Self-propelled Leidenfrost droplets on femtosecond-laser-induced surface with periodic hydrophobicity gradient

The controllable transfer of droplets on the surface of objects has a wide application prospect in the fields of microfluidic devices,fog collection and so on.The Leidenfrost effect can be utilized to significantly reduce motion resistance.However,the use of 3D structures limits the widespread application of self-propulsion based on Leidenfrost droplets in microelectromechanical system.To manipulate Leidenfrost droplets,it is necessary to create 2D or quasi-2D geometries.In this study,femtosecond laser is applied to fabricate a surface with periodic hydrophobicity gradient(SPHG),enabling directional self-propulsion of Leidenfrost droplets.Flow field analysis within the Leidenfrost droplets reveals that the vapor layer between the droplets and the hot surface can be modulated by the SPHG,resulting in directional propulsion of the inner gas.The viscous force between the gas and liquid then drives the droplet to move.

Numerical modeling of condensate droplet on superhydrophobic nanoarrays using the lattice Boltzmann method

In the present study,the process of droplet condensation on superhydrophobic nanoarrays is simulated using a multicomponent multi-phase lattice Boltzmann model.The results indicate that three typical nucleation modes of condensate droplets are produced by changing the geometrical parameters of nanoarrays.Droplets nucleated at the top（top-nucleation mode）,or in the upside interpillar space of nanoarrays（side-nucleation mode）,generate the non-wetting Cassie state,whereas the ones nucleated at the bottom corners between the nanoarrays（bottom-nucleation mode） present the wetting Wenzel state.Time evolutions of droplet pressures at the upside and downside of the liquid phase are analyzed to understand the wetting behaviors of the droplets condensed from different nucleation modes.The phenomena of droplet condensation on nanoarrays patterned with different hydrophilic and hydrophobic regions are simulated,indicating that the nucleation mode of condensate droplets can also be manipulated by modifying the local intrinsic wettability of nanoarray surface.The simulation results are compared well with the experimental observations reported in the literature.

Two-dimensional anisotropic vortex quantum droplets in dipolar Bose−Einstein condensates

Creation of stable intrinsically anisotropic self-bound states with embedded vorticity is a challenging issue.Previously,no such states in Bose−Einstein condensates(BECs)or other physical settings were known.Dipolar BEC suggests a unique possibility to predict stable two dimensional anisotropic vortex quantum droplets(2D-AVQDs).We demonstrate that they can be created with the vortex axis oriented perpendicular to the polarization of dipoles.The stability area and characteristics of the 2D-AVQDs in the parameter space are revealed by means of analytical and numerical methods.Further,the rotation of the polarizing magnetic field is considered,and the largest angular velocities,up to which spinning 2D-AVQDs can follow the rotation in clockwise and anti-clockwise directions,are found.Collisions between moving 2D-AVQDs are studied too,demonstrating formation of bound states with a vortex−antivortex−vortex structure.A stability domain for such stationary bound states is identified.Unstable dipolar states,that can be readily implemented by means of phase imprinting,quickly transform into robust 2D-AVQDs,which suggests a straightforward possibility for the creation of these states in the experiment.

Topology Chemical Process Research on the Condensing and Growing Phase Multi Micro Oil Droplets Based on Hydrodynamics

The hydrodynamic research about the droplet condensing of the multi phase liquid state on the surface of the coal glass and water discusses the deepening process of convex shape curve and the formation of S shape, and puts emphasis on describing the diagram formation method of the later. In the induction period the active diagram of the micro droplet is decided by pH value forming as convex shape diagram or S shape diagram. When pH value is above 4.0, the damage of convex shape diagram cannot be recovered, in that case produce S shape activity diagram. When pH value is equal to or above 12.0, the hard surface with alkali liquid state loses adhesion, so that the micro droplet condensing of the multi phase liquid state stops completely. The research result shows that the water cleaning conditions of getting rid of the oil micro droplets can be decided by the pH value.

Ultradilute self-bound quantum droplets in Bose–Bose mixtures at finite temperature

We theoretically investigate the finite-temperature structure and collective excitations of a self-bound ultradilute Bose droplet in a flat space realized in a binary Bose mixture with attractive inter-species interactions on the verge of meanfield collapse. As the droplet formation relies critically on the repulsive force provided by Lee–Huang–Yang quantum fluctuations, which can be easily compensated by thermal fluctuations, we find a significant temperature effect in the density distribution and collective excitation spectrum of the Bose droplet. A finite-temperature phase diagram as a function of the number of particles is determined. We show that the critical number of particles at the droplet-to-gas transition increases dramatically with increasing temperature. Towards the bulk threshold temperature for thermally destabilizing an infinitely large droplet, we find that the excitation-forbidden, self-evaporation region in the excitation spectrum, predicted earlier by Petrov using a zero-temperature theory, shrinks and eventually disappears. All the collective excitations, including both surface modes and compressional bulk modes, become softened at the droplet-to-gas transition. The predicted temperature effects of a self-bound Bose droplet in this work could be difficult to measure experimentally due to the lack of efficient thermometry at low temperatures. However, these effects may already present in the current cold-atom experiments.

仿生集水纤维研究进展及应用

淡水资源短缺是全球共同面临的严峻挑战。相关研究发现,模仿蜘蛛丝等生物结构从空气中收集水分,是缓解当前水资源危机的有效途径,已成为仿生集水领域的研究焦点。本文从基础润湿理论、液滴定向传输机理、定向集水机制、仿生纤维设计特点及制备方法等方面进行了综述,重点介绍了Young’s方程、Wenzel模型以及Cassie-Baxter模型等基础润湿理论。将纤维集水过程划分为冷凝结露、定向运输和液滴脱附3个阶段,并深入阐述了蜘蛛丝集水过程的内在机制,包括拉普拉斯压力梯度、表面能梯度、滞后效应和液滴悬挂能力。分析了影响集水效率的关键因素,并列举了提升纤维集水效率的常用策略。归纳了仿生纤维结构的主要仿生对象、仿生原理以及所采用的主要制备技术,并对不同技术的优缺点及适用场景进行了详细分析。最后,对不同仿生纤维网状集水器的集水特点和集水效率进行了比较,分析了仿生纤维集水技术在大气水收集、海水淡化、工业蒸气回收以及油水分离等领域的应用潜力,并对该技术的未来发展方向及现有不足提出了改进意见和展望。

Effect of carrier gas pressure on vapor condensation and mass flow-rate in sonic nozzle

Non-equilibrium vapor condensation of moist gas through a sonic nozzle is a very complicated phenomenon and is related to the measurement accuracy of sonic nozzle.A gas-liquid two-phase model for the moist gas condensation flow was built and validated by moist nitrogen experiment of homogeneous nucleation through a transonic nozzle.The effects of carrier gas pressure on position and status of condensation onset in sonic nozzle were investigated in detail.The results show that condensation process is not easy to occur at lower carrier pressure and throat diameter.The main factors influencing condensation onset are boundary layer thickness,heat capacity of carrier gas and expansion rate.All of results can be used to further analyze the effect of condensation on mass flow-rate of sonic nozzle.

OECD/NEA ROSA Project Experiment on Steam Condensation in PWR Horizontal Legs during Large-Break LOCA

Separate-effect experiment simulating steam direct-contact condensation on ECCS （emergency core cooling system） water in PWR （pressurized water reactor） cold legs during reflood phase of large-break LOCA （loss-of-coolant accident） was conducted in OECD/NEA ROSA Project using the LSTF （large scale test facility）. A new test section was furnished in the downstream of the LSTF break unit horizontally attached to the cold leg. Significant condensation of steam appeared in a short distance from the simulated ECCS injection point, and the steam temperature in the test section decreased immediately after the initiation of the ECCS water injection. Total steam condensation rate estimated from the difference between steam flow rates at the test section inlet and outlet was in proportion to the simulated ECCS water mass flux until the complete condensation of steam. Clear images of high-speed video camera were successfully obtained on droplet behaviors through the viewer of the test section, especially for annular mist flow.

西北地区气溶胶垂直分布及其对云微物理影响的飞机观测个例研究

气溶胶分布及其影响云微物理过程对地气系统的辐射平衡及区域乃至全球水循环产生复杂影响,也是气溶胶间接效应关注的热点和重点。利用2021年9月3日在西北地区开展的气溶胶和云的飞机观测个例资料,分析了气溶胶垂直分布及气溶胶与CCN、云滴浓度的关系。结果表明:(1)气溶胶数浓度垂直变化为四层,各层间气溶胶数浓度、有效直径、尺度谱分布均存在明显不同,大气逆温层结对气溶胶垂直分布有重要影响;近地层气溶胶数浓度可达8183.2 cm^(-3)。(2)垂直方向上CCN与气溶胶数浓度之间有较好的线性正相关性。气溶胶活化比率(CCN/Na)较低,低于0.5,气溶胶尺度越大、浓度越低越容易活化成为CCN。(3)对空中CCN的活化谱进行拟合表明西北地区属于清洁大陆型核谱。(4)同高度云内气溶胶数浓度与云滴数浓度和LWC之间有很强的负相关性,相比云外,云内气溶胶浓度明显降低,气溶胶谱增宽,云滴数浓度和LWC均增加,有效直径增大,云侧边界受夹卷混合过程和云滴未过饱和蒸发的影响导致气溶胶数浓度增加和有效直径增大。(5)云下气溶胶与云滴数浓度之间为线性正相关关系,气溶胶转化为云滴的比率为35%;过饱和度0.6%条件下,云下CCN与云滴数浓度之间为线性正相关关系,CCN转化为云滴的比率为38%。

含气溶胶竖直壁面冷凝液演化特性

为了研究壁面气溶胶颗粒层对蒸汽冷凝液生成行为的影响,本文针对不可溶气溶胶沉积竖直壁面上的蒸汽冷凝过程开展研究。采用可视化的方法建立了蒸汽冷凝实验平台并开展实验,观察冷凝液的发展规律,给出了冷凝速率、颗粒沉积密度对冷凝液演化特性的影响。结果表明:竖直壁面凝液演化经历液滴生长、液滴滑落和水流发展等过程,稳态冷凝液分布包括水流、液滴和薄水膜3个区域。高冷凝速率或高颗粒沉积密度环境下,液滴生长时间更短、凝液演化速度更快,随着冷凝速率和沉积密度的增加,水流的数量及其所占面积份额均增加。本文研究结果可为气溶胶冲刷模型优化提供依据。

不同工况下超疏水表面的凝露特性研究

超疏水表面能减少液滴的附着,减少液滴存在带来的热阻增加,提高空调、发电和海水淡化的效率。本文实验研究了不同冷表面温度(2~8℃)、空气湿度(40%~80%)、倾斜角度(0°~90°)下,超疏水表面冷凝液滴的生长特性,分析不同工况对超疏水表面凝露的影响。结果表明:随着冷表面温度的降低,液滴平均半径和表面液滴覆盖率逐渐增大,冷表面温度越低,液滴生长速率越快;在不同湿度工况下,高湿度下超疏水表面液滴生长较快,但随着时间增加,低湿度下液滴生长半径将超过中高湿度,且低中湿度工况下冷表面液滴覆盖率远小于高湿度;随着倾斜角度增大,液滴临界扫掠半径逐渐减小,垂直表面相比水平表面液滴覆盖率减少42%。

离子风强化水蒸气与液滴捕获数值研究

面向工业雾气排放过程的水回收需求,提出一种将空冷式冷凝与静电除雾过程集成的静电水回收方法,可实现水蒸气与液滴的协同捕获。构建水蒸气冷凝与静电捕雾过程相耦合的数学模型,数值分析离子风强化水蒸气冷凝的机理及静电水回收器的性能。研究表明环境空气侧自然对流换热系数仅为雾气侧对流换热系数的10%,通过针状放电极产生离子风在空气侧形成局部冲击射流,可使空气侧的局部对流换热系数呈脉冲状分布,最大强化幅度约13倍。相比空气侧为自然对流的情况,在空气侧设置7层放电极所产生的离子风可使水蒸气收集效率强化1.5倍。在定义的雾气和空气条件下,静电水回收器的水蒸气和液滴收集效率最高分别可达9.2%和97.7%。

Bcl10 phosphorylation-dependent droplet-like condensation positively regulates DNA virus-induced innate immune signaling

B-cell lymphoma 10(Bcl10) is a scaffolding protein that functions as an upstream regulator of NF-κB signaling by forming a complex with Mucosa-associated lymphoid tissue lymphoma translocation protein 1(Malt1) and CARD-coiled coil protein family. This study showed that Bcl10 was involved in type I interferon(IFN) expression in response to DNA virus infection and that Bcl10-deficient mice were more susceptible to Herpes simplex virus 1(HSV-1) infection than control mice. Mechanistically,DNA virus infection can trigger Bcl10 recruitment to the STING-TBK1 complex, leading to Bcl10 phosphorylation by TBK1.The phosphorylated Bcl10 undergoes droplet-like condensation and forms oligomers, which induce TBK1 phosphorylation and translocation to the perinuclear region. The activated TBK1 phosphorylates IRF3, which induces the expression of type I IFNs.This study elucidates that Bcl10 induces an innate immune response by undergoing droplet-like condensation and participating in signalosome formation downstream of the c GAS-STING pathway.

液滴撞击冷超疏水表面动力学特性分析

采用氟化物改性和喷涂法制备出一种具有边缘效应抗冷凝失效性能的宏观蜂窝结构化超疏水涂层,通过高速摄影和图像处理方法,研究液滴撞击普通光滑铝表面、普通超疏水表面和蜂窝状结构化超疏水表面的撞击过程,获得了接触时间、铺展系数的关系。引入分形维数对凝结液滴生长形貌进行分析,研究结果表明,随着凝结量的增加,超疏水表面形貌越复杂,分形维数越高,液滴撞击后纵向伸展长度越小,液滴最终粘附在超疏水表面。而具有边缘效应的宏观蜂窝结构具有一定的抗冷凝失效性能,并且加速液滴的分裂和在表面的脱离。

Effect of charge on growth of droplets with ionic condensation nuclei

A growth kinetics model of droplets with ionic condensation nuclei based on the chemical potential and the kinetic equation of mass transfer is established. The model is simplified and the effect of charge on droplet growth is examined. The theoretical results show that the critical radius for droplet growth with an ionic condensation nucleus is less than that of those without an ionic nucleus. Furthermore, our results also indicate that if the initial droplet with an ionic nucleus has a radius shorter than the critical radius, the droplet will not vanish, but will reach a steady-state radius. As the ionic charge increases, the critical radius for droplet growth will decrease and the corresponding steady-state droplet radius will increase. In addition we show that once a critical charge is reached, all droplets will grow regardless of initial radius.

蒸汽凝结促进PM2.5长大的研究现状

蒸汽凝结促进PM2.5长大是一项非常有前景的除尘预处理技术。对蒸汽在颗粒物表面凝结过程中晶胚的形成机理和影响因素、影响液滴的长大因素、蒸汽凝结技术的应用进行了总结分析,指出了该项技术目前的发展现状,并提出了今后的发展方向。

石家庄地区雾霾天气下云滴和云凝结核的分布特征

2009年5~10月在石家庄地区对雾霾天气下的近地面到高空的云雾滴和云凝结核（CCN）进行了7架次飞机探测.利用PMS云粒子测量仪器、机载温湿仪和连续气流纵向热梯度云凝结核仪获得的云雾粒子和云凝结核（CCN）探测资料,分析了层积云（Sc）和高积云（Ac）中云粒子浓度、液态含水量、粒子算术平均直径和粒子有效平均直径的垂直分布特征;分析了CCN垂直和水平分布特征以及谱分布.结果表明雾霾天气状况下,云滴数浓度在102个/cm3量级上.高云粒子粒径总体大于低云粒子.云含水量平均值范围为0.03~0.14g/m3;地面到600 m高度内,CCN值的平均值为3034cm-3（过饱和度S=0.3%）.对CCN的活化谱进行拟合表明石家庄属于典型大陆性核谱,云对CCN有消耗作用,逆温层的存在使得该区CCN浓度累积增加.

结霜初期超疏水表面凝结液滴的自跳跃脱落及其对结霜过程的影响

制备了具有微纳复合结构的超疏水表面,对其结霜过程进行了可视化观测,揭示了结霜初期表面凝结液滴的自跳跃行为及其对结霜过程的影响,并与普通表面的结霜过程进行了对比研究.实验结果表明,结霜初期,超疏水表面的凝结液滴频繁出现合并后自跳跃现象,根据液滴合并前的尺寸大小,可将自跳跃行为分为3类,而普通表面未观察到类似现象;液滴自跳跃临界半径随着液固接触面积分数的降低和表面接触角的增大而减小.初始凝结液滴的自跳跃降低了超疏水表面液滴覆盖率和分布密度,同时引起表面霜层生长的不均匀性和霜晶结构的差异.与普通表面相比,超疏水表面可有效抑制结霜,延缓霜层生长速率.

壁面曲率及过冷度对液滴铺展特性的影响

从覆冰类型及危害来看,雨凇对于导线产生的危害是最为严重和致命的。液滴撞击壁面的动力学特性对于相变凝固过程中的热质传递有重要影响,进而影响导线覆冰的特性。通过对比液滴撞击常温及过冷弯曲壁面过程中的液滴行为演变的异同,获得了表面过冷度和曲率大小对液滴铺展行为的影响规律。实验结果表明,随着圆柱曲面曲率的增加,周向上液膜铺展更好,轴向上液膜铺展更差。对于低温壁面上液滴的铺展过程,增加表面的过冷度,液滴的铺展更差,液滴振荡弛豫时间更短,表层液膜结冰速率加快。然而,低温壁面上液滴的铺展好于常温壁面上液滴的铺展,通过分析温度对液滴表面张力和黏性的影响规律,推论在铺展过程中,较低的壁面温度使得液滴底层快速形成了一层冰膜,改变了液固之间的界面能,使得液滴更易于铺展。在液滴回缩阶段,可明显观察到底层结冰的现象。该结论可为导线雨凇结冰提供理论参考。

湿蒸汽两相凝结流动中水滴生长模型研究

为了准确描述湿蒸汽两相流中水滴生长过程,以提高数值模拟的精度和可信度,基于传热传质平衡耦合求解方法提出一种水滴生长模型。将建立的模型与目前湿蒸汽两相流计算中广泛使用的几种水滴生长模型进行了对比分析,结果显示在整个克努森数Kn变化范围内,该模型表现良好,明显优于其他模型,特别是在过渡区内具有很高的精确性。同时为了揭示不同水滴生长模型对两相参数的影响,采用各水滴生长模型对一维拉瓦尔Laval喷管中存在的自发凝结的湿蒸汽流动进行数值模拟。结果表明,不同水滴生长率模型对液相成核率、水滴数、水滴半径的影响非常明显,但对蒸汽湿度影响较小。