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ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V010T00A001. doi:10.1115/IMECE2016-NS10.
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This online compilation of papers from the ASME 2016 International Mechanical Engineering Congress and Exposition (IMECE2016) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Advanced Packaging: Sensors and 3D/2.5D Packaging

2016;():V010T13A001. doi:10.1115/IMECE2016-65543.

Thermal modeling and temperature prediction in 3D ICs are important for improving performance and reliability. A number of numerical and analytical models have been developed for thermal analysis of 3D ICs. However, there is a relative lack of experimental work to determine key physical parameters in 3D IC thermal design. One such important key parameter is the inter-die thermal resistance between adjacent die bonded together. This paper describes a novel experimental method to measure the value of inter-die thermal resistance between two die in a 3D IC. The effect of heating one die on the temperature of the other die in a two-die stack is measured over a short time period using high speed data acquisition to negate the effect of boundary conditions. Numerical simulation is performed and based on a comparison between experimental data and the numerical model, the inter-die thermal resistance between two die is determined. There is good agreement between experimental measurement and theoretically estimated value of the inter-die thermal resistance. Results from this paper are expected to assist in thermal design and management of 3D ICs.

Commentary by Dr. Valentin Fuster
2016;():V010T13A002. doi:10.1115/IMECE2016-67619.

The electromigration (EM) resistance of interconnections manufactured by electroplating was investigated from the viewpoint of temperature and diffusion paths in the polycrystalline materials. The crystallinity of the interconnections was evaluated by image quality (IQ) value obtained from electron back-scatter diffraction analysis. The degradation process under the EM test was observed by using the IQ value. The degradation of the interconnections was dominated by the diffusion of component atoms along random grain boundaries with low crystallinity. It was also found that the electrical resistance of the interconnections varied drastically depending on the crystallinity of the material, and thus, the maximum temperature in the interconnections caused by Joule heating during the EM loading also varied drastically because of the change of the resistance. Since the diffusion constant of the component atoms is accelerated by not only the current density but also temperature, the lifetime of the interconnections under the EM loading is a strong function of the crystallinity of the interconnections. It is necessary, therefore, to evaluate and control the crystallinity of the interconnections quantitatively using IQ value to assure their long-term reliability.

Commentary by Dr. Valentin Fuster
2016;():V010T13A003. doi:10.1115/IMECE2016-67737.

In a three-dimensional (3D) packaging systems, the interconnections which penetrate stacked silicon chips have been employed. Such interconnection structure is called TSV (Through Silicon Via) structure, and the via is recently filled by electroplated copper thin film. The electroplated copper thin films often consist of fine columnar grains and porous grain boundaries with high density of defects which don’t appear in conventional bulk material. This unique micro texture has been found to cause the wide variation of physical and chemical properties of this material. In the TSV structure, the shrinkage of the copper thin film caused by thermal deformation and recrystallization of the unique texture during high-temperature annealing is strictly constrained by surrounding rigid Si and thus, high tensile residual stress remains in the thin film after thermal annealing. High residual stress should give rise to mechanical fracture of the interconnections and the shift of electronic function of thin film devices formed in Si.

Therefore, the residual stress in the interconnections should be minimized by controlling the appearance of the porous boundaries during electroplating for assuring the longterm reliability of the interconnections. As the lattice mismatch between Cu and its barrier film (Ta) is as larger as 18%, which is the main reason for the fine columnar structures and porous grain boundaries, it is necessary to control the underlayer crystallinity to improve the crystallinity of electroplated copper thin films.

In this study, the effective method for controlling the crystallinity of the underlayer was investigated by improving the atomic configuration in the electroplated copper thin film. The result showed that by controlling the crystallinity of underlayer, crystallinity of electroplated copper thin films can be improved, the mechanical properties of thin films was improved and thus, stability and lifetime of electroplated copper interconnections can be improved.

Topics: Stability
Commentary by Dr. Valentin Fuster
2016;():V010T13A004. doi:10.1115/IMECE2016-67969.

Alignment and placement of a single nanowire is a crucial task to assemble lab-on-a-chip devices. Nanowires placement techniques have been mostly performed by pick and place techniques or flow control techniques. These techniques require expensive control systems and they cannot be performed in the ambient conditions. This paper introduces a vision-based inexpensive approach for the alignment and placement of individual metal nanowires on a target nanochannel. Through visual observation of the optical microscope, the method aligned the nanowire perpendicular to the nanochannel. The reproducibility of the procedures was experimentally evaluated.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Applications of Micro and Nano Systems in Medicine and Biology

2016;():V010T13A005. doi:10.1115/IMECE2016-66156.

This paper presents the fabrication and testing of electric cell-substrate impedance spectroscopy (ECIS) electrodes on a stretchable membrane. This is the first time when ECIS electrodes were fabricated on a stretchable substrate and ECIS measurements on mammalian cells exposed to cyclic strain of 10% were successfully demonstrated. A chemical was used to form strong chemical bond between gold electrodes of ECIS sensor and polymer membrane, which enable the electrodes keep good conductive ability during cyclic stretch. The stretchable membrane integrated with the ECIS sensor can simulate and replicate the dynamic environment of organism and enable the analysis of the cells activity involved in cells attachment and proliferation in vitro. Bovine aortic endothelial cells (BAEC) were used to evaluate the endothelial function influenced by mechanical stimuli in this research because they undergo in vivo cyclic physiologic elongation produced by the blood circulation in the arteries.

Commentary by Dr. Valentin Fuster
2016;():V010T13A006. doi:10.1115/IMECE2016-66281.

This paper reports on a numerical study on how the measured stiffness distribution of a tumor-embedded tissue via a two-dimensional (2D) tactile sensor varies with the tumor variables (i.e., elasticity, size and depth) and the sensor design parameters. The sensor entails a polydimethylsiloxane (PDMS) microstructure embedded with a 3×3 sensing-plate/transducer array sitting on a Pyrex substrate. Pressing the sensor against a tissue region with a pre-defined indentation depth pattern, the tissue stiffness distribution is extracted from the measured slopes of the deflections of the 3×3 sensing-plate array versus the indentation depth. A finite element model (FEM) of the tissue-sensor interaction, which includes the Pyrex substrate, the microstructure, and a tumor-embedded tissue, is created using COMSOL Multiphysics. The tumor variables and the sensor design parameters are varied in the model to examine how the measured tissue stiffness distribution is affected by them. Based on the numerical results, the relation of the measured tissue stiffness distribution to the tumor variables and sensor design parameters is obtained, shedding insight on establishing a threshold on the stiffness contrast for tumor identification.

Commentary by Dr. Valentin Fuster
2016;():V010T13A007. doi:10.1115/IMECE2016-66735.

In light of the need to diagnose and monitor the heart condition of a heart failure patient, this paper presents a preliminary investigation on the application of a flexible microfluidic-based sensor for measuring the arterial pulse signal during the Valsalva Maneuver (VM), which allows assessment of the patient’s volume status. The core of the sensor is a polydimethylsiloxane (PDMS) microstructure embedded with a 5x1 electrolyte-enabled resistive transducer array. As a time-varying load, an arterial pulse signal acting on the microstructure gives rise to the distributed sensor deflection along the microstructure length and further registers as the resistance changes by the transducer array. The radial pulse signals of four healthy subjects during the VM are measured and are further expressed in terms of the absolute resistance and the sensor deflection. The pulse amplitude change in absolute resistance captures the expected hemodynamic response of a healthy subject to the VM, but the sensor deflection does not manifest such response, due to baseline drift. The corresponding pulse signals of the four subjects at-rest are also measured, verifying that the pulse amplitude change in absolute resistance does not arise from baseline drift. In the future, this sensor will be used to measure the arterial pulse signals of heart failure patients during the VM.

Commentary by Dr. Valentin Fuster
2016;():V010T13A008. doi:10.1115/IMECE2016-67446.

One of the most notable methods for improving microflows is the design of an orthogonal electrode pair that accentuates the non-uniformity in the electric field and, as a result produces stronger net flows at lower voltages. Orthogonal electrodes also have been reported to produce high velocity fluid flow when excited by AC signals, showing potential for micro-pumping applications. Breaking the symmetry of electric fields in the electrode pair produces a unidirectional flow [1] which is salubrious for pumping. As many research groups believe that the Manipulation of microfluidics and particles can be effectively done by AC electrokinetic (ACEK) technique, the current research work in our lab involves in designing a multifunctional system to manipulate the particles to improve the binding process and the fluid flow. This research also explicates the AC electrokinetic processes such as capacitive electrode polarization, Faradic polarization and the AC electrothermal effect, to better explain the directional flow patterns and their role in manipulating the microfluidics. Different flow patterns were obtained by varying the level and frequency of AC potential.

Commentary by Dr. Valentin Fuster
2016;():V010T13A009. doi:10.1115/IMECE2016-67622.

Electric detection using a nanocomponent could lead to platforms for rapid and simple biosensing. Sensors composed of nanostructures have been described for applications requiring high sensitivity on account of their confined geometries. However, both fabrication and use of nanostructured sensors remain challenging. Here, we present a nano-electronic sensor, used as an amperometric biosensor, for the highly sensitive quantification of DNA. The proposed nano-electronic sensor is fabricated by a two-step process; 1) fabricate microscale-cantilever structure using ultraviolet (UV) lithography and anisotropic etching for reliable electrical measurement, and 2) immobilize single-walled carbon nanotubes (SWNCTs) onto the structure for generation of a high electric field. The electrical characteristics of nano-electronic sensor upon binding DNA are studied by I-V measurement in deionized (DI) water. When the DNA is dielectrophoretically captured onto the sensor, the electric current through DI water decreases. The sensitivity test shows that the signal is discernable from the noise level down to 100 attomolar (aM). Measurement results are consistent with fluorescence microscopy. Unlike other optical-based quantification methods, a nano-electronic sensor is capable of rapidly concentrating and detecting small amounts of DNA.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Applied Mechanics and Materials

2016;():V010T13A010. doi:10.1115/IMECE2016-65074.

Shot peening is a cold working process used to produce a compressive residual stress to modify mechanical properties of metals. It causes impacting a surface with shots with significant force to create plastic deformation. The compressive residual stresses developed by shot peening process helps to avoid the propagation of micro-cracks exist in surface. Shot peening process is often used in aircraft industries to relieve tensile stresses built up in the grinding process, and replace them with beneficial compressive residual stresses. Shot peening has been developed to increase the fatigue strength of metallic parts. Compressive residual stress and surface hardening induced by shot peening process are found beneficial to increase the fatigue life and the resistance to stress corrosion cracking within the metallic component. Even though shot peening has been used for more than 50 years, a review of published papers indicates a lack of studies in numerical modeling. In particular, the effect of complex shot peening process to predict the target material responds to the multiple impacts of shots is not fully revealed. Most studies have investigated the fundamental mechanism and characteristics of fatigue improvement by single shot peening, and have studied the compressive residual stress induced by single normal impact on the surface of the specimen. However, single impact model is appropriate and efficient for sensitivity studies, local plastic effect, and indentation estimation. It is well known that the residual stress by single shot model is not suitable for practical use. The residual stress field from multi impacts is the resultant sum of all the fields by repeated and progressive impacts. It is not feasible to extrapolate results from the single impact model to a practical shot peening process with multiple impacts. Therefore, this research attempts to conduct a microscale modeling to study the shot peening effects of aluminum alloy responds to single and multiple impacts. First, a single shot impact model, representing single shot peening process, has been developed for the estimation of indentations at different velocities. The numerical simulations has been performed with the finite element software code LS-DYNA. The validations of the numerical simulations has been made from experimentally measured surface roughness data. Once the finite element code of single shot peening model is validated, additional numerical models are developed to simulate multiple shot peening process, using multiple impact shots. The multiple impact model are developed for the estimation of the residual stress field.

Commentary by Dr. Valentin Fuster
2016;():V010T13A011. doi:10.1115/IMECE2016-65117.

In this study, the sensitivity of two-dimensional four-terminal piezoresistive sensors commonly referred to as “van der Pauw (VDP)” structure is investigated and analyzed. VDP sensors have the potential to obviate some of the limitations of resistor based sensors such as size and temperature effects. In this study, we will consider the VDP sensor to be fabricated on (100) silicon due to its potential application in MEMS pressure sensors or electronic packaging stress measurements. The sensitivity of the VDP sensor may be affected by misalignment (i.e., orientation) during the etching/diffusion process, the size of the sensor relative to the size of the underlying diaphragm, pad size where the current and voltage are determined, and on their global positions. In this study, we have presented how the VDP stress sensitivity is affected by variations in pad size and sensor orientation with respect to the wafer flat direction. First, a 3D finite element analysis (FEA) model is developed representing a piezoresistive VDP sensor fabricated on (100) silicon diaphragm. Then, the FEA model is validated with the closed form analytical solution for different bi-axial loads. Once the FEA model is validated, additional simulations are conducted to understand the influence of different parameters on the resistance measurements. The change in resistivity of the VDP will then be analyzed to predict its sensitivity under a certain set of sensor parameters.

Commentary by Dr. Valentin Fuster
2016;():V010T13A012. doi:10.1115/IMECE2016-65201.

Size-effect is known to influence the mechanical properties of materials at micro- and nanoscales. Mechanisms of fracture and failure are often affected by environmental factors such as temperature and humidity. The latter is postulated to cause stress corrosion cracking in metallic and ceramic Microelectromechanical Systems (MEMS) components. A recently-developed hybrid microtester enclosed in an environmentally-controlled chamber was used to study the effects of temperature on the mechanical properties of small structures. MEMS-scale specimens, prepared from aluminum foam struts as well as covetic aluminum were tested in microtensile testing. Results of these micromechanical tests show that the tensile behavior of Al struts are similar at temperatures of 11 and 42 °C. Further, covetic Al samples show a higher strength at a lower temperature (15 °C), but higher ductility at a higher temperature (44 °C).

Commentary by Dr. Valentin Fuster
2016;():V010T13A013. doi:10.1115/IMECE2016-65531.

Traditionally, mechanical properties of asphalt concrete (AC) is evaluated through macro-scale testing. However, when aggregates are mixed with asphalt binder, it creates a thin film of 20μm to 40μm around the aggregate particles and the primary strength of AC is derived from the interaction between the binder and aggregates. Therefore, to understand the behavior of asphalt concrete it is necessary to study the binder properties in a nanoscale. Nanoindentation test has been adopted to examine the thin film material property. In a nanoindentation test, a loaded nanoindenter is used to indent the sample surface and measure the indenter displacement as a function of load. To this day, most researchers have used the Oliver-Pharr method to analyze the indentation test data and obtain Elastic modulus (E) and hardness (H) of the material. Generally, in a nanoindentation test, there is a loading and unloading phase. In an elasto-plastic material, loading phase has elastic and plastic response and unloading phase has only elastic response. In Oliver-Pharr method, elastic modulus is obtained through the slope of the unloading curve. Therefore, Oliver-Pharr method mostly applicable for the elasto-plastic metals because it does not incorporate any viscous effect. However, in case of visco-elastic material like asphalt, during the unloading phase, the slope of the unloading curve becomes negative due to the viscous flow. Therefore, using Oliver-Pharr (OP) method in this circumstances will yield an inaccurate value of modulus of elasticity. In the current study, the test data was modeled and analyzed using a well-established spring-dashpot-rigid (SDR) model for viscoelastic material to determine the elastic, plastic and viscous properties. The model assumes the indenter displacement is a function of a quadratic spring, a quadratic dashpot and a plastic rigid body. The loading phase of the nanoindentation test has three contributing parameters: elasticity (E), indentation viscosity (η) and hardness (H). During creep, only contributing parameter is indentation viscosity (η) and while unloading the contributing factors are found to be E and η. Nonlinear least square curve fitting technique was employed to model the nanoindentation test data to the SDR model to find out the contributing parameters E, η and H. In addition, the extended dwell time on the asphalt binder samples produced positive load displacement curves, which were further analyzed with Oliver-Pharr method. Comparison between two models results show traditional Oliver-Pharr model predicts the material properties 5 to 10 times lower than SDR model, as Oliver-Pharr does not consider the viscous behavior in the material.

Commentary by Dr. Valentin Fuster
2016;():V010T13A014. doi:10.1115/IMECE2016-65991.

Ensure a safe, long life and efficient combustion within a diesel engine is an important challenge in the applications of engine technology. Much research has been done on thermal stress within engine cylinders and on engine piston heads, and how to reduce some of this stress in order to prevent failure or increase the life of the engine. The failure of a piston head tends to occur from it enduring the gas effect of the high pressures and temperatures. By performing static and dynamic Finite Element Analysis (FEA) on a piston mechanism of a diesel engine proper dimensions for different parts of an engine can be determined and failure of an engine in service can be avoided. In this research finite element analysis has been performed to determine the total deformation, stresses, and other parameters that are essential from design point of views. Real world input data for simulation obtained from running an existing diesel engine have been effectively used. Static structural and dynamic reaction of a piston assembly under the applied load of internal combustion in a diesel engine were closely observed. ANSYS workbench was utilized to perform these simulations. Using SolidWorks a piston assembly model consisting of the piston, connecting pin, connecting rod, cylinder head, crankshaft, and cranks was designed and used for simulation. Simulation results were being collected from the static structural and rigid body dynamics modules.

The static structural simulation was conducted in order to obtain the structural response of the piston assembly under the combustion phase. This simulation was intended to replicate the pressure forces applied to the piston assembly at the moment of combustion. A pressure force of 7 MPa was applied to the top of the piston. From the simulation results, the maximum total deformation 1.9 mm occurred at the top edge of the piston head on the same side as the combustion chamber. Maximum equivalent Von Mises stress 323.9 MPa occurred at the joint of the connecting rod and crankshaft and the minimum equivalent stress 27 kPa occurred at the bottom of the connecting rod. Principal stresses were also examined, where the maximum principal stress 335.1 MPa occurred at the joint of the connecting rod and crankshaft and the minimum principal stress 63.5 MPa occurred inside of the connecting rod joint. The maximum shear stress 177.7 MPa occurred at the joint of the connecting rod and crankshaft and the minimum shear stress 14.26 kPa occurred at the bottom of the connecting rod.

Two types of forces were considered acting upon the geometry in the rigid body dynamic simulation, one is standard earth gravity and the other is a linear dynamic load of 55,000 N applied to the top of the piston head which is used to simulate the act of combustion within the combustion chamber of a cylinder. From the rigid dynamic simulation, it was found that after the first combustion cycle, the linear velocity of the entire system, acceleration of the entire system, and the crank angular velocity reach to the maximum of 24.77 m/s, 17684 m/s2 and 5487 rpm respectively at 0.0187 seconds. Then after the second combustion cycle, the linear velocity of the entire system and the crank angular velocity reach to 27.56 m/s and 6043 rpm respectively at 0.0481 seconds; however the acceleration of the entire system took 0.0551 seconds to reach to 30115 m/s2.

Commentary by Dr. Valentin Fuster
2016;():V010T13A015. doi:10.1115/IMECE2016-66241.

Finite Element Analysis (FEA) has been performed on variety of a driveshaft and universal joints based on different shaft materials and shaft different operating angles. A driveshaft is particularly useful in applications such as taking of transferring torque from one piece of equipment to the other such as in vehicle of all kinds. A driveshaft transfers torque from the transmission to the rear end differential since these two pieces of equipment cannot be connected directly. The driveshaft has universal joints located on both ends of the shaft to allow for fluctuations in the angle of the transmission and rear differential. The driveshaft alone is composed of two parts, a female and male end, connected by a spline to allow changes in the length during operation. The driveshaft must be able to withstand the constant torque that is being applied throughout operation in order to increase safety for the operator and machine. Having a lower polar moment of inertia allows the driveshaft to turn with a lower torque value compared to a driveshaft with a higher moment of inertia. It is noted that driveshaft can be manufactured into a variety of lengths and diameters depending on the use and equipment it will be supporting. This paper describes a method of finite element implemented on variations of driveshaft and universal joints. Effect of material properties, geometry and operating angle of the driveshaft were considered for this numerical investigation. Five different materials such as structural steel, aluminum alloy, polyethylene, titanium, and carbon fiber with an outer diameter of 1.5 in of the driveshaft was used for this analysis. The effect of both metals and composite materials was observed.

Based on the analysis it was found that a 15° operating angle allowed for the longest life cycle of the driveshaft, while the carbon fiber composite presented the highest stress resistance and safety factor, approximately 6 GPa of yield tensile strength and a safety factor of 15. It was also found that titanium had an equivalent safety factor of 15. However, the tensile yield strength of titanium was much lower than that of its composite counterpart. All of the numerical experimentation was done using the Finite Element Analysis software ANSYS. Material properties for all materials were preset in the software except the composite carbon fiber whose properties were easily found from other research papers and experiments. Based on the data collected and the general assumptions that the most effective drive shaft is the one that lasts the longest. It can be concluded that a driveshaft made of carbon fiber operating at an angle of 15° presents the optimum driveshaft design.

Commentary by Dr. Valentin Fuster
2016;():V010T13A016. doi:10.1115/IMECE2016-66353.

In this paper, the static behavior of a micro-electromechanical system (MEMS) based on two electrically coupled parallel clamped-clamped microbeams is investigated. The assumed discretization technique in this investigation is the reduced-order modeling (ROM). The ROM was derived based on the Galerkin expansion method while assuming linear undamped mode shapes of a straight fixed-fixed beam as the basis functions. The results showed that the double-microbeam MEMS switch configuration requires a lower actuation voltage and a lower switching time as compared to the single microbeam actuator. Then, the effects of both microbeams air gap depths were investigated. Finally, the eigenvalue problem was investigated to get the variation of the fundamental natural frequencies of the coupled parallel microbeams with the applied actuating DC load.

Commentary by Dr. Valentin Fuster
2016;():V010T13A017. doi:10.1115/IMECE2016-66958.

Horizontal axis wind turbines (HAWTs) are the dominating technology in large scale energy production utilizing the wind power. With these structures, HAWTs continually becoming more massive in size to produce the most energy possible, greater stresses are imposed on the blades of these turbines. The purpose of this study was to analyze the stresses and deformation imposed on the blades of commonly used airfoils under varying materials and blade arrangements of HAWTs. This structural analysis was performed by the use of ANSYS Workbench software. The pressures applied to the blades were determined by previous studies which used ANSYS Fluent for blade pressure analysis created under varying wind speeds. Use of the airfoil designs denoted as S811, S822, and S826 were implemented, with structural analysis performed solely on the blade, on three and five blades arrangements. The materials used for each of these setups were Aluminum Alloy and Structural Steel. Furthermore, varying mesh types within ANSYS were applied to each of the geometries for comparison. It has been found from this study that the S811 profile models had the lowest stress and deformation for both blade configurations, meshing methods, and materials.

Commentary by Dr. Valentin Fuster
2016;():V010T13A018. doi:10.1115/IMECE2016-67055.

The dynamic behavior of polymer composites is significantly affected by the properties of their micro constituents including shape and size of inclusions and inclusions/matrix adhesion properties. Wave propagation through such a composite is a complex phenomenon as it includes random scattering, absorption and transmittance of the incident wave and is dependent upon factors such as the properties, size and placement of the inclusions inside the matrix. Finite element modeling provides a viable approach for investigating the effects of micro constituent structure on the dynamic behavior of polymer composites. In this paper, we investigate the stress wave attenuation characteristics of a particulate polymer matrix composite using Finite Element (FE) analysis approach. The wave attenuation of ultrasonic sinusoidal waves of frequency ranging from 1 MHz to 4 MHz is evaluated for different FE models. The spherical inclusions are randomly distributed inside the polymer matrix with a certain minimum distance apart from each other. Inclusion-Matrix adhesion properties are studied by modeling a small region at the interface of inclusions and matrix known as interphase region. The interphase region is modeled explicitly using the cohesive zone modeling approach to study how the properties of this region will affect the wave attenuation characteristics of the polymer composite. Cohesive zone models are governed by traction separation law which helps in the measurement of the inclusion-matrix bonding strength and also allow the study of de-bonding at the interface in the critically stressed region produced due application of load. Thus the FE models consist of three phases; polymer matrix, particulate inclusions and the interphase region. Various three dimensional FE models are created using 3D tetrahedral/hexahedral elements by varying the radius of the spherical inclusions and by varying volume fraction of the inclusions. The analyses are performed using a general purpose finite element software LS-Dyna. A rate dependent viscoelastic material model with four terms in prony series expansion is used for modeling the polymer matrix. A linear elastic isotropic material model is used for modeling the inclusions. The wave attenuation is measured as reduction in the amplitude of the wave as it passes through the composite. A comparison of results for various models is done to check for general trend of attenuation coefficient as a function of size of inclusions, volume fraction of inclusions, frequency of loading and interphase region properties. Results show that volume fraction and load frequency have a maximum effect on the wave attenuation coefficient. Interphase region stiffness and interface de-bonding also plays an important role in attenuation characteristics of the polymer composite.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Computational Studies on MEMS and Nanostructures

2016;():V010T13A019. doi:10.1115/IMECE2016-66277.

High quality factor (Q-factor) is a crucial parameter for the development of precision inertial resonators. Q-factor indicates efficiency of a resonator in retaining its energy during oscillations. This paper explores the effects of different design parameters on Q-factor of a 3D hemispherical (wine-glass) inertial resonator. Thermo-elastic damping (TED) loss mechanisms in a 3D non-inverted wine-glass (hemispherical) shell resonator is systematically investigated and presented in this paper. We investigated TED loss resulting from the effects of hemisphere geometric parameters (such as thickness, height, and radius), mass imbalance, thickness non-uniformity, and edge defects. We used glassblowing to fabricate hemispherical 3D shell resonators. The results presented in this paper can facilitate selecting efficient geometric and material properties for achieving desired Q-factor in 3D inertial resonators. Enhancing the Q-factor in MEMS based 3D resonators can further enable the development of high precision resonators and gyroscopes.

Commentary by Dr. Valentin Fuster
2016;():V010T13A020. doi:10.1115/IMECE2016-66600.

In the present work, novelly structured poly(vinylidene fluoride)/lead zirconate titanate (PVDF/PZT) piezoelectric composites with controlled filler orientation were designed. The material coefficients of the proposed composites including elastic stiffness constant (C), piezoelectric constant (e) and dielectric constant (ε) were numerically determined. Specifically, the Comsol Multiphysics connected with Matlab was utilized to create the unit cells representing the piezoelectric composites. In the calculations, the whisker-shaped PZT content was varied in a relatively low range of volume fraction (i.e., 0.3∼3.5 vol.%). Furthermore, the PZT orientation and PZT length-reduction were considered in order to simulate the flow-field effect of micro-injection molding (μIM). The results showed that using a low PZT content was effective for modifying the composite’s material coefficients. In addition, the PZT orientation was identified as an important factor influencing the composite’s properties, which was believed to result from the apparently changed amount of the PZT whiskers along the direction of interest. Finally, the effect of the PZT length-reduction during μIM was found insignificant, which suggests that μIM can be safely adopted to fabricate PVDF/PZT piezoelectric composites taking full use of its advantages such as high efficiency and low cost, without worrying about PZT’s length-reduction.

Commentary by Dr. Valentin Fuster
2016;():V010T13A021. doi:10.1115/IMECE2016-66707.

A thermal switch is a system to control the heat transfer “on/off” for the desired functionalities, and this serves as a basic building block to design advanced thermal management systems in various applications including electronic packaging, waste heat recovery, cryogenic cooling, and new applications such as thermal computers. The existing thermal switches employ the macroscale mechanical-based, relatively slow transient “on/off” switch mechanisms, which may be challenging to provide solutions for micro/nanoscale applications. In this study, a fast and efficient thermal switch mechanism without having extra mechanical controlling system is demonstrated using gas-filled, heterogeneous nanogaps with asymmetric surface interactions in Knudsen regime. Argon gas atoms confined in metal-based solid surfaces are employed to predict the degree of thermal switch, S. Non-equilibrium molecular dynamics simulation is used to create the temperature gradient over the two nanogaps, and the maximum degree of thermal switch is Smax ∼ 13, which results from the difference in adsorption-controlled thermal accommodation coefficient (TAC) and pressure between the two sides of the gaps.

Commentary by Dr. Valentin Fuster
2016;():V010T13A022. doi:10.1115/IMECE2016-66773.

This study investigates bonding and shear flow phenomena for nanoscale BGA (Ball Grid Array) solder joint in electronic package pads with or without intermetallic compounds (IMC). Three types of solder joints have been studied, such as Sn100%, Sn44%-Cu56% and Sn92.5%-Ag3.5%-Cu4%. The IMC layer composes of Cu6Sn5 and Cu3Sn materials. The above materials are arranged according to the single crystal structure. The molecular dynamics method and the embedded atom potential are used to understand the internal micro structure, interface layer and the bonding strength differences for welded joints. The total energy of the simulated system includes the molecular potential energy, kinetic energy and electromagnetic coupling moments. An aging process at 453K for solder joint without IMC layer has been conducted to understand the aging effect.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Design and Fabrication, Analysis, Processes, and Technology for Micro and Nano Devices and Systems

2016;():V010T13A023. doi:10.1115/IMECE2016-65623.

A common method to precisely control the material properties is to evenly distribute functional nanomaterials within the substrate. For example, it is possible to mix a silk solution and nanomaterials together to form one tuned silk sample. However, the nanomaterials are likely to aggregate in the traditional manual mixing processes. Here we report a pilot study of utilizing specific microfluidic mixing designs to achieve a uniform nanomaterial distribution with minimal aggregation. Mixing patterns are created based on classic designs and then validated by experimental results. The devices are fabricated on polydimethylsiloxane (PDMS) using 3D printed molds and soft lithography for rapid replication. The initial mixing performance is validated through the mixing of two solutions with colored dyes. The microfluidic mixer designs are further analyzed by creating silk-based film samples. The cured film is inspected with scanning electron microscopy (SEM) to reveal the distribution uniformity of the dye particles within the silk material matrix. Our preliminary results show that the microfluidic mixing produces uniform distribution of dye particles. Because the microfluidic device can be used as a continuous mixing tool, we believe it will provide a powerful platform for better preparation of silk materials. By using different types of nanomaterials such as graphite (demonstrated in this study), graphene, carbon nanotubes, and magnetic nanoparticles, the resulting silk samples can be fine-tuned with desired electrical, mechanical, and magnetic properties.

Commentary by Dr. Valentin Fuster
2016;():V010T13A024. doi:10.1115/IMECE2016-66002.

This paper reports the effect of particulate contaminants on the static stress response of cantilever type micro-electromechanical systems (MEMS) devices, such as high precision MEMS pressure sensor. The contaminant presence has been qualitatively verified through computational fluid dynamic simulation of the clean room in COMSOL Multiphysics environment and quantitatively estimated for adverse conditions such as ISO-8 cleanliness. There is very little characterization of such impairing of response of cantilever systems though it has well been recognized to be important. Fabrication of MEMS based multi-functional devices demands complex integration of several micro-engineered components to perfection. It is therefore critical to ensure that at every stage of fabrication the contaminants or particles that get deposited on the device parts do not have any deleterious effect on the device performance. As most of the MEMS based devices are fabricated in a clean room environment the effects of contaminants on the device performance is assumed to be minimal. However, if the components are exposed to adverse conditions of cleanliness due to non-functional cleanroom or poor maintenance of cleanroom, the unaccounted mass of contaminants on the cantilever device can affect the static and dynamics response as well as the resonance characteristics. Thus it is important to understand performance with respect to various clean room parameters such as particulate density, temperature and humidity especially for the devices designed to measure very low values of physical/electrical/mechanical parameters.

Commentary by Dr. Valentin Fuster
2016;():V010T13A025. doi:10.1115/IMECE2016-67233.

Inkjet printing has become a promising way to fabricate electrical mechanical devices and it has become a tool for rapid manufacturing technology. In this paper, the fabrication procedure and the characterization of the piezoresistive properties of Carbon nanotube (CNT) - Polyimide (PI) nanocomposites are presented. The suspensions of CNT-PI nanocomposites of five different CNT weight concentration based on the percolation threshold were fabricated, and the suspensions were then deposited on the polyimide substrate by a drop-on-demand piezoelectric inkjet printer. This makes it possible for the uniformity and geometry of the thin film to be highly controlled. Once the nanocomposites were fully cured, the strain sensors were ready for calibration. Under uniaxial tension, the strain and resistance change of the strain sensors were measured, and the gauge factors could be calculated. The temperature and humidity are two potential factors to effect the performance of the strain sensors. The temperature coefficients of the CNT-PI nanocomposites were measured and the temperature compensation methods were proposed. The humidity effect on the nanocomposites was also monitored, and a thin layer of Parylene-C was coated on the surface of the nanocomposites thin film and the effect of the coating was tested. In general, the inkjet printing technique was proved to be a convenient way to fabricate flexible nanocomposites thin film with uniform thickness and precise geometry control. The CNT-PI nanocomposite has good performance as piezoresistive strain sensor.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: General Topics of MEMS/NEMS

2016;():V010T13A026. doi:10.1115/IMECE2016-66104.

Amplifying the signal-to-noise ratio of resonant sensors is vital toward the effort to miniaturize devices into the sub-micro and nano regimes. In this work, we demonstrate theoretically and experimentally amplification through mechanically coupled microbeams. The device is composed of two identical clamped-clamped beams, made of polyimide, connected at their middle through a third beam, which acts as a mechanical coupler. Each of the clamped-clamped microbeams and the coupler are designed to be actuated separately, hence providing different possibilities of actuation and sensing. The coupled system is driven into resonance near its first resonance mode and its dynamics is explored via frequency sweeps. The results show significant amplification in the resonator’s amplitude when the signal is measured at the midpoint of the coupler, compared to the response of the individual uncoupled beams. The static pull-in characteristics of the system are also studied. It is shown that the compliant mechanical coupler can serve as a low-power RF switch actuated at low voltage loads.

Commentary by Dr. Valentin Fuster
2016;():V010T13A027. doi:10.1115/IMECE2016-66402.

The phonon dissipation is investigated through molecular dynamics (MD) simulation modeling graphene flake sliding on supported graphene in this paper. With the help of the advantage of MD, we explore the phonon mode variation of the substrate induced by the behavior of friction in terms of phonon densities of states. Moreover, phonon dissipation modes connected with the relative sliding velocity and the temperature of system are established respectively. The simulation results demonstrate phonon dissipation is represented as special phonon frequencies while those are closely related to the sliding velocities but would not shift as the change of temperatures. For an explanation of the special frequencies, we further simplify the model by directly adding the velocity to the atoms of the flake in the MD model, although it is impractical. It is found that a special frequency of phonon dissipation is generally in agreement with the sliding frequency at low temperature eliminating the interference of temperature in a range of velocities from 50m/s to 250m/s, namely, the velocity is directly related to the modes of phonon dissipation and friction, which is consistent with the previously reported result[1] that the velocity is an influence factor for friction both in experimental and theoretical researches. Therefore, the relationship makes possible the active control of friction. It is the first step toward using this method to reveal the fundamental questions in the study of atomic-scale friction.

Commentary by Dr. Valentin Fuster
2016;():V010T13A028. doi:10.1115/IMECE2016-66418.

In this paper, based on molecular dynamics simulation method, the authors construct a graphene flake sliding on a suspended graphene layer which is anchored on a bed of springs. This graphene-spring system provides an ideal model to replace the multilayer graphene under the top layer. We firstly mimic different layers of suspended graphene through changing the stiffness of spring bed; then the contributions of Van der Waals force of the tip and elastic deformation of the top layer supported by spring bed to friction force are analyzed; finally, an energy dissipation mechanism based on the amount of corrugation potential energy and sample deformation elastic energy is proposed. It is demonstrated that the effects of energy barrier and surface compliance are directly related to the observed friction force. It is helpful to achieve a theoretical basis for the design of graphene-based nano electromechanical systems (NEMS) devices.

Commentary by Dr. Valentin Fuster
2016;():V010T13A029. doi:10.1115/IMECE2016-66700.

This paper demonstrates experimentally a wide bandpass filter based on an electrothermally tuned single MEMS arch resonator operated in air. The in-plane resonator is fabricated from a silicon-on-insulator wafer with a deliberate curvature to form an arch shape. A DC voltage is applied across the anchors to pass current through the resonator to induce heat and modulate its stiffness, and hence its resonance frequencies. We show that the first resonance frequency increases up to twice of the initial value while the third resonance frequency decreases until getting very close to the first resonance frequency. This leads to the phenomenon of veering, near crossing, where both modes exchange roles. Hence, the first resonance frequency becomes insensitive to axial forces and thermal actuation whereas the third resonance natural frequency becomes very sensitive. We demonstrate an exploitation of the veering phenomenon to realize a bandpass filter, where the first and third resonance modes are excited electrostatically simultaneously to achieve a bandpass. We demonstrate also that by driving both modes nonlinearly near the veering regime, so that the first mode shows softening behavior and the third mode shows hardening behavior, sudden jumps in the response from both modes are induced leading to sharp roll off from the bandpass to the stop band. We show a flat, wide, and tunable bandwidth and center frequency by controlling the electrothermal actuation voltage.

Commentary by Dr. Valentin Fuster
2016;():V010T13A030. doi:10.1115/IMECE2016-67471.

Rapid and cost effective fabrication of nanostructures is critical for experimental exploration and translation of results for commercial development. While conventional techniques such as E-beam or Focused Ion beam lithography serve some prototyping needs for nano-scale experimentations, cost and rate considerations prohibit use for manufacturing. Specialized lithographic processes [e.g. nanosphere lithography or interference lithography] are also powerful tools in creating nanostructures but provide limited shapes, positioning and size control of nanostructures. In this work, we demonstrated a liquid-free and mask-less electrochemical writing approach using atomic force microscopy (AFM) that is capable of making arbitrary shapes of silver nanostructures in seconds on a solid state super-ionic (AgI)x (AgPO3)(1−x) glass. Under ambient conditions. silver is extracted selectively on super-ionic (AgI)x (AgPO3)(1−x) glass surface by negatively biasing an AFM probe relative to an Ag film counter electrode.

Both voltage controlled and current controlled writings demonstrated localized extraction of silver. The current controlled approach is shown to be the preferred writing approach to make repeatable and uniform patterns of silver on (AgI)x AgPO3(1−x), where x represents the mole fraction of AgI in the mixture and the control parameter that tunes the conductivity of the sample. We demonstrated current controlled printing of silver on two different compositions of the material (i.e. (AgI)0.125 (AgPO3 )0.875 and (AgI)0.25(AgPO3)0.75 ). Depending on the magnitude of the constant current and tip speed, line-width of the silver pattern can be ∼150 nm. The length of these patterns are limited to the maximum distance the tip can be moved using the AFM position controls. The substrate being optically transparent allows the use of this writing technique for rapid prototyping plasmonic devices. By using the patterned substrate as a template for replica molding of soft materials such as polydimethylsiloxane (PDMS), this writing technique can also be utilized for high throughput nano-channel fabrication in biofluidics and microfluidics devices.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Manufacturing, Materials and Processes in Electronics and Photonics Packaging

2016;():V010T13A031. doi:10.1115/IMECE2016-65880.

In this study, dielectric properties of Acrylonitrile butadiene styrene (ABS) thermoplastic material with different fill-densities are investigated. Three separate sets of samples with dimensions of 25 mm × 25 mm × 5 mm were created at three different machine preset porosities using a LulzBot 3D printer. To understand the actual porosities of the samples, a 3D X-ray computed tomography microscope was used. The great advantage of this 3D microscopy is that it is fully non-destructive and requires no specimen preparation. Hence, the manufacturing defects and lattice variations can be quantified from image data. It is observed that the experimental pore densities are different from the factory preset values. This provides insight to further understand pore distribution-property relationships in these dielectric materials. Micro-strip patch antennas were then created on the 3D printed ABS substrates. The samples were then tested using a vector network analyzer (VNA) and resonant frequencies were measured. It is observed that the resonant frequency increases with an increase in porosity. These results clearly demonstrate the ability to control the dielectric constant of the 3D printed material based on prescribed fill density.

Commentary by Dr. Valentin Fuster
2016;():V010T13A032. doi:10.1115/IMECE2016-67441.

In this work, the morphology and electrocatalytic features of carbon nanotube yarns at the structural level allow for enhanced photoconversion efficiency. The energy conversion of electron-hole pairs within the carbon nanotube yarn (CNY) due to the functionalization with nanostructured photoactive TiO2 phases is remarkable. A well oriented anatase TiO2 thin layer (approximately 100 nm) forms at the interfaces of CNY and TiO2 mesoporous film when the sample is precoated and annealed at 350°C. Field Emission Scanning Electron Microscopy (FESEM) images show the integrity and homogeneity of the TiO2 surface, which is indicative of the overall durability of the CNY-based dye sensitized solar cell (DSSC); Coating TiO2 on self-aligned carbon nanotube yarns provides several benefits from their high chemical stability, excellent functionality, nontoxicity and relatively low cost. The maximum photon to current conversion efficiency (ηAM1.5) achieved was 3.1%.

Commentary by Dr. Valentin Fuster
2016;():V010T13A033. doi:10.1115/IMECE2016-68215.

Stretchable electronics have been a subject of increased research over the past decade [1–3]. Although stretchable electronic devices are a relatively new area for the semiconductor/electronics industries, recent market research indicates the market could be worth more than 900 million dollars by 2023 [4]. At CES (Consumer Electronics Show) in January 2016, two commercial patches were announced which attach to the skin to measure information about the user’s vitals and environmental conditions [5]. One of these measures the sun exposure of the user with a UV sensitive dye — which can communicate with the user’s cell phone to track the user’s sun exposure. Another device is a re-usable flexible patch which measures cardiac activity, muscle activity, galvanic skin response, and user’s motion. These are just two examples of the many devices that will be developed in the coming years for consumer and medical use.

This paper investigates mechanical testing methods designed to test the stretching capabilities of potential products across the electronics industry to help quantify and understand the mechanical integrity, response, and the reliability of these devices. Typically, the devices consist of stiff modules connected by stretchable traces [6]. They require electrical and mechanical connectivity between the modules to function. In some cases, these devices will be subject to bi-axial and/or cyclic mechanical strain, especially for wearable applications. The ability to replicate these mechanical strains and understand their effect on the function of the devices is critical to meet performance, process and reliability requirements. There has been a test method proposed recently for harsh / high-rate testing (shock) of stretchable electronics [7]. The focus of the approach presented in the paper aims to simulate expected user conditions in the consumer and medical fields, whereas earlier research was focused on shock testing.

In this paper, methods for simulating bi-axial and out-of-plane strains similar to what may occur in a wearable device on the human body are proposed. Electrical and / or optical monitoring (among other methods) can be used to determine cycles to failure depending on expected failure modes. Failure modes can include trace damage in stretchable regions, trace damage in functional component regions, or bulk stretchable material damage, among others. Three different methods of applying mechanical strain are described, including a stretchable air bladder method, membrane test method, and lateral expansion method. This work will describe a prototype of the air bladder method with initial results of the testing for example devices. The system utilizes an expandable bladder to roughly simulate the expansion of muscles in the human body. Besides strain and # of cycles, other variables such as humidity, temperature, ultraviolet exposure, and others can be utilized to determine their effect on the mechanical and electrical reliability of the devices.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Micro and Nano Devices

2016;():V010T13A034. doi:10.1115/IMECE2016-66004.

The paper demonstrates the design and complete analysis of 1-axis MEMS capacitive accelerometer. The design is optimized for high linearity, high sensitivity, and low cross-axis sensitivity. The noise analysis is done to assure satisfactory performance under operating conditions. This includes the mechanical noise of accelerometer, noise due to interface electronics and noise caused by radiation. The latter noise will arise when such accelerometer is deployed in radioactive (e.g., nuclear power plants) or space environments. The static capacitance is calculated to be 4.58 pF/side. A linear displacement sensitivity of 0.012μm/g (g = 9.8m/s2) is observed in the range of ±15g. The differential capacitive sensitivity of the device is 90fF/g. Furthermore, a low cross-axis sensitivity of 0.024fF/g is computed. The effect of radiation is mathematically modelled and possibility of using these devices in radioactive environment is explored. The simulated noise floor of the device with electronic circuit is 0.165mg/Hz1/2.

Commentary by Dr. Valentin Fuster
2016;():V010T13A035. doi:10.1115/IMECE2016-67467.

In this paper we report on the current development of the Solid State Inflation Balloon (SSIB), a simple, reliable, low-cost, non-propulsive deorbit mechanism for the full range of small satellites (<180kg). Small satellites typically rely on aerodynamic drag to deorbit within the FAA’s 25 year requirements. The SSIB will enhance aerodynamic drag by inflating a balloon at the end-of-life of a satellite mission. This technology will provide a scalable and non-existing capability, low-cost deorbit, for applications in the full-range of smallsats, from CubeSats to MicroSats. The proposed SSIB system is composed of three major components: a Micro-Electro-Mechanical Systems (MEMS) Solid-State Gas Generator (SSGG) chip, a balloon structure made of thin metallized polyimide films such as Kapton® HN composed of multiple lenticular gores which will form a spherical balloon, and a subsystem package suitable for spacecraft integration. The SSGG is composed of a 2D addressable array of Sodium Azide (NaN3) crystals on a glass substrate. The crystals are contained in wells formed by a thick-film of epoxy polymer (SU-8). Under each well is a resistive heater that is selectively addressed using Metal-Insulator-Metal (MIM) diode networks. When heated to above 350 °C, the NaN3 spontaneously decomposes to generate N2 gas in time scales on the order of 10 milliseconds. Each well can be designed with a typical volume of 10−15 m3 to 10−6 m3 of NaN3. The SSIB system has built-in redundancy due to the fact that the SSGG is a scalable chip design and can incorporate as many gas generating wells as a mission may dictate. Additionally, the SSIB can mitigate balloon leaks by sequential deployment of additional gas wells and can thereby maintain the inflated state of the balloon. The SSIB system will be low power (< 1 W) and have low mass (mass is proportional to the size of the required balloon). Initial simulations have shown that the SSIB can deorbit small satellites from above 1000 km within 25 years.

Commentary by Dr. Valentin Fuster
2016;():V010T13A036. doi:10.1115/IMECE2016-67602.

Large-area and high-quality monolayer graphene was synthesized in order to fabricate a graphene-base highly sensitive strain sensor. A rapid LPCVD (Low Pressure Chemical vaper deposition) synthesis process of monolayer graphene was developed by using acetylene as a resource gas. To synthesize high-quality single-crystal graphene, the surface of copper substrate was strongly orientated to (111) crystallographic plane. By optimizing the concentration of acetylene gas by diluting hydrogen, the high quality of monolayer single-crystalline graphene film was successfully grown on the copper substrate. A strain sensor was fabricated using the graphene-coated Cu foils by applying the MEMS process and reactive ion etching (RIE). Then, the sensor was transferred onto a polydimethysiloxane (PDMS) substrate. Tree-dimensional bending test was performed to investigate the piezoresistive property of the patterned graphene nano-ribbon. It was confirmed that the highly sensitive strain sensor was obtained when the width of the nano-ribbon was thinner than 70 nm.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Microfluidics 2016 Fluid Engineering in Micro- and Nanosystems

2016;():V010T13A037. doi:10.1115/IMECE2016-65088.

We present a novel cell detection device based on a magnetic bead cell assay and microfluidic Coulter counting technology. The device can detect specific target cells ratios, as well as cells size distribution and concentrations. The device consists of two identical micro Coulter counters separated by a fluid chamber where an external magnetic field is applied. Target cells conjugated with magnetic beads are retarded by the magnetic field; transit time of a target cell passing through the second counter is longer than that through the first counter. In comparison, a non-target cell transit through two counters with nearly the same time. We demonstrated the transit time delay increased approximately linearly with the increasing target cell concentration. The limit of detection (LOD) of the assay was estimated to be 5.6% in terms of target cell ratio.

Topics: Microfluidics
Commentary by Dr. Valentin Fuster
2016;():V010T13A038. doi:10.1115/IMECE2016-65594.

In microfluidic devices, polymerase chain reaction (PCR) is a biomedical technique with great potential for on-site evidence collection system of various pathology and food samples. Although microfluidics has exhibited the ability to miniaturize and automate many laboratory procedures, an essential comprehension of the thermofluidic modeling tools is ultimately critical to streamline the design process of microfluidic device. One of the main obstacles for device miniaturization and process simplification of continuous-flow PCR (CF-PCR) device is employing two or more heaters which lead to process complexity. To overcome these complexities, a novel metal alloy assisted hybrid microdevice (polydimethylsiloxane and glass) for CF-PCR employing one heater is considered. In this paper, a two-step conjugate thermal model, solid domain and one pass model, is developed to optimize the thermal efficiency of a hybrid CF-PCR device using one heater. The effects of heat transfer on temperature distribution and thermal gradients in hybrid CF-PCR device are analyzed using ANSYS CFX 15. For optimized design of PCR chip, parameters, such as protrusion length (3 cm, 4 cm, and 5 cm), metal alloy thickness (1 mm, 2 mm, and 3 mm) and boundary conditions are varied to analyze the effect on temperature distribution in a microchannel. The proposed schemes pave the way for system integration and minimizing the accessories, realizing a portable microfluidic device applicable for on-site and direct field uses.

Commentary by Dr. Valentin Fuster
2016;():V010T13A039. doi:10.1115/IMECE2016-65939.

This paper presents an analytical study of the transient electroosmotic flow for Newtonian fluids through a parallel flat plate microchannel with heterogeneous zeta potentials. The dimensionless mathematical model is based on the Poisson-Boltzmann, mass and momentum conservation governing equations together with the lubrication theory. The distribution of the zeta potentials at the walls obeys to a sinusoidal function, which includes dimensional parameters as Δζ that controls the magnitude and polarity of the zeta potentials, being capable to produce slanted velocity profiles and inverse flows. On the other hand, the combination of the phase angle between the sinusoidal functions of the zeta potentials ω, the dimensionless parameter of their amplitude Δζ, and the parameter that controls the frequency of the sinusoidal functions m, induce additional perturbations on the flow, which is directly related to the dimensionless pressure distribution and to the transient flow field. The transient behavior characteristics of the electroosmotic flow are discussed in terms of the zeta potential variations. It is demonstrated that the results for the transient electroosmotic flow, predict the influence of the main dimensionless parameters above mentioned on the velocity profiles and the streamlines. This work about the perturbations on the electroosmotic flow by heterogeneous zeta potentials, contributes to a better understanding of the transport phenomena in microfluidic devices for future mixing applications.

Commentary by Dr. Valentin Fuster
2016;():V010T13A040. doi:10.1115/IMECE2016-66403.

Nanopores, which are promising as single-molecule sensing devices with low cost and high throughput, have offered significant insights into the research fields of static and dynamic molecular activities, properties, or interactions. In particular, due to its inherent sensitivity, high throughput, amplification-free sample preparation, nanopore will be potentially used in DNA sequencing. Nanopore-based sequencing is based on Coulter Counters, by measuring the distinct current reductions from individual DNA bases with different sizes as they are translocating through a nanopore. The sub-molecular details of an individual molecule can be gathered via recording modulations in the ionic current when a molecule passes through the nanopore under a bias voltage applied across the pore by two Ag/AgCl electrodes. The current blockage and dwell time obtained when the dsDNA translocates through nanopore are accumulated into scatter plots. Ionic current trace recorded at 1000 mv as 48kbp dsDNA translocate through 20 nm thickness with 35 nm alumina nanopore. Here, we apply Schrödinger’s first-passage-time distribution formula to study the distribution of DNA translocation time through alumina nanopores. The first-passage-time distribution is solved with the production of Fokker-Plank equation. Two useful parameters yielded the experimental results are analyzed: the diffusion constant of DNA inside the nanopore and the drift velocity of DNA translocation. By changing the pH value from 5.2 to 10.8 of the electrolyte solution, we notice that the drift velocity of DNA translocation and the diffusion constant of DNA inside the nanopore are extremely close to almost as 34 nm/μs. By changing the pH value of the electrolyte solution, we find that the surface charge density of the wall and the charge of the DNA molecule can be turned, which will result in different DNA molecule capture behaviors. The capture rate is about 17 s−1; the DNA molecule translocates through nanopore when the solution pH is 10.8; and 20 s−1 as the solution pH is 5.2. Theoretical modelling has also been conducted to analyze the experimental results. Hopefully, these findings will shed light on the transport properties of DNA in nanopores, which are relevant to future nanopore applications.

Topics: Nanopores , DNA
Commentary by Dr. Valentin Fuster
2016;():V010T13A041. doi:10.1115/IMECE2016-66544.

The two-dimensional layer of Molybdenum disulfide (MoS2) has attracted much interest due to its direct-gap property and potential applications in the field of catalysis, nanotribology, microelectronics, lithium batteries, hydrogen storage, medical, high-performance flexible electronics and optoelectronics. In this paper, based on few-layer MoS2 acquired by mechanical exfoliation method, a MoS2 liquid-gated field effect transistor (L-FET) is fabricated. Simultaneously, the few-layer MoS2 is characterized by Raman spectral. Then, the performance of MoS2-based L-FET devices is investigated by a source meter instrument in the different back gate voltage of 0.1mol/L NaCl solution. The result reveals that the Schottky barriers is formed between platinum and few-layer MoS2 and the back gate voltage has a great control effect with the drain-to-source current of MoS2 field effect transistor.

Commentary by Dr. Valentin Fuster
2016;():V010T13A042. doi:10.1115/IMECE2016-66860.

Experimental and numerical investigations were conducted to explore the viability of single-phase nanofluids for microchannel cooling. The experiments were conducted with water/ethylene glycol-based nanofluids to investigate the thermal conductivity enhancement. In the numerical analysis, micro-channels ranged in width from 40 μm to 90 μm with the fixed channel height were considered.

Thermal conductivity enhancements of nearly 14% at particle concentration of 0.1% by weight was observed in the experiments. Numerical predictions suggest that design variables (particle size and channel aspect ratio) and thermo-physical properties of the nanofluid have a significant effect on the thermal performance of micro-channel heat sinks. It was shown that at fixed Reynold number, reduction of channel width reduces the hydraulic pressure loss and the heat transfer coefficient, and utilizing nanofluids increases these parameters.

Commentary by Dr. Valentin Fuster
2016;():V010T13A043. doi:10.1115/IMECE2016-67473.

In this study, the impact of the cannula geometry on the formation of the depot in subcutaneous tissue is investigated when injecting insulin using an insulin pump. The simulations have been conducted using the Computational Fluid Dynamics (CFD) software ANSYS Fluent. The study is focusing on rapid acting insulin analogues typically used in insulin pump therapy, which enter the bloodstream very shortly after administration. A previously developed 2-dimensional simulation has been transferred into a 3-dimensional case in order to simulate cases with non-axisymmetric geometries. The tissue has been modeled as a homogeneous anisotropic porous media by the use of different porosity values in the parallel and perpendicular direction with respect to the skin surface. The process of absorption is implemented into the model by the use of a locally variable species sink term. The basic case, simulated with a solid cannula, has been compared to other cannula geometries in order to evaluate if the delivery of insulin in the tissue can be improved. The geometries under consideration are the addition of circumferential holes in the wall of the cannula as well as using an array of cannulas instead of a single cannula. The depot formation is analyzed simulating a standard bolus injection of 0.05ml of insulin using an injection time of 25 seconds. It is observed that the addition of multiple holes in the wall of the cannula or using an array of cannulas can alter the shape of the depot quite significantly. The impact of the depot shape on the diffusion of insulin in the tissue has been evaluated by measuring the total volume of the depot after injection.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Posters

2016;():V010T13A044. doi:10.1115/IMECE2016-67729.

In this paper, to improve the mechanical properties of calcium alginate/polyacrylamide double network hydrogel, the graphene oxide is introduced as a nano-reinfrocer in the naocomposite gel. In addition, the swelling property of gels is suppressed with GO.

Topics: Graphene , Hydrogels
Commentary by Dr. Valentin Fuster
2016;():V010T13A045. doi:10.1115/IMECE2016-68210.

This paper presents the design and development of a flexure-based compliant microgripper to handle and manipulate objects of various sizes ranging from 500–1000 μm. A flexure based compliant microgripper is developed using pseudo rigid body (PRB) modeling, which is then optimized using multi-objective genetic algorithm. A simulation based methodology is adopted to predict the motion movement of the PRB-based and designed microgripper. The final prototype developed generates a maximum end deflection of 2200 μm at maximum force of 0.3 N. Linear and rotational positioning systems are incorporated to manipulate objects in 2D. The system has been successfully demonstrated to grip a metal wire of size 750 μm.

Topics: Manufacturing , Design
Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Quality and Reliability of Electronic/Photonic Packaging

2016;():V010T13A046. doi:10.1115/IMECE2016-65171.

Potential challenges with managing mechanical stress and the consequent effects on device performance for advanced 3D IC technologies are outlined. The growing need for a simulation-based design verification flow capable of analyzing and detecting across-die out-of-spec stress-induced variations in MOSFET/FinFET electrical characteristics is highlighted. A physics-based compact modeling methodology for multi-scale simulation of all contributing components of stress induced variability is described. A simulation flow that provides an interface between layout formats (GDS II, OASIS), and FEA-based package-scale tools, is also developed. This tool, can be used to optimize the floorplan for different circuits and packaging technologies, and/or for the final design signoff, for all stress induced phenomena. Finally, a calibration technique based on fitting to measured electrical characterization data is presented, along with correlation of the electrical characteristics to direct physical strain measurements.

Commentary by Dr. Valentin Fuster
2016;():V010T13A047. doi:10.1115/IMECE2016-67007.

Advanced microelectronic packages utilize a multitude of materials with dramatically different mechanical properties. Delamination occurring at the interfaces between these materials, due to poor adhesion and/or moisture exposure, is an important failure mode affecting the thermomechanical reliability of the package. The adhesion strength of these interfaces is a critical mechanical property that plays a role in the reliability performance of these packages. A good adhesion strength metrology is required to perform material selection and enable assembly process optimization in order to avoid the need for expensive assembly builds, followed by reliability testing which leads to long development times. This paper discusses the use of the Double Cantilever Beam (DCB) method for characterizing the adhesion strength of interfaces in advanced microelectronic packages at both room and high temperatures. Previous work in this area was focused only on room temperature testing. However, in order to characterize the adhesion strength of these interfaces at elevated temperatures seen during package assembly and reliability testing, an environmental chamber was designed and fabricated to rapidly and uniformly heat the DCB samples for testing at high temperatures. Depending on the interface tested and the testing temperature, DCB samples failed in one of three fail modes: (1) adhesive (at the interface), (2) cohesive (within the adhesive layer), and (3) brittle cracking of the substrate. Two case studies describing high temperature DCB testing on silicon-capillary underfill samples are presented. With adhesive failure being the desired fail mode in order to rank order materials and processes, it was found that for the underfills tested in this study, the DCB samples failed cohesively within the underfill at room temperature but started failing adhesively at temperatures near 150°C. Adhesion strength also showed a clear degradation with temperature. It is suspected that the change in failure mode from cohesive to adhesive with increasing temperature is due to competing trends of degradation in cohesive strength of the underfill versus degradation in adhesive strength of the interface with temperature.

Commentary by Dr. Valentin Fuster
2016;():V010T13A048. doi:10.1115/IMECE2016-67145.

As semiconductor packaging technologies continues to scale, it drives the use of existing and new materials in thin layer form factors. Additionally, packaging technologies continue to increase in complexity such as multi-chip packages, 3D packaging, embedded dies/passives, and system in package. This increasing packaging complexity implies that materials in thin layers are subject to non-trivial loading conditions, which may exceed the toughness of the material, leading to cracks. Furthermore, the continued focus on cost leads to a growing interest in novel, low-cost materials. It is important to ensure that the reliability of these low-cost materials is at par or better than currently used materials. This in turn, leads to significant efforts in the area of material characterization at the lab level to speed up the development process. The chosen test methods must not only provide accurate and consistent data, but they must also be applicable across a suitably wide range of materials to aid in the optimization process.

Methods for testing and characterizing fracture induced failures in various material systems in electronic packaging are investigated in this paper. The learnings from the different tests methods are compared and discussed here. More specifically, different fracture characterization techniques on (a) freestanding ‘thin’ solder resist films, and (b) filled ‘bulk’ epoxy materials like underfills and epoxy mold compounds are investigated. For thin films, learnings from different test methods for measuring fracture toughness, namely, uniaxial tension (with and without an edge pre-crack) and membrane penetration tests, are discussed. The test methods are compared by characterizing several different thin films, to gauge how well each method could distinguish differences in material (and thickness). Reasonably good agreement was found between the various thin film toughness test methods; however, ease of sample preparation, fixture, and adaptability to environmental testing will be discussed. In the case of filled epoxy resin systems, the single-edge-notch bending (SENB) technique is utilized to obtain the fracture toughness of underfills and mold compounds with filler materials. Learnings on different methods of creating pre-cracks in SENB samples are also investigated and presented. Two methods are explored in this study, namely, razor blade and laser milling. Good agreement in fracture toughness values was obtained with the two precracking methods, along with considerations about ease of sample preparation and consistency of pre-crack dimensions also examined. Morphology of the pre-cracks obtained by these methods, and their effects on fracture toughness measurements, are also discussed.

Commentary by Dr. Valentin Fuster
2016;():V010T13A049. doi:10.1115/IMECE2016-68119.

Validation of surface mounted electronic devices for drop test performance is considered as one of the most challenging tasks for researchers to search for key dynamic parameters either by experimentation or by numerical simulation. It has not only become challenging task to capture some of the important parameters that affect board flexural rigidity, stiffness, dynamic stresses and strains, but also avoid stress concentrations near undesired locations resulting in non-uniform strain distribution throughout the test board. There is a requirement to simulate exact drop condition that quantifies high impact energy on the board and also control drop to improve the board surface stress/strain distribution measured should be independent from standoff stress region. In this paper, an effort to find the importance of viscous and linear hysteric damping characteristics on uniform board response has been made. The influence of damped responses during no ring impact has been analyzed.

Two different types of computational models are developed and an approximate FEA numerical solutions are obtained to compare current JEDEC test board and alternative hexagonal boards at reduced computational time and challenging experimental cost. The effect of board responses with two types of linear damping models are considered to study the effect. An approach towards finding key parameters that affect stress/strain distribution under both free as well as constrained model has been made, with including different pulse shapes parameters into effect. Maximum board strains are validated and compared using Global FEA model and maximum stresses on the components are evaluated using cut boundary interpolation method. Comparative to empirical results data, an effort to improve uniform stress strain distribution of package solder joints has been made and results are correlated.

Commentary by Dr. Valentin Fuster

Micro- and Nano-Systems Engineering and Packaging: Thermal Management of Electronics

2016;():V010T13A050. doi:10.1115/IMECE2016-65602.

In recent years, light emitting diodes (LEDs) have become an attractive technology for general and automotive illumination systems. LEDs have been preferable for automobile lighting due to its numerous advantages such as long life, low power consumption, optical control and light quality as well as robustness for high vibration. Thermal management is one of the main issues due to severe ambient conditions and compact volume. Conventionally, tightly packaged double sided FR4 based printed circuit boards are utilized for both driver electronics components and LEDs. In fact, this approach will be a leading trend for advanced Internet of Things (IOT) applications in near future.

A series of numerical models are developed to determine the local temperature distribution on both sides of a light engine. Results showed that FR4 PCB has a temperature gradient of over 63°C while the maximum temperature is 105°C. This causes a significant degradation of lifetime and lumen extraction as many LEDs are recommended to be operated below 100°C. In addition to FR4, Aluminum metal core and vapor chamber based advanced heat spreader substrates are developed to obtain thermal impact on the substrate due to a wide range of thermal conductivity of three boards. To mimic real application, two special flex circuits are developed for LEDs and driver circuit. 10 red and 6 amber LEDs at one flex-PCB, and driver components are populated on the other flex-PCB are mounted. Both flex circuits are attached each side of the substrate. Experimental results showed that the local hotspots occurred at FR4 PCB due to low thermal conductivity. Later, a metal core printed circuit board is investigated to minimalize local hot spots. High conductivity metal core PCB showed a 19.9% improvement over FR4 based board. A further study has been performed with an advanced heat spreader based on vapor chamber technology. Results showed that a thermal enhancement of 7.4% and 25.8% over Al metal core and FR4 based boards with an advanced vapor chamber substrate.

Commentary by Dr. Valentin Fuster
2016;():V010T13A051. doi:10.1115/IMECE2016-65680.

Water block and thermoelectric cooler (TEC) are two of the main components in a peltier-based cooling solutions. An optimized water block design and high performance TEC are the key to having a good peltier-based cooling solution. In this study, experimental investigations were performed on small form-factor peltier-based cooling solutions designed for high density electronics. The experiments were conducted in four incremental steps in evaluating the thermal performance of water block with different manufacturing options, different sizes and capabilities of the off-the-shelf TECs, TECs’ optimal operating voltage, thermal performance of the peltier-based liquid cooling solutions, and finally the reliability of the TECs through temperature cycling.

Commentary by Dr. Valentin Fuster
2016;():V010T13A052. doi:10.1115/IMECE2016-66199.

Deployment of air-side economizers in data centers is rapidly gaining acceptance to reduce the cost of energy by reducing the hours of operation of CRAC units. Use of air-side economizers has the associated risk of introducing gaseous and particulate contamination into data centers, thus, degrading the reliability of Information Technology (IT) equipment. Sulfur-bearing gaseous contamination is of concern because it attacks the copper and silver metallization of the electronic components causing electrical opens and/or shorts. Particulate contamination with low deliquescence relative humidity is of concern because it becomes wet and therefore electrically conductive under normal data center relative humidity conditions. IT equipment manufacturers guarantee the reliability of their equipment operating in environment within ISA 71.04-2013 severity level G1 and within the ASHRAE recommended temperature-relative humidity envelope. The challenge is to determine the reliability degrading effect of contamination severity levels higher than G1 and the temperature and humidity allowable ranges A1–A3 well outside the recommended range. This paper is a first attempt at addressing this challenge by studying the cumulative corrosion damage to IT equipment operated in an experimental data center located in Dallas, known to have contaminated air with ISA 71.04-2013 severity level G2. The data center is cooled using an air-side economizer. This study serves several purposes including: the correlation of equipment reliability to levels of airborne corrosive contaminants and the study of the degree of reliability degradation when the equipment is operated, outside the recommended envelope, in the allowable temperature-relative humidity range in geographies with high levels of gaseous and particulate contamination. The operating and external conditions of a modular data center, located in a Dallas industrial area, using air-side economizer is described. The reliability degradation of servers exposed to outside air via an airside economizer was determined qualitatively examining the corrosion of components in the servers and comparing the results to the corrosion of components in a non-operating server stored in a protective environment. The corrosion-related reliability of the servers over almost the life of the product was related to continuous temperature and relative humidity for the duration of the experiment. This work provides guidance for data center administration for similar environment. From an industry perspective, it should be noted that in the four years of operation in the hot and humid Dallas climate using only evaporative cooling or fresh air cooling, we have not seen a single server failure in our research pod. That performance should highlight an opportunity for significant energy savings for data center operators in a much broader geographic area than currently envisioned with evaporative cooling.

Commentary by Dr. Valentin Fuster
2016;():V010T13A053. doi:10.1115/IMECE2016-67229.

Due to the compact and modular nature of CubeSats, thermal management has become a major bottleneck in system design and performance. In this study, we outline the development, initial testing, and modeling of a flat, conformable, lightweight, and efficient two-phase heat strap called FlexCool, currently being developed at Roccor1. Using acetone as the working fluid, the heat strap has an average effective thermal conductivity of 2,149 W/m-K, which is approximately four times greater than the thermal conductivity of pure copper. Moreover, the heat strap has a total thickness of only 0.86 mm and is able to withstand internal vapor pressures as high as 930 kPa, demonstrating the suitability of the heat strap for orbital environments where pressure differences can be large. A reduced-order, closed-form theoretical model has been developed in order to predict the maximum heat load achieved by the heat strap for different design and operating parameters. The model is validated using experimental measurements and is used here in combination with a genetic algorithm to optimize the design of the heat strap with respect to maximizing heat transport capability.

Commentary by Dr. Valentin Fuster
2016;():V010T13A054. doi:10.1115/IMECE2016-67320.

Full submersion of servers in dielectric oils offers an opportunity for significant cooling energy savings and increased power densities for data centers. The enhanced thermal properties of oil can lead to considerable savings in both the upfront and operating costs over traditional air cooling methods. Despite recent findings showing the improved cooling efficiency and cost savings of oil as a cooling fluid, this technique is still not widely adopted. Many uncertainties and concerns persist regarding the non-thermal aspects of an oil immersion cooled data center. This paper presents useful information regarding a variety of factors related to the operation of an oil cooled data center. Pertinent material property considerations such as the chemistry, flammability, material compatibility, human health effects, and sustainability of mineral oil are discussed. A general introduction as to the chemical composition and production of mineral oil is provided. A discussion of the trade-offs in thermal performance and cost of the mineral oil is presented. The dielectric nature of oils is critical to their success as a cooling fluid for electronic applications. Factors such as temperature, voltage, and age that affect this property are reviewed. Flammability of oils is a valid concern when immersing costly IT equipment and the pertinent concerns of this aspect are reviewed. The evaporation loss of oil is also mentioned as refueling and safety are important parameters in the establishment of any facility. Leeching of materials, especially plastics, is a reoccurring concern expressed regarding mineral oil immersed IT equipment. Mineral oils are by-products of petroleum refining processes and as such may bring forth sustainability concerns associated with their use and disposal. The long term stability and performance of key physical and material parameters of oils used in applications such as high voltage power are typically monitored. The similarity and implications of the longevity of oils, when used for data center applications, will be examined. Other issues related to the design, operation, and serviceability of submerged IT equipment and racks will also be addressed. Switching to an oil immersion cooled data center typically brings about several designs and operational changes compared to a typical air-cooled approach. A critical element of oil cooling often cited by opponents of the technology is the issue of serviceability of IT equipment. This paper will discuss some of the additional features a data center may need in place to help alleviate these concerns, as well as, best practices based on experience and observations by the authors. This paper also includes Cup Burner Experiment as per ISO 14520/NFPA 2001 standard to determine the minimum design concentration of fire extinguishing agent for the class B hazard of heavy mineral oil and the class C hazard of electronic equipment as a part of the safety concerns for oil cooled data centers. The visual observations of the servers after immersion in oil for 8 months are also explained for a better view of the system related issues. The discussion presented here is based primarily on literature gathered on the subject and quantifiable data gathered by the authors.

Topics: Cooling , Design
Commentary by Dr. Valentin Fuster
2016;():V010T13A055. doi:10.1115/IMECE2016-67639.

For thermal management architectures wherein the heat sink is embedded close to a dynamic heat source, non-uniformities may propagate through the heat sink base to the coolant. Available transient models predict the effective heat spreading resistance to calculate chip temperature rise, or simplify to a representative axisymmetric geometry. The coolant-side temperature response is seldom considered, despite the potential influence on flow distribution and stability in two-phase microchannel heat sinks. This study uses multi-dimensional transient and steady-periodic models to predict spatial and temporal variations of temperature within the heat sink base. The response to arbitrary transient heat inputs is obtained using Duhamel’s method. For time-periodic heat inputs, the steady-periodic solution is calculated using the method of complex temperature. Solution of the coolant-side temperature response in the presence of multiple different transient heat inputs is demonstrated. The degree of spatial and temporal non-uniformity in the coolant-side temperature profiles are mapped as a function of nondimensional geometric parameters and boundary conditions. Several case studies are presented to demonstrate the utility of such maps.

Commentary by Dr. Valentin Fuster
2016;():V010T13A056. doi:10.1115/IMECE2016-67697.

A large fraction of energy consumed in modern microelectronic devices and systems is taken up by memory access operations, which is expected to cause significant temperature rise. Since memory access operations are very short in duration, this is expected to inherently be a transient thermal phenomenon. Despite the critical importance of thermal management in microelectronics, not much work exists on understanding the nature of thermal transport during memory access operations. In this work, a mathematical model to predict the transient temperature rise within a 3D memory chip is presented. Most heat-generating memory access processes occur over a short timescale for which the thermal penetration depth is shorter than the die thickness. This enables the modeling of such processes independent of the nature of chip cooling by treating the chip as a semi-infinite medium. A semi-infinite Green’s function model is developed for one bank of memory on a single layer of a block of the memory chip. This model is validated against finite element simulation results. Validation is also carried out by comparison of the model against the analytical solution for a limiting case. The analytical model is used to analyze transient thermal effects of various memory access processes for multiple banks. These results will help develop an understanding of optimal layouts and processes for 3D memory chips, eventually leading to co-design tools that simultaneously improve thermal and electrical performance of 3D memory chips.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2016;():V010T13A057. doi:10.1115/IMECE2016-67700.

In this paper, heat transfer enhancement using liquid-liquid Taylor flow in mini scale curved tubing for isothermal boundary conditions is examined. The copper tubing has an inner tube diameter of Di = 1.65 mm with different radii of curvature and lengths. Taylor flow is created using water and low viscosity silicone oils (0.65 cSt, 1 cSt, 3 cSt) to examine the effect of Prandtl number on heat transfer rates in curved tubing. A series of experiments are conducted using tubing with constant length and variable curvature, as well as variable length and constant curvature. The experimental results are compared with models for liquid-liquid Taylor flow in straight tubing and single-phase flow in curved tubes. The results of the research develop a new model for liquid-liquid Taylor flow in curved tubing. This research provides new insights into the effect of curvature on heat transfer enhancement for liquid-liquid Taylor flow in mini scale curved tubing, at a constant wall temperature.

Commentary by Dr. Valentin Fuster

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