bluuebunny/crossref_metadata_2025 huggingface dataset:
The Impact of Perforation Geometry on Acoustic Damping Attributes of a Perforated Liner With Bias Flow
Authors: Mazdeh Alireza , Kashani Reza
Published: July 2013

Acoustic damping properties of perforated liners are highly dependent on a number of variables which can be categorized as “flow variables” such as the extent and Mach number of grazing flow as well as bias flow and “geometric variable” such as the shape of the hole which can be rectangular, cylindrical, conical with diverging or converging nozzle, thickness to radius ratio, radius to hole spacing ratio and hole orientation which can be normal to or inclined with respect to the perforated plate. Many of these variables were not incorporated in previous studies.

Theoretical and empirical approaches have provided the foundation for understanding the damping properties of liners but they are based on certain simplifying assumptions making them inadequate in addressing the more realistic conditions encountered in industrial applications. These limitations have highlighted the importance of numerical methods for studying damping behavior of liners. Acoustic attributes of perforated plates (mainly in terms of impedance which is a frequency-dependent complex quantity) as a function of non-dimensional variables like Reynolds, Strouhal, Mach, and Helmholtz numbers have been studied by various researchers, including the authors, using a variety of numerical tools starting from the simple 1D network scheme based on linear acoustics and the wall compliance concept introduced by Howe all the way to the computationally intensive Large-Eddy Simulations (LES) and Scaled Adaptive Simulation (SAS) reconstructing the full unsteady turbulent structures. Although the impacts of some geometry variations such as hole inclination angle and diameter, in conjunction with various fluid dynamic parameters, have been investigated using 1D network tools, the focus of LES has been mainly on analysis of a single circular hole with periodic boundary conditions as the representation of multi-perforation (assuming the perforations are spaced far enough from each other so that there is no interaction between neighboring holes). There is certainly a need for thorough investigation of the acoustics impact of these geometric parameters as well as shape of the holes using LES.

In an on-going research we are extending the numerical modeling work on characterizing the acoustic damping attributes of a perforation, beyond the current state of the art, by including the geometric variables including hole size, shape, orientation, and radius to thickness ratio, amongst others, in the study. In this paper, following a short review of the research conducted in the recent past for comprehension of the acoustic-vortex interaction mechanism in perforated liners resulting in acoustic absorption, we present the findings on the impact of thickness/radius ratio on the acoustic damping attribute of a perforation. The verification of the CFD results are done by comparing the data with analytical solutions.
On the Impact of Shear Flow Instabilities on Global Heat Release Rate Fluctuations: Linear Stability Analysis of an Isothermal and a Reacting Swirling Jet
Authors: Oberleithner Kilian , Schimek Sebastian , Paschereit Christian Oliver
Published: July 2013

The prediction of large-scale flow structures in combustor flows and their impact on the flame dynamics is of great importance to avoid thermoacoustic instabilities in modern gas turbine design. The streamwise growth of these so-called coherent structures depends on the receptivity of the shear layers, which can be predicted numerically by means of linear stability analysis. We demonstrate this approach on an isothermal swirling jet that is dominated by a self-excited helical mode that features a precessing vortex core, showing that this theoretical concept successfully predicts the frequency, the source, and the shape of this mode. The analysis is further applied to a reacting flow with a swirl-stabilized flame, pointing out important connections between the shear layer receptivity and the measured amplitude dependence of the flame transfer function. The theoretical findings suggest that the saturation of the global heat release rate fluctuations observed at moderate forcing amplitudes is caused by vanishing shear layer receptivity.
Chemical Kinetic Modeling of Ignition and Emissions From Natural Gas and LNG Fueled Gas Turbines
Authors: Gokulakrishnan P. , Fuller C. C. , Joklik R. G. , Klassen M. S.
Published: July 2013

Single digit NOx emission targets as part of gas turbine design criteria require highly accurate modeling of the various NOx formation pathways. The concept of lean, premixed combustion is adopted in various gas turbine combustor designs, which achieves lower NOx levels by primarily lowering the flame temperature. At these conditions, the post-flame thermal-NOx pathway contribution to the total NOx can be relatively small compared to that from the prompt-NOx and the N2O-route, which are enhanced by the super-equilibrium radical pathway at the flame front. In addition, new sources of natural gas fuel (e.g., imported LNG) with widely varying chemical compositions including higher order hydrocarbon components, impact flame stability, lean blow-out limits and emissions in existing lean premixed combustion systems. Also, the presence of higher order hydrocarbons can increase the risk of flashback induced by autoignition in the premixing section of the combustor.

In this work a detailed chemical kinetic model was developed for natural gas fuels that consist of CH4, C2H6, C3H8, nC4H10, iC4H10, and small amounts of nC5H12, iC5H12 and nC6H14 in order to predict ignition behavior at typical gas turbine premixing conditions and to predict CO and NOx emissions at lean premixed combustion conditions. The model was validated for different NOx-pathways using low and high pressure laminar premixed flame data. The model was also extended to include a vitiated kinetic scheme to account for the influence of exhaust gas recirculation on fuel oxidation. The model was employed in a chemical reactor network to simulate a laboratory scale lean premixed combustion system to predict CO and NOx. The current kinetic mechanism demonstrates good predictive capability for NOx emissions at lower temperatures typical of practical lean premixed combustion systems.
Development and Testing of a Low NOX Hydrogen Combustion System for Heavy Duty Gas Turbines
Authors: York William D. , Ziminsky Willy S. , Yilmaz Ertan
Published: July 2013

Interest in hydrogen as a primary fuel stream in heavy-duty gas turbine engines has increased as pre-combustion carbon capture and sequestration (CCS) has become a viable option for integrated gasification combined cycle (IGCC) power plants. The US Department of Energy has funded the Advanced IGCC/Hydrogen Gas Turbine Program since 2005 with an aggressive plant-level NOx target of 2 ppm @ 15% O2 for an advanced gas turbine cycle. Approaching this NOx level with highly-reactive hydrogen fuel at the conditions required is a formidable challenge that requires novel combustion technology. This study begins by measuring entitlement NOx emissions from perfectly-premixed combustion of the high-hydrogen fuels of interest.

A new premixing fuel injector for high-hydrogen fuels was designed to balance reliable, flashback-free operation, reasonable pressure drop, and low emissions. The concept relies on distributed, small-scale jet-in-crossflow mixing that is a departure from traditional swirl-based premixing concepts. Single nozzle rig experiments were conducted at pressures of 10 atm and 17 atm, with air preheat temperatures of about 650K. With nitrogen-diluted hydrogen fuel, characteristic of carbon-free syngas, stable operation without flashback was conducted up to flame temperatures of approximately 1850K. In addition to the effects of operating pressure, the impact of minor constituents in the fuel — carbon monoxide, carbon dioxide, and methane — on flame holding in the premixer is presented.

The new fuel injector concept has been incorporated into a full-scale, multi-nozzle combustor can with an energy conversion rate of more than 10 MW at F-class conditions. The full-can testing was conducted at full gas turbine conditions and various fuel compositions of hydrogen, natural gas, and nitrogen. This combustion system has accumulated over 100 hours of fired testing at full-load with hydrogen comprising over 90 percent of the reactants by volume. NOx emissions (ppm) have been measured in the single digits with hydrogen-nitrogen fuel at target gas turbine pressure and temperatures. Results of the testing show that small-scale fuel-air mixing can deliver a reliable, low-NOx solution to hydrogen combustion in advanced gas turbines.
Hydrogen Combustion at High Combustor Airflow Using an Impinging Jet Flame Stabiliser With No Flashback and Low NOx
Authors: Andrews Gordon E. , Altaher Mohamed A. , Li Hu
Published: July 2013

The feasibility of hydrogen as a fuel for industrial gas turbines with low NOx emissions was investigated. Conventional well mixed flame stabilisers are difficult to use with 100% hydrogen owing to the flash back problem, which is potentially seven times worse for hydrogen due to its higher reactivity. This work was carried out using a rapidly mixed Jet Mix design, which had previously been investigated with NG and propane. This consisted of eight radial air jets into which the fuel was injected on their centrelines. These radial jets impinged into eight axial air jets which carried the bulk of the combustion air. Radial jet air flow proportions of 6.5% and 20% were investigated at an overall pressure loss at M1 = 0.047 of 4.3% in a 76mm diameter combustor. The reference Mach number, M1 of 0.047 represents all the compressor exit air entering the combustor with no dilution air. Very lean mixtures are required for low NOx emissions and there is no flame stability issue with hydrogen combustion, so all power turndown can be achieved with one main fuel injector. An inlet temperature of 600K was used at atmospheric pressure and the flames were lean enough to have temperatures where there was no pressure dependence of thermal NOx. For 6.5% radial air NOx emissions of 25ppm at 15% oxygen were demonstrated at 1800K and lower NOx at lower turbine entry temperatures.
Influence of Transverse Acoustic Modal Structure on the Forced Response of a Swirling Nozzle Flow
Authors: O’Connor Jacqueline , Lieuwen Tim
Published: July 2013

This study describes continued investigations of the response of a swirling flow to transverse acoustic excitation. This work is motivated by transverse combustion instabilities in annular gas turbine engine architectures. This instability provides a spatially varying acoustic velocity disturbance field around the annulus, so that different nozzles encounter different acoustic disturbance fields. In this study, we simulate this effect by looking at a standing wave acoustic field where the nozzle is located at either a velocity anti-node, referred to as out-of-phase forcing, and a velocity node, referred to as in-phase forcing. The out-of-phase forcing condition provides an asymmetric forcing field about the center plane of the flow and excites an asymmetric response in the flow field; the in-phase forcing provides a symmetric forcing condition and results in symmetric flow response near the nozzzle.

The symmetric versus asymmetric flow response was measured in two ways. First, in the r-x plane where axial and radial components of velocity are measured using high-speed particle image velocimetry (PIV), a helical and ring vortex rollup of the shear layers is evident in the asymmetric and symmetric forcing condition, respectively. Additionally, the swirling motion of the jet is measured in the r-θ plane at two downstream locations and a spatial decomposition is used to calculate the strength of azimuthal modes in radial velocity fluctuations. At the forcing frequency, the m = 0 mode is strongly excited at the nozzle exit with symmetric forcing, while asymmetric forcing results in a strong peak in the m = 1 mode, or the first helical mode. The results in this plane of view are congruent with those in the r-x plane. Further downstream, however, the mode strengths change as the vorticity is religned and natural asymmetries of the swirling jet set in.

Finally, the low frequency self-excited motion of the vortex core was measured and characterized in the unforced flow. It is composed of an m = −1 and m = −2 mode, and the physical interpretation of these mode numbers is highlighted. High amplitude acoustic forcing decreases the amplitude of oscillation of this structure in both the in-phase and out-of-phase forcing, but to varying degrees.
Impact of the Flameholder Heat Conductivity on Combustion Instability Characteristics
Authors: Hong Seunghyuck , Shanbhogue Santosh J. , Ghoniem Ahmed F.
Published: July 2013

In this paper, we investigate the impact of heat transfer between the flame and the flame-holder on the dynamic stability characteristics in a 50-kW backward facing step combustor. We conducted tests where we use a backward step block made of two different materials: ceramic and stainless steel whose thermal conductivities are 1.06 and 12 W/m/K, respectively. A set of experiments was conducted using a propane/air mixture at Re = 6500 for the inlet temperature of 300–500 K at atmospheric pressure. We measure the dynamic pressure and flame chemiluminescence to examine distinct stability characteristics using each flame-holder material over a range of operating conditions. We find that for tests with a flame-holder made of ceramic, the onset of instability is significantly delayed in time and, for certain operating conditions, disappears altogether. Stated differently, for certain operating conditions, the combustor can be stabilized by reducing the thermal conductivity of the flame-holder. As the thermal conductivity of the flame-holder increases, the combustor becomes increasingly unstable over a range of operating conditions. These results imply that the dynamic stability characteristics depend strongly on the heat transfer between the flame and the combustor wall near the flame anchoring region.
Staged Premix EV Combustion in Alstom’s GT24 Gas Turbine Engine
Authors: Guyot Daniel , Meeuwissen Thiemo , Rebhan Dieter
Published: July 2013

Reducing gas turbine emissions and increasing their operational flexibility are key targets in today’s gas turbine market. In order to further reduce emissions and increase the operational flexibility of its GT24, Alstom has introduced an internally staged premix system into the GT24’s EV combustor.

This system features a rich premix mode for GT start-up and a lean premix mode for GT loading and baseload operation. The fuel gas is injected through two premix stages, one injecting fuel into the burner air slots and one injecting fuel into the centre of the burner cone. Both premix stages are in continuous operation throughout the entire operating range, i.e. from ignition to baseload, thus eliminating the previously used pilot operation during start-up with its diffusion-type flame and high levels of NOx formation.

The staged EV combustion concept is today a standard on the current GT26 and GT24. The EV burners of the GT26 are identical to the GT24 and fully retrofittable into existing GT24 engines. Furthermore, engines operating only on fuel gas (i.e. no fuel oil operation) no longer require a nitrogen purge and blocking air system so that this system can be disconnected from the GT. Only minor changes to the existing GT24 EV combustor and fuel distribution system are required.

This paper presents validation results for the staged EV burner obtained in a single burner test rig at full engine pressure, and in a GT24 field engine, which had been upgraded with the staged EV burner technology in order to reduce emissions and extend the combustor’s operational behavior.
Thermal Performance Measurement for Confined Heat Sinks by Using a Modified Transient Liquid Crystal Technique
Authors: Kuo S. T. , Wang M. P. , Wu M. C. , Hung Y. H.
Published: July 2013

A series of experimental investigations with a new modified transient liquid crystal method on the studies related to the fluid flow and heat transfer characteristics in a channel installed with a heat sink have been successfully performed. The parametric studies on the local and average effective heat transfer characteristics for confined heat sinks have been explored. The influencing parameters and conditions include air preheating temperature at channel inlet, flow velocity and heat sink types. Besides, a concept of the amount of enhanced heat transfer (AEHT) is introduced and defined as the ratio of j/f. The j/f ratio is almost independent of Reynolds number for a specific confined heat sink. The j/f ratios are 0.0603 and 0.0124 for fully-confined and unconfined heat sinks, respectively.
Inkjet Assisted Spray Cooling of Electronics
Authors: Bash Cullen E. , Patel Chandrakant D. , Sharma Ratnesh K.
Published: July 2013

Increases in microprocessor power dissipation and the resulting effect on the cost and complexity of thermal management solutions has been well documented in recent years. Accompanying this increase in overall power dissipation has been a reduction in feature size due to process improvements resulting in a steady decrease in the size of the processing core where most of the power on a die is generated. This trend is expected to continue into the near future and will likely lead to a power dense core covering a fraction of the total die surface area surrounded by areas of reduced power density cache. Evaporative spray cooling has been long identified as a technology that can be used to manage very high power densities (> 100 W/cm2). Limitations in the controllability of individual spray droplets, however, have generally prevented its use in applications that contain marked variation in spatial power density. Since only a relatively uniform spray pattern is possible with existing spray delivery technologies, sections of lower power density become susceptible to pool boiling and thereby place limitations on bulk flow rates, which accordingly limit thermal performance. Conversely, variations in heat transfer coefficients caused by uncontrolled pool boiling across devices can create thermal stresses. In this paper we demonstrate how thermal inkjet technology can be effectively utilized to spray cool a heat source with non-uniform power density. Experimental data is presented for a water-cooled heat source and critical heat fluxes of up to 270 W/cm2 are reported. Additionally, correlations are developed for the unique spray pattern afforded by the technology.
Capacity Control in Refrigerated Systems
Authors: Peeples Johnston W.
Published: July 2013

Powerful refrigeration methods are being deployed to cool electronic devices in test and in end-use application. Cooling capacity control is required to prevent over- or under-cooling. Various levels of control precision are also required. Test applications demand precise temperature control while many end-use applications will accommodate a less sophisticated approach. Important determinants of the method employed to control refrigeration capacity include target operating temperature, absolute and dynamic power dissipation of the device being cooled, control precision required, refrigeration system design and construction, as well as application-related details of the electronics assembly. A variety of capacity control methods are needed to cover the breadth of electronics cooling applications. Control free, or open loop systems meet the needs of some applications. Other systems employ thermal expansion (TX) and hot-gas by-pass valves to provide controlled cooling of very high power electronics cooling vapor compression systems. Modulation of condenser efficiency by varying fan speed provides a very simple but limited range of temperature control. A broad range of precise temperature control requires a combination of approaches to precisely meter refrigerant flow to the cold plate and, if needed, to apply parasitic heat. This paper overviews various vapor compression refrigeration control architectures as they apply to electronics cooling. Comparative cost and performance data are presented.
Dynamic Characterization of Thermal Interface Material for Electronic Cooling
Authors: Shih Rocky , Bash Cullen E.
Published: July 2013

The principle of measuring thermal resistance of thermal interface material (TIM) by sandwiching the material between a hot block and cold block is well known in the industry. TIM manufacturers usually use a variation of the industrial standard ASTM D5470 test method, and subsequently provide data that is difficult for the end user to effectively utilize for product development. This paper will discuss the design and construction of an automated TIM test system based on the ASTM D5470 standard. This automated test vehicle provides an independent study of various TIMs. The instrument enables standardized testing and performance documentation of interface materials from a wide array of manufacturers making it easier for end-users to compare and select the appropriate material for various applications. The automated test method is faster and easier to use than previous methods. It requires minimal operator intervention during the test and can perform preconditioning, and non-uniform heating if required. Experimental results obtained from the instrument will be discussed.
The Dynamic Inverse Method for Thermal Resistance of Cooling Device
Authors: Chien Heng-Chieh , Tseng Ming-Hsi , Chang Wen-Yang
Published: July 2013

A dynamic inverse method for measuring the thermal resistance of cooling device is described. The cooling device is held on a heat capacity block and heating the block higher than environment 50°C, then the thermal resistance of cooling device is deduced from the exponential decay in the temperature difference between the heat capacity block and the environment. This technique is different from conventional measurement in two ways. First, the thermal resistance is usually measured under steady state and always required much time, thus the dynamic measuring technique is needed. Second, the power of heater is always needed to control at a certain value exactly but it isn’t in inverse method. The result reveal that the test time is reduced from several tens minutes to few minutes and made to an accuracy of about ±2%. This rapid and reliable measurement technique is possible used in-line testing of cooling devices for industrial application.
Modeling and Thermal Optimization of a Micro Heat Pipe With Curved Triangular Grooves
Authors: Do Kyu Hyung , Kim Sung Jin , Hwang Gunn
Published: July 2013

Heat transfer and fluid flow characteristics in a micro heat pipe with curved triangular grooves are investigated using numerical and experimental methods. In the numerical part, a one-dimensional mathematical model for micro heat pipe with curved triangular grooves is developed and solved to obtain the maximum heat transport rate, the capillary radius distribution, the liquid and the vapor pressure distributions along the axial direction of the micro heat pipe under the steady-state condition. In particular, the modified Shah method is applied to calculate the pressure drop induced by the liquid-vapor interfacial shear stress. Experiments are conducted to validate the numerical model. In the experiments, the micro heat pipe with 0.56 mm in hydraulic diameter and 50 mm in length is tested. The experimental results for the maximum heat transport rate agree well with those of the numerical investigations. Finally, thermal optimization of the micro heat pipe with curved triangular grooves is performed using the numerical model.
Epoxy/BaTiO3 Composite Embedded Capacitor Films (ECFs) for Organic Substrate Applications
Authors: Cho Sungdong , Hyun Jin-Gul , Paik Kuyng-Wook
Published: July 2013

Embedded capacitor technology is one of the effective packaging technologies for further miniaturization and higher performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been of great interest as embedded capacitor materials, because they have good process compatibility with multilayer organic substrates applications such as printed circuit boards (PCBs). In this work, it was demonstrated that low (less than ±5%) tolerance epoxy/BaTiO3 composite capacitors were successfully fabricated on PCBs using newly developed embedded capacitor films (ECFs), which were composed of specially formulated epoxy resin, latent curing agent, and BaTiO3 powders. And some properties of the capacitors were characterized. Compared with the dielectric layer formation method by spin coating using epoxy/BaTiO3 suspension, ECFs have excellent advantages such as lower (<5%) capacitance tolerance over large area, no waste of materials, good film formation capability, and processability, long shelf life, and good thermo-mechanical stability after final epoxy cure. Dielectric constant about 93 was obtained using two different size BaTiO3 powders mixture. Epoxy resin formulation, curing agent, solvents, and dispersant were optimized to produce good film formation capability, fast curing characteristics at 180°C within 5 minutes, good BaTiO3 powder dispersion control, and excellent shelf life for handling. And the effects of BaTiO3 particle size and BaTiO3 powder content on dielectric constant and adhesion strength were investigated. These capacitor films can be embedded on selective areas of PCBs during build-up processes or other substrates such as Si wafers and ceramic substrates.
Automatic Thermal Modeling for System Level Design of Electronic Equipment
Authors: Aoki Kenichiro , Shimizu Koichi , Ueda Akira , Tamura Akira , Motegi Masanori
Published: July 2013

The development of hardware needs cost reduction by shortening a development period and reducing experimental man-hour. In order to satisfy these demands, thermal fluid analysis with higher accuracy in short time is indispensable for product development. At present, thermal fluid analyses are conducted using different software tools. Each software tool requires model building and meshing for simulations using its own format. That leads to a large investment in time, and therefore cost. VPS/Simulation-Hub software Fujitsu developed is able to convert data from various CADs. It has the features to create a data fitting to numerical analysis software, create an accurate analysis model, and delete unnecessary components. With these main features, VPS/Simulation-Hub greatly contributes to the man-hour reduction for model building and the improvement of analytical accuracy. In this paper, VPS/Simulation-Hub is introduced with the detail explanation of the above 3 main features.
Development of Film Module With Embedded Actives
Authors: Sakurai Daisuke , Tsukahara Norihito , Nishikawa Kazuhiro , Akiguchi Takashi , Nishida Kazuto , Kobayashi Takaya , Saito Mari
Published: July 2013

Since electric products need more effective features in terms of being compact, small, thin and highly performant, a new concept to create the advanced JISSO is required. We have invented the film module manufacturing process, in which the semiconductor is embedded into the thermo-elastic film and wired directly to exposed bumps. In this device, the fundamental process which is the embedded semiconductor into the thermoplastic film PETG, has been developed. This process is essential for the embedded active components film. This technique can be applied to packaging, memory cards, smart cards, flexible multi layer film and so on. The embedding process has the following problems; 1) Stud bumps on the IC may not appear on the surface of the film, 2) Voids may appear in the film during a high temperature press, 3) ICs may crack under high pressure. Subsequently, we solved the thermoplastic film’s flow process during the heat compression process using the rigid-plastic FEM (Finite Element method) analysis. We solved the resin temperature and load during the heat pressing process. It was discovered that ICs (0.18mm) could embed into the PETG film (0.2mm) within 13s. Finally, we applied this embedding process with the contactless IC card, which achieved a distance of calls of 100mm.
Experimental and Numerical Studies of the Thermal Hinge in a Notebook Computer
Authors: Jamal-Eddine Tarek , Mok Lawrence
Published: July 2013

The power of semiconductor chips, especially the CPU chip used in the notebook computer, is increasing nowadays while the size of the computer box is decreasing. To cope with this ever-increasing heat load within the notebook computer, many design engineers tend to use bigger heat sinks and fans. However, these approaches add weight, acoustic noise, and power consumption to the computer, none of which is desirable. A method of transferring heat from a CPU chip to the backside of the liquid-crystal display (LCD) and letting heat dissipate into the surroundings has been explored before. This is sometimes called the thermal hinge method since heat is transferred across the hinge of a notebook computer. In this paper, the structure of a new thermal hinge and its thermal performance will be revealed. This new thermal hinge has two main parts: one is the base, which is stationary and which has a heat pipe connected to a metal plate on top of a CPU chip, and the other is the rotational part, which is mounted on the LCD cover with a heat pipe connected to a heat spreader. The base is supported by a set of springs to ensure that the base is always in good thermal contact with the rotational part of the hinge. This spring-loaded thermal hinge using an aluminum heat spreader on a plastic LCD cover was built and tested and the results were compared with a numerical model that was constructed using a commercially available CFD code. The results from the experiments and numerical modeling agree reasonably well. Because of this, the numerical model has been used to optimize the hinge structure. The effects of the size, thickness, and materials of the heat spreader as well as the materials of the LCD cover on the hinge thermal performance have been studied and will be discussed.
Optimum Airflow Management for Multi-Board Rack-Mount Equipment
Authors: Puranik Bhalchandra , Shabany Younes
Published: July 2013

The airflow management for multi-board rack-mount equipment has to meet certain requirements including a minimum air velocity over the boards, uniform air velocity from board to board and from front to rear, and fan redundancy. These requirements have to be met within certain size, noise level and reliability constrains. Several configurations are usually considered: “push” or pressurized system, “pull” or vacuum system, and “push-pull” system. The purpose of this article is to demonstrate the airflow management design process for the three system configurations mentioned above, and to compare their optimum designs with each other given a set of geometrical constraints such as the overall dimensions of the equipment chassis, the card cage, and the type and thickness of the air filter. The design process is explained as a case study involving a typical multi-board rack mounted telecommunication chassis.
Analysis of Pumping Requirements for Microchannel Cooling Systems
Authors: Singhal Vishal , Liu Dong , Garimella Suresh V.
Published: July 2013

Large pressure drops, and the associated pumping requirements, are often considered the most critical factor hindering widespread commercial use of microchannel heat sinks. Analytical methods are used in the present work to arrive at the pumping requirements for any given microchannel heat sink. A graphical method to check the suitability of a pump to a microchannel heat sink application has been devised. The size of the microchannels is also optimized so that for a specified heat removal rate, the pumping requirements are minimized. A number of commercially available pumps as well as several micropumps presented in the literature are compared based on their flow rate, pressure head and physical size to assess their suitability for a specific representative cooling application.
Thermal Performance of a Thermo-Electric Base Thermal Control Unit Using Various Interface Materials
Authors: Hammoud Jihad Y.
Published: July 2013

Thermal interface materials are crucial to improving the overall performance of an active device and the design/selection of a thermal management system. In most practical thermal management protocols, interface materials are used to enhance heat transfer by reducing thermal resistance across contact surfaces. This improves surface contact by forming a continuous path of heat across an interface. This paper focuses on characterizing a thermal control unit (TCU) and employing the thermo-electric technology (TEC) in a liquid cooling system, using selected interface materials mounted on the TEC surfaces. Qualification tests performed on several common interface materials within the TCU are presented in this paper, with results compared to surface-to-surface contact. Tests included the measurement of minimum achievable device case temperature and the minimum TCU thermal resistance as a function of the net heat using selected interface materials. In addition, package minimum case temperature was measured as a function of pressure exhibited on the interface material to determine the TEC optimum contact pressure. Based on results, graphite base interface material was selected as an optimum interface material between TEC assembly and the TCU internal components.
Low Cycle Fatigue in RF Microwave Module Housings
Authors: Baughn Terry V. , Chen Shea
Published: July 2013

Hermetic housings are required for the vast majority of electronics used in RF microwave electronics to protect the gallium arsenide and silicon devices from the environment. A common housing style includes a metal ring frame that is brazed onto a metal or ceramic base. The housing is populated with electronic devices and circuits and then hermetically sealed with a thin metal lid. For high volume manufacturing, lids are often attached by a resistance weld using a seam seal process. The interior hermitic volume is sealed at or near one atmosphere internal pressure. Since the housing may be subjected to a substantial number of pressure cycles that can yield the lid material, a low cycle fatigue evaluation is required to establish the long-term reliability of the hermetic housing. Kovar is a common lid and housing material because of a good coefficient of thermal expansion match with glass, ceramic and other materials used in RF circuitry. Unfortunately only high cycle fatigue data is available for kovar. A method is proposed to generate an estimate of high cycle end of the low cycle fatigue response from the high cycle fatigue data. The proposed method is verified by comparing a predicted fatigue life with experimental results from hermetic housings subjected to pressure cycling.
A Hybrid Methodology for the Optimization of Data Center Room Layout
Authors: Guggari Shrishail , Agonafer Dereje , Belady Christian , Stahl Lennart
Published: July 2013

Today’s data centers are designed for handling heat densities of 1000W/m2 at the room level. Trends indicate that these heat densities will exceed 3000W/m2 in the near future. As a result, cooling of data centers has emerged as an area of increasing importance in electronics thermal management. With these high heat loads, data center layout and design cannot rely on intuitive design of air distribution and requires analytical tools to provide the necessary insight to the problem. These tools can also be used to optimize the layout of the room to improve energy efficiency in the data center. In this paper, first an under floor analysis is done to find an optimized layout based on flow distribution through perforated tiles, then a complete Computational Fluid Dynamics (CFD) model of the data center facility is done to check for desired cooling and air flow distribution throughout the room. A robust methodology is proposed which helps for fast, easy, efficient modeling and analysis of data center design. Results are displayed to provide some guidance on the layout and design of data center. The resulting design approach is very simple and well suited for the energy efficient design of complex data centers and server farms.
Package and Board Level Study for a Thin Small Outline Package (TSOP) Using Compact Components
Authors: Kulkarni Amit , Agonafer Dereje , Groothuis Steven , Kabir Humayun , Johnson Scott
Published: July 2013

A detail model of 54 lead Thin Small Outline Package (TSOP) was created in Flotherm and validated against experimental data for natural convection and forced convection environments. Next, a compact two-resistor (2R) model was created in Flotherm using compact smart parts. Values of junction-to-case and junction-to-board resistances were taken from experiments. Both the detailed model and the compact model were mounted on a 4-layered standard JEDEC board for natural convection in a standard JEDEC enclosure. With a nominal power of 0.75W applied at the junction, the detailed model and the 2R compact model showed a very good agreement. The results also compared well with experimental data. Next, two models were developed; a detailed model and a corresponding equivalent 2R compact model were mounted on a 4-layered standard JEDEC board and simulated for forced convection with an air velocity of 1 m/s. With a nominal power of 0.75 W applied at the junction, maximum junction temperatures were computed and once again showed very good agreement. Experimental data for forced convection indicated that the maximum junction temperature was in good agreement to the compact model. The study was further extended to do a board level analysis where the detailed TSOP models were mounted on a 6-layered standard DIMM board. In the single sided board arrangement nine such compact models were mounted on one side of the board and maximum junction temperature was noted. Then, the detailed models were replaced by compact models and simulated for forced convection with an air velocity of 1 m/s. Good agreement between detailed model and compact model was seen for the board level analysis. Further the compact models were simulated for a double-sided arrangement in which eighteen such compact models were mounted nine on each sided of the board. The assembly was simulated for forced convection with an air velocity of 1 m/s. Nominal power applied at junction for each of the eighteen modules was 0.3 W. Maximum temperature for the double sided arrangement of DIMM board was thus computed.
Techniques for Controlling Airflow Distribution in Raised-Floor Data Centers
Authors: Karki Kailash C. , Patankar Suhas V. , Radmehr Amir
Published: July 2013

In raised-floor data centers, the airflow rates through the perforated tiles must meet the cooling requirements of the computer servers placed next to the tiles. The data centers house a wide range of equipment, and the heat load pattern on the floor can be quite arbitrary and changes as the data center evolves. To achieve optimum utilization of the floor space and the flexibility for rearrangement and retrofitting, the designers and managers of data centers must be able to modify the airflow rates through the perforated tiles. The airflow rates through the perforated tiles are governed primarily by the pressure distribution under the raised floor. Thus, the key to modifying the flow rates is to influence the flow field in the plenum. This paper discusses a number of techniques that can be used for controlling airflow distribution. These techniques involve changing the plenum height and open area of perforated tiles, and installing thin (solid and perforated) partitions in the plenum. A number of case studies, using a mathematical model, are presented to demonstrate the effectiveness of these techniques.
The Effectiveness of Solar Shield for Outdoor Equipment
Authors: Berhe Mulugeta K. , Shabany Younes
Published: July 2013

The effect of solar shield on the maximum temperature of an active plate was investigated. The focus of this analysis was to determine conditions under which it was advantageous to have a solar shield around a heated plate. Heat transfer correlations for free convection around a vertical plate were used with some corrections for channel flow effects. Results obtained from these correlations were validated using CFD simulations. The results presented in this paper include the effects of some key parameters on the maximum temperature of the active plate, including the effects of heat fluxes from the active plate and solar shield, surface emissivity and sky temperature. The results suggest that there is a limit on the ratio of heat flux from the active plate to the solar heat flux beyond which it is not advantageous to have a solar shield. The results also show that the advantage of having a solar shield diminishes as the effective sky temperature decreases. Furthermore, the emissivity is an important factor and its value can determine whether a solar shield is necessary or not.
Pool Boiling of Water and FC-72 on Copper and Graphite Foams
Authors: Moghaddam Saeed , Ohadi Michael , Qi Jianwei
Published: July 2013

Pool boiling heat transfer of water and FC-72 on thin blocks, 3 mm, of metal and mesophase graphite foams bonded on a high flux heat source is studied experimentally. Two blocks of 80 ppi (90% porosity) and 30 ppi (95% porosity) copper foams, and a block of graphite foam (75% porosity) were tested. Experimental results on foam structures are compared with those of plain surface. Significant enhancement was achieved in boiling of water on the 30 ppi copper foam, while no enhancement was observed on the 80 ppi copper and the graphite foams. In the case of FC-72 boiling, however, a substantial enhancement was achieved on all foams. Results of the experiment and enhancement in different boiling regimes are discussed.
High Heat Flux Liquid-Cooled Porous Metal Heat Sink
Authors: North Mark T. , Cho Wei-Lin
Published: July 2013

An advanced heat sinking technology is described in which heat is dissipated by flowing the liquid coolant through a matrix of well-bonded metallic particles. This porous metal heat sink has the capability to dissipate heat flux of 500W/cm2 or more with a unit area thermal resistance of 0.1°C·cm2/W. The construction of one incarnation of this class of heat sink developed for cooling of a high-power stack of laser diode arrays is described. Tradeoffs between pressure drop and thermal resistance are identified with regard to particle size and other geometric parameters. The patented manifolding geometry allows the cooling area to be scaled up without significantly increasing the overall pressure drop. Experimental data showing thermal resistance and pressure drop at a variety of different water flow rates is also presented. Applications for this technology can include cooling of laser diode arrays and high power electronic components such as CPUs.
Thermal Simulation for Outdoor Optical Network Unit
Authors: Yu Z. Zack , Sahan Ridvan Amir , Sun X. Howard
Published: July 2013

An Optical Network Unit (ONU) used in Fiber-to-the-Curb (FTTC) system is one of the last mile equipment in telecommunications industry. The ONU usually operates in an outdoor environment like many other telecommunications cabinets. The ONU, in this study, is placed inside a CAT12 pedestal. The pedestal provides the housing for the termination block, the cable harness, the gas tube protection, etc. besides the ONU. Due to the proximity to residential areas and the reliability requirement for the operation, most of ONUs uses the passive cooling instead of the active cooling. It is very critical to ensure that all electronics including the optics operate within their thermal specifications. From the thermal perspective, most of the outdoor equipment for telecommunications industry follows the guidelines of GR-487-CORE, Issue 2. The CFD model analysis as well as engineering mockup tests provide the effective tools to meet the thermal requirements in this study. With the baseline model working, it is found that it would be very efficient to predict the thermal trends in different design conditions performing CFD simulations using readily available analysis tool Icepak.
Entrance and Exit Losses for Developing Flow in Plain Fin Heat Sinks
Authors: Webb Ralph L. , Paek Jin Wook
Published: July 2013

Prediction of pressure drop for duct flow through heat sinks involves calculation of inlet and exit losses. These predictions are typically done using Kc and Ke for “parallel plate channels” from the Kays and London book, Compact Heat Exchangers. However, these equations assume fully developed flow at the exit and thus include the effect of full velocity profile development. Electronic heat sinks operate in the “developing flow” region. So, use of the published Kc and Ke from the Kays and London book will result in over-estimate of the actual Kc and Ke values. The authors have performed analysis that allows accurate calculation of Kc and Ke values with parallel plate channels for operation in the “developing flow” region. The results are presented in graphical form as a function of contraction ratio and x+ (= x/DhRe). These results will allow accurate estimate of Kc and Ke values for developing flow. Entrance and exit losses can account for as much as 30% of the total pressure drop in electronic heat sinks having short flow lengths. However, the error associated with evaluation of Kc and Ke based on fully developed flow for parallel plates is small.
Nanoparticle-Assisted High Efficient Polymerase Chain Reaction
Authors: Lin Yu-Cheng , Wu Hua-Lin
Published: July 2013

This paper reports that the Au nanoparticles could dramatically enhance efficiency of polymer chain reaction (PCR) and shorten reaction time. The excellent energy transfer property of the nanoparticles should be the major factor in improving the PCR efficiency. With the addition of 0.7 nM of 13 nm Au nanoparticles into the PCR reagent, the PCR efficiency was increased. The results demonstrated that Au nanoparticles increase the sensitivity of PCR detection 5–10 fold in a slower PCR system (i.e. conventional PCR) and at least 104 fold in a quicker PCR system (i.e. real-time PCR). This innovation could improve the PCR efficiency using non-expensive polymerases, and general PCR reagent.
Benchmark Computations on a Typical Transition Weld of a PWR in Operation
Authors: Bate Steve , Bhandari Surender
Published: July 2013

This paper will present the Synthesis of analyses undertaken in a project of the European Commission EC/DG Environment within the framework of its Codes and Standards activities, entitled: “Evaluation of Fracture Toughness and Fatigue Crack Growth for Transition Welds at Non-Creep Temperatures”. The project deals with two distinct technical parts: Part 1: dealing with collection and review of the Fracture Toughness and Fatigue Crack Growth data on the materials constituting the Transition Welds, Part 2: dealing with Benchmark Calculations on a typical Transition Weld chosen from a real PWR plant. This paper deals with part 2 only and presents the synthesis of the combined effort of a number of participants from different countries who worked on a common problem specification of analysis. The participants were from AEA Technology, Belgatom, EDF, Framatome, Minatom, Siemens and Technatom. The report presents a comprehensive summary of work from each organisation, the key points and recommendations.