bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Characterization of a Raised Floor Data Center Using Rapid Operational Flow Curves Model
Authors: Alissa Husam A. , Nemati Kourosh , Sammakia Bahgat , Seymour Mark , Schneebeli Ken , Schmidt Roger
Published: November 2015

As the number of data centers is exponentially growing globally, pragmatic characterization schemes are considered to be a necessity for measuring and modeling the load capacity and flow pattern of the facility. This paper contains experimental and numerical characterization of a new data center laboratory using practical measurements methods, including tiles and CRAH flow measurements. Then a full physics based CFD model is built to simulate/predict the measured data. A rapid flow curve method is used showing high accuracy and low computational expense.

Detailed descriptions of the data center structure, dimensions, layout (Appendix, A-1) and flow devices are given. Also, modeling parameters are mentioned in details to provide a baseline for any investigative parametric or sensitivity studies. Four experimental room level flow constraint scenarios are applied at which measurements were taken, (Appendix, A-2). The model is then built and calibrated then used to predict measurements.

Measurements of the cooling unit were performed using hot wire anemometry with a traverse duct installed at the top of the CRAH. The tiles measurements were carried out using a flow hood with back pressure compensation. A detailed CFD model is constructed to predict the four experimental cases. For modeling the interdependency between the flow and pressure in flow devices flow curve approach is used. This is a rapid modeling technique that relies on experimentally measured (for IT) or approximated (for CRAH) flow curves. Applying the operational flow curves boundary conditions at the vents of the flow device results in a very accurate simulation model. It is also shown that the flow curves can be used to predict the real-time flow rate of servers at known RPM. This greatly simplifies flow rate measurements of IT in the data center.
Effects of Thermal Cycle Conditions on Thermal Fatigue Life of Substrate With Cu Through-Hole
Authors: Yamayose Yu , Kugimiya Tetsuya , Hirohata Kenji , Happoya Akihiko , Ohno Nobutada , Sakane Masao
Published: November 2015

The Cu through-hole is a structure of electroplated Cu thin film, which penetrates the substrate. Because of the mismatch of the thermal expansion coefficient between the Cu thin film and the substrate along the thickness direction, thermal strain occurs repeatedly at the Cu through-hole part with the variation of temperature. As a result, the thermal fatigue failure of Cu through-hole part is one of the failure modes of the substrate. In this study, the effects of thermal cycle conditions on the thermal fatigue life of the substrate with Cu through-hole were investigated by thermal cycle tests and Finite Element Method (FEM)-based analyses. Thermal cycle tests of the substrate with Cu through-hole were conducted under different thermal conditions. The effects of dwell time, temperature range and maximum temperature were investigated. Among these factors, the maximum temperature shows the greatest influence on the thermal fatigue life of Cu through-hole part. FEM-based thermal cycle analyses were also carried out to understand the effects of thermal cycle conditions. The glass cloth structures of the substrate should be considered in the analyses, because their rigid properties probably affect the generation of the failure at the through-hole part. In this study, glass cloth structures were modeled by taking advantage of a homogenization method. On the other hand, the inelastic constitutive model of the electroplated Cu thin film was introduced in the analyses in order to describe the creep deformation during the dwell process of thermal cycles. The inelastic strain range of the Cu through-hole during thermal cycles was calculated from the analysis results and the effectiveness of the Coffin-Manson law was evaluated. The results showed that the fatigue life prediction using the Coffin-Manson model was effective in the range of the same substrate thickness and the same maximum temperature. Additionally the influences of material model and material constants of epoxy resin were investigated to expand the range of application of the fatigue life prediction.
Tailoring of Permeability in Copper Inverse Opal for Electronic Cooling Applications
Authors: Zhang Chi , Rong Guoguang , Palko James W. , Dusseault Thomas J. , Asheghi Mehdi , Santiago Juan G. , Goodson Kenneth E.
Published: November 2015

Microporous metals are extensively applied in convective cooling of high heat flux systems such as electronics. Traditional fabrication approaches, such as sintering of metallic particles, however, produce materials with limited fluid transport capability. Here, we demonstrate control and enhancement of the permeability of porous copper inverse opals produced via electrodeposition around a sacrificial polymer template. Sintering of the template is used to control the fluid transport network microstructure, with permeability increasing for increasing sintering times. These electrodeposited structures achieve permeabilities greater than 1×10−12 m2 with 5 μm pores, roughly 5 times larger than those of porous sintered copper with comparable feature sizes. The high permeability and small feature sizes, with attendant high specific surface area and strong capillarity, offered by the sintered template electrodeposited copper are attractive for two phase cooling applications.
Thermal Conductivity of Phonon Modes in Graphene Nanoribbon at Localized High Heating
Authors: Zolotoukhina Tatiana
Published: November 2015

The spectral components of the phonon transport in the locally thermally excited graphene samples were studied by molecular dynamics (MD) method. In order to be able to select and analyze separate phonon modes in the time of propagation, the transient Green-Kubo approach to the definitions of density of states (DOS) and thermal conductivity was tested in quasi-equilibrium regimes for limited region of the graphene sample studied. Propagation of single modes at the background of diffusional phonon distribution and energy decay of such modes are studied by calculation of the DOS and dispersion relations, their dependence on the heating condition and temperature is studied. Similar conditions can be generated at localized heating of small areas of graphene structures in electronic devices. In transient regime, many issues of thermal transport evaluation still remain not sufficiently tested, especially phonon dynamics. Thermal conductivity of graphene samples related to transport of separate phonon modes is still not completely investigated, however, recent result give indication on the difference in the contribution of phonon modes. In the study, we consider mostly high temperature transport modes that are generated at the heated spot in order to be able to define their velocities and lifetimes in the limit of transient MD sampling.

The single-layer graphene nanoribbon of 150 nm to 40 nm was relaxed and prepared in equilibrium in zigzag and armchair orientations. REBO potential for graphene was utilized. Our calculation has shown that at the heating to high temperatures of 1000K and higher, the G mode of graphene remains stationary and has a minimal contribution into thermal transport by coherent modes. The coherent phonon mode or modes that contribute the most into thermal transport were confined in the vicinity of 30 THz and can possibly be attributed to the D modes of graphene.
Robust Data Acquisition for Building Lighting Systems
Authors: Pearson Zak , Crenshaw Tanya L. , Dillon Heather , Paulson Erik , Warlen Nick
Published: November 2015

In 2012, 12% of US electricity consumption was due to residential and commercial lighting. By 2030, LED lightbulbs will be more plentiful, projected to drive a 40% reduction in energy [1]. Yet today’s LED lightbulbs have bulky heat sinks that do not leverage modern thermal management techniques. Reducing the size of the heat sink offers lower cost and increased energy efficiency.

To leverage modern techniques, it is valuable to understand how thermal performance degrades light quality as people utilize lights over weeks and months. However, using current data acquisition systems to obtain such massive data sets is expensive, time-consuming, and cable-ridden.

We have developed a robust ground-to-cloud system to acquire temperature and luminosity data for building lighting systems. The data acquisition units are small and may be positioned in existing lighting installations. During acquisition, data is backed up automatically. Usability studies demonstrate that novice users can configure an experiment in less than four minutes.
A Compliance-Based Approach to Study Fatigue Crack Propagation for a Copper-Epoxy Interface
Authors: Samet David , Kwatra Abhishek , Sitaraman Suresh K.
Published: November 2015

As the microelectronics industry continues to advance the boundaries of size and performance, focus on the impact of systems packaging has risen to the forefront of design and material considerations. As interfaces are often constructed of multiple heterogeneous layers, interfacial delamination is an important failure mechanism to consider in microelectronic packaging. This failure is due to, among other factors, the stresses arising from high mismatches in coefficient of thermal expansion (CTE). Most work to date has focused on interfacial crack propagation under monotonic loading that is incurred during fabrication steps such as deposition or curing which occur at elevated temperatures and subsequent cooling to room temperature. This is an important design consideration but it is not sufficient as the operational life of these devices involve high numbers of heating and cooling cycles which result in crack propagation under fatigue loading. As such the study of fatigue effects on these interfaces is paramount to improving the lifetime of microelectronic devices as the field pushes towards both thinner and wider packages.

One such exploration, which is the subject of this work, is to determine the interface incremental crack growth rate as it relates to cyclic loading. In this work, double cantilever beam (DCB) tests are performed at various stress ratios on samples with epoxy mold compound (EMC) atop a copper leadframe. For these tests, force versus displacement curves will be obtained. Given the small dimensions of the interfaces in question, it is desirable to develop a test methodology that does not require in-situ measurement of crack length. Thus, in these tests the compliance of the samples is determined from the force versus displacement curves and used to infer the progress of the crack through an indirect approach. The advantage of this method is that it does not require the observational measurement of the crack length potentially allowing crack monitoring absent any optical or imaging methods. Using the determined crack propagation rate with fatigue cycle under various loading conditions, a generalized fatigue crack propagation model will be developed for mold compound and copper interface, and such a model can be employed to assess packaging reliability in operating conditions.
Mechanical Shock Reliability Analysis and Multiphysics Modeling of MEMS Accelerometers in Harsh Environments
Authors: Lall Pradeep , Kothari Nakul , Glover Jessica
Published: November 2015

MEMS accelerometers have found applications in harsh environments with pressure, temperatures above ambient conditions, high g shock and vibrations. The complex structure of these MEMS devices has made it difficult to understand the failure modes and failure mechanisms of present day MEMS accelerometers. Little work has been done by the researchers in investigating the high g reliability of the MEMS accelerometers by continuous high g drops and quantifying the failure modes. There is little literature addressing the multiphysics finite element modelling of MEMS accelerometers subjected to high g shocks. In defense applications, where these devices are integrated with several other compactly assembled subsystems, lack of knowledge on the physics of failure for the MEMS sensor in harsh environment operation, can be detrimental to the success of the system on the whole. Being able to successfully model inside of an accelerometer, enables the user to better understand the change in parameters like time delay induced in response of successive drops, change in pulse width that indicate failure, reduction in sensed g levels. Some researchers have subjected various accelerometers to repeated drops at their maximum sensing g(not high g) level, and used optical microscopy to detect damaged sensing elements [Beliveau, 1999]. Few researchers have modeled the internal structure of the MEMS device, along with the device packaging under the stresses of operation [Fang 2004, Ghisi 2008, Xiong 2008]. In this paper, a multiphysics model of capacitive and the moving elements of the accelerometer has been developed to model the change in capacitance with respect to stroke and understand the correlation with g-levels, in addition to the transient dynamic response of the accelerometer under high-g shock. This has not been much explored in the past. The accelerometer studied in the paper is the ADXL193, and subjected to repeated drops of 3000g in each 3 axes as per 2002.4 of MIL-STD-883 without preconditioning. A characteristic graph of capacitance vs accelerometer stroke has been obtained from a series of electrostatic simulations and is then used to relate g levels, capacitance, stroke deflection and voltage change using electromechanical transducer elements. The drift in the performance characteristics of the accelerometer have been measured versus the number of shock events. In addition, an attempt has been made to investigate the failure mode in the accelerometer.
Lab-on-a-Chip Device for Hydrogen Sulfide Sensing in Biomedical and Environmental Applications Using Electrochemical Approach
Authors: Baniya A. , Thapa S. , Borquist E. , Bailey D. , Wood D. , Dutta G. , Arumugam P. , Glawe J. , Kevil C. , Weiss L.
Published: November 2015

Hydrogen sulfide (H2S) is rapidly emerging as a biologically significant signaling molecule. In recent studies, sulfide level in blood or plasma has been reported to be in the concentration between 10 and 300 μM suggesting it acts in various diseases. This work reports progress on a new Lab-on-a-Chip (LOC) device for these applications. The uniquely designed, hand-held device uses advanced liberation chemistry that releases H2S from liquid sample and an electrochemical approach to detect sulfide concentration from the aqueous solution.

The device itself consists of three distinct layers of Polydimethylsiloxane (PDMS) structures and a three electrode system for direct and rapid H2S concentration measurement.

In this work specifically, the oxidation of sulfide at the gold (Au) and platinum (Pt.) electrodes has been examined. This is the first known application of electrochemical H2S sensing in an LOC application. The analytical utility and performance of the device has been assessed through direct detection using chronoamperometry (CA) scan and cyclic voltammetry (CV). An electrocatalytic sulfide oxidation signal has been recorded for sulfide concentration range vs, Ag/AgCl at different pH buffers at the trapping chamber. The calibration curve in the range 1 μM to 1 M was obtained using this electrode setup. The detection limit was found to be 0.1 μM. This device shows promise for providing fast and inexpensive determination of H2S concentration in aqueous samples.
Small-Scale Vorticity Induced by a Self-Oscillating Fluttering Reed for Heat Transfer Augmentation in Air Cooled Heat Sinks
Authors: Hidalgo Pablo , Glezer Ari
Published: November 2015

Heat transfer in a high aspect ratio, rectangular mm-scale channel that models a segment of a high-performance, air-cooled heat-sink is enhanced by deliberate formation of unsteady small-scale vortical motions. These small-scale motions are induced by self-fluttering, cantilevered planar thin-film reeds that are placed along the channel’s centerline. Heat transfer is enhanced by significant increases in both the local heat transfer coefficient at the fins surfaces, and in the mixing between the thermal boundary layers and the cooler core flow. The present investigation characterizes the thermal performance enhancement by reed actuation compared to the base flow (in the absence of the reeds) in terms of increased power dissipation over a range of flow rates, along with the associated fluid power. It is shown that because the cooling flow rate that is needed to sustain a given heat flux at a given surface temperature is almost two times higher than in the presence of the reeds, the reeds lead to a four-fold increase in thermal performance (as measured by the ratio of power dissipated to fluid power). The thermal effectiveness of the reeds is tested in a multi-channel heat sink, and it is shown that the improvement in heat transfer coefficient of the base flow is similar to that of the single channel.
Multi-Physics Driven Co-Design of 3D Multicore Architectures
Authors: Xiao He , Yueh Wen , Mukhopadhyay Saibal , Yalamanchili Sudhakar
Published: November 2015

The high heat flux and strong thermal coupling in the 3D ICs has limited the performance gains that would otherwise be feasible in 3D structures. The common practice of adopting worst-case design margins is in part responsible for this limitation since average-case performance would be limited by worst-case thermal design margins. The coupling between temperature and leakage power exacerbates this effect. However, worst-case thermal conditions are not the common state across the package at runtime. We argue for the co-design of the package, architecture, and power management based on the multi-physics interactions between temperature, power consumption and system performance. This approach suggests an adaptive architecture that accommodates the thermal coupling between layers and leads to increased energy efficiency over a wider operating voltage range and therefore higher performance.

In this paper, we target at a 3D multicore architecture where the cores reside on one die and the last level cache (LLC) resides on the other. The DRAM stack may be stacked on top of the package (e.g., 3D) or in the same package (e.g., 2.5D). We propose a novel adaptive cache structure — the constant performance model (CPM) cache — based on voltage adaptations to temperature variations. We construct a HSPICE model for the SRAM to explore the relationship between temperature, supply voltage, and the circuit delay in the context of the LLC. This model is used to investigate, characterize, and analyze the effect of the temperature-delay dependence of the SRAM LLC configuration on the system-level performance and energy efficiency. This analysis gives rise to an intelligent scheme for dynamic voltage regulation in the LLC cache that is sensitive to the temperature of the individual cache banks. Each cache bank is thermally coupled to the associated cores and thus is sensitive to the local core-level power management. We show that this local adaptation to the temperature-delay dependence leads to a significant power reduction in the LLC cache, and improvement of system energy efficiency computed as energy per instruction (EPI). We evaluate our approach using a cycle-level, full system simulation model of a 16-core x86 homogenous microarchitecture in 16nm technology that boots a full Linux operating system and executes application binaries. The advantages of the proposed adaptive LLC structure illustrate the potential of the co-design of the package, architecture, and power management in future 3D multicore architectures.
Mechanical Characterization of Metal Foams for Contact Resistance in Thermal Interface Applications
Authors: Trifale Ninad , Nauman Eric , Yazawa Kazuaki
Published: November 2015

We present a study on the effective mechanical compliance of porous aluminum foams. We develop an experimental setup to characterize the elastic properties as well as evaluate surface deformation with respect to porosity as well as pore size in an effort to correlate the properties to contact resistance of the foams when used as thermal interface materials. There have been multiple studies in the past to evaluate the effective elastic modulus of porous structure as a function of porosity through experimentation, simulation as well as analytic models. This work also serves as a validation for analytic and experimental data published by various researchers in the past. This study is one aspect of a larger study to empirically correlate the area of contact to thermal contact resistance. We evaluate samples with three different porosity and three different PPI (pores per inch) specification. Additionally we analyze effect of presence of filler material in the voids — a phase change material. The filler is used as separate stand-alone TIM in the industry currently.
Full Scale Simulation of an Integrated Monolithic Heat Sink for Thermal Management of a High Power Density GaN-SiC Chip
Authors: Liu Tanya , Houshmand Farzad , Gorle Catherine , Scholl Sebastian , Lee Hyoungsoon , Won Yoonjin , Asheghi Mehdi , Goodson Kenneth , Kazemi Hooman , Vanhille Kenneth
Published: November 2015

Advances in manufacturing techniques are inspiring the design of novel integrated microscale thermal cooling devices seeking to push the limits of current thermal management solutions in high heat flux applications. These advanced cooling technologies can be used to improve the performance of high power density electronics such as GaN-based RF power amplifiers. However, their optimal design requires careful analysis of the combined effects of conduction and convection.

Many numerical simulations and optimization studies have been performed for single cell models of microchannel heat sinks, but these simulations do not provide insight into the flow and heat transfer through the entire device. This study therefore presents the results of conjugate heat transfer CFD simulations for a complex copper monolithic heat sink integrated with a 100 micron thick, 5 mm by 1 mm high power density GaN-SiC chip. The computational model (13 million cells) represents both the chip and the heat sink, which consists of multiple inlets and outlets for fluid entry and exit, delivery and collection manifold systems, and an array of fins that form rectangular microchannels. Total chip powers of up to 150 W at the GaN gates were considered, and a quarter of the device was modeled for total inlet mass flow rates of 1.44 g/s and 1.8 g/s (0.36 g/s and 0.45 g/s for the quarter device), corresponding to laminar flow at Reynolds numbers between 19.5 and 119.3. It was observed that the mass flow rates through individual microchannels in the device vary by up to 45%, depending on the inlet/outlet locations and pressure drop in the manifolds. The results demonstrate that full device simulations provide valuable insight into the multiple parameters that affect cooling performance.
Discrete Control of Air Conditioning Units in Mission Critical Facilities
Authors: Bermudez Sergio A. , Hamann Hendrik F. , Klein Levente J. , Marianno Fernando J. , Claassen Alan C.
Published: November 2015

For redundancy, almost all mission-critical facilities such as data centers are fitted with more air condition units than required. These units are most of the time heavily underutilized, where the fans within the units are still consuming energy circulating air without actually providing cooling. In more modern facilities such fans are equipped with variable frequency drives, which can reduce substantially the energy consumption if proper controls are implemented. While there have several solutions for controlling and optimizing such variable frequency drive operated air conditioning units, control systems without variable frequency drives (discrete on/off ACU controls) have not been addressed thoroughly. In this paper, we present a practical, distributed and automatic control method for such discrete air conditioning units. The technique includes several safety features and is based on dense environmental sensing and events like hotspots or device failures. We discuss this approach by way of example of a case study.
Flow Resistance Network Analysis in Fan-Cooled High-Density Packaging Electronic Equipment
Authors: Fukue Takashi , Hatakeyama Tomoyuki , Ishizuka Masaru , Hirose Koichi , Obata Kazuma , Koizumi Katsuhiro
Published: November 2015

This study describes an application of the flow resistance network analysis to thermal design of fan-cooled electronic equipment. Especially, a modeling method of the flow resistance network was investigated. Current electronic equipment becomes smaller and thinner while their functions become more complex. As a result, flow passages for cooling air become complex. In order to simulate the complex airflow in high-density packaging electronic equipment by using the flow resistance network, we tried to develop the flow resistance network by support of the 3D-CFD analysis. A test model which simulates high-density packaging electronic equipment is prepared and the flow resistance network analysis is applied to the prediction of flow rate distribution in the model. Through the investigation, we obtained information and future problems about the development of the flow resistance network in electronic equipment with lots of electrical components.
Enhancement of Water Cooling Performance in Narrow Flow Passages by Using Micro Heat Sinks With Miniature Vortex Generators
Authors: Obata Kazuma , Fukue Takashi , Hirose Koichi , Kikuchi Mamoru , Ueda Yasuhiko , Kusabuka Shigekado , Miyahara Tomoyasu
Published: November 2015

This study describes a possibility of an improvement of water cooling devices for high-power electronic devices such as inverters for electric vehicles by using a combination of micro heat sinks and miniature vortex generators. Power devices such as IGBT (Insulated Gate Bipolar Transistor) are widely used for controlling an operation of electronic vehicles and hybrid vehicles. Due to the improvement of the performance of the power devices, the heat dissipation density from these devices becomes higher. The water cooling is the commonest method for dissipating heat from the inverter of the electronic vehicles. Therefore the improvement of the water cooling technology is significantly needed in order to manage the increase of the heat dissipation density.

We are now trying to develop a high-performance water cooling device for dissipating the high heat flux from the inverters in the electric vehicles by using a combination of a fine miniature heat sink and a miniature vortex generator. The combination of the miniature heat sink and the vortex generator may increase heat transfer performance of the heat exchanger while inhibiting an increase of pressure drop by generating a swirling turbulent flow in a clearance between the heat sink fins. In this study, the water cooling performance in the narrow flow passage, which simulates the flow passage in the water cooling device, with the miniature heat sink and the miniature vortex generators was investigated by using 3-dimentional CFD analysis. From the analysis, we conclude that the combination of the miniature heat sink and the vortex generator was effective for the heat transfer enhancement in the narrow flow passage of the water cooling device while inhibiting the generation of the pressure drop when we can use the combination with the appropriate manner.
Microscale Layering of Liquid and Vapor Phases Within Microstructures for Self-Regulated Flow Delivery to Local Hot Spots
Authors: Fazeli Abdolreza , Bigham Sajjad , Mortazavi Mehdi , Moghaddam Saeed
Published: November 2015

In this study, a new two-phase heat sink architecture is introduced that operates in two different phase change modes. At low wall superheat temperatures, the heat sink operates at the thin film evaporator mode and transitions to boiling when the wall superheat temperature is increased. This unique function is enabled through constraining the liquid and vapor phases into separate domains using capillary-controlled meniscus formed within a hierarchical 3D structure. The structure is designed to form thin layers of vertically oriented liquid films that directly evaporate into their neighboring vapor space. The dominant mode of heat transfer in this design is thin film evaporation, a very effective boiling sub-process. As the surface superheat temperature is increased and boiling starts, the capillary-controlled meniscus breaks down. A heat transfer coefficient of greater than 200 kW/m2K is achieved at less than 1 °C wall superheat temperature.
Fuming Acid Based Decapsulation Process for Copper-Aluminum Wirebond System Molded With Different EMCs
Authors: Lall Pradeep , Deshpande Shantanu , Nguyen Luu
Published: November 2015

Decapsulation is one of the very powerful technique in failure analysis process. During this process, die and first level interconnects are exposed by dissolving molding compound around them using variety of methods. Typically decapsulation formulation uses red fuming nitric acid at elevated temperatures. This technique work for traditional Gold wire bonds, but does not work for its new alternative Copper. Gold, being inert metal does not react with acid. Copper on the other hand; tends to react with fuming nitric acid, and dissolves rapidly into acid. It is important to develop acid chemistry that can be successfully used to perform decapsulation of Cu-Al incorporated packages for different EMC’s.

In this paper, decap process based on combination of red fuming nitric acid and concentrated sulfuric acid at elevated temperatures is presented. Reduction in wire diameter was monitored for all devices. For some devices decap process was evaluated based on comparison of WB shear strength of decaped part with unmolded part. SEM was used extensively to track down degradation of copper wires. These tests were performed on packages with different EMC’s, wire diameters, pad thickness and some active dies.

Statistical principal components regression model has been developed correlating the decapsulation process parameters with the post decap wire diameter reduction. Principal component regression in conjunction with stepwise regression has been used to identify the influential variables, and to remove the multicollinearity between the predictor variables. Principal component analysis which combines two correlated variables into a single factor is a widely used image processing technique for pattern recognition and image compression. The post molded packages have then used to assess the effect of various decapsulation treatments.
Film Boiling Heat Transfer Enhancement via Electrostatic Leidenfrost State Suppression
Authors: Shahriari Arjang , Bahadur Vaibhav
Published: November 2015

Boiling heat transfer has enormous impact on the effectiveness of various industrial processes like steam generation, desalination, and nuclear reactor operations. Heat transfer in the film boiling regime is significantly reduced as compared to the nucleate boiling regime due to the existence of a vapor layer at the solid-liquid interface (Leidenfrost effect). This vapor layer degrades heat transfer by up to two orders of magnitude and causes dryout, which can result in severe temperature excursions. This work maps out the heat transfer benefits of electrostatic suppression of the Leidenfrost state. Electrical suppression of the Leidenfrost state is observed for a variety of liquids, including organic solvents, water and electrically conducting salt solutions. Successful Leidenfrost state suppression is observed with moderate voltages even at ultrahigh temperatures exceeding 550 °C. Elimination of the vapor layer increases heat dissipation capacity of film boiling by more than one order of magnitude; up to 45X enhancement was measured in this work. This work also introduces the concept of tunable film boiling heat transfer. Overall, electrically-enhanced boiling can enable a new class of technologies for active control and enhancement of boiling heat transfer, with various applications in energy systems.
Embedded Cooling of High Heat Flux Electronics Utilizing Distributed Microfluidic Impingement Jets
Authors: Ditri John , Hahn Joseph , Cadotte Roland , McNulty Michael , Luppa Denise
Published: November 2015

Embedded cooling techniques, utilizing microfluidic channels directly within a die substrate or in a miniature heat sink attached to the base of the die, have been known for decades [1] [2] [3]. Despite their demonstrated thermal benefits, such techniques and devices have not been successfully transitioned from the laboratory to either the commercial or military arena. Some of the hurdles preventing implementation to date have been the inability to miniaturize the supporting hardware, the high unit cost of fabricating individual microfluidic coolers, and the unknown reliability of the new technologies introduced. Recent advances in micro manufacturing and co-design/simulation capabilities have enabled significant progress to be made, aided by a significant new focus on embedded cooling technologies was recently initiated by DARPA [4]. This paper will present a recently fabricated embedded cooling system consisting of a state of the art, micro-miniature, 3D microfluidic manifold suitable for near term integration into existing systems. Computational fluid dynamics (CFD) and conjugate heat transfer (CHT) simulations demonstrate the ground breaking thermal performance achieved by the device, and coupled-field flow, thermal, structural and erosion simulations are also presented to address some of the reliability concerns. Finally, measured thermal performance is presented, validating the predicted thermal performance.
Thermal Design of a Hierarchical Radially Expanding Cavity for Two-Phase Cooling of Integrated Circuits
Authors: Sridhar Arvind , Ong Chin Lee , Paredes Stefan , Michel Bruno , Brunschwiler Thomas , Parida Pritish , Colgan Evan , Chainer Timothy , Gorle Catherine , Goodson Kenneth E.
Published: November 2015

A major challenge in the implementation of evaporative two-phase liquid-cooled ICs with embedded fluid microchannels/cavities is the high pressure drops arising from evaporation-induced expansion and acceleration of the flowing two-phase fluid in small hydraulic diameters. Our ongoing research effort addresses this challenge by utilizing a novel hierarchical radially expanding channel networks with a central embedded inlet manifold and drainage at the periphery of the chip stack. This paper presents a qualitative description of the thermal design process that has been adopted for this radial cavity. The thermal design process first involves construction of a system-level pressure-thermal model for the radial cavity based on both fundamental experiments as well as numerical simulations performed on the building block structures of the final architecture. Finally, this system-level pressure-thermal model can be used to identify the design space and optimize the geometry to maximize thermal performance, while respecting design specifications. This design flow presents a good case study for electrical-thermal co-design of two-phase liquid cooled ICs.
Mechanical Characterization of Assemblies Bonded With Pressure-Sensitive Adhesives (PSAs)
Authors: Huang Hao , Dasgupta Abhijit , Mirbagheri Ehsan , Boddapati Srini
Published: November 2015

The focus of this paper is on the stress-strain behavior and creep response of a pressure-sensitive adhesive (PSA) with and without carrier layers. This study consists of two phases. The first phase focuses on understanding of the effects of fabrication profiles, including bonding pressure, bonding temperature, bonding time, and aging time, on the PSA joint strength. This part of the study is used to identify an acceptable bonding and aging conditions for manufacturing a robust PSA bonded assembly. Specimens fabricated with this selected set of bonding process conditions are then used for mechanical characterization. The second phase focuses on the assembly’s mechanical behavior (stress-strain behavior and the creep curves) under different loading conditions, including loading stress, loading rate, and loading temperature. The mechanical behavior of PSA bonded assemblies is affected not only by the loading conditions, but also by the assembly architecture. The mechanical behaviors and failure modes of PSAs with and without carrier layers are compared. The reasons for these differences are also discussed.
DIC Based Investigation Into the Effect of Mean Temperature of Thermal Cycle on the Strain State in SnAgCu Solder Joint
Authors: Lall Pradeep , Mirza Kazi , Suhling Jeff
Published: November 2015

Electronics in high reliability applications may be subjected to cyclic thermo-mechanical loads after being deployed for extended periods of time in harsh environment. Cyclic thermal excursion may result in solder joint fatigue leading to failure. Previous researchers have shown that exposure to high temperature for extended periods of time results in evolution of the mechanical properties of SnAgCu alloys. Deployment of leadfree electronics in harsh environment applications may result in exposure to a multitude of thermal cycles. The effect of cyclic thermal range and thermal aging on the thermal fatigue reliability has been widely documented; however the effect of the mean temperature on the thermal fatigue reliability and the strain evolution of during cyclic exposure has not been studied. In this paper, an experimental investigation has been undertaken using digital image correlation to quantify the evolution in the strain state under different mean temperatures and cyclic thermal intervals. Three different test vehicles, BGA 144, 256 and 324 were used in this study under three different test conditions 50–150°C, 0–100°C and −50–50°C. A framework to evaluate the effect of mean temperature of thermal cycle has been developed.
Effects of Low CTE Materials on Thermal Deformation of Organic Substrates in Flip Chip Package Application
Authors: Mori Hiroyuki , Kohara Sayuri , Okamoto Keishi , Noma Hirokazu , Toriyama Kazushige
Published: November 2015

Coefficient of thermal expansion (CTE) characteristic of organic materials for substrates in flip chip package application demanded by semiconductor package requirements is becoming lower than ever. In general, height restrictions are imposed on package-on-package (PoP) devices in mobile applications. One should hence establish a tight budget on the height variation in manufacturing of the devices. Given such background, a lowering of the CTE characteristic of package substrates is an attractive solution for reducing package deformation upon manufacturing, since it contributes to minimize CTE mismatch of the substrates with silicon chips. In large-die flip chip applications such as high-end processors, a lower CTE substrate can mitigate mechanical stress not only on low-k layers in back end of the line (BEOL) underneath the chip bumps, but also on underfill layers during thermal cycling. Therefore an introduction of lower CTE materials in organic substrates is becoming essential for future applications of electronic devices. In this paper, thermal deformation behaviors of organic substrates associated with lowering of the CTEs of their constituent materials are analyzed by finite element analysis (FEA). The analyses are done on a 3-2-3 build-up layer structure substrate in order to focus onto typical application specific integrated circuit (ASIC) products. A finite element model for a test substrate is constructed by a method in which the substrate is divided into sections according to its circuitry patterns so that the lateral inhomogeneity of mechanical property is taken into account. The finite element analyses using the model showed that the package warpage decreases with lowering of the effective CTE of the substrate, but the warpage of the substrate itself increases and its surface profile changes from a concave shape to a convex shape. The analysis result of substrate warpage variation with the build-up material’s CTE showed that the selection of build-up materials with appropriate material properties can contribute to reduce the substrate warpage. The analysis also showed that the adverse impact to the substrate’s CTE reduction by such material selection is limited.
Pipe Support Inspections: Review of Select Codes, Standards and Recommended Practices
Authors: Kimball Lange , Bettell Britt
Published: November 2015

The performance of regular inspections of pipe supports and hangers at refineries, power plants and other industrial sites is often overlooked or ignored. The API, ASME and other Codes and Standards have long included recommended or required practices to perform regular monitoring of pipe supports and restraints, especially as it affects the condition of the piping. This is true not only of existing plants but also of new plants. The condition of pipe supports and restraints is an external barometer of hidden problems with the piping and attached equipment. Recognizing pipe support and restraint distress can help prioritize pipe inspections and equipment maintenance. This paper reviews and identifies applicable sections of the various Codes, Standards and Recommended Practices to provide the reader with a source for such information.
Creep-Fatigue Crack for a 2¼Cr1Mo and Inconel Transition Weld
Authors: Shi Jinhua
Published: November 2015

Transition welds have been used in some Advanced Gas-Cooled Reactors to attach a 2¼Cr1Mo spool piece to a hot reheat header, which is fabricated from 316L material. These welds were made using Inconel-82 filler and were post-weld heat-treated (PWHT) at around 705°C. In this paper, a creep-fatigue crack growth assessment has been carried out on the 2¼Cr1Mo ferritic side of the weld using the R5 procedure.

As the welds have been PWHT rather than solution heat treated, therefore there are residual welding stresses present. On the 2¼Cr1Mo ferritic side of the weld, a 60MPa through-wall bending stress has been applied in the axial direction and a 60MPa membrane stress in the hoop direction. These are consistent with the recommendations of R5 Volume 7.

Due to the differing thermal expansion coefficients of Inconel and ferritic materials, thermal mismatch stresses induced from changes in temperatures have been considered. It has been assumed that at the PWHT temperature of 705°C there are no thermal mismatch stresses. Any reduction from this temperature generates thermal mismatch stresses which are accounted for by using secondary Stress Intensification Factor values in the calculation.

On the 2¼Cr1Mo ferritic side of the weld, a 5mm deep by 50mm long circumferential defect (semi-elliptical surface-breaking surface defect) postulated to exist on both internal and external surfaces has been used. Limiting defect sizes have been calculated following the R6 procedure.

Four cases have been investigated. After presenting the investigation results, conclusions are drawn.
Development of Stress Intensity Factors for Deep Surface Cracks in Pipes and Plates
Authors: Hasegawa Kunio , Li Yinsheng
Published: November 2015

Stress intensity factors (SIFs) for pipes with semi-elliptical cracks containing large aspect ratios were calculated by finite element analysis. The cracks were circumferential and axial surface cracks inside the pipes. The parameters of the SIFs are crack aspect ratio, crack depth and the ratio of pipe radius to wall thickness. In comparing SIFs for plates and pipes, it can be clarified that SIFs for both plates and thin pipes with t/Ri ≤1/10 are almost the same, and the SIFs for plates are used as a substitute for pipes with t/Ri ≤1/10, where t is the pipe wall thickness and Ri is the inner radius of the pipe. This means that it is not necessary to provide SIF solutions for pipes with t/Ri ≤1/10, and it is suggested that number of tables for influence coefficients G values for pipes can significantly reduce.
Improving Prediction of Limit Bending Load for Wall-Thinned Pipes by Reconsidering the Effect of Biaxiality
Authors: Mori Kosuke , Meshii Toshiyuki
Published: November 2015

In this paper, a failure criterion applicable to large-strain finite element analysis (FEA) results was studied to predict the limit bending load Mc of the groove shaped wall-thinned pipes, under combined internal pressure and bending load, that experienced cracking. In our previous studies, Meshii and Ito [1] considered cracking of pipes with groove shaped flaw (small axial length δz in Fig. 1) was due to the plastic instability at the wall-thinned section and proposed the Domain Collapse Criterion (DCC). The DCC predicted Mc of cracking for small δz by comparing the von Mises stress σMises with the true tensile strength σB. However, it was indicated that the predictability of Mc was not necessarily sufficient. Thus, in this work, attempts were made to improve the accuracy of Mc prediction with a perspective that multi-axial stress state might affect this plastic instability. As a result of examination of the various failure criteria based on multi-axial stress, it was confirmed that the limit bending load of the groove flawed pipe that experienced cracking could be predicted within 5 % accuracy by applying Hill’s plastic instability onset criterion [2] to the outer surface of the crack penetration section. The accuracy of the predicted limit bending load was improved from DCC’s error of 15% to 5%.
Hydrogen Flammability Mitigation in a Containment Vessel Using a Recombiner
Authors: Kesterson Matthew R. , Askew Neal M. , Hensel Steve J. , Laurinat James E.
Published: November 2015

Plutonium oxide packaged in a 9975 Primary Containment Vessel (PCV) is evaluated in terms of preventing a flammable gas mixture due to hydrogen generation. Hydrogen is generated via radiolysis of adsorbed moisture on the plutonium oxide. A recombiner is placed in the PCV to recombine hydrogen and oxygen at concentrations to prevent hydrogen flammability. A detailed hydrogen diffusion analysis which evaluates expected and bounding conditions in order to demonstrate that hydrogen concentrations will remain below 5% by volume within PCV is presented.
Radioactive Material Release From a Containment Vessel During a Fire Accident
Authors: Hensel Steve J. , Norkus John K.
Published: November 2015

A methodology is presented to determine the source term for leaks and ruptures of pressurized vessels. The generic methodology is applied to a 9975 Primary Containment Vessel (PCV) which losses containment due to a hypothesized fire accident. The release due to a vessel rupture is approximately two orders of magnitude greater than the release due to a leak.
Investigation of In-Flow Fluidelastic Instability of Square Tube Arrays Subjected to Air Cross Flow
Authors: Nakamura Tomomichi , Hagiwara Shinichiro , Yamada Joji , Usuki Kenji
Published: November 2015

In-flow instability of tube arrays is a recent major issue in heat exchanger design since the event at a nuclear power plant in California [1]. In our previous tests [2], the effect of the pitch-to-diameter ratio on fluidelastic instability in triangular arrays is reported. This is one of the present major issues in the nuclear industry. However, tube arrays in some heat exchangers are arranged as a square array configuration. Then, it is important to study the in-flow instability on the case of square arrays.

The in-flow fluidelastic instability of square arrays is investigated in this report. It was easy to observe the in-flow instability of triangular arrays, but not for square arrays. The pitch-to-diameter ratio, P/D, is changed from 1.2 to 1.5. In-flow fluidelastic instability was not observed in the in-flow direction. Contrarily, the transverse instability is observed in all cases including the case of a single flexible cylinder. The test results are finally reported including the comparison with the triangular arrays.