The differential reaction calorimeter: examples of use

A new kind of calorimeter, commercialized by SETARAM SA and operating in isoperibolic mode, appeared 2 years ago: the differential calorimeter DRC^®. This DRC was developed by Aventis Pharma in their own laboratories and has been used as standard tool for 10 years. The Swiss Institute for the promotion of safety and security (Organic Process Research and Development (2002) to be published) has also studied this calorimeter. In order to show the accuracy of this apparatus, we can compare the DRC with the RC1 from Mettler Toledo which is the reference for safety studies. We can demonstrate the exactitude of results in a wide range of reactions: with one step (neutralization) or two steps (aldolisation–crotonisation), semi-batch reactions with addition of one reagent or simultaneous additions of two reagents, slightly or very exothermic reactions. In each situation, DRC will obtain the same data and results in less time with a smaller amount of raw materials.     

高温高湿巷道内不稳定换热系数影响因素分析及模型建立*

为研究高温高湿巷道不稳定换热系数的变化规律,采用Fluent软件对高温高湿巷道内的热湿交换进行数值模拟,通过单因素和正交模拟实验探讨风流温度、风流速度、岩石导热系数、原岩温度以及巷道当量直径对高温高湿巷道不稳定换热系数的影响。研究结果表明:高温高湿巷道不稳定换热系数随时间的变化规律与普通巷道一致,均与通风时间呈负相关,但通风时间为1 a的高温高湿巷道不稳定换热系数较普通巷道增加了12.5%。通过单因素分析得到风流速度、岩石导热系数和当量直径与不稳定换热系数呈正相关。通过极差分析得到各因素对不稳定换热系数的影响程度为:岩石导热系数>当量直径>风流速度>风流温度>原岩温度。利用SPSS软件对正交实验数据进行拟合,建立不稳定换热系数的计算模型,拟为高温高湿巷道内热负荷计算及井下风温预测提供参考。     

烟气消白烟道导流板CFD数值模拟流场设计

Fluent是一款常用CFD软件,在烟气消白工程设计烟道系统过程中增设导流板,采用CFD数值模拟,能优化换热器进口处烟气流场分布,该文通过比较烟道系统中有、无设置导流板流场模拟分析,得出两种不同流场模拟结果,优化后的换热器进口流场不均匀系数为0.085(优化前为0.346),较优化前改善明显,优化后换热器进口处的流场分...     

An experimental study of an LPG tank at low filling level heated by a remote wall fire

This paper describes an experimental study of 2300 L pressure vessels exposed to remote fire heating by a natural gas fuelled wall fire simulator. The tanks were filled to 15% capacity with commercial liquid propane. The flame intensity and distance were varied to study the effect of different heating levels on the tank and its lading.The fire simulator is first characterized with tests including fire thermocouples, radiative flux meters and thermal imaging. With the appropriate positioning of a target tank it is possible to get very realistic fire heat fluxes at the tank surface.Three tests were conducted with the 2300 L tanks filled to 15% capacity with propane. The tanks were positioned at three different distances from the wall fire resulting in measured average peak heat flux at the tank surfaces ranging between 24 and 43 kW m^?2. The data shows rapid rise in vapour space wall temperatures, significant temperature stratification in the vapour space, and moderate rate of pressure rise. These results provide excellent data for the validation of computer models used to predict the response of pressure vessels exposed to moderate heating from a remote fire.     

过渡流下三列圆柱传热特性的数值模拟

为了研究过渡流状态下管外流体流动与传热特性的影响因素,利用基于复合网格系统的计算方法,对不同横向间距比与纵向间距比下的三列交叉圆柱列进行数值研究。研究结果表明,纵向间距一定时,横向间距对旋涡的位置及强弱有显著影响,且因上游圆柱不稳定性尾流对下游圆柱的洗刷作用使圆柱列存在一个最佳横向间距使换热效果最佳;横向间距一定时,三列交叉圆柱列的换热效果均随纵向间距的增大而递减。     

细水雾抑制固体燃料火焰辐射特性的研究

采用热电偶测温系统和热流辐射传感器等仪器对细水雾施加前后火场温度及辐射热流密度进行测量.研究了不同喷雾气压下固体燃烧场的温度及辐射热流密度的变化特性.结果表明,细水雾的蒸发冷却是影响火焰热辐射的一个重要因素.在实验基础上,建立了固体可燃物燃烧场辐射热流密度的计算模型,计算结果与实验结果较为吻合.     

The evolution of flame length for the oil tank fire with different top cover widths and lip heights

This study presents a quantitative analysis and interpretation of the variation in oil tank fire flame lengths for different oil tank sizes, top cover widths, and horizontal air flow velocities. The experimental results show that, at first, the flame length rises slowly with an increase in air flow speed. Then, once over a critical speed (0.6 m/s), the flame length decreases significantly with a further increase in air flow speed. Based on the characteristic length, a new dimensionless heat release rate is obtained, allowing the correlation between flame length, air flow speed, and dimensionless heat release rate to be calculated, which can be used to predict the flame length of an oil tank fire under different air flow speeds, lip heights, and cover widths.     

弱粘煤低温氧化活性基团与热效应的研究*

为研究煤氧化过程中活性基团的演变规律及热效应的变化特征,利用原位红外实验装置,实时测量煤升温过程中官能团的动态变化,数据处理得到弱粘煤红外波谱图,利用差减法对特征温度点下的红外光谱图进行处理,得到煤样的差示光谱,计算特征温度点下的红外结构参数;采用差示扫描量热仪,测量煤氧化过程中热流的变化,得到弱粘煤的热流曲线图,并对热流曲线进行阶段划分和氧化动力学计算。结果表明:弱粘煤中芳环数量比较少,环周围侧链较长,内部结构疏松,内部毛细管比较发达,内表面积较大,更容易发生自燃;整个氧化过程中羟基最为活跃,含氧官能团次之,其次是脂肪烃;红外参数计算结果HAL,I2整体呈减小趋势,I1,I3整体呈增大趋势;弱粘煤放热阶段的活化能值为25.12～61.26 kJ/mol,并随着升温速率的增大而减小,与此阶段放热量随升温速率的增大而增大相对应。     

建筑物通道内火灾烟气运动的数值模拟

发生在各种长通道内的建筑火灾受到人们越来越多的关注.研究此类火灾烟气运动的特点,对于发展火灾烟气控制技术,减少烟气对人员的伤害具有重要的意义.应用场模拟方法,对有自然通风的建筑物通道内的火灾烟气运动进行了数值模拟.模拟得到的通道内烟气温度的分层分布与实验数据基本相符合,烟气对环境空气卷吸量的计算值也与已有经验关系式的结果相一致.利用数值模拟还研究了释热率对通道内火灾烟气运动的影响.结果表明,在有自然通风的条件下,释热率的增大对通道上层热烟气的温度和速度有较明显的影响,导致火灾的危害性变大.     

Calorimetric behaviors of N2H4 by DSC and superCRC

The objective of this study is to obtain information about the thermal decomposition behaviors of hydrazine (N₂H₄) caused by metals, using differential scanning calorimeter (DSC) and SuperCRC. The DSC measurements revealed that the exothermic reactions of N₂H₄ were caused by the reaction conditions such as the type of cells; the T_DSC with a gold pan is 485.2 K and that with a glass capillary is 620.5 K. Besides, the activation energy of the thermal decomposition of N₂H₄, calculated from the Kissinger and Ozawa methods, were found to be about 38±2 kJ mol⁻¹ in the gold pan and 141±8 kJ mol⁻¹ in the glass capillary. Moreover, a heat flow profile was observed with SuperCRC during the mixing of N₂H₄ and the metal ion solution at 298 K. The maximum heat flow was related to the metal ion oxidative characters. The higher oxidative characters would provide a faster acceleration for the exothermic behavior than the lower oxidative ions. Based on this study, Mn(VII) and Cr(VI) were considered to exhibit strongly oxidative characteristics during mixing with N₂H₄.     

周期性风温下矿井巷道围岩换热教学实验装置研制*

为开展矿井热害防治的实验教学,设计并搭建周期性风温作用下巷道非均质围岩换热实验装置,能直观展示高温围岩各岩层的温度变化。利用实验数据可计算出巷道壁面热流密度,进而定量估算巷道围岩的散热量。结果表明:周期性风温通过后,模拟巷道围岩体各处温度随时间也呈简谐波变化;对于非均质的围岩体,导热系数越大的岩层,周期性风温的调热能力越强;巷道壁面处的热流密度也呈周期性变化,但围岩体总体表现为散热,且散热量随时间快速减小,并最终稳定在1.3×104 kJ/m2。     

地热水在矿山深部岩体单一裂隙中的渗流规律分析

选取PKN模型进行岩体裂隙地热水对流换热量的研究,计算了地热水在裂隙内的对流换热量,通过将裂隙截面展开求解对流换热面积,根据牛顿冷却定律计算得出对流换热量;由裂隙张开度的变化量计算岩体裂隙的渗流量,结果表明,在三维应力一定的条件下,岩体裂隙内地热水的渗流量随裂隙倾角变化而变化。从矿山中选取典型岩样进行加工,使之成为200 mm×100 mm×200 mm的标准岩样。试验结果表明,在裂隙倾角α=0°的情况下,裂缝的渗流量随β增加逐渐减小,并且在随β增加到90°的过程中趋于稳定,表明岩体裂缝为水平裂缝时渗流量最小,维持在一个稳定值;在α=90°的情况下,裂缝的渗流量随β增加逐渐增大,在β增加到90°的过程中,裂缝慢慢变为垂直裂缝,渗流量的变化也趋于缓和,增加到一个稳定值。     

基于Fluent/Matlab的地下水流速对交叉流模式热泵性能的影响分析

为了分析地下水源热泵系统地下水交叉流对系统性能参数的影响,基于Fluent/Matlab搭建了协同仿真平台,对多年运行的地下水源热泵系统进行了仿真计算。通过分析可知,当地下水流速较高时,年平均抽水温度保持含水层的初始温度不变,机组COP(EER)及系统能效比在运行周期内保持不变;地下水流速越大,热泵系统抽水温度越趋于稳定,地下水冷水锋面越远离抽水井向水流下游偏移,抽水井附近含水层温度场越稳定,机组COP及系统能效比值越高,于维持系统的长期稳定运行越有利。     

Application of fire suppression materials on suppression of LNG pool fires

An LNG pool fire is considered one of the main hazards of LNG, together with LNG vapor dispersion. Suppression methods are designed to reduce the hazard exclusion zones, distance to reach radiant heat of 5 kW/m², when an LNG pool fire is considered. For LNG vapor dispersion, the hazard exclusion zone is the distance travelled by the LNG vapor to reach a concentration of 2.5% v/v (half of the LNG lower flammability limit).Warming the LNG vapor to reach positive buoyancy faster is one way to suppress LNG vapor dispersion and reduce evaporation rate (thus fire size and its associated radiant heat) and that is the main objective in LNG pool fire suppression. Based on previous research, the use of high expansion foam has been regarded as the primary method in suppressing LNG pool fires. However, in 1980, another method was introduced as an alternative pool fire suppression system, Foamglas^®. The research concluded that 90% of the radiant heat was successfully reduced. Currently-called Foamglas^® pool fire suppression (Foamglas^® PFS) is a passive mitigation system and is deployed after the leak occurs. Foamglas^® PFS is non-flammable, and has a density one-third of the density of LNG, thus floats when an LNG pool is formed.This paper describes the study and confirmation of Foamglas^®PFS effectiveness in suppressing LNG pool fires. In addition, while Foamglas^® PFS is not expected to suppress LNG vapor dispersion, further investigation was conducted to study the effect of Foamglas^®PFS on LNG vapor dispersion. An LNG field experiment was conducted at Brayton Fire Field. The experimental development, procedures, results and findings are detailed in this paper.     

The effect of ventilation on spontaneous heating of coal

Ventilation plays an important role in the spontaneous heating of coal in an underground coal mine. If the ventilation rate is too high, heat is carried away by convection. If the ventilation rate is too low, the reaction rate becomes oxygen-limited. The effect of ventilation on the spontaneous heating of coal was investigated in an isothermal oven in this study. Experiments were conducted on three U.S. coal samples with ventilation rates ranging from 100 to 500 cm³/min. Experiments under ventilation were conducted to determine the critical ambient temperature, which is the minimum oven temperature required for a coal sample to achieve thermal runaway. Spontaneous heating tests were then conducted at various ventilation rates at the critical ambient temperature and the results were compared with spontaneous heating tests without ventilation. It was found that there is an optimum ventilation flow to produce the maximum rate of temperature rise at the critical ambient temperature. When the coal sample particle size was increased, a higher critical ambient temperature was required. The results in this study have application in the prevention of spontaneous combustion in underground coal mines.     

Analysis of the self-heating process of tetrafluoroethylene in a 100-dm3-reactor

There is a lack of data on the self-ignition behaviour of tetrafluoroethylene in industrial sized equipment. Therefore, a facility was designed and constructed for the determination of the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene in a cylindrical reactor with a volume of 100 dm³. Tests with initial pressures of 5 and 10 bar(a) were performed. The Minimum Ignition Temperature of Decomposition of tetrafluoroethylene was observed to decrease with the initial pressure, in agreement with previous experiments with small scale cylindrical vessels. This paper describes the test set-up und gives an overview of the achieved experimental results. In particular the effect of the reactor orientation (vertical or horizontal) is discussed. Furthermore, simplified equations from the Semenov thermal explosion theory are used to attempt extrapolations of previous and current data on the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene to other vessel volumes or initial pressures. Moreover, the experimental data are plotted together against the heated volume to heated surface ratio, which should provide a better extrapolation to other vessel dimensions by taking into account that the efficiency of the dispersion of the heat generated by the reaction is different for two reactors with the same volume but different diameter. Finally, simplified methods for predicting the Minimum Ignition Temperature of Decomposition of tetrafluoroethylene presented previously by the authors are validated for large scale reactors with the experimental data collected within the current work.     

基于监测数据的土壤源热泵系统设计优化分析

针对建筑中地源热泵系统实际地下换热过程复杂、设计困难等问题,以苏州地区某浅埋式地源热泵系统为研究对象,运用TRNSYS软件搭建地源热泵仿真模型,对一定条件下埋管内冷却水流速与地源热泵系统性能的耦合关系进行了模拟分析。仿真结果表明相同蓄热体积下埋管深度对系统性能影响较小。增大冷却水流速有利于土壤温度恢复,但系统耗电量增加。该浅埋式地源热泵系统冷却水流速1~2 m/s均在合理范围内,且埋管深度越大,最佳设计流速越小。     

基于机器学习的热释放速率实时预测方法

火灾态势的实时感知对提升消防救援指挥与决策水平有非常重要的意义。为实现火源热释放速率的实时预测,通过丙烷气体燃烧实验获取火焰体积和高度的实时数据,选取MATLAB中精细高斯SVM做分类训练,建立了基于图像处理的热释放速率预测模型。结果表明,训练完成后的模型可以根据3 s内的火焰体积/高度数据预测得到实时的燃料流量,获取相应的火源热释放速率。该预测模型在已知数据集和未知数据集上都表现出了较高的准确性,为火灾态势发展预测提供了理论和技术基础,有很好的应用前景。     

苯硝化工艺HAZOP分析的定量化研究

为提高危险化工工艺过程风险评估的准确性,通过工艺仿真模拟,研究工艺参数波动对生产装置安全性能的影响。以苯硝化工艺为例,采用危险与可操作性分析对该过程进行定性的风险评估;同时利用Aspen Plus建立苯硝化装置的模拟流程。结合HAZOP分析中偏差与模拟中硝化釜的流程变量之间的联系,以进料混酸的流量和1号硝化釜热负荷及出口温度为量化指标,观察混酸流量在正常操作点17.6 m3/h的±100%范围波动下1号硝化釜热负荷及出口温度的变化。研究结果表明,保持1号硝化釜温度为正常值,随着混酸流量的增大,硝化釜热负荷先增大后减小;保持硝化釜热负荷不变,随着混酸流量的增大,硝化釜温度先增大后减小。其中混酸流量值超过22.95 m3/h时,温度超过报警阈值60℃。