我们承认海军研究局 (赠款 DURIP N00014-12-1-0749) 和国家科学基金会 (赠款 RTG DMS-0943851、CMG ARC-1025523、DMS-1009750 和 DMS-1517879) 提供的资金。此外, 我们承认莎拉. 伯内特的工作, 他帮助开发了早期版本的实验设置和协议。

1。准备零件以建立实验装置
<ol><li>利用附加的 3D CAD 绘图 (. stl 格式) 到 3 d 打印喷油器柱、一个储层、六角连接器和两个用于管道安装的板 (每个几何图形两个)。 注: 或者, 安装的某些部分可以是激光切割。在本报告中, 方厚管已安装激光切割板, 而矩形薄壁管已安装 3 d 印制板。</li>
	<li>获得所需几何的光滑玻璃毛细管。 注: 在本报告中, 使用两个管道几何图形:30 厘米长管的方形断面-内部横断面1毫米 x 1 毫米和壁厚0.2 毫米;30厘米长管, 长方形横断面-内部横断面1毫米 x 10 毫米和壁厚0.7 毫米。方管今后称为厚管, 而矩形管称为细管。</li>
</ol>2。实验装置装配
<ol><li>3维印刷零件的攻丝<ol>
<li>使用1/8 英寸 (0.32 厘米) 不扩散条约水龙头, 在其中安装注射针和染料输入, 在两侧插入喷油器柱。用10-32 水龙头在后面的储物处轻敲, 安装排水管。</li>
		<li>用6-32 个水龙头在水库前面敲四个螺丝孔。用6-32 分路器在顶部和底部点击六角连接件。</li>
	</ol></li>
	<li>准备抽头 3 d 打印部件<ol>
<li>喷油器柱<ol>
<li>用聚四氟乙烯密封胶带覆盖有刺软管接头的螺纹。将准备好的接头拧到喷油器柱的后孔上。切割一条30厘米长的塑料管材 (内径3.30 毫米)。将管子插入软管接头上。</li>
			<li>用聚四氟乙烯密封胶带覆盖不锈钢配药针 (外径0.71 毫米) 的螺纹。把不锈钢配药针钉在前面 (大) 孔上, 放在喷油器柱上。</li>
		</ol>
</li>
		<li>水库<ol>
<li>盖上聚四氟乙烯密封胶带的小刺软管接头的螺纹。将准备好的接头拧在储层 (小孔) 的后孔上。</li>
			<li>切割一条30厘米长的塑料管材 (内径3.30 毫米)。把管子插入软管接头上。用小帽把管子的另一端关上。 注: 这将是水库的排水系统。</li>
			<li>将橡胶 O 形环 (耐油布纳 N O 形环、1/16 英寸 (0.16 厘米) 分宽、破折号数 016) 放在储层管侧的循环衰退中。</li>
		</ol>
</li>
		<li>六角连接器<ol>
<li>盖上聚四氟乙烯密封胶带的小刺软管接头的螺纹。将准备好的接头拧到六角形接头的底孔上。</li>
			<li>切割一条30厘米长的塑料管材 (内径3.30 毫米)。将管子插入软管接头上。</li>
			<li>用聚四氟乙烯密封胶带覆盖软管接头。请确保将软管适配器与螺纹接合。</li>
			<li>切割一条4厘米长的塑料管材 (内径3.30 毫米)。将管子插入软管接头上。</li>
		</ol>
</li>
	</ol></li>
	<li>准备管道<ol>
<li>将一层薄薄的室温硫化橡胶密封胶从管子的每一端分散2毫米。将密封胶均匀地分散在管道的外侧, 确保不堵塞管道与密封胶的接触。</li>
		<li>将管道装入3维印刷板上, 将其小心插入到3维印刷管道适配器的预切孔中。一定要把管子按在至少2毫米, 这样密封胶沿每边与板材接触。</li>
		<li>小心地把密封胶涂到盘子的边缘, 这样管子就会被密封到切口里。等待至少12小时的密封胶, 以充分硫化, 从而密封管到板上。</li>
	</ol></li>
	<li>测量0.40 克荧光素粉制备染料溶液。将粉末稀释成0.50 升的蒸馏水, 以获得所需的染料浓度 (0.80 克/升浓度)。 注: 荧光素在水中的扩散率通过对圆管几何中的分段平均示踪剂分布的第二个矩的解析表达式进行最小二乘拟合, 对实验相同数量的测量。分子扩散系数估计为κ = 5.7 x 10-6厘米2/秒, 与先前公布的在纯净水中荧光素的扩散值一致。</li>
	<li>装配<ol>
<li>注射器泵安装<ol>
<li>用带有蒸馏水的橡胶柱塞填充12毫升塑料注射器。在注射器上插入一个塑料配药尖端。将注射器安装在注射器泵上. 将注射器连接至六角连接器底部插入的30厘米长管。</li>
			<li>用带有蒸馏水的橡胶柱塞填充1毫升塑料注射器。将注射器安装在注射器泵上. 切一条30厘米长的塑料油管 (内径3.30 毫米)。附加到1毫升塑料注射器。 注: 两个注射器灌满蒸馏水都安装在注射器泵 A 上。当泵被激活时, 水会从两个注射器中排出。第一个使用的是12毫升注射器, 所以1毫升注射器需要连接到排水管, 以避免水溢出。这一步是不必要的薄壁矩形管。</li>
		</ol>
</li>
		<li>喷油器设置<ol>
<li>用带有荧光素溶液的橡胶柱塞填充3毫升塑料注射器。在注射器上插入一个塑料配药尖端。</li>
			<li>把连接到注射器背面的管子附着在染料注射器上。</li>
			<li>用染料溶液填充注射器柱, 并通过注射器手动注射染料, 同时保持注射器柱水平 (i. e. 以针向上和在注射器之上)。继续推进注射器, 直到注射器完全充满染料, 并没有空气被困在里面。</li>
			<li>将注射器安装在注射器泵上 b. 将注射器柱夹在实验室工作台的边缘, 使其可通过连接到注射器泵的管子到达。</li>
			<li>在四长螺丝上插入小垫圈 (不锈钢盘头飞利浦机螺丝6-32 螺纹, 2-1/4 英寸 (5.76 厘米) 长度)。在针周围的四个孔中插入四螺钉。 注: 确保螺钉的头部位于注射器柱的背面 (与与染料注射器连接的管子的一侧)。</li>
		</ol>
</li>
		<li>六角连接器<ol>
<li>将两个 O 形环 (耐油布纳-N O 形环, 1/16 英寸 (0.16 厘米) 分式宽度, 破折号数 016) 放在六角连接器两侧的圆形切口上。</li>
			<li>通过将其孔对准四螺钉并将其插入到喷嘴柱上, 将六角连接器连接到喷油器开机自检。一定要有一侧与更大的孔面对喷油器岗位。检查并确保 O 形环在夹在两个零件之间时不会移出位置。</li>
		</ol>
</li>
		<li>管<ol>
<li>通过将其孔与四螺钉对齐, 并将其插入到六角形接头上, 将连接到管道上的一个端板附加到六边形连接器上。密切注意需要进入管道, 因为它正在安装的针。</li>
			<li>通过将四6-32 不锈钢螺母连接到长螺栓的末端, 确保四长螺钉将注射器、六角连接器和管道适配器板一起压缩。确保 O 形环在零件之间夹紧时不移出位置。</li>
			<li>使用四短螺钉和垫圈 (不锈钢盘头飞利浦机螺丝6-32 螺纹, 1/2 英寸 (1.27 厘米) 长度) 将管道的两端连接到储层。检查在两个部件之间压缩时 O 形环是否不移动。</li>
		</ol>
</li>
		<li>把水库夹在桌子上。确保储层与喷油器柱对齐, 不弯曲管道。</li>
		<li>空气萃取系统: 将塑料配药尖端插入连接到六角连接器顶部的管中。将3毫升注射器连接到塑料尖端。 注: 此注射器将用于提取任何空气气泡被困在系统中。</li>
		<li>灯和照相机<ol>
<li>在实验装置的每一侧放置两个61厘米长的紫外线-一管灯。 注: 喷油器和储层两侧都有专门设计的轨道。实验应该在黑暗中运行与紫外线-一个管灯打开。</li>
			<li>将带内存卡的摄像头置于实验装置的上方。 注: 摄像机应位于管道上方至少1米处。这样, 框架将包括整个管道长度。单反相机使用的透镜可调焦距, 24-120 毫米。</li>
			<li>程序相机使用远程触发器拍摄每 1 s 与光圈 5.6f, 快门速度 5, ISO 200。</li>
		</ol>
</li>
	</ol></li>
</ol>3。实验运行
<ol><li>设置<ol>
<li>用蒸馏水将储层填入一个稍高于管子的水平。在注射器泵上加水, 用蒸馏水填充管子。打开紫外线-一个管灯和拉停电窗帘。</li>
		<li>运行可编程注射器泵 A 冲洗任何残留染料的管道。</li>
		<li>取一个单一的参考图像的管道填充纯净蒸馏水。 注意: 这是稍后将在数据处理步骤中使用的引用快照。这张图片需要在黑暗中采取在条件尽可能相似对实验性奔跑。</li>
		<li>将管连接至喷油器柱的管子切换至安装在注射器泵上的1毫升注射器 a. 将12毫升注射器连接到引流管 (以前连接到1毫升注射器)。 注意: 这一步是不必要的薄壁矩形管。</li>
	</ol>
</li>
	<li>初始条件<ol>
<li>通过运行模拟注射器泵 B, 在管道中注入1毫米厚的染料 (3 毫米厚的矩形管)。 注意: 此步骤创建染料初始条件。注射染料的用量取决于所用管子的几何形状。由于其横截面积较大, 薄管需要大量的染料。在实验运行之前, 染料将必须扩散到横断面, 并注入更多的染料, 确保它将足够明亮, 即使在它扩散后, 在照片中捕捉。</li>
		<li>程序注射器泵 A 注入蒸馏水在非常缓慢的流速为0.193 毫升/小时的厚方管 (流量是1.93 毫升/小时的薄矩形管)。将注射器泵运行5分钟, 允许将染料的药丸从针头上输送到管子之外。 注: 5 分钟后, 染料离针大约1厘米。由于细管的体积是厚管的10倍, 因此薄壁管的流量由一级增加。</li>
		<li>手动将染料注射器向后拉, 确保染料无法到达针头。 注: 这将确保在针的末端有蒸馏水, 以便在实验运行过程中不会有更多的染料分散到管道中。</li>
		<li>等待时间 tw > t *d , 使染料丸在管道的横截面上扩散。 注意: 扩散时间 t *d = b2/κ认为特征长度 b 为长截面边的一半。这种计算等待时间的方法是推广到任何剖面, 并选择 b。对于我们的代表性结果, 对于厚方管和 15 h 的薄壁矩形管, 等待时间为15分钟。</li>
	</ol>
</li>
	<li>流<ol>
<li>程序注射器泵 A 到所需的流速为1.93 毫升/小时的厚方管和19.3 毫升/小时的薄壁矩形管。</li>
		<li>启动注射器泵和摄像头上的遥控扳机。运行实验5分钟, 间隔在1秒的图片之间。</li>
		<li>将房间灯打开, 并将标尺的图像置于与管道相同的高度, 并与之平行。 注意: 这将有助于确定数据处理中使用的长度刻度 (像素/毫米)。</li>
	</ol>
</li>
</ol>4. 数据处理
<ol><li>从相机中提取内存卡并将数据下载到计算机上, 图像处理软件将用于分析它。</li>
	<li>MATLAB 分析<ol>
<li>首先从第一个实验图像中减去参照图像拍摄 (在步骤3.1.3 中折断)。</li>
		<li>沿管道的上下边缘裁剪图像。如果管道未与框架对齐, 请确保旋转图像。</li>
		<li>对生成的图像中垂直的绿色通道的强度读数进行求和。 注: 这与总断面染料强度成正比, 是沿管道长度的函数。</li>
		<li>使用校准图像的物理长度刻度 (请参见步骤 3.3.3) 将长度单位从像素转换为 mm。</li>
		<li>对所有剩余图像重复。这将导致曲线的时间序列, 测量沿管道长度的总染料浓度。</li>
	</ol>
</li>
</ol>

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作者没有什么可透露的。

将染料注入管子后, 该丸就会从注射针上用稳定的流量输送出去。然后, 有必要等待足够长的时间, 使染料在通道的横断面上扩散。这样, 就得到了均匀的高斯型分布, 作为实验的初始条件。因此, 用可编程注射器泵创建层流背景流。实验运行持续5分钟, 照片每秒拍摄一次。
安装程序中最常见的问题来自部件和管道的连接。各种 3 d 打印件需要在连接时正确密封, 以避免泄漏。玻璃管非常精致, 必须小心处理和安装。
从薄壁矩形管过渡到粗方管时遇到的一个问题是, 管容积减少了10倍。为了保持相同的横断面平均流速与安装的12毫升注射器, 在注射器泵 A 的柱塞速度需要非常低。在这个程序的速度, 柱塞速度是不均匀的, 并在整个实验运行不能保证稳定的流量。因此, 我们切换到一个更小的1毫升注射器时, 与厚方管在步骤2.5.1。
此外, 我们应该验证在初始条件下, 管道垂直尺寸的平均强度近似均匀。如果不是, 则需要在所有框架中应用筛选掩码来解释此差异。
实验中最不重复的部分是染料注入 (因此是初始分布的宽度)。如前所述, 与蒙特卡罗模拟相匹配并不令人关注, 因为在初始照片的分析中可以重新创建实验初始条件。染料的注射和随之而来的手工提取可能并不总是产生精确相同宽度的染料插头。在设置初始染料丸时需要特别注意。随着研究人员在该协议的这一部分获得经验, 实验变得更加可重复性, 但将来的改进当然是可以做到的。
当将安装与微流控设备进行比较时, 在适当 nondimensionalized 时, 在控制方程中出现的唯一参数是 Péclet 数 Pe (如果跟踪器是被动的),即将跟踪程序演化与流解耦。在低雷诺 (Re < < 1) 的假设下, 动态相似性是隐含的, 它保证了稳定的层流流 u (y、z)。这两个参数都设置了微流控装置与实验尺度的完全相似性。在实际操作中, 管道的物理长度只会限制无量纲时间, 我们可以安全地到达我们的设置。对于非常晚的非维时间, 在这个大规模的设置中, 管道的必要长度可能会成为一个固定 Péclet 数的令人望而却步的长时间。
这个实验协议的一个明显的局限性是, 收集到的数据是3D 几何的投影2D 表示形式, 因为图片是在管道上自上而下拍摄的。目前的过程只允许获得交叉分段平均染料分布的演变。在管中的每个位置, 而不是在其横断面平均值上得到定义的分布, 并与理论和数值预测进行比较是目前研究的主题。
所有的实验安装部件都有技术图纸可供下载, 这使得安装程序易于访问和可定制的任何感兴趣的研究员。根据目前的结果, 同样的设置将被用来研究更复杂和未探索的管道几何以及不同的流动机制。

近年来, 大量的工作集中在开发微流控芯片和实验室设备上, 可以降低成本, 提高化学制剂和诊断的生产率, 用于一系列应用。微流控装置的主要特点之一是压力驱动输送流体和溶解溶质通过微。在这种情况下, 更好地了解微尺度下溶质的控制传递变得越来越重要。特别是, 应用如色谱分离1、2和微流控流注入分析3、4需要改进对溶质传递的控制和理解。微流体的研究人员研究并记录了通道截面形状对溶质传播的影响 5, 6, 7, 8, 以及通道长宽比的作用9,10。
溶质沿通道扩散的分析和数值研究最近导致了管道截面几何与分布9、10的形状之间的相关性的识别。在早期的时间尺度, 分布强烈取决于几何: 长方形管子几乎立刻打破对称, 而椭圆管子保留他们的最初的对称更长的9。另一方面, 随着时间的推移, 溶质分布中的不对称性不再将椭圆与矩形区分开来, 而是由横截长宽比λ (短到长边的比值) 单独设置。考虑到矩形截面的 "管道" 和 "管道", 通过室内实验, 对数值模拟和渐近分析的预测进行了评价。薄通道 (纵横比 < < 1) 产生的溶质到达尖锐的前沿和渐狭的尾巴, 而厚的通道 (纵横比 ~ 1) 呈现相反的行为10。这种健壮的效果对初始条件相对不敏感, 可用于帮助选择任何应用程序所需的溶质分布剖面。
在达到经典的 "泰勒色散" 机制之前, 对薄与厚域进行排序的行为就发生在上面。泰勒色散是指在层流 (低雷诺数、Re) 中增强的被动溶质的扩散, 并提高有效扩散率, 与溶质分子扩散率κ11成反比。只有经过长时间的扩散尺度, 溶质在通道中扩散时, 才会观察到这种增强。此类扩散时间刻度是根据几何图形的特征长度刻度 a 定义的, 如 td =2/κ。Péclet 数是测量流体平流对扩散效应的相对重要性的无量纲参数。我们定义这个参数的最短长度尺度为 Pe = Ua/κ, 其中 U 是特征流速度。(雷诺数可以根据 Péclet 数定义为 Re = Pe κ/ν, 其中ν是流体的运动粘度。微流控应用程序的典型 Péclet 数字值12在10和 105之间有所不同, 分子管内范围从 10-7到 10-5 cm2/秒不等. 因此, 考虑到流速和长度的兴趣尺度, 它至关重要的是了解溶质的行为的中长期时间尺度 (相对于扩散时间), 以及过去的初始观测的几何驱动行为和进入跨部门驱动的制度普遍为大类几何图形。
考虑到微流控应用的兴趣, 大规模实验装置的选择首先可能看起来不自然。本文所报道的实验是毫米级的, 而不是在微流控装置中的微型。然而, 同样的物理行为特征的两个系统和定量研究的相关现象仍然可以通过适当的缩放控制方程, 就像模型的飞机在风洞中评估在设计相。特别是, 匹配相关的无量纲参数 (如我们的实验的 Péclet 数), 确保了实验模型的适应性。在如此大的尺度上工作, 同时保持层流压力驱动的流量, 比传统的微型安装提供了一些优势。特别是, 制造、执行和可视化现有实验所需的设备更易于操作, 成本也更低。此外, 与微一起工作的其他共同挑战, 如频繁堵塞和制造公差的增强影响, 随着安装规模的增大而减轻。此实验设置的另一个可能用途是研究层流流中的停留时间分布 (RTD)13。
在下游溶质分布中产生的不对称现象可以通过统计矩进行分析;特别是, 将偏度定义为中心的、归一化的第三矩, 是测量分布不对称的最低阶积分统计。偏斜度的标志通常指示分布的形状, i. e。如果它是前加载 (负偏斜度) 或背装 (正偏斜)。针对信道的纵横比, 存在着与前置分布的薄几何和具有背载分布的粗几何的明显关联10。另外, 对于椭圆管和矩形管道, 也可以计算出分离这两种相反行为的临界纵横比。这种交叉长宽比是非常相似的标准几何, 特别是, λ * = 0.49031 为管道, 和λ * = 0.49038 为管道, 暗示的普遍性的理论10。
本文所描述的实验装置和方法用于研究在各断面玻璃毛细血管中, 压力驱动的被动溶质在层流流中的扩散。实验的简单性和再现度定义了一种可靠的分析方法, 用于理解管道的几何截面与在下游运输时所产生的注入溶质分布的形状之间的连接。这项工作中讨论的方法已经开发出来, 可以很容易地在物理实验室设置中对数学和数值结果进行基准测试。
本文介绍了一个简单的实验过程, 它突出了射流通道的横截纵横比在确定下游溶质分布形状时所起的决定性作用。实验装置需要一个可编程的注射器泵产生层流稳定的流动, 光滑的玻璃管的各种横断面, 第二注射器泵注入扩散溶质 (e. g. 荧光素染料) 到周围的层流流,和紫外线-一盏灯和一个相机记录溶质的演变。CAD 文件是为安装程序的所有自定义部分提供的, 此类文件可用于在装配前 3 d 打印实验部件。

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the diffusion of passive tracers in laminar shear flow

本文介绍了一种简单的实验观察和测量层流流体中被动示踪剂色散的方法。该方法包括先将荧光染料直接注入灌满蒸馏水的管道中, 使其在管道的横断面上扩散, 获得均匀分布的初始条件。在这段时间内, 用可编程的注射器泵激活层流流, 观察通过管道的对流和扩散的竞争。研究了示踪剂分布的不对称性, 并给出了管道断面与分布形状之间的相关性: 薄通道 (纵横比< < 1) 产生的示踪剂到达尖锐的前沿和逐渐变细的尾巴 (前载分布), 而厚通道 (纵横比 ~ 1) 呈现相反的行为 (背载分布)。该实验程序适用于各种几何的毛细管, 特别与微流控应用的动力学相似性有关。

程序集后的实验设置显示在图 1中。在 MATLAB 中生成的图像显示了三次非维时间的浓度曲线 (图 2) 的经过处理的进化过程中的实验数据。验证了示踪剂的强度与浓度之间存在线性关系。随着时间的推移, 分布变化的形状和染料丸在下游移动。图 2显示了在薄壁矩形管道几何情况下的这种演化。初始染料分布是狭窄和对称的 (关于纵向方向和近似地均匀在横断面,图 2左), 但对称在背景流开始时几乎立刻被打破。分布通过呈现尖锐的前端和长渐狭的尾部 (图 2、中间和右侧) 来断开对称性。
实验结果通过蒙特卡罗模拟进行验证, 并与初始分布和流速匹配 (图 3)。染料扩散系数κ的拟合值是在独立实验 (协议步骤 2.4) 中确定的, 用于此比较。蒙特卡罗方法常用于模拟复杂几何的平流扩散问题的演化, 因为边界条件 (在这种情况下均质纽曼) 可以简单地输入为台球一样的反射规则。该方法是对无量纲形式的平流扩散方程所依据的等价随机微分方程的实现进行抽样:
<img alt="Equation 1" src="/files/ftp_upload/57205/57205eq1v2.jpg">
其中 t (x、y、z、t) 是示踪分布, τ是由 td正常化的无量纲时间, x 是纵向空间坐标, y 为短横向坐标, z 为长横向坐标, 均由短边 a 归一化。流体流 u (y, z) 是由负压梯度驱动的非滑移边界条件下的粘性斯托克斯方程的层流稳态解。在管道纵向方向具有期望方差的高斯初始数据可以通过仅考虑扩散 (Pe = 0) 和演化粒子的期望时间来匹配实验初始数据的宽度9,10.这些具有代表性的结果是使用协议中指定的流速值获得的, 但是我们期望观察到的加载现象一般为层流机制10 (图 3) 所控制。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57205/57205fig1.jpg"> 图 1: 实验设置.(A) 实验装置示意图。此数字已从 Aminianet al中进行了修改。10. (B) 实际设置的表示形式。<a href="https://cloudflare.jove.com/files/ftp_upload/57205/57205fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57205/57205fig2.jpg"> 图 2: 已处理数据在不同时间的快照.顶排: 在增加的非维度时, 沿管子横断面扩散的染料浓度的照片通常观察到长横截方向。为了清晰起见, 垂直轴已缩放5次。底部: 染料浓度的强度计算总结沿长横断面方向。峰值被规范化。<a href="https://cloudflare.jove.com/files/ftp_upload/57205/57205fig2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57205/57205fig3.jpg"> 图 3: 蒙特卡罗模拟与实验的浓度分布的比较.分段平均染料浓度沿管道纵向长度的变化表现在两个瞬时时间: τ = 0.15 和τ = 0.30。虚线是模拟结果, 而实线表示实验数据。顶部: 比较粗 (方形) 通道;底部: 比较薄 (矩形) 通道。每个曲线下的区域归一化为一, x = 0 对应于染料初始插头的中心。此数字已从 Aminianet al中进行了修改。10.<a href="https://cloudflare.jove.com/files/ftp_upload/57205/57205fig3large.jpg" target="_blank">请单击此处查看此图的更大版本.</a>
辅助文件1.包含 3D 六角连接器(<a href="https://cloudflare.jove.com/files/ftp_upload/57205/hex_connector_3D.STL" target="_blank">hex_connector_3D</a>) 的 CAD 绘图
辅助文件2.包含 3D 注入器 Post (<a href="https://cloudflare.jove.com/files/ftp_upload/57205/injector_post_3D.STL" target="_blank">injector_post_3D</a>) 的 CAD 绘图
辅助文件3.包含 3D 库的 CAD 绘图 (<a href="https://cloudflare.jove.com/files/ftp_upload/57205/reservoir_3D.STL" target="_blank">reservoir_3D</a>)
辅助文件4.包含 3D 厚管道板的 CAD 绘图 (<a href="https://cloudflare.jove.com/files/ftp_upload/57205/plate_thick_3D.STL" target="_blank">plate_thick_3D</a>)
辅助文件5.包含 3D 薄壁管板的 CAD 绘图 (<a href="https://cloudflare.jove.com/files/ftp_upload/57205/plate_thin_3D.STL" target="_blank">plate_thin_3D</a>)

Watch this Scientific Journal Video about The Diffusion of Passive Tracers in Laminar Shear Flow at JoVE.com

The Diffusion of Passive Tracers in Laminar Shear Flow

本文提出了一种研究层流压力驱动流中被动示踪剂扩散的协议。该程序适用于各种毛细管几何形状。

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 ...

the-diffusion-of-passive-tracers-in-laminar-shear-flow

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8.4K 次观看.  University of North Carolina at Chapel Hill. 本文提出了一种研究层流压力驱动流中被动示踪剂扩散的协议。该程序适用于各种毛细管几何形状。

视频: The Diffusion of Passive Tracers in Laminar Shear Flow

Experimental Measurement of Settling Velocity of Spherical Particles in Unconfined and Confined Surfactant-based Shear Thinning Viscoelastic Fluids

An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic (VES) fluids. The measurements are made for particles settling in unbounded fluids&#160;and fluids between parallel walls. VES fluids over a wide range of rheological properties are prepared and rheologically characterized. The rheological characterization involves steady shear-viscosity and dynamic oscillatory-shear measurements to quantify the viscous and elastic properties respectively. The settling velocities under unbounded conditions are measured in beakers having diameters at least 25x the diameter of particles. For measuring settling velocities between parallel walls, two experimental cells with different wall spacing are constructed. Spherical particles of varying sizes are gently dropped in the fluids and allowed to settle. The process is recorded with a high resolution video camera and the trajectory of the particle is recorded using image analysis software. Terminal settling velocities are calculated from the data.
The impact of elasticity on settling velocity in unbounded fluids is quantified by comparing the experimental settling velocity to the settling velocity calculated by the inelastic drag predictions of Renaud et al.1&#160;Results show that elasticity of fluids can increase or decrease the settling velocity. The magnitude of reduction/increase is a function of the rheological properties of the fluids and properties of particles. Confining walls are observed to cause a retardation effect on settling and the retardation is measured in terms of wall factors.

This paper demonstrates the experimental procedure to measure terminal settling velocities of spherical particles in surfactant-based shear thinning viscoelastic fluids. Fluids over a wide range of rheological properties are prepared and settling velocities are measured for a range of particle sizes in unbounded fluids and fluids between parallel walls.

无约束和封闭表面活性剂中球形粒子沉降速度的实验测量 剪切变薄粘性流体

An experimental study is performed to measure the terminal settling velocities of spherical particles in surfactant based shear thinning viscoelastic ...

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工程学

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for in-situ measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems.

The technique of diffusive gradients in thin films (DGT) is proposed for speciation studies of plutonium. This protocol describes diffusion experiments probing the behavior of Pu(IV) and Pu(V) in presence of organic matter. DGTs deployed in a karstic spring allow assessment of the bioavailability of Pu.

环境钚的薄膜弥散形态和生物利用度测量

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can ...

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

通过单搭接剪切试验的热塑性复合材料优惠券焊接接头的力学特性的超声波焊接

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

During embryogenesis, the epicardial contribution to coronary vasculature development has been very well established. Cells derived from the epicardium differentiate into smooth muscle cells, fibroblasts and endothelial cells that contribute to the formation of coronary vessels. Here we have established an in vitro culture method for embryonic epicardial cells. Using genetic labelling, we have demonstrated that the majority of the migrating cells in our explant culture are of epicardial origin. Epicardial explant cells also retain the expression of epicardial markers (Wt1 and Tbx18). Furthermore, we provide evidence that epicardial explant cells undergo epithelial to mesenchymal transition (EMT), migrate and differentiate into smooth muscle cells after Transforming growth factor beta 1 (TGF-&#946;1) treatment in a manner indistinguishable from that of epicardial cells in vivo. In conclusion, we provide a novel method for the culture of embryonic epicardial cells, which will help to explore the role of specific genes in epicardial cell biology.

In Vitro Culture of Epicardial Cells From Mouse Embryonic Heart

The epicardium is an essential source of multipotent cardiovascular progenitor cells and paracrine factors that are required for cardiovascular development and regeneration. We describe here a method to culture mouse embryonic epicardial cells.

心外膜细胞小鼠胚胎心脏的体外培养

During embryogenesis, the epicardial contribution to coronary vasculature development has been very well established. Cells derived from the epicardium ...

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

在稳定层流边界层扩散火焰本地热通量和燃烧率的估计实验方法

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Design and Use of a Full Flow Sampling System (FFS) for the Quantification of Methane Emissions

The use of natural gas continues to grow with increased discovery and production of unconventional shale resources. At the same time, the natural gas industry faces continued scrutiny for methane emissions from across the supply chain, due to methane&#39;s relatively high global warming potential (25-84x that of carbon dioxide, according to the Energy Information Administration). Currently, a variety of techniques of varied uncertainties exists to measure or estimate methane emissions from components or facilities. Currently, only one commercial system is available for quantification of component level emissions and recent reports have highlighted its weaknesses.
In order to improve accuracy and increase measurement flexibility, we have designed, developed, and implemented a novel full flow sampling system (FFS) for quantification of methane emissions and greenhouse gases based on transportation emissions measurement principles. The FFS is a modular system that consists of an explosive-proof blower(s), mass airflow sensor(s) (MAF), thermocouple, sample probe, constant volume sampling pump, laser based greenhouse gas sensor, data acquisition device, and analysis software. Dependent upon the blower and hose configuration employed, the current FFS is able to achieve a flow rate ranging from 40 to 1,500 standard cubic feet per minute (SCFM). Utilization of laser-based sensors mitigates interference from higher hydrocarbons (C2+). Co-measurement of water vapor allows for humidity correction. The system is portable, with multiple configurations for a variety of applications ranging from being carried by a person to being mounted in a hand drawn cart, on-road vehicle bed, or from the bed of utility terrain vehicles (UTVs). The FFS is able to quantify methane emission rates with a relative uncertainty of &#177; 4.4%. The FFS has proven, real world operation for the quantification of methane emissions occurring in conventional and remote facilities.

Design and Use of a Full Flow Sampling System FFS for the Quantification of Methane Emissions

We have designed, developed, and implemented a novel full flow sampling system (FFS) for quantification of methane emissions and greenhouse gases from across the natural gas supply chain.

设计和全流采样系统（FFS）的使用甲烷排放的量化

The use of natural gas continues to grow with increased discovery and production of unconventional shale resources. At the same time, the natural gas ...

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy (ATOM)

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the main trend in the advanced development of flow cytometry. Notably, adding high-resolution imaging capabilities allows for the complex morphological analysis of cellular/sub-cellular structures. This is not possible with standard flow cytometers. However, it is valuable for advancing our knowledge of cellular functions and can benefit life science research, clinical diagnostics, and environmental monitoring. Incorporating imaging capabilities into flow cytometry compromises the assay throughput, primarily due to the limitations on speed and sensitivity in the camera technologies. To overcome this speed or throughput challenge facing imaging flow cytometry while preserving the image quality, asymmetric-detection time-stretch optical microscopy (ATOM) has been demonstrated to enable high-contrast, single-cell imaging with sub-cellular resolution, at an imaging throughput as high as 100,000 cells/s. Based on the imaging concept of conventional time-stretch imaging, which relies on all-optical image encoding and retrieval through the use of ultrafast broadband laser pulses, ATOM further advances imaging performance by enhancing the image contrast of unlabeled/unstained cells. This is achieved by accessing the phase-gradient information of the cells, which is spectrally encoded into single-shot broadband pulses. Hence, ATOM is particularly advantageous in high-throughput measurements of single-cell morphology and texture &#8211; information indicative of cell types, states, and even functions. Ultimately, this could become a powerful imaging flow cytometry platform for the biophysical phenotyping of cells, complementing the current state-of-the-art biochemical-marker-based cellular assay. This work describes a protocol to establish the key modules of an ATOM system (from optical frontend to data processing and visualization backend), as well as the workflow of imaging flow cytometry based on ATOM, using human cells and micro-algae as the examples.

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy ATOM

This protocol describes the implementation of an asymmetric-detection time-stretch optical microscopy system for single-cell imaging in ultrafast microfluidic flow and its applications in imaging flow cytometry.

微流控成像流式细胞仪通过不对称检测时间延伸光学显微镜（ATOM）

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the ...

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 ...

Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is not well understood. The flow visualization technique is a promising non-intrusive method to illustrate the complex flow field spatially and temporally. A basic flow visualization setup consists of a high-powered laser and optic lenses to generate the laser sheet, a camera, a tracer particle generator, and a data processor. The wind tunnel setup, the specifications of devices involved, and the corresponding parameter settings are dependent on the flow features to be obtained.
Normal smoke wire flow visualization uses a smoke wire to demonstrate the flow streaklines. However, the performance of this method is limited by poor spatial resolution when it is conducted in a complex flow field. Therefore, an improved smoke flow visualization technique has been developed. This technique illustrates the large-scale global LEV flow field and the small-scale shear layer flow structure at the same time, providing a valuable reference for later detailed particle image velocimetry (PIV) measurement.
In this paper, the application of the improved smoke flow visualization and PIV measurement to study the unsteady flow phenomena over a delta wing is demonstrated. The procedure and cautions for conducting the experiment are listed, including wind tunnel setup, data acquisition, and data processing. The representative results show that these two flow visualization methods are effective techniques for investigating the three-dimensional flow field qualitatively and quantitatively.

Here, we present a protocol to observe unsteady vortical flows over a delta wing using a modified smoke flow visualization technique and investigate the mechanism responsible for the oscillations of the leading-edge vortex breakdown locations.

基于流动可视化方法的三角洲机翼流动结构实验研究

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is ...