A panel research experiment (PRE) was designed, built, and tested as a scaled-down model of a direct absorption receiver (DAR). The PRE is a 3-MWt DAR experiment that will allow flow testing with molten nitrate salt and provide a test bed for DAR testing with actual solar heating. In a solar central receiver system DAR, the heat absorbing fluid (a blackened molten nitrate salt) flows in a thin film down a vertical panel (rather than through tubes as in conventional receiver designs) and absorbs the concentrated solar flux directly. The ability of the flowing salt film to absorb the incident solar flux depends on the panel design, hydraulic and thermal fluid flow characteristics, and fluid blackener properties. Testing of the PRE is being conducted to demonstrate the engineering feasibility of the DAR concept. The DAR concept is being investigated because it offers numerous potential performance and economic advantages for production of electricity when compared to other solar receiver designs. The PRE utilized a 1-m wide by 6-m long absorber panel. The salt flow tests are being used to investigate component performance, panel deformations, and fluid stability. Salt flow testing has demonstrated that all the DAR components work as designed and that there are fluid stability issues that need to be addressed. Future solar testing will include steady-state and transient experiments, thermal loss measurements, responses to severe flux and temperature gradients and determination of peak flux capability, and optimized operation. In this paper, we describe the design, construction, and some preliminary flow test results of the Panel Research Experiment.
An obvious group of applications for HTS materials is microwave and millimeter wave circuitry. Besides low loss, the unique features of these materials, such as flux flow, can be exploited. We have been concentrating on the Tl-Ca-Ba-Cu-O family of materials. The film growth techniques, lithographic processing methods and the characteristics of several devices we have developed will be presented. These devices include a flux flow-based transistor with demonstrated operation at over 35 GHz, real gain in a 50 ω system and potentially useful non-linearities and impedance levels. A number of passive microwave components are under investigation to form a more complete HTS microwave technology group.
Proceedings of the Intersociety Energy Conversion Engineering Conference
Arnold Jr., Charles
The lifetimes of zinc/bromine flow batteries may be limited by the durability of components which are fabricated from thermoplastic materials and exposed to bromine-containing electrolytes. Examples of such components are flowframes and carbon-filled plastic electrodes. In early versions of the zinc/bromine battery, flowframes and electrodes were made from copolymers of propylene and ethylene. In later versions of the zinc/bromine battery, these materials were replaced by poly(vinyl chloride) (PVC) and polyethyle (flowframes) and polyethylene as the plastic component in electrodes. We found that carbon-plastic electrodes made from polypropylene rich copolymers were swelled and chemically attacked by the bromine-containing electrolytes. As a result, warpage occurred and the battery failed. On the basis of accelerated aging studies we estimated the lifetimes of the electrode and its polypropylene based component to be 96 and 10 months, respectively. The enhanced stability of the electrode was attributed to the presence of carbon which is known to be an antioxidant for thermoxidation. In accelerated exposure tests, bromine-containing electrolytes were also found to attack and leach out the additives used in PVC flowframes. PVC itself was only slightly degraded by the electrolyte. A commercial fluorocarbon, TefzelR, which contains no additives, was determined to be stable in bromine-containing electrolytes and is recommended as a replacement for PVC. Currently, aging studies on carbonfilled polyethylene electrodes are in progress.
The state-of-the-art of parabolic dish solar concentrators is the faceted, glass-metal dish. The mass-production costs of glass-metal dishes may be high because they do not incorporate the innovations of design and materials developed over the last eight years. Therefore, Sandia National Laboratories has undertaken to develop two stretched-membrane parabolic dish concentrators for the Department of Energy's Solar Thermal Program. These solar concentrators are being designed for integration with an advanced solar receiver and a Stirling engine/generator in a 25-kWe power production unit. The first dish, which builds on the successful design of the stretched-membrane heliostats, is to be a low-risk, near-term commercial solar concentrator. This solar concentrator comprises twelve large, 3.6-meter diameter, stretched-membrane facets that are formed into parabolic shapes either with a large vacuum or by preforming the thin membranes plastically. The focal length-to-diameter ratios (f/D) for the facets are about 3.0, relatively large for a dish but much lower than heliostats where they typically range from 50 to 100. Two contractors are currently fabricating facets for this dish, and a third contractor is designing the facet support structure and pedestal for the dish. The second stretched-membrane concentrator is a single-element monolithic dish with an f/D of 0.6. The dish is shaped into a parabola by plastically yielding the membrane using a combination of uniform and nonuniform loading. Initial measurements of the of the dish indicate that it has a slope error of 3.6 milliradian (one standard deviation) relative to a perfect parabola. In this paper, the designs of the two stretched-membrane dishes are analyzed using the computer code CIRCE to model the optical performance of the concentrators and a thermal model, which includes conduction, convection, and radiation heat transfer, to calculate the thermal losses from the cavity solar receivers. The solar collector efficiency, defined as the product of the optical efficiency of the collector and the thermal efficiency of the receiver, is optimized for comparing the performance of several solar concentrator configurations. Ten facet arrangements for the faceted stretched-membrane dish and the single-element stretched-membrane dish are modeled and their performances compared with that of a state-of-the art glass-metal dish. Last, the initial designs of these two stretched-membrane dishes are described along with the results of preliminary performance measurements on their respective optical elements.
A three-dimensional finite element structural analysis of the Intermediate Scale Borehole Test at the WIPP has been performed. The analysis provides insight into how a relatively new excavation in a creeping medium responds when introduced into an existing pillar which has been undergoing stress redistribution for 5.7 years. The stress field of the volume of material in the immediate vicinity of the borehole changes significantly when the hole is drilled. Closure of the hole is predicted to be larger in the vertical direction than in the horizontal direction, leading to an ovaling of the hole. The relatively high stresses near the hole persist even at the end of the simulation, 2 years after the hole is drilled.
As part of the Yucca Mountain Project, our research program to develop and validate conceptual models for flow and transport through unsaturated fractured rock integrates fundamental physical experimentation with conceptual model formulation and mathematical modeling. Our research is directed toward developing and validating macroscopic, continuum-based models and supporting effective property models because of their widespread utility within the context of this project. Success relative to the development and validation of effective property models is predicted on a firm understanding of the basic physics governing flow through fractured media, specifically in the areas of unsaturated flow and transport in a single fracture and fracture-matrix interaction.
Construction of well-posed scenarios for the range of conditions possible at any proposed repository site is a critical first step to assessing total system performance. Event tree construction is the method that is being used to develop potential failure scenarios for the proposed nuclear waste repository at Yucca Mountain. An event tree begins with an initial event or condition. Subsequent events are listed in a sequence, leading eventually to release of radionuclides to the accessible environment. Ensuring the validity of the scenarios requires iteration between problems constructed using scenarios contained in the event tree sequence, experimental results, and numerical analyses. Details not adequately captured within the tree initially may become more apparent as a result of analyses. To illustrate this process, we discuss the iterations used to develop numerical analyses for PACE-90 using basaltic igneous activity and human-intrusion event trees.
Three series of measurements were performed on oriented cores of several Yucca Mountain tuffs to determine the importance of mechanical anisotropy in the intact rock. Outcrop and drillhole samples were tested for acoustic velocities, linear compressibilities, and strengths in different orientations. The present data sets are preliminary, but suggest the tuffs are transversely anisotropic for these mechanical properties. The planar fabric that produces the anisotropy is believed to be predominantly the result of the preferred orientation of shards and pumice fragments. The potential of significant anisotropy has direct relevance to the formulation of constitutive formulation and the analyses of an underground opening within Yucca Mountain.
Yucca Mountain, located in southwestern Nevada, is the site for a proposed high-level nuclear waste repository. The hydrologic units at Yucca Mountain appear to have quite different material characteristics. Additionally, measurements show that the material properties within each hydrologic unit vary significantly. Rock core samples taken from this site indicate that the volcanic tuff is highly fractured and nonhomogeneous. Modeling studies were conducted to determine the effects of material heterogeneities on the flow of water through rock. Multiple numerical calculations were made using random variations in spatial distributions of material properties. The results of these material variations on flow resistance, mechanical dispersion, and channeling were determined. Computed results were compared with a linear analytical model. Good agreement was obtained in the majority of the flow cases investigated.
Under the sponsorship of the US Nuclear Regulatory Commission (NRC), Sandia National Laboratories (SNL) is developing a performance assessment methodology for the analysis of long-term disposal and isolation of high-level nuclear wastes (HLW) in alternative geologic media. As part of this exercise, SNL created a conceptualization of ground-water flow and radionuclide transport in the far field of a hypothetical HLW repository site located in unsaturated, fractured tuff formations. This study provides a foundation for the development of conceptual mathematical, and numerical models to be used in this performance assessment methodology. This conceptualization is site specific in terms of geometry, the regional ground-water flow system, stratigraphy, and structure in that these are based on information from Yucca Mountain located on the Nevada Test Site. However, in terms of processes in unsaturated, fractured, porous media, the model is generic. This report also provides a review and evaluation of previously proposed conceptual models of unsaturated and saturated flow and solute transport. This report provides a qualitative description of a hypothetical HLW repository site in fractured tuff. However, evaluation of the current knowledge of flow and transport at Yucca Mountain does not yield a single conceptual model. Instead, multiple conceptual models are possible given the existing information.
Sandia National Laboratories, as a participant in the Yucca Mountain Project, administered by the Nevada Operations Office of the US Department of Energy, is in the process of evaluating a proposed site for geologic disposal of high-level nuclear wastes in the volcanic tuffs at Yucca Mountain, Nevada. In a repository, loads will be imposed on the rock mass as a result of excavation of the openings and heating of the rock by the nuclear waste. In an attempt to gain a better understanding of the thermal, mechanical, and thermomechanical response of fractured tuff, a series of experiments have been performed, and measurements have been taken in the welded and nonwelded tuffs at the G-Tunnel underground test facility at Rainier Mesa, Nevada. Comparisons between measured and calculated data of the G-Tunnel High-Pressure Flatjack Development Experiment are presented in this investigation. Calculated results were obtained from two dimensional finite element analysis using a recently developed compliant-joint rock-mass model. The purpose of this work was to assess the predictive capability of the model based on limited material property data for the G-Tunnel welded tuff. The results of this evaluation are discussed.
A new facility is being constructed for the Primary Standards Laboratory (PSL) at Sandia National Laboratories in Albuquerque, New Mexico. Features of the final design are at the state of the art and were developed over a number of years of study and design effort. Based on experience and evaluation of anticipated needs, a philosophy was established for the design and followed through the effort. A temperature control limit of {plus minus}0.01{degrees}C is required for some of the dimensional measuring spaces; isolation from vibration and electromagnetic interference (EMI) are required for all measurement spaces. The requirements for the facility and the principal design features are presented. 4 refs.
Two devices or tools are described which can be used to evaluate the ability of chip passivation or postbond coatings to protect a Si device from moisture penetration and resultant Al corrosion. The first device is a test chip with a number of Al triple track and other corrosion measurement structures. The authors present HAST data to illustrate the use of this chip in measuring failure rates and determining failure modes. The second device is a rugged, moisture sensitive, porous Si capacitor, which is compatible with high temperature passivation and postbond IC processing. Data are presented showing the stability of the device relative to that of an anodized Al moisture sensor and showing the variation of capacitance with moisture. Data are also presented showing that the capacitor can respond to a point source of water located over the porous region but remotely from the top electrode.
While the backscattered field as a function of angular incidence of a plane wave for dihedral corner reflectors having right, acute, and obtuse angles has been studied extensively, it has generally been stated that the RCS of a 90{degree} dihedral corner reflector oriented for maximum backscattered return to a radar is given by the expression {sigma} = 8{pi}a{sup 2}b{sup 2}/{lambda}{sup 2}. The intent of this paper is to present experimental results which demonstrate that not only does the RCS of a dihedral corner reflector oriented for maximum backscattered return differ significantly from this value, but that high range resolution measurements of the dihedral can serve to identify the dominant contributors to the backscattered field. Further, inclusion of these backscattered components in an analytical calculation will allow an accurate calibration model to be generated. 6 refs., 8 figs.
Computer-aided molecular design (CAMD) has been used to define the structural conformations and intramolecular interactions of bituminous coal models. Molecular dynamics studies have produced representative minimum energy conformations for several published molecular models. These studies show the importance of van der Waals (vdW) and hydrogen-bonding interactions as cohesive forces responsible for the three-dimensional (folded) structures of the coal methods. Calculations on pairs of small ring compounds representative of those found in coal clusters demonstrate that aromatics exhibit stronger vdW interactions compared with saturated ring compounds. Correlations of the vdW interactions compared with saturated ring compounds. Correlations of vdW interactions with boiling points also show differences between aromatics and saturated rings. 23 refs., 2 figs., 1 tab.
Large computational physics codes are increasing in complexity as customers demand improved physics packages and more flexible algorithms and problem specifications. It is not uncommon for a code to exceed one hundred thousand lines of FORTRAN, and some codes are much larger. This poses a considerable challenge for program management. The Computational Physics Research and Development Division at Sandia National Laboratories is aggressively pursuing C++ as the language of choice for new coding efforts. We feel that we cannot meet the stringent customer requirements and delivery schedules we now face with either FORTRAN77 or Fortran-90. 8 refs., 3 tabs.
Cleaning, plating, and painting are chemically intensive processes that involve toxic and potentially carcinogenic materials that pose a significant threat to the environment. EPA/OSHA, the Clean Air Act, and the Montreal Protocol are forcing development of environmentally sound materials and processes. A review is given of the materials and processes that are under investigation that will minimize the environmental impact of these operations. 7 refs.
The Recirculating Linear Accelerator (RLA) is returning to operation with a new relativistic electron beam (REB) injector and a modified accelerating cavity. Upon completion of our pulsed-power test program, we will capture the injected beam on an Ion Focussed Regime (IFR) guiding channel in either a spiral or a closed racetrack drift tube. The relativistic beam will recirculate for four passes through two accelerating cavities, in phase with the ringing cavity voltage, and increase to 8--12 MeV before being extracted. We designed the METGLAS ribbon-wound core, inductively isolated, four-stage injector to produce beam parameters of 4 MeV. 10--20 kA, and 40--55 ns FWHM. The three-line radial cavity is being modified to improve the 1-MV accelerating pulse shape while an advanced cavity design study is in progress. This is a continuation of the Sandia National Laboratory program to develop compact, high-voltage gradient, linear induction accelerators. The RLA concept is based on guiding an injected REB with an IFR channel. This channel is formed from a plasma created with a low energy electron beam inside a beam line containing about 2 {times} 10{sup {minus}4} Torr of argon. The REB is injected onto the IFR channel and is transported down the beamline through a water dielectric accelerating cavity based on the ET-2 design. If the round-tip path of the beam matches the period of the cavity, the REB can be further accelerated by the ringing waveform on every subsequent pass. We have installed the new REB injector because we need a higher amplitude, longer duration., flat-topped pulse shape with a colder beam than that produced by the previous injector. We made extensive use of computer simulations in the form of network solver and electrostatic field stress analysis codes to aid in the design and modifications for the new RLA. The pulsed-power performance of the RLA injector and cavity and the associated driving hardware are discussed.
A major center with emphasis on validation of nondestructive inspection techniques for aging aircraft, the Aging Aircraft NDI Development and Demonstration Center (AANC), has been funded by the FAA at Sandia National Laboratories. The Center has been assigned specific tasks in developing techniques for the nondestructive inspection of static engine parts, assessing inspection reliability (POD experiments), developing test beds for nondestructive inspection validation, maintaining a FAA library of characterized aircraft structural test specimens, and leasing a hangar to house a high flight cycle transport aircraft for use as a full scale test bed. 3 refs.
This paper describes procedure used to produce a test-validated finite element model of a three-stage solid propellant booster system. A series of system-level modal tests were performed for several inert and live propellant configurations. Test-analysis models (TAMs) were used to provide pretest support of the live propellant system tests. Confidence in the model was established by a test-analysis correlation procedure. Optimization techniques were used to determine appropriate model updates. 11 refs., 8 figs., 3 tabs.
Soldering is often referred to as a mature technology whose fundamentals were established long ago. Yet a multitude of soldering problems persist, not the least of which are related to the wetting and spreading of solder. The Buff-Goodrich approach to thermodynamics of capillarity is utilized in a review of basic wetting principles. These thermodynamics allow a very compact formulation of capillary phenomena which is used to calculate various meniscus shapes and wetting forces. These shapes and forces lend themselves to experimental techniques, such as the sessile drop and the Wilhelmy plate, for measuring useful surface and interfacial energies. The familiar equations of Young, Wilhelmy, and Neumann are all derived with this approach. The force-energy duality of surface energy is discussed and the force method is developed and used to derive the Herring relations for anisotropic surfaces. The importance of contact angle hysteresis which results from surface roughness and chemical inhomogeneity is presented and Young's equation is modified to reflect these ever present effects. Finally, an analysis of wetting with simultaneous metallurigical reaction is given and used to discuss solder wetting phenomena. 60 refs., 13 figs.
Titanium dioxide (TiO{sub 2}) is a known photocatalyst for solar detoxification of water containing organic contaminants including PCB's and dioxins. Unfortunately, the UV light used by the photocatalyst only comprises about 4% of the strong spectrum. Metalloporphyrins strongly absorb in the visible and near infrared region. Using visible light, we have investigated Ni(II) uroporphyrin (NiUroP), Sn(IV)Cl{sub 2} uroporphyrin (SnUroP) and Sn(IV)Cl{sub 2} tetrakis(p-carboxyphenyl) porphyrin (SnTCPP) as possible enhancers of destruction of a model organic compound, salicylic acid (SA), by means of photosensitization of colloidal TiO{sub 2} particles. All three porphyrins are found to adsorb reversibly onto the colloidal TiO{sub 2} upon variation of pH. Adsorption of porphyrins results in the increased colloidal stability of fine TiO{sub 2} particles in the pH range 5--8. While NiUroP on TiO{sub 2} does not show any enhancement of photodestruction, the adsorption of SnUroP increases the destruction rate compared to that of the bare TiO{sub 2} surface. The effect of ambient oxygen on the observed photolability of the Sn porphyrins and enhancement of photodestruction of SA was also investigated. SnTCPP does not photodecompose upon illumination either in the presence or absence of TiO{sub 2}, but neither does it bind to the photocatalyst at pH 6. At pH 4.5 it adsorbs onto TiO{sub 2} but it also photodecompose at this pH. We are attempting to stabilize the adsorbed porphyrins by adding suitable peripheral substituents onto the porphyrin macrocycle. 27 refs., 6 figs.
The frequency response of the Faraday rotation in fiber current sensors is computed and measured for sensor coils of noncircular cross section and with displaced coil and conductor axes. Resonances are observed at higher frequencies with magnitudes approaching that of the low frequency response. Narrowband current sensors at frequencies above 100 MHz are reported. 7 refs., 4 figs.