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 millimeters in diameter.In the present work,terrestrial experimental studies were conducted on the floating half zones of 5 Centistokes(cSt) silicon oil and 10 cSt silicon oil.The experimental results show that the critical Marangoni number generally increases with the increasing aspect ratio of the floating half zone and then decreases.Moreover,a further increase of the critical Marangoni number with the increasing aspect ratio occurs for the slender floating half zones.

Influence of the heating rate on the critical Marangoni number of oscillatory thermocapillary convection in the floating half zone

In the present study, numerical simulations were conducted on thermocapillary convection in floating half zones of 5 cSt silicone oil of different scales in comparison with the experimental studies in the microgravity conditions. The effect of heating rate on the marginal instability boundaries is indicated as a possible explanation for the significant quantitative discrepancies between the experimental results in the terrestrial conditions and in the microgravity conditions.

Instability of thermocapillary flow in liquid layers under microgravity

The instability of the thermocapillary flow in liquid layers is studied in the present paper using the linear stability analysis.Based on the two-dimensional steady flow state,the three-dimensional disturbance with a wave number in the spanwise direction is considered.The effects of the aspect ratio and free surface shape of the liquid layer on the flow instability are studied,and the results are compared with the case with the two-dimensional disturbance.

矩形液池内热毛细对流的流动不稳定性

热毛细对流及其不稳定性是微重力流体科学研究的重要内容.对该问题的研究不仅有利于人们对微重力环境下流体行为、对流不稳定性和湍流转捩过程等基础物理现象的进一步认识,而且也将促进晶体生长、薄膜制备等空间和地面高新技术的发展.实验研究了矩形液池中浅液层在水平温度梯度作用下产生的热毛细对流及其稳定性.实验中,成功地利用PIV(particle image velocimetry)技术对1mm2/s硅油液层内的浮力热毛细对流流场结构进行了大量观测.结果表明,液层中的流场结构经历了多种状态的转变,该过程会受到液层厚度的影响.当液层厚度较小时,比如当d=2.8mm时,随着液池两端温差的增大,液层中的流场结构会经历单胞对流到双胞对流再到多胞对流的转变,到达多胞对流状态之后,继续增大温差,对流涡胞的数量会有所减少,而当温差进一步增大到一定程度以后,整个液层转变为三维非定常流动;当液层厚度较大时,比如当d=4.5 mm时,随着温差的增大,流动模式的转变主要体现在水平截面流场截面上面,当温差增大到一定程度以后,在靠近高温端的附近区域会出现具有明显三维效应的"梭形结构",该梭形结构的尺寸随着温差的增大而增长,并在温差超过某个临界值时失去对称性,整个液层转变为三维非定常流动.

PCM液桥固液相变与热毛细对流耦合机理研究

为了揭示空间微重力下相变材料(PCM)液桥相变过程中固液相变与热毛细对流耦合机理,本文建立了两维轴对称PCM液桥数理模型,系统研究了固液界面拓扑结构演化规律、热毛细对流流动特征及相变强化机理。结果表明,小温差作用下,PCM液桥在自由表面附近率先出现单胞热毛细对流结构,并逐渐增大最终向液桥内部扩展,固液相变界面表现为平滑过渡结构。大温差作用下,PCM液桥相变过程中出现热流体波不稳定性,其对流涡胞数量先增大后减小;热毛细对流流场振幅和频率随相变过程发生动态变化,相变固液界面出现波型结构。随着PCM液桥温差增大,相变时间缩短且热毛细强化因子逐渐增强,热毛细对流的转捩、演化或湮灭是存在于固液相变过程的瞬时动力学行为。