感温火灾探测器的预警时间

文章结合建筑火灾的特性和感温火灾探测器的工作原理,分析了感温火灾探测器的换热机理,建立其换热数学模型,并对此模型作详细的求解计算和实例分析,确定了影响感温火灾探测器预警时间的主要因素,计算出感温火灾探测器的预警时间。     

地板辐射供暖简化传热计算模型与实验研究

为简化地板辐射供暖系统的传热计算,将多表面间的辐射传热简化为地板表面与非热表面间的辐射传热,以此建立了地板辐射供暖系统的简化传热计算模型。对地板辐射供暖系统的简化传热计算模型的计算精度及地板辐射传热量占总传热量的比例进行了实验研究。通过实验研究计算得出简化传热计算模型的计算精度为±4%。地板传热量中辐射传热约占60%,在各非热表面中,屋顶面辐射传热比例最大,外墙较内墙大。     

槽式太阳能集热器传热模型及性能分析

槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。     

对窑内辐射传热计算方法的一些意见

分析窑内辐射传热的各个因素,进行窑内辐射传热计算,对掌握和改进窑炉操作,具有很大的意义。对稳定性中空窑炉,例如玻璃池窑,进行辐射传热计算时,多采用公式,不过这个公式推导起来相当复杂。水泥回转窑辐射传热的计算一般采用的方法,这个方法也有一些缺点。1957印南京工学院钱钟韩教授提出了热流线路分析法的不同概念,以Δ(T~4)作为辐射传热的推动力,并对水泥回转窑辐射传热的计算方法提出了与不同的见解(化工学报,第     

基于Gebhart辐射模型的建筑壁面对流辐射传热计算方法

建筑内壁面传热是一种导热、对流和辐射共存的复合传热过程,基于Gebhart辐射模型,建立建筑壁面传热同步模型,可同步计算壁面温度和空气温度,在此基础上分析建筑壁面对流辐射传热特性。研究结果表明:传热同步模型的空气温度理论计算值小于实测值,偏差均在0.25℃以内;壁面温度计算值与实测值的偏差基本在1℃以内。并对南墙加热壁面与地板的导热传热、对流传热及辐射传热进行分析。研究结论为进一步应用Gebhart辐射模型和研究壁面的对流辐射传热提供了参考依据。     

双辐射作用下工业热厂房外墙传热实验研究

为了研究在太阳和内热源的双向辐射作用下自然通风工业热厂房夏季外墙传热过程,搭建了实验模型,在西安夏季室外条件下对室内外参数进行了测试,并对不同余热强度工况时南墙内外壁面边界热流进行了计算和对比分析。结果表明:室内强热源影响墙体内外壁面边界上辐射热流和对流热流的大小和方向。内热源的辐射作用在余热强度大于50W/m3的情况下会对外墙传热过程会造成较大影响。白天有太阳辐射时,外壁面上的辐射散热热流会高于对流散热热流,并且余热强度对辐射对流比影响很小。夜间外壁面上的辐射对流比会随着余热强度的增大而减小,当余热强度大于200W/m3时趋于稳定。     

基于Fluent的埋管式辐射地板传热及供冷能力研究

充分了解辐射供冷系统的传热特性有助于该系统的设计、推广及应用。构建了埋管式辐射地板的三维稳态传热模型,进行供冷工况下地板内部传热情况的数值模拟,得到了辐射地板内部及表面的温度场。经实验验证,建立的传热模型与实际误差小于9.01%。模拟分析了换热盘管长度与供水温度对辐射地板的供回水温差、供冷能力及温度分布的影响。结果表明：在相同供水温度下,换热盘管越长,埋管式辐射地板的供冷能力越弱,温度分布均匀性越差,管长每增加10 m,单位面积辐射地板供冷量约降低1.5 W/m²;在相同换热盘管长度下,供水温度越高,地板的供冷能力越弱,温度分布均匀性越好。     

单片低辐射玻璃谱带模型及其数值模拟

采用谱带模型,考虑了各个波段透射率、反射率对传热的影响,对单片低辐射玻璃的传热过程进行了研究,提出了描述此传热过程的非线性方程组;考虑对流、太阳辐射及外界和室内辐射等边界条件,并采用了牛顿法解方程组.计算结果表明,单片低辐射玻璃镀膜层向室内放置比较合理;另外,讨论了玻璃厚度、室内温度、室外风速对玻璃传热的影响.     

钢外护管真空复合预制直埋管道真空层热力分析

应用稀薄气体分子热运动理论,研究了真空层复合传热机理,提出了真空层当量导热系数计算方法,分析了不同真空层压力和热媒温度对真空层传热量的影响以及导热、对流和辐射传热量在真空层总传热量中所占比例和变化规律,提出优化真空保温管道保温性能的方法。试验结果与计算结果的最大偏差率为7.9%。真空层压力应控制在2kPa以下,以获得满意的保温效果。真空层压力高于101.3kPa时,真空层内传热以对流传热为主;当真空层压力降低到1kPa时,真空层内传热以辐射传热为主。真空层的对流传热不应被忽略。     

PMC-T40X电气火灾监控探测器

1概述 PMC-T40X电气火灾监控探测器（见图1）包括组合式电气火灾探测器、剩余电流式电气火灾探测器和测温式电气火灾探测器,完成对剩余电流、温度和三相电流的实时监控、预警、报警与保护,可有效屏蔽过滤线路中由于高次谐波产生泄漏电流的影响,自适应保护线路的正常漏电波动。     

大空间火灾下铝合金构件温升计算方法

性能化抗火设计过程中,火灾下结构构件的温升计算方法对设计结果具有重大影响.为研究大空间火灾下铝合金构件的温升计算方法及火焰辐射对构件温升的影响,对2种常见的铝合金构件截面试件进行了火灾温升试验.试验结果表明,由于火焰辐射的作用,构件温度与周围空气温度较为接近.基于铝合金构件的导热微分方程,提出了一般室内火灾和大空间火灾...     

Measuring modified glass bulb sprinkler thermal response in plunge and compartment fire experiments

Automatic fire sprinklers use a heat sensitive element such as a glass bulb or fusible link to respond to the heat from a fire. The response of commercial fire sprinkler glass bulbs has been extensively characterised in convection-dominated dry gas flows but in real fires there may be more factors that influence the heat transfer to the bulbs such as radiation from the fire or cooling from adjacent sprinkler sprays. The time of activation is the only indication of the thermal response of typical commercial fire sprinklers using glass bulbs to a fire, but direct temperature measurement using a modified proxy may provide a better understanding of how sprinklers respond in a complex environment. Modified glass bulbs have been created that allow a thermocouple to be inserted in the bulb for direct temperature measurement. In this paper, the thermal response of sprinklers with these modified bulbs has been observed in hot-air wind tunnel plunge experiments and full scale room fire experiments. At the time of activation the measured temperature of the modified sprinklers was found to be higher than the nominal activation temperature specification for the unmodified sprinklers. For the compartment fires, a thermal response model generally predicted longer sprinkler activation times based on ceiling jet temperature and velocity measurements than was observed experimentally.     

Heat transfer model for unprotected steel members in a standard compartment fire with participating medium

A heat transfer model accounting for the radiative properties of combustion products in a compartment standard fire is presented. The model used is based on a conceptual scheme of a grey gas mixture exchanging radiative energy with a black enclosure. The proposed model, with a radiation heat transfer that accounts for the effect of combustion products on the rate of heat transfer from the fire to the structural elements, is simple to use and the predictions of the temperature response of unprotected I-columns heated from all sides are superior to those predicted by the classical method using the Stefan-Boltzmann radiation equation with constant emissivity.     

Spreadsheet method for temperature calculation of unprotected steelwork subject to fire

The determination of fire resistance level of a structural member in a building requires an efficient and accurate assessment of its limiting temperature in an enclosure fire environment. A significant discrepancy in the results of calculation of the limiting temperature could lead to an increase in the size of the structural member or an increase in the thickness of the fire protection materials. In either case, the cost of construction may increase. This paper introduces an efficient and accurate method for temperature prediction of steel members under four‐sided fire exposure conditions. The method is based on the heat transfer principles commonly adopted in current codes of practice. However, the proposed method emphasizes the effect of gaseous composition of the combustion products on the evaluation of heat transfer coefficients that most codes of practice ignore. In addition, the complex forms of heat transfer coefficients have been simplified for practical use while the accuracy is still maintained. This method is well suited for practising engineers performing structural design for fire as the calculation procedure can be carried out entirely on a spreadsheet. Copyright © 2003 John Wiley & Sons, Ltd.     

海上平台原油发电机火灾对邻近设施影响分析

海上平台原油发电机火灾事故产生的高温、热辐射会对邻近设备设施产生不利影响。以某海上平台原油发电机火灾事故为例,运用KFX软件对该火灾过程进行数值模拟,研究了邻近钢支撑、进油软管等关键构件处的温度、热辐射等参数的变化特征。基于温度准则和热辐射准则,研究了温度、热辐射通量临界点变化处时间点与持续时间参数。研究发现,邻近钢支撑2和3表面温度高达1 600 ℃以上,热辐射通量超过25 kW/m2,持续时间长,到达其发生变形与破坏的条件,泡沫释放时间过长造成极大影响。进油软管C处的热辐射强度超过15 kW/m2,到达了其熔化破坏条件,感烟探测器响应时间过长是其主要影响因素。以上研究结果,可为灾后支撑构件强度校核、火气系统响应时间设置等提供参考。     

Assessing the Sprinkler Activation Predictive Capability of the BRANZFIRE Fire Model

This paper describes an investigation into the sprinkler response time predictive capability of the BRANZFIRE fire model. A set of 22 fire/sprinkler experiments are simulated where the sprinkler activation time and the heat release rate (HRR) for each individual experiment had been determined. The experiments provided data for use in validating the sprinkler activation prediction algorithms in the BRANZFIRE zone model. A set of base case values were chosen and input files constructed for the simulations. The experiments were then simulated by the fire model using both the NIST/JET ceiling jet and Alpert’s ceiling jet options (which are the two ceiling jet correlations available in the BRANZFIRE zone model). The fire model included a heat transfer calculation for the temperature of the heat sensitive sprinkler element. Different sprinkler operational parameters such as the conduction factor, response time index (RTI) and the sprinkler depth below ceiling were also varied to assess the sensitivity of their effect on the activation time. Results showed that using the NIST/JET ceiling jet algorithm gave a closer prediction of the sprinkler response time in a small room than Alpert’s correlation. This was expected, since the former includes the effect of a hot upper layer while the latter applies to unconfined ceilings. The experiments available for comparison had been conducted inside an enclosure with a developing hot upper layer. The findings also signified that changing the sprinkler operational parameters can change the predicted sprinkler activation time significantly.     

体育建筑非空调区照明与间歇运行对分层空调负荷影响的分析

传统分层空调负荷计算方法的辐射热转移负荷仅考虑非空调区高温壁面对空调区低温壁面辐射引起的负荷,并未考虑非空调区照明设备与空调区之间的辐射热转移负荷,而将非空调区照明得热形成的负荷全数作为非空调区空气得热。为研究非空调区照明设备与空调区之间的辐射热转移后对热转移负荷的影响,以某体育中心比赛大厅为研究对象,在现行大空间分层空调负荷计算方法的基础上,将非空调区照明负荷假想成比赛区非空调区上空一均匀面热源,假定照明灯具均带不透明的灯罩,并近似认为不影响室内气流流动。根据面热源辐射散热比例,通过计算该面热源与空调区地板之间的辐射量并附加一定的修正系数(取1.3)得到空调区辐射热转移量。同时,考虑到体育馆经常为间歇性运行工况,为研究间歇性运行工况与连续性运行工况之间的差别,对研究对象进行了相关调查研究,假想设定了一些通常存在的间歇性工况并基于间歇运行工况进行了照明辐射散热对负荷的影响。研究非空调区照明向空调区转移的辐射热转移负荷发现:在非空调区,与不考虑照明辐射散热相比,考虑非空调区照明总散热中辐射散热占比为50%时,间歇运行对流和辐射总热转移负荷增加了8.8%;考虑照明总散热中辐射散热占比为0%~100%时,间歇运行对流和辐射总热转移负荷增加了0.0%~19.0%。通过分析体育建筑运行及其空调负荷构成特点,提出了针对体育馆间歇运行特征的分层空调负荷计算方法。由论文设定的间歇运行工况计算得出间歇运行负荷是连续运行的92.3%。同时,还得到间歇运行时重型建筑分层空调负荷是轻型建筑的93.3%等结论。     

CFD and experimental studies of room fire growth on wall lining materials

CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO₂ and H₂O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.     

基于场模型的大空间建筑火灾钢构件升温的简化计算方法

高大空间建筑火灾中，热量主要通过热烟气的辐射传热和对流传热方式，向无防火保护层的钢构件表面或钢构件的防火保护层传递，防火保护层再以热传导方式向钢构件表面传递。假定钢构件截面温度均匀分布，将高大空间建筑火灾中的实用空气升温曲线作为构件升温边界条件，对集总热容法建立的热平衡方程求解，得出钢构件在火灾下的温度一时间曲线。为便于工程应用，在钢构件升温影响参数分析的基础上，通过曲线拟舍得出实用的钢构件升温计算公式，为研究大空间钢结构建筑在火灾下的结构全过程反应，提供钢构件升温条件。     

不同通风条件下船舶舱室火灾热量分布研究

以某全尺度船舱火灾试验为基础,依据能量守恒定律定量分析了不同通风条件下火灾过程中舱壁升温、以辐射及对流方式向周围舱室传热、高温烟气传热等方式进行热量扩散的比重关系.结果表明,在该试验条件下,高温烟气扩散和舱壁升温占据主要部分,而经舱壁向相邻舱室扩散的热量最大不到10％.