Gas chromatographic analysis of calibration gas mixtures

Gas mixtures of accurately known composition are essential for the calibration of air quality monitors. In order to obtain large enough quantities for use in the field, these mixtures are usually purchased commercially, analyzed or unanalyzed. In either case, confirmation of the stated analysis of the mixture prior to its use is necessary, especially where instability may be suspected. This paper describes how analysis by gas-solid chromatography can be used to establish or verify the composition of a variety of mixed gases. Using chromatographic packings derived from carbon, rapid and reliable measurement of oxygen, nitrogen, carbon dioxide, methane and carbon monoxide in a mixture is possible. Mixtures of sulfur-containing gases can also be calibrated. The value of this type of analysis to an air pollution monitoring network is discussed. Automobile exhaust gases can be analyzed in a similar manner.     

Toxicity of binary mixtures of organic chemicals to microorganisms

Inhibition of microorganisms by single and binary mixtures of organic chemicals was experimentally determined using the respirometric technique. Single chemical dose-response relationships in these assays most closely fit the Probit versus the Weibit and Logit transformations. A QSAR-based approach was developed to predict the joint effects in the binary mixtures. The validity of the proposed approach was demonstrated by comparing the predicted values against the experimentally determined values. Good agreement between the two was found with a coefficient of determination, r² = 0.892.     

The accuracy of compressed gas mixtures

A large number of compressed gas mixtures in the parts per million range have been analyzed to establish their accuracy. Cylinders were obtained from commercial suppliers and included mixtures of nitric oxide, carbon monoxide and methane. The mixtures were analyzed with air-monitoring instruments which were calibrated with standard mixtures prepared volumetrically in-house. The method of preparing the standards was verified by comparison with primary standards obtained elsewhere. The accuracy of the volumetric method was estimated to be ±2% of the component and the precision of mixing ±1% of the component.It was concluded that commercial mixtures of carbon monoxide and methane are usually reliable but that this is not the case for nitric oxide mixtures. The method of preparing standard cylinders in the laboratory was found to provide an alternative to commercial cylinders. Thirty-litre quantities of gas at 200 psig can be prepared for immediate use, thus assuring accuracy and eliminating possible stability problems encountered with long storage periods.     

Interactions in binary halon mixtures used as fire suppressants

Tests were conducted using different ratios of the Halons 1301 and 1211 to determine their effectiveness in extinquishing fires when used in combination. The author discusses the test method and the test results. Note: This work was supported by E. I. du Pont de Nemours and Company, Wilmington, Delaware. The testing was conducted by the author while employed at the Factory Mutual Research Corp., Norwood, Massachusetts.     

Laboratory characterization and modelling of the thermal-mechanical properties of binary soil mixtures

Binary soil mixtures are extensively used in the construction of geothermal-related earth structures such as geothermal energy piles (GEP), ground source heat pumps (GSHP) and earth air tunnel heat exchangers (EATHE). An evaluation of the binary soil’s thermal-mechanical properties is the key process in determining the final performance of geothermal-related projects. Therefore, the thermal-mechanical properties of binary soil mixtures were systematically investigated in this paper. A series of thermal and mechanical property tests was conducted on five sand-kaolin clay mixtures with sand contents ranging from 0% to 100% by dry weight. The experimental results indicated that the sand-clay mixtures achieved the theoretically densest state when the sand content reached the critical threshold. The further the binary mixture’s sand content was from the critical threshold, the lower the mixture’s density was. As the sand content increased, the shear stress-strain curves gradually shifted from strain-softening behavior to strain-hardening behavior due to the decrease in suction stress. The relationship between the sand content and the shear strength of the mixtures exhibited an “S” shape, which is attributed to the interaction between the sand and clay particles and varied with the sand contents. The shear wave velocity of the sand clay mixtures was found to decrease continuously with the increase in sand content until the sand skeleton had formed. In addition, the thermal conductivity of the binary mixed soil changed linearly with the sand content, and the upper bound of the critical threshold interval (77%) was found to separate the two different heat conduction modes. Finally, an elastic shear modulus (G₀) model, which correlated to the tangent elastic modulus of the binary mixture (E_m), and a more generalized thermal conductivity (K) model were formulated for the binary sand-clay mixtures, and the effectiveness and feasibility of the proposed models were validated by comparing the values predicted with the model and the experimental data.     

沥青混合料质量分析及控制

分析了沥青混合料的力学强度、耐久性、抗滑性、和易性等对路面的影响 ,并指出了改进措施。特别对影响沥青混合料质量的重要因素油石比的控制进行了阐述 ,使沥青混合料路面质量得到了有效控制     

易燃液体二元混合物闪点、自燃点实验研究

利用自动低温闭口闪点测定仪、自动引燃温度测定仪对醇、酮、醚、酯等不同情况下组成的二元混合液体的闪点、自燃点变化规律进行了实验研究,采用Taylor多项式,拟合出了常压下二元混合液体闪点、自燃点随组分配比变化的经验计算公式,并通过实验数据对其进行了验证.     

Deformation and water/gas flow properties of claystone/bentonite mixtures

As a potential engineered barrier material for disposal of radioactive waste in clay formations,claystone aggregate excavated from the Opalinus clay(OPA),its mixture with bentonite MX80 in a mass ratio of 7/3,and pure bentonite were extensively investigated with respect to the hydro-mechanical properties and performances.With these materials,a series of parallel experiments was performed under sequentially applied conditions of hydration with synthetic porewater of the clay formation,consolidation and water flow under increased stresses,and gas injection into the water-saturated and compacted materials under loading.Significant responses of the clay mixtures were observed.Main findings include:(1) the hydration and induced swelling of the mixtures are mainly dominated by bentonite content and dry density;(2) the consolidation decreases the porosity and water permeability exponentially by 2-3 orders of magnitude to low values of 10~(-18)-10~(-20) m~2 at stresses of 2-5 MPa,depending upon bentonite content;and(3) the gas penetration in the water-saturated and compacted bentonite is characterised by a cyclic pressure rising/dropping process limited in between the upper breakthrough and lower shut-off boundaries,whereas the compacted claystone and claystone/bentonite mixture allow for gas release at low and moderate pressures.The results are helpful for design of the engineered barriers for safe isolation of radioactive waste in repositories.     

Experimental research on water retention and gas permeability of compacted bentonite/sand mixtures

Highly compacted bentonite-based materials are often considered as buffer or sealing materials for deep high-level radioactive waste repositories. In situ, the initial state of bentonite-based materials is only partially saturated, which has a very high suction that will promote water absorption from the host rock. In addition, a gradient of water saturation will be formed between the external part and the central part of the compacted bentonite blocks. In this paper, water retention tests, under both constant-volume and free-swelling conditions, were performed to investigate the suction behavior of a compacted bentonite/sand mixture. In order to investigate the sealing ability of the partially saturated bentonite/sand mixture, gas permeability tests were also carried out under the in situ confining stress. It was found that the confining conditions have a limited effect on the water retention capacity of the compacted bentonite/sand mixture at lower levels of relative humidity (RH), while this influence is significant at higher RH levels. The results of gas permeability tests show that gas permeability is very sensitive to the water content and the confining pressure. When the sample (stable at RH=98%) was subjected to a in situ confining pressure (7–8 MPa), the gas permeability was very low (1.83×10^–14 m/s) which indicates that gas tightness can be obtained even though the sample is not fully saturated.     

燃气热泵的应用与分析

介绍了以天然气为能源的燃气热泵系统,以某示范工程为例,分析了其初投资和运行费用,并与电空调系统、电空调＋锅炉系统、直燃机系统相比较,认为燃气热泵系统的一次能源利用率高,供暖性能好,调控容易,运行维护费用低,符合节能环保要求。     

回燃现象与气体爆炸的相似性分析

利用火灾理论分析回燃与轰燃两种特殊现象的产生过程,区分两种现象的差异,明确回燃现象的特性,阐述了气体爆炸的分类、定义及特点,并与回燃现象进行了对比分析,最后,通过燃烧热和气体流动特性两方面研究讨论能够产生回燃现象的最低可燃气体组分高于其气体爆炸极限的原因,同时提出了一些减少回燃现象危害的建议。     

吸附瓦斯含量对煤与瓦斯突出的影响与能量分析

煤层中高压瓦斯主要以吸附态为主,为了研究吸附瓦斯含量对煤与瓦斯突出的影响,利用吸附性依次增强的氦气、氮气、甲烷和二氧化碳模拟相同气压下吸附瓦斯含量的不同。将0.75 MPa的上述4种气体充入物理力学性质相同的型煤并充分吸附,模拟游离瓦斯含量相同、吸附瓦斯含量不同的煤体,考虑4种不同强度型煤开展16次瞬间揭露试验。试验发生9次持续时间1 s左右的突出现象,对于低强度型煤试验不吸附的氦气也发生突出现象;试验结果表明随吸附气体含量增加,型煤发生突出的风险增大,吸附气体含量越大其突出强度越大。提出吸附气体膨胀能的测定方法,根据突出能量公式计算发生突出的煤体弹性能、吸附及游离气体膨胀能等突出潜能和煤体破碎功、抛出功等突出耗能,突出潜能与突出耗能基本相等验证吸附气体膨胀能测定方法的合理性。能量分析表明参与突出过程的吸附气体膨胀能占总气体膨胀能的7.9%~32.3%,占突出潜能的6.5%~25.6%,且其占比随吸附气体含量增大而增大。研究成果为揭示、量化吸附瓦斯含量在突出中的作用提供参考和依据。     

Kinetics and mechanisms of UV-photodegradation of chlorinated organics in the gas phase

Over the last two decades, the application of photodegradation for the destruction of a wide spectrum of organic compounds in air has gained considerable interest in abating environmental pollution. This paper presents the results of a fundamental study conducted to evaluate the gas phase oxidation kinetics of volatile organic compounds (VOCs) with respect to different parameters pertinent to the operating conditions of air stripping and soil vapor extraction processes. Photodegradations of three chlorinated VOCs: chloroform, carbon tetrachloride (CTC) and trichloroethylene (TCE), were investigated in a semi-batch reactor using a low-pressure mercury UV lamp. The effects of different experimental parameters, such as the initial concentrations of the VOCs, the reaction medium, relative humidity, light intensity, temperature and the effect of mixture that may influence the kinetics of the gas phase photodegradation were evaluated. Mechanisms of photodegradation as supported by the experimental data are also proposed.     

沸石对气体混合物吸附分离性能的分子模拟研究

采用分子模拟的方法研究了21种具有不同拓扑结构的沸石对二氧化碳/甲烷、二氧化碳/氮气两个混合体系的分离能力。通过研究这些沸石结构和性质得到沸石吸附选择性与材料结构参数之间的关联关系。结果表明:对于所研究的两个混合体系,沸石均优先吸附二氧化碳,即二氧化碳的吸附量远大于甲烷和氮气的吸附量。为了定量描述沸石结构-性质之间的关系,尝试将沸石的吸附选择性与材料常用的结构参数(如两个气体组分无限稀释状态下的吸附热差、孔体积、孔率和比表面积)进行关联,发现沸石材料的选择性与常用的单一的材料结构参数没有好的关联,但沸石的吸附选择性与吸附度关联较好。该结果可应用到沸石的分离以及沸石材料预筛选的评价中。     

桥梁结构检测与加固处理

随着桥梁崩塌事故的增多,针对桥梁的结构进行科学的检测与及时的加固处理已经成了绝大多数劣质桥梁不出现坍塌事故的唯一解决之道。此外,年久失修的桥梁也必须进行适时的结构检测与加固处理。     

DDS应用的频率规划及相位抖动分析

介绍了DDS原理,以及DDS应用的频率规划的意义和主要内容。并以相位抖动为出发点,详细分析了其相位误差。运用傅里叶级数,研究DDS在有相位抖动时,D/A输出端的频谱特征,给出DDS输出频谱杂散散布顺序。     

天然气加气站的消防安全分析

对山西太原加气站的基本情况进行了简要介绍,阐述了天然气加气站的分类及工艺流程,并通过对天然气加气站火灾危险性的分析,研究了加气站应采取的消防安全措施,以确保天然气加气站的安全运营。     

燃气燃烧过程效率的热力学分析

概述了天然气燃烧利用的过程,介绍了不同燃烧过程热效率和有用能效率的计算结果,并就天然气燃烧利用过程的效率问题进行了探讨。