Simulation of concentrated photovoltaic cooling system

This paper reports work underway in converting a dish-Stirling system to a dish-PV system at UNLV. The existing SAIC dish---Stirling system is being retrofitted with new fixed-focus facets and an Amonix photovoltaic receiver to replace the Stirling-engine/generator package. As is the case with photovoltaic systems generally, the Amonix cells being used in this application tend to lose efficiency as their temperatures increase. To combat this effect, cooling is provided by circulating liquid through channels in the backing plate. The liquid is then pumped through an array of automotive type radiators and the excess heat is rejected to the ambient air; Reported here is the development of a numerical model for the cooling system. Experimental data are taken to determine the various properties of the individual components to be used in the system and these data are used in a MATLAB-based simulation. The cooling system model can then be linked to a similar model for the receiver and cell assembly and the optimization functions included in MATLAB can be used to select the input parameters (liquid flow rate, number of radiators, air flow rate, etc.) that maximize the overall efficiency of the system. The predictions of the model can be used in the selection of the final cooling system design and the validity of the model can be checked against the actual performance of the unit

Finite element elastic-plastic-creep and cyclic life analysis of a cowl lip

Results are presented of elastic, elastic-plastic, and elastic-plastic-creep analyses of a test-rig component of an actively cooled cowl lip. A cowl lip is part of the leading edge of an engine inlet of proposed hypersonic aircraft and is subject to severe thermal loadings and gradients during flight. Values of stresses calculated by elastic analysis are well above the yield strength of the cowl lip material. Such values are highly unrealistic, and thus elastic stress analyses are inappropriate. The inelastic (elastic-plastic and elastic-plastic-creep) analyses produce more reasonable and acceptable stress and strain distributions in the component. Finally, using the results from these analyses, predictions are made for the cyclic crack initiation life of a cowl lip. A comparison of predicted cyclic lives shows the cyclic life prediction from the elastic-plastic-creep analysis to be the lowest and, hence, most realistic

Progress in materials and structures at Lewis Research Center

The development of power and propulsion system technology is discussed. Specific emphasis is placed on the following: high temperature materials; composite materials; advanced design and life prediction; and nondestructive evaluation. Future areas of research are also discussed

Mechanisms of High-Temperature Fatigue Failure in Alloy 800H

The damage mechanisms influencing the axial strain-controlled Low-Cycle Fatigue (LCF) behavior of alloy 800H at 850 C have been evaluated under conditions of equal tension/compression ramp rates (Fast-Fast (F-F): 4 X 10(sup -3)/s and Slow-Slow (S-S): 4 X 10(sup -5)/s) and asymmetrical ramp rates (Fast-Slow (F-S): 4 x 10(sup -3)/s / 4 X 10(sup -5/s and Slow-Fast (S-F): 4 X 10(sup -5) / 4 X 10(sup -3)/s) in tension and compression. The fatigue life, cyclic stress response, and fracture modes were significantly influenced by the waveform shape. The fatigue lives displayed by different loading conditions were in the following order: F-F greater than S-S greater than F-S greater than S-F. The fracture mode was dictated by the ramp rate adopted in the tensile direction. The fast ramp rate in the tensile direction led to the occurrence of transgranular crack initiation and propagation, whereas the slow ramp rate caused intergranular initiation and propagation. The time-dependent processes and their synergistic interactions, which were at the basis of observed changes in cyclic stress response and fatigue life, were identified. Oxidation, creep damage, dynamic strain aging, massive carbide precipitation, time-dependent creep deformation, and deformation ratcheting were among the several factors influencing cyclic life. Irrespective of the loading condition, the largest effect on life was exerted by oxidation processes. Deformation ratcheting had its greatest influence on life under asymmetrical loading conditions. Creep damage accumulated the greatest amount during the slow tensile ramp under S-F conditions

Thermal Fatigue Limitations of Continuous Fiber Metal Matrix Composites

The potential structural benefits of unidirectional, continuous-fiber, metal matrix composites (MMC's) are legendary. When compared to their monolithic matrices, MMC's possess superior properties such as higher stiffness and tensile strength, and lower coefficient of thermal expansion in the direction of the reinforcing fibers. As an added bonus, the MMC density will be lower if the fibers are less dense than the matrix matErial they replace. The potential has been demonstrated unequivocally both analytically and experimentally, especially at ambient temperatures. Successes prompted heavily-funded National efforts within the United States (USAF and NASA) and elsewhere to extend the promise of MMC's into the temperature regime wherein creep, stress relaxation, oxidation, and thermal fatigue damage mechanisms lurk. This is the very regime for which alternative high-temperature materials are becoming mandatory, since further enhancement of state- of-the-art monolithic alloys is rapidly approaching a point of diminishing returns

Life assessment of structural components using inelastic finite element analyses

The need for enhanced and improved performance of structural components subject to severe cyclic thermal/mechanical loadings, such as in the aerospace industry, requires development of appropriate solution technologies involving time-dependent inelastic analyses. Such analyses are mandatory to predict local stress-strain response and to assess more accurately the cyclic life time of structural components. The NASA-Lewis Research Center is cognizant of this need. As a result of concerted efforts at Lewis during the last few years, several such finite element solution technologies (in conjunction with the finite element program MARC) were developed and successfully applied to numerous uniaxial and multiaxial problems. These solution technologies, although developed for use with MARC program, are general in nature and can easily be extended for adaptation with other finite element programs such as ABAQUS, ANSYS, etc. The description and results obtained from two such inelastic finite element solution technologies are presented. The first employs a classical (non-unified) creep-plasticity model. An application of this technology is presented for a hypersonic inlet cowl-lip problem. The second of these technologies uses a unified creep-plasticity model put forth by Freed. The structural component for which this finite element solution technology is illustrated, is a cylindrical rocket engine thrust chamber. The advantages of employing a viscoplastic model for nonlinear time-dependent structural analyses are demonstrated. The life analyses for cowl-lip and cylindrical thrust chambers are presented. These analyses are conducted by using the stress-strain response of these components obtained from the corresponding finite element analyses

An On-sun parametric study of solar hydrogen production using WO3 photoanodes

The solar production of hydrogen using photoactive electrodes is a topic receiving much attention in recent years. The use of thin metal oxide films as photoanodes allows the water splitting reaction to occur at a much lower applied voltage than would be necessary with a straight electrolysis process. Researchers have reported up to 18% solar to hydrogen efficiencies over short periods. The University of Nevada Las Vegas in conjunction with the UK based firm Hydrogen Solar have developed a prototype of this type of cell using a WO3 photoanode. An on-sun test facility has been constructed by the UNLV Center for Energy Research where a study is being conducted with regard to the effects various design parameters on the rate of hydrogen evolution. Parameters being studied include electrolyte temperature, electrolyte flow rate, electrolyte resistivity, applied voltage, and membrane to electrode spacing. The data collected will be used in a parametric study of the cell performance. This study will be used to establish general trends as to the effects of these parameters on the performance of the cells outside of a laboratory environment

The Power of Light Zine 2 - Why does life exist? - an epistemically insightful way to explore the nature of science and research at Diamond Light Source, UK

In the STFC funded Epistemic Insight Initiative project, The Power of Light, a series of resources have been designed informed by co-creation activities, pilot lessons, and workshops that involved children in schools and with their families in community spaces. Through this project with Diamond, we brought into classrooms and community spaces how light can be used to help investigate the world around us, address real-world problems and inform our thinking about Big Questions. The resources we develop support teachers' and their students' sense of agency when exploring 'how knowledge works' and how knowledge is built through different disciplines (including the natural sciences, the arts, and the humanities). This 'zine', with its focus on how scientists have been working with paleotonologists to investigate evidence, found inside the fossilised leg of a thescelosaurus, of the cataclysmic event that led to the extinction of dinosaurs. Zine 2 'Why does life exist?' has been developed through co-creative activities involving research scientists at Diamond Light Source (UK), academics, primary school teachers, STEM ambassadors, and Diamond's public engagement team. Zines use an appealing combination of text and images to create a concise comic-like narrative format to generate enthusiasm about a particular area of interest - the series of zines designed for this project focuses on research taking place at the Diamond facility. The Diamond Light Source facility houses a synchrotron which is used to conduct research in a variety of applied fields of science and technology. This zine is designed to be accessible to ages 8+, and works well with a short animation (available in both Zenodo and on the Epistemic Insight You Tube channel) that has been created with additional funding from STFC. Teaching notes are available for this zine, with guidance and activity sheets to support working with the Power of Light resources. This zine explores these discussion questions: 1) What is needed for living things to exist on Earth? 2) What helps us to learn more about past events? 3) What enables us to be able say we 'know' something

The Power of Light Zine 3 - Why do we explore the world around us? - an epistemically insightful way to explore the nature of science and research at Diamond Light Source, UK

In the STFC funded Epistemic Insight Initiative project, The Power of Light, a series of resources have been designed informed by co-creation activities, pilot lessons, and workshops that involved children in schools and with their families in community spaces. Through this project with Diamond, we brought into classrooms and community spaces how light can be used to help investigate the world around us, address real-world problems and inform our thinking about Big Questions. The resources we develop support teachers' and their students' sense of agency when exploring 'how knowledge works' and how knowledge is built through different disciplines (including the natural sciences, the arts, and the humanities). This 'zine', with its focus on how scientists have been working with astronomers, geographers, and other disciplines to explore relationships between matter in environments that we cannot directly experience here on Earth, in space, and into the future through the use of scientific modelling and a synchrotron. Zine 3, with its focus on space and energy, has been developed through co-creative activities involving research scientists at Diamond Light Source (UK), academics, primary school teachers, STEM ambassadors, and Diamond's public engagement team. Zines use an appealing combination of text and images to create a concise comic-like narrative format to generate enthusiasm about a particular area of interest - the series of zines designed for this project focuses on research taking place at the Diamond facility. The Diamond Light Source facility houses a synchrotron which is used to conduct research in a variety of applied fields of science and technology. This zine is designed to be accessible to ages 8+, and works well with a short animation (available in both Zenodo and on the Epistemic Insight You Tube channel) that has been created with additional funding from STFC. Teaching notes are available for this zine, with guidance and activity sheets to support working with the Power of Light resources. This zine explores these discussion questions: 1) What do we know bout our planet Earth (and how it 'works')? 2) What can help us build knowledge about things beyond planet Earth? 3) What might help to inform our thinking when making choices and decisions