大型自然通风冷却塔环境影响的预测分析研究

大多数内陆核电厂将采用大型自然通风冷却塔作为其二次循环冷却方式,本文基于美国核管会推荐的SACTI程序,给出了该模型的基本原理和框架结构,并以江西彭泽核电厂为例,采用该程序预测分析了该核电厂大型自然通风冷却塔所造成的雾羽和太阳辐射损失的影响。并进一步研究了不同环境风速、相对湿度条件下对冷却塔造成的太阳辐射损失的影响。SACTI模型可以根据厂址逐时气象观测数据,较好地计算可见雾羽的长度、抬升高度和太阳辐射损失,其结果可以作为冷却塔环境影响评价的依据。     

Thermodynamic coupling characteristics in hybrid (dry/wet) cooling system

A hybrid cooling system consisting of both a dry section and wet section is proposed in this paper as a means to conserving energy and water by combining the benefits of both dry and wet cooling modes. A new thermodynamic coupling characteristics computing model was established to identify the best combination of dry and wet cooling subsystems in the hybrid tower throughout year-round operation based on its air thermodynamic state under the “no plume” principle. A hybrid cooling tower in Inner Mongolia, China, consisting of an elliptical tube heat exchanger with rectangular fins and counter-flow wet packing, was designed as an example under the no plume principle. The minimum number of heat exchanger units in service and the corresponding thermodynamic operating parameters were obtained under a year-round operation. The tower exhibited notable advantages in regards to water conservation compared to the traditional evaporative cooling tower at an estimated yearly savings of 3.74 × 10⁷ kg water.     

Homogeneous and heterogeneous photolysis of nitrate in the atmosphere: state of the science,current research needs,and future prospects

● Recent advances in the photolysis of nitrate/HNO₃ are reviewed. ● Mechanisms and key factors affecting the photolysis of nitrate/HNO₃ are summarized. ● Atmospheric implications and future research recommendations are provided. Nitrate is an important component of atmospheric particulate matter and affects air quality, climate, human health, and the ecosystem. Nitrate was previously considered a permanent sink for nitrogen oxides (NO_x). However, this viewpoint has been challenged in recent years because growing research evidence has shown the transformation of nitrate into NO_x (i.e., renoxification). The photolysis of nitrate/HNO₃, especially in the particulate phase or adsorbed on particles, can be a significant renoxification process in the atmosphere. The formation and photolysis of nitrate in aerosol not only change the diurnal variation of NO_x, but also provide long-distance transport of NO_x in the form of nitrate, which affects local and regional atmospheric chemistry and air quality. This review summarizes recent advances in the fundamental understanding of the photolysis of nitrate/HNO₃ under various atmospheric conditions, with a focus on mechanisms and key factors affecting the process. The atmospheric implications are discussed and future research is recommended.     

核电厂野外示踪试验的三维数值模拟研究

为深入分析国内某拟选滨海核电厂址的大气扩散特征,在现场野外示踪试验的基础上,采用计算流体动力学（CFD）软件Fluidyn-PANACHE,结合三维GIS、结构化贴体网格构建、区域加密等技术方法,创建了可模拟野外示踪试验的精细化大气扩散模拟系统.相比于高斯模式,CFD模式能够更好地模拟示踪剂在不同下风距离处的峰值浓度和烟羽宽度,对近场及复杂下垫面条件下的扩散模拟更贴合实际,且可在稳态模拟的基础上获得连续变化风场中接近实时模拟的仿真效果.模拟结果的偏差统计分析表明,CFD稳态模拟和高斯模拟的统计学评价指标均位于国际公认的可接受范围内,CFD模拟的随机偏差优于高斯模拟.因此,CFD模式可用于辅助和优化其他核电厂址的野外示踪试验工作,提高我国核安全审评的效率和针对性.     

COMPARISON OF THERMAL SCANNING AND IN SITU TECHNIQUES FOR MONITORING THERMAL DISCHARGES1

ABSTRACT: In situ and remote sensing techniques for measuring thermal plumes are compared for data taken at the Point Beach Nuclear Power Plant on Lake Michigan for five separate occasions. The in situ method employed a boat whose position was determined with a microwave ranging system. Temperatures at the surface and at various depths were measured with fast response thermistor probes. The remote sensing technique utilized an infrared scanner in the 8 to 14 micron range. Comparison of the plumes indicates good agreement with respect to plume configurations, areas within isotherms and centerline temperature decays for all except one occasion, a calm day characterized by no waves, low wind and ambient current velocities. Robable reasons for disagreement under such ambient conditions are discussed. The inherent advantages and disadvantages of each method are discussed in light of the results of the five sets of data. This includes both the data collecting and data analyzing procedures. It is concluded that judicious combination of both methods offers a better picture of thermal plumes than can be obtained by either technique alone.     

PRECISE WATER VELOCITY MEASUREMENTS USING PHOTOGRAMMETRIC TECHNIQUES1

ABSTRACT Necessary input parameters for studying mixing zone characteristics of thermal plumes are horizontal surface and subsurface water velocities. Using time lapse aerial photography and analytical photogrammetric techniques, movements of drogues in an effluent plume were traced. From these traces accurate velocity vectors were obtained. Photographic coordinates of drogue images were measured using a glass scale. From the photo coordinates and the results of a ground control survey, an analytical solution was made for positions of drogues in the water at known intervals of time. Drogue positions were mapped for selected exposures thereby providing a visual display of velocity vectors in the study area. A rigorous error analysis was performed to determine the validity of the computed results.     

浮力羽流低风速的多点实时测量

作者发展了一种浮力羽流低风速的多点实时测量技术。测头端部安装耐热玻璃小球,直径0.8mm,球内装有热电偶和加热电阻丝,测头将风速转换为热电偶的电势。每支测头必须经过专用校准热风洞的单支校验。使用巡回检测系统记录多个测头的电位,得到流场各点风速的统计平均值,实现了低风速场的多点实时测量。本测量系统对火灾科学、环境科学和气象学的实验研究和实地观测是很有用的测量技术。     

隧道火灾纵向通风下羽流触顶区温度变化研究

根据Boussinesq相似性,利用流体力学基本方程,建立隧道火灾羽流三维模型,并借助量纲分析方法,推导了触顶区温升公式.在假设的隧道模型下,通过改变火源功率和纵向风速设计了多个算例,利用温升公式进行计算,并与场模拟结果比较,归纳了触顶区温度的变化规律.结果表明,同一火源功率下,触顶区温度随纵向风速增加而降低,并趋于一稳定值,其大小约为最高温度的1/3.还对温降过程中的突变现象进行了分析,讨论了中心低温区及不同羽流对温度的影响.最后对火灾救援的通风策略提出了建议.     

Improved electrospray design for aerosol generation and flame propagation analysis

Although the hazards of aerosol fires and explosions have been studied for decades the data for aerosol flame propagation is still scarce. Additionally there is a lack of standard techniques and measurement apparatus, which impedes the development of optimal aerosol hazard mitigation measures. The focus of this study is development of an improved aerosol electrospray device for the generation of high quality aerosol data. The goal is achieved through higher nozzle packing, precise nozzle and mesh hole alignment and adding two ground meshes. In addition to a flat ground mesh, the utilization of a cylindrical ground mesh demonstrated improved confinement and guidance of droplets. Duratherm 600, heat transfer fluid, was examined to demonstrate the modified electrospray device capabilities as compared to previous design. Results show the modified electrospray can produce more uniform droplets, more even test chamber dispersion, smaller droplet size and higher concentration aerosol, which is essential to study aerosol flame propagation. Accordingly, the results of aerosol flame speed tests for the improved design were more reproducible. Moreover, it was found that a traditional propane pilot flame was unable to ignite the smaller aerosol droplet size due to the strong turbulence generated by the open flame. However, by careful modification of the pilot flame length, the turbulence decreased dramatically and the small droplet size aerosol can be tested.     

A sneak peek into the phenomenology of fuel mist explosions: The key role of vapor fractions

The modern world depends greatly on hydrocarbons, which are ubiquitous, indispensable fuels used in nearly every existing industry. Although important, their use may trigger dangerous incidents, whether in their production, handling, storage, or transporting phase, especially when aerosolized. In light of proposing a standard procedure to assess the flammability and explosivity of fuel mists, a new test method was established based on the EN 14034 standards series. For the previous purposes, a gravity-fed mist generation system was designed and employed in a modified 20 L explosion vessel. This test method allowed the determination of the ignition sensitivity of several fuels. In addition, their explosion severity was represented by the explosion overpressure P_ex, and the rate of pressure rise dP/dt_ex, two thermo-kinetic parameters determined with a specifically developed control system and custom software. Nonetheless, a noticeable difference in the ignition sensitivity and the explosion severity was perceived when changing suppliers or petroleum cuts of some fuels. Moreover, sensitivity studies showed that both the droplet size distribution and the temperature of the droplets play a significant role in fuel mist explosion. These parameters can be directly related to the vapor fraction surrounding a droplet during its ignition. Consequently, this study focuses on the influence of varying the composition of three well-known and abundantly used fuels. Different petroleum cuts were introduced in different fractions into isooctane, Jet A1 aviation fuel, and diesel fuel mixtures, which were then aerosolized into a uniformly distributed turbulent mist cloud and ignited using spark ignitors of 100 J. Subsequently, complementary tests were executed in a vertical flame propagation tube coupled with a high-speed video camera allowing the visualization of the flame and the determination of the spatial flame velocity, and a tentative estimation of the laminar burning velocity. The latter was also estimated from the pressure-time evolution in the 20 L sphere using existing correlations. Indeed, the determination of the laminar burning velocity can be useful in modeling such accidents. Finally, highlighting the essential role of the mist and vapor fraction during their ignition has led to a better understanding of their explosion mechanisms.