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The 90th Anniversary of the Fluids Engineering Division (FED) of ASME will he celebrated on July 10-14, 2016 in Washington, DC. The venue is ASME’s Summer Heat Transfer Conference (SHTC), Fluids Engineering Division Summer Meeting (FEDSM), and International Conference on Nanochannels and Microchannels (1CNMM). The occasion is an opportune time to celebrate and reflect on the origin of FED and its predecessor—the Hydraulic Division (HYD), which existed from 1926-1963. Therefore, the FED Executive Committee decided that it would be appropriate to publish concurrently a history of the HYD/FED. Accordingly, they commissioned Paul Cooper, C. Samuel Martin, and Timothy O’ Hern to prepare this paper, which would document the division’s past. A brief work in this direction had appeared in the 2010 FED Newsletter (Morgan, W. B., 2010, Brief History of ASME’s HydrauliclFluids Engineering Division, Fluids Engineering Division Newsletter, New York, pp. 6-7), and the research by Martin for the present paper had been under way for several years prior to that (Cooper, P., 2010, “Histoiy of the FED," FED Executive Committee at the ASME-CSME Fluids Engineering Summer Conference (FEDSM-2010), Montreal, OC, Canada, Aug., p. 14). [ABSTRACT FROM AUTHOR]

A TOBI (tangential on board injection), or preswirl, system is a critical component of a high pressure turbine cooling delivery system. Its efficient performance and characterization are critical because the blade and disk life depend on the accuracy of delivering the required flow at the correct temperature and pressure. This paper presents a TOBI flow discharge coefficient validation process applied to a low radius radial configuration starting from a 1 dimensional (1D ) network flow analysis to a 3 dimensional ( 3 D ) frozen rotor computational fluid dynamics (CFD) analysis of the rotor cooling air delivery system. The analysis domain commences in the combustor plenum stationary reference frame, includes the TOBI, transitions to the rotating reference frame as the flow travels through the rotating cover plate orifice, continues up the turbine disk into the slot bottom blade feed cavity, and terminates in the turbine blade. The present effort includes matching a 1D network model with 3D CFD results using simultaneous goal-matching of the pressure predictions throughout the circuit, defining test rig pressure measurements at critical "nondisturbing" locations for quanification of pressure ratio across the TOBI, and finally comparing the TOB1 flow coefficient resulting from stationary cold flow tests with what was obtained from the 3D CFD results. An analysis of the results indicates that the discharge coefficient varies with the pressure ratio and that the traditional method of using a constant discharge coefficient extracted from a cold flow test run under choked conditions leads to overpredicting turbine cooling flows. The TOBI flow coefficient prediction for the present study compares well with the stationary data published by other researchers for the configuration under investigation and the process described in this paper is general for any TOBI configuration [ABSTRACT FROM AUTHOR]

Accurately predicting both average flow quantities and acoustic sources ati the front window of today's ground vehicles are still a considerable challenge to automotive companies worldwide. One of the most important aspects in terms of obtaining not only trus!worthy results but also the most tedious one and therefore perhaps overlooked, is the control and outcome of the mesh generation process. Generating unstructured volume meshes suitable for large eddy simulations with high level representation of geometrical details is both a time consuming and an extremely computer demanding activity. This work investigates two different mesh generation processes with its main aim to evaluate their outcome with respect to the prediction of the two dominating dipole sources in a temporal form of the CurIe `s equation. Only a handful of papers exists that report a high level representation of the vehicle geometry and the aim of predicting the fluctuating exterior noise sources. To the author's knowledge no studies have been conducted in which both these source tenns are evaluated quantitatively against measurements. The current paper investigates the degree to which the amplitude of these two source terms can be predicted by using the traditional law–of–the–wall and hex–dominant meshes with isotropic resolution boxes for a detailed ground vehicle geometry. For this purpose, the unstructured segregated commercial FLUENT finite volume method code is used. The flow field is treated as incompressible and the Smagorinsky–Lilly model is used to compute the subgrid stresses. Mean flow quantities are measured with a 14 hole probe for 14 rakes downstream of the side mirror The dynamic pressure sensors are distributed at 16 different positions over the side window to capture the fluctuating pressure signals. All measurements in this work were conducted at Ford's acoustic wind tunnel in Cologne. All three simulations accurately predict the velocity magnitude closest to the window and downstream of the mirror head recirculation zone. Some variations in the size and shape of this recirculation zone are found between the different meshes, most probably caused by differences in the detachment of the mirror head boundary layer. The Strouhal number of the shortest simulation was computed from the fundamentalfrequency of the drag force coefficient. The computed Strouhal number agrees well with the corresponding results from similar objects and gives an indication of an acceptable simulation time. The dynamic pressure sensors at 16 different locations at the vehicle side window were also used to capture the levels of the two dipole source terms. These results are compared with the three simulations. With the exception of three positions, at least one of the three simulations accurately captures the levels of both source terms up to about 1000 Hz. The three positions with less agreement as compared with measurements were found to be in regions sensitive to small changes in the local flow direction. [ABSTRACT FROM AUTHOR]

This paper describes optimality principles for the design of an engineering bifurcating-tube tree consisting of the convection and diffusion zones to attain the most effective gas transport. An optimality principle is formulated for the diffusion zone to maximize the total diffusion mass-transfer rate of gas across tube walls under a constant total-volume constraint. This optimality principle produces a new diameter distribution for the diffusion zone in contrast to the classical distribution for the convection zone. In addition, this paper gives a length distribution for an engineering tree based on an optimality principle for minimizing the total weight of the tree under constraints of a finite surface and elastic criteria for structural stability. Furthermore, the optimum branching angles are evaluated based on local optimality principles for a single bifurcating-tube branch. [ABSTRACT FROM AUTHOR]

Fillet weld joint is widely used in engineering structures, but a lot of failures have been generated in the fillet joint affected greatly by weld residual stress, and it is very important to decrease the residual stress. Therefore, this paper proposes a new method using overlay welding and cutting (OWC) to reduce the residual stress in the fillet weld. First, the overlay welding is applied on the root surface of fillet weld, and then the overlaid metal is removed again by cutting. In order to verify this method, a thermal-elasto-plastic analysis method, using finite-element analysis (FEA) techniques, is developed to evaluate the residual stress change during the process of OWC. The impact indention measurement is also used to measure the surface residual stress. The results of FEA were compared with experimental data to confirm the accuracy of the developed finite-element method (FEM). In order to provide a guideline for design, the dimension effects including overlay weld width and height on residual stress have been investigated. It finds that OWC can decrease 25-40% of the as-weld residual stress, and increasing the overlay width and height is helpful to decrease the residual stress, which provides a reference for the reduction of residual stress in the fillet weld. [ABSTRACT FROM AUTHOR]

The linear matching method (LMM), a direct numerical method for determining shakedown and ratchet limits of components, has seen significant development in recent years. Previous verifications of these developments against cyclic nonlinear finite element analysis (FEA) have shown favorable results, and now this verification process is being extended to include comparisons with experimental results. This paper presents a comparison of LMM analysis with experimental tests for limit loads and shakedown limits available in the literature. The limit load and shakedown limits were determined for pipe intersections and nozzle-sphere intersections, respectively, thus testing the accuracy of the LMM when analyzing real plant components. Details of the component geometries, materials and test procedures used in the experiments are given. Following this a description of the LMM analysis is given which includes a description of how these features have been interpreted for numerical analysis. A comparison of the results shows that the LMM is capable of predicting accurate yet conservative limit loads and shakedown limits. [ABSTRACT FROM AUTHOR]

In order to study the mechanical properties of defect-free thin walled elbows (TWE), and evaluate impacts of the intermediate principal stress effect, tension/compression ratio, and strain-hardening of materials into logical consideration, this research, in the framework of finite deformation theory, derived the computational formula of burst pressure for defect-free TWE according to unified strength theory (UST). In addition, influences of various factors on burst pressure were analyzed, which include strength disparity (SD) effect of materials, intermediate principal stress, curvature influence coefficient, strain-hardening exponent, yield to tensile (Y/T) and thickness/radius ratio. The results show that the greater the tension/compression ratio is, the higher the burst pressure is. The influence of the SD effect of materials is more obvious with the increase of elbow curvature and intermediate principal stress. The intermediate principal stress effect can bring the self-bearing capacities and strength potential of materials into a full play, which can achieve certain economic benefits for projects. Moreover, the burst pressure of defect-free TWE increases with the growth of yield ratio and thickness/radius ratio, while decreases with the rise of curvature influence coefficient and strain-hardening exponent. It is also concluded that the Tresca-based and Mohr-Coulomb-based solutions of TWE are the lower bounds of the burst pressure, the twin shear stress (TSS)-based solution is the upper bound of the burst pressure, and the solutions based on the other yield criteria are between the above two. The unified solution in this paper is suitable for all kinds of isotropous materials which have the SD effect and intermediate principal stress effect. As the deduced formula has unified various burst pressure expressions proposed on the basis of different yield criteria for elbows of any curvature (including straight pipelines), and has established the quantitative relationships among them, its applicability is broader. Therefore, the unified solution is of great significance in security design and integrity assessment of defect-free TWE. [ABSTRACT FROM AUTHOR]

In this paper, the mixing enhancement of a micromixer consisting of a step channel and a shuttlecock rotor suspended in the step is numerically analyzed. Asymptotic mixing performance is investigated as a function of Strouhal and Peclet numbers by particle tracking simulation and the Eulerian approach. The simulation results show that the rotor creates downward and inward flows in behind the rotor paddles, whereas the upward and outward flows are produced in front of the rotor paddles. At a small Strouhal number, convective mixing is very poor. However, the mixing direction is rotated by 90 deg, which can reduce the mixing time by the square of the aspect ratio of the cross section of the channel. In contrast, at a relatively large Strouhal number, good convective mixing occurs. Quantitative analysis of mixing performance of the mixer demonstrates that the mixing structures are similar for the same Strouhal number and mixing is improved with increasing Strouhal number. The mixing efficiency of the mixer decreases linearly with increasing log of the Peclet number at a relatively large Strouhal number. [ABSTRACT FROM AUTHOR]

In this paper; we present experimental test data for the validation of a recently introduced mathematical model for centrifugal compression systems with variable impeller axial clearances. Employing the active magnetic bearings (AMBs) of a compressor built for the experimental study of surge, the axial clearance between the impeller and the static shroud is servo controlled, and the mneasu red variations in the compressor output flow are compared with the mathematical model. The steady state and the dynamnic responses of the compression system induced by varying the impeller tip clearance are measured and compared with the theoretical predictions, and the stares of the compression system in surge condition are collected and analyzed. Parameters in the compression system model, such as the Greitzer parameter B and Helmholtz frequency ωH are experimentally identified. Also, ihe servo dynamics of the magnetic bearing that controls the axial impeller position is determined experimentally. To further validate the mathematical model and the feasibility of using the impeller tip clearance for controlling surge, we present a design example for an active surge controller based on the derived model, and simulate the response of the compression system. This design exercise also helps us understand the possible challenges that one could face in the design and implementation of a successful surge controller. [ABSTRACT FROM AUTHOR]

A study. of controlling dynamical systems with uncertain and varying time delays is presented in this paper The uncertain time delay is assumed to fall in a range with known upper and lower bounds. We apply the supervisory control algorithm to deal with uncertainties in the time delay. An index is defined for each of the predetermined controls for a discrete set of time delays sampled from the range. Based on this index, a hysteretic switching rule selects a control from the predetermined controls with optimal feedback gains. Each predetermined control must be stable for any time delay in the range. Two control design methods are discussed, namely, the mapping method and a higher order approach. Examples of linear systems are used to demonstrate the theoretical work. [ABSTRACT FROM AUTHOR]

Large eddy simulation (LES) is employed in this paper to model the axial flow along a circular array of rods with a focus on anisotropic large-scale turbulence. The circular array consists of four whole rods and eight half rods, with a pitch-to-diameter ratio of 1.08. A dynamic Smagorinsky model with SIMPLE coupling method and a bounded central difference scheme are used to reduce numerical errors. The high demands for computations of the three-dimensional turbulent flows are afforded through parallel processing and utilization of 20 processors. The numerical results obtained using LES are compared with independent experimental data available in the literature; good agreement is achieved. The LES model was developed to accurately predict (i) the dependence of turbulence intensity and dominant frequency on the gap size and (ii) the turbulence structure in different directions. [ABSTRACT FROM AUTHOR]

Journal bearings are widely used for supporting high-speed rotating machinery, such as turbine, compressor, and HDD spindle, because of their high load carrying capacity, stability, and durability. Recently, the engineering trend is oriented to higher speed and smaller sizes of rotating machinery, and then it is important to enhance stabilities for the small-bore journal bearings. Tilting pad journal bearing is generally used for high-speed rotating machineries because of their advantages of stabilization. However, there are some problems using compact size rotating machineries for their high manufacturing cost and complicated structure. Therefore, it is necessary to enhance the stability of more simple bearings compared with tilting pad bearing in order to use for small-size rotating machinery. This paper describes the stabilization method of the small-bore journal bearing based on the combination mechanism with starved lubrication and orientation angle change. It is found that the stabilization of small-bore journal bearings is improved drastically by hybrid lubrication combining these two kinds of mechanism. [ABSTRACT FROM AUTHOR]

Manufacturing process routes of materials can be adapted to manipulate their microstructure and hence their tribological performance. As industrial demands push the applications of tribological materials to harsher environments of higher stress, starved lubrication, and improved life performance, manufacturing processes can be tailored to optimize their use in particular engineering applications. The aim of this paper was therefore to comprehend the structure:property relationships of a wear resistant cobalt-based alloy (Stellite 6) produced from two different processing routes of powder consolidated hot isostatic pressing (HIPing) and casting. This alloy had a nominal wt % composition of Co-28Cr-4.5W-1C, which is commonly used in wear related applications in harsh tribological environments. However, the coarse carbide structure of the cast alloy results in higher brittleness and lower toughness. Hence this research was conducted to comprehend if carbide refinement, caused by changing the processing route to HlPing, could improve the tribomechanical performance of this alloy. Microstructural and tribomechanical evaluations, which involved hardness, impact toughness, abrasive wear, sliding wear, and contact fatigue performance tests', indicated that despite the similar abrasive and sliding wear resistance of both alloys, the HIPed alloy exhibited an improved contact fatigue and impact toughness performance in comparison to the cast counterpart. This difference in behavior is discussed in terms of the structure-property relationships. Results of this research indicated that the HlPing process could provide additional impact and fatigue resistance to this alloy without compromising the hardness and the abrasive/sliding wear resistance, which makes the HIPed alloy suitable for relatively higher stress applications. Results are also compared with a previously reported investigation of the Stellite 20 alloy, which had a much higher carbide content in comparison to the Stellite 6 alloy, caused by the variation in the content of alloying elements. These results indicated that the fatigue resistance did not follow the expected trend of the improvement in impact toughness. In terms of the design process, the combination of hardness, toughness, and carbide content show a complex interdependency, where a 40% reduction in the average hardness and 60% reduction in carbide content had a more dominating effect on the contact fatigue resistance when compared with an order of magnitude improvement in the impact toughness of the HIPed Stellite 6 alloy. [ABSTRACT FROM AUTHOR]

This paper discusses the phenomena of flow-acoustic coupling between an unstable shear layer across a slot covering a cavity, thereby forming a Helmholtz resonator The flow was caused by a turbulent boundary layer flowing over the slot. The physical phenomena implicated were responsible for the generation of high-amplitude sound level that occurred at the resonant frequencies of the system. it concerns a wide variety of applications, especially in the transport industry. Cavity oscillations have been studied steadily for some 50 years and there is by now a vast and conflicting literature on the measured tonal frequencies, the physical explanations, and the predictive models for them. A theory was presented to predict the onset of the instability. it was based on the identification of the main parameters that played a role in the shear layer Particularly it was suggested to use the frequency dependent phase velocity instead of the flow velocity. The theory was then confronted with results obtained from an experimental study carried out in a wind tunnel on several models. This validation underlined the sturdiness and the efficiency of the model, which made it useful for engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation conducted to evaluate the effect of initial tube-tubesheet diametral clearance on the integrity of roller-expanded tube-to-tubesheet joints in overenlarged tubesheet holes. The criteria of evaluating joint integrity include the pullout force and hydraulic tightness of the joints in which tubes were expanded to 5% wall reduction after metal to metal contact of the tube with the tubesheet hole. The levels of clearance investigated were selected to cover a range that exceeded by ten times that prescribed by the Tubular Exchangers Manufacturers Association (TEMA) standards (Standards for the Tubular Exchanger Manufacturers Association, 1988, 7th ed., TEMA, Tarrytown, NY). The pullout test results showed that, within the investigated range of clearance, the joint strength has not declined below the strength of joints with clearance levels within the TEMA range, In fact, the pullout force exhibited a slight linear increasing trend with the increase in initial clearance, which is attributed to the effect of tube strain hardening. The hydrotest results indicated that all joints within the investigated clearance levels were hydraulicidly tight when they were tested at 1.5 times the design pressure of the heat exchanger for a duration of 30 min. A relationship between rolling specific energy and initial joint clearance has been developed. [ABSTRACT FROM AUTHOR]

Seven burner/furnace systems, three of which vibrated and four of which did not vibrate in operation are evaluated for thermoacoustic oscillations. The evaluation is based on the Rijke and Sondhauss models representing the combined burner/furnace (cold/hot) thermoacoustic systems. Frequency differences between the lowest vulnerable furnace acoustic frequencies in the burner axial direction and those of the systems' Rijke and Sondhauss frequencies are evaluated to check for resonances. Most importantly, the stability of the Rijke and Sondhauss models is checked against the published design stability diagram of Eisinger (1999, "Eliminating Thermoacoustic Oscillations in Heat Exchanger and Steam Generator Systems," ASME J. Pressure Vessel Technol., 121, pp. 444-452) and Eisinger and Sullivan (2002, "Avoiding Thermoacoustic Vibration in Burner/Furnace Systems," ASME J. Pressure Vessel Technol., 124, pp. 418-424). It is shown that thero moacoustic oscillation can be well predicted by the published design stability diagram with the vibrating cases falling into the unstable zone above the stability line and the nonvibrating cases congregating in the stable zone below the stability line. The evaluation suggests that the primary criterion for predicting thermoacoustic oscillations is the stability of the thermoacoustic system and that frequency differences or resonances appear to play only a secondary role. It is concluded, however, that in conjunction with stability, the primary criterion, sufficient frequency separation shall also be maintained in the design process to preclude resonances. The paper provides sufficient details to aid the designers. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to demonstrate that the burst pressure of a cylindrical shell subjected to internal pressure can be accurately predicted by using finite element method. The computer software ANSYS (Swanson Analysis System Inc., 2003, "Engineering Analysis Systems User's Manual") is employed to perform a static, nonlinear analysis (both geometry of deformation and material behavior) using three-dimensional 20 node structural solid elements. The "Newton-Raphson method" and the "arclength method" are both employed to solve the nonlinear equations. A comparison with various empirical equations shows that the static finite element method simulation using the arclength method can be employed with sufficient accuracy to predict the burst pressure of a cylindrical shell. It is also shown that the Barlow equation is a good predictor of burst pressure of cylindrical shells. [ABSTRACT FROM AUTHOR]

Based on basic equations of steady-state creep of spherically symmetric problems, a simple and efficient iterative method is proposed in this paper to determine creep deformations and stresses in thick-walled spherical vessels with varying creep properties subjected to internal pressure. The convergence of the proposed iterative method and the influences of varying and constant material properties on stresses and equivalent strain rate are discussed. How different material parameters involved in Norton's law affect radial and circumferential stresses together with the equivalent strain rate in thick-walled spherical vessels under internal pressure is investigated. [ABSTRACT FROM AUTHOR]

The angled crack problem has been given special attention in the recent years by fracture mechanics investigators due to its close proximity to realistic conditions in engineering structures. In the present paper, an investigation of fatigue crack initiation and propagation in line pipes containing an inclined surface crack is presented. The inclined angle of the surface crack with respect to the axis of loading varies between 0 deg and 90 deg. Based on the concept of the effective stress intensity factor range Δkeff, the rate of fatigue crack propagation db/dN is postulated to be a function of the effective strain energy density factor range ΔSeff. This concept is applied to predict the crack growth due to fatigue loading. Furthermore, the threshold condition for nongrowth of the initial crack was established and assessed based on the experimental data. [ABSTRACT FROM AUTHOR]

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly, in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a program of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks and a global value (i.e., the overall crack contours)for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. (1991, "Leakage Flow Through Small Cracks--Report of Second Stage of Experimental Work," unpublished) gives .better agreement with measured flow rates than that due to Button et al. (1978, "Gas Flow Through Cracks," ASME J. Fluids Eng., 100, pp. 453-458), which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified. [ABSTRACT FROM AUTHOR]

Assessment of the local thin area should be undertaken for both tension and compression bending. In this paper, simplified reference stresses for a flaw in a cylinder are proposed. By using these results, a newly developed p-M (internal pressure ratio and external bending moment ratio) diagram which can evaluate the collapse condition for pressure equipment such as vessels, piping, and storage tanks with a local thin area simultaneously subjected to internal pressure p and external bending moment M due to earthquake, etc., is proposed. The p-M line is verified by comparison with the finite element analysis results and the numerous results of experiment for a cylinder with a volumetric flaw obtained through the reference literatures. It was clarified that the differences in collapse limit between the p-M line and DNV guideline under both internal pressure and compression moment became evident where the outer diameter/wall thickness of a cylinder is large and the yield ratio of the material is small. [ABSTRACT FROM AUTHOR]

This paper presents various approaches for finite element modeling of a cylindrical lightweight composite vessel for blast containment purposes. The vessel has a steel liner that is internally reinforced with throttle and gusset steel plates and wrapped with a basalt fiber/epoxy composite. The vessel design is fairly complex, including many geometric details and several components with different material models. The objective of this work is to determine an accurate and efficient procedure for modeling this type of vessels. This model can be used within an iterative optimization process. Different modeling approaches using various combinations of element types, material models, and geometric details are explored. Results of these models are compared to available experimental data. Accuracy and computational time between all these models are also compared. A suitable modeling method is recommended based on these findings. [ABSTRACT FROM AUTHOR]

This paper focuses on the usage of direct route for design by analysis, which is included in the new European standard for unfired pressure vessels (CEN, 2002, "Unfired Pressure Vessels-Part 3: Design," European Committee for Standardization No. EN 13445-3, Current Issue 14-2005). The direct route addresses failure modes directly, having, therefore, advantages in comparison to the traditional method, which is stress categorization. Special attention is given to the progressive plastic deformation design check (PD-DC) with space and time-dependent temperature distribution and the fatigue design check (F-DC) with stress components, which do not vary simultaneously. As a simple demonstration example, a nozzle with cold media injection is used to show how the direct route can be applied in such cases. This example is analyzed with abruptly changing injection temperature, which makes a transient thermal analysis necessary. In the case of the PD-DC, Melan's shakedown theorem and cycling of a finite element model with a linear-elastic ideal-plastic material model are used. In the case of the F-DC, some problems are discussed: One of them is cycle counting in the case of nonproportional loading, and the other one is the use of structural stresses and stress concentration factors. [ABSTRACT FROM AUTHOR]

The disturbed state concept (DSC) with the hierarchical single surface (HISS) plasticity model have been proposed and validated previously for a wide range of problems in electronic packaging. In this paper, detailed analyses are performed with the DSC/HISS model to study the effect of various factors, such as computational and geometrical aspects and material parameters, on the failure life of chip substrate systems. The results and the methodology can be used for parametric analyses and optimal design of problems in electronic packaging. [ABSTRACT FROM AUTHOR]

Light emitting diodes (LEDs) historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors has allowed them to penetrate specialty and general illumination applications. The increased electrical currents used to drive the LEDs have resulted in higher heat fluxes than those for average silicon integrated circuits (i.e., 1Cs). This has created a need to focus more attention on the thermal management engineering of LED power packages. The output of a typical commercial high brightness, 1 mm², LED has exceeded 100 tm at drive levels approaching 3 W. This corresponds to a heat flux of up to 300 W/cm². Novel thermal solutions need to address system architectures, packaging, phosphors for light color conversion, and encapsulants and fillers for optical extraction. In this paper, the effect of thermal management on packaging architectures, phosphors, encapsulants, and system design are discussed. Additionally, discussions of microscopic defects due to packaging problems as well as chip active layer defects are presented through experimental and computational findings. [ABSTRACT FROM AUTHOR]

The popularity and increased usage of insulated gate bipolar transistors (IGBTs) in power control systems have made the problem of cooling them a subject of considerable interest in recent years. In this investigation, a heat flux of 825 W/cm² at the die was achieved when air-water spray cooling was used to cool IGBTs at high current levels. The junction temperature of the device was measured accurately through voltage-to-temperature characterization. Results from other cooling technologies and other spray cooling experiments were reviewed. A discussion of electrical power losses in IGBTs, clue to switching and conduction, is included in this paper. Experiments were conducted on 19 IGBTs, using data collection and software control of the test set. Three types of cooling were explored in this investigation: single-phase convection with water, spray cooling with air-water and spray cooling with steam-water. The results of these experiments show clear advantages of air-water spray cooling IGBTs over other cooling technologies. The applications of spray cooling IGBTs are discussed in open (fixed) and closed (mobile) systems. Current and heat flux levels achieved during this investigation could not have been done using ordinary cooling methods. The techniques used in this investigation clearly demonstrate the superior cooling performance of air-water spray cooling over traditional cooling methods. [ABSTRACT FROM AUTHOR]

The problem of heat removal in energetic processes represents a big challenge especially because of the enhanced requirements of the modern industry. The thermal exchange systems therefore have to guarantee better performances in correspondence to ever more severe dimensional constraints. This paper shows a numerical approach, based on computational fluid dynamics (CFD) software, for the evaluation of the heat exchange performances of finned (straight fins) surfaces made of highly heat conductive material. The same geometric constraints assumed in a reference work were adopted. This research attempts to develop an easy-to-use method to face what was previously solved by the powerful approach of Bejan's Constructal theory. The results obtained show a good agreement between CFD and the Constructal theory's results, validating, therefore, the simplified approach proposed and encouraging its application to a broader variety of geometries. [ABSTRACT FROM AUTHOR]

Recent advances in compact thermal models have led to the emergence of a new concept allowing models to be created at any desired order of accuracy. Traditionally, increasing precision was attained by increasing the number of nodes. This strategy faces many problems; in particular, for the case of multiple heat sources (MCM) and/or stacked dies, because different operating conditions will lead to different temperature and heat flux profiles that will require different node partitioning in order to be matched. In fact, classical approaches face a difficulty in selecting appropriate node size and position, as well as the inability to provide an a priori estimate of the number of nodes needed. The new concept is based on the use of a flexible profile to account for different possible uses of the model. In particular, it can deal with different patterns of heat generation encountered in MCM and stacked dies, and hence it is truly boundary conditions independent. Moreover, the new approach gives access to the tangential temperature gradient. This valuable information for designers in order to assess reliability cannot be predicted by classical compact model approaches. The concept was presented earlier for a simple rectangular 2D structure with surface heating (2004, 10th THERMINIC Conference, pp. 273-280). In this paper, the concept will be generalized to 3D parallelepiped boxes with both surface and/or volumetric heating. The second achievement is the possibility to deal with geometries that can be decomposed into boxes. [ABSTRACT FROM AUTHOR]

The recent introduction and advancements in design of simple, constant-force mechanisms have created the potential for small-scale, low-cost, constant-force electronic connectors (CFECs). CFECs differ from traditional connectors by the separation or disassociation of contact normal force and contact deflection. By removing the traditional constraints imposed by forces and deflections that are dependent on each other, new types of electronic connectors can be explored. These new designs may lead to smaller and more reliable electronic connectors. In this paper, constant-force mechanisms are adapted to satisfy current industry practices for the design of electronic connectors. Different CFEC configurations are explored and one is selected, prototyped, and used as a proof-of-concept connector for a personal digital assistant (PDA) docking station. The modeling, optimization, and verification of the prototype CFEC is presented. Adaptation of constant-force technology to electronic connectors creates new possibilities in electronic connector designs, including allowing an optimal contact force to be utilized to decrease the effects of fretting and wear, lowering required manufacturing tolerances, reducing the system's sensitivity to variations introduced by the user, and increasing the system's robustness in applications where movement or vibrations exist. [ABSTRACT FROM AUTHOR]

The article discusses the different topics within the issue focusing on the theme of flow behavior and rheology of complex fluids with electric phenomena in the micro and nano scale. The papers presented during the symposium by the Fluids Engineering Division and the Materials Division in 2007. They include various topics in fluids engineering applications.

The article discusses papers published within this issue including one on modified equation analysis and another on simulations of extremely complex flows of interest in engineering.