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71.
A 20 L spherical explosive device with a venting diameter of 110 mm was used to study the vented pressure and flame propagation characteristics of corn dust explosion with an activation pressure of 0.78–2.1 bar and a dust concentration of 400∼900 g/m3. And the formation and prevention of secondary vented flame are analyzed and discussed. The results show that the maximum reduced explosion overpressure increases with the activation pressure, and the vented flame length and propagation speed increase first and then decrease with time. The pressure and flame venting process models are established, and the region where the secondary flame occurs is predicted. Whether there is pressure accompanying or not in the venting process, the flame venting process is divided into two stages: overpressure venting and normal pressure venting. In the overpressure venting stage, the flame shape gradually changes from under-expanded jet flame to turbulent jet flame. In the normal pressure venting stage, the flame form is a turbulent combustion flame, and a secondary flame occurs under certain conditions. The bleed flames within the test range are divided into three regions and four types according to the shape of the flame and whether there is a secondary flame. The analysis found that when the activation pressure is 0.78 bar and the dust concentration is less than 500 g/m3, there will be no secondary flame. Therefore, to prevent secondary flames, it is necessary to reduce the activation pressure and dust concentration. When the dust concentration is greater than 600 g/m3, the critical dust concentration of the secondary flame gradually increases with the increase of the activation pressure. Therefore, when the dust concentration is not controllable, a higher activation pressure can be selected based on comprehensive consideration of the activation pressure and destruction pressure of the device to prevent the occurrence of the secondary flame. 相似文献
72.
The prevalence of older drivers’ engagement in distracting activities while driving is largely unexplored. Face-to-face interviews were conducted in the city of Braunschweig, Germany, comparing a sample of older drivers (n = 205) to a group of middle-aged drivers (n = 209). The drivers were interviewed on their engagement in distracting activities during the last half an hour of their driving trip, including the frequency and duration of these activities, their perception of the risk associated with these distracting activities and the role of these activities in at-fault crashes. Middle-aged drivers were significantly more likely to engage in certain distracting activities than older drivers. With regard to the duration of interactions with the passengers older drivers were significantly more talkative than middle-aged drivers. Middle-aged drivers rated most of the distracting activities as significantly less dangerous than older drivers. Distraction-related crashes are not a special problem of older drivers but seem to be very comparable to the middle-aged drivers. It is concluded that older drivers’ reluctance to engage in distracting tasks while driving is either a process of self-regulation or their age-related prudence. The study is the first to gather knowledge about distraction in German older drivers. Although older drivers are not currently overrepresented in distraction-related crashes, it is important to note that future cohorts of older drivers might differ in the way they engage with vehicles and technologies, which in turn may influence their driving patterns and willingness to engage in potentially distracting activities. 相似文献
73.
Xinshu Liu Xiaoman Su Sijie Tian Yue Li Rongfang Yuan 《Frontiers of Environmental Science & Engineering》2021,15(4):75
74.
Detlef Hinneburg Eberhard Renner Ralf Wolke 《Environmental science and pollution research international》2009,16(1):25-35
Background, aim, and scope The fraction of ambient PM10 that is due to the formation of secondary inorganic particulate sulfate and nitrate from the emissions of two large, brown-coal-fired
power stations in Saxony (East Germany) is examined. The power stations are equipped with natural-draft cooling towers. The
flue gases are directly piped into the cooling towers, thereby receiving an additionally intensified uplift. The exhausted
gas-steam mixture contains the gases CO, CO2, NO, NO2, and SO2, the directly emitted primary particles, and additionally, an excess of ‘free’ sulfate ions in water solution, which, after
the desulfurization steps, remain non-neutralized by cations. The precursor gases NO2 and SO2 are capable of forming nitric and sulfuric acid by several pathways. The acids can be neutralized by ammonia and generate
secondary particulate matter by heterogeneous condensation on preexisting particles.
Materials and methods The simulations are performed by a nested and multi-scale application of the online-coupled model system LM-MUSCAT. The Local
Model (LM; recently renamed as COSMO) of the German Weather Service performs the meteorological processes, while the Multi-scale
Atmospheric Transport Model (MUSCAT) includes the transport, the gas phase chemistry, as well as the aerosol chemistry (thermodynamic
ammonium–sulfate–nitrate–water system). The highest horizontal resolution in the inner region of Saxony is 0.7 km. One summer
and one winter episode, each realizing 5 weeks of the year 2002, are simulated twice, with the cooling tower emissions switched
on and off, respectively. This procedure serves to identify the direct and indirect influences of the single plumes on the
formation and distribution of the secondary inorganic aerosols.
Results and conclusions Surface traces of the individual tower plumes can be located and distinguished, especially in the well-mixed boundary layer
in daytime. At night, the plumes are decoupled from the surface. In no case does the resulting contribution of the cooling
tower emissions to PM10 significantly exceed 15 μgm−3 at the surface. These extreme values are obtained in narrow plumes on intensive summer conditions, whereas different situations
with lower turbulence (night, winter) remain below this value. About 90% of the PM10 concentrations in the plumes are secondarily formed sulfate, mainly ammonium sulfate, and about 10% originate from the primarily
emitted particles. Under the assumptions made, ammonium nitrate plays a rather marginal role.
Recommendations and perspectives The analyzed results depend on the specific emission data of power plants with flue gas emissions piped through the cooling
towers. The emitted fraction of ‘free’ sulfate ions remaining in excess after the desulfurization steps plays an important
role at the formation of secondary aerosols and therefore has to be measured carefully. 相似文献
75.
Many secondary materials are being considered for use as substitutes for natural aggregates in highway applications due to their suitable engineering and economic properties. During the design life of the application, recycled materials are exposed to freeze/thaw cycles and other aging processes such as carbonation, coupled with intermittent infiltration/wetting by precipitation events. In such scenarios, leaching of material constituents is a primary pathway for environmental impact. This paper presents results of the effect of freezing and thawing on the leaching behavior of major and minor constituents from a laboratory formulated granular cement-based material. Scenarios considered included water percolating through the material (flow-through) and run-off (flow-around), both important leaching pathways in highway environments. The effect of moisture content at the time of freezing, number of freeze/thaw (F/T) cycles, and material size reduction were investigated. F/T exposure and subsequent infiltration/wetting resulted in consolidation and self-cementing of the granular cement-based material. For the flow-around scenario, F/T exposure resulted in a reduction in constituent release with time and increasing F/T cycles. For the flow-through scenario, moisture content at the time of freezing was an important parameter and an increase in the release was initially observed due to preferential flow/cracks and/or constituent redistribution prior to a decrease that resulted from self-cementing during further thawing and percolation. 相似文献
76.
A dynamic hydrological Monte Carlo simulation model to inform decision-making at Lake Toolibin,Western Australia 总被引:1,自引:0,他引:1
Lake Toolibin, an ephemeral lake in the agricultural zone of Western Australia, is under threat from secondary salinity due to land clearance throughout the catchment. The lake is extensively covered with native vegetation and is a Ramsar listed wetland, being one of the few remaining significant migratory bird habitats in the region. Currently, inflow with salinity greater than 1000 mg/L TDS is diverted from the lake in an effort to protect sensitive lakebed vegetation. However, this conservative threshold compromises the frequency and extent of lake inundation, which is essential for bird breeding. It is speculated that relaxing the threshold to 5000 mg/L may pose negligible additional risk to the condition of lakebed vegetation. To characterise the magnitude of improvement in the provision of bird breeding habitat that might be generated by relaxing the threshold, a dynamic water and salt balance model of the lake was developed and implemented using Monte Carlo simulation. Results from best estimate model inputs indicate that relaxation of the threshold increases the likelihood of satisfying habitat requirements by a factor of 9.7. A second-order Monte Carlo analysis incorporating incertitude generated plausible bounds of [2.6, 37.5] around the best estimate for the relative likelihood of satisfying habitat requirements. Parameter-specific sensitivity analyses suggest the availability of habitat is most sensitive to pan evaporation, lower than expected inflow volume, and higher than expected inflow salt concentration. The characterisation of uncertainty associated with environmental variation and incertitude allows managers to make informed risk-weighted decisions. 相似文献
77.
Analysis of Damaging Hydrogeological Events: The Case of the Calabria Region (Southern Italy) 总被引:3,自引:0,他引:3
A period of bad weather conditions due to prolonged intense rainfall and strong winds can trigger landslides, floods, secondary
floods (accumulation of rain on surfaces with low permeability), and sea storms, causing damage to humans and infrastructure.
As a whole, these periods of bad weather and triggered phenomena can be defined as damaging hydrogeological events (DHEs).
We define a methodological approach based on seven simple indexes to analyze such events. The indexes describe the return
period (T) and trend of rainfall, the extent of hit areas, and the level of damages; they can be considered attributes of
georeferenced features and analyzed with GIS techniques. We tested our method in an Italian region frequently hit by DHEs.
In a period of 10 years, 747 damaging phenomena (landslides, 43%; floods, 38%) and 94 DHEs have been classified. The road
network and housing areas are the most frequently damaged elements, threatened by all types of damaging phenomena. T classes
are almost in accordance with the level of damage. These results can be used to outline warning levels for civil protection
purposes, to forecast the areas most likely to be hit and the potential ensuing damage, to disseminate information concerning
vulnerable areas, and to increase people’s awareness of risk. 相似文献
78.
79.
Dissolved organic matter removal using magnetic anion exchange resin treatment on biological effluent of textile dyeing wastewater 总被引:3,自引:0,他引:3
This study investigated the removal of dissolved organic matter(DOM) from real dyeing bio-treatment effluents(DBEs) with the use of a novel magnetic anion exchange resin(NDMP).DOMs in two typical DBEs were fractionized using DAX-8/XAD-4 resin and ultrafiltration membranes. The hydrophilic fractions and the low molecular weight(MW)(〈3 kDa) DOM fractions constituted a major portion(〉50%) of DOMs for the two effluents. The hydrophilic and low MW fractions of both effluents were the greatest contributors of specific UV254absorbance(SUVA254),and the SUVA254 of DOM fractions decreased with hydrophobicity and MW. Two DBEs exhibited acute and chronic biotoxicities. Both acute and chronic toxicities of DOM fractions increased linearly with the increase of SUVA254 value. Kinetics of dissolved organic carbon(DOC) removal via NDMP treatment was performed by comparing it with that of particle active carbon(PAC). Results indicated that the removal of DOC from DBEs via NDMP was 60%,whereas DOC removals by PAC were lower than 15%. Acidic organics could be significantly removed with the use of NDMP. DOM with large MW in DBE could be removed significantly by using the same means. Removal efficiency of NDMP for DOM decreased with the decrease of MW. Compared with PAC,NDMP could significantly reduce the acute and chronic bio-toxicities of DBEs. NaCl/NaOH mixture regenerants,with selected concentrations of 10% NaCl(m/m)/1%NaOH(m/m),could improve desorption efficiency. 相似文献
80.
SO_4~(2-) and NO_3~- are important chemical components of fine particulate matter(PM_(2.5)),especially during haze periods.This study selected two haze episodes in Beijing,China with similar meteorological conditions.A monitoring-modeling approach was developed to estimate the secondary conversion ratios of sulfur and nitrogen based on monitored and simulated concentrations.Measurements showed that in Episode 1(24th–25th October,2014),the concentrations(proportions)of SO_4~(2-) and NO_3~- reached 35.1μg/m~3(14.9%) and 55.0μg/m~3(22.9%),while they reached 14.4μg/m~3(9.3%) and 59.1μg/m~3(38.1%)in Episode 2(26th–27th October,2017).A modeling system was applied to apportion Beijing's SO_4~(2-) and NO_3~- in primary and secondary SO_4~(2-)/NO_3~- emitted from local and regional sources.Thus,secondary conversion contributions considering the local and regional level were defined.The former primarily focused on Beijing atmospheric oxidation ability and the latter mainly considered the existence form of Beijing SO_4~(2-)/NO_3~- under the regional transport impacts.Finally,secondary oxidation ratios were estimated through combining secondary conversion contribution coefficients for simulated and monitored concentrations.At regional level,sulfur oxidation ratios in polluted(clean)days during two sampling periods were0.57–0.72(0.07–0.52)and 0.74–0.80(0.08–0.61),nitrogen oxidation ratios were 0.20–0.29(0.05–0.15)and 0.34–0.38(0.02–0.29),indicating that atmospheric oxidation was enhanced when considering regional transport through 2014–2017.At the local level,sulfur oxidation ratios were 0.66–0.71(0.04–0.48)in haze(clean)days,while nitrogen oxidation ratios were0.16–0.29(0.02–0.16).The atmospheric oxidation ability markedly increased in PM_(2.5)pollution days,but changed only slightly between the two periods. 相似文献