Name: film control to study contributions of waves to droplet impact dynamics on thin flowing liquid films
Uploaded: 2018-08-18T13:00:00.000+00:00
Duration: 7 min 8 s
Description: Watch this Scientific Journal Video about Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films at JoVE.com

这项工作是由石油技术发展基金 (尼日利亚 PTDF) 和英国工程和自然科学研究理事会 (赠款编号 EP/K003976/1) 赞助的。作者还感谢 Zhizhao 博士的卓有成效的讨论。

1. 实验台安装
注: 见图 1。
<ol><li>
降膜单元
	<ol>
<li>首先用干净的软布清洁基板 (玻璃) 表面。确保不粘附在其表面上的污垢, 这将改变液体的性质。</li>
		<li>将玻璃基底的枢轴设置为所需倾角。在这项工作中使用了一个倾斜角, β, 15˚。</li>
		<li>打开电泵, 确保薄膜表面有正常的液体流动, 进一步清洁玻璃基体。对于这项工作, 测试液是去离子水。</li>
		<li>确保承印物的整个表面被润湿。</li>
		<li>使用流量计测量胶片流量。对于这项工作, 流量是不同的 1.667 x 10-3和 10 x 10-3 m3/秒与相应的胶片雷诺数,再 = ρq/wµ, 范围在55.5 和333之间。w是下落的影片宽度, 0.30 m。</li>
		<li>逐步调整流量连接上的阀门, 以获得所需的玻璃基板的流量。</li>
		<li>在胶片入口调整一组千分尺步骤, 以对应的努塞尔膜厚度值为所选流速, 避免在胶片进气道上进行水力跳跃或将空气回流到配电室。</li>
		<li>手动虹吸分配室中的所有空气, 以获得在薄膜表面下游的均匀流。</li>
	</ol>
</li>
	<li>
胶片控制单元
	<ol>
<li>通过数据采集卡 (DAC) 确保功能发生器通过非闭锁中继连接到电磁阀。</li>
		<li>开关电磁阀和功能发生器。</li>
		<li>将函数生成器设置为所需的强制频率。在这项工作中, 使用了2和 3 Hz 的频率。</li>
		<li>选择所需的波形信号 (正弦波、锯齿波、方波等) 。在这项工作中, 使用了正弦波信号。图 2A和2B显示了控制膜与受控薄膜的对比度。</li>
	</ol>
</li>
	<li>
液滴生成系统
	<ol>
<li>把一个干净的塑料油管连接到充水的注射器上。</li>
		<li>将注射器插入液滴发生器中。</li>
		<li>将所选尺寸的注射器针 (取决于所需的水滴直径) 粘贴到塑料管材的另一端。研究的雾滴直径范围介于0.0023 到0.0044 米之间。</li>
		<li>调整薄膜表面上方的跌落高度。在这项工作中, 下落的下落高度从0.005 到 0.45 m 是不同的, 给冲击速度在0.30 里-0.02-2.96 @ 0.06 米/s 之间。</li>
		<li>同样, 设置从胶片入口滴的流向冲击点。这在这项工作中设置为0.3 米, 以确保波浪在撞击之前形成良好的波形。</li>
		<li>设置注射器泵所需的流量。</li>
		<li>调整流量以达到比薄膜表面形成的波的波长大的雾滴产生频率;确保水滴连续撞击受控薄膜的不同区域。见图 2C;随着图 2D中奇异波形的增大, 显示出每个区域19、20下的流剖面上的不同之处在。</li>
	</ol>
</li>
	<li>
高速成像设置
	<ol>
<li>将相机放在三脚架架上 (或任何其他合适的安排)。</li>
		<li>选择需要焦距的宏透镜并将其连接到照相机。</li>
		<li>打开高速摄像机, 确保直接聚焦在胶片表面上。将相机与7˚和12˚的水平和垂直偏差分别对准胶片表面。这给出了影响过程的极好的侧面视图图像, 从而分别在流向和展方向上产生了67.5 µm/像素和46.6 µm/像素的分辨率。</li>
		<li>使用精确放置在液滴撞击点上的校准项, 调整相机透镜 (最大光圈) 的焦距。</li>
		<li>一旦获得了尖锐的焦点, 减少光圈, 以确保只有少量的光线进入相机。</li>
		<li>设置高速相机所需的帧速率、分辨率和快门速度。本工作采用帧速率为 5000 fps, 800 x 600 分辨率, 孔径 1/16, 快门速度为1µs。</li>
		<li>将光扩散器放在光源的前面, 如图 1C所示, 以确保光线在成像区域内均匀扩散。</li>
		<li>电源上的光源, 以确认均匀传播光在成像区域。</li>
	</ol>
</li>
</ol>2. 校准
注: 见图 3。
<ol><li>把尺子放在胶片的流动方向上 (正好在撞击现场), 并获得胶片表面上测量点的快照。</li>
	<li>重复 2.1, 但与统治者在展方向。</li>
	<li>使用上面的空间分辨率来获取胶片表面。</li>
</ol>3. 视频记录和数据采集
<ol><li>一旦在钻机上建立了薄膜流, 启动注射器泵并观察滴水滴对薄膜表面的影响。</li>
	<li>启动函数发生器, 观察薄膜表面 spatiotemporally 规则波的产生。</li>
	<li>确保连续水滴对受控薄膜表面的不同区域产生影响。</li>
	<li>观察触发后的帧数, 并将其设置为视频长度的大约一半, 以充分捕捉影响。</li>
	<li>电源上的光源, 并触发图像捕获一旦影响发生。</li>
	<li>一旦图像捕获完成, 就关闭光源电源, 以避免液体膜过热。</li>
	<li>在计算机屏幕上直观地分析获得的快照。检查是否在平面薄膜、毛细管波或波浪驼峰区域中发生了撞击。</li>
	<li>将视频修剪到显示影响过程的部分, 并将帧范围保存为视频/图像格式。</li>
	<li>重复 3.5-3.8, 记录个人对胶片表面上所有区域的影响, 即孤立的驼峰、毛细管波和平板薄膜。</li>
</ol>4. 图像后处理和分析
<ol><li>将标尺放在视图字段中, 计算空间分辨率, 方法是计算1厘米的像素大小. 使用标定图像, 获得图像尺寸测量的比例因子。</li>
	<li>将撞击过程的结果与高速图像的不同撞击区域进行比较。检查以看到显著的差异。</li>
	<li>采用合适的 MATLAB 图像处理程序, 测量冲击过程产品的特性特征: 即在飞溅模式下, 测量树冠高度、直径、壁厚、倾角、顶面方向、数量和尺寸喷射二次滴的分布。</li>
	<li>对低韦伯的影响进行类似的定量分析, 如4.3。从时间帧图像中计算出卫星下落的时间, 测量二次滴下的部分聚结中形成的柱的先端长度和宽度。测量被弹出的二次水滴的大小。计算重复的收缩过程中的级联数。</li>
	<li>观察每个区域的质量差异。</li>
</ol>

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作者没有什么要申报的。

在本节中, 我们提供了一些必要的提示, 以确保从协议中获得质量结果。首先, 必须保持液体膜流动的玻璃基片完全无污垢, 以确保液膜的性能保持不折不扣。这是可以实现的定期清洁 (可能使用适当的洗涤剂, 并擦过托盘, 以避免溶解进入系统)。同样地, 在试验过的几回合后, 应定期更换整个试验液, 以保证准确的结果。
其次, 流体分配室必须良好的啮合, 并保持气密, 以确保出水液膜是均匀的。这可以通过手动将空气从配电箱中抽取出来, 然后再进行实验。还建议在胶片进气口使用千分尺步骤, 将胶片入口的间隙高度设置为在相应雷诺数努塞尔估计的胶片流的精确胶片厚度。这将防止水力跳跃或回流在入口。
电磁阀的操作也必须始终进行正确的检查和确定。这是因为需要一个适当的脉动的流量, 以确保生产的强迫波。这可以从正常点击的电磁阀的声音, 以及感知脉动沿连接管道。液体流量进入注射器泵也必须小心设置, 以确保水滴被弹出的方式, 避免任何前加速度下降之前。
必须确保高速相机的适当校准, 以获得非常准确的结果。考虑到景深、曝光时间和整体图像亮度等参数, 还必须仔细选择孔径大小。对于在视频录制过程中触发的摄像头, 用户还需要估计在触发前应该记录多少帧。这可能与个人不同, 这取决于下落影响时间, 因此, 建议在实际测量之前进行几次练习试验。同样, 光源必须正确排列和扩散, 以最小化图像中的阴影。
重要的是要注意和记住, 研究的主要焦点是波浪对下落下落的冲击动力学的贡献, 因此规则波浪结构的形成是对基础物理的精确研究的必要。在观测到波浪结构迅速过渡到三维结构的情况下, 建议将基底倾角减小14,19 , 以促进波浪结构的缓慢过渡。.
在没有测量装置的情况下, 观察到在每个撞击区域的实际瞬时膜厚度时, 该技术的一个局限性。这将提供关于整个观察到的现象的更多细节。
总之, 本报告概述的程序也可以用来研究简单的波演化动力学, 而所描述的高速成像系统可以应用到许多研究领域的快速动力学, 如液滴分解21,22/聚结23, 颗粒射流24,等重要现象在微观时间刻度上观察到。

水滴撞击是自然界中非常常见的现象, 吸引了好奇的观察者1的注意。它是一个活跃的研究领域, 因为它的许多应用, 包括喷雾冷却, 防火, 喷墨打印, 喷涂, 在印制电路板上的焊点沉积, 内燃机的设计,表面清洗和细胞印刷2。它的应用也延伸到农业,例如喷洒灌溉和作物喷洒3,4。创业的工作可以追溯到 19世纪, 与沃灵顿5的工作, 而主要的进展是最近才作出的, 因为出现了高速成像6。从那时起, 进行了几项研究;使用不同类型的撞击面, 从固体7,8, 浅,9和深液池10,11到薄膜12,13。
然而, 尽管大量的研究液滴撞击液体表面 (即浅和深池和淡静膜), 对流动薄液膜的影响没有得到重视。此外, 迄今为止, 研究忽略了波浪空间结构对水滴撞击动力学的贡献。
在本报告中, 我们提出了一个详细的实验程序, 以研究液滴冲击过程的流动薄膜, 其动力学受进口强迫的液体流速;下面, 我们把它们称为 "受控" 的电影。我们发现, 这些在多相工业中有许多应用 (例如,在冷却塔, 精馏塔, 以及在两相流中观察到的环状流系统), 尤其是薄膜控制已经成为在许多过程工业中强化传热和传质14。感兴趣的读者被提到我们以前的工作15 , 更多的细节, 我们的研究成果, 在这方面。
这一应用的频率振荡的入口流量产生的规则波在薄膜表面的形成。我们专注于孤立波家庭, 它的特点是广泛分离的窄峰, 前面是一系列前运行的毛细管波16,17,18。我们研究了与孤波结构的三主要部分有关的影响的结果: "平板薄膜"、"波浪驼峰" 和前运行的 "毛细管波" 区域。我们还将这些结果与不受控制的流动薄膜相比较。结果表明, 在不受控薄膜上的波出现的随机性质明显地影响了水滴撞击的结果, 而控制膜的分离区域也显示出新的机制, 我们在定性和定量。
在前15篇论文中, 采用相同的程序, 研究了膜控制对溅淋体系中液滴冲击动力学的影响。所得结果表明, 在冠层形态 (高度、直径、壁厚、倾角和方向) 上的数量和质量差异, 以及喷射二次滴的数量和大小分布。
在本报告中, 我们描述了设计的设置, 以了解这些空间结构在液滴撞击动力学中所起的关键作用, 同时也提供了我们的研究结果的简明细节, 不仅在飞溅的机制, 也为其他结果的水滴冲击 (即弹跳, 滑动, 部分/总接合)。按照下面描述的标准协议, 薄膜控制对液滴撞击动力学的影响可以以可重现的方式进行研究。

<table><tbody><tr><td>Function generator</td><td>GW INSTEK</td><td>AFG 2005 Series, Digital. Geo0852266</td><td>Produces a varied type of wave signals, ranging from sine, square to saw-tooth wave at different frequencies (0.1 Hz - 5 MHz).</td></tr><tr><td>Syringe pump</td><td>Braintree Scientific Inc.</td><td>Bs-8000 /225540</td><td></td></tr><tr><td>Solenoid valve</td><td>SMC-VXD</td><td>2142A.&lt;br/&gt; 0AE-5001</td><td>Series-pilot-operated-two-port</td></tr><tr><td>Relay</td><td>Takamisara</td><td>A5W-K.&lt;br/&gt; 154424C-03L</td><td></td></tr><tr><td>Electric pump</td><td>Clarke SP</td><td>SPE1200SS 1</td><td></td></tr><tr><td>Flow meter</td><td>RS Component</td><td>CYNERGY3 UF25B 14011600040110</td><td>Measurement range: 0.2-25 L/min</td></tr><tr><td>Micrometer step</td><td>RS Component</td><td>Micrometer Head</td><td>0.01 mm/0 -13 mm</td></tr><tr><td>High-speed camera</td><td>Olympus</td><td>I-SPEED 3.</td><td>Capable of recording at up to 100, 000 frames per second.</td></tr><tr><td>Light source</td><td>TLC Electrical supplies</td><td>IP54 -black</td><td>Double enclosed halogen floodlight. Rating 500 W.</td></tr><tr><td>Light diffusor</td><td>OptiGraphix</td><td>DFPMET</td><td>250 &amp;mu;m thickness</td></tr><tr><td>Glass substrate</td><td>Instrument Glasses Ltd</td><td>Soda Lime Float Glass; 570 mm x 300 mm x 4 mm</td><td>Flatness tolerance 0.02/0.04.</td></tr><tr><td>Macro-lenses</td><td>(a) Nikon&lt;br/&gt; (b) Sigma</td><td>(a) AF-Micro-Nikkor 60 mm f/2.8 D&lt;br/&gt; (b) 105 mm f/2.8 Macro-Ex</td><td></td></tr><tr><td>Test-liquid</td><td>De-ionized water from the Imperial College Analytical Lab.</td><td>Standard solution&lt;br/&gt; (AnalaR)</td><td></td></tr></tbody></table>

film control to study contributions of waves to droplet impact dynamics on thin flowing liquid films

水滴撞击是自然界中常见的一种现象, 由于其审美魅力和广泛应用, 引起了人们的关注。以往对流动液体薄膜的研究忽略了波浪空间结构对撞击结果的贡献, 而这最近被证明对水滴撞击动力学有很大的影响。在本报告中, 我们概述了一步一步的过程, 以研究一个流动的液体膜周期性进口强迫的影响, 导致生产 spatiotemporally 规则波结构的下降冲击动力学。一个与电磁阀连接的函数发生器用来激发这些 spatiotemporally 的规则波结构在薄膜表面, 而均匀大小的水滴的撞击动力学使用高速相机捕获。然后研究了三个不同的区域;即峰、扁膜区和波浪驼峰区前的毛细管波区。研究了膜雷诺、降韦伯和 Ohnesorge 数等重要无量纲量对膜流速、降速度和降径参数的影响。我们的结果显示了有趣的, 迄今未被发现的动态, 这一应用的电影进口强迫的流动薄膜的低和高惯性下降。

Watch this Scientific Journal Video about Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films at JoVE.com

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

本文提出了一种研究波浪对液滴撞击动力学的影响的协议。

薄膜控制研究波浪对液滴冲击动力学的影响薄流动液体薄膜

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous ...

film-control-to-study-contributions-waves-to-droplet-impact-dynamics

Research

JoVE Journal

Engineering

7.4K 次观看.  Imperial College London. 本文提出了一种研究波浪对液滴撞击动力学的影响的协议。

视频: Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

快速成像技术来研究非牛顿流体的跌落冲击动力学

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

科研

工程学

Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics

Digital microfluidics (DMF), a technique for manipulation of droplets, is a promising alternative for the development of &#8220;lab-on-a-chip&#8221; platforms. Often, droplet motion relies on the wetting of a surface, directly associated with the application of an electric field; surface interactions, however, make motion dependent on droplet contents, limiting the breadth of applications of the technique.
Some alternatives have been presented to minimize this dependence. However, they rely on the addition of extra chemical species to the droplet or its surroundings, which could potentially interact with droplet moieties. Addressing this challenge, our group recently developed Field-DW devices to allow the transport of cells and proteins in DMF, without extra additives.
Here, the protocol for device fabrication and operation is provided, including the electronic interface for motion control. We also continue the studies with the devices, showing that multicellular, relatively large, model organisms can also be transported, arguably unaffected by the electric fields required for device operation.

The protocol for fabrication and operation of field dewetting devices (Field-DW) is described, as well as the preliminary studies of the effects of electric fields on droplet contents.

以减少液滴表面的相互作用来优化Bioanalytes运输中的数字微流体

Digital microfluidics (DMF), a technique for manipulation of droplets, is a promising alternative for the development of &#8220;lab-on-a-chip&#8221; ...

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

高速喷液嵌塞对移动表面的可视化

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal microfluidic device. W/O microdroplets have recently been used in powerful methods that enable miniaturized chemical experiments. Therefore, developing a versatile method to yield monodisperse W/O microdroplets is needed. We have developed a method for generating monodisperse W/O microdroplets based on a capillary-based centrifugal axisymmetric co-flowing microfluidic device. We succeeded in controlling the size of microdroplets by adjusting the capillary orifice. Our method requires equipment that is easier-to-use than with other microfluidic techniques, requires only a small volume (0.1-1 &#181;l) of sample solution for encapsulation, and enables the production of hundreds of thousands number of W/O microdroplets per second. We expect this method will assist biological studies that require precious biological samples by conserving the volume of the samples for rapid quantitative analysis biochemical and biological studies.

Here, we demonstrate a simple production method for size-controllable, monodisperse, water-in-oil (W/O) microdroplets using a capillary-based centrifugal microfluidic device. This method requires only a small sample volume and enables high-yield production. We expect this method will be useful for rapid biochemical and cellular analyses.

基于毛细管的离心微流体装置单分散微滴的大小可控的形成

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal ...

Fabricating High-viscosity Droplets using Microfluidic Capillary Device with Phase-inversion Co-flow Structure

The generation of monodisperse droplets with high viscosity has always been a challenge in droplet microfluidics. Here, we demonstrate a phase-inversion co-flow device to generate uniform high-viscosity droplets in a low-viscosity fluid. The microfluidic capillary device has a common co-flow structure with its exit connecting to a wider tube. Elongated droplets of the low-viscosity fluid are first encapsulated by the high-viscosity fluid in the co-flow structure. As the elongated low-viscosity droplets flow through the exit, which is treated to be wetted by the low-viscosity fluid, phase inversion is then induced by the adhesion of the low viscosity droplets to the tip of the exit, which results in the subsequent inverse encapsulation of the high-viscosity fluid. The size of the resultant high-viscosity droplets can be adjusted by changing the flow rate ratio of the low-viscosity fluid to the high-viscosity fluid. We demonstrate several typical examples of the generation of high-viscosity droplets with a viscosity up to 11.9 Pas, such as glycerol, honey, starch, and polymer solution. The method provides a simple and straightforward approach to generate monodisperse high-viscosity droplets, which may be used in a variety of droplet-based applications, such as materials synthesis, drug delivery, cell assay, bioengineering, and food engineering.

A phase-inversion co-flow device is demonstrated to generate monodisperse high-viscosity droplets above 1 Pas, which is difficult to realize in droplet microfluidics.

反相共流微流控毛细管装置制备高粘度水滴的方法

The generation of monodisperse droplets with high viscosity has always been a challenge in droplet microfluidics. Here, we demonstrate a phase-inversion ...

化学

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 &#181;m to 80 &#181;m in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

Semi-3-Dimensional 流聚焦微流控装置产生尺寸控制的聚乙二醇二丙烯酸酯液滴

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.

Two different methods for characterizing the incipient particle motion of a single bead as a function of the sediment bed geometry from laminar to turbulent flow are presented.

从层流到湍流条件下的规则基底表面初始粒子运动的可视化表征

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to ...

Impacts of Free-falling Spheres on a Deep Liquid Pool with Altered Fluid and Impactor Surface Conditions

Vertical impacts of spheres on clean water have been the subject of numerous water entry investigations characterizing cavity formation, splash crown ascension and Worthington jet stability. Here, we establish experimental protocols for examining splash dynamics when smooth free-falling spheres of varying wettability, mass, and diameter impact the free surface of a deep liquid pool modified by thin penetrable fabrics and liquid surfactants. Water entry investigations provide accessible, easily assembled and executed experiments for studying complex fluid mechanics. We present herein a tunable protocol for characterizing splash height, flow separation metrics, and impactor kinematics, and representative results which might be acquired if reproducing our approach. The methods are applicable when characteristic splash dimensions remain below approximately 0.5 m. However, this protocol may be adapted for greater impactor release heights and impact velocities, which augurs well for translating results to naval and industry applications.

This protocol demonstrates the basic experimental configuration for water entry experiments with free-falling spheres. Methods for the alteration of liquid surface with penetrable fabrics, the preparation of chemically non-wetting spheres, and steps for splash visualization and data extraction are discussed.

自由落体对变液和冲击物表面条件下深层液池的影响

Vertical impacts of spheres on clean water have been the subject of numerous water entry investigations characterizing cavity formation, splash crown ...

Measuring the Interaction Force Between a Droplet and a Super-hydrophobic Substrate by the Optical Lever Method

The goal of this paper is to investigate the interaction force between droplets and super-hydrophobic substrates in the air. A measurement system based on an optical lever method is designed. A millimetric cantilever is used as a force sensitive component in the measurement system. Firstly, the force sensitivity of the optical lever is calibrated using electrostatic force, which is the critical step in measuring interaction force. Secondly, three super-hydrophobic substrates with different grid fractions are prepared with nanoparticles and copper grids. Finally, the interaction forces between droplets and super-hydrophobic substrates with different grid fractions are measured by the system. This method can be used to measure the force on the scale of sub-micronewton with a resolution on the scale of nanonewton. The in-depth study of the contact process of droplets and super-hydrophobic structures can help to improve the production efficiency in coating, film and printing. The force measurement system designed in this paper can also be used in other fields of microforce measurement.

The protocol aims to investigate the interaction between droplets and super-hydrophobic substrates in the air. This includes calibrating the measurement system and measuring the interaction force at super-hydrophobic substrates with different grid fractions.

用光学杠杆方法测量液滴和超疏水基板之间的相互作用力

The goal of this paper is to investigate the interaction force between droplets and super-hydrophobic substrates in the air. A measurement system based on ...

High Throughput Analysis of Liquid Droplet Impacts

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters such as material properties, impact conditions, and experimental configurations. Compounding this, drop impacts are often studied using data-rich high-speed photography, so that it is difficult to analyze many experiments in a detailed and timely manner. The purpose of this method is to enable efficient study of droplet impacts with high-speed photography by using a systematic approach. Equipment is aligned and calibrated to produce videos that can be accurately processed by a custom image processing code. Moreover, the file structure setup and workflow described here ensure efficiency and clear organization of data processing, which is carried out while the researcher is still in the lab. The image processing method extracts the digitized outline of the impacting droplet in each frame of the video, and processed data are stored for further analysis as required. The protocol assumes that a droplet is released vertically under gravity, and impact is recorded by a camera viewing from side-on with the drop illuminated using shadowgraphy. Many similar experiments involving image analysis of high-speed events could be addressed with minor adjustment to the protocol and equipment used.

This protocol enables efficient collection of experimental high-speed images of liquid drop impacts, and speedy analysis of those data in batches. To streamline these processes, the method describes how to calibrate and set up apparatus, generate an appropriate data structure, and deploy an image analysis script.

液滴冲击的高通量分析

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters ...