密闭腔室内高压七氟丙烷喷放与局部过冷研究

摘 要：针对高压七氟丙烷气体喷放行为,建立了密闭腔室高压气体小孔喷射动态发展与演化模型,基于数值分析研究了高压七氟丙烷小孔喷射过程中的组分场、温度场和速度场等特性,并开展了相应喷放试验研究。计算结果表明,七氟丙烷喷射后易形成气体回卷,继而在障碍物靠近喷射口一侧形成七氟丙烷稀薄区域。七氟丙烷发生意外喷射时,尽管在喷口附近产生的最低温度低至-20 ℃,当七氟丙烷喷射口距离电子设备超过1.75 m时,则相应的低温影响往往在可接受范围。     

舰船舱室吸气式火灾探测报警系统设计及试验验证

针对舰船舱室环境采用吸气式感烟探测器设计火灾探测报警系统,用于舰船电气阴燃火的早期探测,同时对于设计结果进行了实火试验,将响应时间与传统点型探测报警系统的响应性能进行比对,依此对火灾探测报警系统的响应时间能进行了分析,得出该火灾探测报警系统的有效性和适应性。并开展了保护部位数值模拟仿真计算。通过实火试验和仿真计算的比对分析,检验了仿真计算方法与理论的适用性,采用仿真计算对设计的合理性和有效性进行系统性能评估,预计系统中最不利点在既定火灾场景下的火灾探测报警响应时间。     

变电站电缆沟火灾探测试验与数值仿真研究

为探讨火灾探测器灵敏度对电缆沟火灾响应的影响程度,验证火灾监控系统的准确性,应用点式温度探测器、点式烟雾探测器、电缆式感温探测器和吸入式烟雾探测器4种火灾探测器,在标准变电站电缆沟防火分区内进行了全尺寸电缆火灾试验,测试不同灵敏度火灾探测器的火灾报警序列。根据电缆沟的实际尺寸,利用FDS搭建模拟明火和阴燃两种不同火灾场景,对不同灵敏度火灾探测器的温度场、有毒气体质量浓度和火灾报警顺序进行了分析和讨论。试验结果表明,在变电站电缆沟火探测中,电缆式感温探测器、吸入式烟雾探测器、点式感烟探测器火灾平均响应时间分别为41.2,111.4,331.8 s;吸入式感烟探测器的灵敏度对探测结果影响较大,其火灾报警响应时间比电缆型线性温度探测器约延迟50%。     

Lag times associated with fire detection and suppression

The effectiveness of fire detection systems and fire mitigation strategies can be related to three distinct time lags associated with building fires: a transport time lag, a detection time lag, and a suppression time lag. The impacts of these lag periods on fire detection and suppression are developed. Transport lag periods are considered in terms of available correlations of fire plume and ceiling jet data, detection lag periods in terms of available heat detector response models that use these data correlations. Suppression lags are developed in terms of expected response times for automatic and manual suppression. Example calculations are presented.     

线型光束感烟火灾探测器克服光干扰的方法

针对常规的线型光束感烟火灾探测器抗环境光干扰能力较差,在白炽灯、氙灯以及太阳光等干扰下易误报或丧失火灾探测能力的问题,在对国内外十余厂家生产的线型光束火灾探测器产品的性能、特点,以及在大型公共建筑的工程应用情况进行了详细调研后,建立了该探测器数据采集系统及试验平台,采取了一系列软、硬件有效技术改进措施,经试验和示范工程验证,克服了环境光干扰对线型光束感烟火灾探测器的影响.     

点型光电广谱感烟火灾探测器的研制

开发了红外光对典型烟雾颗粒0°～180°可变散射角感烟实验装置,以确定峰值波长为(900±100)nm红外光适宜和最佳的前向、后向散射感烟角.研制了一种实用新型光电感烟火灾探测器.通过试验研究4种试验火典型烟雾对此传感器的响应规律,确立了甄别黑烟或白烟的火灾探测报警算法处理技术.试验证明探测器对于可燃物阴燃或明火产生的不同粒径、不同颜色、不同温度的广谱烟雾达到了良好的均衡灵敏响应性能.     

公路交通隧道火灾探测技术研究

通过油盘火试验和模拟研究隧道火灾探测技术.油盘火试验分汽车下着火和汽车后方着火,模拟分为发动机舱着火和乘客舱着火.只有闭路电视图像探测器和感烟探测器能探测到车辆下方火灾,线型光纤感温探测系统探测车辆后方火灾较快.探测系统对乘客舱火灾的响应时间比发动机舱火灾的响应时间长.以50 km/h行驶的移动车辆着火,所有探测器无响应.建议采用两种及以上技术进行探测.     

A Probabilistic Model for Fire Detection with Applications

A probabilistic model for estimating the activation time of ceiling-mounted fire detection devices is described. The probabilistic model builds on the deterministic model, DETACT, by introducing probability distribution functions in place of point estimates for the parameters governing fire detector response, including the fire heat release rate history, the detector activation temperature, response time index and conductance parameter and the location of the device. The probabilistic model incorporates only parameter uncertainty. Model uncertainties associated with the deterministic model for estimating the activation time of ceiling mounted fire detectors have not been addressed. An example application of the probabilistic model is discussed. The probabilistic results provide valuable insights about the relevant parameters involved in a time to detection analysis.     

Early Warning Fire Detection System Using a Probabilistic Neural Network

The Navy program, Damage Control-Automation for Reduced Manning is focused on enhancing automation of ship functions and damage control systems. A key element to this objective is the improvement of current fire detection systems. As in many applications, it is desired to increase detection sensitivity and,more importantly increase the reliability of the detection system through improved nuisance alarm immunity. Improved reliability is needed, such that fire detection systems can automatically control fire suppression systems. The use of multi-criteria based detection technology continues to offer the most promising means to achieve both improved sensitivity to real fires,and reduced susceptibility to nuisance alarm sources. A multi-criteria early warning fire detection system, has been developed to provide reliable warning of actual fire conditions, in less time, with fewer nuisance alarms,than can be achieved with commercially available smoke detection systems. In this study a four-sensor array and a Probabilistic Neural Network have been used to produce an early warning fire detection system. A prototype early warning fire detector was built and tested in a shipboard environment. The current alarm algorithm resulted in better overall performance than the commercial smoke detectors, by providing both improved nuisance source immunity with generally equivalent or faster response times.     

ASET-A computer program for calculating available safe egress time

In the event of a fire in a building compartment the time available for occupants to safely evacuate the compartment, the Available Safe Egress Time (ASET), depends on the time of fire detection and on the time of the onset of hazardous conditions. In order to estimate these two times a dynamic simulation of the developing fire environment in the compartment is required. Also required are specific criteria for the simulation of detection and onset of hazard. A user-oriented computer program which carries out the required simulations and provides estimates for the ASET has been developed. This paper describes the program and its use. For fire growth in a particular fuel assembly, a single program run can be used to evaluate the ASET from enclosures (which are assumed to contain the fuel assembly) of different heights and areas, and under a variety of different detection and hazard criteria. The program can be used in either an interactive or batch mode. It is written in ANSI FORTRAN and requires no computer specific subroutines.     

防虫网对点型感烟火灾探测器迟滞时间的影响

迟滞时间是反映点型感烟探测器对环境变化跟随性的指标，防虫网是影响火灾探测器迟滞时间的较大因素之一。通过实验研究了防虫网对报警迟滞时间的影响程度，提出了根据环境合理选择点型感烟探测器的方法。     

Advanced fire detection algorithms using data from the home smoke detector project

The primary goal of this study is to develop fire detection algorithms for use in residential occupancies that reduce the nuisance sensitivity and detect fires at least as fast as conventional ionization and photoelectric detectors. An analysis is conducted using the output from ionization, photoelectric and carbon monoxide (CO) detectors, and a thermocouple measurement from 32 fire tests and 11 nuisance tests. Eight parameters are identified from the data collected from the four sensors by considering the magnitude and rate of rise of the output from each sensor. Algorithms are developed from these eight parameters using three approaches: analyzing the value of a single parameter relative to the response of commercial detectors given fire and nuisance sources, conducting the same analysis with two or three parameters and conducting the same analysis with a principal component analysis (PCA) of all eight parameters. The best fire sensitivity and nuisance immunity was observed for three algorithms: temperature rise and CO; CO and ionization detector; and temperature rise, CO and ionization detector.     

缩尺度试验火烟气特性实验研究

基于4种标准试验火开展缩尺度试验火烟气特性实验,研究试验火烟气特性在其尺度逐渐缩减过程中的变化规律,分析火灾烟气减光系数随时间的变化以及货架火灾探测器、吸气式感烟火灾探测器、点型感烟火灾探测器对各尺度试验火的报警响应特性。给出适用于高灵敏火灾探测器检测和评价的缩尺度试验火做法建议。     

Investigation of Multi-Sensor Algorithms for Fire Detection

There is widespread interest in the development of advanced fire detectors. A primary objective of fire detection is to provide prompt indication of the presence of a fire, without responding to deceptive signatures from nuisance sources. The principal purpose of this project is to identify the characteristics of a discriminating fire detector for Naval shipboard applications incorporating ionization, photoelectric, carbon dioxide and carbon monoxide sensors. Test data from previously conducted full-scale tests involving fire and nuisance sources are being analyzed to develop an algorithm involving combinations of the magnitude or slope of the response signal from each sensor. Acceptability of a particular algorithm is judged based on the number of correct classifications (fire vs. nuisance) and response time to fire sources.     

Prediction of heat and smoke movement in enclosure fires

In order to understand the response of a detector to a given fire in an enclosure, it is necessary to relate the local thermal and aerosol characteristics actually sensed by the detector to the physical and geometrical properties of the fire and the enclosure. This paper presents computations designed to predict the evolution of the size distribution of smoke aerosol as it ages, as well as the large-scale air movement and temperature fields generated by an enclosure fire.

The computations contain three main ingredients: first, a finite difference solution for the air movement and temperature generated by a prescribed source of heat used to represent a fire in a closed form; second, the computer evaluation of an exact solution to the ageing equation correspond to the evolution of an experimentally observed size distribution; and third, a particle tracking scheme which permits the smoke aerosol to be followed in space and time as it gradually fills the room. No nonphysical empirical parameters (e.g. turbulence models) are employed in these calculations. The mathematical and physical models are summarized briefly, but most emphasis is placed on displaying results. Sample calculations are presented, comparisons are made with relevent experiments, and predictions of the local environment experienced by a detector due to the occurrence of an enclosure fire are shown.     

A composite detection algorithm using signal trend information of two different sensors

A detection algorithm, based on the well known two-input Kendall-Tau trend detector is presented. The necessary modifications and preprocessing requirements for fire detection purposes are discussed. Experimental results are shown, concerning the detection capability and the false alarm resistance of the detection algorithm under realistic environmental conditions. A method for automated optimization of decision thresholds in a given installation environment is proposed.     

Detection of spacecraft fire signatures and post-fire aerosols—Part I: Ground-based results

Preventing fires in spacecraft and other remote platforms is an important facet of avoiding fires that potentially compromise missions, hardware, and crew. If a fire occurs, the objective is to detect the associated fire signatures at the earliest possible time from inception, thus minimizing propagation and collateral damage while providing maximal margin for suppression. The goal is to provide detection sensitivity without introducing spurious false alarms that compromise operations and trigger responsive abatement and containment provisions. A related issue in sealed, self-contained environments is post-fire clean up, and sensors to evaluate the environmental suitability in crewed quarters. In both situations, knowledge of the particulate and/or gaseous fire signatures as they occur under the unique combination of a reduced-gravity environment and materials typical of spaceflight applications is essential for the design of spacecraft fire detectors and habitat sensors. This paper describes recent ground and spaced-based data on fire signatures, and the response of a novel multi-channel optical scattering sensor. This detector, known as the Multi-Parameter Aerosol Scattering Sensor (MPASS), determines multiple moments of the aerosol distributions. The methodology for designing a sensor with the desired response function is discussed, as well as test results that demonstrate the performance of prototype devices.     

Fire detector systems with ‘distributed intelligence’ the pulse polling system

Well over a million fire detectors are currently in use in the Federal Republic of Germany. Provided they are correctly installed and efficiently maintained, they detect fires reliably at a very early stage. At the present time, the false alarm rate equals about 1% of the number of installed detectors per annum. This false alarm rate must be at least proportionately reduced as further detectors are installed.

Since it is scarcely possible to improve tried-and-tested detector designs, the employment of higher-grade detector signal processing methods suggests itself.

However, ‘more intelligent’ detector signal processing using microprocessors calls for an entirely new fire detection system structure: detectors which independently ‘decide’ whether an alarm criterion is met and then initiate an alarm are replaced by sensors which continuously transmit their measured values to the ‘intelligence’ panel for evaluation. Passive panels which simply receive alarm signals from activated detectors and indicate these or transmit them to the fire brigade are replaced by active processors using permanently improved algorithms for the detection of real fires.

A structural change of this type is possible provided the positive — and the customary — characteristics of the conventional technique are not lost, viz. two-wire lines between detector and panel, simple installation and handling, easy detector replaceability, low cost, etc.

The pulse detector technology is described in detail; it combines the simplicity of conventional fire detection systems with new characteristics, e.g. identification of individual detectors, permanent functional check of all connected detectors, automatic notification of maintenance requirement prior to a slowly developing fault (e.g. such as that caused by corrosion or contamination), uniform response sensitivity unaffected by drifting from the operating points of the detectors and, above all, greater protection against false alarms.     

Analyzing fire-induced dispersion and detector response in complex enclosures using salt-water modeling

The current investigation examines suitability of the hydraulic analog for analysis of fire-induced dispersion within a complex enclosure. This analog has been implemented using salt-water modeling and planar laser induced fluorescence (PLIF) diagnostics providing quantitative visualization of simulated fire-induced flows. The non-intrusive PLIF diagnostics are used to temporally and spatially characterize dispersion from a buoyant source within a 1/7th scale room–corridor–room enclosure. This configuration is geometrically similar to a full-scale fire test facility, where local fire conditions were characterized near five ionization type smoke detectors placed throughout the enclosure. The full-scale fire and salt-water model results were scaled according to the dimensionless fundamental equations that govern source dispersion.An evaluation of the local conditions and dispersive event times for both the systems was used to explore the ability of the hydraulic analog to predict smoke detector response times. The dispersive event (front arrival) times predicted by the salt-water model, which represents a necessary event for detector activation, were in excellent agreement with the fire test data. A methodology using these front arrival times along with local conditions at the detector location is introduced in this paper. However, the complex nature of detector response and fidelity limitations of the analog make precise predictions of detector response time challenging. The predicted dimensionless response times were within 25% for all detector locations, with the exception of the first-room ceiling detector location. For this latter, a shorter dimensionless response time by less than 40% of that in the actual fire was predicted.     

感温火灾探测器预警时间的传热分析

分析了感温火灾探测器的传热机理,建立了考虑辐射传热影响的数学模型,并经数值积分获得了求解预警时间的一种新算法,计算表明：当环境温度较低,而探测器的响应温度设置过高时,辐射传热对预警时间的影响不应忽略。本文对消防工程的安全评估及报警系统的选型设计具有一定的参考价值。