Name: the diffusion of passive tracers in laminar shear flow
Uploaded: 2018-05-01T13:30:00.000+00:00
Duration: 8 min 1 s
Description: Watch this Scientific Journal Video about The Diffusion of Passive Tracers in Laminar Shear Flow at JoVE.com

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。

<table><tbody><tr><td>Flourescein Dye</td><td>Flinn Scientific&amp;nbsp;</td><td>LOT: 118362&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp; CAS NO: 518-47-8</td><td></td></tr><tr><td>PhD ULTRA Hpsi Syringe Pump</td><td>Harvard Apparatus</td><td>703111</td><td>programmable digital syringe pump</td></tr><tr><td>Compact Infusion Pump Model 975</td><td>Harvard Apparatus</td><td>55-1689</td><td></td></tr><tr><td>Form 2 SLA 3D Printer</td><td>Formlabs</td><td>100-240</td><td></td></tr><tr><td>Glass pipes</td><td>VitroCom</td><td>4410 and 8100</td><td></td></tr><tr><td>PTFE sealing tape</td><td>Teflon</td><td>4934A12</td><td></td></tr><tr><td>PVC tubing (1/8&quot; ID)</td><td>McMaster</td><td>5231K144</td><td>5 Foot Length</td></tr><tr><td>Reusable Stainless Steel Dispensing Needle 22 Gauge, .016&quot; ID, .028&quot; OD, 1/8&quot; NPT Thrd, 2&quot; Lg&amp;nbsp;</td><td>McMaster</td><td>7590A45&amp;nbsp;</td><td>1 Required</td></tr><tr><td>RTV silicone rubber sealant</td><td>McMaster</td><td>74945A69</td><td></td></tr><tr><td>Plastic Syringe Manual, w/ Luer Lock Connection, .34 oz Capacity, Packs of 10&amp;nbsp;</td><td>McMaster</td><td>7510A653&amp;nbsp;</td><td>1 required</td></tr><tr><td>Plastic Syringe Manual, w/ Luer Slip Connection, .034 oz Cap, Packs of 10&amp;nbsp;</td><td>McMaster</td><td>7510A603&amp;nbsp;</td><td>1 required</td></tr><tr><td>Plastic Syringe Manual, w/ Luer Lock Connection, 0.1 oz Capacity, Packs of 10&amp;nbsp;</td><td>McMaster</td><td>7510A651&amp;nbsp;</td><td>2 required</td></tr><tr><td>Plastic dispensing tip</td><td>McMaster</td><td>6699A1&amp;nbsp;</td><td>3 required</td></tr><tr><td>6&quot; C-Clamps</td><td>McMaster</td><td>5133A18</td><td>2 required</td></tr><tr><td>Type 18-8 Stainless Steel Flat Washer Number 6 Screw Size, 0.156&quot; ID, 0.312&quot; OD, Packs of 100&amp;nbsp;</td><td>McMaster</td><td>92141A008&amp;nbsp;</td><td>8 required</td></tr><tr><td>18-8 SS Pan Head Phillips Machine Screw 6-32 Thread, 2-1/4&quot; Length, Packs of 50&amp;nbsp;</td><td>McMaster</td><td>91772A167&amp;nbsp;</td><td>4 required</td></tr><tr><td>Oil-Resistant Buna-N Multipurpose O-Ring 1/16 Fractional Width, Dash Number 016, Packs of 100&amp;nbsp;</td><td>McMaster</td><td>9452K6&amp;nbsp;</td><td>3 required</td></tr><tr><td>Type 18-8 Stainless Steel Hex Nut 6-32 Thread Size, 5/16&quot; Wide, 7/64&quot; High, Packs of 100&amp;nbsp;</td><td>McMaster</td><td>91841A007&amp;nbsp;</td><td>4 required</td></tr><tr><td>18-8 SS Pan Head Phillips Machine Screw 6-32 Thread, 1/2&quot; Length, Packs of 100&amp;nbsp;</td><td>McMaster</td><td>91772A148&amp;nbsp;</td><td>4 required</td></tr><tr><td>24&quot; Black Light Fixture with bulb</td><td>American DJ</td><td>B0002F5544</td><td>2 required</td></tr><tr><td>DSLR camera&amp;nbsp;</td><td>Nikon&amp;nbsp;</td><td>D300</td><td></td></tr><tr><td>24-120 mm lens</td><td>Nikon</td><td>2193</td><td></td></tr><tr><td>Remote programmable trigger</td><td>Nikon</td><td>4917</td><td>remote programmable trigger</td></tr><tr><td>Memory Card</td><td>SanDisk&amp;nbsp;</td><td>SDCFX-032G-E61</td><td></td></tr><tr><td>Metric ruler</td><td>McMaster</td><td>20345A35</td><td></td></tr></tbody></table>

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 ...

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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

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

密闭静态和流动胶体聚合物混合物的共聚焦成像

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

科研

化学

Parallel-plate Flow Chamber and Continuous Flow Circuit to Evaluate Endothelial Progenitor Cells under Laminar Flow Shear Stress

The overall goal of this method is to describe a technique to subject adherent cells to laminar flow conditions and evaluate their response to well quantifiable fluid shear stresses1.
Our flow chamber design and flow circuit (Fig. 1) contains a transparent viewing region that enables testing of cell adhesion and imaging of cell morphology immediately before flow (Fig. 11A, B), at various time points during flow (Fig. 11C), and after flow (Fig. 11D). These experiments are illustrated with human umbilical cord blood-derived endothelial progenitor cells (EPCs) and porcine EPCs2,3.
This method is also applicable to other adherent cell types, e.g. smooth muscle cells (SMCs) or fibroblasts.
The chamber and all parts of the circuit are easily sterilized with steam autoclaving. In contrast to other chambers, e.g. microfluidic chambers, large numbers of cells (&gt; 1 million depending on cell size) can be recovered after the flow experiment under sterile conditions for cell culture or other experiments, e.g. DNA or RNA extraction, or immunohistochemistry (Fig. 11E), or scanning electron microscopy5. The shear stress can be adjusted by varying the flow rate of the perfusate, the fluid viscosity, or the channel height and width. The latter can reduce fluid volume or cell needs while ensuring that one-dimensional flow is maintained. It is not necessary to measure chamber height between experiments, since the chamber height does not depend on the use of gaskets, which greatly increases the ease of multiple experiments. Furthermore, the circuit design easily enables the collection of perfusate samples for analysis and/or quantification of metabolites secreted by cells under fluid shear stress exposure, e.g. nitric oxide (Fig. 12)6.

We are describing a method to subject adherent cells to laminar flow shear stress in a sterile continuous flow circuit. The cells' adhesion, morphology can be studied through the transparent chamber, samples obtained from the circuit for metabolite analysis and cells harvested after shear exposure for future experiments or culture.

平行板流动腔和评估内皮祖细胞层流剪应力下连续流电路

The overall goal of this method is to describe a technique to subject adherent cells to laminar flow conditions and evaluate their response to well ...

生物工程

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

A method is demonstrated to monitor macroscopic translational diffusion using electron paramagnetic resonance (EPR) imaging. A host-guest system with nitroxide spin probe 3-(2-Iodoacetamido)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (IPSL) as a guest inside the periodic mesoporous organosilica (PMO) aerogel UKON1-GEL as a host and ethanol as a solvent is used as an example to describe the protocol. Data is shown from a previous publication, where the protocol has been applied to both IPSL and Tris(8-carboxy-2,2,6,6-perdeutero-tetramethyl-benzo[1,2-d:4,5-d&#8242;]bis(1,3)dithiole) methyl (Trityl) as guest molecules and UKON1-GEL and SILICA-GEL as host systems. 
A method is shown to prepare aerogel samples that cannot be synthesized directly in the sample tube for measurement due to a size change during synthesis. The aerogel is attached to sample tubes using heat shrink tubing and a pressure cooker to reach the necessary temperature without evaporating the solvent in the process. The method does not assume a clearly defined initial distribution of guest molecules at the start of the measurement. Instead, it requires a reservoir on top of the aerogel and experimentally determines the influx rate during data analysis.
The diffusion is monitored continually over a period of 20 hr by recording the 1d spin density profile within the sample. The spectrometer settings for the imaging experiment are described quantitatively. Data analysis software is provided to take the resonator sensitivity profile into account and to numerically solve the diffusion equation. The software determines the macroscopic translational diffusion coefficient by least square minimization of the difference between the experiment and the numerical solution of the diffusion equation.

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

A protocol for the in situ monitoring of the diffusion of guest molecules in porous media using electron paramagnetic resonance (EPR) imaging is presented.

在多孔介质中使用电子顺磁共振成像客体分子扩散的原位监测

A method is demonstrated to monitor macroscopic translational diffusion using electron paramagnetic resonance (EPR) imaging. A host-guest system with ...

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 ...

工程学

A Permanent Window for Investigating Cancer Metastasis to the Lung

Metastasis, accounting for ~90% of cancer-related mortality, involves the systemic spread of cancer cells from primary tumors to secondary sites such as the bone, brain, and lung. Although extensively studied, the mechanistic details of this process remain poorly understood. While common imaging modalities, including computed tomography (CT), positron emission tomography (PET), and magnetic resonance imaging (MRI), offer varying degrees of gross visualization, each lacks the temporal and spatial resolution necessary to detect the dynamics of individual tumor cells. To address this, numerous techniques have been described for intravital imaging of common metastatic sites. Of these sites, the lung has proven especially challenging to access for intravital imaging owing to its delicacy and critical role in sustaining life. Although several approaches have previously been described for single-cell intravital imaging of the intact lung, all involve highly invasive and terminal procedures, limiting the maximum possible imaging duration to 6-12 h. Described here is an improved technique for the permanent implantation of a minimally invasive thoracic optical Window for High-Resolution Imaging of the Lung (WHRIL). Combined with an adapted approach to microcartography, the innovative optical window facilitates serial intravital imaging of the intact lung at single-cell resolution across multiple imaging sessions and spanning multiple weeks. Given the unprecedented duration of time over which imaging data can be gathered, the WHRIL can facilitate the accelerated discovery of the dynamic mechanisms underlying metastatic progression and numerous additional biologic processes within the lung.

Here, we present a protocol for the surgical implantation of a permanently indwelling optical window for the murine thorax, which enables high-resolution, intravital imaging of the lung. The permanence of the window makes it well-suited to the study of dynamic cellular processes in the lung, especially those that are slowly evolving, such as metastatic progression of disseminated tumor cells.

研究癌症转移至肺部的永久窗口

Metastasis, accounting for ~90% of cancer-related mortality, involves the systemic spread of cancer cells from primary tumors to secondary sites such as ...

癌症研究

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index1-3. The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a two-dimensional projection of the disturbed light produced by three-dimensional inhomogeneity.
To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator4. For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process.

Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image.

由微型条纹分析技术在微流控设备混合不均匀

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren ...

Fluorescence Recovery after Merging a Droplet to Measure the Two-dimensional Diffusion of a Phospholipid Monolayer

We introduce a new method to measure the lateral diffusivity of a surfactant monolayer at the fluid-fluid interface, called fluorescence recovery after merging (FRAM). FRAM adopts the same principles as the fluorescence recovery after photobleaching (FRAP) technique, especially for measuring fluorescence recovery after bleaching a specific area, but FRAM uses a drop coalescence instead of photobleaching dye molecules to induce a chemical potential gradient of dye molecules. Our technique has several advantages over FRAP: it only requires a fluorescence microscope rather than a confocal microscope equipped with high power lasers; it is essentially free from the selection of fluorescence dyes; and it has far more freedom to define the measured diffusion area. Furthermore, FRAM potentially provides a route for studying the mixing or inter-diffusion of two different surfactants, when the monolayers at a surface of droplet and at a flat air/water interface are prepared with different species, independently.

We present a new technique to measure the lateral diffusion of a surface active species at the fluid-fluid interface by merging a droplet monolayer onto a flat monolayer.

合并一个液滴后荧光恢复来衡量磷脂单层的二维扩散

We introduce a new method to measure the lateral diffusivity of a surfactant monolayer at the fluid-fluid interface, called fluorescence recovery after ...

Controlling Flow Speeds of Microtubule-Based 3D Active Fluids Using Temperature

We present a method for using temperature to tune the flow speeds of kinesin-driven, microtubule-based three-dimensional (3D) active fluids. This method allows for tuning the speeds in situ without the need to manufacture new samples to reach different desired speeds. Moreover, this method enables the dynamic control of speed. Cycling the temperature leads the fluids to flow fast and slow, periodically. This controllability is based on the Arrhenius characteristic of the kinesin-microtubule reaction, demonstrating a controlled mean flow speed range of 4&#8211;8 &#181;m/s. The presented method will open the door to the design of microfluidic devices where the flow rates in the channel are locally tunable without the need for a valve.

The goal of this protocol is to use temperature to control the flow speeds of three-dimensional active fluids. The advantage of this method not only allows for regulating flow speeds in situ but also enables dynamic control, such as periodically tuning flow speeds up and down.

使用温度控制基于微管的3D活性流体的流速

We present a method for using temperature to tune the flow speeds of kinesin-driven, microtubule-based three-dimensional (3D) active fluids. This method ...

Quantifying Mixing using Magnetic Resonance Imaging

Mixing is a unit operation that combines two or more components into a homogeneous mixture. This work involves mixing two viscous liquid streams using an in-line static mixer. The mixer is a split-and-recombine design that employs shear and extensional flow to increase the interfacial contact between the components. A prototype split-and-recombine (SAR) mixer was constructed by aligning a series of thin laser-cut Poly (methyl methacrylate) (PMMA) plates held in place in a PVC pipe. Mixing in this device is illustrated in the photograph in Fig. 1. Red dye was added to a portion of the test fluid and used as the minor component being mixed into the major (undyed) component. At the inlet of the mixer, the injected layer of tracer fluid is split into two layers as it flows through the mixing section. On each subsequent mixing section, the number of horizontal layers is duplicated. Ultimately, the single stream of dye is uniformly dispersed throughout the cross section of the device.
 Using a non-Newtonian test fluid of 0.2% Carbopol and a doped tracer fluid of similar composition, mixing in the unit is visualized using magnetic resonance imaging (MRI). MRI is a very powerful experimental probe of molecular chemical and physical environment as well as sample structure on the length scales from microns to centimeters. This sensitivity has resulted in broad application of these techniques to characterize physical, chemical and/or biological properties of materials ranging from humans to foods to porous media 1, 2. The equipment and conditions used here are suitable for imaging liquids containing substantial amounts of NMR mobile 1H such as ordinary water and organic liquids including oils. Traditionally MRI has utilized super conducting magnets which are not suitable for industrial environments and not portable within a laboratory (Fig. 2). Recent advances in magnet technology have permitted the construction of large volume industrially compatible magnets suitable for imaging process flows. Here, MRI provides spatially resolved component concentrations at different axial locations during the mixing process. This work documents real-time mixing of highly viscous fluids via distributive mixing with an application to personal care products.

Magnetic resonance imaging (MRI) provides a powerful tool to evaluate the effectiveness of process equipment during operation. We discuss the use of MRI to visualize mixing in a static mixer. The application is relevant to personal care products, but can be applied to a broad range of food, chemical, biomass and biological fluids.

量化混合使用磁共振成像

Mixing is a unit operation that combines two or more components into a homogeneous mixture.  This work involves mixing two viscous liquid streams using an ...

生物学

Surface Dye Flow Visualization: A Qualitative Method to Observe Streakline Patterns in Supersonic Flow

Flow visualization around or on a body is an important tool in aerodynamics research. It provides a method to qualitatively and quantitatively study flow structure, and it also helps researchers theorize and verify fluid flow behavior. Flow visualization can be divided into two categories: off-the-surface visualization and surface flow visualization. Off-the-surface flow visualization techniques involve determining the flow characteristics around the body of interest. They include but are not restricted to particle image velocimetry (PIV), Schlieren imaging, and smoke flow visualization. These techniques can provide qualitative as well as quantitative data on the flow around a body. However, these techniques are generally expensive and difficult to set-up. Surface flow visualization techniques, on the other hand, involve coating the body of interest with a dye to study flow on the surface. These techniques, which are more invasive in practice, include dye flow visualization and, more recently, use pressure-sensitive paint, which gives a detailed image of the flow on the body&#39;s surface. This allows researchers to visualize different flow features, including laminar bubbles, boundary layer transitions, and flow separation. Dye flow visualization, the technique of interest in the current experiment, provides a qualitative picture of the surface flow and is one of the simplest and most cost-effective surface flow visualization methods, specifically for visualizing gaseous flows on a body.
In this experiment, the surface flow behavior on six bodies are studied in supersonic flow. The streakline patterns are obtained using the dye flow visualization technique, and the flow paths, degree of flow attachment and separation, and location and type of shocks are identified and studied from the flow images.

Surface Dye Flow: Streakline Patterns in Supersonic Flow

表面染料流可视化:观察超音速流中条纹模式的定性方法

Flow visualization around or on a body is an important tool in aerodynamics research. It provides a method to qualitatively and quantitatively study flow ...