Name: ultrasound velocity measurement in a liquid metal electrode
Uploaded: 2015-08-05T13:00:00.000+00:00
Duration: 8 min 41 s
Description: Watch this Scientific Journal Video about Ultrasound Velocity Measurement in a Liquid Metal Electrode at JoVE.com

We are grateful for the design and fabrication assistance of D. De La Cruz, for equipment borrowed from M. Zahn, and for insightful discussions with D. R. Sadoway and the talented electrochemists of his group.

1.系统设置和大会<ol><li>清洁的超声换能器，用异丙醇。 </li><li>装入手套箱。 <ol><li>负载所需的设备和材料（包括超声换能器，ePbBi，搅拌棒，和热电偶）插入手套箱，以下手套箱制造商的说明书，以减少的氧和湿气的侵入。 </li><li>在手套箱前厅保持多孔材料在真空条件下12小时进入手套箱之前。 </li></ol></li><li>调整PID控制器（仅第一次）。 <ol><li>放置固体ePbBi相同数量的插入到将在实验（840克）所使用的电池容器中。 </li><li>周围放置了电池容器内的炉中保温，如果它已不存在，然后将盖顶上的电池容器中，沿着与负极集电体和热电偶。 </li><li>使热电偶和炉功率的所有电连接， 如图 <strong&gt; URE 2B。 </li><li>发起PID控制器的自动调谐，使用150℃作为设置点。注意:该步骤的细节将有所不同，这取决于PID控制器制造商和型号。这里使用的自动调谐通过控制四个全热循环，从RT到工作温度，在一个小时的过程控制器。 <ol><li>使用箭头键来调节设定值（调整后的控制器默认显示），以150℃。 </li><li>按住循环按钮3秒，进入隐藏的循环。然后反复按循环按钮，直到控制器屏幕显示"TUNE"。使用箭头键将其更改为YES。 </li></ol></li><li>插入一个热电偶，并使用工作站来监视和记录温度。 </li><li>一旦自动调谐完成时，记录该PID控制器已自动通过控制器接口选择的比例，积分和微分参数，按吨Ø制造商的说明。 </li></ol></li></ol> 2.声速测量<ol><li>使用炉熔化足够ePbBi用于实验，至少400克注意:需要的量将随不同的设备，并ePbBi熔点为125℃。 <ol><li>如果有必要，用搅拌棒从ePbBi的顶面掠过它去除多余的氧化物。 </li><li>插入一个超声换能器成音速测定装置，并拧紧挤压连接，以防止泄漏，然后插入一个热电偶，并使用工作站来监视和记录温度。 </li></ol></li><li>熔融金属转移到声速测量装置。 <ol><li>放置声速测量装置在炉基和离开那里进行2分钟，以逐渐增加的温度，并避免热冲击。 </li><li>准备一个安全转移通过从区域移除热量敏感的设备或材料。 </li><li>添加小点熔融金属在一个时间ounts，因为热冲击会损坏超声换能器。添加ePbBi直到探头表面和微米头都完全淹没。 </li><li>等到至少5分钟温度保持稳定在1℃以内开始测量之前，由于声音的速度依赖于温度。 </li></ol></li><li>测量的超声回波在两个位置。 <ol><li>测微头设定为任意的，但已知的位置。记录超声回波测量，下面由仪器制造商提供的说明。 </li><li>使用千分表，通过公知的距离移动微米小费。记录超声回波测量。 </li></ol></li><li>从声音速度测量装置中取出的熔融金属并将其存储在一个热耐受容器。 </li><li>要确定的声音的速度，情节回波振幅的回波时间为每两次测量的功能。通过拟合高斯曲线找到回声到每一回波峰值，如在图 茜 4。通过将位移距离由回波峰值时间差计算声速。 </li></ol> 3.超声速度测量<ol><li>熔体足够ePbBi做实验（840克），如果有必要去除多余的氧化物。注:为获得最佳效果，请使用ePbBi被用来调整的PID控制器相同的数量。 <ol><li>插入一个超声换能器到电池容器中，并拧紧挤压连接，以防止泄漏，确保该炉基是水平的。 </li></ol></li><li>熔融金属转移到电池容器。 <ol><li>将电池壳上炉底座，让它有5分钟逐渐增加温度，避免热冲击。准备一个安全转移通过从区域移除热量敏感的设备或材料。 </li><li>添加少量的熔融金属的时间，因为热冲击会损坏微升trasound传感器。 </li><li>等到温度达到150℃开始测量前，因为声速取决于温度。 </li></ol></li><li>完成组装该装置。 <ol><li>周围放置了电池容器内的炉中保温，如果它已不存在。放置在盖顶上的电池容器中，沿着与负极集电体和热电偶。要确保所有的精确和可重复定位;轴环非常适用于此。 </li><li>使这两个功率和信号的所有电连接， 如图 茜 2B。用欧姆表确认没有意外的电路路径存在， 即检查负电流收集器和所有信号引线之间的电阻至少为1MΩ。 </li></ol></li><li>开始进行测量。 <ol><li>开始记录和监控温度，加热功率，电池电压和电池电流。注:在这里，工作站运行定制的LabVIEW代码是用来记录所有测量，与相应的时间戳。 </li><li>调整超声仪器设置是必要的。 <ol><li>一定要设置声音的速度，使用适当的温度，根据公认的模型19。为ePbBi在如下使用150℃，速度设置为1760米/秒。 </li><li>调整脉冲重复频率，使得回声深度紧密间隔（通常为0.25毫米）。 </li><li>调整使得从远处血管壁的强回声出现在最后几门的门数;它提供了一个有用的完整性检查进行故障排除信号强度问题。 </li><li>使用由制造商提供的说明，将仪器设置为硬件触发。 </li></ol></li><li>通过启动从工作站触发开始与超声仪器记​​录和监视速度。每秒记录四幅速度剖面30分钟。 </li></ol></li><li>设置为5 A的电池电流，等待5分钟的流量稳定下来，然后30分钟录制每秒4的速度分布。 </li><li> 10 A，15 A，20 A，25 A，30 A.重复步骤3.5 注意:许多其它实验方案也是可能的，包括温度变化和在当前平滑变化。气氛在低氧气和水分可以用几个小时以上良好的信号质量的实验。 </li><li>一旦试验完成后，停止记录数据并关闭炉。断开电气连接和取下炉盖。从电池容器中取出熔融金属，利用该填充的容器时被用于安全传输的相同步骤。存储熔融ePbBi在热耐受容器。添加额外的氩气的手套箱;其压力将下降，因为它的大气冷却。 </li></ol>

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The authors have nothing to disclose.

超声技术可以在数百或数千的位置在一个透明的或不透明的液体，每秒钟多次产生的速度测量。施加到液态金属电极，超声技术遇到高温，化学活性，和导电性的挑战。该方法克服这些挑战，并测量流中活性液体金属电极已被描述。首先，将电极材料受到相同的物理的高温液态金属电池的电极（550℃），但操作在低得多的温度（150℃），简化了与温度有关的挑战。一个定制的炉和调整控制系统用?...

液态金属电池是一种很有前途的技术，为全球范围内对电网1提供大规模储能。这些电池提供高能量密度，功率密度高，循环寿命长，成本低，可理想用于电网规模储能3。引入液态金属电池能源网将使调峰，提高电网的稳定性，并使更广泛地使用间歇性可再生能源如太阳能，风能，和潮汐发电。液态金属电池组成的熔盐电解质隔开两液体金属电极，如在现有工作1中更详细地描述。虽然金属和电解质许多不同的组合会导致工作液体金属电池，工作原理保持相同。所述金属被选择成使得它是能量上有利的为他们形成合金;因此，合金化放电的电池，和去合金收费吧。该SA选择所述层，使得它允许金属离子在两个电极之间通过，但中性物种的块传输，从而提供了系统的电化学控制。 这项工作将通过量化和控制大众交通的影响推动液态金属电池技术。这里介绍的方法是由液态金属电池由Sadoway 等人开发的电化学方法知情1-4以及在阿贡国家实验室的前面5,6液态金属电池的工作，以及更广泛的社会电化学的工作（巴德和福克纳7提供了许多相关的参考资料）。这里介绍的方法也建立在以前的流体动力学研究。超声测速技术的开发和第一次在水中使用8,9和已经被应用到液态金属镓，包括10,11，12,13钠，14汞，铅，铋15，铜锡15 &lt;/ SUP&gt;，和铅锂16，等等。埃克特等，提供测速的有用审查液态金属17。 类似于在这里18中的那些最近使用的工作方法表明，电池的电流可以增强集体运输液态金属电极。因为质量传递中的正电极是负责液态金属电池和放电的限速步骤，混合因此允许更快的充电和放电比其他可能的。此外混合防止了电极，可形成固体的限制电池的循环寿命局部不均匀性。在正在进行的工作，我们继续研究在液态金属电池，它产生由于热和电磁力的正极流体流动的作用。热梯度开车经过浮力对流和电池电流通过诱导面糊的磁场相互作用带动流量Ÿ电流自己。在使用以下描述的方法的实验中，我们观察到流动雷诺数50 &lt;重新&lt;200，从电极深度和根均方速度计算出。一个彻底的实验表征正在进行和将使用产生的数据集建立预测型号的电池。此论文的重点是对实验设计和所需的，以产生这样的数据的程序。超声测速提供大量的测量，和实验条件，必须以在液态金属成功使用超声波来仔细控制。高温，化学活性，和电导率都必须小心管理。 首先，液态金属电池在高温下工作不一定，因为金属和分隔它们必须是熔融盐。一个有前途的材料的选择，它使用锂作为负极，铅锑作为正电子角处接上和锂盐作为电解质的共晶混合物，需要大约550℃的温度。在如此高的温度下测量的不透明流体的流动是相当困难的。高温超声换能器，该分离的微妙电声部件从测试流体的声波导，已经证明15和商业化。然而，因为换能器具有插入损耗邻近40分贝的，并且因为在这种温度下工作的一般困难，替代系统已被选定为初始研究:一个液态金属电池也可以使用钠作为负极，共晶制成44％铅56％铋（以下ePbBi）作为正电极，和钠盐（10％的碘化钠和38％的氢氧化钠，52％钠酰胺）作为电解液的三共晶混合物。这种电池是完全熔化高于127°C，使得它更适合于实验室研究。因为它是由三个液体层是通过密度分离，它受相同的物理和其他液态金属电池。而且它是与现成超声换能器，这是在额定至230℃兼容，涉及无波导损失，成本比高温传感器少得多。这些实验通常发生在150℃。在该温度下，ePbBi的粘度ν= 2.79×10 -7平方米 /秒，热扩散率κ= 6.15×10 -6米2 /秒，和磁扩散η=0.8591米2 /秒，使得其普朗特数是PR =ν/κ= 4.53×10 -2及其磁普朗特数为PM =ν/η= 3.24×10 -7。 虽然这种低温液态金属电池化学物质，使流动的研究更容易比他们将在炎热的电池，温度仍然必须谨慎管理。作为精致的电声器件，超声换能器是susceptiblE按热冲击损坏，因此必须逐渐加热。高品质的超声测量也需要仔细调节温度。超声测速的工作方式类似声纳， 如图1:换能器发出蜂鸣声（在此，频率为8兆赫），然后监听回波。通过测量的回波的飞行时间，以呼应体的距离可以被计算，并且通过测量的回波的多普勒频移，身体的速度的一个部件也可以计算出来。在水，示踪粒子必须被添加到产生的回声，但没有示踪粒子需要在液态金属，即不理解详细但通常归因于小的金属氧化物粒子的存在的事实。每次测量的平均值在询问卷中的所有示踪粒子;在这项工作中，其最小直径为2毫米，在距离30mm处的探针。虽然氧化可能最终限制的实验的持续时间，使用第下面描述ë方法，我们不断进行的测量，只要8小时。 计算任一距离或速度需要知道声音的测试流体的速度，且将该速度随温度而变化。此处所描述的工作着重于流在ePbBi负极，其中，声音的速度是1766米/秒，在150℃，1765米/秒，在160℃，1767米/秒，在140℃下19。因此温度控制不当会在超声测量引入系统误差。的装置被构造成测量声音在ePbBi速度，查找与发表和接受核能机构19（见下文）相一致的值。最后，由于热对流是流动在液体金属电池的主要推动力，两者的平均温度和ePbBi电极的顶部和底部之间的温度差直接影响观测。对于一致的结果，精确热控制是必不可少的。 因此，温度是至少有三个K型热电偶连续测量，记录他们的测量电子与基于计算机的捕获装置和一个自定义编写的LabView程序。该方案还控制提供电池电流，通过USB连接电源;记录该电池的电流和电压;并发送触发脉冲的超声仪器，使得它的数据可以与其他测量来同步。一种系统，图中示出在图2中，加热是由一个定制炉（也示于图2），它包含两个500W的工业加热元件供电切换由比例-积分-微分中继（PID），提供控制器。支持电池单元的基板是由固体铝;因为它的热导率是一个数量级高于不锈钢届的热导率鳗鱼电池容器，它包含19 ePbBi，炉底的温度大致均匀。此外铝基兼作电电流通过电极的路径。其电导率也幅度比不锈钢或ePbBi高出一个数量级，所以在炉底板的电压也大致均匀。绝缘腿从替补分开底座顶部下方，防止烫伤和短裤。电池容器的侧面被绝缘的二氧化硅陶瓷隔热，切向紧密贴合在容器但留有余地接入小区的超声端口。最后，一​​个聚四氟乙烯（PTFE）盖绝缘细胞从上方并保持该负集电体和热电偶到位。虽然市售加热板能够达到所需的这些实验的温度下，我们的定制炉保持温度与幅值较小的变化，一个的顺序ND也可以让我们直接测量热功率。 除了与温度相关的挑战，存在与化学活性相关的挑战。在150℃，一个ePbBi正极与许多常见的材料化学相容。钠负电极，然而，侵蚀许多材料，容易氧化，并且具有防潮剧烈的化学反应。锂负极也是积极的，尤其是因为锂基液态金属电池通常在运行温度高得多。虽然这些较高温度系统是这项工作的范围之外，许多用于管理化学活性同样的措施在这里用作这些系统。此处描述的所有实验发生在含有氧气或湿气的仅微量充满氩气的手套箱中。电池容器由合金制成的304不锈钢，其腐蚀最小甚至与锂在550℃。热电偶和负电流集电极也由不锈钢制成。该容器的几何形状被选择以匹配用于液态金属电池电化学测试容器，以尽可能接近建模为可能正在商业化的系统。容器中， 如图2所示，是圆柱形的，具有一个88.9毫米内径和67毫米深度。所有的血管壁6.4毫米厚。该容器不同于那些用于早期的实验，但是，在于它具有一个超声端口。端口穿过侧壁沿着所述圆柱体的水平直径，并且该端口的中心为6.6毫米以上的容器地板。端口是8毫米直径以容纳8mm的超声换能器，和密封件围绕与型模的换能器。在这些实验中，液体金属电极仅仅是足够深，以覆盖超声波换能器，通常13毫米。 为了实现强大的超声波信号，一个需要良好的声学传输之间的超声换能器和流体其探针（ePbBi）。发送最大声功率时换能器的材料的声阻抗和测试流体是相同的;当阻抗不同，信号受到影响。放置在与清洁ePbBi直接接触的超声换能器（如成为可能由上述的端口）提供了充足的信号，通常在一个小时的时间。金属氧化物，然而，有非常不同的阻抗，并且还可以通过改变表面张力干扰润湿。如果ePbBi实质上氧化，超声信号降解并很快消失。再次，在惰性气氛是至关重要的。如果氧气痕量引起一些氧化尽管如此，金属氧化物的表面转印ePbBi到电池容器之前被脱脂。 最后，由于电流的情况下的这些实验提出了挑战。虽然电流是我们的中央科学和技术间美国东部时间，他们有足够的（30 A）大造成损害，如果不正确地路由。接地热电偶确保有害的电流不通过数据获取设备或支持它的计算机，因为接地热电偶具有从保护护套要么信号线没有内部电连接。同样有必要使用不接地超声换能器（信号处理中的SA，TR0805LTH），以防止杂散电流而损坏有价值超声仪（信号处理中的SA，DOP 3010）。如前所述，在炉的底座用来传导电流，并且还必须从它的周围环境电隔离。 在ePbBi电极，电流引起的欧姆加热，有可能破坏的温度。因此，自动热控制系统必须能适应变化的热输入。 图3显示了如何ePbBi电极的温度变化作为CUR租金流经它，以及如何将PID控制器调节来补偿。保持稳定的温度有大的电流（50 A = 800毫安/平方厘米）将需要额外的冷却，但在较低的电流更现实的工业应用中的液体金属电池（典型地17 A =275毫安/厘米1），该控制器能够以补偿的欧姆加热并保持温度变化至2℃。

<table><tbody><tr><td>K Type Thermocouple Probe</td><td>McMaster-Carr</td><td>3856K83</td><td>http://www.mcmaster.com/</td></tr><tr><td>Red Lion PID Controller</td><td>Red Lion</td><td>P1610000</td><td>http://store.redlion.net/store/p16.html</td></tr><tr><td>Measurement Computing Data Acquisition Device</td><td>Measurement Computing Corporation</td><td>USB-2408</td><td>http://www.mccdaq.com/index.aspx</td></tr><tr><td>Power Supply</td><td>TDK-Lambda</td><td>GEN 8-90-USB-U</td><td>http://us.tdk-lambda.com/hp/</td></tr><tr><td>Ultrasound Instrument</td><td>Signal Processing SA</td><td>DOP3010</td><td>http://www.signal-processing.com/index.html</td></tr><tr><td>Ultrasound Transducer</td><td>Signal Processing SA</td><td>TR0805LTH</td><td>http://www.signal-processing.com/index.html</td></tr><tr><td>Bismuth-Lead Eutectic</td><td>VWR</td><td>AA40949-P2</td><td>https://us.vwr.com/</td></tr></tbody></table>

ultrasound velocity measurement in a liquid metal electrode

越来越多的电化学技术依赖于流体流​​动，并经常流体是不透明的。测量的不透明流体的流动本身就比测量的透明流体的流动较困难，因为光学方法是不适用的。超声可用于测量不透明流体，不仅在孤立点的速度，但在沿行排列，具有良好的时间分辨率几百点或数千。当施加到液态金属电极，超声波测速涉及额外的挑战:高温，化学活性，和导电性。在这里，我们描述实验装置和克服这些挑战，并允许流动的测量在液体金属电极，因为它传导电流，在操作温度的方法。温度是用一个比例 - 积分 - 微分（PID）控制器，功率的定制炉在±2℃调节。化学活性的男人老化通过仔细选择容器材料和包封的实验配置在充满氩气的手套箱中。最后，非预期的电路径被小心防止。自动化系统记录控制设置和实验测量，使用硬件触发信号同步设备。此装置和这些方法可产生测量是不可能与其它技术，并允许优化和电化学技术，如液态金属电池的控制。

用于测量的声音的速度（在上面详细描述的）的方法改编自用于信号处理的SA的方法。原则上，声音的速度可以很容易地通过测量的回波的飞行时间从一个壁在已知范围内获得。但精确测量探头表面的有效位置是困难的，所以不是一个可以测量的飞行时间的两倍，用千分尺由测量之间的已知距离来置换壁。该位移距离，并在飞行测量的时间差，以及产生的声音的速度。用于测量在这些实验中的声?...

Watch this Scientific Journal Video about Ultrasound Velocity Measurement in a Liquid Metal Electrode at JoVE.com

Ultrasound Velocity Measurement in a Liquid Metal Electrode

Ultrasound velocimetry is used to study mixing by fluid flow in liquid metal electrodes. The focus of this manuscript is to illustrate the methods used for making precise, spatially-resolved ultrasound measurements while limiting oxidation and controlling and monitoring temperature, applied current, and the heater power being supplied.

超声速度测量的液态金属电极

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently ...

ultrasound-velocity-measurement-in-a-liquid-metal-electrode

Research

Education

JoVE Journal

JoVE Core

Physics

Engineering

Unit 1

Sound

SCIENTISTS IN ACTION

11.6K 次观看.  University of Rochester. Ultrasound velocimetry is used to study mixing by fluid flow in liquid metal electrodes. The focus of this manuscript is to illustrate the methods used for making precise, spatially-resolved ultrasound measurements while limiting oxidation and controlling and monitoring temperature, applied current, and the heater power being supplied.

视频: Ultrasound Velocity Measurement in a Liquid Metal Electrode

Echo Particle Image Velocimetry

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.2 For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.3,4,5,6 In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine7 with a PC running commercial particle image velocimetry (PIV) software8 is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported.
For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/&delta;t. (See 9 for a review of ultrasound imaging.)
For a typical EPIV experiment, the frame rate is between 20-60 fps, depending on flow conditions, and 100-1000 B-mode images of the spatial distribution of the tracer particles in the flow are acquired. Once acquired, the B-mode ultrasound images are transmitted via an ethernet connection to the PC running the PIV commercial software. Using the PIV software, tracer particle displacement fields, D(x,y)[pixels], (where x and y denote horizontal and vertical spatial position in the ultrasound image, respectively) are acquired by applying cross correlation algorithms to successive ultrasound B-mode images.10 The velocity fields, u(x,y)[m/s], are determined from the displacements fields, knowing the time step between image pairs, &Delta;T[s], and the image magnification, M[meter/pixel], i.e., u(x,y) = MD(x,y)/&Delta;T. The time step between images &Delta;T = 1/fps + D(x,y)/B, where B[pixels/s] is the time it takes for the ultrasound probe to sweep across the image width. In the present study, M = 77[&mu;m/pixel], fps = 49.5[1/s], and B = 25,047[pixels/s]. Once acquired, the velocity fields can be analyzed to compute flow quantities of interest.

An echo particle image velocimetry (EPIV) system capable of acquiring two-dimensional fields of velocity in optically opaque fluids or through optically opaque geometries is described, and validation measurements in pipe flow are reported.

回声粒子图像测速技术

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 ...

科研

工程学

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

制造，操作和表面声波驱动声逆流微流体流动可视化

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

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 ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

方法通过表面氧化还原操纵液态金属的表面张力

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

化学

AC Electrokinetic Phenomena Generated by Microelectrode Structures

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro- and nano-scale, which is essential for Lab-on-a-Chip applications. AC electrokinetic phenomena use electric fields to generate forces that act on fluids or suspended particles (including those made of dielectric or biological material) and cause them to move in astonishing ways1, 2. Within a single channel, AC electrokinetics can accomplish many essential on-chip operations such as active micro-mixing, particle separation, particle positioning and micro-pattering. A single device may accomplish several of those operations by simply adjusting operating parameters such as frequency or amplitude of the applied voltage. Suitable electric fields can be readily created by micro-electrodes integrated into microchannels. It is clear from the tremendous growth in this field that AC electrokinetics will likely have a profound effect on healthcare diagnostics3-5, environmental monitoring6 and homeland security7.

In general, there are three AC Electrokinetic phenomena (AC electroosmosis, dielectrophoresis and AC electrothermal effect) each with unique dependencies on the operating parameters. A change in these operating parameters can cause one phenomena to become dominant over another, thus changing the particle or fluid behavior. 

It is difficult to predict the behavior of particles and fluids due to the complicated physics that underlie AC electrokinetics. It is the goal of this publication to explain the physics and elucidate particle and fluid behavior. Our analysis also covers how to fabricate the electrode structures that generate them, and how to interpret a wide number of experimental observations using several popular device designs. This video article will help scientists and engineers understand these phenomena and may encourage them to start using AC Electrokinetics in their research.

Manipulating fluids and suspended particles in the micro- and nano-scale is becoming more of a reality as enabling technologies, like AC electrokinetics, continue to develop. Here, we discuss the physics behind AC electrokinetics, how to fabricate these devices and how to interpret the experimental observations.

微电极结构产生的交流电动现象

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro- and nano-scale, ...

生物学

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 ...

Generation and Control of Electrohydrodynamic Flows in Aqueous Electrolyte Solutions

To drive electrohydrodynamic (EHD) flows in aqueous solutions, the separation of cation and anion transport pathways is essential because a directed electric body force has to be induced by ionic motions in liquid. On the other hand, positive and negative charges attract each other, and electroneutrality is maintained everywhere in equilibrium conditions. Furthermore, an increase in an applied voltage has to be suppressed to avoid water electrolysis, which causes the solutions to become unstable. Usually, EHD flows can be induced in non-aqueous solutions by applying extremely high voltages, such as tens of kV, to inject electrical charges. In this study, two methods are introduced to generate EHD flows induced by electrical charge separations in aqueous solutions, where two liquid phases are separated by an ion-exchange membrane. Due to a difference in the ionic mobility in the membrane, ion concentration polarization is induced between both sides of the membrane. In this study, we demonstrate two methods. (i) The relaxation of ion concentration gradients occurs via a flow channel that penetrates an ion-exchange membrane, where the transport of the slower species in the membrane selectively becomes dominant in the flow channel. This is a driving force to generate an EHD flow in the liquid. (ii) A long waiting time for the diffusion of ions passing through the ion-exchange membrane enables the generation of an ion-dragged flow by externally applying an electric field. Ions concentrated in a flow channel of a 1 x 1 mm2 cross-section determine the direction of the liquid flow, corresponding to the electrophoretic transport pathways. In both methods, the electric voltage difference required for an EHD flow generation is drastically reduced to near 2 V by rectifying the ion transport pathways.

The rectification of ion transport pathways is an effective method to generate one-directional ion-dragged electrohydrodynamic flows. By setting an ion-exchange membrane in a flow channel, an electrically polarized condition is generated and causes a liquid flow to be driven when an electric field is externally applied.

水电解质溶液中 Electrohydrodynamic 流的产生与控制

To drive electrohydrodynamic (EHD) flows in aqueous solutions, the separation of cation and anion transport pathways is essential because a directed ...

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

用于原子化和抗波流体的厚度模式压电器件的制造和特性

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate

Here, a conduction micropump with symmetric planar electrode pairs prepared on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) is fabricated. It is used to investigate the influence of chamber dimensions on the performance of a conduction micropump and to determine the reliability of the conduction pump when acetone is used as the working fluid. A testing platform is set up to evaluate conduction micropump performance under different conditions. When the chamber height is 0.2 mm, the pump pressure reaches its peak value.

This paper presents a protocol for the fabrication of a conduction micropump using symmetric planar electrodes on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) to test the influence of chamber dimensions on the performance of a conduction micropump.

FR-4 铜包电极板导电微泵性能测试平台

Here, a conduction micropump with symmetric planar electrode pairs prepared on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) is ...

生物工程

Ultrasound-based Pulse Wave Velocity Evaluation in Mice

Arterial stiffness can be evaluated by calculating pulse wave velocity (PWV), i.e., the speed with which the pulse wave travels in a conduit vessel. This parameter is being increasingly investigated in small rodent models in which it is used for assessing alterations in vascular function related to particular genotypes/treatments or for characterizing cardiovascular disease progression. This protocol describes an image processing algorithm which leads to non-invasive arterial PWV measurement in mice using ultrasound (US) images only. The proposed technique has been used to assess abdominal aorta PWV in mice and evaluate its age-associated changes.
Abdominal aorta US scans are obtained from mice under gaseous anesthesia using a specific US device equipped with high-frequency US probes. B-mode and Pulse-Wave Doppler (PW-Doppler) images are analyzed in order to obtain diameter and mean velocity instantaneous values, respectively. For this purpose, edge detection and contour tracking techniques are employed. The single-beat mean diameter and velocity waveforms are time aligned and combined in order to achieve the diameter-velocity (lnD-V) loop. PWV values are obtained from the slope of the linear part of the loop, which corresponds to the early systolic phase.
With the present approach, anatomical and functional information about the mouse abdominal aorta can be non-invasively achieved. Requiring the processing of US images only, it may represent a useful tool for the non-invasive characterization of different arterial sites in the mouse in terms of elastic properties. The application of the present technique can be easily extended to other vascular districts, such as the carotid artery, thus providing the possibility to obtain a multi-site arterial stiffness assessment.

Arterial stiffness represents a key factor in cardiovascular disease and pulse wave velocity (PWV) can be considered as a surrogate index for arterial stiffness. This protocol describes an image processing algorithm for calculating PWV in mice based on ultrasound image processing that is applicable at different arterial sites.

基于超声脉搏波速度评价小鼠

Arterial stiffness can be evaluated by calculating pulse wave velocity (PWV), i.e., the speed with which the pulse wave travels in a conduit vessel. This ...