bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Lean Blowout in Premixed Combustion With Hydrogen Addition
Authors: Zhu Shengrong , Acharya Sumanta
Published: July 2013

An experimental study of lean premixed combustion in a swirl-stabilized combustor is undertaken to characterize the dynamics and time scales close to Lean Blow Out (LBO) conditions. Due to the recent interest in syngas fuels, the effect of hydrogen addition on LBO is studied. In present study, both confined and unconfined turbulent methane air premixed flames have been examined with different hydrogen levels during the extinction transition with high speed imaging of OH* chemiluminescence at 2 KHz. Planar laser induced fluorescence measurement of OH is also performed for studying the flame structure. The blowout conditions are approached by reducing the flow rate of fuel mixture or the equivalence ratio with constant air flow rate. The estimated extinction times from high speed imaging and corresponding flame structures are analyzed and compared between confined and unconfined flames with different hydrogen blends. The extinction time scale and the heat release fluctuations show inverse trends with hydrogen addition for the confined and unconfined flames, and are indicative of different stabilization and blow out mechanisms for the two configurations. These mechanisms which involve heat losses from the flame, inner- and corner recirculation zones and unsteady flame dynamics are described in the paper.
On the Influence of the Combustion Model on the Result of Turbulent Flames Numerical Simulations
Authors: Gherman Bogdan , Florean Florin Gabriel , Cârlănescu Cristian , Porumbel Ionuţ
Published: July 2013

The paper is aimed at evaluating the impact of the combustion model on the accuracy of the results of the numerical simulations of turbulent reactive flows. For this, two numerical simulations of the well known Sandia Flame D case are carried out: a three-dimensional RANS integration of the Navier–Stokes equations using the Eddy Dissipation combustion Model (EDM), and a one-dimensional one, where simplified reaction–diffusion equations are numerically integrated over the radial direction, while the axial convection is modeled by empirical laws. The one-dimensional simulation, however, is based on a more physics related combustion model, the Linear Eddy Mixing model, which also controls the radial turbulent mixing and the large scale radial convection.

The results of the two numerical simulations are compared to experimental data in the literature, showing a significantly better accuracy of the Linear Eddy Mixing (LEM) numerical simulation.
Nitric Oxide Predictions for Low NOx Radial Swirlers With Central Fuel Injection Using CFD
Authors: King Phil T. , Andrews Gordon E. , Pourkashanian Mohamed M. , McIntosh Andy C.
Published: July 2013

A radial swirl low NOx combustor was investigated using CFD at 0.5 equivalence ratio and 600K inlet temperature at 1 bar. The equilibrium pdf combustion model using 16 species chemistry was shown to give a slightly improved prediction for the temperature distribution, but a poorer prediction for the CO distribution, over similar work using the flamelet model with 53 species chemistry. The NOx model was applied as a post-processing application and was shown to give a vastly superior result for the equilibrium pdf model using 16 species chemistry over the flamelet model using 53 species chemistry. Various NOx model configurations were tested and it was shown that only the mixture fraction based turbulence chemistry interaction model was able to provide a good result and all other models drastically under-predicted the peak nitric oxide levels. Combustion model predicted O modeling with excluded and combustion model predicted OH modeling were both shown to give a good match against measurements for the peak nitric oxide levels within the combustor when using mixture fraction based turbulence chemistry interaction.
Application of an Inter-Turbine Burner Using Core Driven Vitiated Air in a Gas Turbine Engine
Authors: Spytek Christopher J.
Published: July 2013

An Inter-Turbine Burner (ITB) that is capable of increasing the thrust of a gas turbine engine with minimal effect on SFC has been developed. Gas turbine engines using multistage turbine sections have the inherent disadvantage of temperature loss through the turbine section. This occurs when each successive turbine stage extracts energy from the superheated mass airflow stream. The net result is limited energy potential due to the first stage turbine temperature limits. An Inter-Turbine Burner (ITB) is able to utilize constant temperature burning through the turbine section by adding burners between the turbine stages. The resultant engine is suited for missions requiring large amounts of constant or intermittent power extraction. The Spytek ITB incorporates a modified version of an Ultra-Compact Combustor (UCC) [1] (high-g burner) which was originally developed by the Air Force Research Laboratory in Dayton, Ohio.

The ITB has been incorporated into a gas turbine engine and has been successfully tested operating at a near constant temperature (NCT) cycle. The engine/ITB is specifically configured and packaged for high power density use. Temperature rises across the ITB (T6-7) were tested in ranges from 421K-588K with representative increases in power take-off noted. The burner, positioned directly upstream of the ITB turbine, operates with vitiated air taken directly from the core engine exhaust stream. The engine tested is a two spool turbo-jet (ITB shaft inclusive), in the 1334(N) class. The ITB is cross shaft linked to an axial compressor booster stage, attached to the engine inlet which super-charged the core engine.

The two major areas addressed in development were the ability to provide air into the primary burn zone of the ITB to sustain combustion and second, the ability to successfully entrain the combustion products from the ITB vortex chamber into the main air stream without causing undue restrictions or hot-streak problems which can affect the life of the ITB turbine. Flexibility in ITB testing is further enhanced through the use of two adjustable test features, 1) a variable flow splitter, capable of adjusting the amount of air diverted into the ITB combustor, and 2) a variable nozzle guide vane pack upstream of the ITB turbine. A proprietary entrainment system rapidly mixes the ITB combustor products with the main stream dilute flow products without any undo effects on the ITB turbine. The Mark#1 version of the ITB system exhibits power on demand increases of 16%–22%.
Numerical and Experimental Characterization of Low NOx Micromix Combustion Principle for Industrial Hydrogen Gas Turbine Applications
Authors: Funke H. H.-W. , Boerner S. , Keinz J. , Kusterer K. , Kroniger D. , Kitajima J. , Kazari M. , Horikawa A.
Published: July 2013

The international effort to reduce the environmental impact of electricity generation, especially CO2-emissions requires considerations about alternative energy supply systems. An effective step towards low pollution power generation is the application of hydrogen as a possible alternative gas turbine fuel, if the hydrogen is produced by renewable energy sources, such as wind energy or biomass. The use of hydrogen and hydrogen rich gases as a fuel for industrial applications and power generation combined with the control of polluted emissions, especially NOx, is a major key driver in the design of future gas turbine combustors.

The micromix combustion principle allows a secure and low NOx combustion of hydrogen and air and achieves a significant reduction of NOx-emissions. The combustion principle is based on cross-flow mixing of air and gaseous pure hydrogen and burns in multiple miniaturized diffusion-type flames. For the characterization of the jet in cross-flow mixing process, the momentum flux ratio is used.

The paper presents an experimental analysis of the momentum flux ratio’s impact on flame anchoring and on the resultant formation of the NOx-emissions. Therefore several prototype test burner with different momentum flux ratios are tested under preheated atmospheric conditions. The investigation shows that the resultant positioning and anchoring of the micro flames highly influences the NOx-formation.

Besides the experimental investigations, numerical simulations have been performed by the application of a commercial CFD code. The cold flow simulation results show the mixing of the air and hydrogen after the injection, in particular in the Counter Rotating Vortices (CRV). Furthermore, the hydrogen jet interacts also with another vortex system resulting from a wake flow area behind the combustor geometry. Furthermore, reacting flow simulations have been performed by the application of a Hybrid Eddy Break-Up (EBU) combustion model. The combustion pressure has been varied from atmospheric conditions up to a pressure of 16 bar.

The experimental and numerical results highlight further potential of the micromix combustion principle for low NOx-combustion of hydrogen in industrial gas turbine applications.
Flammability of High Flash Point Liquid Fuels
Authors: Kay Peter J. , Crayford Andrew P. , Bowen Philip J. , Luxford James
Published: July 2013

Current European Health and Safety Legislation was implemented to limit the chance of a serious explosion occurring in the workplace by highlighting potentially explosive atmospheres and ensuring that ignition sources are not present in these areas. Though hazardous area classification for gaseous and dust explosion hazards are well established, the same cannot be said for mists especially for high flash point liquids. However, a recent literature review of a range of (some fatal) incidents has shown that mist explosions are more common and the consequences more severe than previously anticipated. This work is, for example, applicable to the safe use of fuels and lubricants utilised in the gas turbine power generation and propulsion industries.

Previous studies of jet breakup regimes and idealised flammability studies have indicated that low pressure releases (<10 bar) of low volatility fuels may still give rise to combustion hazards. Impingement of accidental releases onto surfaces has been shown to exacerbate the potential hazard, or broaden the range of hazardous release conditions. However, although a theoretical case can be made for generating flammable environments under moderate release conditions, very little evidence has been provided to bridge the gap between ‘idealised’ studies and full-scale incidents. The aim of this first programme of work is to start the process of bridging this gap, leading to well founded safety guidance.

The test programme was conducted in a custom built spray chamber located in the Gas Turbine Research Centre (GTRC) of Cardiff University. The fuel was released at a predefined range of pressures of industrial relevance at atmospheric temperature. Igniters were positioned at three downstream locations and the continuous electrical discharge had an energy no greater than 4 mJ. Tests were conducted for ‘free sprays’ where the spray was directed along the length of the chamber, and for impinging sprays where the spray was aligned to impinge normal to a flat un-heated surface.

Gas oil (flash point > 61 °C) ignited as a free jet at a working pressure consistent with previous hypotheses. However, when the jet impinged on a solid surface then the resulting spray could be ignited at considerably lower delivery pressures. Although the impingement process is complex, the data will be discussed in light of contemporary models that predict initial jet/spray characteristics along with post-impingement characteristics. This paper presents a first step towards consolidating previous studies and improving future safety guidelines concerned with the risk posed by the flammability of accidental releases of pressurised high flashpoint fuels.
Passive Mitigation of Noise in a Duel Fuel Combustor Using Porous Inert Media
Authors: Meadows Joseph , Agrawal Ajay K.
Published: July 2013

In the past, we have utilized porous inert media (PIM) to suppress noise and thermo-acoustic instabilities in swirl-stabilized combustion systems operated on gaseous fuels. The same concept will also be shown to work in liquid fueled combustion systems. This study presents experimental results to evaluate the PIM concept for suppressing combustion noise in a duel fuel combustor. Experiments for gaseous fuel combustion are performed using natural gas premixed with air upstream of the combustor dump plane. Experiments for liquid fuel combustion are performed using kerosene fuel supplied through a commercial air-blast atomizer. In this combustor, the flame stabilizes downstream of the dump plane by central and corner recirculation zones. Multiple ring shape PIM pieces are inserted into the combustor to alter the flow field in an advantageous manner. Each PIM piece has the same outer diameter but different inner diameters. Results are presented to investigate the effects of equivalence ratio and heat release rate for gaseous fuel combustion and air to liquid mass ratio and heat release rate for liquid fuel combustion. Attempts were also made to create thermo-acoustic instabilities by positioning four loudspeakers radially around the primary air flow upstream of the combustor. Measurements of sound pressure levels (SPL), and CO and NOx emissions were taken to characterize the combustion process. Results show that PIM can passively mitigate combustion noise in a duel fuel combustor without adversely affecting the emissions.
Laminar Burning Velocity and Markstein Length Characterisation of Compositionally Dynamic Blast Furnace Gas
Authors: Pugh Daniel , O’Doherty Tim , Griffiths Anthony , Bowen Philip , Crayford Andrew , Marsh Richard , Giles Anthony , Hopkins Andrew
Published: July 2013

Blast Furnace Gas is a poor quality process gas comprising proportions of CO, H2, CO2, and N2, with a low energy density typically in the order of 3 MJ·kg−1. Produced in large quantities as a by-product of blast furnace iron making, it is one of the process gases indigenous to integrated steelworks worldwide. The inherently dynamic nature of furnace operation causes compositional variation and therefore leads to fluctuation in the fuel characteristics, often dissuading engineers from fully utilising the gas in increasingly complex and efficient technologies such as gas turbines. Characterisation studies were undertaken in a new constant volume bomb to determine the sensitivity to change in laminar burning velocity and Markstein length experienced as a result of increasing the volumetric H2 fraction in the range of 1–7%. Experiments were performed by measuring outwardly propagating spherical flame evolution, recorded using a Schlieren flame visualisation technique for a range of equivalence ratios, and processed using nonlinear data analysis. The relative performance of the experimental technique was benchmarked against other works using well-investigated CH4 and yielded results in good agreement with published values. Peak laminar burning velocity was shown to increase by a factor of approximately 3.5 over the tested range, with H2 concentration and equivalence ratio shown to greatly influence the effect of flame stretch. Comparisons of results were also made with values obtained from different reaction mechanisms employed using the PREMIX code developed by Sandia National Laboratories.
On the Prediction of Pollutant Emission Indices From Gas Turbine Combustion Chambers
Authors: LaViolette Marc , Perez Ruben
Published: July 2013

This paper surveys existing emissions models used in the prediction of NOx. The prediction of jet engine emission indices from fundamental principles have proven to be difficult due to the complex physical and chemical interactions occurring within their combustion chambers. Present day prediction of engine emission indices during engine development relies on published models, which are based on limited sets of data measured on older combustion chambers where minimizing pollutant emissions was not a major design criteria. Such empirical and semi-empirical models can, however, provide upper emission limits for new engine designs. A database comprising a wider range of experimental data (over 2000 measured points) taken from the literature was used to test the models. Advanced techniques were applied to optimize the coefficients of proportionality of governing equations of the best models in the literature. Most models tend to consistently over or under predict the measured values. In most cases, even though the standard deviation of the predicted values was not reduced, the correlation error was improved by removing this bias.
Development of a Simplified Back-Up Liquid Fuel System for a Heavy Duty Industrial Gas Turbine
Authors: Zucca Alessandro , Asti Antonio , Evulet Andrei , Khayrulin Sergey , Shershnyov Borys , Myers Geoff
Published: July 2013

Heavy duty gas turbines for power generation and mechanical drive applications are typically fired on natural gas as a primary fuel, providing heat and power with high efficiency and low exhaust emissions. However, fuel gas is not always available when power is needed, and distillate oil is often employed as an easily stored and handled back-up fuel. The present paper describes the development and initial component validation testing of a new, simplified liquid fuel injection system that will provide a back-up liquid fuel option for dry, low NOx combustion systems used in heavy duty industrial gas turbines. This new liquid fuel system offers reduced initial cost and operating cost, lower NOx emissions, and reduced water consumption relative to current technology. Spray test, sub-component ignition test, and full-scale combustion chamber test results will be discussed.
Thermal Analysis for Three-Dimensional Heat Spreader Integrated With Heat Sink
Authors: Wu Y. C. , Chen H. T. , Lin C. C. , Hung Y. H.
Published: July 2013

An effective thermal analyzer for exploring the thermal performance of 3-D heat spreader having discrete heat sources integrated with heat sink has been successfully developed in the study. The thermal performances such as local temperature distributions and isotherms on heat spreader surfaces; and overall resistance of heat spreader/sink assembly are investigated. Besides, a series of parametric studies have been performed. The parameters and conditions explored include the size and heat dissipation rate of heat sources, size and material of heat spreaders and heat sinks, type of convection in heat sink, and contact conditions between heat spreader and heat sink. The superiority of the developed thermal analyzer through two sample cases having multi-discrete heat sources has finally been demonstrated.
Performance Prediction for Partially-Confined Heat Sinks
Authors: Jeng Tzer-Ming , Wang Meng-Ping , Hung Ying-Huei
Published: July 2013

In the present study, the forced air convection heat transfer for unconfined and confined heat sinks by considering flow bypass effect is studied on a semi-empirical basis. The flow bypass effect for unconfined heat sinks is firstly investigated. For unconfined heat sinks with specified fin spacing and fin height, the results reveal that the value of Ui/(ε·Us), which represents the flow bypass capability, increases from a very small Reynolds number up to a certain Reynolds number, say Rei = 60–200; and then gradually decrease with further increasing Reynolds number. At a specified Reynolds number, the Ui/(ε·Us) will generally increase when the fin spacing decreases or the fin height increases. For heat sinks partially confined in a channel, a novel concept to estimate an imaginative flow domain, in which the flow is influenced due to the existence of heat sink in the channel, is postulated in the study. Accordingly, an effective method for predicting the flow velocity between fins, flow rate through the heat sink and the fin heat transfer coefficient in both unconfined flow and confined flow is presented. Finally, in order to explore the optimal number of fins, a performance parameter defined as the ratio of thermal conductance to the required pumping power is introduced; an optimal procedure to determine the maximum performance parameter for a heat sink partially confined in a channel is postulated. The results manifest that the optimal number of fins increases with increasing inlet flow velocity.
Optimization of Elliptical Fin Heat Sink Design in Forced Convection: Single and Multiple Heat Sink Scenarios
Authors: Kadangode Subha M. , Mason John R.
Published: July 2013

A parametric evaluation of elliptical pin fin heat sinks was performed using a commercially available CFD software package. The investigation involved variation of fin length, fin height, fin gap width, and air velocity while holding the heat flux and fin geometry as constants. The effect of these variables on the thermal performance and airflow impedance characteristics of the heat sink was studied and an optimum heat sink design was selected for a given set of conditions. Additionally, an often-encountered user requirement of multiple heat sinks in a row was also studied with these variables. In line and staggered elliptical fins as well as plate or extruded fins were analyzed although the main focus of the evaluation was based upon in line elliptical fins.
Understanding Longitudinal Fin Heat Sink Orientation Sensitivity for Light Emitting Diode (LED) Lighting Applications
Authors: Petroski James
Published: July 2013

Light Emitting Diodes (LEDs) have progressed in recent years from emitting indicator level lighting to emitting enough light for illumination applications. This has opened a new field for LED applications, resulting in significant advantages over conventional light sources and creating some application challenges unique to LEDs. Conventional lighting methods provide little guidance for LED thermal problems since these usually involve a very high temperature source, such as a filament or an arc, and radiant heat transfer dissipates the thermal energy. LED junction temperatures are limited to much lower values and hence the heat transfer system cannot depend upon radiant energy transfer. This means the cooling methods for lighting now shift from primarily radiation to conduction and natural convection, and this paradigm shift lighting designers must recognize when moving to LEDs. In this paper, the development of a LED-based spot module heat sink in a free convective cooling system is discussed. The rationale for choosing a cylindrical tube, longitudinal fin (CTLF) heat sink is shown, as is the performance of five different configurations of the heat sink in various orientations. The requirement for using heat sinks in various orientations comes from lighting applications, where the light may be installed in various directions, such as vertical up, vertical down, horizontal, or at almost any other angle. Heat sink test results are plotted for Nussult number versus standard and modified channel Rayleigh number, showing a similar correlation to the parallel plate heat sinks investigated first by Elenbaas. A different correlation for the isolated-plate limit section is proposed for CTLF heat sinks, as well as a proposed area of operation on these Nu-Ra curves for orientation-insensitive heat sinks. Finally, explanations for the different levels of sensitivities observed in different areas of the Nu-Ra curves are offered.
Low-Profile Synthetic Jet Cooling for Portable Computers
Authors: Mahalingam Raghav , Glezer Ari
Published: July 2013

This paper explores the novel technique of forced synthetic jet cooling within high-aspect ratio ducts that can be accommodated within low-profile electronic systems. A synthetic jet is an intense, small-scale turbulent jet that is synthesized directly from the fluid in the system in which it is embedded and is formed when fluid is alternately sucked and ejected from the cavity by the motion of a diaphragm bounding the cavity, so that there is no net mass addition to the system. This feature obviates the need for input piping or complex fluidic packaging and makes synthetic jets ideally suited for the low-profile geometries of portables. In the current work, a simple configuration of a 2-D synthetic jet ejector in a rectangular channel is used to ascertain the flow and thermal performance curves, overall thermal resistance and effectiveness for the synthetic jet ejector channel flow.
Effective Thermophysical Properties of Thermal Interface Materials: Part I — Definitions and Models
Authors: Savija I. , Culham J. R. , Yovanovich M. M.
Published: July 2013

The conductivity of thermal interface materials are typically determined using procedures detailed in ASTM D 5470. The disadvantages of using these existing procedures for compliant materials are discussed along with a proposed new procedure for determining thermal conductivity and Young’s modulus. The new procedure, denoted as the Bulk Resistance Method, is based on experimentally determined thermal resistance data and an analytical model for thermal resistance in joints incorporating thermal interface materials. Two versions of the model are presented, the Simple Bulk Resistance Model, based on the interface material thickness prior to loading and a more precise version denoted as the General Bulk Resistance Model, that includes additional parameters such as surface characteristics and thermophysical properties of the contacting solids. Both methods can be used to predict material in situ thickness as a function of load.
Thermal Modeling of Plated-Through Hole Vias in a FBGA Package
Authors: Sun X. Howard , Zhao Z. , Sahan R.
Published: July 2013

The objective of this study is to compare different geometric models to represent thermal vias (plated though holes - PTH) in the substrate of a 196-ball FBGA package. The baseline model, which models each via individually as PTHs, was compared with models that model each via individually by solid cylinders and square cross-section prismatic blocks, and a compact model that models all vias by one prismatic block. The computational fluid dynamics (CFD) simulations were carried out using Icepak®. It was found that all simplifications led to some degree of under-prediction of the junction temperature. The results showed that the detailed models with the cylindrical cross-section and the square cross-section under-predicted the junction temperature by about 3–4% compared to the baseline model. The compact model, however, under-predicted the junction temperature by about 10% compared to the baseline model. The explanation for this error produced by the compact model is that it cannot model the constriction effect of the small individual thermal vias. The conclusion of this study is that all simplifications led to some degree of under-prediction of the junction temperature, and the popular technique to model the thermal vias by a block can lead to appreciable errors in predicting the die temperature.
Experimental Study of Innovative Heat Sinks for High Power Density Electronic Components
Authors: Fabbri Giampietro , Lorenzini Marco
Published: July 2013

In this work, some simple air-cooled high-effectiveness heat sinks are proposed for the cooling of electronic devices such as microprocessors for personal computers. The performance of the heat sinks are experimentally investigated. In particular the temperature of the heat sink surface in contact with the devices to be cooled is measured together with the air temperature and flow, by varying the air flow rate. The pressure drop in the air through the heat sinks is also measured. The thermal resistance of the disspators is then calculated and compared to that of commercially available heat sinks.
Performance Analysis, Optimum and Verification for Parallel Plate Heat Sink Associated With Single Non-Uniform Heat Source
Authors: Lin Vincent , Chen Sih-Li
Published: July 2013

This paper develops an analytical model to predict the overall thermal resistance of a parallel plate heat sink associated with a non-uniform heat source. Using constrictive ratio and apparent interface ratio to interpret equivalent heat source area and maximal heat flux on source-to-sink contacting surface, the non-uniform heat source problem can be simplified as an equivalent uniform heat source problem. Then by using the existed correlations the present model can calculate the overall thermal resistance as a function of heat sink geometry, properties, interface conditions, and airflow velocity. An experimental investigation is performed to verify the theoretical model. Prediction results show good agreement with experimental measurements over a number of testing units. A case study of optimum is also proposed to demonstrate and understand the effects of variable constrictive ratio and apparent interface resistance.
The Thermal Resistance of Pin Fin Heat Sinks in Transverse Flow
Authors: Kang Sukhvinder , Holahan Maurice
Published: July 2013

This paper presents a physics based analytical model to predict the thermal behavior of pin fin heat sinks in transverse forced flow. The key feature of the model is the recognition that unlike plate fins, streamwise conduction does not occur in pin fin heat sinks. Thus, the heat transfer from each fin depends on its local air temperature or adiabatic temperature and the local adiabatic heat transfer coefficient. Both experimental data and simplified CFD simulations are used to develop the two building blocks of the model, the thermal wake function and the adiabatic heat transfer coefficient. These building blocks are then used to include the effect of the thermal wake from upstream fins on the adiabatic temperature of downstream fins in determining the fin-by-fin heat transfer within the pin fin array. This approach captures the essential physics of the flow and heat transport within the fin array and yields an accurate model for predicting the thermal resistance of pin fin heat sinks. Model predictions are compared with existing experimental data and CFD simulations. The model is expected to provide a sound basis for a consistent performance comparison with plate fin heat sinks.
A Numerical Analysis on the System Impedance in a Fan Cooling System
Authors: Kim Dong-Il , Bok Ki-So , Lee Han-Bae
Published: July 2013

To seek the fan operating point on a cooling system with fans, it is very important to determine the system impedance curve and it has been usually examined with the fan tester based on ASHRAE standard and AMCA standard. This leads to a large investment in time and cost, because it could not be executed until the system is made actually. Therefore it is necessary to predict the system impedance curve through numerical analysis so that we could reduce the measurement time and effort. This paper presents how the system impedance curve (pressure drop curve) is computed by CFD in substitute for experiment. In reverse order to the experimental principle of the fan tester, pressure difference was adopted first as inlet and outlet boundary conditions of the system and then flow rate was calculated. After determining the system impedance curve, it was compared with experimental results. Also the computational domain of the system was investigated to minimize computational time.
Thermal Behavior of Next Generation of Raman Pump Lasers in Telco Equipment
Authors: Refai-Ahmed Gamal , Trottier Stephanie
Published: July 2013

The present investigation concluded that the thermal behavior of the laser diode can be numerically modeled using the parabolic transient conduction equation. In addition, the current study compared the thermal performance of the continuous wave pump lasers versus the modulated wave pump lasers. This comparison revealed that the temperature of the modulated wave pump laser can approach the temperature of the continuous wave pump laser with the same average power dissipation when the frequency approaches infinity. Finally, the resulting thermal behavior was correlated and expressed in an empirical form, which physically described the thermal performance of the modulating pump laser.
Temperature Distribution in Two-Layered Composites
Authors: Yeung Wing K. , Lam Tung T.
Published: July 2013

The thermal wave propagation behavior within a two-layered anisotropic substrate is investigated in this study using a two-dimensional hyperbolic heat conduction model. The governing equations are solved by a flux splitting algorithm based on the Godunov numerical scheme. Special attention is given to the nature of heat propagation and reflection within the composite substrate after an instantaneous release of energy. The influences of the thermal lagging behavior, anisotropic thermal conductivity, and material interfacial effect on temperature distributions are investigated. Comparisons are made between results obtained by the thermal diffusion and wave models.
Indirect Cooling of IC Chips Using a Two Phase Closed Thermosyphon Loop
Authors: Gima Satoru , Nagata Takashi , Zhang Xing , Fujii Motoo
Published: July 2013

This paper reports on indirect cooling of high-power IC chips of notebook computers using a two phase closed thermosyphon loop with Fluorinert (FC-72) as the working fluid. The experimental set-up consists of an evaporator and a condenser connected by flexible tubing. The evaporator corresponds to a high-power IC chip, and the condenser represents a cooling plate located behind the display of notebook computer. The evaporator and the condenser have the outer dimensions of 50mm × 50mm × 20mm and 150mm × 200mm × 20mm, respectively. The effects of the heat input Q and the charged volume of Fluorinert liquid F on the heat transfer characteristics of the cooling system were studied experimentally. Further, the experiment for the evaporator with plate fin to enhance the boiling in the evaporator was carried out. It has been confirmed that the heater surface temperature for the evaporator with plate fin reduces about 10% in comparison with those for the evaporator without fin. It is found that enhancing the boiling in the evaporator is very effective to reduce the surface temperature of heater. In the case of the evaporator with the plate fin, the temperature difference between the heater surface and ambient is kept around 60K for the highest heat input Q = 30W in the present experiments.
Evaluation of Surface Finish on Build Up Substrate
Authors: Hung L. Y. , Wang Y. P. , Hsiao C. S.
Published: July 2013

In recent years, the most explosive technologies in electronic systems have demanded ever-higher functionality, ever-faster circuit speeds, and always increasing interconnection density. Electrolytic and electroless nickel/gold (Ni/Au) deposition process are used commonly to provide flat, solderable pad surface finish on area array (BGA or CSP) packages and printed wiring boards (PWB). The electroless nickel/immersion gold (ENIG) process is widely used which do not requires plating lines for electrolytic plating, better meets the fine pitch wiring requirements. However, ENIG deposition process may cause or contribute to catastrophic, brittle, interfacial solder joint fractures. ENIG plating has previously shown lower reliability at solder joints. This is because Phosphorous segregation at the interface Sn-Ni intermetallic and Ni layer caused poor adhesion at that interface, especially high phosphorous content (10∼15%) of the electroless Ni. There have been many studies verified that Ni3P formation is a major factor, which causes weaker joint strength and flat fracture surface. Owing to sodium hypophosphite (NaH2PO2) was used to provide electron and return Ni ion to deposit on Cu pad for ENIG plating, it is not dodge that phosphorous element exist at the Ni layer. Hence, ph value, temperature and loading factor (plating area/ plating tank volume) in the plating path are controlled to reduce phosphorous content (less than 10%) to avoid Ni3P formation. Furthermore, ENIG has a potential risk of black pad, because Porous Au plating layer caused the oxidation of Ni layer underneath the Au plating to occur solder joint failure and low shear forces after assembly. In order to overcome foregoing problem, a flip chip ball grid array (FCBGA) test vehicle is used to compare three kinds surface finish electroless Ni/Au, direct gold and solder on Cu pad in this study 63Sn/37Pb solder bump is reflowed onto these substrates. High temperature storage test (HTS) is used to evaluate thickness and structure of IMC to affect solder joint attachment reliability. Ball shear test is used to measurement joint strength at various HTS time. Optical microscopy (OM) and scanning electron mcroscopy (SEM) are used to observe failure modes after ball shear.
Design Optimization of LTCC Interconnects With Meshed Ground Planes
Authors: Wai Lai L. , Lu Albert Chee W. , Fan Wei , Jin Lin , Low Lee A.
Published: July 2013

Coupling between interconnects in high density structures limits the broadband performance, leading to degradation in insertion loss and cross talk characteristics. This paper describes the solution space analysis of LTCC interconnects with meshed planes. The impact of metal coverage, interconnect structures and mesh geometry was evaluated through detailed 3-D FEM based simulations.
Effects of Boundary Conditions and Source Dimensions on the Effective Thermal Conductivity of a Printed Circuit Board
Authors: Shabany Younes
Published: July 2013

The heat conduction equation and its boundary conditions were used to show that the planar and normal thermal conductivities of an orthotropic model of a printed circuit board were functions of source to board size ratio, top and bottom side boundary conditions, and thickness and thermal conductivity of each layer. Numerical solutions of the heat conduction equation were used to quantify the dependence on source to board size ratio and top and bottom boundary conditions. It was shown that the thermal conductivities were stronger functions of the source to board size ratio for smaller values of this ratio. This dependence was more pronounced for boards with stronger convection heat transfer on their top side, and for boards with thicker component side copper layer. The thermal conductivities were less sensitive to the variation of the convection heat transfer on the bottom side of the board.
Novel Method for Estimating Thermal Film Coefficients for Analysis of Thermal Cycling of Microelectronic Packages
Authors: Chambers Benjamin C.
Published: July 2013

A failure analysis on microelectronic packages subjected to temperature cycling between liquid baths required the need for realistic boundary conditions in the thermal analysis portion of the overall thermal stress analysis. Prior arts found in literature for thermal film coefficients in immersion cooling focused only on metallurgical quenching. The results indicated that these data are highly dependant on temperature, thus not applicable since they were derived for quenching of steel at higher initial temperatures. An alternative technique was developed here by assuming that the package could be modeled as a semi-infinite solid for the time interval of interest, and that the fluid is quiescent for the time interval. The effects on the film coefficient of the motion of the package into the liquid bath are neglected. These assumptions enable the use of the available analytical solution for bringing two semi-infinite solids in contact. By being able to model the fluid as a semi-infinite solid, we can then differentiate the solution for transient heat flow in a semi-infinite body subject to a step change in surface temperature to obtain the heat flux from the surface of the package. The temperature difference between the package surface and the bulk fluid temperature then cancel out of the equation for the film coefficient leaving a closed form solution for the effective calculation of a time dependent film coefficient, which can then be applied as a boundary condition in a numerical thermal analysis. The expression for the film coefficient was found to be proportional to the fluid effusivity divided by the square root of the elapsed time.
Design Optimization of Power Distribution Design Networks Using Embedded Passive Technology
Authors: Lu Albert Chee W. , Fan Wei , Wai Lai L. , Yamazaki Toshiro , Jarcia Jacinto Jun , Chin Kim H.
Published: July 2013

This paper describes a design optimization of power distribution networks using embedded passive technology. A frequency-domain methodology was used to study the impedance characteristics of printed circuit board power planes with embedded decoupling capacitors, and also the interaction with discrete capacitors, package structures and on-chip capacitors. Two different thin-core materials were analyzed. Key aspects of power distribution networks including plane spreading inductance, plane pair via inductance and transfer impedance were also analyzed. Utilizing broadband PDN models, extracted with full-wave EM techniques to account for frequency-dependent behaviour, frequency-domain SPICE simulations were carried out to determine the system impedance characteristics at multiple port locations up to 2 GHz. The frequency-domain analysis shows that in bare boards, significant SSN interaction between different port locations within the printed circuit board is present. It is concluded that the proper use of high-K distributed capacitors at optimal locations on the printed circuit board helps to alleviate SSN interaction between different port locations. Several multi-layer test vehicles have been fabricated and characterized, with good correlation between simulation results and measured values.
Reverse Mount Packages and Their Cooling
Authors: Ahmad Mudasir , Narasimhan Susheela
Published: July 2013

The density of packaging in electronic enclosures is increasing rapidly and the real estate available for packaging high power ASICs and processors is decreasing very rapidly as well. This work presents a study where packages are mounted below the board and the ASICs are cooled using the sheet metal tray as the heat spreader. The heat is transferred from the processor or the chip to the sheet metal tray through metallic blocks or heat spreaders by conduction and then the sheet metal tray is cooled convectively by airflow between two successive boards. There are various issues to be encountered when we do such a design for reverse mount packages like the maximum stress exerted on the ASIC, the kind of interface material that should be used to minimize the stress induced on the ASIC and also keeping in mind the thermal impedance of the interface material. The study presents simulation and experimental results that illustrate the concept of using the sheet metal tray as a heat spreader and also discuss potential applications of this concept. Considerations and precautions to be taken while executing this concept are also addressed.
Integrated Avionics System (IAS): Integrating 3D Technology on a Spacecraft Panel
Authors: Hunter Don J.
Published: July 2013

As spacecraft designs converge toward miniaturization, and with the volumetric and mass challenges placed on avionics, programs will continue to advance the “state of the art” in spacecraft system development with new challenges to reduce power, mass and volume. Traditionally, the trend is to focus on high-density component packaging technologies. Industry has made significant progress in these technologies, and other related internal and external interconnection schemes. Although new technologies have improved packaging densities, a system packaging architecture is required that not only reduces spacecraft volume and mass budgets, but increase integration efficiencies, provide modularity and flexibility to accommodate multiple missions while maintaining a low recurring cost. With these challenges in mind, a novel system packaging approach incorporates solutions that provide broader environmental applications, more flexible system interconnectivity, scalability, and simplified assembly test and integration schemes. The Integrated Avionics System (IAS) provides for a low-mass, modular distributed or centralized packaging architecture which combines ridged-flex technologies, high-density COTS hardware and a new 3-D mechanical packaging approach, Horizontal Mounted Cube (HMC). This paper will describe the fundamental elements of the IAS, HMC hardware design, system integration and environmental test results.
Very High Performance Thermal Interface Material and Attachment Technology
Authors: Webb Ralph L. , Paek Jin Wook , Pickrell David
Published: July 2013

This paper provides an update on work at Penn State University on advanced thermal interface material (TIM) and attachment technology. The TIM concept consists of a “Low Melting Temperature Alloy” (LMTA) bonded to a thin copper substrate. The present work includes analytical modeling to separate the interface resistance (Rint) into “material” and “contact” resistance. Modeling indicates that contact resistance accounts for 1/3 of the interface resistance (Rint). Additional alloys have been identified that have thermal conductivity approximately three-times those identified in the previous 2002 publication. Thermal degradation of the LMTA TIM was also observed in the present work after extended thermal cycling above the melting point of the alloy. Possible mechanisms for this degradation are oxidation and contamination of the alloy layer rather than the inter-metallic diffusion. Use of the high thermal conductivity alloys, and soldered contact surfaces will provide very low Rint as well as minimizing the thermal degradation. It appears that Rint as small as, or less than, 0.005 cm2-K/W may be possible. Description of the modified Penn State TIM tester is provided, which will allow measurement of Rint = 0.01 cm2-K/W with less than 30% error.
Cooling Solution for Next Generation High-Power Processor Boards in 1U Computer Servers
Authors: Roknaldin Farzam , Sahan Ridvan A.
Published: July 2013

Processor powers of 30–60W are becoming very common in electronic industry. With constraints such as available heat sink space and the cost of the thermal solution, heat sink optimization has become one of the major concerns in the final design process. In this work two (new) strategies are proposed along with the traditional heat sink optimization process (i.e. fin/base thickness and fin spacing optimization). First, heat pipes are embedded into the aluminum base extruded heat sink to reduce spreading resistance. The resulting heat sink is more efficient and even cheaper when compared to the bounded-fin technology on a copper base. Second, the angled base modification is introduced to reduce the spreading resistance in the flow direction. It is observed that up to 5 degrees angle in the base can reduce the thermal resistance of an active heat sink by 8–10%.
Influence of Package-Sink Interface Materials on Die Performance and Reliability
Authors: Jung Henry H. , Ankireddi Sai , Pecavar Stanley , Jones James
Published: July 2013

For high-power electronic packages, it is generally accepted that the package-sink interface materials used in the thermal solution influence hot-spot temperature(s) and junction-to-ambient thermal resistance. In this article we show how these package-exterior materials can noticeably influence across-die temperature gradients also. The numerical results reveal that the across-die thermal gradient can nearly double over a narrow range of conductivities typical of commercially available package-sink interface materials. Results show that the chip hot-spot temperature can be reduced 4 to 7 C by increasing the thermal interface material conductivity from 1 to 3 W/mk. This improvement can reduce the total thermal resistance from chip to ambient.