多液滴热毛细迁移的研究

通过密度匹配方法地面模拟微重力环境,以豆油和硅油作为实验系统母液和液滴,研究非均匀温度场中液滴热毛细迁移行为. 用马赫- 泽德干涉仪测量实验系统背景温度场. 用阴影法观测液滴热毛细迁移. 单液滴实验中,得到与YGB 理论预测趋势相一致的结果;双滴实验中,观察到小液滴超越大液滴现象;实验表明液滴迁移过程中液体的黏性系数起重要作用,小液滴超越大液滴过程中,两液滴水平位移都出现明显偏移,且大液滴横向位移更显著. 创新性的设计了三相多液滴热毛细迁移实验,为实际工业生产中多相分离问题提供科学研究基础.      

液滴热毛细迁移问题的研究进展

液滴或气泡的迁移现象无论是在流体力学的基础研究中,还是在材料加工,化学工程等实际应用中都是一个很重要的课题。在微重力环境中,如果在液滴或气泡所在的母液中外加一个温度场,则液滴或气泡就会由于表面张力分布的不均匀而发生迁移运动。这种运动被称为Marangoni迁移或热毛细迁移运动。本文综述了液滴或气泡的热毛细迁移问题历史研究中理论分析,数值模拟以及实验方面的主要结果,阐述了该问题的研究发展过程。目前液滴迁移问题的研究状况,理论分析解还只限于线性及弱非线性的定常问题,数值模拟工作已经得到了在热对流作用比较小的时候液滴的非定常迁移过程,但是对于热对流影响很大的情况(Marangoni数大于100)则尚未得到过与实验中观测到的相一致的理论结果。本文在总结前人研究的基础上,同时给出了在对于热对流作用较大时液滴热毛细迁移非定常问题的最新的数值模拟的结果,并对该问题在此情况下产生的新的变化也给予了分析。最后,文中分析了当前研究中所存在的问题并进一步展望了液滴热毛细迁移问题在未来的发展方向。      

黏弹性液滴热毛细迁移的对流不稳定

液滴在温度分布不均的固壁面上产生的热毛细迁移广泛存在于微流控、喷墨印刷等应用中,对其流动进行稳定性分析对液滴迁移的精准控制具有重要意义.本文采用线性稳定性理论研究了附壁黏弹性液滴在热毛细迁移中的对流不稳定性,得到了不同Prandtl数(Pr)下的临界Marangoni数(Mac)与弹性数的函数关系,并分析了临界模态的流...     

激光驱动液滴迁移的机理研究

液滴热毛细迁移是微重力流体科学中的典型科学问题, 微重力液滴动力学研究不仅具有流体力学的理论意义, 而且具有重要的实际应用价值. 建立了二维轴对称激光驱动液滴迁移模型, 通过仿真计算研究微重力环境下激光驱动液滴迁移的过程, 研究了液滴直径、母液参数等对液滴迁移速度及行为的影响. 首先研究了母液和液滴对激光系数均较小, 液滴初始位置不同时液滴的迁移行为; 然后研究了母液对激光吸收系数较小, 液滴对激光吸收系数较大时, 不同液滴直径与母液宽度比条件下液滴的迁移行为. 仿真结果表明: 当母液和液滴对激光的吸收系数都很小时, 液滴迁移的方向主要受到液滴初始位置的影响; 当母液对激光的吸收系数较小, 液滴对激光的吸收系数较大时, 液滴会朝激光方向迁移, 液滴初始位置对迁移方向影响较小, 但液滴直径与母液宽度之比会影响液滴迁移行为. 将模拟结果与YGB理论对比, 仿真结果与理论结果趋势一致. 研究激光驱动液滴迁移的物理机制, 探索界面张力作用机理, 得到激光驱动液滴迁移的规律, 探索对液滴的驱动控制方法.      

实践十号卫星项目——热毛细对流振荡特征的地面研究

上部开口环形液池在水平径向温度梯度作用下会出现内部温度和自由面的振荡,本文研究了二者发生的临界条件.环形液池内柱加热外壁制冷,以0.5℃/min的速率线性升温得到水平径向温差,T型热电偶测量液层内部单点温度,高精度激光位移传感器测量液层自由面某点形变.随两端温差增加,当超过某一临界温度ΔTct时,开始出现振荡.实验结果表明,对同一种硅油,两种振荡的临界条件随液层厚度具有相同的变化趋势.对不同普朗特(Prandtl)数(Pr)的硅油,振荡临界条件临界马兰哥尼数(Macr)随着邦德数(Bo)的增加而变大.本文工作是中国科学院科学先导专项SJ-10返回式科学实验卫星项目-热毛细对流表面波空间实验研究的地面研究结果,该工作为空间实验提供前期的基础科学研究数据和实验保障.     

搭载实践十号卫星的蒸发液滴空间实验研究

实践十号蒸发对流实验以微重力环境中的蒸发相变流体界面过程为主要研究内容,利用空间微重力条件下浮力对流消失和热毛细对流起主导作用的特殊环境,实验研究置于加热底板的蒸发液滴相变过程中表面蒸发与表面张力驱动对流的耦合机理.利用研制的空间蒸发对流装置完成了在轨工况的科学匹配实验,得到了不同工况(温度、液滴大小、加热底板材料)下蒸发液滴形貌和热流量、蒸发速率等变化规律.为后续空间实验结果的比对分析提供了前期结果.     

热毛细对流表面波空间实验研究

介绍了实践十号返回式科学实验卫星19项科学项目载荷之一:热毛细对流箱表面波空间实验研究,包括项目研究目标、意义、研究内容、空间实验模型及地面匹配实验结果等.阐述了本项目开展空间实验研究的必要性,用科学的地面实验研究数据预测和对比微重力条件下可能获得的研究结果,展望本项目可能取得的成果.     

热毛细对流温度场全息干涉检测研究

本文采用Ｈｅｌｅ－Ｓｈａｗ盒体,在地面上模拟二维热毛细对流,应用全息干涉技术对热毛细对流温度场进行了测试研究,为了获得感兴趣的热毛细对流温度增量分布,文中提出了将背景温度分布条纹与热毛细对流温度增量分布条纹相分离的方法。     

热毛细对流温度场ESPI检测研究

在地面上用二维液体盒研究了热壁下气泡周围液体中的热毛细对流现象,并应用电子散斑干涉技术（ESP）对热毛细对流温度场进行了实时检测研究,给出了部分典型的实验结果。     

热毛细对流速度场测试研究

为了探索微重力状态下表面张力驱动流速度场的测试技术，本文在地面进行了模拟实验，对位于热壁下流体中气泡周围的表面张力驱动流进行了研究，并用ＰＩＶ技术测量了流场的速度分布．     

Thermocapillary migration and interaction of two nondeformable drops

A numerical study on the interaction of two spherical drops in the thermocapillary migration is presented in the microgravity environment. Finite-difference methods are adopted. The interfaces of the drops are captured by the front-tracking technique. It is found that the arrangement of the drops directly influences their migration and interaction, and the motion of one drop is mainly determined by the disturbed temperature field because of the existence of the other drop.     

Experimental study on thermocapillary convection

In the present paper, the experimental studies on thermocapillary convection are reviewed. The author‘s interest is mainly focused on the onset of oscillatory thermocapillary convection,the features of oscillatory flow pattern, and the critical Marangoni number related with temperature and free surface oscillation. The coordinated measurement in a microgravity environment of a drops haft is also addressed.     

Unsteady model of drop Marangoni migration in microgravity

The experiments of drop Marangoni migration have been performed by the drop shift facility of short period of 4.5 s, and the drop accelerates gradually to an asymptotic velocity during the free fall. The unsteady and axisymmetric model is developed to study the drop migration for the case of moderate Reynolds numberRe=O(1), and the results are compared with the experimental ones in the present paper. Both numerical and experimental results show that the migration velocity for moderate Reynolds number is several times smaller than that given by the linear YGB theory. The project supported by the National Natural Science Foundation (19789201) and the Ministry of Science and Technology of China (95-Yu-34)     

Calculations for circular arc type corrugated membrane

Using Chien Wei-zang’s general Solutions of axial symmetrical ring shells, we calculate the stress and displacement of circular are type corrugated membrane under axial loads in this paper.According to the results of calculation, we plot the usable graphs for engineering.Scientists and lechnicians can keep these graphs for easy reference.     

Self-similar solution of the one-dimensional problem of thermocapillary motion of an emulsion

It is proved that the problem of one-dimensional motion of an emulsion under the action of thermocapillary forces has a self-similar solution in a semi-infinite interval. The behavior of the solution is illustrated by numerical examples for aluminum-lead emulsions, in which the carrier phase is lead or aluminum. The solution is compared with the solution of the self-similar problem linearized in the low impurity concentration. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 5, pp. 61–70, September–October, 2007.     

A model of film deformation and rupture under the action of thermocapillary forces

A model of the deformation of a free weightless liquid film with rims fixed at a plane contour and subject to the action of thermocapillary forces is investigated. The film free-surface temperature is assumed to be a known function of the coordinates and time. The equation describing the film thickness evolution in the long-wave approximation is of the second order with respect to time and of the fourth order with respect to the longitudinal coordinates. A model plane nonstationary problem is calculated, making it possible to estimate the lifetime of the film as a function of the rate of variation of the temperature profile curvature on the free boundary. If the characteristic time of the temperature variation is large as compared with the film’s natural oscillation period, the problem can be considered in the quasi-steady approximation, which is studied in detail for the plane and axisymmetric cases. The critical values of the temperature profile curvature, for which the film thickness on the symmetry axis vanishes, resulting in the rupture of the film, are calculated.     

Three-dimensional numerical simulation of sedimenting drops inside a vertical channel

Numerical simulation of sedimenting deformable drops inside a vertical channel has been performed at finite Reynolds numbers. The channel is confined by two vertical walls in x-direction and is periodic in y- and z-directions. Results are obtained using a finite difference/front-tracking method. The main dimensionless parameters are the Reynolds number, the Bond number and ratio of the length of channel to the diameter of drops. The effect of these parameters on lateral migration of drops is investigated. It is found that the wall repulsion is the main mechanism of the lateral migration of the drop, and drop migrates toward the channel axis. When the Reynolds number is relatively low, two different lateral migration regimes are observed: migration with monotonic approach and migration with damped oscillations. These regimes are affected by the dimensionless parameters. When the Bond number increases, the oscillations of drop around the centerline of channel are stronger and drop reaches the channel centerline in a larger period. Results of lateral migration of one drop are consistent with perturbation theory, and two-dimensional numerical simulations performed by Feng et al. (1994). The drag coefficient has also been calculated, and effect of various parameters has been discussed. Two drops interaction is similar to that observed by Feng et al. (1994) for two-dimensional circular cylinders. Results are consistent with experiments performed by Wu and Manasseh (1998). Simulations of four sedimenting drops show that depending on the relative size of drops, they either fall in two rows or they form a single horizontal layer and settle with a unique velocity.     

DROPLET INTERACTIONS IN THERMOCAPILLARY MIGRATION

通过密度匹配方法地面模拟微重力环境,以豆油和硅油作为实验系统母液和液滴,研究非均匀温度场中液滴热毛细迁移行为. 用马赫- 泽德干涉仪测量实验系统背景温度场. 用阴影法观测液滴热毛细迁移. 单液滴实验中,得到与YGB 理论预测趋势相一致的结果;双滴实验中,观察到小液滴超越大液滴现象;实验表明液滴迁移过程中液体的黏性系数起重要作用,小液滴超越大液滴过程中,两液滴水平位移都出现明显偏移,且大液滴横向位移更显著. 创新性的设计了三相多液滴热毛细迁移实验,为实际工业生产中多相分离问题提供科学研究基础.