Heat Release Rate Of Fire Source Research Articles

Prediction of fire source heat release rate based on machine learning method

Accurate measurement of fire source heat release rate is crucial for comprehensively understanding the fire evolution process. However, the widely used oxygen consumption method requires expensive equipment, incurring high costs. This study proposes a comprehensive framework based on machine learning to predict fire source heat release rate using temperature as input. Firstly, fire scenarios with different parameters in ISO9705 room were simulated using FDS software to obtain temperature at various locations, establishing a fire database. Then, two recursive feature elimination algorithms based on the Lasso and the Random Forest (RF) models were employed separately for feature selection, resulting in two different low-dimensional feature subsets and a control group. Finally, different feature subsets were input to analyse and compare the prediction performance on the heat release rate of three typical algorithms: linear regression (LR), K-nearest neighbor (KNN), and lightGBM. Results indicate that the LightGBM model trained with the feature subset selected by the recursive feature elimination algorithm based on the Random Forest model exhibits the best predictive performance, with root mean square error (RMSE) and mean absolute error (MAE) of 23.89 kW and 15.49 kW respectively, and a coefficient of determination (R2) of 0.9916. This comprehensive framework based on machine learning demonstrates excellent predictive performance and is cost-effective, providing a new and effective approach for predicting fire source heat release rate.

Numerical study on plug-holing of double fires in tunnel with centralized smoke exhaust

In tunnel fires, smoke is the main fatal factor causing casualties. The technical parameters of tunnel smoke extraction are particularly critical. However, the parameters related to smoke control have rarely been experimentally and quantitatively studied in a tunnel caused by two adjacent fire sources. Numerical simulations were performed to study the plug-holing phenomenon in the centralized smoke exhaust tunnel with multi-fire sources. A 1:10 small-scale tunnel (length 25 m; width 1.2 m; height 0.8 m) was built using FDS. The effects of different fire heat release rates Q̇, fire source separation distances, and smoke exhaust velocities (v) on the plug-holing were considered. Firstly, the smoke layer height beneath the exhaust vent gradually increases as the exhaust velocity becomes higher and then remains almost unchanged until the plug-holing phenomenon occurs. Additionally, the smoke layer height becomes lower as the fire source separation distance increases for the fires with constant heat release rate. For all Q̇ values, the critical plug-holing velocity increases with the increasing separation distance S and Q̇. In addition, by modifying the critical Froude number (Frc), a predictive model of the critical plug-holing velocity considering the dimensionless fire source heat release rate and separation distance is obtained. Furthermore, the modified critical Froude number model, accounting for two adjacent fires with different separation distances, is established. The correlation between the new model and the simulation results shows quite good agreement, indicating that the proposed model can provide a satisfactory prediction for the critical smoke exhaust velocity in plug-holing conditions of double fire sources. This work can provide valuable guidance for tunnel design concerning fire safety.

Numerical study of the convective heat transfer coefficient for steel column surrounded by localized fires

The convective heat transfer coefficient hc characterizes the heat transfer capacity between the fluid-solid interface in a thermal convection phenomenon. At present, values adopted from specifications are mostly used to define the hc coefficients in localized fire researches. In this paper, the specific scenario of the steel column surrounded by fire plume is selected as a typical case to explore the surface hc change rules of the steel column under the action of the fire source at the bottom. Different from the application of the concept of adiabatic surface temperature (AST) to achieve fluid-solid thermal coupling, this paper takes the scenario with the fire source heat release rate (HRR) being 81 kW as an example and conducts a two-way coupling simulation analysis of the fire and the thermal models by means of CFD codes. First, the validity of this simulation methodology is verified by comparing the results of the numerical model and the experiment. Following this, the distribution laws of the spatial velocity and temperature fields are analyzed, and the hc coefficient of the steel column surface is explored in detail using theoretical formula and traditional empirical formula respectively. It is noted that the hc results obtained based on theoretical formula can comprehensively consider the velocity boundary layer and temperature boundary layer situations above the column surface, which is a direct result of the definition of the convective heat transfer coefficient. It is found that the hc‾ is lower at the bottom of the column and increases with height, with relative maximum value in the lower and middle parts of the column, reaching around 40 W/m2 K. The hc‾ results decrease along the axial direction, with the value of upper part of the column being about 20 W/m2 K. In contrast, the hc‾ distributions along the height obtained by the empirical formulas are similar to the distribution of fire plume velocity along the height. In other words, it considers only the effect of the velocity boundary layer, while the effect of significant changes in fluid temperature on convective heat transfer behavior is less considered. Compared to the results based on the theoretical definition, the hc‾ results obtained by empirical formulas are significantly smaller in the lower and middle parts of the column, and higher at the top of the column. Finally, a new hc‾ practical formula for the column surfaces surrounded by fire plume is proposed, which agrees well with the results based on the theoretical definition in several cases.

Full-scale experimental and numerical study of smoke spread characteristics in a long-closed channel with one lateral opening

This paper aims to study the characteristics of smoke flow in a long-closed channel with one lateral opening at one end. A series of full-scale experiments with different longitudinal positions and heat release rates of fire sources were carried out. And, the corresponding numerical simulations were conducted to help explain the law of smoke flow field. The characteristics of the smoke spread on both sides of the fire source, the thermal plume distribution within the channel, and the maximum ceiling excess temperature were analyzed. Results show that the existence of the end walls in the long channel causes the smoke to accumulate, which further results in the smoke settlement going through three stages. The lateral opening causes a significant difference of smoke flow and other characteristics from the channel with both ends open. When the fire source approaches the closed end without opening, the vertical fire-induced plume inclines to the closed end because of the asymmetrical air supplementation. Due to the limited air supply, the combustion will change to ventilation-controlled as the fire source heat release rate increases. The maximum ceiling excess temperature is higher than that with both ends open and is basically not influenced by fire positions studied in this work. It has been verified that the dimensionless maximum ceiling excess temperature of the smoke is also proportional to the dimensionless heat release rate. This study can provide a reference for fire prevention and smoke exhaust strategies for long channels.

Experimental study on the smoke movement and flame extension length characteristics of strong fire plumes in a sealed tunnel

Sealing strategy is one of the methods available to extinguish tunnel fires. In this study, based on a 1/10 reduced-scale model tunnel, the fire source heat release rate and source-ceiling height were changed, and the sealing walls with various sealing ratios and opening positions were set to study the smoke movement and flame extension length characteristics of strong fire plumes. The results show that for the total sealing ratio of 75%, the competition between smoke overflow and air supplement when the opening position is in the middle area is stronger than that when the opening position is in the upper area or lower area. For the total sealing ratio of 50%, the competition between smoke overflow and air supplement is not obvious due to the large opening area. The flame extension length beneath tunnel ceiling increases with fire source heat release rate and decreases as source-ceiling height increases. When the total sealing ratio is 50%, the flame extension length beneath tunnel ceiling is close to that without sealing, and the flame extension length beneath tunnel ceiling becomes longer when the total sealing ratio is 75%. As the total sealing ratio increases, the stability of the flame extension beneath tunnel ceiling decreases. Based on dimensional analysis, empirical models are developed to predict the flame extension length beneath ceiling in the sealed tunnel.

Numerical Analysis of Ultimate Mechanical Characteristics of Suspension Bridges’s Cable in High Temperature Fire

Relying on the joint research project, research is carried out on the ultimate mechanical characteristics of suspension bridge slings under high temperature fire. The establishment of a local transient temperature field heat transfer model based on the FDS software, and the analysis of the temperature distribution law of the fire source at different wind speeds. The most unfavorable fire condition is the combination of the fire source heat release rate of 300MW and the wind speed of 14m/s; the overall structure model of the bridge is modeled by ANSYS software. Firstly, the modal analysis of the whole bridge model is carried out to verify the accuracy of the modeling, and then the thermal structural coupling analysis is carried out under the most unfavorable fire conditions to obtain the structural response of the whole bridge structure under the sling fire. According to the change trend of the structure response of the cable under fire, the fire resistance limit of the bridge structure is obtained as 460°C; Under the most unfavorable fire burning situation, when the limit number of broken cable in the span is 3, the cable will be caused into collapsing continuously; the composite protective layer has a significant effect on the fire resistance of the cable.

Numerical simulation on the maximum temperature and smoke back-layering length in a tilted tunnel under natural ventilation

The present study investigates the maximum temperature and smoke back-layering length S in the downhill direction from the fire source in a tilted tunnel under natural ventilation. Numerical simulations were conducted using FDS to study the smoke flow behaviors for a fire in a tunnel with nine tunnel slopes of 0, 1%, 2%, 3%, 4%, 5%, 6%, 7% and 8%. It was found that, due to the stack effect, the smoke stagnated at a distance from the fire source in the downhill direction. The effects of tunnel slope, α, fire source heat release rate, Q̇, source-ceiling height H and tunnel width W on the maximum temperature and smoke back-layering length were studied. Results showed that the maximum temperature under the ceiling decreased with the increasing of tunnel slope or the decreasing of tunnel width. However, it increased with the increasing of heat release rate or the decreasing of source-ceiling height. A model was proposed for the maximum temperature rise. The smoke back-layering length S decreased with the increasing of the tunnel slope. Fire source heat release rate and tunnel width had no significant effect on the smoke back-layering length. And the smoke back-layering length decreased with the decreasing of source-ceiling height. Based on dimensional analysis, a simple model including the effects of both the tunnel slope and source-ceiling height H, was proposed to predict the smoke back-layering length.

An experimental investigation and scaling analysis on flame sag of pool fire in cross flow

Flame sag, a phenomenon observed as flame sinks downwards along the leeward sidewall, occurs for a pool fire having its rim above the ground in cross flows. Few data or investigations of this phenomenon have been reported in the literature. In the present study, the length of flame sag measured from the lowest point of sunk flame to the pool rim; as well as the critical speed of the cross flow under which the lowest point of sunk flame reaches the ground level (namely flame sag length equaling sidewall height), were quantified. Experiments were carried out by employing square quartz sand box pool fires with dimensions in the range of 10–20 cm for various cross flow air speeds, heat release rates and pool rim heights. Propane is used as the fuel. The results showed that the length of the flame sag increased with the increasing of the fire source heat release rate. And it also increased with the increasing of the air speed of the cross flow. However, the flame sag length decreased with increasing pool size. The critical air speed of the cross flow at which the flame sag reached the ground increased with increasing pool size and rim height, meanwhile decreased with increasing heat release rate. A scaling analysis for the interaction physics of the fuel flow near the base with the cross flow, and the total buoyant flow (heat release rate) of the fire with the cross flow, was provided to characterize the flame sag behavior. Two dimensionless quantities(ρa-ρf)gDρaUw2, Q̇/DgρacpTaUw3, namely an inverse Froude number for the base and an inverse Froude number for the interaction of total buoyancy of the fire with cross flow, were derived from the analysis with a new length scale found as ξL=ρaUw2(ρa-ρf)g. The data of flame sag length, as well as the critical value of the cross flow speed for flame sag reaching ground level, were shown to correlate well to the proposed dimensionless quantities.

Influence of mechanical smoke exhaust on smoke spread in underground tunnel

The model of a tunnel in Beijing is established, and the smoke reflux, the smoke reflux length and the influence of longitudinal wind speed on temperature distribution of the tunnel vault are studied using numerical simulation method. The length of the tunnel is 150 m, the cross section is circular, the height of the tunnel is 6.3 m and the width is 6 m. The simulation results show that the smoke reflux length of the subway tunnel fire decreases with the increase of the longitudinal positive pressure wind speed, and the reflux length decreases linearly with the increase of wind speed when the reflux length is more than 10 m. The gradient of the reflux length decreases with the increase of the wind speed when the distance from the fire source decreases. The temperature curve of tunnel vault is consistent. Under the same fire source heat release rate, the flue gas temperature decreases with the increase of ventilation wind speed, and the distance between the highest temperature of the ceiling and the fire source decreased with the increase of the longitudinal ventilation wind speed.

Numerical Simulation Study on Sprinkler Control Effect in UBS Fuel Tank Room of Nuclear Power Plants

FDS (Fire Dynamics Simulator) is the software to computing fluid dynamics which taking the flowing in fire as the main simulation target. In this paper, a model closed to real fire scenario of UBS (emergency diesel generator) fuel tank room of NPP is established by FDS. By analyzing this model, details on the effectiveness of controlling the fire source heat release rate, the key point temperature and the slices in the process of fire extinction based on sprinkler systems are discussed. In addition, it will show the advantages and feasibilities of FDS in NPP(nuclear power plant) application.

One-dimensional analysis of the global chimney effect in the case of fire in an inclined tunnel

A one-dimensional computational analysis is presented of the global chimney effect due to a fire source in an inclined tunnel. Fire-induced flows are not accounted for in the present study: the computed velocity, due to global heating, is to be superposed as an initial and/or boundary condition in detailed computational fluid dynamics (CFD) simulations in a region of interest. The results must not be used as a replacement for such detailed simulations in e.g. network problems. Two calculation options are explained for the global chimney effect. The first method is based on the global heating of the entire tunnel part between the fire source and the higher positioned tunnel outlet. In the other method, the initial fire-influenced region is restricted to a certain distance and, as soon as a prescribed temperature rise is met, the fire-influenced region length increases until the tunnel outlet is reached. The treatment of the enthalpy flow rate through the fire-influenced region boundaries is discussed. In order to identify the most important parameters and to quantify their influence on the global chimney effect, a sensitivity study is presented with respect to the different model ingredients. The following quantities are examined: fire source heat release rate, tunnel inclination angle, tunnel length, tunnel wall roughness, ambient temperature, ambient pressure conditions, tunnel cross-section area, and fire source position. Attention is focused onto the fire-influenced region mean temperature and the air velocity at the tunnel inlet. The inlet air velocity is quantified by means of a correlation, taking into account the parameters mentioned.