共查询到19条相似文献,搜索用时 171 毫秒
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MORPHOLOGY AND FORMATION MECHANISM OF LINEAR DEFECTS ON SOLAR-ENERGY MULTICRYSTALLINE SILICON WAFERS
研究了定向凝固生长的多晶硅线切割过程中在多晶硅片表面产生的线状缺陷的形貌特征及其形成机制.分别采用扫描电子显微技术和X射线衍射技术对多晶硅片线切割引起的线状缺陷的形貌特征及夹杂物进行研究,结果表明:多晶硅片表面线切割过程中形成的线状缺陷是因SiC夹杂物的存在而引起的,当切割钢丝与多晶硅中的SiC夹杂物相遇时,在拉力作用下钢丝爬越SiC夹杂物,同时在SiC夹杂物的表面发生研磨现象,在多晶硅片表面留下线状缺陷. 相似文献
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用激光多普勒测速仪对旋流器产生的强湍流有自由射流的速度场和湍流场进行了实验研究。实验结果表明,这种旋流器十分有利于中心回流区的形成,射流的平均速度分布沿轴向快速地衰减,有旋自由射流呈现湍流各向异性,特别是在回流区域中,本文对流场中湍流动量传递的方向进行了讨论。 相似文献
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结合晶内铁素体的形核机制与异质形核理论,系统介绍了可以诱发晶内铁索体形核的夹杂物的类型和尺寸范围.分析认为,诱导IGF的有效形核核心一般为复合夹杂物,夹杂物上须有与IGF共格品面错配度较小的析出相.内部氧化物与边缘析出相形成的凹形边缘为IGF的形核提供了有利条件.诱导IGF形核的夹杂物类型不同,几何尺寸也有所差异,但均... 相似文献
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柴油机涡流室连接通道结构参数对其空气流动特性影响的研究 总被引:1,自引:0,他引:1
利用建立的各向异性k-ε湍流模型和精确测量的通道入口的边界条件,计算研究了不同连接通道位置和角度下涡流室内的空气湍流流动特性。 相似文献
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利用VOF方法建立两相湍流瞬态流动模型对FTSC结晶器内钢-渣界面运动和钢液流场分布进行了数值模拟计算,考察了水口结构、拉速对钢液流动及钢渣界面运动行为的影响作用。计算结果表明:采用不同结构的4孔水口进行浇注时,在结晶器内宽面方向一侧形成数量不等、位置不同的回流区;结晶器内的钢渣界面形状及出现液面裸露的位置由于水口结构的不同均有所差异。 相似文献
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针对某钢厂中厚板卷厂采用铁水倒罐→铁水预处理→转炉冶炼→出钢脱氧合金化→LF精炼炉→RH真空炉→钙处理→连铸生产X70管线钢生产工艺,采取系统取样分析,对P、S等杂质元素,N、H、O等气体的脱除规律以及夹杂物的控制规律进行了研究。研究表明,成品成分可以稳定控制水平为:w([P])≤0.004 5%,w([S])≤0.001 00%,w([O])≤0.000 85%,w([N])≤0.003 00%,w([H])≤0.000 15%,夹杂物以小于10μm的CaO-CaS为主,且单位面积总夹杂物数量小于12个/mm~2,成品钢具有很高的洁净度水平。 相似文献
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为了提高20#碳钢连铸管坯的产品质量,通过对气泡和非金属夹渣的形成机理以及对中间包内钢水流场数值模拟的研究分析,发现中间包的结构与操作对20#钢连铸坯的生产质量具有较大影响,因此,对中间包的结构与操作进行了优化研究,研究结果显示:(1)通过对中间包的结构优化提高了中间包的钢水液面高度,增加了钢水在中间包内的滞留时间,有利于夹杂物和气泡的消除,从而提高了钢水的均匀性;(2)改进钢水流入、流出中间包的操作,能避免钢流与空气的直接接触,减少钢水的二次氧化;(3)连铸钢水过热度的严格控制,有利于减少钢水的二次氧化和对包衬耐火材料的浸蚀,从而起到降低铸坯中非金属夹渣物的效果。采取这些措施后,2#钢连铸坯的质量取得了显著提高,设备寿命明显延长。 相似文献
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通过检测与分析,认为柴油机油底壳薄钢板发生层状开裂事故是由于钢液中的炉渣、耐火衬料或脱氧产物未除尽,卷入连铸结晶器,残留于钢中形成夹渣,轧制时沿轧制方向分布,使钢板产生分层,破坏了其结构上的连续性,在冲压时于夹渣聚集处开裂。 相似文献
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Heat Transfer Characteristics of Printed Circuit Heat Exchanger with Supercritical Carbon Dioxide and Molten Salt 总被引:1,自引:0,他引:1
《热科学学报(英文版)》2021,(3)
Molten salt and supercritical carbon dioxide (S-CO_2) are important high temperature heat transfer media,but molten salt/S-CO_2 heat exchanger has been seldom reported.In present paper,heat transfer in printed circuit heat exchanger (PCHE) with molten salt and S-CO_2 is simulated and analyzed.Since S-CO_2 can be drove along passage wall by strong buoyancy force with large density difference,its heat transfer is enhanced by natural convection.In inlet region,natural convection weakens along flow direction with decreasing Richardson number,and the thermal boundary layer becomes thicker,so local heat transfer coefficient of S-CO_2 significantly decreases.In outlet region,turbulent kinetic energy gradually increases,and then heat transfer coefficient increases for turbulent heat transfer enhancement.Compared with transcritical CO_2 with lower inlet temperature,local heat transfer coefficient of S-CO_2 near inlet is lower for smaller Richardson number,while it will be higher for larger turbulent kinetic energy near outlet.Performance of PCHE is mainly determined by the pressure drop in molten salt passage and the heat transfer resistance in S-CO_2 passage.When molten salt passage width increases,molten salt pressure drop significantly decreases,and overall heat transfer coefficient slightly changes,so the comprehensive performance of PCHE is improved.As a result,PCHE unit with three semicircular passages and one semi-elliptic passage has better performance. 相似文献
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利用课题组自行配制的二元混合熔融盐(KNO3-Ca(NO3)2)开展导热油与低熔点熔融盐的管内强制对流实验研究。通过实验得到导热油与低熔点熔融盐的总换热系数,并通过最小二乘法和Wilson分离法得到了管内低熔点熔融盐侧的对流换热系数及其准则关联式。与不同的经典传热关联式对比,最大偏差为+23%。考虑高温熔融盐的变物性特征,利用黏度项对Dittus-Boelter方程关联式进行修正。经过修正后的Dittus-Boelter方程与实验测试结果最大偏差为-15%,偏差值明显减小。过渡流实验数据和Hausen方程及Gnielinski方程的最大偏差均为10%,实验结果验证了传热关系式仍适用于高温熔融盐的结论。 相似文献
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The melting and solidification stages of a continuous copper–nickel dissimilar metal conduction mode laser welding have been simulated numerically in this study. The heat, mass and momentum transports in molten metal pool have been analysed using both laminar and turbulent flow models separately for the same process parameters. The phase change aspects related to solidification and melting are accounted for by a modified enthalpy–porosity technique while the turbulent transport is modelled by a high Reynolds number k–ε model. It has been observed that temperature fields obtained from both laminar and turbulent transport simulations are qualitatively similar to each other. The molecular thermal diffusivity of the molten metal mixture is found to be in the same order of magnitude as eddy thermal diffusivity, as a result of which the thermal field gets marginally affected by fluid turbulence. By contrast, eddy viscosity remains much greater than molecular viscosity, which leads to greater amount of momentum diffusion in the case of a turbulent molten metal pool, in comparison to that obtained from the corresponding laminar simulation. This is reflected in the reduction in maximum velocity magnitude in the turbulent simulation in comparison to the maximum velocity obtained from laminar simulation. In the case of species transport, the turbulent mass diffusivity is found to be about 107–108 times greater than molecular mass diffusivity. As a result, the species field in turbulent simulation shows characteristics of better mixing between two dissimilar molten metals than the species field obtained using the laminar transport model. The species distribution obtained from turbulent transport is shown to be in better agreement with experimental data reported in literature than the corresponding mass fraction distribution obtained from laminar simulation. It is also found that species distribution in the molten pool is principally determined by advective and diffusive transport during the melting stage and species transport by advection and eddy diffusion in turbulent pool increasingly weakens with decreasing temperature during the cooling following the laser melting stage. 相似文献
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Yu-Ting Wu Cong ChenBin Liu Chong-Fang Ma 《International Communications in Heat and Mass Transfer》2012
In this paper, experiments are carried out to obtain convective heat transfer coefficients of turbulent flow and transition flow of molten Hitec salts in a circular tube. The present experimental data together with experimental data of four kinds of molten salts from the existing literature are correlated for transitional and turbulent convective flow respectively. In addition, the Prandtl number dependence of convective heat transfer with different working fluids is examined. It is shown that the present experimental data are in good agreement with existing correlations. 相似文献