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71.
Transient computations with full hydrogen chemistry were performed to reveal the flame structure and extinguishment process of co-flow, hydrogen diffusion flame suppressed by water vapor. As the concentration of water vapor was increased, the flame detached away from the burner brim and formed an edge flame at the flame base. Water vapor showed larger chemical inhibition effect than nitrogen when extinguishing hydrogen flame, which was attributed to its enhanced third body effect in the reaction H + O2 + M = HO2 + M. The minimum extinguishing concentration (MEC) of water vapor and nitrogen was predicted by Senecal formula and perfectly stirred reactor (PSR) model respectively. The MECs predicted by PSR model agree with the MECs calculated by Fluent, which shows that 1) the flame extinction is controlled by the flame base, and 2) radiation absorption is negligible. The measured MECs are in a reasonable agreement with the values calculated by Fluent, which demonstrates the accuracy of the CFD model. A simple model was used to investigate the relative importance of extinguishing mechanisms of water vapor. The results show that in a co-flow configuration the thermal cooling and chemical inhibition effect are the main extinguishing mechanisms in suppressing hydrogen diffusion cup burner flame. 相似文献
72.
Conveyor belt fires in an underground mine pose a serious life threat to miners. Water sprinkler systems are usually used to extinguish underground conveyor belt fires, but because of the complex interaction between conveyor belt fires and mine ventilation airflow, more effective engineering designs are needed for the installation of water sprinkler systems. A computational fluid dynamics (CFD) model was developed to simulate the interaction between the ventilation airflow, the belt flame spread, and the water spray system in a mine entry. The CFD model was calibrated using test results from a large-scale conveyor belt fire suppression experiment. Simulations were conducted using the calibrated CFD model to investigate the effects of sprinkler location, water flow rate, and sprinkler activation temperature on the suppression of conveyor belt fires. The sprinkler location and the activation temperature were found to have a major effect on the suppression of the belt fire, while the water flow rate had a minor effect. 相似文献
73.
A study of explosions in several elongated cylindrical vessels with length to diameter L/D = 2.4–20.7 and ignition at vessel's bottom is reported. Ethylene–air mixtures with variable concentration between 3.0 and 10.0 vol% and pressures between 0.30 and 1.80 bara were experimentally investigated at ambient initial temperature. For the whole range of ethylene concentration, several characteristic stages of flame propagation were observed. The height and rate of pressure rise in these stages were found to depend on ethylene concentration, on volume and asymmetry ratio L/D of each vessel. High rates of pressure rise were found in the early stage; in later stages lower rates of pressure rise were observed due to the increase of heat losses. The peak explosion pressures and the maximum rates of pressure rise differ strongly from those measured in centrally ignited explosions, in all examined vessels. In elongated vessels, smooth p(t) records have been obtained for the explosions of lean C2H4–air mixtures. In stoichiometric and rich mixtures, pressure oscillations appear even at initial pressures below ambient, resulting in significant overpressures as compared to compact vessels. In the stoichiometric mixture, the frequency of the oscillations was close to the fundamental characteristic frequency of the tube. 相似文献
74.
评述了提高火焰原子吸收灵敏度的各种途径 ,诸如包括MIBK -萃取 ,离子交换和沉淀在内的富集分离法 ,在线流动注射法 ,原子捕集法以及间接测定法等技术。 相似文献
75.
试验了用非全量消解—悬浮液直接进样火焰原子吸收光谱法测定煤灰中的铜和铅,结果表明:铜和铅的方法检出限(3σ)分别为0.038mg/L和0.23mg/L,测定吸光度与其浓度的线性范围均为0.5mg/L—5.0mg/L,样品加标回收率在87%—97%之间,相对标准差(n=4)小于7%。 相似文献
76.
77.
Soylak M Divrikli U Saracoglu S Elci L 《Environmental monitoring and assessment》2007,127(1-3):169-176
Cellulose nitrate membrane filter was used for the preconcentration-separation of Cu, Co, Cd, Pb and Cr ions. The analyte
ions were collected on the membrane filter by the aid of carmine. Then membrane filter was dissolved by using nitric acid.
The levels of the analytes in the final solutions were determined by flame atomic absorption spectrometry (FAAS). The analytical
parameters including pH, amounts of carmine, sample volumes etc. have been optimized. No influences have been observed from
the matrix ions. The detection limits for analytes were in the range of 0.08 μg/l-0.93 μg/l. The validation of the procedure
was checked by the analysis of standard reference sediment (GBW 07309). The present method has been successfully applied for
the FAAS determinations of analyte ions in real samples including black tea and magnesium salts. 相似文献
78.
A solid phase extraction method for the determination of gold(III) at trace levels by flame atomic absorption spectrometer
(FAAS) was developed. The method was based on retention of gold as chloro complexes through the Amberlite XAD-2000. The effect
of some analytical parameters including hydrochloric acid concentration, sample volume, sample and eluent flow rates, eluent
volume, eluent concentration and interfering ions on the recovery of gold(III) was investigated. The retention of gold(III)
from 1.5 mol l−1 HCl solution and the recovery of gold with 0.07 mol l−1 NH3 solution were quantitative (≥95%). The relative standard deviation (RSD) was calculated as 3.2% (n = 10). The detection limit for gold was 2 μg l−1. The accuracy was checked with the determination of gold spiked an artificial seawater and a pure copper samples. 相似文献
79.
80.
A methodology for the computationally efficient CFD simulation of hydrogen-air explosions (including transition to detonation) in large volumes is presented. The model is validated by means of the largest ever conducted indoor DDT experiments in the RUT facility. A combination of models is proposed with a particular focus on the influence of flame-instabilities, especially of thermal-diffusive nature, which are crucial for very lean mixtures. Excellent agreement is achieved in terms of flame acceleration. The quality of DDT predictions itself depends on the underlying mechanism. Whereas DDT by shock-focusing is successfully simulated on under-resolved meshes, DDT by local explosions in the vicinity of the turbulent flame brush remains a challenge. Adaptive mesh refinement therefore emerges as a key technique to resolve more of the essential phenomena at reasonable computational costs affordable by industry. Finally, a generic case demonstrates the influence of mixture inhomogeneity, which can promote flame acceleration and ultimately DDT. 相似文献