bluuebunny/crossref_metadata_2025 huggingface dataset:
The free delivery and caesarean policy in Morocco: how much do households still pay?
Authors: Boukhalfa C. , Abouchadi S. , Cunden N. , Witter S.
Published: November 2015

Background

The Free Deliveries and Caesarean Policy (FDCP) entitles all women in Morocco to deliver free of charge within public hospitals. This study assesses the policy's effectiveness by analysing household expenditures related to childbirth, by delivery type and quintile.

Methods

Structured exit survey of 973 women in six provinces at five provincial hospitals, two regional hospitals, two university hospitals and three primary health centres with maternity units.

Results

Households reported spending a median of US$ 59 in total for costs inside and outside of hospitals. Women requiring caesareans payed more than women with uncomplicated deliveries (P < 0.0001). The median cost was US$45 for a uncomplicated delivery, US$50 for a complicated delivery and US$65 for a caesarean section. The prescription given upon exiting the hospital comprised 62% of the total costs. Eighty‐eight per cent of women from the poorest quintiles faced catastrophic expenditures. The women's perception of their hospital stay and the FDCP policy was overwhelmingly positive, but differences were noted at the various sites.

Conclusion

The policy has been largely but not fully effective in removing financial barriers for delivery care in Morocco. More progress should also be made on increasing awareness of the policy and on easing the financial burden, which is still borne by households with lower incomes.
Prediction of systolic blood pressure using peripheral pulse palpation in cats
Authors: Reineke Erica L. , Rees Colleen , Drobatz Kenneth J.
Published: November 2015

Objective

To evaluate the ability of peripheral pulse palpation to predict systolic blood pressure (SBP) in cats presenting as emergencies.

Design

Prospective observational study performed over an 8‐month period.

Setting

University veterinary teaching hospital.

Animals

One hundred two cats presenting to the emergency service. Eligibility for inclusion in the study included a physical examination and a SBP via Doppler technique performed prior to treatment.

Interventions

None.

Measurements and Main Results

Femoral and metatarsal pulses were digitally palpated and the quality of the pulses was assessed as either strong, moderate, poor, or absent. A concurrent SBP was also recorded. The median SBP for all cats was 92.5 mm Hg (range, 30–240 mm Hg). Femoral pulse quality was found to strongly correlate with the admission SBP (P< 0.001, rho = 0.6755). The median SBP for each femoral pulse quality category (strong, moderate, poor, or absent) was significantly different (P< 0.05). For metatarsal pulses, the median SBP for cats with either absent or strong pulses was significantly different (P< 0.001). Cats with absent metatarsal and femoral pulses had a median SBP of 30 mm Hg (range, 30–105 mm Hg), whereas cats with strong metatarsal pulses had a median SBP of 135 mm Hg (range, 58–210 mm Hg). Absent metatarsal pulses correctly identified cats with a blood pressure of 75 mm Hg or less 84% the time (area under the curve: 0.89, confidence interval 0.81, 0.97).

Conclusions

In cats, peripheral pulse quality assessment by emergency room veterinarians correlates with SBP. With progressive decreases in blood pressure, metatarsal pulses will disappear and it is only with severe hypotension that femoral pulses are absent. An assessment of both dorsal metatarsal pulse and femoral pulse quality during triage may be useful in identifying abnormalities in blood pressure.
Penoxsulam‐resistant barnyardgrass (Echinochloa crus‐galli) in rice fields in China
Authors: Chen Guoqi , Wang Qiong , Yao Zhengwei , Zhu Longfen , Dong Liyao
Published: November 2015

Barnyardgrass (Echinochloa crus‐galli) proliferation seriously threatens rice production worldwide. Whole‐plant bioassays were conducted in order to test the sensitivity to penoxsulam of 52 barnyardgrass populations and the resistance of six penoxsulam‐resistant populations to 12 other herbicides that are commonly used in rice fields. Among the 48 populations that had escaped penoxsulam control in the rice fields, 8.3% showed a very high level of resistance, 58.3% showed a high level of resistance and 10.4% showed a moderate level of resistance. Multiple resistance was confirmed in all six penoxsulam‐resistant populations that were tested further. They exhibited at least a moderate level of resistance; that is, to 6–10 of the total of 13 herbicides that was tested. Most of the six penoxsulam‐resistant populations showed at least a moderate level of resistance to bispyribac‐sodium, quinclorac, metamifop, cyhalofop‐butyl and oxadiazon, three populations held at least a moderate level of resistance to oxyfluorfen and pretilachlor, two populations also held at least a moderate level of resistance to pyrazosulfuron‐ethyl, pyribenzoxim and fenoxaprop‐P‐ethyl, but the resistance indices of the six populations to pendimethalin were all low. This study has confirmed resistance to pretilachlor and oxadiazon in weeds for the first time.
Hydrologic design aid for urban grass filter strips
Authors: Akan A. Osman , Atabay Serter
Published: November 2015

A set of generalised charts are presented in this article as a design aid for hydrologic sizing of grass filter strips. The charts express the volume of runoff and the peak flow rate from a grass strip and the residence time in terms of the size and surface and subsurface characteristics of the grass strip as well as the size and surface characteristics of the area draining to the filter strip. These charts are developed by using a mathematical model based on a kinematic‐wave formulation of overland flow and Green‐and‐Ampt formulation for infiltration. The results are obtained in terms of dimensionless parameters and generalised through the principle of hydrologic similarity. An example is included to demonstrate the use of the charts in a practical design problem.
Analysis of Input Current Ripple and Optimum Filter Capacitor for Fuel-Cell-Based Single-Phase Inverter
Authors: Sarkar Tirthajyoti , Mazumder Sudip K.
Published: November 2015

Most single-phase inverters, being sourced by fuel cell stacks (FCSs), subject the stacks to reflected low-frequency (120 Hz) current ripples that ride on average dc currents. The ripple current impacts the sizing and efficiency of the FCS. As such and typically, a passive or active filter is required at the input of the inverter (or output of the FCS) to mitigate the ripple current. Toward that end, this paper outlines a guideline to choose the optimum size of a passive input-filter capacitor for a fuel-cell-based power system from the standpoints of the overall system energy density and cost. Detailed case-specific simulation results, based on an analytical approach, are provided to illustrate key issues for both unity power factor as well as harmonic loads.
Vortex Suppression in an Air Induction System Using Mesh Grid Structures
Authors: Avireddi Prashanth , Boone Anthony , Oka Naoki , Hunt Frank
Published: November 2015

The air required for the combustion process in automobiles is provided by an air induction system. The air induction system induces air naturally through air ramming the automobile or artificially using a compressor while the automobile is in operation. During the induction process it is important to measure the air flow rate supplied for the combustion process as the amount of fuel supplied for combustion is dependent on the air intake. In air induction systems with high turbulence intensity the measurement of air flow rate has high noise. The high noise value affects the rate of fuel supplied for combustion. The current study focuses on using grid mesh structures to reduce the turbulence intensity in the induced air flow and improve the air flow metering. An experimental and numerical simulation study have been performed to correlate the effect of grid mesh size, distance of the grid from the measurement device (Hotwire) and flow Reynolds number. The paper provides details of experimental and numerical study which indicate that adopting mesh grid structures will reduce the turbulence intensity (noise) and also provide the ideal location for the flow measurement device such that it outputs less noise.
The Least Squares Spectral Element Method for the Navier-Stokes and Cahn-Hilliard Equations
Authors: Park Keunsoo , Dorao Carlos A. , Chiapero Ezequiel M. , Fernandino Maria
Published: November 2015

The least squares spectral element method (LS-SEM) offers many advantages in the implementation of the finite element model compared with the traditional weak Galerkin method. In this article, the LS-SEM is used to solve the Navier-Stokes (NS) and the Cahn-Hilliard (CH) equations. The NS equation is solved with both C0 and C1 basis functions and their performance is compared in terms of accuracy. A two-dimensional steady-state solver is verified with the case of Kovasznay flow and validated for the cavity flow, and a two-dimensional unsteady solver is verified by a transient manufactured solution case. The phenomenon of phase separation in binary system is described by the CH equation. Due to the fourth-order characteristics of the CH equation, only a high order continuity approximation is used by employing C1 basis function for both space and time domain. The obtained solutions are in accordance with previous results from the literature and show the fundamental characteristics of the NS and CH equations. The results in this study give the possibility of developing a solver for the coupled NS and CH equations.
Physical Modelling of Tornado-Like Flow Field
Authors: Refan Maryam , Hangan Horia , Siddiqui Kamran
Published: November 2015

The challenges in the field measurements of tornado flow field and its physical simulation in a laboratory environment are major obstructions in the advancement of scientific knowledge about tornados and their interaction with the ground structures. In this paper, we report on new research facilities at the University of Western Ontario in Canada that can physically simulate tornado-like vortex. Both facilities are geometrically similar but have more than an order of magnitude scale difference. Qualitative and quantitative results showed that both facilities can physically simulate tornado-like vortex. The results also show that the radial and tangential turbulent velocities have strong dependency on the swirl ratio when a transition from laminar to turbulent takes place in the vortex core. Further investigations are underway to study the scaling effects in terms of physical simulation of the tornado-like vortex flow in the two facilities.
Study on Unsteady Tip Leakage Vortex Cloud Cavitation in an Axial Flow Pump Using an Improved Numerical Method
Authors: Zhang Desheng , Shi Weidong
Published: November 2015

The aim of the present investigation is to simulate and analyze the formation of three-dimensional tip leakage vortex (TLV) cloud cavitation and the periodic collapse of TLV-induced vortices cavitation. The improved SST k-ω turbulence model and the homogeneous cavitation model were validated by the simulation of unsteady cavitation shedding flow around the NACA66-mod hydrofoil, and then the unsteady TLV cloud cavitation and unstable vortices cavitation in an axial flow pump were predicted by using the improved numerical method. The predicted three-dimensional cavitation structure of TLV and vortices as well as the collapse features show a qualitative agreement with the high speed photography results. Numerical results show that the TLV cavitation cloud in the axial flow pump mainly includes tip clearance cavitation, shear layer cavitation and TLV cavitation, and TLV-induced vortices cavitation occurs in the downstream of blade trailing edge (TE). TLV cavitation cloud is relatively steady before about 80% blade chord with the high vapor volume fraction inside the TLV core. The unsteady TLV cavitation cloud occurs near the TE of blade where the transient cavity shapes of sheet cavitation and TLV cavitation all fluctuate, which results in the decrease of the axial velocity in the tip region. It is found that the unstable vortices cavitation in shear layer in the downstream of TE collapses periodically. The correlation analysis shows that TLV cavitation cloud and vortices cavitation collapse are significantly associated with the interaction between TLV breakdown and boundary layer in the downstream of blade TE.
Numerical Simulation for Thermal Design of a Gas Water Heater With Turbulent Combined Convection
Authors: Yari Ali , Hosseinzadeh Siamak , Golneshan Ali Akbar , Ghasemiasl Ramin
Published: November 2015

This article investigates the effects of geometric parameters on a turbulent asymmetrical heat transfer in vertical channels with radiation and blowing from a wall. Hydrodynamic behaviour and heat transfer results are obtained by the solution of the complete Navier–Stokes and energy equations using a control volume finite element method. In this paper, commercial codes were used to solve the equations. The equations involved were numerically solved with three turbulent models including Spalart-Allmaras, R-N-G k-ε with ‘standard wall function’ wall nearby model, R-N-G k-ε with ‘enhanced wall treatment’ wall nearby model and ‘ray tracing’ radiation techniques. Turbulent flow with ‘low Reynolds Spalart-Allmaras turbulence model’ and radiation with ‘discrete transfer radiation method’ was modelled. The results were compared with experimental data and appropriate methods were selected for turbulent modelling. The problems of different Grashof number, Reynolds number, radiation parameters and Prandtl number were solved and the effects of geometric parameters on the fluid flow, radiation-convection-blowing heat transfer and the total efficiency were determined.
Effect of Double-Volute Casing on Impeller Radial Force for a Large Double-Suction Centrifugal Pump
Authors: Zhang Zichao , Wang Fujun , Yao Zhifeng , Xiao Ruofu
Published: November 2015

The operation stability of lager double-suction centrifugal pump is becoming an important issue. High radial force could result in fatigue failure of pump shaft and vibration of impeller. In order to find the effect of double-volute casing on impeller radial force, a double-suction centrifugal pump with two casing configurations is investigated by using CFD approach. The two casings have same geometry, the difference is that one is single-volute casing without dividing rib structure, another is double-volute casing with dividing rid structure. Results show that the dividing rib structure of double-volute casing could result in static pressure surrounding the impeller outlet is symmetry at every operating conditions, this is the reason why radial force of double-volute casing is lower than single-volute casing. The radial force vector diagrams for two casings are all hexagonal. However, radial force of double-volute casing is nearly equal at every operating condition, the centre of hexagon for double-volute casing is nearer to origin of coordinate, these results indicate radial force of double-volute casing is lower than single-volute casing. The rotating frequency and the blade passing frequency dominate the radial force fluctuation in single-volute casing, while both of them are almost not existed in double-volute casing. The results indicate that double-volute casing could significantly reduce radial force fluctuation in double-suction centrifugal pump.
Off Design Performance Map Similarity Study of Radial Type Turbomachinery in Supercritical CO2 Brayton Cycle
Authors: Cho Seong Kuk , Lee Jekyoung , Lee Jeong Ik
Published: November 2015

A supercritical carbon dioxide (S-CO2) Brayton cycle has received attention as one of the future power conversion systems because of its high thermal efficiency at relatively low turbine inlet temperature. However, the design process of the S-CO2 compressor is known to be difficult because the fluid properties vary significantly near the critical point. This paper discusses about the design methodology of a S-CO2 compressor on the basis of the existing design practice and performance map of Sandia National Laboratory, which is the only reported experimental data for the S-CO2 compressor. Five parameters are mainly used for verifying the turbomachinery similarity. When all of 5 parameters coincide with the prototype and the conceptually designed turbomachinery, similar performance can be assumed.

As a result, the data of SNL are insufficient to design a single stage compressor which is able to compress from near critical point to 20MPa. The optimum cycle pressure ratio is reported to be around 2.6∼2.7 in the previous S-CO2 Brayton cycle research works. The minimum number of stages is required at least two to utilize the existing data in the compressor design. So this study focuses on two main purposes. The first is to check whether the SNL data can be extended for the larger scale S-CO2 system. Second, the performance map obtained from KAIST_TMD, which is from an in-house code developed by the Korea Advanced Institute of Science and Technology (KAIST) research team, was compared to the SNL data, so that KAIST_TMD can be used as a design tool for a larger scale S-CO2 power conversion system in the future.
An Investigation Into Performance Characteristics of an Axial Flow Fan Using CFD for Electronic Devices
Authors: Hashim Hafiz M. , Dogruoz Baris , Arik Mehmet , Parlak Murat
Published: November 2015

Rotating fans are widely utilized in thermal management applications and their accurate characterization has recently become even a more critical issue for thermofluids engineers. The present study investigates the characterization of an axial fan computationally and experimentally. Using the three-dimensional CAD models of the fan, a series of computational fluid dynamics (CFD) simulations were performed to determine the flow and pressure fields produced by the axial mover over a range of flow rates. In order to validate the computational model findings, experiments were conducted to obtain the pressure drop values at different flow rates in an AMCA (Air Movement and Control Association) standard 210-99, 1999 wind tunnel. These data sets were also compared with the fan vendor’s published testing data. A reasonably good agreement was obtained among the data from these three separate sources. Furthermore, an attempt was made to understand the overall fan efficiency as a function of the volumetric flow rate. It was determined that the maximum overall fan efficiency was less than 27% correlating well with the computational results.
Topology Optimization, Additive Layer Manufacturing, and Experimental Testing of an Air-Cooled Heat Sink
Authors: Dede Ercan M. , Joshi Shailesh N. , Zhou Feng
Published: November 2015

Topology optimization of an air-cooled heat sink considering heat conduction plus side-surface convection is presented. The optimization formulation is explained along with multiple design examples. A post-processing procedure is described to synthesize water-tight solid model computer-aided design (CAD) geometry from 3-D point-cloud data extracted from the optimization result. Using this process, a heat sink is optimized for confined jet impingement air cooling. A prototype structure is fabricated out of AlSi12 using additive layer manufacturing (ALM). The heat transfer and fluid flow performance of the optimized heat sink is experimentally evaluated, and the results are compared with benchmark plate and pin-fin heat sink geometries that are conventionally machined out of aluminum and copper. In two separate test cases, the experimental results indicate that the optimized ALM heat sink design has a higher coefficient of performance relative to the benchmark heat sink designs.
A Computational Study on the Momentum and Heat Transfer Distribution of a Low Frequency Round Impinging Synthetic Jet
Authors: Ikhlaq Muhammad , Dogruoz Baris , Ghaffari Omidreza , Arik Mehmet
Published: November 2015

Impinging synthetic jets have been considered as a possible solution for cooling miniature structures. It has been shown that synthetic jet performance is sensitive to the distance between the jet nozzle and the target surface where enhancement of heat transfer decreases with a reduction in nozzle-to-target plate distance. At low nozzle-to-target spacing, no detailed information about the momentum and temperature fields have been shown in prior literature, therefore further investigation is needed. In this study, a 3-D computational fluid dynamics model was constructed to determine the flow and temperature fields of a meso-scale synthetic jet at a nozzle-to-target surface spacing of H/D = 2, ReD,j= 1400 and f = 500 Hz. Unlike the majority of previous computational studies, rather than specifying the boundary conditions at the nozzle, the flow inside the synthetic jet device was solved by specifying the time dependent boundary conditions on the vibrating diaphragm and utilizing the moving mesh technique. Local surface pressure and heat transfer coefficient distributions were determined and discussed. It was found that the pulsating flow at the nozzle exit for a round jet generates vortex rings and these rings seem to have some considerable effects on the target surface profiles.
A Study on Flow Boiling in Microchannel With Piranha Pin Fin
Authors: Yu X. , Woodcock C. , Wang Y. , Plawsky J. , Peles Y.
Published: November 2015

In this paper we reported an advanced structure, the Piranha Pin Fin (PPF), for microchannel flow boiling. Fluid flow and heat transfer performance were evaluated in detail with HFE7000 as working fluid. Surface temperature, pressure drop, heat transfer coefficient and critical heat flux (CHF) were experimentally obtained and discussed. Furthermore, microchannels with different PPF geometrical configurations were investigated. At the same time, tests for different flow conditions were conducted and analyzed. It turned out that microchannel with PPF can realize high-heat flux dissipation with reasonable pressure drop. Both flow conditions and PPF configuration played important roles for both fluid flow and heat transfer performance. This study provided useful reference for further PPF design in microchannel for flow boiling.
An Efficient Bump Pad Design to Mitigate the Flip Chip Package Induced Stress
Authors: Gonzalez Mario , De Vos Joeri , Van der Plas Geert , Beyne Eric
Published: November 2015

A numerical analysis using Finite Element Models of different stress buffer configurations has been proposed for improving the reliability of solder joints and at the same time decrease the induced stresses in the back-end-of-line (BEOL). A non-underfilled Flip Chip with a silicon die size of 10×10 mm2 mounted on a FR4 board has been used as test vehicle. The die to substrate interconnection is done by using copper pillars and Sn solder with a diameter of 50 μm and a total standoff of 50 μm. The thickness of the passivation, a copper pedestal fabricated as a redistribution I/O pad and a polymeric buffer layer with different geometric configurations were used in combination to minimize the induced stresses in the BEOL and increase the flexibility of the copper pillar interconnections. It was found that a stiff layer below the copper pillar has the major contribution to reduce the stress in the BEOL, while the softer buffer layer minimizes the induced plastic strain in the solder interconnection. Fabrication of the samples with optimal configuration are under progress.
A Study on Strain Concentration Around V Notch in Lead Free Solder Material and the Low Cycle Fatigue Life
Authors: Kawakami Takashi , Kinoshita Takahiro , Oriyama Hirokazu
Published: November 2015

Solder joints are sometimes opened under thermal cyclic loads as low cycle fatigue phenomena. The fatigue crack is usually initiated around the edge of the interface where stress and strain very severely concentrate, having stress strain singularity. In this study, Sn-3.0Ag-0.5Cu test pieces with V shape notch were supplied to low cycle fatigue tests at 100°C. And inelastic stress strain simulations, which were based on time-dependent non-unified material model, were carried out under several cyclic load levels to obtain strain distributions around the bottom of the V notch. By results of fatigue test and inelastic simulation, the depth from the bottom of the V notch, where the strain range agrees with the prediction of the fatigue life based on smooth test pieces on Coffin-Manson rule, was investigated as the mechanical design rule for lead free solder joints.
Novel Thermal Management of GaN Electronics: Diamond Substrates
Authors: Kuball Martin , Pomeroy James W. , Calvo Julian Anaya , Sun Huarui , Simon Roland B. , Francis Daniel , Faili Firooz , Twitchen Daniel , Rossi Stefano , Alomari Mohammed , Kohn Erhard , Tóth Lajos , Pécz Béla
Published: November 2015

Microwave and power electronics based on GaN enables the performance of systems and their safe operating area to be driven to ‘extremes’. One of the major issues that then arises is thermal management. This includes heat transfer limitations across interfaces, however also the need of incorporating novel high thermal conductivity materials such as diamond. Thermal parameters of these novel device systems and their implications on the near junction temperature in the devices are not well known. The role of interfaces between the GaN transistor and the diamond substrate, and of the diamond thermal properties themselves near this interface are discussed, and novel thermal characterization approaches, such as enabling fast determination of the thermal resistance on the wafer level, as well as of lateral diamond thermal conductivity, are presented.
Measuring and Optimizing Thermal Interface Material Performance for VR Heatsink Designs
Authors: Lu Jun , Lin Michelle C. , Short Bernie
Published: November 2015

With increasingly high powers on processors, memories, and chipsets, the voltage regulators (VR) become heavily loaded and a heatsink is often required to prevent overheating the surrounding components on the board. For VR heatsink designs, thermal interface silicone gap filler pads are often used and there is an increasing need to improve VR thermal solutions by reducing thermal resistance of the TIM. A series of TIM2 thickness and performance measurements based on thermal testing was performed in order to understand gap filler characteristics, optimize TIM performance, and utilize best retention design. By utilizing a VR thermal and mechanical test board in wind tunnel testing using the same VR heatsink, thermal performance of TIM2 using gap filler pads over a range of airflow velocities can be measured and compared. The study shows how the optimum TIM performance can be achieved by using the gap filler pads with appropriate thickness for the given designed heatsink standoff heights. The benefit of choosing the right thickness pads over others can be significant and is a valuable learning that can be applied to future VR heatsink designs. Furthermore, the silicone gap filler characteristics and its relationship to board bending and result TIM thickness and thermal performance are investigated and further improved. The learnings help understand the limitations and where the area of improvement can be for future VR heatsink designs.
Consideration for Running Data Center at High Temperatures and Using Free Air Cooling
Authors: He Yongzhan , Chen Guofeng , Zhang Jiajun , Zhou Tianyu , Liu Tao , Zhu Pinyan , Liu Chao , Ahuja Nishi
Published: November 2015

The advent of the big data era, the rapid development of mobile internet, and the rising demand of cloud computing services require increasingly more compute capability from their data center. This compute increase will most likely come from higher rack and room power densities or even construction of new Internet data centers. But an increase in a data center’s business-critical IT equipment (servers, hubs, routers, wiring patch panels, and other network appliances), not to mention the infrastructure needed to keep these devices alive and protected, encroaches on another IT goal: to reduce long-term energy usage. Large Internet Data Centers are looking at every possible way to reduce the cooling cost and improve efficiency. One of the emerging trends in the industry is to move to higher ambient data center operation and use air side economizers. However, these two trends can have significant implications for corrosion risk in data centers.

The prevailing practice surrounding the data centers has often been “The colder, the better.” However, some leading server manufacturers and data center efficiency experts share the opinion that data centers can run far hotter than they do today without sacrificing uptime, and with a huge savings in both cooling related costs and CO2 emissions. Why do we need to increase the temperatures? To cool data center requires huge refrigeration system which is energy hog and also cost of cooling infrastructure, maintenance cost and operation cost are heavy cost burden.

Ahuja et al [1] studied cooling path management in data center at typical operating temperature as well as higher ambient operating temperatures. High Temperatures and Corrosion Resistance technology will reduce the refrigeration output and how this innovation will open up new direction in data centers.

Note that, HTA is not to say that the higher the better. Before embracing HTA two keys points need to be addressed and understood. Firstly, server stability along with optimal temperature from data center perspective. Secondly, corrosion resistant technology. With Fresh air cooling the server has to bear with the seasons and diurnal variation of temperatures and these can be over 35 degree C, therefore to some extent, we have to say, HTA design is the premise of corrosion resistant design.

In this paper, we present methods to realize precise HTA operation along with corrosive resistant technology. This is achieved through an orchestrated collaboration between the IT and cooling infrastructures.
Quantitative Visualization of Vapor Bubble Growth in Diabatic Vapor-Liquid Microchannel Slug Flow
Authors: Kingston Todd A. , Weibel Justin A. , Garimella Suresh V.
Published: November 2015

Slug flow is a commonly encountered flow regime in microchannels due to the influence of surface tension and vapor confinement at small length scales. Few experimental studies have considered diabatic vapor-liquid slug flow, owing to difficulties in generating a well-controlled and repeatable slug flow regime; generation of vapor by wall heating typically leads to large, stochastic variations in the vapor bubble characteristics. To facilitate the study of flow behavior and vapor-liquid interfaces under precisely controlled conditions, a diabatic, one-component, two-phase microchannel flow was generated by separately injecting HFE-7100 vapor and liquid into a T-junction. Injection at independently controllable liquid and vapor flow rates allows the creation of vapor-liquid slug flow patterns in a downstream borosilicate microchannel of circular cross-section with a 500 μm inside diameter. The outside surface of the microchannel was coated with a 100 nm-thick layer of indium tin oxide (ITO) to generate a uniform wall heat flux via Joule heating while allowing full optical access for flow visualization. The growth of individual vapor bubbles was quantitatively visualized at different imposed heat fluxes, in terms of the percentage change in vapor bubble length along the heated microchannel. The results demonstrate the ability of the T-junction to generate diabatic, one-component, two-phase microchannel slug flow that is suitable for generating results for the validation of flow boiling models.
Influence of Reynolds Number of Tube Flow on Coalescence of Droplets in a Tube Creeping Flow
Authors: Muraoka Masahiro , Kumagai Yuuki , Yatagawa Yuuta , Ueno Ichiro
Published: November 2015

Coalescence phenomena of droplets in a tube creeping flow were examined. Coalescence time of two droplets was measured. Clearance diameter of clearance area between droplets was also measured. The coalescence time obtained experimentally is compared with semi-theoretical formulas. Trends of semi-theoretical formulas of coalescence time and those of the experiments generally agreed. Influence of Reynolds number of tube creeping flow on coalescence of droplets was investigated.
Multi-Objective Optimization of Micro Pin-Fin Arrays for Cooling of High Heat Flux Electronics With a Hot Spot
Authors: Reddy Sohail R. , Abdoli Abas , Dulikravich George S. , Pacheco Cesar C. , Vasquez Genesis , Jha Rajesh , Colaco Marcelo J. , Orlande Helcio R. B.
Published: November 2015

The ability of various arrays of micro pin-fins to reduce maximum temperature of an integrated circuit with a 4 × 3 mm footprint and a 0.5 × 0.5 mm hot spot was investigated numerically. Micro pin-fins having circular, symmetric airfoil and symmetric convex lens cross sections were optimized to handle a background uniform heat flux of 500 W cm−2 and a hot spot uniform heat flux of 2000 W cm−2. A fully three-dimensional conjugate heat transfer analysis was performed and a multi-objective, constrained optimization was carried out to find a design for each pin-fin shape capable of cooling such high heat fluxes. The two simultaneous objectives were to minimize maximum temperature and minimize pumping power, while keeping the maximum temperature below 85 °C. The design variables were the inlet average velocity and shape, size and height of the pin-fins. A response surface was generated for each of the objectives and coupled with a genetic algorithm to arrive at a Pareto frontier of the best trade-off solutions. Stress–deformation analysis incorporating hydrodynamic and thermal loads was performed on the three Pareto optimized configurations. Von-Mises stress for each configuration was found to be significantly below the yield strength of silicon.
Experimentally Validated Numerical Model of a Fully-Enclosed Hybrid Cooled Server Cabinet
Authors: Nemati Kourosh , Alissa Husam A. , Murray Bruce T. , Sammakia Bahgat , Seymour Mark
Published: November 2015

Because of the rapid growth in the number of data centers combined with the high density heat dissipation in the IT and telecommunications equipment, energy efficient thermal management of data centers has become a key research focus in the electronics packaging community. Traditional legacy data centers still rely largely on chilled air flow delivered to the IT equipment racks through perforated tiles from the raised floor plenum. When there is large variation in the amount of heat dissipated by the racks in a given aisle, the standard air cooling approach requires over-provisioning.

Localized hybrid air-water cooling is one approach to more effectively control the cooling when there is wide variation in the amount of dissipation in neighboring racks. In a closed hybrid air-water cooled server cabinet, the generated heat is removed by a self-contained system that does not interact with the room level air cooling system. In this study, a comprehensive procedure for CFD validation in a close coupled hybrid cooled enclosed cabinet is described. The commercial enclosure has been characterized experimentally in an earlier study, where the effectiveness values were applied as boundary conditions to the compact heat exchanger model.

Here, the previously obtained experimental data are used to validate the results from computational modeling. Two cases with different air flow rates are compared. Very good agreement is achieved, with the maximum overall average error less than 4%. Due to relatively high pressure inside the cabinet, it is possible that air leakage from the cabinet may be responsible for the discrepancy between the model and experimental results. A sensitivity study was applied to the validated model to investigate the effect leakage had on the cabinet’s performance.
Experimental Investigation of Fluid Motion in Pulsating Heat Pipe
Authors: Noh Hyung Yun , Kim Sung Jin
Published: November 2015

In this research, operating characteristics and heat transfer phenomena in 2-turn pulsating heat pipe operating in a circulation mode were experimentally investigated. Temperature, pressure and high-speed flow visualization data were obtained with the variation of diameters (1.2 mm, 1.7 mm and 2.2 mm) and input powers. The overall pressure variation from start-up to steady state was measured using the pressure transmitters in the evaporator section. Heat transfer phenomena were investigated using homogeneous-equilibrium model. Thermodynamic state of two-phase mixture at the exit of evaporator is identified as a saturation state using obtained temperature and pressure data. The ratio of sensible heat to latent heat changed with the variation of diameters and input powers. It was found that each evaporator has a different ratio and latent heat was dominant in most experimental cases.
Two-Dimensional Monolayer MX2 (M=Mo, W; X=S, Se) Synthesis, Characterization and Device Applications
Authors: Xiang Bin , Yang Lei , Huang Jian , Fu Qi
Published: November 2015

Recently two-dimensional layered semiconductors with promising electronic and optical properties, have opened up a new way for applications in atomically thin electronics and optoelectronics. Here we demonstrate large area synthesis of monolayer MoS2 and WSe2 using a chemical vapor deposition method at ambient pressure. The atomic analysis of the as-grown monolayer was conducted by spherical-aberration-corrected high resolution scanning transmission electron microscopy and atomic force microscopy. Raman spectroscopy was utilized to identify the monolayer configuration of the as-grown samples. Strong photoluminescence peaks at a visible wavelength were observed at room temperature in the as-grown monolayer samples. The mobility and carrier concentrations were calculated in as-grown monolayer-based transistor devices. The emergency of these two dimensional materials provides grand possibilities for future semiconductor device applications.
Theoretical (Ideal) Module Cooling and Module Cooling Effectiveness
Authors: Ellsworth Michael J. , Campbell Levi A.
Published: November 2015

When contemplating processor module cooling, the notion of maximum cooling capability is not simple or straight forward to estimate. There are a multitude of variables and constraints to consider; some more rigid or fixed than others. This paper proposes a theoretical maximum cooling capability predicated on the treatment of the module heat sink or cold plate as a heat exchanger with infinite conductive and convective behavior. The resulting theoretical minimum heat sink thermal resistance is a function of the bulk thermal transport of the fluid dependent only on the fluid’s density, specific heat (at constant pressure) and volumetric flow rate. An ideal module internal thermal resistance will also be defined. The sum of the two resistances constitutes the theoretical minimum total module thermal resistance and defines the ideal thermal performance of the module. Finally, a module cooling effectiveness relating the actual module thermal performance to the ideal thermal performance will defined. Examples of both air and water cooled modules will be given with discussion on the relevance and utility of this methodology.
Thermal and Optical Performance of Eco-Friendly Silk Fibroin Proteins as a Cavity Encapsulation Over LED Systems
Authors: Yuruker Sevket Umut , Arik Mehmet , Tamdogan Enes , Melikov Rustamjon , Nizamoglu Sedat , Press Daniel Aaron , Durak Ilkem
Published: November 2015

The demand for high power LEDs for illumination applications is increasing. LED package encapsulation is one of most critical materials that affect the optical path of the generated light by LEDs, and may result in lumen degradation. A typical encapsulation material is a mixture of phosphor and a polymer based binder such as silicone. After LED chips are placed at the base of a cavity, phosphor particles are mixed with silicone and carefully placed into the cavity. One of the important technical challenges is to ensure a better thermal conductivity than 0.2 W/m-K of current materials for most of the traditional polymers in SSL applications.

In this study, we investigated an unconventional material of the silk fibroin proteins for LED applications, and showed that this biomaterial provides thermal advantages leading to an order of magnitude higher thermal performance than conventional silicones. Silk fibroin is a natural protein and directly extracted from silk cocoons produced by Bombyx mori silkworm. Therefore, it presents a “green” material for photonic applications with its superior properties of biocompatibility and high optical transparency with a minimal absorption. Combining these properties with high thermal performance makes this biomaterial promising for future LED applications.

An experimental and computational study to understand the optical and thermal performance is performed. A computational fluid dynamics study with a commercial CFD software was performed and an experimental set-up was developed to validate the computational findings to determine the thermal conductivity of the proposed material.
Benchmarking Study on the Thermal Management Landscape for 3D ICs: From Back-Side to Volumetric Heat Removal
Authors: Brunschwiler Thomas , Sridhar Arvind , Ong Chin Lee , Schlottig Gerd
Published: November 2015

An overview of the thermal management landscape with focus on heat dissipation from 3D chip stacks is provided in this study. Evolutionary and revolutionary topologies, such as single-side, dual-side and, finally, volumetric heat removal, are benchmarked with respect to a high-performance three-tier chip stack with an aggregate power dissipation of 672 W. The thermal budget of 50 K can be maintained by three topologies, namely, 1) dual-side cooling, implemented by a thermally active interposer, 2) interlayer cooling with 4-port fluid delivery and drainage at 100 kPa pressure drop, and 3) a hybrid approach combining interlayer with embedded back-side cooling.

Of all the heat-removal concepts, interlayer cooling is the only approach that scales with the number of dies in the chip stack and hence, enables extreme 3D integration. However, the required size of the microchannels competes with the requirement of low TSV heights and pitches. A scaling study was performed to derive the TSV pitch that is compatible with cooling channels to dissipate 150 W/cm2 per tier. An active IC area of 4 cm2 was considered, which had to be implemented on the varying tier count in the stack. A cuboid form factor of 2 mm × 4 mm × 2.55 mm results from a die count of 50. The resulting microchannels of 2 mm length allow small hydraulic diameters and thus a very high TSV density of 1837 1/mm2. The accumulated heat flux and the volumetric power dissipation are as high as 7.5 kW/cm2 and 29kW/cm3, respectively.
Challenges and Opportunities in Thermal Management of Multi-Chip Packages
Authors: Dhavaleswarapu Hemanth K. , Jha Chandra Mohan , Smith Susan F. , Kothari Shrenik , Bicen Baris , Saha Sanjoy K. , Gupta Ashish
Published: November 2015

Multi-chip packages (MCPs) based solutions are becoming increasingly adopted as it results in higher signal count, density and enables increasing bandwidth demands and allows for heterogeneous integration [1,2]. However, manufacturing tolerances impose a variability in these stacks which results in new requirements for thermal interface materials. This paper describes the thermal, mechanical, and reliability challenges associated with MCP packages, and highlights need for novel thermal interface materials.
Enhanced Melting for Transient Thermal Management
Authors: Rozenfeld T. , Hayat R. , Kozak Y. , Ziskind G.
Published: November 2015

The present study deals with transient thermal management using phase change materials (PCMs). These materials can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect is attractive for passive thermal management, particularly where the device is intended to operate in a periodic regime, or where the relatively short stages of high power dissipation are followed by long stand-by periods without a considerable power release. Heat transfer in PCMs, which have low thermal conductivity, can be enhanced by fins that enlarge the heat transfer area. However, when the PCM melts, a layer of liquid is growing at the fins creating an increasing thermal resistance that impedes the process.

The present work aims to demonstrate that performance of a latent-heat thermal management unit may be considerably affected by achieving a so-called close-contact melting (CCM), which occurs when the solid phase is approaching a heated surface, and only a thin liquid layer is separating between the two. Although CCM was extensively studied in the past, its possible role in finned systems has been revealed only recently by our group. In particular, it depends heavily on the specific configuration of the fins.

In the present work, close-contact melting is modeled analytically for a geometry which includes two symmetrically inclined fins. A quasi-steady approach is used for calculating the rate of melting based on the force and energy balances.

The results are expressed in terms of the time-dependent melt fraction and Nusselt number, showing their explicit dependence on the Stefan and Fourier numbers. Moreover, the approach used in the present study may be applied to other geometries in which the heated surface is not horizontal or where there are a number of heated surfaces or fins.
Experimental Characterization of the Transient Response of Air/Water Crossflow Heat Exchangers for Data Center Cooling Systems
Authors: del Valle Marcelo , Ortega Alfonso
Published: November 2015

Data Center hybrid air/liquid cooling systems such as rear door heat exchangers, overhead and in row cooling systems enable localized, on-demand cooling, or “smart cooling.” At the heart of all hybrid cooling systems is an air to liquid cross flow heat exchanger that regulates the amount of cooling delivered by the system by modulating the liquid or air flows and/or temperatures. Due the central role that the heat exchanger plays in the system response, understanding the transient response of the heat exchanger is crucial for the precise control of hybrid cooling system. This paper reports on the transient experimental characterization of heat exchangers used in data centers applications. An experimental rig designed to introduce controlled transient perturbations in temperature and flow on the inlet air and liquid flow streams of a 12 in. × 12 in. heat exchanger test core is discussed. The conditioned air is delivered to the test core by a suction wind tunnel with upstream air heaters and a frequency variable axial blower to allow the control of air flow rate and bulk temperature. The conditioned water is delivered to the test core by a water delivery system consisting of two separate water circuits, one delivering cold water, and the other hot water. By switching from one circuit to the other or mixing water from both circuits, the rig is capable of generating step, ramp and frequency perturbations in water temperature at constant flow or step, ramp or frequency perturbations in water flow at constant temperature or combinations of temperature and water flow perturbations. Experimental data are presented for a 12×12 heat exchanger core with a single liquid pass under different transient perturbations.
Attributes of Advanced Thinning and Planarization Processes in 2.5D and 3D Packaging Recognized by Market Demands
Authors: Wei Frank
Published: November 2015

During the fabrications of 2.5D and 3D advanced packages, the needs for intermediate thinning and planarization processes persistently exit. This paper highlights the attributes of successful implementations, i.e., increased performances and yields for these processes, which have been identified by the market requirements for a variety of applications. Different packages with different materials systems and product goals lead to different requirements. This paper includes the thinning and polishing of TSV wafers in bonded wafer pairs for Si IC devicess or interposers, the thinning of overmolded, reconstituted wafers in eWLB applications, and the planarizations of metal bumps and RDL features in PoP, CSP, or fine line-and-space (L/S) substrate fabrications.