on burning rate, flame shape, and melt pool diameter

Pool Age and Local Habitat Are Associated with Effective Number of Breeders in Spotted Salamander Populations Colonizing Created Vernal Pools

Population genetics can reveal whether colonization of created habitats has been successful and inform future strategies for habitat creation. We used genetic analysis to investigate spotted salamander (Ambystoma maculatum) colonization of created vernal pools and explored the impact of habitat characteristics on the genetic diversity and connectivity of the pools. Our first objective was to examine genetic structure, differentiation, diversity, and potential for a founder effect. Our second objective was to determine if habitat characteristics were associated with effective number of breeders, relatedness, or genetic diversity. We sampled spotted salamander larvae in 31 created vernal pools (1–5 years old) in Monongahela National Forest (WV) in May and June 2015 and 2016. The youngest pools exhibited genetic differentiation, a founder effect, and low effective number of breeders. Effective number of breeders was positively associated with pool age, vegetation cover, pool diameter, and sample size. Vegetation cover was also negatively associated with relatedness. Genetic diversity did not have strong environmental predictors. Our results indicated the effective number of breeders increased and genetic differentiation decreased within 4–5 years of pool creation, a sign of rapid colonization and potential population establishment. Our research also showed that higher vegetative cover within the pool and larger pool diameters could impact habitat quality and should be incorporated into future pool creation.

Effect of circulation on flame heights over liquid fuel pools

A striking feature of fire whirls is that they tend to have higher mean flame heights than free buoyant pool fires at the same heat release rates, which has been extensively studied in the past. Different from the mean flame height, the instantaneous flame height of a fire whirl reflects its dynamic nature in time domain, but has received less attention so far. This work experimentally investigated the effect of imposed circulation on flame heights over liquid fuel pools, including the mean and instantaneous flame heights, as a fundamental model of fire whirls. Both the rotating-screen and half-cylinder types of test facilities with different mechanisms for generating eddies were employed with circular ethanol pools of different diameters as fuel sources. Results showed that the scaling law proposed in previous studies can well estimate the mean flame heights of conical fire whirls, but does not work for the cases when a conical fire whirl-to-extinction transition or vortex breakdown occurs. Meanwhile, the characteristic flame pulsation frequency of a fire whirl is lower than that of a free buoyant pool fire with the same pool diameter, but increases with an increase in the imposed circulation due to enhanced air entrainment. A scaling law based on dimensional analysis is proposed to estimate the dimensionless flame pulsation frequency of a conical fire whirl by a combination of the fuel Froude number and the dimensionless circulation. Furthermore, with an increase in the imposed circulation, the instantaneous flame height transitions from a lower and less volatile position to a higher and more volatile position due to flame precession (an inherent instability of a conical fire whirl). Scaling laws for estimating the maximum instantaneous flame height difference in time domain and the flame precession frequency are deduced to summarize the data from small- and medium-scale tests.

Lip height effects on pool fire: An experimental investigation

This work studies lip height effects on the heat transfer and combustion characteristics of pool fire. Fire experiments of n-heptane and ethanol with pool diameters (D) of 0.1 m, 0.15 m and 0.2 m were carried out, in which the lip height (h) was increased from 0 until the burning could not be sustained. Results show that for both fuels, as the lip height increases, the flame enters the pool and the flame sheet becomes wrinkled and deformed. The n-heptane fire shows two distinct burning behaviors inside and outside the pool, and the burning rate decreases with the lip height due to heat feedback attenuation and air entrainment restriction. The conductive feedback rate remains almost unchanged with different lip heights for both fuels. For n-heptane, the radiative and convective heat feedback rates generally decrease with the lip height, and the convective heat feedback fraction increases as the flame enters into the pool, suggesting intensified turbulence motion. For ethanol, the radiative heat feedback rate decreases monotonically with the lip height, and the convective heat feedback rate increases slightly, followed by a decrease with h/D. A mass flux correlation based on the modified stagnant film theory is developed for the convection-dominated pool fires, which is in good agreement with the experimental data.

Feasibility of Using Green Laser in Monitoring Local Scour around Bridge Pier

Scour around bridge piers is considered as one of the major factors which causes failure of bridges in the United States. An undetected scour can affect the stability of the bridge, eventually leading to the collapse of the bridge. The experimental investigation of scour around a pier using a non-contact measuring method is carried out in this research. A green laser-based non-contact ranging technique is performed on a prefabricated scour hole to study the factors influencing the ability to reconstruct the shape of a scour hole. The experiment was conducted in a 10 ft diameter pool and Leica scan station II was used for the scanning of the scour hole. The turbidity of the water was changed by adding Kaolinite powder to the water. The turbidity was varied from 1.2 NTU to 20.8 NTU by adding Kaolinite. The lab experiments involved changing the turbidity of water to simulate real world conditions. The results from the experimental study show that the turbidity of the water has a direct dependence on the efficiency of the green laser to map the underwater scour profile. The ability of the green laser to capture the fabricated scour hole and pool bed topography were decreased as the turbidity was increased even when the water depth of the pool was reduced. The results from the study show that the green laser is effective in underwater scanning and can be also used for bathymetry profiling and the detection of underwater objects. The method of underwater scanning using a green laser for detecting scour around bridge pier is safe, efficient, and economical.

Modeling and Performance of Continuous Wave Laser Polishing of Electron Beam Melted Ti6Al4V

Continuous wave laser polishing is a promising technique for post-built smoothening of rough metallic surfaces produced by additive manufacturing. In laser polishing, a laser source melts a thin surface layer and redistributes the material resulting in a reduction of surface roughness. This paper develops a first principles-based three-dimensional numerical model for continuous wave laser polishing. The model is validated by comparing the simulated melt pool dimensions to laser polished rolled Ti6Al4V samples. The model predictions of melt pool diameter and melt depth are within 10% of the experimental results. Further, the performance of continuous wave laser polishing as a method to polish rough surfaces of electron beam melted Ti6Al4V parts is investigated. Laser polishing resulted in a maximum reduction of ∼87.6 % in surface roughness average, reducing it from 10.5 microns to 1.3 microns. The melt depth predictions from the numerical model were compared with those of polished electron beam melted samples. The model underestimates the melt depth as it assumes an initially flat surface and does not account for the energy accumulation due to light entrapment between peaks and valleys of the rough electron beam melted surface. It was also observed that this energy accumulation due to initial surface roughness has a significant impact at higher scan speeds than at lower scan speeds.

Experimental study on the burning rate of continuously released spill fire on open surface with measurement of burning fuel thickness

Failure of the storage containers often leads to the release of flammable liquid. The fuel may burn while spread, and forms a spill fire. The fuel depth in a spill fire is quite shallow, which makes the burning rate of the spill fire much different with that of the pool fire. In this paper, the n-heptane spill fire was experimentally studied on both flat surface and inclined surface. The burning fuel thickness was measured for the first time. The burning fuel thickness helps establish a theoretical model for the spill fire burning rate, which shows consistent with the experimental data. The result indicates that the spill fire was dominated by the convection, with more than 90% of the total thermal heat feedback, for equivalent diameter ranging from 0.15 m to 0.35 m. It proves that the pool diameter in a spill fire for characterizing the transition from the convective control to the radiative control is larger than that in the pool fire. A comprehensive understanding for the spill fire may be achieved with further studies towards the burning fuel depth, based on the measurement method presented in this work.

Experimental Study on Combustion Characteristics of Transformer Oil Pool Fire with Different Scales

To study the combustion characteristics of transformer oil pool fire with different sizes, transformer oil pool fire experiments with diameters of 40cm, 50cm, and 60cm are carried out to analyze the evolution laws of flame height, fire plume temperature, and oil temperature of oil pool fire with different diameters. The results show that the ignition process of the transformer oil pool can be divided into three typical stages: initial growth stage, full development stage, and extinguished stage. According to the characteristics of combustion rate and flame height, the full development stage is subdivided into the stable combustion stage and boiling combustion stage. The flame height of the boiling combustion stage is about 1.1 times higher than that of the stable combustion stage. With the increase of diameter, the range of intermittent flame area of oil pool fire with three diameters increases by 1.2 times. The heat transfer analysis of the full development stage shows that the oil temperature presents the phenomenon of temperature stratification. There is a boiling layer below the liquid level. Its temperature is about 330 °C and its thickness is about 2.3 mm. The oil temperature under the boiling layer decreases in a gradient, and the boiling layer thickness and temperature have no significant correlation with the oil pool diameter.

Local contributions of resolved and subgrid turbulence-radiation interaction in LES/presumed FDF modelling of large-scale methanol pool fires

The present study aims to quantify individual contributions to turbulence-radiation interaction (TRI) in LES of large methanol pool fires with diameters ranging from 1m to 4m. These simulations feature a steady laminar flamelet (SLF)/presumed Filtered Density Function (FDF) combustion model and the Rank Correlated Full Spectrum k-distribution (RC FSK) for spectral gas radiation. This quantification has a fundamental interest to, on the one hand, understand how these contributions affect the radiative heat transfer from the flame to the surroundings that controls fire growth in industrial fires and, on the other hand, to provide guidance for the development of simplified models for TRI. This analysis is accomplished by exercising a well-validated fire model and using a scaling strategy that preserves the relative contributions of resolved-scale and subgrid-scale (SGS) scalar fluctuations. Large-scale non-luminous pool fires feature large optical thicknesses that increase significantly with the pool diameter. As a result, applying the optically-thin fluctuation approximation (OTFA) leads to a noticeable overestimation of the global radiative loss. The fire plume dynamics is governed by the puffing process whose frequency decreases with the pool size, and, in turn, affects the levels of turbulent intensity. As a result, emission TRI increases in the continuous flame and decreases in the high intermittent flame regions. The contribution of SGS emission TRI to global emission TRI becomes progressively dominant as the pool size increases. The largest contributions to both resolved-scale and SGS emission TRI are the temperature self-correlation and the absorption coefficient-temperature cross correlation, although this latter becomes negligible at the subgrid scale for pool diameters larger than 1m. In addition, the SGS absorption-coefficient self-correlation is also found to be negligible.