共查询到20条相似文献,搜索用时 140 毫秒
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《功能材料》2016,(12)
采用数值模拟的方法研究了微重力条件下Czochralski法生长硅晶体过程中熔体热毛细对流的基本特征,探讨了水平和垂直温度梯度的耦合对熔体流动的影响。熔体自由表面与外界辐射换热,水平温度梯度Marangoni(Ma)数选取(0~3 000),底部热流Q选取(1.39×10-2~1.76×10-2)。结果表明,当Q和Ma数均较小时,流动为稳态,液池内产生3个流胞,熔体流动由Q主导,减小Q或增大Ma数可使流动更稳定。当Ma数增大到一定值时,流动从稳态转变为非稳态,流动的临界Mac数随Q的增大而显著减小。流动失稳后,出现了新的流动转变方式,Ma数为影响表面波动形式的关键因素,Q会改变热流体波数,是晶体附近的热流体波产生的决定因素。随着Ma数和Q的不断增强,自由表面最终形成弯曲条幅状热流体波。 相似文献
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为了解环形液池内耦合热-溶质毛细对流的转变特征,建立了环形液池内的耦合热-溶质毛细对流的物理数学模型,采用有限容积法进行二维数值模拟,得到了环形液池内耦合热-溶质毛细对流失稳的临界条件,并对耦合热-溶质毛细对流失稳机理进行了分析。结果表明:环形液池内流态从稳态到非稳态的转变为霍普夫分岔;随着深宽比、半径比和普朗特数的增加,流动更容易失稳;当刘易斯数大于1时,临界毛细雷诺数随着刘易斯数的增大而减小,流动失稳是由于溶质Marangoni效应的主导作用和流动的惯性共同作用的结果;而当刘易斯数小于1时,随着刘易斯数的增大,临界毛细雷诺数增大,流动失稳则是由于热Marangoni效应的主导作用和流动的惯性共同作用的结果。 相似文献
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环形池内双层流体浮力-热毛细对流的实验研究 总被引:1,自引:0,他引:1
液封提拉法生长晶体过程中,液封流体与熔体形成了不相溶的双层流体。除了自由表面的热毛细力作用外,液-液界面的热毛细力以及浮力共同驱动了双层系统内浮力-热毛细对流的产生。为了了解环形池内双层流体的复杂流动和传热特征,本工作对环形池内0.65cSt硅油与水组成的双层流体浮力-热毛细对流进行了实验观察。实验记录了不同的液层厚度比和深宽比条件下流动失稳的临界温差与流动形态。结果表明,液层总厚度的增大会削弱系统的流动稳定性。流动失稳的流动形态有三种,即第一种热流体波、第二种热流体波和三维稳态流动。实验还观察到了流动分岔现象。 相似文献
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不相溶混的双层流体系统的传热传质现象广泛地存在于自然界和工程技术领域中,尤其是芯片工业与微电子工业中半导体材料的液封提拉法生长制备工艺中,双层流体的流动稳定性直接影响着晶体材料的生长质量.微重力条件下,由于没有了重力的影响,可以增强双层流体流动的稳定性以获得更为优异的晶体生长环境,然而,两相界面处的热毛细力引起的热毛细对流却对双层流体系统中的传热传质现象影响甚大.目前,可采用实验研究的方法对水平温度梯度作用下的双层流体的热毛细对流进行可视化研究,以观测流动特性及失稳的耗散结构.在空间实验中,由于低Prandtl数流体不可透视的特性,故在实验中鲜少采用其作为观察工质,多采用高Prandtl数流体.关于双层流体的热毛细对流,前人的研究主要集中在矩形腔体内环形池内的低Prandtl数双层流体的流动特性,对环形液池中高Prandtl数双层流体的流动特性及失稳耗散结构的研究还鲜见报道.本工作针对微重力条件下,水平温度梯度作用下的环形液池内B2 O3/蓝宝石熔体、5cSt硅油/HT-70、水/FC-75三组工质对的热毛细对流特性进行了研究,采用数值模拟的方法获得了R-Z截面的流函数、温度分布,以及监测点的速度和温度周期波动,揭示了流动失稳后的振荡流型.研究结果表明,运动粘度会影响流动流型,对于运动粘度较低的5cSt硅油/HT-70、水/FC-75的工质对,流动失稳为热毛细对流失稳,而高运动粘度的B2 O3/蓝宝石熔体则出现了热毛细对流失稳与Marangoni失稳.对比三种工质对的流动失稳临界Marangoni数,发现上下液层Prandtl数比值越大,则临界Marangoni数越大,选择较大的上下液层Prandtl数比值,可增强环形双液层流体流动稳定性. 相似文献
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采用格子Boltzmann方法研究纳米颗粒形状影响下方腔内纳米流体热毛细对流的强化传热效果,主要分析了纳米粒子体积分数、颗粒形状以及Marangoni数Ma等相关参数对于纳米流体热毛细对流换热过程的影响。结果表明:长径比(长/半径)对纳米流体换热效果有影响,形状因子越大,平均Nu数Nuave越大。随着体积分数的增加,棒状、盘状和正方体状纳米颗粒均使热毛细对流的Nuave数减少,球状纳米颗粒条件下热毛细对流的Nuave数增加。Ma数越大,纳米流体热毛细对流的自由表面速度越大,对流换热效果也随之增强。 相似文献
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轴向磁场对硅单晶Czochralski生长过程的影响 总被引:1,自引:0,他引:1
利用有限元方法对炉内的传递过程进行了全局数值模拟,假定熔体和气相中的流动都为准稳态轴对称层流,熔体为不可压缩流体,Cz炉外壁温度维持恒定,模拟磁场强度范围为(0~0.3)T,研究了用Czochralski(Cz)法生长单晶硅轴向磁场对熔体流动和氧传输过程的影响.结果表明:轴向磁场可有效地抑制熔体内的流动,但增大加热器功率和结晶界面处晶体内的轴向温度梯度;对于常规Cz炉,轴向磁场可增大结晶界面平均氧浓度,而对于具有气体导板的Cz炉,则会减小结晶界面平均氧浓度. 相似文献
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利用有限元方法对硅单晶Czochralski(Cz)法生长炉内的流动和传输过程进行了全局数值模拟,研究了表面张力温度系数对硅单晶生长过程的影响,模拟的表面张力温度系数范围是(0~0.35)×10-3N/m·K.结果表明:随着表面张力温度系数的增加,由Marangoni效应驱动的熔体表面流动能强化熔体的自然对流,从而减小了通过熔体自由界面的温差,降低了加热器的功率.但是,结晶界面更凸向熔体,在结晶界面处晶体内的轴向温度梯度减小;对常规Cz炉,结晶界面处的平均氧浓度先减小然后增大,而对于具有气体导板的Cz炉,Marangoni效应总是使结晶界面处的平均氧浓度减小. 相似文献
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In order to investigate the fundamental characteristics of thermocapillary convection in the detached solidification under microgravity, the finite-difference method was adopted to perform the numerical simulations. The results show that the flow of molten liquid is steady with the low Marangoni number and it only exists in the vicinity of the free surface. Moreover, with the Marangoni number increasing, the flow is expanded toward the inner part of molten liquid gradually, and at the same time the flow velocity on the free surface increases. However, the flow is unstable when the Marangoni number exceeds the critical Marangoni number. 相似文献
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The flow pattern and the velocity distribution of a liquid metal in the flow control mold(FC-mold) were investigated with a mercury model by analogy to the molten steel during continuous casting.The velocity measurement was conducted by the ultrasonic Doppler velocimeter(UDV)under various magnetic distributions and flux densities.The impingement intensity and the scouring intensity of the liquid metal to the narrow wall of the mold were calculated based on the measured data,and the influence of the magnetic flux density on the liquid metal flow in the mold was analyzed.The results showed that the surface of the liquid metal became more active when only the lower magnet was assembled,and the surface fluctuation was suppressed when further applying the upper magnetic field.It was indicated that when the upper and lower magnetic flux densities were 0.18 T and 0.5 T,respectively,the optimum conditions could be obtained,under which the free surface fluctuation could be suppressed,and a flow recirculation could rapidly form. 相似文献
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P. Chapelle A. Jardy D. Ablitzer Yu. M. Pomarin G. M. Grigorenko 《Journal of Materials Science》2008,43(9):3001-3008
Electromagnetic levitation of a liquid metal droplet is of great interest to study gas–liquid metal reactions. An important
prerequisite for the evaluation of the overall mass transfer between the gas and metal is to characterize the geometry of
the deforming molten droplet, which determines the interfacial reaction area. In this article, the free surface shape and
dynamics of a molten 80%Ni–20%Cr droplet is investigated both experimentally and numerically. The frequencies associated to
the oscillatory translational motions of the drop and to the vibrations of its free surface are measured using high-speed
video image analysis. A 2D transient model is then presented, in which three interacting phenomena are considered: electromagnetic
phenomena, the turbulent flow of liquid metal in the drop and the change in the drop shape. The numerical results presented
demonstrate the capabilities of the model. 相似文献
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为探究切削液扰动下BTA深孔镗削系统横向振动频率的影响,通过建立BTA深孔镗杆系统计及内、外切削液流固耦合及其自由液面效应的横向振动模型,解析系统不同情况下的横向振动的一、二阶频率表达式,并以不同情况下,深孔镗杆内、外切削液的横截面面积及其对深孔镗杆的附加质量来表征对应的自由液面变化,通过计算,明确了BTA深孔镗杆的横向振动频率对切削液流速、轴向力的敏感性及其运动转换趋势。BTA深孔镗杆横向振动频率对轴向力的敏感性规律为:在共振脊区域,在内、外切削液都无自由液面时最大;内、外切削液都有自由液面时最小;在共振翅区域,只内切削液有自由液面时最大,内、外切削液都无自由液面时最小。BTA深孔镗杆横向振动频率对切削液流速的敏感性规律为:在共振脊区域,只内切削液有自由液面时最大,内、外切削液都无自由液面时最小;在共振翅区域,内、外切削液都无自由液面时最大,只内切削液有自由液面时最小。系统在切削液流速、轴向力达到临界等效值时,发生弯曲或屈曲;在静力失稳后,系统将会在更高的切削液流速值以混阶模态形式发生耦合颤振等复杂运动。该研究结果可为BTA深孔镗削加工的生产实践提供一定理论指导。 相似文献
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Dennis Haake Joerg Klatte Aleksander Grah Michael E. Dreyer 《Microgravity science and technology》2010,22(2):129-138
An open capillary channel is a structure that establishes a liquid flow path when the capillary pressure caused by surface
tension forces dominates in comparison to the hydrostatic pressure induced by gravitational or residual accelerations. To
maintain a steady flow through the channel the capillary pressure of the free surface has to balance the pressure difference
between the liquid and the surrounding constant pressure gas phase. Due to convective and viscous momentum transport the pressure
along the flow path of the liquid decreases and causes the free surface to bend inwards. The maximum flow rate through the
channel is reached when the free surface collapses and gas ingestion occurs near the outlet. This stability limit depends
on the geometry of the channel and the properties of the liquid. In this paper we present an experimental setup which is used
in the low-gravity environment of the Bremen Drop Tower. Experiments with convective dominated systems have been performed
where the flow rate was increased up to the maximum value. In comparison to this we present a one-dimensional theoretical
model to determine important characteristics of the flow, such as the free surface shape and the limiting flow rate. Furthermore
we present an explanation for the mechanism of flow rate limitation for these flow conditions which is similar to the choking
problem for compressible gas flows. 相似文献
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A new curvature technique calculation for surface tension contribution in PLIC-VOF method 总被引:1,自引:0,他引:1
The volume of fluid (VOF) methods have been used for numerous numerical simulations. Among these techniques used to define
the moving interface, the piecewise linear interface reconstruction (PLIC-VOF) is one of the most accurate. A study of the
superficial tension impact on two-phase flow with free surface is presented. A new method based on direct staggered grid is
developped to include surface tension in PLIC-VOF. The new numerical curvature calculation method doesn't need smoothed colour
function and leads to less “spurious current”. This technique is applied to the calculus of surface tension force in the case
of the rise of air bubble in viscous liquid and the fall of liquid drop in the same liquid on free surface. Droplets, thin
layer and capillarity waves are observed after the free surface rupture for different Bond number. The influence of surface
tension calculus is then obvioused and when the drop hit the free surface, wavelets propagate toward the virtual boundaries
imposed. 相似文献
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Linhao Fei Koichi Ikebukuro Takeshi Katsuta Toshihiro Kaneko Ichiro Ueno Donald R. Pettit 《Microgravity science and technology》2017,29(1-2):29-36
A series of terrestrial, parabolic-flight and on-orbit experiments on thermocapillary-driven flows in free liquid films are carried out. We focus on the basic flow patterns induced in the film formed in a rectangular hole by varying the film volume in order to make a comparison with the results of the fluid physics experiments under microgravity conditions conducted by one of the authors, Pettit, on the International Space Station. The free liquid film is formed in a rectangular hole of O(0.1 mm) in thickness under a designated temperature difference between the end walls. The temperature dependence of the surface tension results in a non-uniform surface tension distribution over the free surfaces. A liquid generally has a negative temperature coefficient of surface tension; i.e., the fluid over a free surface is driven from a higher-temperature region to a lower-temperature region. In the case of a thin free liquid film with two free surfaces, however, an unusual flow pattern is realized. That is, the fluid seems to be driven toward the heated region from a colder region. In order to understand the physical mechanism of this behavior in the free liquid film, a series of on-orbit and ground experiments were conducted. We indicate several flow patterns in the film and corresponding film profiles as well as the surface temperature distribution. We also try to illustrate the cross-sectional flow structures in the thin free liquid film with two free surfaces. 相似文献
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The transition from the steady to the oscillatory thermocapillary flow of high Prandtl number fluid in the rectangular container
configuration under various cold wall temperatures effects have been studied experimentally. The fluid is heated by a thin
wire placed along the free surface. The effects of buoyancy on the transport phenomenon are carefully assessed. The thermocapillary
flow field is described based on a flow visualization and temperature measurement. The critical temperature difference for
the onset of oscillations varies when the cold wall temperature is varied. The heat loss at the liquid free surface is identified
to be responsible for this effect. 相似文献
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Alberto Passerone 《Journal of Materials Science》1974,9(7):1050-1056
A study of the problems connected with the coating of aluminium by molten lead has been made. A theoretical approach shows that lead only wets the aluminium surface if the latter is completely free of oxide. Contact of liquid lead with a “clean” aluminium surface may be effected by using an intermediate layer of molten chlorides as a flux and this process has been studied using electrochemical methods. It has been shown that the flux (formed by a eutectic mixture of KCl and ZnCl2) reacts with the aluminium to form a surface layer of various Al-Zn alloys as shown by electron probe microanalysis. After removal of all traces of chlorides, the resulting surface may be readily wetted by molten lead at the appropriate temperature. 相似文献