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柱状晶向等轴晶转变(CET)是在一定的凝固过程中必须控制的一种显微组织转变.本文针对铝合金连铸坯凝固过程中柱状晶向等轴晶的转变,综合运用了正交试验研究、数值模拟计算、数学拟合等方法,分析了连铸过程主要工艺因素拉坯速度、一冷水量、二冷水量和浇注温度对连铸坯凝固过程中柱状晶向等轴晶转变位置的影响,提出了柱状晶向等轴晶转变的转变位置判据,即当连铸坯某一位置处的固相率等于0.3时,温度梯度G与冷却速度R满足函数关系G0.8072/R=0.469时,在该位置处将发生柱状晶向等轴晶的转变. 相似文献
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In this paper, the effect of the wall roughness on the water behavior related to the PEMFCs gas channel is investigated by the two-phase flow simulation. And, the different wetting conditions of the wall surface are considered, i.e. hydrophilic surface and hydrophobic surface. The relative roughness height and the roughness element density as well as the roughness element type are also considered in the study. And the results show: (1) for hydrophilic surface, water behavior for smooth case is different from the roughness cases, due to the effect of roughness on the water slug morphology even for r/H = 0.2% roughness. (2) r/H = 0.2% is positive for water removal and will not lead to the high pressure drop for hydrophilic surface, (3) r/H = 5% is advantageous for water removal for hydrophilic surface but disadvantageous for hydrophobic case, and the pressure drop greatly increases for both cases, (4) for hydrophobic surface, roughness of r/H = 1% and r/H = 2% slow down the water removal speed, but will not affect the amount of the removable water, (5) there is nearly no effect for r/H = 0.2% for hydrophobic case, (6) for both conditions, the average pressure drop obviously increases when r/H ≥ 2%. (7) Increase of the roughness element can help water removal for hydrophilic case but no obvious function for hydrophobic surface. (8) The triangle roughness element is better than rectangle element with the same height. 相似文献
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An energy analysis of three typical solid oxide fuel cell (SOFC) power systems fed by methane is carried out with detailed thermodynamic model. Simple SOFC system, hybrid SOFC‐gas turbine (GT) power system, and SOFC‐GT‐steam turbine (ST) power system are compared. The influences of air ratio and operative pressure on the performance of SOFC power systems are investigated. The net system electric efficiency and cogeneration efficiency of these power systems are given by the calculation model. The results show that internal reforming SOFC power system can achieve an electrical efficiency of more than 49% and a system cogeneration efficiency including waste heat recovery of 77%. For SOFC‐GT system, the electrical efficiency and cogeneration efficiency are 61% and 80%, respectively. Although SOFC‐GT‐ST system is more complicated and has high investment costs, the electrical efficiency of it is close to that of SOFC‐GT system. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Treatment of solidification latent heat is a key point in solidification simulation by the finite difference method. When latent heat is dealt with in a traditional method of equivalent latent heat, it was found that heat was increased when casting with a high cooling rate, and then the simulation result was distorted. In this paper, a new method is proposed to deal with solidification latent heat. Moreover, a mathematical model was suggested, in which the latent heat can be dealt with accurately under high or normal cooling rates. By contrasting the simulation results from this new method with the traditional one, it was indicated that this new model can obtain more accurate simulation results than the traditional model under high or normal cooling rates. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(2): 115–121, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20104 相似文献
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Zhengkun Xie Xiaowei An Zhijun Wu Xiyan Yue Jiajia Wang Xiaogang Hao Abuliti Abudula Guoqing Guan 《材料科学技术学报》2021,74(15):119-127
Electrolyte formulation with high stability towards both Li metal anode and high-voltage cathode is considered as one of key points for the high-energy density lithium metal batteries (LMBs).In our previous study,by adding only 2% of 2-fluoropyridine (2-FP) as the additive in the carbonate and ether-based electrolyte formulations effectively suppressed Li dendrite growth.In this study,we further found that the main fluoropyridine (FP) family members can serve as not only the effective additive but also the excellent electrolyte solvent in the electrolyte formulations to enhance the performance of LMBs.For the 2-FP,when it was also used the electrolyte solvent and paired with single-salt lithium bis(trifluoromethylsulfonyl)imide (LiTFSI),the obtained electrolyte formulation of 1 M LiTFSI in pure 2-FP solvent not only allowed faster ion transport though solvation effect,but also possessed impressive oxidation stability window over 4.3 V.As a result,the high-voltage LiNi1/3Mn1/3Co1/3O2 (1.5 mA h cm-2)|Li metal battery with it exhibited a capacity retention of more than 80 % over a long-term cycle even at 0.45 mA cm-2 with a lean electrolyte (30 μL).Meanwhile,for another FP family member (i.e.,3-FP) as the electrolyte additive,the 4.3 V LMBs with the carbonate-based electrolyte containing only 1 % of 3-FP maintained 83.9 % of initial capacity after 200 cycles at 0.75 mA cm-2.Density functional theory (DFT) calculations and experiments confirmed that three typical FPs,i.e.,2-FP,3-FP and 4-FP can not only regulate the initial Li nucleation process,but more importantly also induce a protective layer,leading to a uniform and dendrites-free Li deposition.This bifunction of the FP family member as either electrolyte solvent or additive in the electrolyte formulations should be promising for the achieving of dendrites-free high-energy density LMBs. 相似文献
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液化石油气是一种成分复杂的混合物,这就大大增加了对其爆炸进行数值计算的难度。采用CFD(Computational Fluid Dynamics,计算流体力学)方法,对石油气的混合成分进行了简化处理,进而对石油气爆炸进行了数值模拟,建立了描述液化石油气爆燃的理论模型,采用SIMPLE算法对模型进行了求解。计算的超压与实验值相比较,球形容器内最大偏差为9.09%,平均偏差为4.58%;开敞空间情况下,最大偏差9.02%,平均偏差3.92%。还对工业上可能产生的液化石油气可燃气云爆燃威力进行了预测,当气云半径为100 m时,最大超压可达48.432 kPa。研究表明,大尺寸气云可以产生具有破坏力的超压。 相似文献