The authors are grateful to DOE and RPSEA for the financial support and to the companies sponsoring the JIP on Hydraulic Fracturing and Sand Control at the University of Texas at Austin (Air Liquide, Air Products, Anadarko, Apache, Baker Hughes, BHP Billiton, BP America, Chevron, ConocoPhillips, ExxonMobil, Ferus, Halliburton, Hess, Linde Group, Pemex, Pioneer Natural Resources, Praxair, Saudi Aramco, Schlumberger, Shell, Southwestern Energy, Statoil, Weatherford, and YPF).

1. Preparation of the Fluids
A polymer-free, viscoelastic, two-component, surfactant-based fluid system is used for this experimental study. This fluid system has been used in oil and gas wells in many producing fields for hydraulic fracturing treatments44,45. This fluid system is used for this study because it is optically transparent and the rheology can be controlled by systematically varying the concentrations and proportions of the two components. The fluid system consists of a an anionic surfactant (such as sodium xylene sulfonate) as component A and a cationic surfactant (such as N,N,N-trimethyl-1-octadecamonium chloride) as component B.
<ol>
	<li>Add a given concentration of component A to distilled water and mix at high rpm using an overhead mixer to ensure proper mixing. Allow it to mix for 2-3 min.</li>
	<li>Add a given concentration of component B to this mixture and allow it to mix for an additional&#160;2-3&#160;min.</li>
	<li>Rest the mixture for 2-6 hr to vent out the air bubbles. Note: The final fluid mixture is optically transparent. For this study seven fluid mixtures of different concentrations are used. The concentrations are chosen to obtain fluid mixture over a wide range of viscosities.</li>
</ol>
2. Measurement of Settling Velocities in Unbounded Fluids
Glass spheres of diameters ranging from 1-5 mm are used.
<ol>
	<li>Use a high resolution microscope to measure the diameter of the glass spheres. Ensure that the spheres have smooth surfaces and are near-perfect spheres.</li>
	<li>Store the liquid in glass containers with diameter at least 25x the diameter of particles to ensure that there is no effect of the confining walls on the settling velocity of particles.</li>
	<li>Record the room temperature and fluid temperature using a laboratory thermometer. The measurement of temperature is important because the rheological measurements of the fluid should be made at the temperature at which the settling experiment is performed.</li>
	<li>Place a meter stick alongside the container.</li>
	<li>Gently immerse the glass particle in the liquid and allow it to settle. Record the settling process with a high resolution video camera.</li>
	<li>Track the position of the particle at different time steps from the recorded video using an image analysis application. Note: In this work, a software application called &#39;Tracker&#39; is used (<a href="http://www.cabrillo.edu/~dbrown/tracker/" target="_blank">http://www.cabrillo.edu/~dbrown/tracker/</a>).</li>
	<li>Plot the vertical position of the particle versus time and calculate the terminal settling velocity from the slope of the line.</li>
	<li>Repeat the experiment under the unique set of conditions at least 3x to ensure reproducibility. Perform the image analysis for different measurements and report the settling velocity for a given particle diameter in a particular fluid using error bars.</li>
	<li>Repeat the above steps for different diameter particles and record the settling velocities. Plot the settling velocity versus particle diameter. Note: Figure 1 shows the settling velocity of five different size particles in one fluid.</li>
</ol>
3. Measurement of Settling Velocities for Fluids Between Parallel Walls
To measure the settling velocities in presence of parallel walls, two experimental cells made of Plexiglas&#160;are used.
<ol>
	<li>While designing and constructing the cell, ensure that the walls are smooth and perfectly parallel to each other. Keep the aspect ratio of the cells low to ensure that there is no effect of the walls orthogonal to the parallel walls. Note: The gap between the walls in the two cells in this study is 3.6 mm and 8 mm, respectively. Figure 2 shows a schematic of one experimental cell.</li>
	<li>Fill the cell with the liquid and gently release the particle in the cell through the inlet/outlet port. Seal the inlet/outlet port with a rubber stopper and allow the particle to settle until it reaches the middle of the cell.</li>
	<li>At this point, carefully position the cell vertically and allow the particle to settle.</li>
	<li>Place a meter stick alongside the cell and record the settling using the high resolution video camera.</li>
	<li>Record the room temperature and fluid temperature using a laboratory thermometer. This is important because the rheological measurements of the fluid should be made at this temperature.</li>
	<li>As with the unbounded settling velocity measurements, measure the settling velocity in software application &#39;Tracker&#39;. Repeat the measurements at least three times to ensure reproducibility and to obtain error bars on each measurement.</li>
</ol>
4. Rheological Characterization of Fluids
<ol>
	<li>Perform the steady shear-viscosity measurements to measure the viscosity of the fluid as a function of shear rate. Note: In this work, the ARES rheometer by TA Instruments with a double wall concentric cylinder fixture (inside cup diameter: 27.95 mm, inside bob diameter: 29.50 mm, outside bob diameter: 32.00 mm, outside cup diameter: 34.00 mm, bob length: 32.00 mm) is used.</li>
	<li>Vary the shear rate from 0.1-800 sec-1 and take measurements at 10 points/decade. Ensure that the temperature of the cup is the same at which the settling experiment was performed in the same fluid. Figure 3 shows viscosity versus shear rate for one fluid sample on a log-log plot.</li>
	<li>For the same fluid, calculate the range of shear rate which the particles encountered in the settling experiments. Use the surface averaged particle shear rate defined by 2V/dp 20,23, where V is the settling velocity of the particle and dp is the particle diameter.</li>
	<li>Fit a power-law curve &#956;=K&#947;n-1in this range of shear rates on the viscosity versus shear rate plot. On a log-log plot this fit will be a straight line. Determine the parameters K (flow consistency index) and n (flow behavior index). 
	K and n quantify the viscosity of the fluids. Figure 3 shows the power-law fit on the same plot.</li>
	<li>Perform the dynamic oscillatory-shear measurements over the range of frequencies from 0.1-100 rad/sec and measure the elastic modulus, G&#39; and viscous modulus, G&#39;&#39;. Take measurement at 10 points/decade. 
	Figure 4 shows the G&#39; and G&#39;&#39; for a fluid sample.</li>
	<li>Calculate the ratio of the two moduli, G&#39;&#39;/G&#39; from this data. Fit the ratio of moduli to a Maxwell model using a regression analysis and calculate the relaxation time (&#955;) of the fluid. The equation for the ratio of the two moduli for a Maxwell model is46,47:</li>
</ol>
<img alt="Equation 12" fo:src="/files/ftp_upload/50749/50749eq12highres.jpg" src="/files/ftp_upload/50749/50749eq12.jpg" /> 
The relaxation time of the fluid quantifies the elasticity of the fluid. Greater the relaxation time, more elastic is the fluid. Figure 5 shows the G&#39;&#39;/G&#39; for the fluid sample along with the Maxwell fit. The fitting is performed by minimizing the sum of the variance measure over the frequency range. 
<img alt="Equation 13" fo:src="/files/ftp_upload/50749/50749eq13highres.jpg" src="/files/ftp_upload/50749/50749eq13.jpg" />
5. Determining the Influence of Elasticity on Unbounded Settling Velocities
<ol>
	<li>Denote the experimental settling velocity of a particle in unbounded fluid by V&#8734;VE where &#39;&#8734;VE&#39; refers to unconfined viscoelastic fluids. Compare this experimental settling velocity with the settling velocity (V&#8734;INEL) calculated on the basis of apparent viscosity data based on the power-law parameters. Use the expressions developed by Renaud et al.1 to calculate V&#8734;INEL. The expressions are mentioned in the Introduction section. &#39;&#8734;INEL&#39; refers to unconfined inelastic fluids.</li>
	<li>Calculate the ratio V&#8734;EL/V&#8734;INEL , and refer to the ratio as the velocity ratio. 
	The value of the velocity ratio illustrates the influence of elasticity on settling velocity. Velocity ratio greater than 1 suggests velocity increase/ drag reduction due to fluid elasticity. Velocity ratio less than 1 suggests velocity reduction/drag enhancement due to fluid elasticity.</li>
	<li>Plot the velocity ratio as a function of particle diameter for different fluids to observe the effect of elasticity on settling velocity of different diameter particles in fluids of different rheologies. Figure 6 shows the velocity ratio as a function of particle diameter in one of the fluids.</li>
</ol>
6. Quantifying the Retardation Effect of Parallel Walls on Settling Velocities
<ol>
	<li>Calculate the wall factor, Fw for a given diameter particle by dividing the settling velocity in the presence of parallel walls, V&#8734;VE to the settling velocity in the unbounded fluid, V&#8734;VE.</li>
	<li>For a given fluid, plot the wall factors as a function of the particle diameter to wall spacing ratio, r. Figure 7 shows the wall factors for particles settling in one of the fluids. The plot helps quantify the retardation effect of the confining walls on settling velocity. Lower the wall factor, higher the wall retardation effect.</li>
</ol>

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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Settling+of+Spherical+Particles+in+Unbounded+and+Confined+Surfactant-Based+Shear+Thinning+Viscoelastic+Fluids:+An+Experimental+Study.">Settling of Spherical Particles in Unbounded and Confined Surfactant-Based Shear Thinning Viscoelastic Fluids: An Experimental Study.</a> Chemical Engineering Science. 84, 646-655 (2012).</li><li>Zhang, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluids+for+Fracturing+Subterranean+Formations.U.S.">Fluids for Fracturing Subterranean Formations.U.S.</a> US patent. , (2002).</li><li>Gupta, D. V. S., Leshchyshyn, T. T., Hlidek, B. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surfactant+gel+foam/emulsions:+History+and+field+application+in+the+western+Canadian+sedimentary+basin.">Surfactant gel foam/emulsions: History and field application in the western Canadian sedimentary basin.</a> , (2005).</li><li>Ferry, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Viscoelastic Properties of Polymers. , (1970).</li><li>Yesilata, B., Clasen, C., McKinley, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonlinear+shear+and+extensional+Flow+dynamics+of+wormlike+surfactant+solutions.">Nonlinear shear and extensional Flow dynamics of wormlike surfactant solutions.</a> Journal of Non-Newtonian Fluid Mechanics. 133, 73-90 (2006).</li></ol>

The authors would like to point out that the goal of this publication is visual demonstration of experimental procedure for measuring settling of particles. For detailed results and analyses the readers should refer to the earlier publication43.

The experimental study focuses on measurement of settling velocities of spherical particles in shear thinning viscoelastic fluids under unconfined and confined conditions. Detailed experimental procedure to obtain repeatable measurements of settling velocities is presented. Results are presented to show that fluid elasticity can increase or decrease the settling velocity. Walls exert a retardation effect on settling and this effect is measured in terms of wall factors.
Prior to the experiments...

Suspensions of particles in liquids are encountered in applications including pharmaceutical manufacturing, wastewater treatment, space propellant reinjection, semiconductor processing, and liquid detergent manufacturing. In the oil industry, viscoelastic fracturing fluids are used to transport proppants (typically sand) in hydraulic fractures. Upon the cessation of pumping the proppants keep the fracture open and provide a conductive pathway for hydrocarbons to flow back.
Settling of particles is governed by the rheology and density of fluid, size, shape and density of particles and effect of confining walls. For a spherical particle settling in a Newtonian fluid in the creeping flow regime, the settling velocity is given by Stokes equation, derived by Stokes in 1851. Expressions to calculate the drag force at higher Reynolds numbers have been presented by subsequent researchers2-6. Confining walls reduce the settling velocities by exerting a retardation effect on particles. Wall factor, Fw, is defined as the ratio of terminal settling velocity in presence of confining walls to the settling velocity under unbounded conditions. The wall factor quantifies the retardation effect of the confining walls. Many theoretical and experimental studies to determine wall factors for spheres settling in Newtonian fluids in different cross-section tubes over a wide range of Reynolds numbers are available in the literature7-13. In all, there is an extensive body of information available to determine the drag on spheres in Newtonian fluids.
The past work on determination of settling velocity of particles in nonNewtonian fluids, particularly viscoelastic fluids, is less complete. Various numerical predictions14-18 and experimental studies19-24 are available in literature to determine the drag force on a sphere in inelastic power-law fluids. Using the theoretical predictions of Tripathi et al.15 and Tripathi and Chhabra17, Renaud et al.1 developed the following expressions to calculate the drag coefficient (CD) in inelastic power-law fluids.
For RePL&#60;0.1 (creeping flow regime)
<img alt="Equation 1" fo:src="/files/ftp_upload/50749/50749eq1highres.jpg" src="/files/ftp_upload/50749/50749eq1.jpg" /> 
where X(n) is the drag correction factor13. RePL is the Reynolds number for a sphere falling in a power law liquid defined as:
<img alt="Equation 2" fo:src="/files/ftp_upload/50749/50749eq2highres.jpg" src="/files/ftp_upload/50749/50749eq2.jpg" /> 
where &#961;f is the density of the liquid. The drag correction factor was fitted with the following equation1:
<img alt="Equation 3" fo:src="/files/ftp_upload/50749/50749eq3highres.jpg" src="/files/ftp_upload/50749/50749eq3.jpg" /> 
Using the definition of drag coefficient, the settling velocity is calculated as:
<img alt="Equation 4" fo:src="/files/ftp_upload/50749/50749eq4highres.jpg" src="/files/ftp_upload/50749/50749eq4.jpg" /> 
For 0.1&#60;RePL&#60;100
<img alt="Equation 5" fo:src="/files/ftp_upload/50749/50749eq5highres.jpg" src="/files/ftp_upload/50749/50749eq5.jpg" /> 
where X is the ratio of the surface area to the projected area of the particle and is equal to 4 for spheres. CD0 is the drag coefficient in the Stokes region (RePL &#60; 0.1) given by Equation 1, CD&#8734; is the value of drag coefficient in the Newton&#39;s region (RePL &#62; 5 x 102) and is equal to 0.44. The parameters&#160;&#946;, b, k are expressed as:
<img alt="Equations 6-8" fo:src="/files/ftp_upload/50749/50749eq6-8highres.jpg" src="/files/ftp_upload/50749/50749eq6-8.jpg" /> 
&#945;o = 3 and &#945; is the correction for the average shear rate related to X(n) as:
<img alt="Equation 9" fo:src="/files/ftp_upload/50749/50749eq9highres.jpg" src="/files/ftp_upload/50749/50749eq9.jpg" /> 
To calculate the settling velocity the dimensionless group Nd 25 is used:
<img alt="Equation 10" fo:src="/files/ftp_upload/50749/50749eq10highres.jpg" src="/files/ftp_upload/50749/50749eq10.jpg" /> 
Nd is independent of the settling velocity and can be calculated explicitly. Using this value and the drag coefficient expression in Equation 5, RePL can be solved iteratively. The settling velocity can be then calculated using:
<img alt="Equation 11" fo:src="/files/ftp_upload/50749/50749eq11highres.jpg" src="/files/ftp_upload/50749/50749eq11.jpg" /> 
The expressions in Equations 1-9 were based on theoretical predictions obtained for values 1 &#8805; n &#8805; 0.4. Chhabra13 compared the predictions from the above expressions with experimental results of Shah26-27 (n varied from 0.281-0.762) and Ford et al.28 (n varied from 0.06-0.29). The expressions were shown to predict the drag coefficients accurately. Based on these analyses, the above formulation can be used to calculate the settling velocity of spherical particles in inelastic power-law fluids for 1 &#8805;&#160;n&#160;&#8805;&#160;0.06. This predicted settling velocity in inelastic power-law fluids is compared with the experimental velocity in the power-law viscoelastic fluids to determine the influence of fluid elasticity on settling velocity. The detailed steps are mentioned in the next section.
The determination of settling velocity of particles in viscoelastic fluids has also been a topic of research with varying observations by different researchers; (i) In the creeping flow regime the shear thinning effects completely overshadow viscoelastic effects and the settling velocities are in excellent agreement with purely viscous theories29-32, (ii) particles experience a drag reduction in and outside the creeping flow regime and the settling velocities increase due to elasticity30,33,34, (iii) settling velocity reduces due to fluid elasticity35. Walters and Tanner36 summarized that for Boger fluids (constant viscosity elastic fluids) elasticity causes a drag reduction at low Weissenberg numbers followed by drag enhancement at higher Weissenberg numbers. McKinley37 highlighted that the extensional effects in the wake of the sphere cause the drag increase at higher Weissenberg numbers. After a comprehensive review of prior work on settling of particles in unbounded and confined viscoelastic fluids, Chhabra13 highlighted the challenge of incorporating a realistic description of shear rate dependent viscosity together with fluid elasticity in theoretical developments. The study of wall effects on settling of spherical particles has also been an area of research over the past years38-42. However, all the work has been performed on settling of spherical particles in cylindrical tubes. No data is available for spherical particles settling in viscoelastic fluids between parallel walls.
This work attempts to experimental study the settling of spheres in shear thinning viscoelastic fluids. The goal of this experimental study is to understand the impact of fluid elasticity, shear thinning and confining walls on settling velocity of spherical particles in shear thinning viscoelastic fluids. This paper focuses on the experimental methods used for this study along with some representative results. The detailed results along with the analyses can be found in an earlier publication43.

<table border="1">
	<tbody>
		<tr>
			<td>Name of the reagent / equipment</td>
			<td>Company</td>
			<td>Catalogue number</td>
			<td>Comments </td>
		</tr>
		<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

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.

The experiments are performed for five different diameter particles in seven different fluid mixtures with unique K, n and &#955; values. Figure 1 shows the settling velocity as a function of particle diameter in one fluid. The error bars shows the variability in the three measurements. The room temperature measured during the experiment is 23 &#176;C. It can be observed that the settling vel...

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

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.

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

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13.2K Views.  The University of Texas at Austin. 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.

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

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

Ultrasound Velocity Measurement in a Liquid Metal Electrode

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within &#177;2 &#176;C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries.

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

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

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their behavior for single stages of a process or even an entire process. For the simulation with occurring particle-particle and particle-wall contacts, the value of the coefficient of restitution is required. It can be determined experimentally. The coefficient of restitution depends on several parameters like the impact velocity. Especially for fine particles the impact velocity depends on the air pressure and under atmospheric pressure high impact velocities cannot be reached. For this, a new experimental setup for free-fall tests under vacuum conditions is developed. The coefficient of restitution is determined with the impact and rebound velocity which are detected by a high-speed camera. To not hinder the view, the vacuum chamber is made of glass. Also a new release mechanism to drop one single particle under vacuum conditions is constructed. Due to that, all properties of the particle can be characterized beforehand.

The coefficient of restitution is a parameter that describes the loss of kinetic energy during collision. Here, a free-fall setup under vacuum conditions is developed to be able to determine the coefficient of restitution parameter for particles in micrometer range with high impact velocities.

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

Experimental Methods for Investigation of Shape Memory Based Elastocaloric Cooling Processes and Model Validation

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor compression based cooling process. Nickel-Titanium (Ni-Ti) based alloy systems, especially, show large elastocaloric effects. Furthermore, exhibit large latent heats which is a necessary material property for the development of an efficient solid-state based cooling process. A scientific test rig has been designed to investigate these processes and the elastocaloric effects in SMAs. The realized test rig enables independent control of an SMA&#39;s mechanical loading and unloading cycles, as well as conductive heat transfer between SMA cooling elements and a heat source/sink. The test rig is equipped with a comprehensive monitoring system capable of synchronized measurements of mechanical and thermal parameters. In addition to determining the process-dependent mechanical work, the system also enables measurement of thermal caloric aspects of the elastocaloric cooling effect through use of a high-performance infrared camera. This combination is of particular interest, because it allows illustrations of localization and rate effects &#8212; both important for efficient heat transfer from the medium to be cooled.
The work presented describes an experimental method to identify elastocaloric material properties in different materials and sample geometries. Furthermore, the test rig is used to investigate different cooling process variations. The introduced analysis methods enable a differentiated consideration of material, process and related boundary condition influences on the process efficiency. The comparison of the experimental data with the simulation results (of a thermomechanically coupled finite element model) allows for better understanding of the underlying physics of the elastocaloric effect. In addition, the experimental results, as well as the findings based on the simulation results, are used to improve the material properties.

Experimental methods for investigation of solid state cooling processes and characterization of elastocaloric material properties of Shape Memory Alloys (SMA) are presented. A custom-built test rig has been designed for controlling and comprehensive monitoring of elastocaloric cooling processes. Furthermore, it provides a validation platform for thermomechanically coupled modeling approaches.

Shape Memory Alloys (SMA) using elastocaloric cooling processes have the potential to be an environmentally friendly alternative to the conventional vapor ...

Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

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.

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

The Diffusion of Passive Tracers in Laminar Shear Flow

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 first injecting fluorescent dye directly into a pipe filled with distilled water and allowing it to diffuse across the cross-section of the pipe to obtain a uniformly distributed initial condition. Following this period, the laminar flow is activated with a programmable syringe pump to observe the competition of advection and diffusion of the tracer through the pipe. Asymmetries in the tracer distribution are studied and correlations between the pipe cross-section and the shape of the distribution is shown: thin channels (aspect ratio &#60;&#60; 1) produce tracers arriving with sharp fronts and tapering tails (front-loaded distributions), while thick channels (aspect ratio ~1) present the opposite behavior (back-loaded distributions). The experimental procedure is applied to capillary tubes of various geometries and is particularly relevant to microfluidic applications by dynamical similarity.

A protocol for the study of the diffusion of passive tracers in laminar pressure-driven flow is presented. The procedure is applicable to various capillary pipe geometries.

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 ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...