bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimized Realization of Fault-Tolerant Heteropolar Magnetic Bearings
Authors: Na Uhn Joo , Palazzolo Alan
Published: July 2002

Flux coupling in heteropolar magnetic bearings permits remaining active coils to assume actions of failed coils to produce force resultants identical to the un-failed actuator. This fault-tolerant control usually reduces load capacity because the redistribution of the magnetic flux which compensates for the failed coils leads to premature saturation in the stator or journal. A distribution matrix of voltages which consists of a redefined biasing voltage vector and two control voltage vectors can be optimized in a manner that reduces the peak flux density. An elegant optimization method using the Lagrange multiplier is presented in this paper. The linearized control forces can be realized up to certain combination of 5 poles failed for the 8 pole magnetic bearing. Position stiffness and voltage stiffness are calculated for the fault-tolerant magnetic bearings. Simulations show that fault-tolerant control of the multiple poles failed magnetic bearings with a horizontal flexible rotor can be achieved with reduced load capacity. [S0739-3717(00)01103-X]
High-Temperature Oxidation Behavior of 214Cr-1Mo Steel in Air–Part 2: Scale Growth, Metal Loss Kinetics, and Stress Enhancement Factors During Creep Testing
Authors: Bueno Levi O. , Marino Luiz
Published: July 2002

The oxide-scale growth and metal loss kinetics during oxidation in air of 2 1/4 Cr-1 Mo steel were studied at 600, 700, and 800°C for times up to 1000 h, with cylindrical specimens similar to creep test pieces. The scale thickness (x) was observed to exhibit a gradually decreasing growth rate with the exposure time (t) according to approximated parabolic behavior of type x2=Koss˙t at the temperature levels of 700 and 800°C. The coefficient Kos exhibited Arrhenius-type temperature dependence with an activation energy value of 212 kJ/mol. At 600°C, parabolic behavior was not verified, and the scale thickness growth follows better a relation of type logx=A+Bs˙logt. The metal thickness (y) was observed to exhibit a gradually decreasing loss rate with the exposure time according to parabolic behavior of type y2=Kmls˙t at the three temperature levels. The coefficient Kml also exhibited Arrhenius-type dependence with an activation energy value of 215 kJ/mol. These two values of Q are close do the value for diffusion of iron on the chromium-rich internal oxide layer formed in the material. Based on the equations of metal loss kinetics, the variation of the cross-sectional area of the specimens with time could be determined and plots of stress enhancement factors developed to assess the effect of oxidation on creep testing results.
Thermal Model of an Absolute Solar Radiometer Designed for Future Satellite Missions
Authors: Shen, Y. J. , Chen, and D. H. , Zhang Z. M.
Published: July 2002

This paper describes a finite-element thermal model of an absolute radiometer designed for total solar irradiance (TSI) measurement in future satellite missions. The cavity-type absolute radiometer employs the electrical-substitution technique and active temperature control to determine the radiant power entering the receiving cavity. The nonequivalence between the shutter-open mode and shutter-closed mode due to different temperature distributions is a major factor that affects the radiometric accuracy. The analysis shows that the nonequivalence is a function of sensor positions and can be minimized by properly choosing the electrical heating method and the temperature sensor location.
The Analytical Imbalance Response of Jeffcott Rotor During Acceleration
Authors: Zhou Shiyu , Shi Jianjun
Published: July 2002

Since many rotor systems normally operate above their critical speeds, the problem of accelerating the machine through its critical speeds without excessive vibration draws increasing attention. This paper provides an analytical imbalance response of the Jeffcott rotor under constant acceleration. The response consists of three parts: transient vibration due to the initial condition of the rotor, “synchronous” vibration, and suddenly occurring vibration at the damped natural frequency. This solution provides physical insight to the vibration of the rotor during acceleration.
Simulations of Cavitating Flows Using Hybrid Unstructured Meshes
Authors: Ahuja Vineet , Hosangadi Ashvin , Arunajatesan Srinivasan
Published: July 2002

A new multi-phase model for low speed gas/liquid mixtures is presented; it does not require ad-hoc closure models for the variation of mixture density with pressure and yields thermodynamically correct acoustic propagation for multi-phase mixtures. The solution procedure has an interface-capturing scheme that incorporates an additional scalar transport equation for the gas void fraction. Cavitation is modeled via a finite rate source term that initiates phase change when liquid pressure drops below its saturation value. The numerical procedure has been implemented within a multi-element unstructured framework CRUNCH that permits the grid to be locally refined in the interface region. The solution technique incorporates a parallel, domain decomposition strategy for efficient 3D computations. Detailed results are presented for sheet cavitation over a cylindrical head form and a NACA 66 hydrofoil.
Simulation and Analysis of a Magnetoelastically Driven Micro-Pump
Authors: Beskok A. , Srinivasa A. R.
Published: July 2002

The operation of a micro-pump system driven by a magnetoelastic polymeric membrane developed at Texas A&M University is analyzed by numerical simulations. Unsteady, incompressible Navier-Stokes equations in a moving boundary system are solved by a spectral element methodology, employing an Arbitrary Lagrangian Eulerian (ALE) formulation on unstructured meshes. The performance of the micro-pump is evaluated as a function of the Reynolds number and the geometric parameters. The volumetric flowrate is shown to increase as a function of the Reynolds number. The system is simulated by assuming the deformation of the membrane. The required voltage and current are then calculated by a lumped parameter analysis.
Boundary Element Formulation for Thermal Stresses During Pulsed Laser Heating
Authors: Tehrani P. H. , Hector, L. G. , Hetnarski R. B. , Eslami M. R.
Published: July 2002

Pulsed lasers are used in a variety of materials processing applications that range from heating for metallurgical transformation to scribing vehicle identification numbers on anodized aluminum strips. These lasers are commonly configured to deliver a large quantity of heat energy in very short time intervals and over very small areas due to the manner in which radiant energy is stored within, and then released from, the laser resonator. At the present time, little is known about the effect of pulse duration on thermomechanical distortion during heating without phase change. To explore this issue, a boundary element method was developed to calculate temperature, displacement, and thermal stress fields in a layer that is rigidly bonded to an inert semi-space. The layer absorbs thermal energy from a repetitively pulsed laser in the plane of its free surface. The effects of two pulse durations, which differ by four-orders-of-magnitude, were examined in this work. The temporal profiles of ultrafast pulses of the order of ten picoseconds (such as those emitted by a mode-locked laser), and pulses of the order of tens-of-nanoseconds (such as those emitted by a Q-switched Nd:YAG laser) were mathematically modeled using a rectified sine function. The spatial profile of each pulse was shaped to approximate a Gaussian strip source. The equations of coupled thermoelasticity, wherein the speed of mechanical distortion due to material expansion during heat absorption is finite, but the speed of heat propagation within the layer is infinite, were solved for both pulse durations. The resulting temperature and stress fields were compared with those predicted in the limit of no thermomechanical coupling.
Integrated Experimental and Numerical Approach for Fuel-Air Mixing Prediction in a Heavy-Duty Gas Turbine LP Burner
Authors: Mori G. , Razore S. , Ubaldi M. , Zunino P.
Published: July 2002

An integrated experimental-numerical procedure has been developed for fuel-air mixing prediction in a heavy-duty gas turbine burner. Optical measurements of the degree of mixing have been performed in a full-scale test rig operating with cold flow. Experimental data have been utilized to validate a CFD RANS numerical model. In fact, it is recognized that the turbulence behavior of jets in swirling air-flow stream is not accurately described by standard k-ε turbulence models; therefore advanced turbulence models have been assessed by means of experimental data. The degree of mixing between simulated fuel and air streams has been evaluated at the burner exit section by means of a planar Mie scattering technique. The experimental apparatus consists of a pulsed Nd:YAG laser and a high resolution CCD video camera connected to a frame grabber. The acquired instantaneous images have been processed through specific procedures that also take into account the laser beam spatial nonuniformity. A second-order discretization scheme with a RSM turbulence model gives the best accordance with the experimental data. Such CFD model will be part of a more general method addressed to numerical prediction of turbulent combustion flames in LP technology.
Design and Validation of an Unconstrained Loading System to Measure the Envelope of Motion in the Rabbit Knee Joint
Authors: Milne Andrew D. , Giffin J. Robert , Chess David G. , Johnson James A. , King Graham J. W.
Published: July 2002

An unconstrained loading system was developed to measure the passive envelope of joint motion in an animal model commonly used to study ligament healing and joint arthritis. The design of the five-degree-of-freedom system allowed for unconstrained knee joint loading throughout flexion with repeated removal and reapplication of the device to a specimen. Seven New Zealand White rabbit knees were subjected to varus, valgus, internal and external loads, and the resulting envelopes of motion were recorded using an electromagnetic tracking device. Intra-specimen reproducibility was excellent when measured in one specimen, with maximal rotational differences of 0.6 and 0.3 deg between the fourth and fifth testing cycles for the varus (VR) and valgus (VL) envelopes, respectively. Similarly, the maximal internal (INT) and external (EXT) envelope differences were 0.5 and 0.4 deg, respectively, between the fourth and fifth cycles. Good inter-animal envelope reproducibility was also observed with consistent motion pathways for each loading condition. A maximal VR-VL laxity of 17.9±2.3 deg was recorded at 95 deg flexion for the seven knees tested. The maximal INT-EXT laxity of 75.2±4.8 deg occurred at 50 deg flexion. Studies on measurement reproducibility of re-applying individual testing components demonstrated a maximal error of 1.2 ± 0.7 deg. Serial removal and re-application (test–retest) of the complete measuring system to one cadaveric knee demonstrated maximal envelope differences of less than 0.7 deg for VR-VL rotation and 2.1 deg for INT-EXT rotation. Our results demonstrate that the measuring system is reproducible and capable of accurate evaluation of knee joint motion. Baseline in vitro data were generated on normal joint kinematics for future in-vivo studies with this system, evaluating ligament healing and disease progression in arthritis models.
An Experimental Study of Impingement on Roughened Airfoil Leading-Edge Walls With Film Holes
Authors: Taslim M. E. , Pan Y. , Spring S. D.
Published: July 2002

Airfoil leading-edge surfaces in state-of-the-art gas turbines, being exposed to very high gas temperatures, are often life-limiting locations and require complex cooling schemes for robust designs. A combination of convection and film cooling is used in conventional designs to maintain leading-edge metal temperatures at levels consistent with airfoil life requirements. Compatible with the external contour of the airfoil at the leading edge, the leading-edge cooling cavities often have complex cross-sectional shapes. Furthermore, to enhance the heat transfer coefficient in these cavities, they are often roughened on three walls with ribs of different geometries. The cooling flow for these geometries usually enters the cavity from the airfoil root and flows radially to the airfoil tip or, in the more advanced designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes in the wall separating the two cavities. In the latter case, the crossover jets impinge on a smooth leading-edge wall and exit through the showerhead film holes, gill film holes on the pressure and suction sides, and, in some cases, form a crossflow in the leading-edge cavity, which is ejected through the airfoil tip hole. The main objective of this investigation was to study the effects that film holes on the target surface have on the impingement heat transfer coefficient. Available data in the open literature are mostly for impingement on a flat smooth surface with no representation of the film holes. This investigation involved two new features used in airfoil leading-edge cooling, those being a curved and roughened target surface in conjunction with leading-edge row of film holes. Results of the crossover jets impinging on these leading-edge surface geometries with no film holes were reported by these authors previously. This paper reports experimental results of crossover jets impinging on those same geometries in the presence of film holes. The investigated surface geometries were smooth, roughened with large and small conical bumps as well as tapered radial ribs. A range of flow arrangements and jet Reynolds numbers were investigated, and the results were compared to those of the previous study where no film holes were present. It was concluded that the presence of leading-edge film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly. The smaller conical bump geometry in this investigation produced impingement heat transfer coefficients up to 35 percent higher than those of the smooth target surface. When the contribution of the increased area in the overall heat transfer is taken into consideration, this same geometry for all flow cases as well as jet impingement distances Z/djet provides an increase in the heat removal from the target surface by as much as 95 percent when compared with the smooth target surface.
Linear Instability Analysis of a Horizontal Two-Phase Flow in the Presence of Electrohydrodynamic Extraction Force
Authors: Feng Y. , Seyed-Yagoobi J.
Published: July 2002

The flow regimes associated with a horizontal internal two-phase (liquid-vapor) flow in the presence and absence of the electric field are investigated with the linear stability analysis. The momentum interchange due to the entrainment between the two phases is included in the analysis. The presence of the electric field promotes instability by providing the electrohydrodynamic (EHD) extraction force. Qualitative stability maps for the annular two-phase flow are provided with and without the electric field presence. Onset of the instability is compared with the experimental data and it is shown that the transition between the EHD-enhanced and EHD-suppressed convective boiling heat transfer is located near the annular-to-mist transition region.
Effect of Grain Boundaries on PLC Plastic Instabilities
Authors: Kova´cs Zs. , Fa´tay D. , Nyilas K. , Lendvai J.
Published: July 2002

The effect of single grain boundaries on the Portevin Le Cha^telier (PLC) effect was investigated by depth sensing Vickers indentation. The experiments were carried out in load control. Independently appearing PLC bands were observed in the plastic volume and they were attributed to the hindered dislocation motion through the grain boundary. The hardening effect of the grain boundary and the release of the piled-up dislocations were also observed. This transient effect is manifested in a dynamic over-shooting in the hardness decrease, which is the consequence of the PLC effect as it is reproduced also by a phenomenological numerical model.
Investigation of the Microstructural Evolution During Large Strain Cold Working of Metals by Means of Synchrotron Radiation—A Comparative Overview
Authors: Zehetbauer M. , Schafler E. , Unga´r T. , Kopacz I. , Bernstorff S.
Published: July 2002

Dislocation densities, arrangements and long range internal stresses in cold rolled polycrystalline Cu, Ni, and Al, as well as in cold torsioned Fe, were determined by X-ray diffraction profile analysis using synchrotron radiation. At different deformation degrees, scanning measurements across single grains with a focal spot of less than 50 μm were carried out, in order to inform on the features of the deformation induced substructure. At small deformations including stage III, the dislocation densities and internal stresses are uniform within single grains while at higher deformations in stages IV and V, the dislocation densities and long range internal stresses exhibit opposite fluctuations. In stage IV these fluctuations correspond to the formation of polarized tilt walls (PTW’s) from polarized dipole walls (PDW’s). In contrast to the PDW’s, the PTW’s cause a much higher misorientation in between adjacent lattice areas. This transformation, which is the main element of the progressing fragmentation process during large strain deformation, occurs in all metals studied regardless of dislocation mobility and/or lattice type. Approaching higher strains in stage V, however, these parameters gain some importance especially when the deformation occurs in an iterative way. If the mobility is high, marked static recovery takes place between the single deformation passes, which results in decreases of both dislocation density and local internal stress, and no formation of PTW’s is observed.
Certain Anomalies in the Analysis of Hyperbolic Heat Conduction
Authors: Haji-Sheikh A. , Minkowycz W. J. , Sparrow E. M.
Published: July 2002

The hyperbolic diffusion equation is often used to analyze laser heating of dielectric materials and in thermal processing of nonhomogeneous materials. In this paper, anomalies in existing solutions of the hyperbolic heat equation are identified. In particular, the singularities associated with the interaction of a wave front and a boundary may cause a violation of the imposed boundary condition. This violation may give rise to physically unacceptable results such as a temperature drop due to heating or a temperature rise due to cooling. The development of appropriate remedies for these happenings is a major focus of this paper. In addition, the unique mathematical features of the hyperbolic heat equation are studied and set forth. Green’s function solutions for semi-infinite and infinite bodies are presented. For finite bodies, it is demonstrated that the relevant series solutions need special attention to accelerate their convergence and to deal with certain anomalies.
Critical Wavelengths for Gap Nucleation in Solidification— Part I: Theoretical Methodology
Authors: Yigit F. , Hector, L. G.
Published: July 2002

A theoretical model of the gap nucleation process during pure metal solidification on a deformable mold of finite thickness is presented. Both surfaces of the mold follow a sinusoidal lay for which the ratio of the amplitude to the wavelength, or aspect ratio, is much less than one. This makes the aspect ratio a convenient perturbation parameter for the thermal and mechanical problems since it is indicative of the spatial variation in the surfaces. The thermal and mechanical fields are coupled along the upper surface of the mold through a pressure-dependent thermal contact resistance. The main goal of the model is to develop a means for examining the contact pressure along the mold-shell interface and how variation of the mold surface wavelength affects the time and location of gap nucleation. Gaps, which result from irregular distortion of the shell due to the modest variation of the mold surface geometry, are assumed to nucleate when the contact pressure locally falls to zero. The model leads to two coupled differential equations for the shell thickness and contact pressure perturbations which are solved with a numerical scheme. Using a series solution methodology, it is shown that the contact pressure perturbation predicted by the present model reduces to that for a rigid, perfectly conducting mold (which was considered in another work) in the limit of zero mold thickness. In the companion paper, we specifically examine various combinations of pure materials acting either as the shell or the mold material. The concept of a critical wavelength, which separates those wavelengths that lead to gap nucleation at the crests, from those that lead to gap nucleation at the troughs, is introduced. The potential for development of design criteria for mold surface topographies using the present theoretical model as a limiting solution for finite element models of more complex casting processes is discussed. [S0021-8936(00)03201-3]
Critical Wavelengths for Gap Nucleation in Solidification— Part II: Results for Selected Mold-Shell Material Combinations
Authors: Yigit F. , Hector, L. G.
Published: July 2002

In this second part, we examine the contact pressure ratio, Ptr, at the lowest points of the upper mold surface troughs in a directional solidification process using the theoretical methodology developed in Part I. Since there is ample experimental evidence that the mold surface topography affects gap nucleation at the mold-shell interface and the uniformity of the shell, we explore how the wavelength of the upper mold surface impacts the evolution of Ptr for specific material combinations and process parameters. For this purpose, the mold-shell materials are assumed to be combinations of four pure materials, viz., aluminum, copper, iron and lead: these materials offer a wide range of thermal and mechanical properties. Critical wavelengths, for which Ptr and its time derivative simultaneously equal zero, are predicted for all mold-shell material combinations. The theoretical model also predicts the existence of wavelength bands which are delimited by upper and lower critical wavelengths. All wavelengths that lie within the bands lead to gap nucleation, whereas all wavelengths that lie outside of the bands do not. The effects of distortivity ratio, which is a measure of the extent to which the mold-shell interface deforms under a given thermal loading, and selected process parameters (such as the mean mold thickness, contact resistance, and pressure) on bandwidth size, are considered in detail. Extensions of the present work to more sophisticated models that might lead to rudimentary mold topography design criteria are considered. [S0021-8936(00)03301-8]
Creep Rupture Properties of High-Temperature Bainitic Steels After Weld Repair
Authors: Indacochea J. E. , Wang G. , Seshadri R. , Oh Y. K.
Published: July 2002

Welded high-temperature power plant components can experience a greater risk of failure by creep during service, when compared to similar as-wrought components. The heat-affected zone (HAZ) of alloy steels is usually the region of a weldment exhibiting poor mechanical properties. The arc welding of an ASTM A470, Class 8-rotor steel in this study identified the intercritical heat affected zone (ICHAZ) as the weakest region in terms of creep rupture life. The type of welding procedure significantly affects this region, but most important are the welding parameters utilized. Because of the microstructural heterogeneity of the HAZ and sensitivity of these microstructures to changes when exposed to elevated temperatures, their performance at later times is difficult to predict. Extrapolation techniques are limited in value for predicting service lives of homogeneous materials, because these do not incorporate the microstructure changes of the materials during high temperature operation. They are even less useful for predicting the operating lives of weldments. This paper considers the creep performance and structure stability of the ICHAZ of 12 percent Cr and 214-1Mo vanadium modified weldments produced on a retired CrMoV rotor steel. [S0094-4289(00)00303-0]
A System for First Order Reliability Estimation of Solder Joints in Area Array Packages
Authors: Deshpande Anand M. , Subbarayan Ganesh , Rose Dan
Published: July 2002

In this paper, a methodology, and a program based on the methodology, are presented, which, using the reliability of solder joints for various values of design/process parameters, can be estimated in seconds on a personal computer. The proposed methodology accurately captures the behavior of a solder joint in an artificial neural network (ANN) model trained to relate design as well as analysis parameters to fatigue life. The proposed methodology is novel since such simultaneous analysis and design (SAND) procedures do not appear to have been employed until now for reliability estimation of solder joints. The use of Moire´ interferometry as an experimental technique to estimate the analysis-related inputs to the neutral network model is also presented in the paper. [S1043-7398(00)01101-4]
Effects of Belt Flexural Rigidity on the Transmission Error of a Carriage-driving System
Authors: Tai Hung-Ming , Sung Cheng-Kuo
Published: July 2002

This paper investigates the effects of belt flexural rigidity and belt tension on transmission error of a carriage-driving system. The beam model associated with both the clamped and moving boundary conditions at two ends is utilized to derive the governing equation of the belt. The belt flexural rigidity is obtained and verified by an experimental technique. In addition, a numerical method is proposed to determine the belt profile, transmission error and transmission stiffness. Results show that transmission error of a carriage-driving system increases when the carriage moves away from the driving pulley due to finite belt flexural rigidity. According to the analyses, application of appropriate tension on the belt can significantly reduce the error. Furthermore, the transmission stiffness for representing the entire rigidity between the carriage and pulley is investigated based on the proposed beam model. A three-dimensional plot that indicates the relationship among the transmission stiffness, belt tension and the position of the carriage is obtained. [S1050-0472(00)01102-8]
Temperature Measurement of Workpieces in Conventional Surface Grinding
Authors: Kato T. , Fujii Hiroshi
Published: July 2002

Temperature at various depths from the ground surface in workpiece is measured accurately by using the newly developed PVD film method, in which a thin film deposited on the workpiece is used as a thermal sensor. The influence of workpiece speed, depth of cut and wheel speed on the temperature of the workpiece was investigated under conventional surface grinding with no grinding fluids. The measured results were compared with Takazawa’s approximation based on Jaeger’s heat conduction solution to the moving heat source problem. The maximum temperature rise at the surface and the temperature gradient close to the surface were obtained and correlated with the residual stress induced at the surface. [S1087-1357(00)70302-9]
A New Friction Factor Model and Entrance Loss Coefficient for Honeycomb Annular Gas Seals
Authors: Al-Qutub Amro M. , Elrod D. , Coleman Hugh W.
Published: July 2002

A new experimental friction factor model for a honeycomb surface was developed using a static seal tester. Three clearances and three lengths were tested for the seals, and Reynolds number ranged from 3000 to 49,000. It was found that the friction factor was a function of Reynolds number and seal clearance only. The clearance effect was dominant and the friction factor was found to increase with increased clearance. A new uncertainty analysis was developed for the experimental friction factor when calculating friction factor using Mach number curve fit. The entrance loss coefficient was found to be constant for both smooth and honeycomb seals. The entrance loss coefficient of Honeycomb seals was found to be 50 percent higher than that of smooth seals. [S0742-4787(00)02102-0]
PVRC Division on Continued Operation of Equipment
Authors: Sims J. Robert
Published: July 2002

[S0094-9930(00)02301-5]
Damage Mechanics Considerations for Life Extension of High-Temperature Components
Authors: Ling Xiang , Tu Shan-Tung , Gong Jian-Ming
Published: July 2002

Continuum damage theory has proven to be an effective tool in creep damage simulation. In order to establish some mechanical principles for life extension of components at elevated temperature, a numerical scheme based on the localized creep damage theory is introduced. To illustrate the strength potential of structures for life extension, the method is first applied to a simple case of two-bar structure. Typical components of geometrical discontinuity, material discontinuity, and temperature inhomogenity are then analyzed. In terms of the damage distribution or life exhaustion of the components, some principles for life extension are proposed. [S0094-9930(00)00202-X]
Air Tests of Commercially Available Transport Vessel PRVs
Authors: Pierorazio A. J. , Birk A. M.
Published: July 2002

An experimental study of boiling liquid expanding vapor explosions (BLEVE) was recently completed at Queen’s University in Canada. The results clearly showed that the severity of the BLEVE was directly related to the energy stored in the vessel, and this energy storage was significantly affected by pressure relief valve (PRV) behavior. During the tests, the PRV operating characteristics were highly variable. Since these valves play a large role in the control of energy accumulation and storage in a pressure vessel, it was decided to study their dynamic behavior in detail and quantify their effect on energy storage. As an initial step, 60 small (1-in. NPT) transport vessel PRVs representing equivalent designs from each of three manufacturers were procured through a third party and tested on an air test bench. These tests were conducted in accordance with the certification procedures specified by various agencies (ASME, UL, CSA, CGA). Four characteristic pressures were measured: simmer (start-to-discharge), pop (full open), reseat, and reseal (bubble-tight reclosure). After initial testing, the valves were stored for various periods of time and retested. This paper details the equipment, procedures, and results of this testing and contains a significant discussion about the expected and observed operation of relief valves. [S0094-9930(00)00702-2]
Process Piping Design: A Century of Progress
Authors: Koves William J.
Published: July 2002

The Process Piping Code—ASME B31.3, (“Chemical Plant and Petroleum Refinery Piping,” 1998 Edition, ASME, New York, NY) has undergone significant changes over the years to better serve the industries that it supports (Koves, W. J., and Frikken, D. R., 1996, “ASME B31.3: Recent Changes and Future Developments,” Pressure Vessel and Piping Conference, ASME PVP-Vol. 338). The Code has changed in response to changing technology, inquiries to the committee, technical needs, clarification of requirements and editorial considerations. This paper discusses the history of its development and provides and overview of the most significant changes to the Code. [S0094-9930(00)01303-2]
High density plasma oxide etching using nitrogen trifluoride and acetylene
Authors: Pruette Laura , Karecki Simon , Chatterjee Ritwik , Reif Rafael , Sparks Terry , Vartanian Victor
Published: July 2002

The use of nitrogen trifluoride (NF3) and acetylene (C2H2) in the presence of helium has been examined for oxide etching in an inductively coupled, high density plasma etch tool. Oxide etch rates have been measured for blanket films and for patterned wafers with features of 0.6, 0.45, and 0.35 μm nominal critical dimension, while process performance has been assessed with cross-sectional scanning electron microscopy. Optical emission spectroscopy has been employed in situ to characterize the species present in the plasma, and quadrupole mass spectrometry has been used to analyze process effluent sampled between the chamber outlet and the turbo pump inlet. Polymer film deposited on the surface of the oxide layer has been studied with time-of-flight secondary ion mass spectrometry. Global warming emissions for a range of process conditions have been quantified using Fourier transform infrared spectroscopy, and are compared to emissions from more typical oxide etch processes on the same tool type. Results indicate that the NF3/C2H2 chemistry is capable of etching oxide anisotropically, while offering a significantly lower global warming impact than current oxide etch chemistries.
On the 10-year static vacuum integrity of vacuum foil insulation for an implantable artificial heart
Authors: Svedberg R. C.
Published: July 2002

Vacuum multifoil insulation systems are being developed for an implantable artificial heart. These insulation systems are thermally efficient and physically compact, being able to limit heat losses to less than 0.024 W/cm2 with an 832 °C temperature gradient across a 0.5-cm insulation thickness. The maintenance of a 10−3-Torr static vacuum for 10 yr is critical to the success of the implantable artificial heart. The determination of the maximum allowable pressure for satisfactory vacuum foil insulation performance is reported. Also, the outgassing characteristics of several Ti and Nb–1Zr insulation packages were evaluated after 300 h of thermal testing and about 3600 h after final fabrication. The only gas found in the system was hydrogen, and possible sources of hydrogen are considered. Finally, outgassing characteristics of specific vacuum foil insulation material such as electroplated Ni, as well as procedures used to eliminate gas loads from this material are reported.
An Inexpensive Automatic Liquid Nitrogen Level Control System Using an Integrated Circuit
Authors: Sandhu H. S. , Bulinckx M. J.
Published: July 2002

A highly reliable, automatic liquid nitrogen level control system using an integrated circuit is described. Inexpensive standard components are used in the device. Construction of the system is simple and straightforward.
Atmospheric Pressure Leak Detector
Authors: Jain S. K. , Sundersingh V. P.
Published: July 2002

An atmospheric pressure leak detector has been constructed for finding leaks in vacuum and pressurized systems, using a thermistor as a sensing element. Heat transfer calculations for the thermistor in free air to determine its biasing point have been undertaken with the aid of a computer. The current through the thermistor at a given temperature, as determined theoretically and experimentally, is in agreement to within 8%.
Vapor-Phase Formation of Submicron ZrO2-Coated Chromium Particles
Authors: Bryant W. A.
Published: July 2002

Submicron particles of chromium, produced by evaporation and condensation at reduced pressure in a helium atmosphere, were entrained in a stream of helium where they were coated with ZrO2. Factors affecting the chromium-particle growth rate were evaporation temperature and inert-gas overpressure. A model of particle growth was formulated which predicted particle sizes which were in reasonable agreement with those produced experimentally. The difference noted by other investigators in particle size resulting from substitution of one inert gas for another is also explained by the model.
Theory, Design, and Selection of Vacuum Metallurgical Heat Treating and Processing Equipment
Authors: Durant John H.
Published: July 2002

Process advantages of vacuum are compared with conventional inert-gas atmospheres with respect to purity, repeatability, and operating cost. Recognition of vapor pressures of workloads, containers, and furnace hot-zone parts is essential to predicting system performance parameters, maintenance schedules, and pumping equipment selection. Cooling requirements of batch equipment are evaluated with respect to quench characteristics, equipment turn-around time, and workpiece surface quality. Design features of system details are evaluated for such factors as heat removal (jacketing vs traced cooling), safety (one-piece electrode design), integrity at full vacuum, and partial pressure operation. Typical systems are examined for conformity to design criteria established.
Auger Electron Energies (0–2000 eV) for Elements of Atomic Number 5–103
Authors: Yasko R. N. , Whitmoyer R. D.
Published: July 2002

Auger electron energies for elements of atomic number 5 to 103 have been calculated using the atomic energy level values of Siegbahn et al., and a system of programs. The Auger electron energy table provides a listing of the element, the Auger transition, and all the calculated energies in ascending order from 0 to 2000 eV. These data are in the range of interest to Auger electron spectroscopists involved in surface studies.
Development Related to Rotatrode Melting as Applied to Production Practice
Authors: von Tiesenhausen E. , Schlienger M.
Published: July 2002

Two separate aspects of nonconsumable melting of titanium alloys were discussed. The first one dealt mainly with the general characteristics and type of equipment suitable for this type of melting while the second part dealt with actual production experiences on the nonconsumbale furnace using the rotatrode electrode. The major nonconsumable melting systems which are presently in use for reactive metals were mentioned. Emphasis was placed on the actual design criteria used in the developmeut of a nonconsumable furnace with particular emphasis being placed on the three different methods of melting and/or withdrawing and pouring. Particular emphasis was given to the design and safety interlocks embodied in the various control systems such as the electrode and crucible controls. A short discussion of the viewing and feeding systems was made. Basic variables affecting the nonconsumable arc were discussed. Data taken on the factors affecting arc length, i.e., pressure, voltage, and amperage were presented but no theoretical explanations of the curves were given. While considerable progress has been made in nonconsumable melting technology, a large amount of research and development work still needs to be done.
Integrally Cast Airfoil Components for Small Gas Turbine Engines
Authors: Boyle J. H. , Ingalls J. E.
Published: July 2002

In the past two decades, remarkable progress has been made in investment casting of airfoil components for gas turbine engines. Cast turbine blades, operating at high stresses and high temperatures, have been widely accepted. Improved production techniques, notably vacuum melting and casting, have stimulated development of greatly improved nickel and cobalt based superalloys. Although individual turbine blades and vanes have been produced in large quantities since 1950, a more recent development is high-volume production of integrally cast turbine wheels and nozzles for small gas turbine engines. This paper is a review of the state of the art in integrally cast airfoil components. The Monoshell process, as applied to integral castings is reviewed and representative illustrations of a wide range of engine castings are presented.
Pressures and Consumable-Electrode Arcs
Authors: Wood F. W. , Calvert E. D.
Published: July 2002

An investigation of arc zone pressures during CEVAR (consumable-electrode vacuum-arc remelting) experiments has shown that pressure differences and gradients within furnaces are functions of pressure itself, electrode composition, and the degree of arc-zone confinement. There is evidence also that some previously puzzling contrasts in arc-furnace behavior may be explainable on the basis that two pressure dependent forms of electrical discharge operate with distinct potentials. The lower voltage form tends to become unstable at pressures <0.5 Torr and behaves best at pressures >1 Torr. The higher voltage form seems to be most stable at pressures <0.1 Torr. For continuous operation and maximum versatility, a CEVAR furnace should be able to accommodate both discharge forms by providing for variability of vacuum conditions.
High-Rate rf Sputtering System
Authors: Grantham D. H. , Paradis E. L. , Quinn D. J.
Published: July 2002

A sputtering target system utilizing high vacuum as the electrical insulator is described. This technique permits the application of high rf power to the target. Power up to 5000 W has been applied to a 7.3-cm-diam electrode bonded to a 10-cm-diam Al2O3 target. Under the proper conditions of geometry, gas pressure, and magnetic field, this has resulted in deposition rates of Al2O3 in excess of 6300 Å/min. For an SiO2 target with 3000-W input, deposition rates in excess of 10 000 Å/min have been obtained. Typical deposition rates of Al2O3, are given for this target system as a function of rf power, magnetic field, and gas pressure.
Departure from Free Molecular Flow During the Boat Evaporation of Permalloy
Authors: Carson K. R. , Wierum F. A. , Rudee M. L.
Published: July 2002

Evaporation of an alloy from most of the common vapor sources is normally considered to obey free molecular flow. Under these conditions, Knudsen’s Cosine law predicts that a film deposited on the walls of a spherical shell tangent to and including the melt would be of uniform thickness and composition. It is demonstrated here that significant deviations from free molecular flow can occur in quite typical deposition conditions. A Ni–Fe alloy was evaporated from g resistance heated tungsten boat at various rates and the vapor collected to reveal departures from the cosine law. At very. high evaporation rates, the evaporant was found to be concentrated in a direction normal to the boat surface. In addition, the composition of the vapor possessed on angular distribution.
Aluminum Sorption Roughing Pump for Small Vacuum Systems
Authors: Danielson P. M.
Published: July 2002

Sputter-ion pumped vacuum systems are commonly roughed with sorption pumps. This paper describes the design and performance of a new pump that is tailored for use with small systems. The new pump is designed to maximize heat transfer between the liquid-nitrogen coolant and the Molecular Sieve by means of an aluminum pump housing and by providing internal aluminum rods welded to the bottom of the housing. The performance of the new pump was assessed by three series of tests on a small (4.65-liter) vacuum system. These tests showed that the pump performs satisfactorily without internal gas access screens or prechilling, and that it can repeatedly (>20 times) evacuate the test system without loss of maximum (1×10−2 Torr in 7.5 min and 1×10−3 Torr in 40 min) performance.
Interdependence of the Electrical Properties and the Defect Structure in Heteroepitaxial Germanium and Silicon
Authors: Dumin D. J.
Published: July 2002

The electrical properties of thin films of germanium and silicon are heavily dependent on the crystalline perfection of the films. Defects in the thin films have strikingly different energy levels in germanium and in silicon. In germanium the defects introduce a relatively shallow acceptor, with activation energy less than 0.15 eV, and this level tends to lead to heteroepitaxial films that are P type and to limit the range of doping densities available in these films. The defects introduce scattering centers that lower the Hall mobilities. In silicon the defects introduce a donor-acceptor pair, both of which are far removed from the bandedges. These deep levels act as charge trapping centers and as scattering centers which can lower carrier concentration, Hall, mobilities, and minority carrier lifetimes. The effects of these defect levels on the electrical properties of germanium and silicon are discussed, with some specific examples being chosen to demonstrate the various effects.
A Nondestructive Measurement of Thickness and Composition of Thin Silicon Oxide Films
Authors: White Marlin L. , Weitzenkamp L. A.
Published: July 2002

Thickness and composition of thin dielectric films are frequently dependent upon the system deposition parameters. A method is described for determining both thickness and composition of a film containing a mixture of two materials, provided the refractive index and relative permittivity is known for each of the two components. A combination of scanning interferometry and capacitance measurements was used to test the method of the Si–SiO–SiO2 system, obtaining an over-all accuracy in thickness on the order of 250 Å for film thickness on the order of 0.4 μ.
Gas Flux Patterns in Cylindrical Vacuum Systems
Authors: Moore Boude C.
Published: July 2002

Gas flux patterns in cylindrical vacuum chambers are computed assuming diffuse reflection and molecular flow conditions. The surface is divided into equal area zones up to 500 in number. Gas input and sticking coefficient may be specified for each zone. The results agree closely with previous work on open tube transmission fractions and wall flux patterns. Flux patterns for closed cylinders are given. Orifice and uniform gas inlet geometries are compared; the difference in flux patterns becomes small away from the inlet end. Gage correction factors are given for the International Standards Organization proposed geometry for diffusion pump speed measurement. The change in correction factor with pump geometry and sticking coefficient is shown. An iterative process is required to select the correction factor for a particular measurement. A spherical calibration geometry is proposed to minimize these correction factors.
Electron Optical Aspects of a Sequential Mass Spectrometer
Authors: Hartnagel H. , Herkman I.
Published: July 2002

The phenomena of ion trapping in electron beams are studied experimentally. For a tubular electron beam the total trapped ion charge equals that of the electron charge if no opening of the trap occurs by any negative potential electrode. When a second electron beam is introduced along the axis of the tubular beam, very high ion densities can be established, because the slow electrons created by ionizing collisions of the axial electron beam can neutralize the ionic charge on the axis.
A study of electron impact ionization, x-ray photoionization, and x-ray photoemission currents in silicon diode array camera tubes
Authors: Fukui H. , Morris F. J.
Published: July 2002

When the target of a camera tube is biased sufficiently negative with respect to the cathode that the primary-electron beam is prevented from striking the target, the current collected by the target has three major components: one due to electron impact ionization of the residual gas, one due to soft x-ray photoionization of the residual gas, and one due to photoelectron emission from the target by soft x-rays. The effects of tube pressure and electrostatic potentials on the various components of target current were investigated. The soft x-rays generated by the electron beam striking the mesh are shown to be a significant factor in determining the target current. The study has resulted in a technique for determining the residual gas pressure in a completed camera tube.
Appearance potential spectrum of barium
Authors: Ramachandran K. N. , Cox C. D.
Published: July 2002

When the conventional tungsten filament in an appearance potential spectrometer was replaced by an oxide coated filament, barium contamination was detected on the iron specimen being examined. The spectrum obtained showed prominent M structure of barium in addition to weak iron L structure. Even after the work function correction is applied, the barium edges are shifted by several eV from the respective energy levels quoted in the literature. This is presumably the effect of chemical binding of the barium atoms on the surface. The iron and the barium spectra showed slight changes in structure when the specimen was heated in situ.