环境温度和火灾强度对自然通风隧道火灾温度场的影响

为了掌握环境温度和火灾强度对自然通风城市隧道温度场的影响,运用火灾模拟软件FDS,对在不同环境温度和火灾强度下自然通风隧道火灾进行模拟,得到各种火灾工况下的模拟结果,并对各种工况下的温度场进行对比分析。     

隧道火灾烟气发展的模拟计算研究

分析了隧道火灾的特点，运用区域模拟和场模拟的方法，通过一假定的隧道火灾算例，分析了几种不同情况下隧道火灾的烟气发展情况。讨论了烟气温度、高度的变化情况，得到了不同区段火和烟气对人构成威胁和对隧道结构造成破坏的情况，最后对隧道火灾的防治提出了一些建议。     

自然通风城市隧道火灾温度分布试验研究

设定了两种火灾规模,以1：10模型比例对南京市某自然通风城市隧道进行了火灾时隧道内温度场的分布规律的模拟试验。试验结果表明,在大火灾强度下,温度场纵向影响范围相应增加;在隧道两口部存在温差的情况下,隧道内烟气主要向口部温度较高一侧的通风口扩散;在烟气经过通风竖井之后,烟气的温度有显著降低,证明自然通风竖井能够排出大量的烟气,并带走大部分热量,烟气会因热动力不足而发生沉降现象。     

竖井型城市隧道自然通风理论研究

对竖井型城市隧道自然通风的原理与流动特征进行分析,建立了隧道内有害气体浓度分布的数学模型,提出利用有害气体浓度来评价城市隧道卫生效果的方法,为竖井型城市隧道自然通风的理论计算、方案设计和分析提供必要的理论依据。     

自然通风作用下室内甲醛浓度分布数值模拟分析

在理论分析的基础上,利用CFD软件对自然通风作用下室内甲醛浓度的分布进行数值模拟。结果表明：利用自然通风可以减小室内甲醛的含量,通过比较卧室床放置在不同位置时的甲醛浓度分布和速度分布,得出了床在靠近门一侧时,最舒适并最有利于人体的健康。并模拟了这一方案时整个房间的流场,得到在x、y、z三个平面上的速度分布和甲醛浓度分布规律。     

竖井型城市隧道自然通风模型实验研究

以连续竖井的静压分布特性为基础,采用分段模型实验方法,搭建了南京市某隧道模型,对正常交通状况下隧道交通风压进行实验,得到了隧道的自然通风特性及竖井通风的一般规律;建立了通风量与有害气体浓度之间关系的数学模型,研究了评价竖井对城市隧道自然通风效果影响的方法,并对该实际隧道通风效果做出评价,得出了竖井型城市隧道自然通风的相关结论,为此类城市隧道的设计及运营管理提供一定的参考。     

坡度隧道火灾自然排烟特性研究

通过模型试验,研究了坡度隧道火灾自然排烟特性,试验结果表明：（1）受坡度影响,火羽流向上坡侧发生偏转,且偏转角几乎不受火源位置与HRR的影响,只随坡度的升高而线性增大;（2）顶壁下方最高烟气温度随坡度的升高而降低,基于理论分析和模型试验结果,得到了顶壁下方最高烟气温度的计算模型;（3）火源上坡侧的顶壁下方烟气温度受坡度变化的影响较小,下坡侧的顶壁下方烟气温度随坡度的降低而升高,并在坡度降为0时与上坡侧烟气温度关于火源对称分布,结合理论分析,得出了火源段顶壁下方烟气温度的衰减模型。     

坡度对地铁区间隧道火灾烟气流动影响的数值模拟

为探讨坡度对地铁区间隧道火灾烟气流动特性的影响,论文在综合分析国内外地铁区间隧道火灾研究的基础上,采用数值模拟软件FDS分别研究了自然通风条件下无坡度、1％坡度、2％坡度、3％坡度对区间隧道内烟气的流动特点、临界风速的影响.结果表明:坡度对地铁区间隧道火灾烟气的流动及临界风速有一定的影响.上坡隧道的临界风速相对于无坡度隧道的临界风速有所减小,且临界风速随着隧道坡度的增大而减小.下坡隧道的临界风速相对于无坡度隧道的临界风速有所增加,且临界风速随着隧道坡度的增大而增大.     

顶部开孔组合方式对城市公路隧道自然通风的影响

利用SES模拟软件,采用数值计算方法研究了城市公路隧道采用顶部开孔的自然通风方式时隧道内的气流运动和污染物扩散的问题。根据实际隧道几何尺寸,截取1000米隧道作为算例,研究了自然通风孔布置情况对隧道内空气流动及污染物扩散的影响。结果表明:在开孔数量和总开孔面积不变的情况下,与多个通风孔集中布置时相比单个通风孔均匀布置时隧道内通风换气效果最差,隧道沿程排放污染物能力最弱;而多个通风孔集中布置时五个孔一组的通风换气效果最好,隧道沿程排放污染物能力最强。     

连续隧道洞口间烟气扩散特性研究

当上下游隧道的洞口间距较短时,上游隧道的火灾烟气可能扩散至下游隧道,对下游隧道造成影响。采用CFD数值模拟方法建立连续隧道模型,对不同纵向风速、不同火源位置、不同热释放率、不同洞口间距以及不同横向风速下的烟气窜流情况进行模拟分析。结果表明：（1）上游隧道纵向风速的增大将导致烟气往下游隧道方向水平扩散的距离增大,因此,烟气的窜流量增大;（2）火源距离上游隧道出口越远,热释放率越小,上游隧道出口处烟气温度就越低,烟气的水平惯性力上升,更容易窜流至下游隧道;（3）烟气窜流随着洞口间距的增大而不断减弱,当洞口间距足够大时,不会出现烟气窜流的现象;（4）当存在横向风时,洞口间烟气的流动轨迹会发生偏移,并且烟气窜流会随横向风速的增大而减弱。     

Magnetic Field Influence on the Low Temperature Heat Capacity and Heat Release of (TMTSF)2PF6

We have measured under applied magnetic field the heat capacity c _p and heat release of the quasi-1D conductor (TMTSF)₂PF₆ in its spin density wave (SDW) ground state. The low-temperature heat capacity (T < 0.5 K) is dominated by a Schottky anomaly contribution. A corresponding term was also found for the heat release. In this T-range both properties are strongly sensitive to moderate magnetic fields (i.e., below 0.5 T): their amplitudes have a sharp maximum for H _c=0.2 T. We show that the corresponding density of two-level states N _S undergoes a sharp maximum at H _c, which rules out an extrinsic origin for the two-level states. Instead we suppose an intrinsic origin, such as defects of commensurability of the SDW, as the (slow) excitations related to the domain walls. This effect is found to be independent on the field orientations H a and H a.     

Molar Heat Capacity at Constant Volume of Trifluoromethane (R23) from the Triple-Point Temperature to 342 K at Pressures to 33 MPa

Molar heat capacities at constant volume (C _v) of trifluoromethane (R23) have been measured with an adiabatic calorimeter. Temperatures ranged from the triple point to 342 K, and pressures up to 33.5 MPa. Measurements were conducted on the liquid in equilibrium with its vapor and on compressed liquid and gaseous samples. The samples were of high purity, as verified by chemical analysis. Calorimetric quantities are reported for the two-phase (C ⁽²⁾ _v), saturated-liquid (C or C_x), and single-phase (C _v) molar heat capacities. The C ⁽²⁾ _v data were used to estimate vapor pressures for values less than 100 kPa by applying a thermodynamic relationship between the two-phase internal energy U ⁽²⁾ and the temperature derivatives of the vapor pressure. The triple-point temperature and the enthalpy of fusion were also measured. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) is estimated to be 0.7% for C _v, 0.5% for C ⁽²⁾ _v, and 0.7% for C .     

Molar Heat Capacity at Constant Volume of 1,1-Difluoroethane (R152a) and 1,1,1-Trifluoroethane (R143a) from the Triple-Point Temperature to 345 K at Pressures to 35 MPa

Molar heat capacities at constant volume (C _v) of 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) have been measured with an adiabatic calorimeter. Temperatures ranged from their triple points to 345 K, and pressures up to 35 MPa. Measurements were conducted on the liquid in equilibrium with its vapor and on compressed liquid samples. The samples were of high purity, verified by chemical analysis of each fluid. For the samples, calorimetric results were obtained for two-phase ((C _v ⁽²⁾ ), saturated-liquid (C or C _x ^' ), and single-phase (C _v) molar heat capacities. The C data were used to estimate vapor pressures for values less than 105 kPa by applying a thermodynamic relationship between the saturated liquid heat capacity and the temperature derivatives of the vapor pressure. The triple-point temperature and the enthalpy of fusion were also measured for each substance. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) for C _v is estimated to be 0.7%, for C _v ⁽²⁾ it is 0.5%, and for C it is 0.7%.