Soret效应对环形浅池内溶液热毛细对流的影响

采用三维数值模拟方法研究了Soret效应对深宽比为0.1的环形浅液池内双组分溶液热毛细对流的影响。结果表明,当热毛细Reynolds数较小时,溶液流动为二维轴对称稳态流动,相同热毛细Reynolds数下双组分溶液热毛细对流强于纯工质。由于双组分溶液中Soret效应的作用,冷壁面附近溶质浓度大于热壁面附近溶质浓度,且溶质毛细力方向与热毛细力方向一致,因此,溶液流动加强,相比纯工质更易失稳。流动失稳后,双组分溶液中呈现出热流体波与三维振荡流动并存的流动结构,且Soret效应对热流体波波数和主频有明显影响。     

旋转环形液池内双组分溶液热毛细对流研究

通过毛细对流可视化实验系统和三维数值模拟研究了旋转环形液池内受Soret效应影响的双组分溶液热毛细对流,探究了泰勒数和液池深宽比对双组分溶液热毛细对流的稳定性及失稳后产生的振荡流型的影响。结果表明,旋转液池内受Soret效应影响的热毛细对流的基础流为逆时针流胞形成的轴对称稳态流动,液池旋转对基础流径向流动的影响较小,但会明显增大流体的相对周向流动。临界热毛细雷诺数随泰勒数的增大而增大,随深宽比的增大而减小。泰勒数和深宽比的变化会明显改变双组分溶液热毛细对流失稳后产生的振荡流型。随着泰勒数的增大,液池中会出现HTWs和内部波动共存的振荡流型,内部振荡由包含在基态流动中的旋转流胞产生。     

表面散热对双组分溶液热-溶质毛细对流的影响

为了了解表面散热对耦合热-溶质毛细对流的影响,对环形浅液池内考虑Soret效应的双组分溶液耦合热-溶质毛细对流进行了三维数值模拟。环形液池深宽比和半径比分别为0.1和0.5,工质为质量分数等于26.27%的甲苯/正己烷混合溶液。结果表明,当流动为二维稳态时,在Soret效应作用下,溶质会向内侧壁转移,浓度梯度和温度梯度方向相反。随着Biot数增加,流动失稳的临界热毛细雷诺数和临界振荡频率均减小,但波数增加。流动失稳后,在自由表面会出现与温度波动类似的浓度波动;随着热毛细雷诺数增加,不论自由表面是否绝热,流动均会过渡到混沌状态。     

毛细力比对环形液池内耦合热-溶质对流的影响

为了了解毛细力比R_σ对耦合热溶质毛细对流的影响,对深宽比为0.15的环形浅液池内双组分溶液耦合热-溶质毛细对流进行了三维数值模拟。液池内、外壁分别维持恒定温度和浓度,工质为甲苯/正己烷混合溶液,Prandtl数为5.54,Lewis数为25.8。结果表明,当热毛细Reynolds(ReT)数较小时,耦合热-溶质毛细对流为三维稳态流动,当ReT数超过临界值后,流动将转变为三维周期性振荡流动;在计算范围内(-1≤R_σ≤0),随着毛细力比的增加,流动失稳的临界Re_T数会逐渐减小。     

旋转对邱克拉斯基结构内双组分溶液流动稳定性的影响

为了了解晶体和坩埚旋转对具有水平温度梯度的邱克拉斯基(Czochralski)结构液池内双组分溶液热毛细-浮力对流的影响,以质量分数为50%的正癸烷/正己烷双组分溶液为工质进行了一系列实验。结果表明,当晶体/坩埚单独旋转时,随着晶体转速增加,旋转首先会抑制流动失稳,然后促进失稳,失稳后的振荡主频逐渐增大;坩埚单独旋转会抑制流动失稳,失稳后的振荡主频随坩埚转速增加先减小、后增大,相同条件下双组分溶液比纯工质易于失稳。当晶体/坩埚同时旋转时,随着晶体转速增加,同向旋转时主频逐渐增大,反向旋转时主频先减小、后增大。     

深径比对双层热毛细-浮力对流的影响

三维数值研究了环形液池内双层流体热毛细-浮力对流的流动特性,考察了液池深径比对流动的影响,其中外壁面维持高温,内壁面维持低温。结果显示,上、下层流体热毛细-浮力对流的流动结构依赖于液池深径比的大小,其内在机制是由浮力和热毛细对流相对强度所决定;随着深径比的减小,热毛细-浮力对流不稳定性的周向温度波数先增大后减小,存在发生流动不稳定性的最佳深径比;热毛细对流的振荡周期随着深径比的减小逐渐减小,而周向速度平均扰动幅度逐渐增大.     

分离结晶过程中熔体热毛细对流的转变

为了了解微重力条件下新型分离结晶生长过程中熔体热毛细对流的基本特征,利用有限差分法进行了数值模拟,熔体深径比A取1和2,自由界面无因次宽度B分别取0.05、0.075和0.1.当熔体上表面为自由表面时,得到了分离结晶Bridgman生长过程中熔体热毛细对流的流函数和温度分布.计算结果表明:当Ma数较小时,在上下两个自由表面的表面张力的驱动下,熔体内部产生了两个流动方向相反的流胞,流动为稳态流动,随着Ma数的增加,上下自由表面速度增大,温度分布的非线性增加;当Ma数超过某一临界值后,流动将转化为非稳态流动;与熔体上表面为固壁时相比,A=1时的临界Ma数减小,而A=2时的临界Ma数增大;流动失稳的物理机制是流速的变化和阻力的变化之间存在滞后.     

双向温度梯度作用下Cz池内热对流的数值模拟

为了了解双向温度梯度作用下Cz液池内复杂流动和传热特性,利用有限容积法对底部施加不同垂直热流密度(3.0~4.0 W/cm~2)的Cz结构内硅熔体流动进行了三维数值模拟。结果表明,当3.0 W/cm~2≤q≤3.4 W/cm~2时,液池内为稳态轴对称流动,自由表面上温度波动呈直辐条结构,液池内最高温度出现在坩埚侧壁(即T_h);当3.6 W/cm~2≤q≤4.0W/cm~2时,流动失稳,液池内总体温度水平提高,最高温度高于壁面温度,其出现的位置离开壁面逐渐向液池中心移动。     

Pr数对环形浅液池热毛细对流的影响

为了解流体普朗特数(Pr)对热毛细对流的影响,通过线性稳定性分析,确定了环形浅液池内硅熔体(Pr＝0.011)和几种硅油(Pr数从6.7至57.9)热毛细对流失稳的临界条件,获得了它们在临界条件下的热流体波,特别是高Pr数硅油的热流体波.结果发现:当Pr≤15.9时,临界Ma数随Pr数的增加迅速上升,此时环形池内只有一...     

浮力对环形液池内热毛细对流的影响

为了了解浮力的影响,对水平温度梯度作用时环形液池内的热毛细对流进行了非稳态三维数值模拟,环形液池外壁被加热,半径为40 mm,内壁被冷却,半径为20 mm,液池深度为(1-17)mm,流体为0．65cSt的硅油,其Pτ数为6．7．模拟结果表明,当水平温度梯度较小时,流动为轴对称稳态流动,随着温度梯度的增加,流动将会失去其稳定性,在浅液池内,转化为热流体波,浮力对失稳后的流型无影响,但会使热流体波的振幅下降;在深液池内,在常重力条件下,转化成三维稳定流动,在微重力和小重力条件下,转化为三维振荡流动．     

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

数值分析环形池硅熔体旋转-热毛细对流及其稳定性

数值模拟了内半径20 mm、外半径40 mm、深5 mm环形池内硅熔体在旋转和热毛细力共同驱动下的热对流,通过线性稳定性分析确定了旋转-热毛细对流失稳的临界Marangoni数等临界条件。研究结果表明,液池低速旋转会降低轴对称热毛细对流的稳定性,而较高速度的旋转能增强热毛细对流的稳定性。临界条件下旋转-热毛细对流耗散结构波纹的传播方向与液池的旋转方向相同,临界周向波数随旋转速度的增加而增加。在较大的旋转速度下,液池底部出现涡胞,底部涡胞对热毛细对流的稳定性具有削弱作用。     

旋转环形浅液池内双组分溶液耦合热-溶质毛细对流渐近解

为了了解水平温度梯度作用下旋转环形浅液池内耦合热-溶质毛细对流基本特征, 采用匹配渐近展开法对旋转环形浅液池内耦合热-溶质毛细对流过程进行了求解, 获得了中心区域的速度、温度和浓度分布,分析了旋转、Soret效应、浮力、溶质扩散 系数和液池的几何尺寸对流动结构的影响.将所得到的渐近解和文献中的已有结果进行对比,证明了所求结果的正确性;在浅液池内,耦合热-溶质毛细力对流体流动起主导作用, 旋转和浮力对流动的影响较小,溶质扩散系数和几何尺寸有较明显影响;当各种耦合的 驱动力作用方向相同时,流动增强;否则, 流动减弱. 关键词： 旋转 环形浅液池 耦合热-溶质毛细对流 渐近解     

Transient mixed convection in a channel with two facing discretely heated semicircular cavities: Buoyancy,inclination angle,and channel aspect ratio effects

Space-averaged surface temperature distributions and overall Nusselt number measurements have been carried out to study the transient mixed convection heat transfer in a channel with two facing and symmetrically heated semicircular cavities. Effects of buoyancy, channel orientation, and channel aspect ratio on thermal behavior have been investigated from Re 500 to 1,500. Depending on the parametric set, steady, oscillatory, and irregular thermal regimes have been identified. The natural frequencies and time scales of the oscillatory regimes have been obtained using spectral analysis. Results show that with increase in channel aspect ratio, the heat transfer performance reduces for all inclination angles.     

新型分离结晶法的三维数值模拟研究

本文借助三维数值模拟的方法,对微重力条件下新型分离结晶Bridgman生长过程中熔体内部的热毛细对流进行模拟计算。结果表明:(1)Ma数较小时,流动为稳态流动;当Ma数超过一定数值后,流动发展为非稳态热毛细对流。(2)狭缝宽度越大,流动越容易失稳。(3)随着高径比的增大,狭缝处流胞的流动范围增大。     

Period-doubling bifurcations of the thermocapillary convection in a floating half zone

This study experimentally explored the fine structures of the successive period-doubling bifurcations of the time-dependent thermocapillary convection in a floating half zone of 10 cSt silicone oil with the diameter d0=3.00 mm and the aspect ratio A=l/d0=0.72 in terrestrial conditions.The onset of time-dependent thermocapillary convection predominated in this experimental configuration and its subsequent evolution were experimentally detected through the local temperature measurements.The experimental results revealed a sequence of period-doubling bifurcations of the time-dependent thermocapillary convection,similar in some way to one of the routes to chaos for buoyant natural convection.The critical frequencies and the corresponding fractal frequencies were extracted through the real-time analysis of the frequency spectra by Fast-Fourier-Transfor-mation(FFT).The projections of the trajectory onto the reconstructed phase-space were also provided.Furthermore,the experimentally predicted Feigenbaum constants were quite close to the theoretical asymptotic value of 4.669 [Feigenbaum M J.Phys Lett A,1979,74:375-378].     

环形浅液池内中等Pr数流体的热毛细对流

为了了解微重力下水平温度梯度作用时环形浅液池内的热毛细对流特性,利用有限差分法进行了非稳态二维数值模拟,环形液池外壁被加热,内壁被冷却,流体为 0.65 cSt的硅油,其Pr 数为 6.7。结果表明,当温度梯度较小时,流动为稳态流动,随着温度梯度的增加,流动将会失去其稳定性,转化成各种振荡流动,模拟结果与实验结果基本吻合。     

Thermocapillary deformation of a thin locally heated horizontal liquid layer

In this paper, steady thermocapillary flow in a thin horizontal layer of a viscous incompressible liquid with a free surface is considered. An axially symmetric steady problem with a localized thermal action on a horizontal liquid layer with a deformable free surface is solved in a thin-layer approximation. In addition to the thermocapillary effect, the model takes into account the capillary pressure caused by the free surface variable curvature and the convective mechanism of heat transfer in the liquid. Analytical expressions for the velocity vector components as functions of the liquid layer thickness and surface temperature are obtained. The free surface and velocity profiles caused by various kinds of heating are calculated. The influence of convective heat transfer on the flow pattern is analyzed.