作者感谢美国能源部和RPSEA的财政支持，以及赞助德克萨斯大学奥斯汀分校水力压裂和防沙的JIP的公司（液体空气、空气产品、阿纳达科、阿帕奇、贝克休斯、必和必拓、英国石油公司美国公司、雪佛龙公司、康菲石油公司、埃克森美孚公司、费鲁斯公司、哈里伯顿公司、赫斯公司、林德集团公司、佩梅克斯公司、先锋自然资源公司），普拉克斯尔，沙特阿美，斯伦贝谢，壳牌，西南能源，挪威国家石油公司，韦瑟福德和YPF）。

1. 液体的准备
本实验研究采用无聚合物、粘胶、双成分、表面活性剂为基础的流体系统。这种流体系统已用于许多生产领域的油气井，用于水力压裂处理44，45。此流体系统用于此研究，因为它具有光学透明度，流变学可以通过系统地改变两个组件的浓度和比例来控制。流体系统由一种离子表面活性剂（如硫化钠）作为组件A和一种离子表面活性剂（如N、N、N-三甲基-1-氯化钙）作为组件B。
<ol><li>在蒸馏水中加入A组件的给定浓度，然后使用架空搅拌机在高转速下混合，以确保正确混合。允许它混合2-3分钟。</li>
	<li>在此混合物中加入给定浓度的组件 B，并允许其混合 2-3 分钟。</li>
	<li>将混合物休息2-6小时，以排出气泡。注意:最终的液体混合物是光学透明的。在这项研究中，使用了七种不同浓度的液体混合物。选择浓度是为了获得各种粘度的液体混合物。</li>
</ol>2. 测量未绑定流体中的沉降速度
使用直径为 1-5 毫米的玻璃球体。
<ol><li>使用高分辨率显微镜测量玻璃球体的直径。确保球体表面光滑，球体近乎完美。</li>
	<li>将液体存放在直径至少是颗粒直径 25 倍的玻璃容器中，以确保密闭壁不会对颗粒的沉降速度产生影响。</li>
	<li>使用实验室温度计记录室温和流体温度。温度测量很重要，因为流体的风湿测量应在进行沉降实验的温度下进行。</li>
	<li>将一根米棒放在容器旁边。</li>
	<li>轻轻地将玻璃颗粒浸入液体中，使其沉淀。用高分辨率摄像机记录沉降过程。</li>
	<li>使用图像分析应用程序从录制的视频中跟踪粒子在不同时间步骤的位置。注意:在这项工作中，使用了名为"跟踪器"的软件应用程序<a href="http://www.cabrillo.edu/~dbrown/tracker/" target="_blank">（http://www.cabrillo.edu/~dbrown/tracker/）。</a></li>
	<li>绘制粒子与时间的垂直位置，并计算从线的斜坡的终端沉降速度。</li>
	<li>在特殊条件下重复实验至少 3 倍，以确保可重复性。执行不同测量的图像分析，并使用错误条报告特定流体中给定粒子直径的沉降速度。</li>
	<li>重复上述步骤以处理不同直径的颗粒，并记录沉降速度。绘制沉降速度与粒子直径。注: 图1 显示一个流体中五个不同大小粒子的沉降速度。
</li>
</ol>3. 平行墙体间流体沉降速度测量
为了测量平行墙面下的沉降速度，使用了两个由Plexiglas制成的实验细胞。
<ol><li>在设计和建造单元时，确保墙壁平滑且完全平行。保持低细胞的纵横比，以确保墙壁正交对平行壁没有影响。注意:本研究中两个细胞的壁间隙分别为3.6毫米和8毫米。 图2 显示了一个实验单元的示意图。</li>
	<li>将细胞填充液体，并通过入口/出口端口轻轻释放细胞中的颗粒。用橡胶塞密封入口/出口端口，让颗粒沉淀，直到到达细胞中间。</li>
	<li>此时，小心地垂直定位细胞，让粒子沉淀。</li>
	<li>将一米棒放在细胞旁边，然后使用高分辨率摄像机记录沉降。</li>
	<li>使用实验室温度计记录室温和流体温度。这一点很重要，因为流体的风湿测量应在此温度下进行。</li>
	<li>与无限制的沉降速度测量一样，测量软件应用程序"跟踪器"中的沉降速度。重复测量至少三次，以确保可重复性，并获取每个测量的误差条。</li>
</ol>4. 流体的流体特征
<ol><li>执行稳定的剪切粘度测量，以测量流体的粘度作为剪切率的函数。注意: 在本作品中，由TA仪器采用的 ARES 流湿计采用双壁同心圆柱夹具（内杯直径:27.95 毫米，内鲍勃直径:29.50 毫米，外鲍勃直径:32.00 毫米，外侧杯径:34.00 毫米，鲍勃长度:32.00 毫米）。
</li>
	<li>将剪切速率从 0.1-800 秒 -1 变为10 点/十点测量。确保杯子的温度与在同一液体中进行沉降实验的温度相同。 图 3 显示日志绘图上一个流体样本的粘度与剪切率。</li>
	<li>对于同一流体，计算沉降实验中粒子遇到的剪切速率范围。使用表面平均粒子剪切速率定义为2V/dp 20，23，其中V是粒子的沉降速度，dp是粒子直径。</li>
	<li>在粘度与剪切率图的这一系列剪切率中 ，μ=Kγn-1适合功率定律曲线。在日志日志绘图上，此拟合将是一条直线。确定参数 K（ 流一致性索引）和 n（ 流行为索引）。 K 和 n 量化流体的粘度。 图3 显示了权力法适合同一情节。</li>
	<li>在 0.1-100 rad/秒的频率范围内执行动态振荡剪切测量，并测量弹性模数 、G'和粘性模组 、G'。以 10 点/十点进行测量。 图4显示了流体样本的G'和G'。</li>
	<li>从此数据中计算两个模组（G'/G）的比例。使用回归分析将莫杜利与麦克斯韦模型的比例调整，并计算流体的放松时间（λ）。麦克斯韦模型的两个模组比率等式为46，47:</li>
</ol><img alt="Equation 12" fo:src="/files/ftp_upload/50749/50749eq12highres.jpg" src="/files/ftp_upload/50749/50749eq12.jpg"> 液体的放松时间量化了液体的弹性。放松时间越大，液体的弹性就越大。图5显示了流体样本的G'/G'以及麦克斯韦适合。 安装通过最大限度地减少频率范围内方差测量的总和来执行。 <img alt="Equation 13" fo:src="/files/ftp_upload/50749/50749eq13highres.jpg" src="/files/ftp_upload/50749/50749eq13.jpg">
5. 确定弹性对无限沉降速度的影响
<ol><li>表示V∞VE）无界流体中粒子的实验沉降速度，其中'∞VE'是指未受约束的粘性流体。将此实验沉降速度与基于功率定律参数的明显粘度数据计算的沉降速度（V∞INEL）进行比较。使用雷纳德等人开发的表达式。1计算V∞伊内尔。导言部分提到了这些表达式。"∞INEL"是指未受约束的无弹性液体。</li>
	<li>计算V∞EL/V∞INEL的比例，并将该比率称为速度比。 速度比的价值说明了弹性对沉降速度的影响。速度比大于 1 表示由于流体弹性，速度增加/阻力减少。速度比小于 1 表示由于流体弹性，速度降低/拖动增强。</li>
	<li>绘制速度比作为不同流体粒子直径的函数，以观察弹性对不同流变流体中不同直径粒子沉降速度的影响。 图6 显示速度比作为其中一个流体中粒子直径的函数。</li>
</ol>6. 量化平行墙对沉降速度的延迟效应
<ol><li>计算壁系数，Fw为给定直径粒子，通过在平行墙体存在的情况下划分沉降速度，V∞VE到无边界流体中的沉降速度，V∞VE。</li>
	<li>对于给定的流体，将墙体因子绘制为粒子直径与墙体间距比 的函数， r . 图7 显示了在其中一个流体中沉降粒子的壁因子。该图有助于量化密闭墙对沉降速度的阻滞效应。降低墙体因子，提高墙体阻滞效果。</li>
</ol>

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作者想指出，本出版物的目标是直观地演示测量粒子沉降的实验程序。有关详细结果及分析，读者应参考较早的刊物43。

实验研究的重点是在未受约束和封闭的条件下，测量剪切稀释粘性流体中球形粒子的沉降速度。介绍了详细的实验程序，以获得可重复测量的沉降速度。结果表明，流体弹性可以增加或降低沉降速度。墙体对沉降产生延缓效应，这种效应是用墙体因素来衡量的。
在实验之前，应确保粒子接近表面光滑的完美球体。球体的直径应准确测量。实验过程，包括图像分析，应该通过在无限牛顿流体（如 甘油溶液）中进行一些初步实验，并将实验沉降速度与斯托克斯分析解决方案进行比较来验证。
实验至少应重复三次，以确保可重复性。应注意在实验时测量液体温度，并在相同的温度下测量流变学。

在药物制造、废水处理、空间推进剂再注入、半导体加工和液体洗涤剂制造等应用中，液体颗粒的悬浮。在石油工业中，粘性压裂液用于在液压断裂中运输质子（通常是砂）。停止抽水后，前体保持断裂打开，并为碳氢化合物回流提供导电途径。
粒子的沉降受流体的流变学和密度、颗粒的大小、形状和密度以及密闭壁的影响的制约。对于在蠕变流系中沉淀在牛顿流体中的球形粒子，沉降速度由斯托克斯方程给出，斯托克斯于 1851 年得出。在随后的研究人员2-6中提出了计算高雷诺兹数字阻力的表达方式。封闭壁通过对粒子施加阻滞作用来降低沉降速度。墙体因子 ，Fw，被定义为在无限制条件下将墙限制在沉降速度的终端沉降速度比率。墙系数量化了密闭墙的阻滞效应。文献7-13提供了许多理论和实验研究，以确定在不同断面管中以不同断面管中沉淀的球体的壁因子。总之，有大量的信息可用于确定牛顿流体中球体的阻力。
过去关于确定非内托输液中颗粒的沉降速度的工作，特别是粘性流体，并不完整。各种数值预测14-18和实验研究19-24可用于文献，以确定在无弹性功率定律流体的球体上的阻力。使用特里帕蒂等人的理论预测。15和特里帕蒂和查布拉17日，雷纳德等人。1开发以下表达式以计算无弹性功率定律流体中的阻力系数（CD）。
对于重新pl<0.1 （爬行流系统）
<img alt="Equation 1" fo:src="/files/ftp_upload/50749/50749eq1highres.jpg" src="/files/ftp_upload/50749/50749eq1.jpg"> 其中 X（n） 是拖动校正因子13。RePL是属于权力法液体中的球体的雷诺兹数字，定义为:
<img alt="Equation 2" fo:src="/files/ftp_upload/50749/50749eq2highres.jpg" src="/files/ftp_upload/50749/50749eq2.jpg"> 其中ρ f是液体的密度。拖动校正因子安装下列方程1:
<img alt="Equation 3" fo:src="/files/ftp_upload/50749/50749eq3highres.jpg" src="/files/ftp_upload/50749/50749eq3.jpg"> 使用拖动系数的定义，将沉降速度计算为:
<img alt="Equation 4" fo:src="/files/ftp_upload/50749/50749eq4highres.jpg" src="/files/ftp_upload/50749/50749eq4.jpg"> 对于 0.1<RePL<100
<img alt="Equation 5" fo:src="/files/ftp_upload/50749/50749eq5highres.jpg" src="/files/ftp_upload/50749/50749eq5.jpg"> 其中 X是表面积与粒子预测面积的比率，球体等于 4。CD0是方程 1给出的斯托克斯区域（rePL < 0.1）的阻力系数，C D∞是牛顿区域的拖动系数值（rePL > 5 x 102），等于 0.44。参数β，b，k表示为:
<img alt="Equations 6-8" fo:src="/files/ftp_upload/50749/50749eq6-8highres.jpg" src="/files/ftp_upload/50749/50749eq6-8.jpg"> αo = 3 和 α 是与 X（n） 相关的平均剪切率的修正如下:
<img alt="Equation 9" fo:src="/files/ftp_upload/50749/50749eq9highres.jpg" src="/files/ftp_upload/50749/50749eq9.jpg"> 要计算沉降速度，使用无维组Nd 25: 
<img alt="Equation 10" fo:src="/files/ftp_upload/50749/50749eq10highres.jpg" src="/files/ftp_upload/50749/50749eq10.jpg"> Nd 独立于沉降速度，可以明确计算。使用这个值和 方程5中的阻力系数表达，可以反复解决RePL。 然后，可以使用:
<img alt="Equation 11" fo:src="/files/ftp_upload/50749/50749eq11highres.jpg" src="/files/ftp_upload/50749/50749eq11.jpg"> 方程1-9中的表达基于对值1≥n≥0.4的理论预测。 查布拉13日将上述表述的预测与沙阿26-27（n变化为0.281-0.762）和福特等人的实验结果进行了比较。 28 （n变化从 0.06-0.29）.这些表达式被证明能够准确预测阻力系数。基于这些分析，上述配方可用于计算无弹性功率定律流体中球形粒子的沉降速度为 1 ≥ n ≥ 0.06。将无弹性功率定律流体的沉降速度与功率定粘液中的实验速度进行比较，以确定流体弹性对沉降速度的影响。下一节中提到了详细的步骤。
测定粘胶液中颗粒的沉降速度也是不同研究人员不同观测的课题:（一） 在爬行流系中，剪切变薄效应完全掩盖粘性效应和沉降速度与纯粘性理论29-32非常一致，（ii） 粒子在爬行流系内外经历阻力减少，由于弹性30，33，34而沉降速度增加，（iii） 沉降速度因流体弹性35而降低。沃尔特斯和坦纳36 总结说，对于博格流体（恒定粘度弹性流体）弹性导致低威森博格数字的阻力减少，其次是在较高的魏森博格数字的阻力增强。麦金利37 强调，球体后的延伸效应导致威森伯格数字的阻力增加。Chhabra13 在对先前在无限制和密闭粘性流体中沉降粒子的工作进行了全面回顾后，强调了在理论发展中结合切变率依赖粘度和流体弹性的现实描述的挑战。在过去几年中，对球形粒子沉降的壁效应的研究也是研究的一个领域。然而，所有的工作都完成了球形粒子在圆柱形管中的沉降。没有关于球形粒子在平行墙体之间沉淀在粘性流体中的数据。
这项工作试图实验研究球体在剪切稀释粘性液体中的沉降。这项实验研究的目的是了解流体弹性、剪切变薄和墙体密闭对剪切稀释粘液中球形粒子沉降速度的影响。本文重点介绍了本研究的实验方法以及一些具有代表性的结果。详细的结果，连同分析，可以在较早的出版物43中找到。

<table><tbody><tr><td>Glass Microspheres</td><td>Whitehouse Scientific</td><td>#GP1750</td><td>Available in different sieve fractions.</td></tr><tr><td>Rheometer</td><td>TA Instruments</td><td>ARES</td><td>Any standard rheometer capable of taking dynamic and static measurements</td></tr><tr><td>Anionic Surfactant (Component A)</td><td></td><td>Proprietary fluid</td><td>Used in oil field services for hydraulic fracturing. Sodium Xylene Sulfonate can be used as a substitute.</td></tr><tr><td>Cationic Surfactant (Component B)</td><td></td><td>Proprietary fluid</td><td>Used in oil field services for hydraulic fractuing. N,N,N-Trimethyl-1-Octadecamonium Chloride can be used as a substitute.</td></tr></tbody></table>

experimental measurement of settling velocity of spherical particles in unconfined and confined surfactant-based shear thinning viscoelastic fluids

进行了一项实验性研究，以测量基于表面活性剂的剪切变薄粘性 （VES） 流体中球形粒子的终端沉降速度。测量是针对在平行墙体和平行墙之间的无边界流体和流体中沉淀的粒子进行测量的。VES 流体具有广泛的风湿特性，具有风湿学特征。风湿特征包括稳定的剪切粘度和动态振荡切变测量，分别量化粘度和弹性特性。在无限制条件下的沉降速度以直径至少是颗粒直径25倍的烧嘴来测量。为了测量平行墙之间的沉降速度，构建了两个具有不同墙间距的实验单元。不同大小的球形粒子被轻轻地掉入流体中，并允许沉降。该过程使用高分辨率摄像机进行记录，粒子轨迹使用图像分析软件进行记录。终端沉降速度是根据数据计算的。
通过比较实验沉降速度与 Renaud 等人的无弹性阻力预测计算的沉降速度，可以量化弹性对无边界流体沉降速度的影响 。1结果表明，流体的弹性可以增加或降低沉降速度。减少/增加的幅度是流体的流变特性和粒子特性的函数。观察到封闭壁对沉降造成延缓效应，并根据墙体因素测量阻滞。

实验对七种不同流体混合物中的五种不同直径粒子进行了实验，这些混合物具有独特的K、n和λ值。 图1显示沉降速度作为一个流体中粒子直径的函数。错误栏显示三个测量中的变异性。实验期间测量的室温为23°C。可以观察到，沉降速度随着粒子直径的增加而增加。图 3显示了在 23 °C 的温度下执行的相同流体的稳定剪切粘度测量。 图显示了流体的粘度作为剪切率的函数。液体表现出剪切变薄行为。从图1中的沉降速度，所有粒子的剪切速率计算为2V/dp。在这个剪切速率范围内，功率定律（K， n）模型是适合如图 3所示。K的拟合值为 0.666 Pa.sn和n = 0.31。
图4显示弹性模块化和粘度模块化与同一流体在23°C的角频率。图5显示G'/G'作为角频率函数的比例。它与方程12给出的麦克斯韦模型相配。适合也显示在同一个情节。放松时间的价值是0.175秒。
图6 显示速度比作为其中一个流体中粒子直径的函数。观察到，速度比大于两个较小球体的一个，三个较大的球体的速率小于一个。换句话说，较小的球体体验减阻力，较大的球体体验阻力增强。这表明流体弹性可以增加或降低球体的沉降速度。 表2 显示使用 方程2计算的粒子的雷诺兹数字。结果表明，颗粒在小雷诺兹数字下会经历减阻力/增加。在其他流体中也进行了类似的实验，观察到速度比不仅仅是粒子直径的函数，而是球形粒子流体的流体特性和密度。详细的结果可以在马尔霍特拉和夏尔马43找到。读者应该看到德拉格-魏森伯格数字地图 图8 在马尔霍特拉和夏尔马43。数据显示，在低魏森博格数字下，阻力减少，随后过渡到高威森博格数字的阻力增强，即使对于在爬行流系统中沉淀的粒子（RePL < 0.1）。
图7显示墙体因子（Fw） 作为粒子直径与墙面间距比（r）的函数，用于在 3.6 mm 和 8 mm 的平行隔间距墙壁之间沉降的球体。数据点在 0-1 的r完整范围内均匀间隔。可以观察到，壁因子随着r值的增加而减少，这表明随着粒子直径与墙体间距的可比性，墙体阻滞效应也会增加。还观察到，在r值，Fw 不是唯一的（不像牛顿流体），并依赖于墙间距。
<img alt="Figure 1" src="/files/ftp_upload/50749/50749fig1.jpg"> 图1。在 VES 流体中稳定不同直径颗粒的速度。
<img alt="Figure 2" src="/files/ftp_upload/50749/50749fig2.jpg"> 图2。用于在平行壁前测量沉降速度的实验单元的示意图。 细胞由丛球制成，墙壁之间的间距为8毫米。
<img alt="Figure 3" src="/files/ftp_upload/50749/50749fig3.jpg"> 图3。粘度作为 VES 流体样品剪切率的函数（稳定剪切粘度测量）。 粘度随着剪切率的降低而降低，说明剪切变薄行为。在粒子剪切率的实验范围内安装的功率定律（K， n）也显示在绘图上。
<img alt="Figure 4" src="/files/ftp_upload/50749/50749fig4.jpg"> 图4。弹性模块化（G'）和粘性模块化（G''）作为 VES 流体样本（动态振荡-剪切测量）的角频率函数函数。
<img alt="Figure 5" src="/files/ftp_upload/50749/50749fig5.jpg"> 图5。粘度与弹性模块化的比例作为角频率的函数。 情节上显示了麦克斯韦适合。适合的放松时间为 0.183 秒。
<img alt="Figure 6" src="/files/ftp_upload/50749/50749fig6.jpg"> 图6。VES 流体样本中不同大小颗粒的速度比。 结果表明，较小的球体会减少阻力，而较大的颗粒会经历阻力增强。
<img alt="Figure 7" src="/files/ftp_upload/50749/50749fig7.jpg"> 图7。墙体因子作为 VES 流体样品中粒子直径与壁间距比的函数。 封闭符号是指在有 8 毫米间距的墙壁之间沉降的粒子的数据点，而打开的符号是指在 3.66 mm 间距的墙壁之间沉降的粒子。

<table><tbody align="center">
<tr>
<td>
粒子直径 （毫米）</td>
			<td>
雷诺兹号码 （使用 方程2计算）</td>
		</tr>
<tr>
<td>1.74</td>
			<td>0.3</td>
		</tr>
<tr>
<td>2.03</td>
			<td>0.44</td>
		</tr>
<tr>
<td>2.94</td>
			<td>1.42</td>
		</tr>
<tr>
<td>3.63</td>
			<td>2.09</td>
		</tr>
<tr>
<td>4.17</td>
			<td>2.63</td>
		</tr>
</tbody></table>表2。使用方程 2 计算的粒子的雷诺兹数字 。

Watch this Scientific Journal Video about Experimental Measurement of Settling Velocity of Spherical Particles in Unconfined and Confined Surfactant-based Shear Thinning Viscoelastic Fluids at JoVE.co

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

本文演示了测量表面活性切变粘液中球形粒子终端沉降速度的实验过程。准备了各种风湿特性的流体，并测量了平行壁之间无边界流体和流体中一系列粒子大小的沉降速度。

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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Unit 1

Fluid Statics

Application of Newton's Laws of Motion

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13.2K 次观看.  The University of Texas at Austin. 本文演示了测量表面活性切变粘液中球形粒子终端沉降速度的实验过程。准备了各种风湿特性的流体，并测量了平行壁之间无边界流体和流体中一系列粒子大小的沉降速度。

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

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

Measuring Material Microstructure Under Flow Using 1-2 Plane Flow-Small Angle Neutron Scattering

A new small-angle neutron scattering (SANS) sample environment optimized for studying the microstructure of complex fluids under simple shear flow is presented. The SANS shear cell consists of a concentric cylinder Couette geometry that is sealed and rotating about a horizontal axis so that the vorticity direction of the flow field is aligned with the neutron beam enabling scattering from the 1-2 plane of shear (velocity-velocity gradient, respectively). This approach is an advance over previous shear cell sample environments as there is a strong coupling between the bulk rheology and microstructural features in the 1-2 plane of shear. Flow-instabilities, such as shear banding, can also be studied by spatially resolved measurements. This is accomplished in this sample environment by using a narrow aperture for the neutron beam and scanning along the velocity gradient direction. Time resolved experiments, such as flow start-ups and large amplitude oscillatory shear flow are also possible by synchronization of the shear motion and time-resolved detection of scattered neutrons. Representative results using the methods outlined here demonstrate the useful nature of spatial resolution for measuring the microstructure of a wormlike micelle solution that exhibits shear banding, a phenomenon that can only be investigated by resolving the structure along the velocity gradient direction. Finally, potential improvements to the current design are discussed along with suggestions for supplementary experiments as motivation for future experiments on a broad range of complex fluids in a variety of shear motions.

A shear cell is developed for small-angle neutron scattering measurements in the velocity-velocity gradient plane of shear and is used to characterize complex fluids. Spatially resolved measurements in the velocity gradient direction are possible for studying shear-banding materials. Applications include investigations of colloidal dispersions, polymer solutions, and self-assembled structures.

测量材料在微流使用1-2面流小角中子散射

A new small-angle neutron scattering (SANS) sample environment optimized for studying the microstructure of complex fluids under simple shear flow is ...

工程学

Image-based Lagrangian Particle Tracking in Bed-load Experiments

Image analysis has been increasingly used for the measurement of river flows due to its capabilities to furnish detailed quantitative depictions at a relatively low cost. This manuscript describes an application of particle tracking velocimetry (PTV) to a bed-load experiment with lightweight sediment. The key characteristics of the investigated sediment transport conditions were the presence of a covered flow and of a fixed rough bed above which particles were released in limited number at the flume inlet. Under the applied flow conditions, the motion of the individual bed-load particles was intermittent, with alternating movement and stillness terms. The flow pattern was preliminarily characterized by acoustic measurements of vertical profiles of the stream-wise velocity. During process visualization, a large field of view was obtained using two action-cameras placed at different locations along the flume. The experimental protocol is described in terms of channel calibration, experiment realization, image pre-processing, automatic particle tracking, and post-processing of particle track data from the two cameras. The presented proof-of-concept results include probability distributions of the particle hop length and duration. The achievements of this work are compared to those of existing literature to demonstrate the validity of the protocol.

The manuscript presents a protocol for the conduction of bed-load sediment transport experiments where the moving particles are tracked by image analysis. The experimental facility, the procedures for run realization and data processing, and finally some proof-of-concept results are presented here.

基于图像的拉格朗日粒子跟踪在床载荷实验

Image analysis has been increasingly used for the measurement of river flows due to its capabilities to furnish detailed quantitative depictions at a ...

环境科学

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

挑战流变特性高度集中悬架 - 为例进行丝网印刷银浆

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

一种研究稠密气体和液体分子流体力学过程的模拟宏观技术

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

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 ...

Simultaneous Measurement of Turbulence and Particle Kinematics Using Flow Imaging Techniques

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine micro-organisms, and/or sediments in the ocean, or fluidized bed reactors and combustion processes in engineered systems. In order to study the effect of turbulence on the kinematics of particles in such flows, simultaneous measurements of both the flow and particle kinematics are required. Non-intrusive, optical flow measurement techniques for measuring turbulence, or for tracking particles, exist but measuring both simultaneously can be challenging due to interference between the techniques. The method presented herein provides a low cost and relatively simple method to make simultaneous measurements of the flow and particle kinematics. A cross section of the flow is measured using a particle image velocimetry (PIV) technique, which provides two components of velocity in the measurement plane. This technique utilizes a pulsed-laser for illumination of the seeded flow field that is imaged by a digital camera. The particle kinematics are simultaneously imaged using a light emitting diode (LED) line light that illuminates a planar cross section of the flow that overlaps with the PIV field-of-view (FOV). The line light is of low enough power that it does not affect the PIV measurements, but powerful enough to illuminate the larger particles of interest imaged using the high-speed camera. High-speed images that contain the laser pulses from the PIV technique are easily filtered by examining the summed intensity level of each high-speed image. By making the frame rate of the high-speed camera incommensurate with that of the PIV camera frame rate, the number of contaminated frames in the high-speed time series can be minimized. The technique is suitable for mean flows that are predominantly two-dimensional, contain particles that are at least 5 times the mean diameter of the PIV seeding tracers, and are low in concentration.

The technique described herein offers a low cost and relatively simple method to simultaneously measure particle kinematics and turbulence in flows with low particle concentrations. The turbulence is measured using particle image velocimetry (PIV), and particle kinematics are calculated from images obtained with a high-speed camera in an overlapping field-of-view.

流成像技术同时测量湍流和粒子运动学

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine ...

In Situ Mapping of the Mechanical Properties of Biofilms by Particle-tracking Microrheology

Bacterial cells are able to form surface-attached biofilm communities known as biofilms by encasing themselves in extracellular polymeric substances (EPS). The EPS serves as a physical and protective scaffold that houses the bacterial cells and consists of a variety of materials that includes proteins, exopolysaccharides and DNA. The composition of the EPS may change, which remodels the mechanic properties of the biofilm to further develop or support alternative biofilm structures, such as streamers, as a response to environmental cues. Despite this, there are little quantitative descriptions on how EPS components contribute to the mechanical properties and function of biofilms. Rheology, the study of the flow of matter, is of particular relevance to biofilms as many biofilms grow in flow conditions and are constantly exposed to shear stress. It also provides measurement and insight on the spreading of the biofilm on a surface. Here, particle-tracking microrheology is used to examine the viscoelasticity and effective crosslinking roles of different matrix components in various parts of the biofilm during development. This approach allows researchers to measure mechanic properties of biofilms at the micro-scale, which might provide useful information for controlling and engineering biofilms.

In Situ Mapping of the Mechanical Properties of Biofilms by Particle-tracking Microrheology

Particle-tracking microrheology investigates the viscoelasticity of materials. Here, the technique is used to determine the viscoelasticity, creep compliance and effective crosslinking roles of different matrix components of a bacterial biofilm. The matrix consists of polymeric substances secreted by the bacteria and its components determine biofilm structure and mechanical properties.

在生物膜的力学性能原位制图粒子追踪Microrheology

Bacterial cells are able to form surface-attached biofilm communities known as biofilms by encasing themselves in extracellular polymeric substances ...

生物工程

Accurate Determination of the Equilibrium Surface Tension Values with Area Perturbation Tests

We demonstrate two robust protocols for determining the equilibrium surface tension (EST) values with area perturbation tests. The EST values should be indirectly determined from the dynamic surface tension (DST) values when surface tension (ST) values are at steady-state and stable against perturbations. The emerging bubble method (EBM) and the spinning bubble method (SBM) were chosen, because, with these methods, it is simple to introduce area perturbations while continuing dynamic tension measurements. Abrupt expansion or compression of an air bubble was used as a source of area perturbation for the EBM. For the SBM, changes in the rotation frequency of the sample solution were used to produce area perturbations. A Triton X-100 aqueous solution of a fixed concentration above its critical micelle concentration (CMC) was used as a model surfactant solution. The determined EST value of the model air/water interface from the EBM was 31.5 &#177; 0.1 mN&#183;m-1 and that from the SBM was 30.8 &#177; 0.2 mN&#183;m-1. The two protocols described in the article provide robust criteria for establishing the EST values.

Two protocols for determining the equilibrium surface tension (EST) values using the emerging bubble method (EBM) and the spinning bubble method (SBM) are presented for a surfactant-containing aqueous phase against air.

通过区域扰动测试精确测定平衡表面张力值

We demonstrate two robust protocols for determining the equilibrium surface tension (EST) values with area perturbation tests. The EST values should be ...

Macro-Rheology Characterization of Gill Raker Mucus in the Silver Carp, Hypophthalmichthys molitrix

The silver carp, Hypophthalmichthys molitrix, is an invasive planktivorous filter feeder fish that infested the natural waterways of the upper Mississippi River basin due to its highly efficient filter feeding mechanism. The characteristic organs called gill rakers (GRs), found in many such filter feeders, facilitate the efficient filtration of food particles such as phytoplankton that are of a few microns in size.
The motivation to investigate the rheology of the GR mucus stems from our desire to understand its role in aiding the filter feeding process in the silver carp. The mucus-rich fluid, in a &#8216;thick and sticky&#8217; state may facilitate the adhesion of food particulates. The permeation and transport through the GR membrane are&#160;facilitated by the action of external shear forces that induce varying shear strain rates. Therefore, mucus rheology can provide a vital clue to the tremendous outcompeting nature of the silver carp within the pool of filter feeding fish. Based on this it was posited that GR mucus may provide an adhesive function to food particles and act as a transport vehicle to assist in the filter feeding process.
The main objective of the protocol is to determine the yield stress of the mucus, attributed to the minimum shear stress required to initiate flow at which irreversible plastic deformation is first observed across a structured viscoelastic material. Accordingly, rheological properties of the GR mucus, i.e., viscosity, storage, and loss moduli, were investigated for its non-Newtonian, shear-thinning nature using a rotational rheometer. &#160;
A protocol presented here is employed to analyze the rheological properties of mucus extracted from the gill rakers of a silver carp, fished at Hart Creek location of the Missouri River. The protocol aims to develop an effective strategy for rheological testing and material characterization of mucus assumed to be a structured viscoelastic material.

Macro-Rheology Characterization of Gill Raker Mucus in the Silver Carp, Hypophthalmichthys molitrix

This protocol presents a method to perform rheology characterization of mucus that resides on gill rakers (GRs) of the silver carp. Viscoelastic characteristics of GR-mucus, obtained by measuring viscosity, storage and loss moduli, are evaluated for the apparent yield stress to understand the filter feeding mechanism in GRs.

银鲤鱼中吉尔 · 拉克 · 穆库斯的宏观流变特征， 低语种米希里斯 · 莫利特里克斯

The silver carp, Hypophthalmichthys molitrix, is an invasive planktivorous filter feeder fish that infested the natural waterways of the upper Mississippi ...

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

摘要

探索更多视频

此视频中的章节

密闭静态和流动胶体聚合物混合物的共聚焦成像

测量材料在微流使用1-2面流小角中子散射

基于图像的拉格朗日粒子跟踪在床载荷实验

挑战流变特性高度集中悬架 - 为例进行丝网印刷银浆

一种研究稠密气体和液体分子流体力学过程的模拟宏观技术

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

流成像技术同时测量湍流和粒子运动学

在生物膜的力学性能原位制图粒子追踪Microrheology

通过区域扰动测试精确测定平衡表面张力值

银鲤鱼中吉尔 · 拉克 · 穆库斯的宏观流变特征，低语种米希里斯 · 莫利特里克斯

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

摘要

探索更多视频

此视频中的章节

密闭静态和流动胶体聚合物混合物的共聚焦成像

测量材料在微流使用1-2面流小角中子散射

基于图像的拉格朗日粒子跟踪在床载荷实验

挑战流变特性高度集中悬架 - 为例进行丝网印刷银浆

一种研究稠密气体和液体分子流体力学过程的模拟宏观技术

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

流成像技术同时测量湍流和粒子运动学

在生物膜的力学性能原位制图粒子追踪Microrheology

通过区域扰动测试精确测定平衡表面张力值

银鲤鱼中吉尔 · 拉克 · 穆库斯的宏观流变特征， 低语种米希里斯 · 莫利特里克斯

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

银鲤鱼中吉尔 · 拉克 · 穆库斯的宏观流变特征，低语种米希里斯 · 莫利特里克斯