这项工作得到了中国 nsf 赠款 (41706033、91752108和 41476167)、Grangdong nsf 赠款 (2017A030313242 和 2016A030311042) 和 LTO 赠款 (LTOZZ1801) 的支持。

1. 工作箱
注: 实验在矩形罐中进行。该油箱包括顶部和底部板和侧壁。顶部和底部板是由铜与电镀表面。在上面的盘子里有一个水室。在底板上插入电加热垫。侧壁由透明有机玻璃制成。油箱大小为 Lx = 257 毫米 (长度), ly = 65 毫米 (宽度) 和 Lz = 257 毫米 (高度)。侧壁厚度为9.5 毫米。
<ol><li>用蒸馏水仔细清洗铜板和有机玻璃侧壁。</li>
	<li>用螺钉装配油箱, 以确保水箱的水密。</li>
	<li>在光学表上设置不锈钢支撑架 (高度为150毫米), 并将罐体上方的隔热板固定在车架上方, 这就限制了工作箱对工作台的散热。</li>
	<li>将三热敏电阻 (温度稳定度为0.01 摄氏度) 插入到每个板中, 并将其连接到数字万用表。注意这些热敏电阻用于监测顶部和底部板的温度。</li>
	<li>将微尺度电导率和温度仪 (MSCTI) 放置在水箱内, 并将其连接到多功能数据采集 (MDA)。将 MSCTI 固定在机动精度转换阶段 (MPTS)。 注: 注意 MSCTI 可由垂直移动上下移动, 从而达到工作液的温度和盐度剖面。在这里, MSCTI 的温度稳定性为0.01 摄氏度, 盐度稳定性为1%。MPTS 的定位精度为0.005 毫米。</li>
	<li>设置数字万用表相应软件程序中的参数和多功能数据采集, 如采样率、数据采集通道和存储路径。在这里, 分别将数字万用表和多功能数据采集的采样率设置为1.0 和128赫兹。</li>
	<li>在 MPTS 软件程序中设置运动参数, 包括初始位置、最低和最高位置、移动速度和加速度 MSCTI。在这里, 设置移动速度和加速度为1毫米/秒和0.5 毫米/秒2, 并设置最低和最高的位置为20和220毫米以上的底部板。这就导致了 404s MPTS 的一个时间段。将 MSCTI 的初始位置设置为最低位置。</li>
	<li>保持室温几乎恒定大约24°c 与二个大功率空调器 (工作力量 3000 W)。</li>
</ol>2. 光学仪器
注: 在试验过程中, 采用皮影技术对直流楼梯的演变进行监测, 符合以下程序
<ol><li>在油箱的外面附上一张追踪纸 (25.7 厘米 x 25.7 厘米)。</li>
	<li>使用窄光束 LED 灯作为光源。将光源约5米远离坦克的另一侧, 使几乎准直的光可以产生。注意, 在实验过程中, 由于流体的密度变化 (对应于折射率的变化), 在跟踪纸上照亮了直流层状流体结构。</li>
	<li>将高速摄像机放在跟踪纸的同一侧。离油箱约1米, 可以记录全尺寸水箱的分层结构。</li>
	<li>设置摄像机的采样速率。请注意, 取样率应该是正确的, 以捕捉楼梯演变的细节。在这里, 摄像机的采样率为25赫兹。</li>
	<li>打开灯和摄像机, 稍微调整他们的药水和距离, 以确保摄像机能捕捉到清晰的图像。</li>
</ol>3. 工作液
<ol><li>在两个水箱里准备盐水和淡水。<ol>
<li>将两个相同的矩形罐 (坦克 A 和坦克 B) 由一个灵活的管 (10 厘米长, 6 毫米内径和10毫米外径) 从底部的每一个。</li>
		<li>用盐水填充罐 A, 其盐的质量浓度 (即盐度) 在本例中为60克/千克。</li>
		<li>将油箱 B 装满相同容积的脱毒气淡水, 并使用电磁搅拌器连续融汇液体。</li>
		<li>保持两个水箱内的初始流体温度与室温相同 (24 摄氏度)。</li>
	</ol>
</li>
	<li>在工作槽内建立线性密度分层。<ol>
<li>采用双罐法29建立了工作箱盐水的初始线性分层。</li>
		<li>将油箱 A 和 B 置于同一高度, 比工作槽高30厘米。加入罐 B 和工作槽与另一软管 (长度50厘米, 2 毫米内径和5毫米外径) 从他们的底部。由于这两个坦克的流体压力差, 坦克 B 中的流体可以慢慢地注入到工作槽中。</li>
		<li>控制流速与蠕动泵在0.45 毫升/秒. 注: 工作箱充水时间约为3小时. 基于29的工作槽底部盐度计算 <img alt="Equation 1" src="/files/ftp_upload/58316/58316eq1.jpg">(1) 其中 Sa、v 和 v0分别为罐 a 的盐度、工作槽的最终液量和罐 a (或 B) 的初始流体体积。利用底部 SB的盐度和顶部的淡水, 初始分层 N0的浮力频率是 <img alt="Equation 2" src="/files/ftp_upload/58316/58316eq2.jpg">(2) 当 g 为引力加速度时, ρ0为参考密度, β为盐度收缩系数。注意在本例中, N0被计算为 1.14 rad/秒。</li>
	</ol>
</li>
</ol>4. 运行实验
<ol><li>设置工作槽的边界条件。<ol>
<li>将顶板的水室与八均匀分布的塑料软管 (长度为150厘米, 内径10毫米, 外径15毫米) 的冷藏循环器连接起来。注意, 顶板的温度取决于冷冻循环器的温度。将顶板的温度设置为与室温相同 (24 °c)。</li>
		<li>将底板内的电热垫连接到直流电源。注意在本实验中为工作流体提供恒定热流, 计算结果为 <img alt="Equation 3" src="/files/ftp_upload/58316/58316eq3.jpg">(3) 其中 U、R 和 A 分别为电热垫所提供的电压、电阻和有效面积。在这个例子中, 电阻和有效面积是44.12 欧姆和 1.89×10-2米2。将所提供的电压设置为 60 V, 使总热流量 F为4317瓦特/米2。</li>
	</ol>
</li>
	<li>打开摄像机以记录流模式。</li>
	<li>打开数字万用表, 多功能数据采集, 以监测顶底板和底部板的温度, 以及使用 MSCTI 的液体的温度和盐度。</li>
	<li>打开 MPTS 移动 MSCTI, 以达到工作流体的温度和盐度剖面。</li>
	<li>打开冷冻循环器和直流电源, 实现工作液的上、下边界条件。 注: 请注意, 整个实验将体验到直流楼梯的产生、发展、融合和消失, 并将持续约5小时。在所有 DC 楼梯消失后, 依次关闭直流电源、冷冻循环器、MPTS、数字万用表、多功能数据采集和摄像机。</li>
</ol>5. 数据处理
<ol><li>皮影图像<ol>
<li>使用 Matlab 程序将摄像机录制的视频转换为连续图像, 以便进一步分析。调整这些图像, 以强调坦克内的流动模式。将数字图像强度设置为 I (x、z), 其中 (x、z) 表示与图像左下角的原点的水平和垂直坐标。注 I (x, z) 变化 (0, 1), 灰度为256。将背景图像正常化为30的图像 <img alt="Equation 4" src="/files/ftp_upload/58316/58316eq4.jpg">(4) 在<img alt="Equation 5" src="/files/ftp_upload/58316/58316eq5.jpg">应用冷却和加热之前, 平均图像强度在10以上的图像中, <img alt="Equation 6" src="/files/ftp_upload/58316/58316eq6.jpg">是指图像的强度.这样, 图像中的固定缺陷就可以被删除。为了研究直流模式的时间演化, 通过计算图像强度波动 (即强度的根均方根), 可以将<img alt="Equation 7" src="/files/ftp_upload/58316/58316eq7.jpg">每个图像转换为单个垂直强度涨落剖面, 并沿水平方向<img alt="Equation 7" src="/files/ftp_upload/58316/58316eq7.jpg"> </img>。绘制连续图像的强度<img alt="Equation 7" src="/files/ftp_upload/58316/58316eq7.jpg">起伏剖面, 随着时间的推移显示直流楼梯的演变。</li>
	</ol>
</li>
	<li>温度和盐度剖面<ol>
<li>注意在本实验中, 通过上下运动 MSCTI 测量工作液的温度和盐度的垂直剖面。计算 MSCTI 的时间高度、h (t)、平均运动速度 w、时间 t、起始时间 t0 (对应于最低位置)、最低位置 hL和最高位置 hh, 作为 <img alt="Equation 8" src="/files/ftp_upload/58316/58316eq8.jpg">(5) <img alt="Equation 9" src="/files/ftp_upload/58316/58316eq9.jpg"> MSCTI 移动周期从最低 (最高) 到最高 (最低) 位置, n 和δ分别是积分和小数部分。然后计算时间高度 h (t) 作为 <img alt="Equation 10" src="/files/ftp_upload/58316/58316eq10.jpg">(6) 注在等式 (6), 如果 n 甚而, MSCTI 移动;否则, MSCTI 就会向下移动。以高度 h (t) 为依据, 绘制时间序列温度 t (t) 和盐度 S (t), 得到垂直温度和盐度剖面。</li>
	</ol>
</li>
</ol>

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Q., Ahlers, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatiotemporal+chaos+in+electroconvection+of+a+homeotropically+aligned+nematic+liquid+crystal.">Spatiotemporal chaos in electroconvection of a homeotropically aligned nematic liquid crystal.</a> Physical Review E. 74 (4), 046212 (2006).</li></ol>

作者没有什么可透露的。

本文介绍了一种用于模拟矩形储罐环流直流楼梯结构的详细实验协议。采用双槽法构造了工作液的初始线性密度分层。顶板保持在恒定的温度和底部一个在恒定的热流。采用皮影技术, 对直流楼梯的产生、发展、融合、消失等全过程进行了可视化处理, 用高精度探针记录了温度和盐度的变化。通过这些测量, 不仅可以定性地观察楼梯的变化, 还能定量分析温度、盐度和密度的变化。此外,在原位</e...

双扩散对流 (DDC) 是最重要的垂直混合过程之一。当分层水柱的垂直密度分布受两个或多个相反方向的标量分量梯度控制时, 其成分具有明显的不同的分子管内1。它广泛发生在海洋学2, 大气3, 地质学4, 天体物理学5, 材料科学6, 冶金7, 和建筑工程8。DDC 在全球海洋中几乎有一半存在, 对海洋多尺度过程乃至气候变化有重要影响9。
DDC 有两种主要模式: 盐指 (SF) 和扩散对流 (DC)。SF 发生时, 当一个温暖, 咸水大量覆盖冷却器, 新鲜的水在分层的环境。当温暖和咸水位于寒冷和淡水之下, DC 将形成。DC 的显著特征是温度、盐度和密度的垂直剖面是阶梯状的, 由交替的均匀对流层和薄的、强烈的分层界面组成。DC 主要发生在高纬度海域和一些内部盐湖, 如北极和南极海、鄂霍次克海、红海和非洲基伍湖10。在北冰洋, 有盆宽和持续的 DC 楼梯在上部和深海11,12。它对全密度在大洋中的混合具有重要的影响, 并可能对冰的融化产生显著影响, 这在13的海洋学界引起了越来越多的关注。
直流楼梯结构最早在 1969年14在北冰洋被发现。之后, Padman & 迪伦15, Timmermans等。11、Sirevaag &16、周 & 路12、和al。17、Bebieva & Timmermans18、Shibley 等。19测量了北冰洋不同盆地的直流楼梯, 包括对流层和界面的垂直和水平尺度、楼梯的深度和总厚度、垂直传热、直流过程中尺度涡和阶梯结构的时空变化。施密德等。20和索默等。21用基伍湖中的显微组织探查器观察了直流楼梯。报告了直流输电的主要结构特点和热流, 并与现有的参数公式进行了比较。随着计算机处理速度的提高, 最近对 DC 进行了数值模拟, 以检验界面结构和不稳定性, 通过接口进行传热, 层合并事件等22,23,24。
野外观测大大提高了海洋学家对海洋 DC 的认识, 但由于不确定的海洋水流环境和仪器, 测量受到了强烈的限制。例如, DC 接口的垂直尺度非常小, 在一些湖泊和海洋中的比例小于0.1 米,需要一些特殊的高分辨率仪器。实验表明, 它在探索直流电的基本动力和热力学规律方面具有独特的优越性。通过实验室实验, 可以观察直流楼梯的演变, 测量温度和盐度, 并提出26、27大洋应用的一些参数。此外, 在实验室实验中, 受控参数和条件根据需要随时进行调整。例如, 特纳在1965年首次模拟了实验室中的直流楼梯, 并提出了跨扩散界面的传热参数化, 这在原位海洋观测中经常得到更新和广泛应用28.
本文介绍了一个详细的实验协议, 用于模拟直流楼梯的演化过程, 包括从下面加热的分层盐水的产生、发展和消失。温度和盐度由微尺度仪和皮影技术监测的直流楼梯测量。详细介绍了实验装置、进化过程、数据分析和结果讨论。通过改变初始条件和边界条件, 本实验设置和方法可用于模拟其它海洋现象, 如海洋水平对流、深海热液喷发、表层混合层加深、海底地热的海洋环流等。

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evolution of staircase structures in diffusive convection

扩散对流 (DC) 发生在垂直分层密度由两个对立的标量梯度控制, 具有明显不同的分子管内, 和更大和更小的扩散率标量梯度有负和正密度分布的贡献, 分别。DC 发生在许多自然过程和工程学应用, 例如, 海洋学, 天体物理学并且冶金学。在海洋中, DC 最显著的特征之一是垂直温度和盐度剖面是阶梯状结构, 由连续的台阶组成, 具有厚的均匀对流层和相对稀薄和高梯度的界面。在许多海洋中, 特别是在北极和南极海洋中观察到了 DC 楼梯, 并在海洋环流和气候变化方面发挥了重要作用。在北冰洋, 上层和深海存在盆宽和持续的直流楼梯。直流过程对全密度在上层海洋中的混合具有重要影响, 并可能对地表融冰产生显著影响。与现场观测的局限性相比, 实验室实验表明, 通过严格调整边界条件和受控参数, 可以有效地检测 DC 的动态和热力过程, 具有独特的优越性。本文详细介绍了一种用分层盐水填充的矩形储罐中直流楼梯结构的演化过程, 包括其产生、发展和消失。详细介绍了实验装置、进化过程、数据分析和结果讨论。

图 1显示了实验设置的示意图。协议中描述了它的组成部分。主要部件如图 1a所示, 详细的工作槽如图 1b所示。图 2显示了底部的温度变化 (tb, 红色曲线) 和顶部 (tt, 黑色曲线) 板块。结果表明, 两个板块的温度与室温 (24 °c) 基本相同。在 t = 641s, 顶部冷却和底部加热被应用。然后, tb开...

Watch this Scientific Journal Video about Evolution of Staircase Structures in Diffusive Convection at JoVE.com

Evolution of Staircase Structures in Diffusive Convection

扩散对流 (DC) 广泛地发生在自然过程和工程应用中, 其特征是一系列具有均匀对流层和分层界面的楼梯。本文用实验的方法模拟了直流楼梯结构的演化过程, 包括矩形储罐的产生、发展和消失。

扩散对流中阶梯结构的演化

Diffusive convection (DC) occurs when the vertical stratified density is controlled by two opposing scalar gradients that have distinctly different ...

evolution-of-staircase-structures-in-diffusive-convection

Research

JoVE Journal

Environment

6.4K 次观看.  Chinese Academy of Sciences. 扩散对流 (DC) 广泛地发生在自然过程和工程应用中, 其特征是一系列具有均匀对流层和分层界面的楼梯。本文用实验的方法模拟了直流楼梯结构的演化过程, 包括矩形储罐的产生、发展和消失。

视频: Evolution of Staircase Structures in Diffusive Convection

Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed that, under the proper conditions, ice can be produced when water is introduced to a bath of cold brine. To make ice form, in addition to having the brine and water mix, the rate of heat transfer must bypass that of mass transfer. When water is introduced in the form of tiny droplets to the brine surface, the mode of heat and mass transfer is by diffusion. The buoyancy stops water from mixing with the brine underneath, but as the ice grows thicker, it slows down the rate of heat transfer, making ice more difficult to grow as a result. When water is introduced inside the brine in the form of a flow, a number of factors are found to influence how much ice can form. Brine temperature and concentration, which are the driving forces of heat and mass transfer, respectively, can affect the water-to-ice conversion ratio; lower bath temperatures and brine concentrations encourage more ice to form. The flow rheology, which can directly affect both the heat and mass transfer coefficients, is also a key factor. In addition, the flow rheology changes the area of contact of the flow with the bulk fluid.

Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

冰生成和传热传质现象将水引入到盐水冷水浴

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed ...

科研

工程学

Magnetically Induced Rotating Rayleigh-Taylor Instability

Classical techniques for investigating the Rayleigh-Taylor instability include using compressed gasses1, rocketry2 or linear electric motors3 to reverse the effective direction of gravity, and accelerate the lighter fluid toward the denser fluid. Other authorse.g. 4,5,6 have separated a gravitationally unstable stratification with a barrier that is removed to initiate the flow. However, the parabolic initial interface in the case of a rotating stratification imposes significant technical difficulties experimentally. We wish to be able to spin-up the stratification into solid-body rotation and only then initiate the flow in order to investigate the effects of rotation upon the Rayleigh-Taylor instability. The approach we have adopted here is to use the magnetic field of a superconducting magnet to manipulate the effective weight of the two liquids to initiate the flow. We create a gravitationally stable two-layer stratification using standard flotation techniques. The upper layer is less dense than the lower layer and so the system is Rayleigh-Taylor stable. This stratification is then spun-up until both layers are in solid-body rotation and a parabolic interface is observed. These experiments use fluids with low magnetic susceptibility, |&#967;| ~ 10-6 - 10-5, compared to a ferrofluids. The dominant effect of the magnetic field applies a body-force to each layer changing the effective weight. The upper layer is weakly paramagnetic while the lower layer is weakly diamagnetic. When the magnetic field is applied, the lower layer is repelled from the magnet while the upper layer is attracted towards the magnet. A Rayleigh-Taylor instability is achieved with application of a high gradient magnetic field. We further observed that increasing the dynamic viscosity of the fluid in each layer, increases the length-scale of the instability.

We present a protocol for preparing a two-layer density-stratified liquid that can be spun-up into solid body rotation and subsequently induced into Rayleigh-Taylor instability by applying a gradient magnetic field.

磁感应旋转瑞利 - 泰勒不稳定性

Classical techniques for investigating the Rayleigh-Taylor instability include using compressed gasses1, rocketry2 or linear electric motors3 to reverse ...

Experimental Investigation of Secondary Flow Structures Downstream of a Model Type IV Stent Failure in a 180&#176; Curved Artery Test Section

The arterial network in the human vasculature comprises of ubiquitously present blood vessels with complex geometries (branches, curvatures and tortuosity). Secondary flow structures are vortical flow patterns that occur in curved arteries due to the combined action of centrifugal forces, adverse pressure gradients and inflow characteristics. Such flow morphologies are greatly affected by pulsatility and multiple harmonics of physiological inflow conditions and vary greatly in size-strength-shape characteristics compared to non-physiological (steady and oscillatory) flows 1 - 7.
Secondary flow structures may ultimately influence the wall shear stress and exposure time of blood-borne particles toward progression of atherosclerosis, restenosis, sensitization of platelets and thrombosis 4 - 6, 8 - 13. Therefore, the ability to detect and characterize these structures under laboratory-controlled conditions is precursor to further clinical investigations.
A common surgical treatment to atherosclerosis is stent implantation, to open up stenosed arteries for unobstructed blood flow. But the concomitant flow perturbations due to stent installations result in multi-scale secondary flow morphologies 4 - 6. Progressively higher order complexities such as asymmetry and loss in coherence can be induced by ensuing stent failures vis-&#224;-vis those under unperturbed flows 5. These stent failures have been classified as &#34;Types I-to-IV&#34; based on failure considerations and clinical severity 14.
This study presents a protocol for the experimental investigation of the complex secondary flow structures due to complete transverse stent fracture and linear displacement of fractured parts (&#34;Type IV&#34;) in a curved artery model. The experimental method involves the implementation of particle image velocimetry (2C-2D PIV) techniques with an archetypal carotid artery inflow waveform, a refractive index matched blood-analog working fluid for phase-averaged measurements 15 - 18. Quantitative identification of secondary flow structures was achieved using concepts of flow physics, critical point theory and a novel wavelet transform algorithm applied to experimental PIV data 5, 6, 19 - 26.

Stent implants in stenosed arterial curvatures are prone to "Type IV" failures involving the complete transverse fracture of stents and linear displacement of the fractured parts. We present a protocol for detection of secondary flow (vortical) structures in a curved artery model, downstream of clinically relevant "Type IV" stent failures.

在180°弧形动脉试验段的二次流动结构下游的型号IV型支架失败的实验研究

The arterial network in the human vasculature comprises of ubiquitously present blood vessels with complex geometries (branches, curvatures and ...

生物工程

The Diffusion of Passive Tracers in Laminar Shear Flow

A simple method to experimentally observe and measure the dispersion of a passive tracer in a laminar fluid flow is described. The method consists of first injecting fluorescent dye directly into a pipe filled with distilled water and allowing it to diffuse across the cross-section of the pipe to obtain a uniformly distributed initial condition. Following this period, the laminar flow is activated with a programmable syringe pump to observe the competition of advection and diffusion of the tracer through the pipe. Asymmetries in the tracer distribution are studied and correlations between the pipe cross-section and the shape of the distribution is shown: thin channels (aspect ratio &#60;&#60; 1) produce tracers arriving with sharp fronts and tapering tails (front-loaded distributions), while thick channels (aspect ratio ~1) present the opposite behavior (back-loaded distributions). The experimental procedure is applied to capillary tubes of various geometries and is particularly relevant to microfluidic applications by dynamical similarity.

A protocol for the study of the diffusion of passive tracers in laminar pressure-driven flow is presented. The procedure is applicable to various capillary pipe geometries.

无源示踪剂在层流剪切流中的扩散

A simple method to experimentally observe and measure the dispersion of a passive tracer in a laminar fluid flow is described. The method consists of ...

Simulation of Early Earth Hydrothermal Chimneys in a Thermal Gradient Environment

Deep sea hydrothermal vents are self-organizing precipitates generated from geochemical disequilibria and have been proposed as a possible setting for the emergence of life. The growth of hydrothermal chimneys in a thermal gradient environment within an early Earth vent system was successfully simulated by using different hydrothermal simulants, such as sodium sulfide, which were injected into an early Earth ocean simulant containing dissolved ferrous iron. Moreover, an apparatus was developed to sufficiently cool the ocean simulant to near 0 &#176;C in a condenser vessel immersed in a cold water bath while injecting a sulfide solution at hot to room temperatures, effectively creating an artificial chimney structure in a temperature gradient environment over a period of a few hours. Such experiments with different chemistries and variable temperature&#160;gradients resulted in a variety of morphologies in the chimney structure. The use of ocean and hydrothermal fluid simulants at room temperature resulted in vertical chimneys, whereas the combination of a hot hydrothermal fluid and cold ocean simulant inhibited the formation of robust chimney structures. The customizable 3D printed condenser created for this study acts as a jacketed reaction vessel that can be easily modified and used by different researchers. It will allow the careful control of injection rate and chemical composition of vent and ocean simulants, which should help accurately simulate prebiotic reactions in chimney systems with thermal gradients similar to those of natural systems.

The goal of this protocol is to form simulated hydrothermal chimneys via chemical garden injection experiments and introduce a thermal gradient across the inorganic precipitate membrane, using a 3D printable condenser that can be reproduced for educational purposes.

热梯度环境中早期地球热液烟囱的模拟

Deep sea hydrothermal vents are self-organizing precipitates generated from geochemical disequilibria and have been proposed as a possible setting for the ...

环境科学

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

可缩放邮票印刷及不堪砌面的制作

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

Thermocapillary Convection Space Experiment on the SJ-10 Recoverable Satellite

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary convection in an annular liquid pool is one of the 19 scientific experimental projects on the SJ-10 recoverable satellite. Presented is a design for a payload for space experimental study on thermocapillary convection that includes the experimental model, measurement system, and control system. The specifics for the construction of an experimental model of an annular liquid pool with variable volume ratios is provided. The fluid temperatures are recorded by six thermocouples with a high sensitivity of 0.05 &#176;C at different points. The temperature distributions on the liquid free surface are captured by means of an infrared thermal camera. The free surface deformation is detected by a displacement sensor with a high accuracy of 1 &#181;m. The experimental process is fully automated. The research is focused on thermocapillary oscillation phenomena on the liquid-free surface and convective pattern transitions through analyses of experimental data and images. This research will be helpful to understand the mechanism of thermocapillary convection and will offer further insights into the nonlinear characteristics, flow instability, and bifurcation transitions of thermocapillary convection.

A protocol for the space payload design, the space experiment on thermocapillary convection, and analyses of experimental data and images are presented in this paper.

SJ-10可回收卫星的热印对流空间实验

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary ...

Preparation of Free-Surface Hyperbolic Water Vortices

Free surface vortices are present in industry in flow regulation, energy dissipation, and energy generation. Although investigated extensively, detailed experimental data regarding free surface vortices are lacking, particularly regarding the turbulence at the interface. The present paper reports on a special type of free surface vortex first proposed by Walter Schauberger in the 1960s that has an oxygen volumetric mass transfer coefficient exceeding the value of similar systems. This special type of vortex forms in a hyperbolic funnel. Different stable regimes can be stabilized with different hydraulic characteristics. Other advantages of this technology are its energy efficiency, simple design, and scalability. The flow in this hyperbolic funnel is characterized by strong turbulence and an increased surface area of the air-water interface. The local pressure strongly varies along the surface, resulting in a pronounced wavey air-water boundary layer. Due to the helical flow, these perturbations move inward, pulling the boundary layer with them. The resultant pressure gradient draws a certain air volume into the water vortex. The construction of the basic hyperbolic funnel setup and operational examples, including high-speed visualization for three different stable regimes, are presented in this work.

This paper describes how three different water vortex regimes in a hyperbolic Schauberger funnel can be created, their most important characteristics, and how associated parameters such as the oxygen transfer rates can be calculated.

自由表面双曲水涡的制备

Free surface vortices are present in industry in flow regulation, energy dissipation, and energy generation. Although investigated extensively, detailed ...

Flow Visualization in a Water Tunnel: Observing the Leading-edge Vortex Over a Delta Wing

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The delta wing, shown in Figure 1D, is a popular design in high-speed airplanes due to its superb performance in transonic and supersonic flight regimes. This type of wing has a small aspect ratio and high sweep angle, which reduces drag at high subsonic, transonic and supersonic flight regimes. The aspect ratio is defined as the wing span divided by the average chord <img align="middle" src="/files/ftp_upload/10459/10459eq1a.jpg" />.
An important advantage of the delta wing is its high stall angle. The stall of a delta wing is delayed compared to the stall of a high aspect ratio wing. This is because the lift of a delta wing is enhanced by the leading-edge vortex over the wing.
An effective way to observe this vortex flow phenomenon and study the vortex breakdown in a delta wing is by visualizing the flow in a water tunnel. By injecting dye in the flow surrounding a model from dye ports on the leading-edge, the vortex development and breakdown can be observed and its position measured. The data can also be used to estimate the stall angle.
<img src="/files/ftp_upload/10459/10459fig1.jpg" />
Figure 1. Typical wing planform shapes: A) Rectangular, with constant chord along span, B) elliptical, C) tapered, with variable chord along the span, and D) delta wing, an aft-swept wing with zero taper ratio.

Flow in a Water Tunnel: Leading-edge Vortex over a Delta Wing

水隧道中的流量可视化:在三角洲翼上观察前沿涡流

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The ...

教育

JoVE Science Education

航空工程

Steady, Laminar Flow Between Parallel Plates

Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
Considering two horizontal plates aligned along the x-axis and spaced a distance &#39;2h&#39; apart, with the y-axis perpendicular to the plates, fluid motion is assumed to be parallel. Here, the continuity equation indicates no change in velocity along the x-axis, and the Navier-Stokes equations reduce as follows:
<img alt="Equation 1" src="/files/ftp_upload/18063/18063_Equation_1.svg" style="text-align: center; height: 30px;" />
The equations in the y and z directions show no pressure gradient along these axes, indicating that pressure varies hydrostatically in the y-direction, allowing integration to yield:
<img alt="Equation 2" src="/files/ftp_upload/18063/18063_Equation_2.svg" style="text-align: center; height: 12px;" />
For parallel plates with a pressure gradient along the x-axis, the equation simplifies:
<img alt="Equation 3" src="/files/ftp_upload/18063/18063_Equation_3.svg" style="text-align: center; height: 30px;" />
By integrating twice and applying boundary conditions (u = 0 at y = +h and y = -h), we obtain:
<img alt="Equation 4" src="/files/ftp_upload/18063/18063_Equation_4.svg" style="text-align: center; height: 30px;" />
This expression reveals that the velocity profile across the gap between the plates is parabolic, with maximum velocity at y = 0, midway between the plates. The volumetric flow rate through a unit width of the plates is obtained by integrating the velocity profile across the gap.
Understanding laminar flow between parallel plates has practical applications in groundwater flow, wastewater treatment, and lubrication. For instance, this model can approximate flow in soil layers, where water moves between soil particles like flow between plates. Knowing the flow rate and velocity distribution helps engineers design efficient drainage systems and predict groundwater movement.

平行板之间的稳定层流

Steady, laminar flow between two parallel plates describes fluid movement in a narrow, confined channel, often used to model simple fluid systems.
For ...