Flame Heights and Heat Transfer in Façade System Ventilation Cavities

The design of buildings using multilayer constructions poses a challenge for fire safety and needs to be understood. Narrow air gaps and cavities are common in many constructions, e.g. ventilated façade systems. In these construction systems flames can enter the cavities and fire can spread on the interior surfaces of the cavities. An experimental program was performed to investigate the influence of the cavity width on the flame heights, the fire driven upward flow and the incident heat fluxes to the inner surfaces of the cavity. The experimental setup consisted of two parallel facing non-combustible plates (0.8 × 1.8 m) and a propane gas burner placed at one of the inner surfaces. The cavity width between the plates ranged from 0.02 m to 0.1 m and the burner heat release rate was varied from 16.5 kW to 40.4 kW per m of the burner length. At least three repeated tests were performed for each scenario. In addition, tests with a single plate were performed. The flame heights did not significantly change for Q′/W < 300 kW/m² (where Q′ is the heat release rate per unit length of the burner and W is the cavity width). For higher Q′/W ratios flame extensions up to 2.2 times were observed. When the distance between the plates was reduced or the heat release rate was increased, the incident heat fluxes to the inner surface increased along the entire height of the test setup. The results can be used for analysing methodologies for predicting heat transfer and fire spread in narrow air cavities.     

Numerical Simulation of Fire Exposed Façades Using LEPIR II Testing Facility

The fire behavior of external wall insulation system on façades is assessed during LEPIR II testing. This facility involves a 600 kg wood crib fire in a 30 m³ lower compartment of a two levels high concrete structure. External flames develop in front of the façade from the fire compartment through windows with dimensions 1?×?1.5 m (W?×?H). In order to predict the fire exposure of a façade during the test, CFD simulations were carried out with the computational fluid dynamics code Fire Dynamics Simulator (FDS) for two full-scale experiments. The main objective of this study was to evaluate the ability of FDS to reproduce quantitative results in terms of gas temperatures and heat fluxes close to the tested façade. This is an important step before the fire performances of any insulation system can be predicted by numerical tools. A good repeatability was observed in terms of measured gas temperatures for experiments. Maximum heat release rate of the fire, close to 5 MW, was achieved after 5 min of test. When experimental results were compared with numerical calculations, good agreement was found for every quantity. The most critical zone on the facade is located above the fire room and is directly impacted by external flame outgoing from the fire compartment. Temperatures up to 500°C were observed in this zone. For the thermocouples located up to the second level opening, these probes were not located directly in the flames, but rather in the hot gases above the fire plume. The maximum temperature achieved was thus close to 400°C. The proposed model gives correct thermal loads and flames shape near the façade during calibration tests and can be used for further evaluation of combustible material on façade.     

Variation of Intumescent Coatings Revealing Different Modes of Action for Good Protection Performance

Thermal insulation and mechanical resistance play a crucial role for the performance of an intumescent coating. Both properties depend strongly on the morphology and morphological development of the foamed residue. Small amounts (4 wt%) of fiberglass, clay and a copper salt, respectively, are incorporated into an intumescent coating to study their influence on the morphology and performance of the residues. The bench scale fire tests were performed on 75 × 75 × 2 mm³ coated steel plates according to the standard time–temperature curve in the Standard Time Temperature Muffle Furnace⁺ (STT Mufu⁺). It provided information about foaming dynamics (expansion rates) and thermal insulation. Adding the copper salt halved the expansion height, whereas the clay and fiberglass change the height of the residue only moderately. The time to reach 500°C was improved by 31% for clay and 15% for the other two fillers. Nondestructive micro computed tomography is used to assess the inner structure of the residues. A transition of the residue from a black, carbonaceous foam with closed cells into an inorganic, residual open cell sponge occurs at high temperatures. This transition is due to a loss of carbon; the change in microstructure is analyzed by scanning electron microscopy. Additional mechanical tests are performed and interpreted with respect to the results of the morphology analysis. Adding clay or copper salt improved the mechanical resistance tested by a factor 4. The additives significantly influence the thickness and foaming dynamics as well as the inner structure of the residues, whereas their influence on insulation performance is moderate. In conclusion, different modes of action are observed to achieve similar insulation performance during the fire test.     

The Breakage of Float Glass with Four-Edge Shading Under the Combined Effect of Wind Loading and Thermal Loading

The glass breakage in high-rise building fires may be significantly influenced by both the compartment fire and the environmental wind. In this work, float glass panes supported by the frame with a dimension of 600 × 600 × 6 mm³ were employed to study the glass breakage under the combination of wind and fire effects. The first breaking time, glass temperature, crack patterns, and fallout were obtained. With an increase of wind speed, the average value of temperature difference between the mean temperature at the heated exposed side and that at the ambient shaded side decreased gradually when crack initiated. The average time to first crack was maximum without wind loading and decreased gradually as the wind speed increased. Comparing with the glass breakage only under thermal radiation, the combination of environmental wind accelerated the glass breaking. The present results suggest that the wind effect should be considered for building fire protection in the window glass design.     

Measurements of the transmission of radiation through water sprays

The effectiveness of water spray curtains in preventing fire spread depends on the amount of thermal radiation transmitted through the spray. The authors have measured the transmission of radiation through spray curtains from a sprinkler and a nozzle producing a flat spray at both high and low water pressures. They conclude that with proper nozzles, a water curtain of low transmission could be produced from water flows comparable with those of sprinkler installations. Note: The following equivalents may be helpful in perusing this paper: 1 cm=.394 in.; 1 m=3.28 ft; 1 atmosphere=14.7 psi; temperature (°C)+17.78×1.8=temperature (°F); 1 milliliter per second=.0159 gpm; 1 cal/sec/cm²=13,272 Btu/hr/ft².     

Structure and Evaluation of the Process for Origin Determination in Compartment Fires

The science behind the formation of fire patterns and their ensuing use in the forensic analysis of fire scenes has been questioned since their introduction in the 1940s. This paper provides an overview of a prototype method for determining the area of origin based on fire patterns analysis, named the process for origin determination (POD). The POD is a seven step reasoning process for evaluating fire damage, which starts by identifying the value in further analysis of each surface and compartment of a structure and then procedurally evaluates each surface for use within the overall determination. This paper outlines the application of the POD with test subjects and presents an analysis of the outcomes showing its benefits. To facilitate testing the POD, numerical simulations and physical experiments were employed. The numerical simulations were completed through the use of fire dynamics simulator simulating a single compartment measuring 3.66 m × 3.66 m × 2.44 m with a single ventilation opening. The physical experiments were tests conducted specifically for fire patterns where accuracy rates had been previously identified in the literature. Sixty test subjects participated in the evaluation of thirty-two different origin scenarios. A decrease in variability, which indicates an increase in reliability, was noted in 21 of the 32 scenarios (66%) when participants used the POD. Three accuracy measurements were employed, all three of which illustrated an increase in accuracy when participants used the POD. The accuracy was shown to increase between 50% and 94% when participants used the POD.     

专用防火涂料对电缆受热时绝缘失效的影响

利用红外辐射加热炉及绝缘电阻测量系统,研究了涂敷不同厚度防火涂料的VV电缆、ZC-YJV电缆在ISO834标准火灾条件下绝缘电阻的失效时间及温度。结果表明,涂敷防火涂料能够明显延长电缆受热时绝缘失效时间;两种电缆的绝缘失效时间均与涂层厚度成正比例关系,但是从失效时间延长率来看,相似厚度的防火涂料对VV电缆的保护效果更明显。     

Experimental Study on Downslope Fire Spread over a Pine Needle Fuel Bed

The downslope fire represents a percentage of wildland fireline while the heat transfer mechanism of this process is poorly understood. In this study, the experiments were carried out in a fuel bed of dead pine needles with the slopes of ??30°, ??20°, ??10° and 0° for 0.4 and 0.8 kg/m² fuel loads. Flame length, flame angle, temperatures over the fuel bed, flow speed at the fuel bed surface, radiation heat flux near the end of the fuel bed were measured. The rate of spread shows a parabolic shape which decreases firstly and then increases from 0° to ??30°. The combustion interface, reconstructed from the temperature histories of two vertical thermocouples, was perpendicular to the fuel bed under all slope conditions for two fuel loads. The measured radiation heat flux is higher at ??30° slope than level ground, which is attributed to higher flame emissivity. A quasi-physical model was developed to describe the heat transfer mechanism of downslope fire spread. The calculation results show that the flame radiation dominated the downslope fire spread process and the combustion zone radiation should not be neglected in the near flame region.     

Fire protection of LPG tanks with thin sublimation and intumescent coatings

The results of two full scale fire engulfment tests on a 3.6 m³-LPG tank protected with a sublimation coating (THERMOLAG 440) and on a 4.85 m³-LPG tank protected with an intumescent coating (CHARTEK III) are presented. The tests have demonstrated a sufficient vessel safety during 90 minutes of full fire engulfment. Additional furnace tests on CHARTEK III-coated steel plates have been carried out to optimize the necessary coating thickness.This article is reprinted with permission fromHazard Prevention, Third Quarter, 1991.     

火焰厚度对钢筋混凝土柱耐火性能的影响

为正确评估火焰厚度对钢筋混凝土构件耐火性能的影响,以矩形截面四面受火柱为研究对象,以标准火为受火条件,采用数值分析方法研究构件表面和试验炉壁面温度,分析火焰厚度对构件耐火性能的影响。结果表明:炉壁温度略低于构件表面温度,不会向构件辐射传热;火焰厚度越大,构件温度越高,承载力越小,对硅骨料混凝土该现象尤为明显;因标准耐火试验炉炉腔尺寸较小,其试验结果可能过高地估计了构件的抗火能力,建议在耐火设计与评估中考虑实际火焰厚度对结构的影响。     

建筑内明敷消防电缆防火措施有效性试验研究

利用红外辐射加热炉及绝缘电阻测量系统,研究了ZC-YJV和YJV两种电缆,在穿涂有不同厚度钢结构防火涂料金属管保护方式下,模拟ISO 834标准火灾条件时,绝缘电阻的失效时间及温度。结果表明,两种型号的电缆在试验的涂层厚度范围内,绝缘失效时间与涂层厚度呈正比例关系,幂指数为1.3,当金属管外防火涂料的涂层厚度小于1 mm或大于3 mm时,保护效果均不明显,防火涂料的涂层厚度范围应以1～2.5 mm为宜。不同型号的电缆其绝缘失效温度有所不同,绝缘失效温度越高耐火性能越好,在火灾中保持线路完整性的能力越强。     

Enhanced Oil Spill Clean-Up Using Immersed Thermally Conductive Objects

A method for rapid burning of hazardous oil spills on water is investigated with the ultimate goal of designing a burner for faster clean-up of hazardous spills in offshore and other remote environments. A thermally conductive object, which comprises of a 0.25 cm thick copper porous mesh, with or without conical copper coils, is used. The influence of this object on the burning rate of an Alaska North Slope crude oil slick (1 cm thick) on saline water is studied. For the mesh-alone case, heat from flame is transferred to the mesh, which rapidly gets heated up and transmits the heat to the oil slick. This heat transfer is much higher than that in the baseline case. In the case with conical coils, which are engulfed in the flame, the heated up coils transfer the heat to the copper mesh more effectively. Thus, the object enhances the mass burning rate. Experimental results reveal that the copper mesh reaches a temperature higher than the boiling point of the oil, such that onset of nucleate boiling is possible. The mesh-coil system is able to burn thin slick of oil resting on water achieving an efficiency of?~?400% above baseline. A simple integral model is also proposed to predict the temperature profiles in mesh, oil, and water layers. The predicted temperature profiles show good agreement with the experimental results. A parametric study using the integral model is also reported. The model can be used as a guideline to optimize the mesh porosity and thickness for different hazardous spill scenarios.     

EcoSmart Fire as Structure Ignition Model in Wildland Urban Interface: Predictions and Validations

EcoSmartFire is a Windows program that models heat damage and piloted ignition of structures from radiant exposure to discrete landscaped tree fires. It calculates the radiant heat transfer from cylindrical shaped fires to the walls and roof of the structure while accounting for radiation shadowing, attenuation, and ground reflections. Tests of litter burn, a 0.6 m diameter fire up to 250 kW heat release under a Heat Release Rate (HRR) hood, with Schmidt-Boelter heat flux sensors in the mockup wall receiving up to 5 kW/m² radiant flux, in conjunction with Fire Dynamic Simulator (FDS) modeling verified a 30% radiant fraction, but indicated the need for a new empirical model of flame extinction coefficient and radiation temperature as function of fire diameter and heat release rate for use in ecoSmartFire. The radiant fluxes predicted with both ecoSmartFire and FDS agreed with SB heat flux sensors to within a few percent errors during litter fire growth. Further experimental work done with propane flame heating (also with 30% radiant fraction) on vertical redwood boards instrumented with embedded thermocouples validated the predicted temperature response to within 20% error for both models. The final empirical correlation for flame extinction coefficient and temperature is valid for fire diameters between 0.2 and 7.9 m, with heat release rates up to 1000 kW. From the corrected radiant flux the program calculates surface temperatures for a given burn time (typically 30 s) and weather conditions (typically dry, windy, and warm for website application) for field applications of many trees and many structural surfaces. An example was provided for a simple house exposed to 4 burning trees selected on a Google enhanced mapping that showed ignition of a building redwood siding. These temperatures were compared to damage or ignition temperatures with output of the percentage of each cladding surface that is damaged or ignited, which a homeowner or a landscaper can use to optimize vegetation landscaping in conjunction with house exterior cladding selections. The need for such physics-based fire modeling of tree spacing was indicated in NFPA 1144 for home ignitability in wildland urban interface, whereas no other model is known to provide such capability.     

Fire Performance of Phase Change Material Enhanced Plasterboard

Sustainable construction materials are increasingly being used to reduce the carbon footprint of modern buildings. These materials have the potential to change the fire dynamics of compartments by altering the compartment energy balance however there is little quantitative understanding of how these materials behave in the event of a real fire. The changes in fire dynamics may be due to increased fuel load in a compartment, reduced time to failure or promotion of flame spread. The objective of this research is to quantify how Phase Change Materials (PCMs) perform in realistic fire scenarios. It was found that a plasterboard product containing microencapsulated PCMs will behave similarly to a charring solid and have the potential to contribute significant fuel to a compartment fire but that they maintain integrity for the duration of flaming period. The critical heat flux for this product was determined in the cone calorimeter to be 17.5 ± 2.5 kW m^?2, the peak heat release rate and mass loss rate ranged from 60.2 kW m^?2 to 107 kW m^?2 and 1.88 g s^?1 m^?2 to 8.47 g s^?1 m^?2 respectively for exposures between 20 kW m^?2 and 70 kW m^?2. Sample orientation was found to increase the peak heat release rate by up to 25%, whilst having little to no effect on the mass loss rate. These parameters, in addition to the in-depth temperature evolution and ignition properties, can be used as design criteria for balancing energy savings with quantified fire performance.     

Experimental Studies on the Fire Behaviour of High Performance Concrete Thin Plates

In recent decades, the use of structural high performance concrete (HPC) sandwich panels made with thin plates has increased as a response to modern environmental challenges. Fire endurance is a requirement in structural HPC elements, as for most structural elements. This paper presents experimental investigations on the fire behaviour of HPC thin plates (20 or 30 mm thick) being used in lightweight structural sandwich elements. Tests were undertaken using a standard testing furnace and a novel heat-transfer rate inducing system (H-TRIS), recently developed at the University of Edinburgh. The parametric assessment of the specimen performance included: thickness of the specimen, testing apparatus, and concrete mix (both with and without polypropylene fibres). The results verified the ability of H-TRIS to impose an equivalent thermal boundary condition to that imposed during a standard furnace test, with good repeatability, and at comparatively low economic and temporal costs. The results demonstrated that heat induced concrete spalling occurred 1 to 5 min earlier, and in a more destructive manner, for thinner specimens. An analysis is presented combining the thermal material degradation, vapour pore pressure, stress concentrations, and thermo-mechanical energy accumulation in the tested specimens. Unexpectedly, spalling at the unexposed surface was observed during two of the tests, suggesting a potentially unusual, unwanted failure mode of very thin-plates during fire. On this basis it is recommended to favour 30 mm thick plates in these applications, since they appear to resist spalling better than those with 20 mm thickness.     

Predicting the structural response of a compartment fire using full-field heat transfer measurements

Inverse heat transfer analysis (IHT) was used to measure the full-field heat fluxes on a small scale (0.9 m×0.9 m×0.9 m) stainless steel SS304 compartment exposed to a 100 kW diffusion flame. The measured heat fluxes were then used in a thermo-mechanical finite element model in Abaqus to predict the response of an aluminum 6061-T6 compartment to the same exposure. Coupled measurements of deflection and temperature using Thermographic Digital Image Correlation (TDIC) were obtained of an aluminum compartment tested until collapse. Two convective heat transfer coefficients, h =35 W/m²-K and h =10 W/m²-K were examined for the thermal model using the experimentally measured heat fluxes. Predictions of the thermal and structural response of the same compartment were generated by coupling Fire Dynamics Simulator (FDS) and Abaqus using the two values for h, h =35 W/m²-K and h from convection correlations. Predictions of deflection and temperature using heat fluxes from IHT and FDS with h=35 W/m²-K agreed with experimental measurements along the back wall. The temperature predictions from the IHT-Abaqus model were independent of h, whereas the temperature predictions from the FDS-Abaqus model were dependent on h.     

受振动影响的钢结构防火涂装应用技术

钢结构构件在振动荷载影响下,其表面的防火涂层特别是厚涂层防火涂料容易受振动脱落,使防火涂料失去防火的功能,甚至有可能造成坠落伤人的安全事故。因此,对涂装在此类钢构件表面的防火涂料除要求具有轻质、附着力强等外,还要求有附加的钢丝网片锚固措施。以工程实际为例,推荐一种国外新型的厚涂层防火涂料,综合介绍该种防火涂料的防火特性和涂装工艺、质量控制以及验收手段。     

The effect of surface coatings on fire growth over composite materials in a corner configuration

Structural composites are vulnerable to fire in two respects: (1) their resin content may ignite and enable the spread of flames over the surface of the structure; (2) the resin may degrade from the heat of a localized fire exposure thus weakening the composite structure. The present study focuses mainly on the first issue, in particular, on the ability of various commercial coatings to prevent flame spread. The second issue is examined briefly by applying thermocouples to the back surface of test specimens. Four commercial coatings have been tested over an unretarded vinyl ester/glass composite. In addition an uncoated phenolic/glass composite and a polyester/glass composite coated with a fire retarded resin were tested. In all cases the configuration was a 3.3 m high corner with a 53 cm square propane gas burner at its base, operated at 250 kW as the fire exposure. The results show that, with the proper choice of coating and coating thickness, fire growth can be suppressed quite effectively. Two of the coatings, applied at a substantial thickness, were reasonably effective at slowing the penetration of heat to the back of the composite panels. The other coatings, much thinner in application, were notably less effective at slowing heat penetration.     

Study on phase change material and its appropriate thickness for controlling solar cell module temperature

ABSTRACT

Appropriate thickness of phase change material (PCM) to control the solar cell module temperature for increasing power generation was carried out. A PCM, RUBITHERM RT42, with the melting point at 42°C and a thickness of 50?mm was used to absorb heat at the back of a 250?W_p polycrystalline solar cell. A numerical enthalpy method to predict the melting phenomenon of the PCM, RT35, 42, 47, and 55, and the solar cell module temperature was developed. The results agreed well with those of the experimental data. It was found that the maximum generated power was around 167?W in comparison with 147?W of the normal unit at a solar radiation of 867?W/m². The daily power outputs were 0.707 and 0.642?kWh, respectively. From the simulation under Chiang Mai climate, for RT42 PCM, it was found that the appropriate thickness was around 40?mm.