大气降尘测定中蒸发方式的选择

为了加快大气降尘样品的蒸发速度和报出数据的及时,经过分析总结,得出蒸发样品的步骤为:先电热套蒸发再水浴蒸发最后用电热板蒸发,这样既可以节省时间,又可以节约能耗,避免样品在空气中放置时间过长,空气中的尘粒进入样品中,影响样品测定的结果。     

土壤水分对幼龄桉树蒸腾和生长的影响

通过盆栽试验,研究不同土壤水分对幼龄桉树蒸腾和生长的影响.结果表明,土壤含水量越高,桉树蒸腾量越大.随着桉树增长,植株蒸腾量逐月增大,但蒸腾强度却逐月下降,说明桉树叶面积增长速度,大于蒸腾量增长速度.不同土壤水分条件下桉树的蒸腾量、蒸腾时间长短和最大蒸腾量出现的时间不同.水分亏缺对桉树的影响是多方面的,外观表现为幼嫩枝梢萎蔫,分枝少、叶片少、叶面积下降、叶色变深、变暗,植株下部叶子叶尖枯死;生理上表现为气孔导度降低,阻力增大,气孔关闭,光合速率降低,养分吸收量减少.总的影响是生长量显著降低.在试验条件下,桉树每生产1 kg干物质所付出的蒸腾耗水量与土壤水分有关,土壤干旱时桉树的水分利用效率最低.     

人为干扰强度对村级景观结构特征的影响

以研究点与村落中心间的距离作为人为干扰强度的划分指标 ,把村落按重度人为干扰、中度人为干扰和轻度人为干扰 3个等级分为中心区、过渡区和基质区 ,分析不同人为干扰强度与村级景观特征的相互关系。结果表明 :随着人为干扰强度的增强 ,多样性指数、相对丰富度指数和均匀度指数均相应增大 ,在中度人为干扰强度区 ,上述 3种指数均最大 ,但优势度指数最小。随着干扰强度的增强 ,与人们生活密切相关的景观类型的分形维数减小 ,斑块的相似性增强     

Transesterification of waste vegetable oil under pulse sonication using ethanol,methanol and ethanol–methanol mixtures

This study reports on the effects of direct pulse sonication and the type of alcohol (methanol and ethanol) on the transesterification reaction of waste vegetable oil without any external heating or mechanical mixing. Biodiesel yields and optimum process conditions for the transesterification reaction involving ethanol, methanol, and ethanol–methanol mixtures were evaluated. The effects of ultrasonic power densities (by varying sample volumes), power output rates (in W), and ultrasonic intensities (by varying the reactor size) were studied for transesterification reaction with ethanol, methanol and ethanol–methanol (50%-50%) mixtures. The optimum process conditions for ethanol or methanol based transesterification reaction of waste vegetable oil were determined as: 9:1 alcohol to oil ratio, 1% wt. catalyst amount, 1–2 min reaction time at a power output rate between 75 and 150 W. It was shown that the transesterification reactions using ethanol–methanol mixtures resulted in biodiesel yields as high as >99% at lower power density and ultrasound intensity when compared to ethanol or methanol based transesterification reactions.     

燃气-蒸汽联合循环供热项目主机选型方案刍议

发展燃气-蒸汽联合循环供热对于解决经济发展和环境保护具有重要作用，在我国经济发达地区已经开始大规模推广。阐述了燃气一蒸汽联合循环发电、供热技术、特点等，对主机选型方案提出建议。     

The effects of different mixing intensities during anaerobic digestion of the organic fraction of municipal solid waste

Mixing inside an anaerobic digester is often continuous and is not actively controlled. The selected mixing regime can however affect both gas production and the energy efficiency of the biogas plant. This study aims to evaluate these effects and compare three different mixing regimes, 150 RPM and 25 RPM continuous mixing and minimally intermittent mixing for both digestion of fresh substrate and post-digestion of the organic fraction of municipal solid waste. The results show that a lower mixing intensity leads to a higher biogas production rate and higher total biogas production in both cases. 25 RPM continuous mixing and minimally intermittent mixing resulted in similar biogas production after process stabilization, while 150 RPM continuous mixing resulted in lower production throughout the experiment. The lower gas production at 150 RPM could not be explained by the inhibition of volatile fatty acids. Cumulative biogas production until day 31 was 295 ± 2.9, 317 ± 1.9 and 304 ± 2.8 N ml/g VS added during digestion of fresh feed and 113 ± 1.3, 134 ± 1.1 and 130 ± 2.3 N ml/g VS added during post digestion for the 150 RPM, 25 RPM and minimally mixed intensities respectively. As well as increasing gas production, optimal mixing can improve the energy efficiency of the anaerobic digestion process.     

Trends in Rainfall Exceedances in the Observed Record in Selected Areas of the United States1

Bonnin, Geoffrey M., Kazungu Maitaria, and Michael Yekta, 2011. Trends in Rainfall Exceedances in the Observed Record in Selected Areas of the United States. Journal of the American Water Resources Association (JAWRA) 47(6): 1173–1182. DOI: 10.1111/j.1752‐1688.2011.00603.x Abstract: Semantic differences have led to a gap in the understanding of the impacts of climate change on precipitation frequency estimates. There is popular perception that heavy rainfalls have become more frequent, and that this trend will increase with global warming. Most of the literature examines this question from the point of view of climatology using definitions of “heavy,”“very heavy,” or “extreme” rainfall, which are different from those commonly used by civil engineers. This article identifies the differences in meaning used by the climate and civil engineering communities and examines trends in the observed record in the frequency of exceedances (not trends in magnitudes). Using concepts recognized as the basis for design of the Nation’s civil infrastructure, we look at trends in the number of exceedances of thresholds for a variety of precipitation frequencies and event durations used by civil engineers. We found that the estimated trends in exceedances at one‐day and multiday durations were statistically significant and increasing for the Ohio River Basin and surrounding states but the reverse was true for the Semiarid Southwest (i.e., not significant and decreasing trends). In addition, we found the magnitude of the trends was small for all but the more frequent events and also small with respect to the uncertainty associated with the precipitation frequency estimates themselves.     

压力容器表面裂纹断裂参数的有限元计算与分析

借助ANSYS软件建立了适合压力容器表面裂纹断裂分析的有限元模型,能方便地计算出应力强度因子和J积分,与理论近似表达式的计算值对比,该方法具有较高的精度,能满足工程应用的要求.在验证模型合理的基础上,构造表征表面裂纹形状和尺寸的无量纲因子,通过分析其对J积分弹塑性分量的影响,指出断裂分析中除应力水平外,还应当将裂纹形状...     

2018～2020年北京市大气PM2.5污染特征及改善原因

利用2018～2020年北京市33个环境评价站和5个区域评价站的空气质量数据,以及气象数据和北京市城区PM_2.5组分数据,研究了3年间北京PM_2.5的浓度演变、时空变化和重污染发生情况,并对PM_2.5组分和气象条件变化进行比较分析.结果发现,3年间北京市ρ(PM_2.5)分别为51、42和38μg·m^-3,2020年的PM_2.5相比2017年下降30.9%,但仍超过国际标准8.6%;北京市PM_2.5空间分布依旧维持南高北低的特征,但南北差异逐年减小,区域浓度趋于均一化;1～3月PM_2.5浓度相对较高,8～9月PM_2.5浓度相对较低,采暖季各污染物浓度均显著高于非采暖季,NO_x和CO分别偏高58.4%和52.9%,PM_2.5偏高27.5%;采暖季和非采暖季PM_2.5日变化出现反向特征,采暖季夜间PM_2.5明显...     

Gasification of Inferior Coal with High Ash Content under CO2 and O2/H2O Atmospheres

The gasification reaction of Nantong inferior coal was investigated in a laboratory fixed-bed reactor under CO₂ and O₂/H₂O atmospheres. The effects of the bed temperature and inlet-gas concentration on the yields of CO, H₂, and CH₄ were studied. The effects of coal ash and particle size on the fixed-carbon conversion were also investigated, and kinetic analysis was conducted with a homogeneous model. The product-gas-heating value and fixed-carbon conversion increased when the temperature was increased from 950 °C to 1100 °C under CO₂ atmosphere. When the inlet-CO₂ concentration was increased from 50 to 100 vol.%, the low heating value of the product gas and carbon conversion ratio slightly increased. During the gasification of inferior coal under the O₂/H₂O atmosphere, the CO concentration increased rapidly with increasing temperature. The H₂ and CH₄ concentrations increased initially and then decreased. The maximum gas heating value of 7934 kJ/m³ was obtained under the O₂ concentration of 70 vol.% at a bed temperature of 1050 °C. The cold-gas efficiency increased with increasing temperature and became 40.6% and 86.4% at 1100 °C under the CO₂ and O₂/H₂O atmospheres, respectively. The gasification reaction of the Nantong inferior coal strongly depended on the content of inherent inorganic matter. The gasification rates for both the CO₂ and O₂/H₂O atmospheres were independent of the particle size. The activation energy for the CO₂ and O₂/H₂O gasification reactions were 137 and 81 kJ/mol, respectively. The gasification reactions of the Nantong coal, which was performed under two different atmospheres, were compared and the reaction activity of the gasification reaction under CO₂ atmosphere was found to be much lower than that under the O₂/H₂O atmosphere.