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841.
Indoor pollutant mixing time in an isothermal closed room: an investigation using CFD 总被引:1,自引:0,他引:1
A. J. Gadgil C. Lobscheid M. O. Abadie E. U. Finlayson 《Atmospheric environment (Oxford, England : 1994)》2003,37(39-40):5577
We report on computational fluid dynamics (CFD) predictions of mixing time of a pollutant in an unventilated, mechanically mixed, isothermal room. The study aims to determine: (1) the adequacy of the standard Reynolds Averaged Navier Stokes two-equation (k−) turbulence model for predicting the mixing time under these conditions and (2) the extent to which the mixing time depends on the room airflow, rather than the source location within the room. The CFD simulations modeled the 12 mixing time experiments performed by Drescher et al. (Indoor Air 5 (1995) 204) using a point pulse release in an isothermal, sealed room mechanically mixed with variable power blowers. Predictions of mixing time were found in good agreement with experimental measurements, over an order of magnitude variation in blower power. Additional CFD simulations were performed to investigate the relation between pollutant mixing time and source location. Seventeen source locations and five blower configurations were investigated. Results clearly show large dependence of the mixing time on the room airflow, with some dependence on source location. We further explore dependence of mixing time on the velocity and turbulence intensity at the source location. Implications for positioning air-toxic sensors in rooms are briefly discussed. 相似文献
842.
羧甲基壳聚糖的制备及絮凝性能探讨 总被引:13,自引:0,他引:13
制备了具有水溶性、无毒羧甲基壳聚糖(以下简称NOCC),将其作为絮凝剂与聚丙烯酰胺(PAM)一道处理生活污水,通过测定其沉降时间,沉降絮体高度,沉降速度,沉降后溶液透光率等参数,表征了其絮凝能力,提出了普遍认为聚丙烯酰胺处理一般污水具有良好絮凝能力的不同看法,为壳聚糖的开发利用做了有益的探索。 相似文献
843.
August Kaiser Helfried Scheifinger Wolfgang Spangl Andrea Weiss Stefan Gilge Wolfgang Fricke Ludwig Ries Danijel Cemas Brigita Jesenovec 《Atmospheric environment (Oxford, England : 1994)》2007,41(40):9273-9287
The Alpine stations Zugspitze, Hohenpeissenberg, Sonnblick, Jungfraujoch and Mt. Krvavec contribute to the Global Atmosphere Watch Programme (GAW) of the World Meteorological Organization (WMO). The aim of GAW is the surveillance of the large-scale chemical composition of the atmosphere. Thus, the detection of air pollutant transport from regional sources is of particular interest. In this paper, the origin of NOx (measured with a photo-converter), CO and O3 at the four Alpine GAW stations is studied by trajectory residence time statistics. Although these methods originated during the early 1980s, no comprehensive study of different atmospheric trace gases measured simultaneously at several background observatories in the Alps was conducted up to present.The main NOx source regions detected by the trajectory statistics are the northwest of Europe and the region covering East Germany, Czech Republic and southeast Poland, whereas the main CO source areas are the central, north eastern and eastern parts of Europe with some gradient from low to high latitudes. Subsiding air masses from west and southwest are relatively poor in NOx and CO.The statistics for ozone show strong seasonal effects. Near ground air masses are poor in ozone in winter but rich in ozone in summer. The main source for high ozone concentration in winter is air masses that subside from higher elevations, often enhanced by foehn effects at Hohenpeissenberg. During summer, the Mediterranean constitutes an important additional source for high ozone concentrations.Especially during winter, large differences between Hohenpeissenberg and the higher elevated stations are found. Hohenpeissenberg is frequently within the inversion, whereas the higher elevated stations are above the inversion.Jungfraujoch is the only station where the statistics detect an influence of air rich in CO and NOx from the Po Basin. 相似文献
844.
Influence of indoor transport and mixing time scales on the performance of sensor systems for characterizing contaminant releases 总被引:2,自引:0,他引:2
Priya Sreedharan Michael D. Sohn William W Nazaroff Ashok J. Gadgil 《Atmospheric environment (Oxford, England : 1994)》2007,41(40):9530-9542
Optimizing real-time sensor systems to detect and identify relevant characteristics of an indoor contaminant event is a challenging task. The interpretation of incoming sensor data is confounded by uncertainties in building operation, in the forces driving contaminant transport, and in the physical parameters governing transport. In addition, simulation tools used by the sensor interpretation algorithm introduce modeling uncertainties. This paper explores how the time scales inherent in contaminant transport influence the information that can be extracted from real-time sensor data. In particular, we identify three time scales (within room mixing, room-to-room transport, and removal from the building) and study how they affect the ability of a Bayesian Monte Carlo (BMC) sensor interpretation algorithm to identify the release location and release mass from a set of experimental data, recorded in a multi-floor building. The research shows that some limitations in the BMC approach do not depend on details of the models or the algorithmic implementation, but rather on the physics of contaminant transport. These inherent constraints have implications for the design of sensor systems. 相似文献
845.
高占祥 《城市环境与城市生态》2003,16(3):58-59
文章揭示了造成环境监测仪器的氨气敏电极损坏的原因,提出了延长其使用寿命的方法。首先要保护电板的引线,必须严格按照使用说明书定期进行认真的保养维护,实施氨气敏复合电极膜及其填充液的更换,保护好电极,可延长其寿命。 相似文献
846.
Summary. We tested the hypothesis that aggregation behaviour of the
firebrat, Thermobia domestica (Packard) (Thysanura: Lepismatidae), an
inhabitant of enclosed microhabitats, is mediated, at least in part, by
a pheromone. Individual insects were released into the central chamber
of a 3-chambered olfactometer and test stimuli were placed in lateral
chambers. Paper discs previously exposed for 3 days to 10 female, male,
or juvenile T. domestica were all preferred by female, male, or juvenile
T. domestica over unexposed paper discs, indicating the presence of an
aggregation/arrestment pheromone. In additional experiments, frass and
scales from female T. domestica, tested singly and in combination,
proved not to be the source of the pheromone. Physical contact was
required for pheromone recognition, indicating that the pheromone
arrests rather than attracts conspecifics. Arrestment by the
long-tailed silverfish, Ctenolepisma longicaudata Escherich
(Thysanura: Lepismatidae), but not by the common silverfish, Lepisma
saccharina L. (Thysanura: Lepismatidae), to T. domestica exposed
paper discs suggests closer phylogenetic relatedness between C.
longicaudata and T. domestica, than between C.
longicaudata and L. saccharina. Whether C.
longicaudata or L. saccharina produce an aggregation
signal, and whether T. domestica respond to this signal is unknown.
Received 10 June 2002; accepted 30 September 2002. 相似文献
847.
Patrice Lucchetta Emmanuel Desouhant Eric Wajnberg Carlos Bernstein 《Behavioral ecology and sociobiology》2007,61(9):1409-1418
The reproductive success of insect parasitoids depends on two activities, searching for hosts to obtain immediate fitness
rewards (offspring) and searching for food to extend life span and enhance future reproductive opportunities. Models suggest
that to deal with this trade-off and to cope with the variability of the resources they depend on, parasitoids should simultaneously
integrate information originating from three distinct sources: host and food availabilities in the environment (environmental
information) and the metabolic reserves of the parasitoid (internal information). We tested whether, in the parasitic wasp
Venturia canescens, these three types of information are perceived simultaneously and interact during host-patch exploitation. Experiments were
performed with strains originating from two different geographical locations and with individuals of the two reproductive
modes, arrhenotoky and thelytoky. We hypothesised that there would be differences between modes of reproduction as they thrive
in different ecological conditions. Our results show that metabolic state, food availability and the number of ovipositions
performed simultaneously modulate patch residence time in V. canescens of both populations and reproductive modes. Unfed wasps left their host patch earlier than fed ones. The tendency to leave
the patch increased with an increasing probability of finding food. Our study confirms that globally, each oviposition increases
the patch-leaving tendency (decremental mechanism). This effect was modulated by both the metabolic reserves and food availability,
and the relationship depended on the geographic origin of populations. Individuals of one of the populations switched from
a decremental to an incremental patch-leaving mechanism depending on the presence or absence of food in the vicinity. Differences
between reproductive modes in the responses to environmental cues can be explained by the different ecological conditions
they live in. 相似文献
848.
为探究不同外热部位对18650型锂离子电池热失控特性的影响,通过自主设计的试验平台对电荷量为100%的18650型锂离子电池开展不同外热部位下热失控试验,探讨不同部位外热源对电池热失控行为过程、热失控响应时间、温度特性、电池破裂部位的影响。结果表明:在相同热源功率条件下,外热源位置对电池热失控过程中初爆与二次燃爆间的时间间隔存在影响,顶部加热时安全阀打开瞬间便发生二次燃爆,底部和中部加热工况下,时间间隔分别延迟至18 s和40 s;中部加热时池体温升速率最慢,为0.873℃/s,分别为顶部和底部加热时的77.5%和77.8%;中部加热时热失控响应时间最长达290 s,顶部和底部加热时分别缩短12.4%和30.0%;顶部和底部加热时,热失控破裂部位集中于顶部"褶皱处"和底部防爆阀,但在中部加热工况下,电池发生破裂部位的随机性增加,其外壳破坏程度也有增加。 相似文献
849.
Deposition of combustible dust on a hot surface is a hidden danger of fire. In this work, polymethylmethacrylate (PMMA) dust was selected to analyse the influence of dust layer diameter, dust particle size and dust layer thickness on the ignition characteristics of PMMA dust layer. Critical heating temperatures and ignition time had been measured. The STA-GC/MS-FTIR analysis was used to determine that the main products of PMMA pyrolysis were MMA, CO, CO2, and C2H4, of which CO and C2H4 were transported to the ambient to cause gas phase combustion on the surface of the dust layer. For 10 mm thick dust layer, the critical heating temperatures of 5 μm PMMA, 100 nm PMMA, and 30 μm PMMA were 300 °C, 330 °C, and 320 °C. As the thickness of the dust layer increased, the gas transport path became longer, the critical heating temperature and ignition time increased. The characteristic particle size (D [3,2]) was utilized to represent the true particle size, and the ignition time increased with the increase of the characteristic particle size. The increase in the diameter of the dust layer had a slight effect on the temperature history and ignition time of the dust layer. 相似文献
850.
为研究盾构隧道火灾时大客车人员构成比例及满载系数对下车时间影响,采用现场试验及Pathfinder数值模拟,分析不同人员构成比例及满载系数下大客车人员下车过程。结果表明:不考虑人员疏散反应时间情况,大客车下车时间为54~68 s,大客车平均下车时间为60.68 s,每位人员平均下车时间为1.22 s;老人下车时间最长,成年女士下车时间最短,成年男士与儿童下车时间基本相等。当老人比例在30%~80%范围变化时,下车时间随老人比例增大显著增加;成年女士比例对大客车下车时间影响较小;大客车人员下车时间与满载系数相关,随满载系数增加而增加,并趋于正比例函数关系。 相似文献