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排序方式: 共有622条查询结果,搜索用时 15 毫秒
91.
The safety of hydrogen generation process is a major concern. This paper discusses the quantitative analyzes of the risk imposed on neighborhood from the operation of a hydrogen generator using natural gas reforming process. For this purpose, after hazard identification, the frequency of scenarios was estimated using generic data. Quantitative risk assessment was applied for consequence modeling and risk estimation. The results revealed that, jet fire caused by a full bore rupture in Desulphurization reactor has the highest fatality (26person) and affects the largest area of 5102 m2. The lethality radius, maximum radiation and safe distance of this incident were 140 m, 370 kW/m2 and 225 m respectively. A full bore rupture in Reformer can lead to the most dangerous flash fire. In this incident the concentration of released material in LFL zone (area of 1483.17 m2) and ½ LEL zone (area of 1970.74 m2) were 61,125 ppm and 40,000 ppm respectively. QRA is a credible method to assess the risks of hydrogen generation process. 相似文献
92.
Hassan Jafari Mohd Hasbullah Idris Ali Ourdjini Majid Karimian Gholamhassan Payganeh 《钢铁研究学报(英文版)》2010,17(12):38-38
In this study, the effect of gating systems, mould coating and sand grain size on metallurgical and mechanical properties of TWDI casting were investigated. Two different gating systems; stepped and tapered runners, were used to cast strip samples. The thicknesses of the samples cast were 2.3, 3.3, 4.5, 5.4, 6.5, 7.5 and 8.5 mm. The samples were cast in CO2/silicate process moulds of two different sand grain sizes of 151 and 171 according to the AFS standard. To assess the effect of mould coat on the properties of TWDI, half of the moulds were coated with graphite-based zircon whilst the rest were left uncoated. The carbon equivalent (CE) of the molten metal prepared was 4.29% and poured at the temperatures of 1450°C. The microstructure of the cast specimens was analyzed by optical and scanning electron microscopes. Clemex Image Analyzer (CIA) was used to evaluate graphite nodule count, graphite nodules area fraction, roundness and diameter of the nodules of the TWDI cast samples. Brinell hardness and tensile tests were also conducted on all the samples. The results show that by using stepped runner gating system with uncoated and coarse sand grain size mould, roundness and graphite nodule counts decrease. However, graphite nodules diameter and area fraction increase. The results also show that finer sand grain size and coated mould produce longer distance of molten metal travel. 相似文献
93.
Aside from their zero fuel costs, the pumped-storage units can reduce emissions of thermal generating units. The objective of this study is to investigate (a) thermal unit commitment with considerations for environmental constraints (ECUC), and (b) pumped-storage and thermal unit commitment with considerations for environmental constraints (PSECUC) based on a new optimization methodology. The PSECUC determines the start-up and shut-down schedules of pumped-storage and thermal generating units that meet the required demand so that the costs for fuel, start-up, and emissions (TC) are minimized. For the ECUC (thermal generating units only), the results show improvements of 0.03 and 0.50% in TC and excess emissions (EXEM), respectively. For the PSECUC, it is determined that 2-pumped-storage units can simultaneously decrease the TC and EXEM by 1.20 and 60%, respectively. 相似文献
94.
Ultraviolet radiation which exists in environment around can be regarded as a major source of textile materials. In this study, the effect of UV exposure on the cut-pile carpet was investigated. A UV chamber was used to expose different levels of accelerated UV radiation on the samples of the machine-woven pile carpet. Wear test were then carried out on all samples using a Hexapod tumbler machine. The short-term static loading was applied to the carpets and the thickness loss percent (TL) and recovery percent (RP) of the samples at different times after load removal was measured using standard methods. Factorial experimental design and response surface method were applied for to create polynomial regression models and predict each of the thickness loss and recovery percent of carpet samples. The model is capable to determine the contribution of different variables. The results of the modeling revealed a desirable fit. The adjusted R2 values were also high and significant. The ANOVA test indicated that the presented models were valid at 5% significant level. 相似文献
95.
Sahar Jafari 《纺织学会志》2017,108(11):1905-1909
Different combinations of spring and dashpot systems are usually considered to model the mechanical behavior of textile materials. In this work, Jeffery’s mechanical model, which is a combination of spring and dashpot components, was used to model the recovery behavior of the pile carpet after static loading. The carpet samples were exposed to different levels of UV radiation. The short-term static loading was applied to the samples. The recovery response or thickness vs. time was then measured. By analyzing this model and using the best curve fitting based on the least square method, the viscoelastic parameters in each UV exposure time were calculated. Four attributes of compression were then studied. The results showed that the thickness loss and the maximum compression under a constant load were mainly dominated by the deterioration of the dashpot elements (Plastic part of deformation). The thickness loss and the maximum compression were both higher at longer UV exposure times. The thickness loss showed a good linear correlation with the inverse of the first dashpot constant, 1/η1. In contrast, the speed of recovery and the potential stored energy were mainly dominated by the parameters of the Voigt–Kelvin body, i.e. the elastic part of the compression. 相似文献
96.
Taraneh Jafari Behbahani Shokoufe Tayyebi 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2016,38(14):2135-2139
Asphaltene is the fraction of crude oil which is soluble in toluene but insoluble in light hydrocarbon solvents such as pentane or heptanes. In this work, a new approach has been proposed to account critical properties of asphaltene, and the proposed approach was verified using experimental data reported in the literature. The results show that the proposed approach correlates more accurately the critical properties of asphaltene data and is in agreement with data reported in the literature with an average absolute deviation of 6.7%. Therefore, the correlations obtained from this proposed approach resulted in a good agreement with data which show a significant improvement in comparison with the previous models in the available literature. 相似文献
97.
Ebrahim Jahanshahi Javaran Mohammad Rahnama Saeed Jafari 《Advanced Powder Technology》2013,24(6):1109-1118
Using walls to introduce shear into a domain causes wall effects in the calculation of rheological properties of suspensions. Employing Lees–Edwards boundary conditions as an alternative method, removes these effects. Earlier methods of solid–fluid interactions in the framework of lattice Boltzmann method, such as Ladd and ALD methods, violate conservation law of the translational and rotational momentum (Galilean invariance). In the present study, Lees–Edwards boundary condition has been combined with smoothed profile method (SPM) intending to eliminate Galilean invariance errors. The combined method is validated by allowing a particle to cross a Lees–Edwards boundary. Moreover, third-order interpolation is used for particle distribution functions leaving the domain in the velocity gradient direction to eliminate bumps in the angular velocity of the particle when crossing the Lees–Edwards boundary. As another test case, two interacting circular cylinders placed in a sheared domain using Lees–Edwards boundary condition. Comparing results with the ones presented in the literature shows good agreement. 相似文献
98.
Hamid Tajizadegan Majid Jafari Mehdi Rashidzadeh Reza Ebrahimi-Kahrizsangi Omid Torabi 《材料科学技术学报》2013,29(10):915-918
ZnO nanosheets and nanoflakes were grown on alumina particles in the absence of surfactants via heterogeneous precipitation using urea, zinc acetate and bayerite as precursors. Thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used and the results indicated the formation of only two phases: wurtzite-type ZnO and γ-Al2O3. ZnO nanoflakes were grown on alumina particles in the samples with ZnO content of 40 and 60 wt%, By increasing the ZnO content to 80 wt%, a porous hierarchical structure of ZnO with nanosheet arrays appeared. Both of these nanoflakes and nanosheets were about 40-80 nm in thickness and about 1-2 μm in diameter. It was proposed that Zns(CO3)2(OH)6 nuclei undergo higher growth rates in thin sheets at edges of bayerite particles with a higher surface energy. The Brunauer-Emmett-Teller (BET) measurements proved a reachable high surface area for hierarchical structures of ZnO nanosheets, which could mainly be attributed to their unique growth on alumina particles. Also, UV absorption results revealed that ZnO--Al2O3 compositions still show the UV characteristic absorption of ZnO, which can evidence the presence of photocatalytic properties in ZnO-Al2O3 compositions. 相似文献
99.
Karkhaneh M Naghavi M Rowe BH Hagel BE Jafari N Saunders LD 《Accident; analysis and prevention》2008,40(1):192-199
Bicyclists are vulnerable road users for severe injury all over the world. The nature and extent of such injuries are less well known in Iran. Using data from a comprehensive survey conducted by the Ministry of Health and Medical Education in 13 health divisions of Iran, in 2003, we examined circumstances around bicyclist injury and death. Trained health workers completed the survey instruments by interviewing patients who stayed more than 24h in hospitals and/or relatives, hospital personnel and by reviewing patient charts. Data were cross-matched with medico-legal documents to prevent missing deaths. The information that was collected from 64 cities/towns' emergency departments (EDs), over the study period, showed that 440 injured cyclists were hospitalized and/or died due to traffic collisions. Most injuries occurred in males (94.8%) and in the young (median age: 14 years with 75% =18 years). Head injury occurred in 14% of all hospitalized and in 90% of fatally injured bicyclists. Striking a moving vehicle increased the odds of death (OR: 32.3; 95% CI 3.5-291.0) as well as the odds of severe injury (OR: 1.9; 95% CI 1.2-3.2) compared with other mechanisms of injury. As a conclusion, bicyclists in Iran, particularly males and young children, are vulnerable to severe injury and death when struck by moving vehicles on highways. 相似文献
100.
M. A. Boorboor Ajdari S. Jalili M. Jafari J. Zamani M. Shariyat 《Journal of Mechanical Science and Technology》2012,26(9):2783-2791
The objective of this research is determining the buckling load of composite truncated conical shells under external loading by theoretical and numerical methods. The boundary conditions are assumed to be clamped. At first, basic equations and stability relations of conical shells were derived. The analysis is carried out using Donnel-type stability equations for thin cross-ply conical shells. By applying Galerkin??s method, these equations are converted to a system of ordinary time dependent differential equations. Ritz method is employed for finding the dynamic stability load. Finally, the critical static and dynamic buckling loads and the corresponding wave numbers have been found analytically. Then comparison of results is considered. Results of analytical calculations are compared with numerical results and with other researchers?? analytical results. The effects of geometric parameters, the cone semi-vertex angle, number of layers and material of fibers on buckling loads are discussed. 相似文献