共查询到19条相似文献,搜索用时 703 毫秒
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针对国内某电厂200MW四角切圆锅炉NOx排放量较高,结渣严重的问题,利用CFD软件平台,采用数值模拟方法对其改造前后炉内燃烧过程进行研究。计算结果表明:由于附壁射流的作用,使得高温区集中在炉膛中部,有效地防止了锅炉结渣;改造后炉内有比常规燃烧方式锅炉更大的还原气氛区域,抑制了NOx的产生,使其排放降低34.6%。改造后的计算结果与试验相符的较好,所以此次数值模拟为锅炉设计、改造和运行提供理论依据。 相似文献
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切向燃烧煤粉锅炉燃烧和污染物排放的数值模拟 总被引:9,自引:0,他引:9
借助FLUENT CFD软件平台,对1台20MW切向燃烧锅炉炉内燃烧流动进行了三维数值模拟。计算了炉内流场、温度场、组分场,还对炉内污染物NO排放规律进行了计算。计算结果显示,整个炉膛空间存在旋转流场,直到炉膛出口还有旋转残余。炉内的温度场的最高温度出现在燃烧器区域,各组分浓度场与温度场都有很大关系,NO的生成主要是在燃烧过程中,沿炉膛高度浓度逐渐减小,与炉膛中氧气组分的浓度也有一定的对应关系。计算结果为工业运行、设计和改造提供了参考。图11参1表6 相似文献
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针对某GDI发动机的喷雾、燃烧过程进行了CFD模拟,并对缸内滚流、涡流形成、壁面油膜生成、以及点火、火焰传播等情况进行了评估,系统地展示了缸内燃烧模拟技术在发动机正向设计中的应用。 相似文献
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《International Journal of Hydrogen Energy》2020,45(46):25344-25356
To investigate the thermal and structural characteristics of a flight-scale LH2 tank during ground fillings, a CFD model and a structural analysis model are established to simulated the chill-down process and the induced thermal stress behavior of the tank, respectively. Results show that, at the early stage of filling, a severe temperature gradient appears at the liquid level, leading to a remarkable local concentration of thermal stress, while the maximal thermal deformation is at the outlet region. After the local wall is chilled down sufficiently, the temperature jump at the interface vanishes as well as the local thermal stress, while the maximal thermal deformation is located at the middle height of tank. The thermal stress is most serious at the beginning stage of filling and the maximum appears at the tank bottom. Moreover, the non-uniformity of the temperature distribution and the average thermal stress level within the tank wall both increase with the filling rate. At a filling rate of 7.5 kg·s−1, the maximal thermal stress and thermal deformation of the target tank are more than 70 MPa and 30 mm. 相似文献
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运用分岔理论对连续流动均匀搅拌反应器(CSTR)中甲烷燃烧过程的分岔特性进行了详细分析,采用了甲烷的详细化学反应机理.分别以系统温度、滞留时间为分岔参数,详细讨论了CSTR系统的各种工况(系统压力、混合气过量空气系数、系统温度及滞留时间)对甲烷燃烧过程分岔特性的影响.结果表明,在甲烷的整个燃烧过程中,出现了双着火点,即部分着火点和完全着火点;同时,出现了3个阶段,即部分着火阶段、完全着火阶段和熄火阶段.当以系统温度为分岔参数时,随着系统压力的升高、滞留时间的延长、过量空气系数的增加,甲烷的完全着火温度也随之降低.当以滞留时间为分岔参数时,随着系统温度、系统压力的升高,甲烷发生完全着火所需要的滞留时间随之缩短;过量空气系数对甲烷发生着火所需要的滞留时间影响较小. 相似文献
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《International Journal of Hydrogen Energy》2023,48(23):8716-8730
The underlying physical mechanisms leading to the generation of blast waves after liquid hydrogen (LH2) storage tank rupture in a fire are not yet fully understood. This makes it difficult to develop predictive models and validate them against a very limited number of experiments. This study aims at the development of a CFD model able to predict maximum pressure in the blast wave after the LH2 storage tank rupture in a fire. The performed critical review of previous works and the thorough numerical analysis of BMW experiments (LH2 storage pressure in the range 2.0–11.3 bar abs) allowed us to conclude that the maximum pressure in the blast wave is generated by gaseous phase starting shock enhanced by combustion reaction of hydrogen at the contact surface with heated by the shock air. The boiling liquid expanding vapour explosion (BLEVE) pressure peak follows the gaseous phase blast and is smaller in amplitude. The CFD model validated recently against high-pressure hydrogen storage tank rupture in fire experiments is essentially updated in this study to account for cryogenic conditions of LH2 storage. The simulation results provided insight into the blast wave and combustion dynamics, demonstrating that combustion at the contact surface contributes significantly to the generated blast wave, increasing the overpressure at 3 m from the tank up to 5 times. The developed CFD model can be used as a contemporary tool for hydrogen safety engineering, e.g. for assessment of hazard distances from LH2 storage. 相似文献
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《International Journal of Hydrogen Energy》2020,45(4):3340-3371
Understanding local transport behaviour of steam-air-hydrogen mixture inside the containment and associated hydrogen combustion issues are essential to ensure integrity of the nuclear reactor containment in the event of a severe accident. During a severe accident, various mechanisms occurring inside and outside of reactor pressure vessel may lead to generation of steam, and subsequently hydrogen, which eventually gets released in the containment space. Hydrogen may deflagrate in the presence of an ignition source/hot spot depending on local mixture composition of steam-air-hydrogen; this may further lead to flame acceleration, deflagration to detonation transition, and finally to detonation depending upon local conditions and geometric factors, further increasing the internal pressure and temperature of the containment. The fraction of non-condensable gases may also rise due to simultaneous on-going steam condensation, which not only elevates the possibility of hydrogen combustion, but also in turn, affects the eventual local and average steam condensation rates. In this background, this paper reviews the coupled issues between steam condensation, hydrogen transport, hydrogen combustion criteria, location of its sources, and stratification inside reactor containment under plausible severe accident scenarios. Several experiments in the context of containment thermal-hydraulics and hydrogen combustion are elaborated. Looking into the complexity of the problem, necessity to adopt simulation approach is highlighted. Two types of codes, i.e., lumped-parameter (LP) and computational fluid dynamic (CFD), are scrutinized based on their specific applications and limitations. It is inferred that the containment thermal-hydraulics and ensuing safety strategies must address the issue of steam condensation and hydrogen management simultaneously, through a comprehensive and integrated approach. 相似文献
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800MW旋流对冲燃烧锅炉低NOx改造的数值模拟 总被引:1,自引:1,他引:0
针对某800MW超临界锅炉NOx排放量较高的问题,设计了配风方式不同的3种工况.利用CFD软件,对3种工况进行了炉内燃烧、传热及污染物排放等方面的数值计算,并分析了炉内的温度、NOx及cO组分的分布情况.结果表明:计算结果与实测数据吻合较好,空气分级燃烧使主燃区温度降低,CO体积分数升高,N0x质量浓度明显降低;燃尽风对燃料的燃尽率和炉膛出口烟温产生了不利影响,从而影响机组的经济性和安全性.通过对各个工况燃料的燃尽率及炉膛出口烟温进行综合比较分析,得出工况3为较理想的改造方案. 相似文献
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Numerical study on the autothermal reforming of n‐hexadecane, which can be used in proton exchange membrane fuel cell for automotive applications, in microchannels is necessary. A 2D computational fluid dynamics (CFD) model, with combustion and reforming channels thermally coupled and separated by a metal medium wall, is developed and studied in terms of hydrogen production and catalyst activity. Rh supported on CeO2 is used as a catalyst and applied to the inner surface of the channels, where the catalytic endothermic and exothermic reactions occur. CFD analysis shows considerable results in terms of reactor performance. Along the reactor channel length, the mole percentage of hydrogen is 86% after over 2 hours of catalyst activity. The corresponding fuel conversion in respective channels is 85% on the catalytic surface of the reactor. The predicted hydrogen production from the CFD model is 59% higher than that as equilibrium conditions. Heat conduction through the medium solid wall depends on the thermal conductivity of a material. In this model, a metal solid wall with thermal conductivity of 40 W/m K, which transfers heat from the combustion channel within milliseconds, is used. The calculated model operating temperature in the reforming channel ranges from 660 to 850 K. 相似文献
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Shahin Hosseini Periasamy Vijay Khaliq Ahmed Moses O. Tadé Vishnu Pareek Ranjeet Utikar 《国际能源研究杂志》2017,41(11):1563-1578
A dynamic tank in series reactor model of a direct internally reforming solid oxide fuel cell is presented and validated using experimental data as well as a computational fluid dynamics (CFD) model for the spatial profiles. The effect of the flow distribution pattern at the inlet manifold on the cell performance is studied with this model. The tank in series reactor model provides a reasonable understanding of the spatio‐temporal distribution of the key parameters at a much lesser computational cost when compared to CFD methods. The predicted V–I curves agree well with the experimental data at different inlet flows and temperatures, with a difference of less than ±1.5%. In addition, comparison of the steady‐state results with two‐dimensional contours from a CFD model demonstrates the success of the adopted approach of adjusting the flow distribution pattern at the inlet boundaries of different continuous stirred tank reactor compartments. The spatial variation of the temperature of the PEN structure is captured along with the distributions of the current density and the anode activation over‐potential that strongly related to the temperature as well as the species molar fractions. It is found that, under the influence of the flow distribution pattern and reaction rates, the dynamic responses to step changes in voltage (from 0.819 to 0.84 V), fuel flow (15%) and temperature changes (30 °C), on anode side and on cathode side, highly depend on the spatial locations in the cell. In general, the inlet points attain steady state rapidly compared to other regions. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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燃尽风喷口位置对NOx排放的影响 总被引:2,自引:2,他引:0
针对一台采用旋流式燃烧器的煤粉炉NOx排放质量浓度较高的问题,采用空气分级燃烧方式以降低NOx排放量,基于CFD软件平台,在额定负荷下,分别对3种不同燃尽风喷口位置的改造方案进行了炉内燃烧及污染物生成的数值模拟,并通过综合比较炉内各参数的变化确定了最佳燃尽风喷口位置.结果表明:燃尽风喷口位置的上移降低了主燃区氧气的体积分数,同时使炉膛内的最高温度降低了23~29K.燃尽风喷口位置对NO,的还原效果、出口烟气温度以及煤粉焦炭转化率的影响较大.当燃尽风喷口位置升高时,NOx质量浓度降低,炉膛出口烟气温度升高,煤粉焦炭转化率下降.经综合比较炉膛出口烟气温度、NOx质量浓度以及煤粉焦炭转化率得出,距最上层燃烧器7.7m处为最佳燃尽风喷口位置. 相似文献