bluuebunny/crossref_metadata_2025 huggingface dataset:
Dental service trends for older U.S. adults, 1998–2006
Authors: Skaar Daniel D. , O’Connor Heidi
Published: March 2012

This study of the Medicare Current Beneficiary Survey (MCBS) updates trends in utilization of dental services between 1998 and 2006 for community‐dwelling U.S. adults of age 65 years and older. Bivariate comparisons were made between dependent variables (annual dental visits and types of dental procedures) and independent variables (age, gender, race, income, education, population density, marital status, U.S. Census Bureau regions, and self‐reported health). The estimated percentage of community‐dwelling Medicare beneficiaries with a dental visit for the years studied increased from 45.0% in 1998 to 46.3% in 2006. The age group of respondents who were 85 years and older had the greatest percentage increase in dental visits. Those reporting visits with preventive procedures increased from 87.8% to 91.2% whereas those reporting visits with nonpreventive procedures declined from 63.9% to 58.4%. The prevalence of dental visits continues to trend upward for this population of older adults.

Increasing delivery of preventive services will likely impact the future mix of dental services as U.S. adults live longer.
Periodontal findings in a patient with Mauriac syndrome: A case report
Authors: Avula Haritha
Published: March 2012

Mauriac syndrome is a rare condition that affects people with uncontrolled diabetes. The case history of a 17‐year‐old female patient diagnosed with Mauriac syndrome and concurrently suffering from type 1 diabetes mellitus (T1DM), stunted growth, hepatomegaly, and severe periodontal disease is described. Non‐surgical periodontal therapy was the treatment provided.

Severe periodontal destruction was seen in conjunction with the unique features of this syndrome, such as hepatomegaly, dwarfism, moon‐shaped face, cushingoid fat deposition, delayed puberty, and brittle diabetes. Treatment resulted in decreased plaque and gingival scores.

A bi‐directional relationship has been established between diabetes mellitus and periodontal disease and there is an increasing emphasis on perio‐systemic interrelationships. Given the effect that such systemic disorders have on periodontal health, periodontists should be involved in the early diagnosis and treatment of such patients.
Age‐related changes in biochemical and hematologic variables inBorzoi andBeagle puppies from birth to 8 weeks
Authors: Rosset Emilie , Rannou Benoit , Casseleux Grégory , Chalvet‐Monfray Karine , Buff Samuel
Published: March 2012

Background

Nonspecific signs of illness and availability of only limited information about expected biochemical and hematologic values in puppies make formulation of a differential diagnosis challenging for veterinarians.

Objectives

The objectives of this prospective study were to describe age‐related changes in biochemical and hematologic variables inBorzoi andBeagle puppies from birth to 8 weeks and to compare results with adult reference intervals (RIs).

Methods

Biochemical and hematologic analytes in blood collected in heparin andEDTAfrom 31 clinically healthy puppies (21Beagle and 10Borzoi dogs) were measured or calculated each week from birth to 8 weeks of age.RIs were calculated using the parametric robust method afterBox–Cox transformation.

Results

There were no significant differences between values of puppies and adults forALTactivity, glucose concentration,MCHC,WBCcount, and platelet count. Total protein concentration,RBCcount, andHCTwere lower and creatine kinase activity was higher in puppies of all ages compared with these variables in adults. Compared with adultRI, in puppies urea concentration was higher at birth and week 1, creatinine concentration was lower at weeks 1–5,ALPactivity was higher at all weeks except for weeks 4 and 6, hemoglobin concentration was lower at weeks 1–8,MCVwas higher at birth and week 1, and reticulocyte count was higher at all weeks except week 1. Statistically, mixed models accounted for evaluation of the same puppies each week and in most cases demonstrated an effect of age and sometimes breed. Some reference intervals should be used with caution owing to potential outliers. The 90% confidence intervals exceeded those recommended by theInternationalFederation ofClinicalChemistry.

Conclusions

Clinicians should be aware of temporal changes in biochemical and hematologic values for puppies during the first 2 months of life to avoid misinterpretation of results.
An atypical case of recurrent cellulitis/lymphangitis in a Dutch Warmblood horse treated by surgical intervention
Authors: Oomen A. M. , Moleman M. , van den Belt A. J. M. , Brommer H.
Published: March 2012

The case reported here describes an atypical presentation of cellulitis/lymphangitis in an 8‐year‐old Dutch Warmblood mare. The horse was presented with a history of recurrent episodes of cellulitis/lymphangitis and the presence of fluctuating cyst‐like lesions on the left hindlimb. These lesions appeared to be interconnected lymphangiectasias. Surgical debridement followed by primary wound closure and local drainage was performed under general anaesthesia. Twelve months post surgery, no recurrence of cellulitis/lymphangitis had occurred and the mare had returned to her former use as a dressage horse.
Evoked prior learning experience and approach to learning as predictors of academic achievement
Authors: Trigwell Keith , Ashwin Paul , Millan Elena S.
Published: March 2012

Background. In separate studies and research from different perspectives, five factors are found to be among those related to higher quality outcomes of student learning (academic achievement). Those factors are higher self‐efficacy, deeper approaches to learning, higher quality teaching, students’ perceptions that their workload is appropriate, and greater learning motivation. University learning improvement strategies have been built on these research results.

Aim. To investigate how students’ evoked prior experience, perceptions of their learning environment, and their approaches to learning collectively contribute to academic achievement. This is the first study to investigate motivation and self‐efficacy in the same educational context as conceptions of learning, approaches to learning and perceptions of the learning environment.

Sample. Undergraduate students (773) from the full range of disciplines were part of a group of over 2,300 students who volunteered to complete a survey of their learning experience. On completing their degrees 6 and 18 months later, their academic achievement was matched with their learning experience survey data.

Method. A 77‐item questionnaire was used to gather students’ self‐report of their evoked prior experience (self‐efficacy, learning motivation, and conceptions of learning), perceptions of learning context (teaching quality and appropriate workload), and approaches to learning (deep and surface). Academic achievement was measured using the English honours degree classification system. Analyses were conducted using correlational and multi‐variable (structural equation modelling) methods.

Results. The results from the correlation methods confirmed those found in numerous earlier studies. The results from the multi‐variable analyses indicated that surface approach to learning was the strongest predictor of academic achievement, with self‐efficacy and motivation also found to be directly related. In contrast to the correlation results, a deep approach to learning was not related to academic achievement, and teaching quality and conceptions of learning were only indirectly related to achievement.

Conclusions. Research aimed at understanding how students experience their learning environment and how that experience relates to the quality of their learning needs to be conducted using a wider range of variables and more sophisticated analytical methods. In this study of one context, some of the relations found in earlier bivariate studies, and on which learning intervention strategies have been built, are not confirmed when more holistic teaching–learning contexts are analysed using multi‐variable methods.
Continuous time modelling with individually varying time intervals for oscillating and non‐oscillating processes
Authors: Voelkle Manuel C. , Oud Johan H. L.
Published: March 2012

When designing longitudinal studies, researchers often aim at equal intervals. In practice, however, this goal is hardly ever met, with different time intervals between assessment waves and different time intervals between individuals being more the rule than the exception. One of the reasons for the introduction of continuous time models by means of structural equation modelling has been to deal with irregularly spaced assessment waves (e.g., Oud & Delsing, 2010). In the present paper we extend the approach to individually varying time intervals for oscillating and non‐oscillating processes. In addition, we show not only that equal intervals are unnecessary but also that it can be advantageous to use unequal sampling intervals, in particular when the sampling rate is low. Two examples are provided to support our arguments. In the first example we compare a continuous time model of a bivariate coupled process with varying time intervals to a standard discrete time model to illustrate the importance of accounting for the exact time intervals. In the second example the effect of different sampling intervals on estimating a damped linear oscillator is investigated by means of a Monte Carlo simulation. We conclude that it is important to account for individually varying time intervals, and encourage researchers to conceive of longitudinal studies with different time intervals within and between individuals as an opportunity rather than a problem.
Welding Induced Distortions and Strains of a Built-Up Panel, Experiment and Numerical Validation
Authors: Bayley Christopher , Goldak John
Published: March 2012

Weld build-up or weld cladding is a welding process in which weld metal can be deposited in order to reclaim the material thickness. In certain applications, welding induced distortions must be controlled while simultaneously minimizing welding induced residual strains. In order to examine the relative effect of the weld build-up region on welding induced distortion and residual strains, two panels were fabricated with either a small 100 × 100 × 3 or large 200 × 200 × 3 mm depression that was subsequently filled by welding. During welding, the strains, displacements, and temperature were continuously monitored in order to compare the transient solution with companion finite element method (FEM) models of the same structures. The coupled thermo-mechanical problem was solved using Goldak Technology Inc., vrsuite program, with the level of agreement of the measured distortions, strains, and temperature profiles dependent on their location and history. Both the numerical and experimental tests showed that despite the differences in the geometry, both panels developed the same strain state, although the large welded patch had greater peak value and larger distortions.
Risk Analysis for the Urban Buried Gas Pipeline With Fuzzy Comprehensive Assessment Method
Authors: Miao Chunsheng , Zhao Jianping
Published: March 2012

Based on the statistical analysis from a great deal of failure cases, generally, the failure causes of buried pipeline can be classified into four factors, namely, third-party damage, erosion–corrosion damage, design and construction error, and incorrect operation. The factors influencing the failure of pipeline are complicated, varied and fuzzy. Especially, the influence factors of third-party damage of buried pipeline are of the character of fuzziness, which are difficult to express with the accurate mathematic models. In this paper, the failure factors of buried gas pipeline are first analyzed by fault tree analysis method. Then, the failure likelihood and failure consequence, two parts of the risk, are evaluated with fuzzy comprehensive assessment method, respectively. Finally, the in-service risk of the buried gas pipeline for a certain city is expressed by the risk matrix, which is established with the failure likelihood as vertical ordinate and the failure consequence as horizontal ordinate. It is concluded that there are two pipeline units belong to high risk category, 24 pipeline units belong to medium-high risk category, 160 pipeline units belong to medium risk category, and 392 pipeline units belong to low risk category.
Thermophysical Property Measurement of Nitrate Salt Heat Transfer Fluids
Authors: Siegel Nathan P. , Bradshaw Robert W. , Cordaro Joseph B. , Kruizenga Alan M.
Published: March 2012

Nitrate salts have been used for decades in the concentrating solar power industry as heat transfer fluids and thermal storage media. For most of this time these inorganic fluids have been restricted to use in central receiver platforms due to the useful working temperature range of the most widely researched formulation, a near eutectic mixture of sodium and potassium nitrate, which melts at 220°C and is stable in air to nearly 580°C. Recent research efforts have led to the development of nitrate salt mixtures that melt at lower temperatures and are suitable for use in parabolic trough systems. These mixtures include three or more components and generally have melting points in the range of 100°C, with stability in air up to 500°C. The design of parabolic trough systems that utilize molten salt heat transfer fluids is complicated by the fact that the properties of these fluids are considerably different from the organic heat transfer fluids that they may replace. In this paper we present measured thermophysical property data for several commercial and non-commercial molten salt mixtures that can be used in the system level design of parabolic trough and central receiver power plants. The data presented include heat capacity, density, thermal conductivity, viscosity, all as a function of temperature, along with melting point and thermal stability limits. Some properties, such as density, can be predicted by simple mixing rules. The dependence of viscosity was strongly influenced by the composition of the molten salts and, particularly, the proportion of calcium nitrate.
Investigation on the Optimum Performance of an Irreversible Solar Powered Absorption Refrigeration System
Authors: Wei Fang , Zhang Houcheng , Wu Lanmei , Lin Guoxing
Published: March 2012

An irreversible solar powered absorption refrigeration system is put forward, in which finite-rate heat transfer with the convection mode from the solar collector to the absorption refrigerator and the radiation-convection heat loss from the solar collector to the ambient, the internal irreversibility inside the working fluid are taken into account. On the basis of thermodynamic analysis and log mean temperature difference (LMTD) methods, the expression between the overall coefficient of performance (COP) of the solar powered absorption refrigeration system and the operating temperature of the solar collector is derived. The influences of heat loss of the solar collector, the irreversibility inside the working fluid, the isobaric temperature ratio, the ratio of heat-transfer coefficients on the optimal performance characteristic of the solar powered absorption refrigeration system are revealed. The results obtained in the present paper are helpful to the optimal parameter design of actual solar powered absorption refrigerators.
Integrated Oxygen-Free Gasification-Gas Turbine Power Concept: A Low-Emissions Alternative for Small-Scale Coal Plants
Authors: Monaghan Rory F. D. , Alyaser Monem H.
Published: March 2012

A power plant concept with the potential to replace the large fleet of ageing, small-scale (< 50 MWe), inefficient, polluting, and soon-to-be obsolete coal-fired power plants is proposed. The proposed plant comprises a bituminous coal-fed oxygen-free gasifier, low-temperature syngas cleanup system and an open-cycle gas turbine with heat recovery. Heat is supplied to the gasifier through combustion of a portion of the cleaned syngas produced by it. Since the proposed plant employs only a gas turbine, with no steam bottoming cycle, heat recovery from the gas turbine and its integration with the rest of the plant is crucial. A thermodynamic model of the plant has been created to assess its feasibility based on overall efficiency and emissions of CO2, SO2, mercury and particulates. The model comprises submodels for feedstock composition and enthalpy, as well as first-order thermodynamic models for each of the plant components including the gasifier, feedstock preparation, heat exchangers and steam generators, contaminant removal, combustors and turbomachinery. The results of the analysis show base case plant thermal efficiency of 38.2% on a HHV basis, which is roughly 5% points higher than that for a similarly-sized pulverized coal combustion (PCC) plants. Emissions of CO2, SO2, mercury and particulates per unit electrical energy produced in the base case are: 0.774 kg/kWh, 47.2 g/MWh, 2.37 g/GWh and 28.2 g/MWh, respectively. These values are well below emissions from similarly-sized PCC plants, which have been assessed using a spreadsheet model. The model of the proposed plant has been used to assess overall performance when torrefied pine wood is co-gasified with coal. Results show a slight decrease in plant efficiency with increasing co-gasification, with large decreases in CO2, SO2 and mercury emissions. Emissions of particulates increase slightly with co-gasification. Finally the model has been used to perform sensitivity analysis on the proposed system. Sensitivity analysis highlights the need for greater understanding of gasifier performance under a range of conditions.
Economic Potential of Innovative Receiver Concepts With Different Solar Field Configurations for Supercritical Steam Cycles
Authors: Singer Cs. , Buck R. , Pitz-Paal R. , Mu¨ller-Steinhagen H.
Published: March 2012

The cost reduction potential of solar power towers (SPT) is an important issue concerning its market introduction. Raising the steam process temperature and pressure can lead to a cost reduction due to increased overall plant efficiency. Thus, for new receiver configurations a supercritical steam cycle operated at 300 bar / 600°C / 610°C live steam conditions was assumed. The considered systems include innovative direct absorption receivers, either with conventional or beam down heliostat field layouts. For the beam down option the receiver is assumed to be a cylindrical vessel with a flow-through porous absorber structure at the internal lateral area of the cylinder. The direct absorption receiver option consists of a cylindrical barrel with downwards oriented aperture, whose absorber structure at the internal lateral area is cooled by a molten salt film. For the assessment, CFD based methods were developed to be able to examine the receiver efficiency characteristics. Based on the receiver thermal efficiency characteristics and the solar field characteristics the annual performance is evaluated using hourly time series. The assessment methodology is based on the European Concentrated Solar Thermal Roadmap (ECOSTAR) study and enables the prediction of the annual performance and the levelized cost of electricity (LCOE). Applying appropriate cost assumptions from literature the LCOE were estimated for each considered SPT concept and compared to tubular receiver concepts with molten salt and liquid metal cooling. The power level of the compared concepts and the reference case is 200 MWel. The sensitivity of the specific cost assumptions was analyzed. No detailed evaluation was done for the thermal storage, but comparable storage utilization and costs were assumed for all cases. At optimized plant parameters the results indicate a LCOE reduction potential of up to 0.5% for beam down and of up to 7.2% for the direct absorption receiver compared to today’s state of the art molten salt solar tower technology.
Direct Absorption Volumetric Molten Salt Receiver With Integral Storage
Authors: Codd Daniel S. , Slocum Alexander H.
Published: March 2012

A new design is presented for a concentrating solar power central receiver system with integrated thermal storage. Concentrated sunlight penetrates and is absorbed within a passive molten salt pool, also acting as a single-tank assisted thermocline storage system. The receiver has a relatively small aperture, open to the environment without requiring a transparent window to isolate the system, exhibiting low losses while achieving high temperatures needed for efficient power generation. The use of an insulated divider plate provides a physical and thermal barrier to separate the hot and cold salt layers within the receiver. The position of the divider plate is controlled throughout the day to enhance the natural thermocline which forms within the salt. As a result, continuous, high temperature heat extraction is possible even as the average temperature of the salt is declining. Experimental results are presented for an optically heated 5 L capacity sodium-potassium nitrate salt volumetric receiver equipped with a movable divider plate.
Development of a High-Performance Concrete to Store Thermal Energy for Concentrating Solar Power Plants
Authors: John Emerson E. , Hale W. Micah , Selvam R. Panneer
Published: March 2012

Researchers in their quest to find a suitable candidate material for solid sensible heat storage have identified concrete as an acceptable medium. However, at temperatures of 500°C and beyond the thermo-mechanical properties of ordinary concrete change significantly. This paper presents seven concrete mixtures of various material components and proportions that were developed and tested for resistance to temperatures up to 500°C. After exposure to 10 thermal cycles from ambient temperature to 500°C, six of the seven mixtures maintained in excess of 50% of their mechanical properties. This result is favorable for concrete to be used as a thermal energy storage medium. With concrete exhibiting acceptable mechanical and thermal properties at very high temperatures, the amount of energy stored per unit volume is increased, higher steam temperatures are available to facilitate power generation and the concrete can last for the design lifetime of the power generating system into which it is integrated.
Experimental Tests on Parabolic Trough Receivers Employing Bifurcated, Air-Filled Annuli
Authors: Al-Ansary Hany , Zeitoun Obida
Published: March 2012

A new parabolic trough receiver design is tested. In this design, the annulus of the receiver is bifurcated such that the half facing away from the parabolic mirror, and receives minimal concentrated sunlight, is filled with an insulating material, whereas the half receiving the majority of the concentrated sunlight is allowed to be filled with air. By insulating the outward facing half of the annulus, heat loss by radiation is minimized. In the mean time, heat loss by natural convection due to the presence of air in the lower half of the annulus is expected to be significantly subdued, since the hotter air will be closer to the heat collection element, which is at a generally higher position than the glass envelope. Experimental tests were performed on roof-mounted troughs which utilize receivers with air-filled annuli. The system consists of two identical but independent rows. The receivers in the first row have normally air-filled annuli, while the receivers in the second row have annuli that are half-filled with an insulating material and half-filled with air. The results have shown that the thermal performance of the modified receiver was indeed superior to conventional receivers with air-filled annuli.
Analysis of Performance of Direct Dry Cooling for Organic Rankine Cycle Systems
Authors: Zimmerle Daniel , Cirincione Nicholas
Published: March 2012

The performance of dry-cooled ORC systems varies significantly with environmental conditions, diurnally and seasonally. This study analyzes the impact of environmental conditions on overall performance and operational control of dry-cooled ORC systems with fixed and variable geometry expanders. Performance analysis results are extended to time-series environmental data to determine the expected performance of a system over long durations. Analysis results indicate that, if other factors are held constant, variable speed condenser fans produce minimal performance improvement, while variable-geometry expanders have a significant impact.
Convective Heat Transfer Enhancement in Solar Receivers Using Minimum Entropy Generation Optimization
Authors: Li Qi , Yuan Xigang , Neveu Pierre , Flamant Gilles
Published: March 2012

Convective heat transfer enhancement can significantly improve the thermal efficiency in the conversion, utilization, recovery and storage of energy (in particular solar thermal). Modifying velocity field is the most direct approach to enhance convective heat transfer. However, in most cases the optimal velocity field is unknown and difficult to find even for an experienced researcher. In this paper, a predictive optimization methodology in convective heat transfer enhancement based on minimum entropy generation (MEG) principle was developed. A set of Euler’s equations were derived by the variation calculus to the Lagrange function established by governing equations, specific constraints and objective functional—total entropy generation rate. The solution of these equations resulted in the optimal velocity fields, leading to the minimum entropy generation. To validate and demonstrate the future application of this methodology to solar absorbers used to convert concentrated solar energy, the steady laminar convection heat transfer process in a two-dimensional channel with fixed heat flux boundaries was optimized for given total viscous dissipations. The numerical simulation results showed that lower value of maximum wall temperature was obtained by MEG optimization, which means cheaper and safer materials. The present work indicated that the new methodology could be a good guide in convective heat transfer enhancement design work, especially in CSP receivers.
Optical and Thermal Analysis for Immersed Cooling of Photovoltaic Cells in a Highly Concentrated Beam
Authors: Darwish Ahmed , Boehm Robert F.
Published: March 2012

Concentrated solar radiation can be utilized to generate electrical power from photovoltaic cells, but it increases the photovoltaic cell temperature. This can lead to a degradation of the cell efficiency and too high of a temperature can damage the cell integrity. This is particularly important in dish and tower systems where a maximum uniform flux may be difficult to achieve. While a variety of approaches have been used to the keep the cells cool, most are based upon removal of heat from the back (opposite to the incident flux) of the cell. This paper reports on an immersion cooling technique for the cells, where a coolant is circulated over the complete cell including the front surface. An analysis is given where the cells are placed in a cylindrical glass tube where a liquid is circulated. The impacts of the various thermal processes that result from this approach are described here. A comparison is made to limited experimental data.
Compressed Air Energy Storage Flow and Power Analysis
Authors: Darwish Ahmed , Boehm Robert F.
Published: March 2012

It is being recognized that an increase in the electricity generated from central facilities of time-varying renewable energy sources will require some means of smoothing the variations with time. While thermal storage may be appropriate for solar trough and tower plants, additional approaches for storage might prove to be beneficial for other types of generation schemes. One approach to storage that has been examined to varying degrees over the years is Compressed Air Energy Storage (CAES). Compressed air can be supplied to large size tanks or underground caverns, and later this stored air can be used to generate power to shave the peak demand of electricity or maintain nearly uniform levels of power generation. The tank discharge process is time dependent on the temperature, pressure, and mass flow rate of the air leaving. Of course, this time dependency also affects the power output of the system. In the following analysis an attempt was given to determine: 1- an analysis of the charging and discharging processes; 2- a power-time relation during the discharge process; 3- an approximation for the size required for a certain energy generated (m3/MW h) as a function of the initial air pressure; 4- a relation between the discharge area and the time to stabilize the mass flow; and 5- a supplemental heat input is examined in the discharge process to maintain nearly constant discharge power. Using a thermodynamic analysis for the system the power-time history is found.
Finite Element Modeling and Ray Tracing of Parabolic Trough Collectors for Evaluation of Optical Intercept Factors With Gravity Loading
Authors: Christian Joshua M. , Ho Clifford K.
Published: March 2012

Predicting the structural and optical performance of concentrating solar power (CSP) collectors is critical to the design and performance of CSP systems. This paper presents a performance analysis which utilizes finite-element models and ray-tracing of a parabolic trough collector. The finite-element models were used to determine the impact of gravity loads on displacements and rotations of the facet surfaces, resulting in slope error distributions across the reflective surfaces. The geometry of the LUZ LS-2 parabolic trough collector was modeled in SolidWorks, and the effects of gravity on the reflective surfaces are analyzed using SolidWorks Simulation. The ideal mirror shape, along with the 90° and 0° positions (with gravity deformation) were evaluated for the LS-2. The ray-tracing programs APEX and ASAP are used to assess the impact of gravity deformations on optical performance. In the first part of the analysis, a comprehensive study is performed for the parabolic trough to evaluate a random slope error threshold (i.e., induced by manufacturing errors and assembly processes) above which additional slope errors caused by gravity sag decrease the intercept factor of the system. The optical performance of the deformed shape of the collector (in both positions) is analyzed with additional induced slope errors ranging from zero up to 1° (17.44 mrad). The intercept factor for different solar incident angles found from ray-tracing is then compared to empirical data to demonstrate if the simulations provide consistent answers with experimental data.
Improved High Temperature Solar Absorbers for Use in Concentrating Solar Power Central Receiver Applications
Authors: Ambrosini Andrea , Lambert Timothy N. , Bencomo Marlene , Hall Aaron , vanEvery Kent , Siegel Nathan P. , Ho Clifford K.
Published: March 2012

Concentrating solar power (CSP) systems use solar absorbers to convert the heat from sunlight to electric power. Increased operating temperatures are necessary to lower the cost of solar-generated electricity by improving efficiencies and reducing thermal energy storage costs. Durable new materials are needed to cope with operating temperatures < 600°C. The current coating technology (Pyromark High Temperature paint) has a solar absorptance in excess of 0.95 but a thermal emittance greater than 0.8, which results in large thermal losses at high temperatures. In addition, because solar receivers operate in air, these coatings have long term stability issues that add to the operating costs of CSP facilities. Ideal absorbers must have high solar absorptance (>0.95) and low thermal emittance (<0.3 at receiver surface operating temperatures), be stable in air, and be low-cost and readily manufacturable. Recent efforts at Sandia National Laboratories have begun to address the issue of more efficient solar selective coatings for tower applications. This paper will present an overview of these efforts which address the development of new coatings on several fronts.
Modeling of a Parabolic Trough Solar Field for Acceptance Testing: A Case Study
Authors: Wagner Michael J. , Mehos Mark S. , Kearney David W. , McMahan Andrew C.
Published: March 2012

As deployment of parabolic trough concentrating solar power (CSP) systems ramps up, the need for reliable and robust performance acceptance test guidelines for the solar field is also amplified. Project owners and/or EPC contractors often require extensive solar field performance testing as part of the plant commissioning process in order to ensure that actual solar field performance satisfies both technical specifications and performance guaranties between the involved parties. Performance test code work is currently underway at the National Renewable Energy Laboratory (NREL) in collaboration with the SolarPACES Task-I activity, and within the ASME PTC-52 committee. One important aspect of acceptance testing is the selection of a robust technology performance model. NREL1 has developed a detailed parabolic trough performance model [1] within the SAM software tool [2]. This model is capable of predicting solar field, sub-system, and component performance. It has further been modified for this work to support calculation at sub-hourly time steps. This paper presents the methodology and results of a case study comparing actual performance data for a parabolic trough solar field to the predicted results using the modified SAM trough model. Due to data limitations, the methodology is applied to a single collector loop, though it applies to larger subfields and entire solar fields. Special consideration is provided for the model formulation, improvements to the model formulation based on comparison with the collected data, and uncertainty associated with the measured data. Additionally, this paper identifies modeling considerations that are of particular importance in the solar field acceptance testing process and uses the model to provide preliminary recommendations regarding acceptable steady-state testing conditions at the single-loop level.
Design, Fabrication and Testing of an Apparatus for Material Compatibility Testing in Nitrate Salts at Temperatures Up to 700°C
Authors: Gill David D. , Siegel Nathan P. , Bradshaw Robert W. , Ho Clifford K.
Published: March 2012

Thermal energy storage is one of the key differentiators between Concentrating Solar Power (CSP) and other renewable energy technologies. Molten salt is an effective and affordable method of storing thermal energy. Current salt storage systems charge at temperatures between 390°C and 585°C (oil filled parabolic trough systems to molten salt towers). It is highly desirable to increase the operating temperature of salt storage systems in order to increase the efficiency of the power cycle and to permit the use of alternative, high-temperature cycles. However, higher salt temperatures cause increased reactivity and thus increased corrosion rates in many materials. In order to utilize molten salt at higher temperature, it is necessary to test and understand these corrosion interactions at elevated temperature. A corrosion test system has been designed and built for evaluating molten salt/material interactions to 700°C. The primary components of this system are several salt containment vessels that are constructed of 6″ dia. × 24″ long stainless steel, aluminum diffusion treated pipes with flat plate welded to one end and a flanged lid on the other. The vessels are designed to operate with a charge of 10 kg of molten salt and accommodate a “sample tree” on which corrosion test coupons may be suspended. The salt vessels are heated and insulated on the bottom half, roughly to the salt fill level, and cooled on the top half to protect the flange gasket and feedthrough ports. The samples trees have a stainless plate that reduces radiative heat transfer from the molten salt to the lid. Finite element analysis was performed to determine the pipe length and heating and cooling requirements to maintain molten salt at 700°C while limiting the lid gasket to 300°C or less. The vessels are designed to have an oxygen atmosphere in the ullage region to mitigate nitrate decomposition. Oxygen systems for operation at 700°C require careful design including the sizing, routing, cleanliness, and material selection of components in order to reduce risk of fire. Additionally, the system is designed to run at 1–2 psig which requires specialized low pressure / high temperature components. In this paper we present the design of the molten salt corrosion test system including details related to the containment vessels, oxygen handling system, and control software along with a discussion of the safety considerations necessary for these high temperature, high oxygen partial pressure tests.
Heat Loss Characteristics of a Roof Integrated Solar Micro-Concentrating Collector
Authors: Sultana Tanzeen , Morrison Graham L. , Bhardwaj Siddarth , Rosengarten Gary
Published: March 2012

Concentrating solar thermal systems offer a promising method for large scale solar energy collection. It is feasible to use concentrating solar thermal systems for rooftop applications such as domestic hot water, industrial process heat and solar air conditioning for commercial, industrial and institutional buildings. This paper describes the thermal performance of a new low-cost solar thermal micro-concentrating collector (MCT), which uses linear Fresnel reflector technology and is designed to operate at temperatures up to 220°C. The modules of this collector system are approximately 3 meters long by 1 meter wide and 0.3 meters high. The objective of the study is to optimize the design to maximise the overall thermal efficiency. The absorber is contained in a sealed enclosure to minimise convective losses. The main heat losses are due to natural convection inside the enclosure and radiation heat transfer from the absorber tube. In this paper we present the results of a computational investigation of radiation and convection heat transfer in order to understand the heat loss mechanisms. A computational model for the prototype collector has been developed using ANSYS-CFX, a commercial computational fluid dynamics software package. Radiation and convection heat loss has been investigated as a function of absorber temperature. Preliminary ray trace simulation has been performed using SolTRACE and optical efficiency has been evaluated. Finally, the MCT collector efficiency is also evaluated.
Comparison Studies of Reactivity on Nickel-Ferrite and Cerium-Oxide Redox Materials for Two-Step Thermochemical Water Splitting Below 1400°C
Authors: Kodama Tatsuya , Imaizumi Nobuki , Gokon Nobuyuki , Hatamachi Tsuyoshi , Aoyagi Daiki , Kondo Ken
Published: March 2012

A two-step thermochemical water splitting cycle using a redox system of non-volatile metal oxide is one of the promising processes for converting concentrated solar high-temperature heat into clean hydrogen in sun-belt regions. In the 1st step of the cycle or the thermal reduction step, metal oxide is thermally reduced to release oxygen molecules in an inert gas atmosphere at a higher temperature above 1400°C. In the second step or the water-decomposition step at a lower temperature, the thermally-reduced metal oxide reacts with steam to produce hydrogen. As the reactive redox metal oxide materials to be capable of working below 1400°C, nickel-doped iron oxides or Ni-ferrites supported on zirconia, and non-stoichiometric cerium oxides are the promising working materials. In the present work, a series of the nickel-ferrite redox materials of monoclinic-zirconia-supported, cubic-YSZ(yttrium-stabilized zirconia)-supported, and non-supported Ni-ferries and non-stoichiometric cerium oxide were compared on reactivity for two-step thermochemical water splitting cycle. The monoclinic-zirconia-supported Ni-ferrite produced the most quantity of hydrogen in the repeated cycles when the thermal reduction step was performed for 30 min at 1400°C and the water decomposition step for 60 min at 1000°C.
Optimization of a Coupled Vapor Compression and Absorption Cooling System Driven by Gas Fueled IC Engine
Authors: Atallah Fady , Madala Srikanth , Sadineni Suresh B. , Boehm Robert F.
Published: March 2012

In recent years, due to the increased fossil fuel costs and environmental concerns, there has been a renewed interest in absorption cooling (using low-grade heat source) systems for refrigeration and space cooling applications. Although, the stand-alone coefficient of performance (COP) is a concern with such systems, absorption cooling can be a useful add-on that improves the overall efficiency of conventional vapor compression cooling cycle. A local company based in Las Vegas which is involved in the development of advanced HVAC technologies, has developed a natural gas fueled internal combustion (IC) engine driven heat pump. This system recovers the rejected heat from the IC engine during the heating cycle, thus, increasing the heat delivered and improving the system’s overall efficiency. However, during the cooling cycle the rejected heat is dissipated to the ambient air through radiators. The overall efficiency of the system can be improved if the heat rejected during the cooling cycle can be recovered and used for space cooling or refrigeration applications. In this study, a vapor compression refrigeration system coupled with an absorption cooling system is simulated using MATLAB. The vapor compression system is driven by a natural gas fueled IC engine and the waste heat from the engine is used to drive the absorption cooling system. The waste heat is recovered both from gas exhaust and engine cooling systems. The developed simulation model is used to find the transients of both the vapor absorption and compressions systems for varied cooling demands. Important parameters such as coolant temperature and exhaust gas temperature are obtained from experimental data. This paper presents the most efficient load distribution between the vapor compression and absorption cooling systems.
Water, Energy, and Land Use Planning on Maui Island, Hawaii: Estimating Surface Water Supply
Authors: Grubert Emily A. , Webber Michael E.
Published: March 2012

Maui Island in the State of Hawaii faces land use and freshwater allocation challenges associated with a growing population and a changing economic base as plantation agriculture has declined. Debate about whether water should be restored to environmental flows, allocated to new urban development for residents and tourists, or be used to irrigate food or fuel crops has highlighted Maui’s opportunity to make integrated resource decisions that consider land, water, and energy in particular. One major potential water demand on Maui is for irrigation for biofuels crops, such as sugarcane for ethanol. While Maui’s energy system is currently low in water intensity, using irrigated biofuels could increase the need for local water investment in energy systems. This paper aims to characterize surface water supply on Maui in order to draw conclusions about supply adequacy for biofuel irrigation. Narrow-scope empirical equations linking streamflow and precipitation tend to produce more accurate estimates for individual streams: for example, equations based only on northeast Maui streams tend to predict northeast Maui stream flows better than equations based on all of Maui’s streams. However, specific equations do not exist for most regions of Maui. This paper finds that general and specific empirical equations for northeast Maui predict nearly identical aggregate streamflows. Irrigation ditch flow comprises aggregate streamflow from a given region, so it is likely that existing, general equations can predict irrigation ditch flows with acceptable accuracy.
Hydrokinetic Energy Harvesting System From Vortex Induced Vibrations of Submerged Bodies
Authors: Lobo Varun , Banerjee Arindam , Mainsah Nyuykighan , Kimball Jonathan
Published: March 2012

A Vortex Induced Vibration (VIV) based hydrokinetic energy system is discussed in this paper. Vibrations induced on a body (facing an external flow) due to the periodic irregularities in the flow caused by boundary layer separation are called as VIV. This separation of the boundary layer from the surface causes vortex formation in the wake region of the cylinder. The lift-force or the transverse oscillation of the vibrating cylinder depends upon the strength and modes of the vortex formed. The VIV energy harvesting system is based on the idea of maximizing rather than spoiling vortex shedding and was discovered in 2004 at the University of Michigan by Bernitsas and Raghavan. The vibrating bodies will in turn be used to harness energy using an efficient power-take-off system. In this paper, we discuss the hydrodynamic design of such a VIV based energy harvesting system using computational fluid dynamics. A fluid structure interaction calculation is performed to determine the forces on the surface of a bluff body due to separation of vortices from the surface. The hydrodynamic forces that act on such a system depend on the cylinder diameter, flow velocity, modes of vortex shedding and arrangement of cylinder(s). A detailed computational study on the effect of different design parameters listed above are first carried on a single cylinder arrangement; this is followed by a more detailed analysis that is extended to multiple cylinders. For a two-cylinder arrangement, the positions in which the cylinders are placed are also found to play an important role, as the vortex shed from one cylinder may be used to enhance the forces of lift on another cylinder present in its wake. Furthermore, the design of a VIV generator requires optimal damping and low mass ratio to enable high energy conversion via an efficient power take-off mechanism. The working and design considerations of the energy converter is outlined starting with a set of basic definitions pertaining to this technology. A tubular linear interior permanent magnet generator (TL-IPM) connected to a power converter is used; a linear generator was chosen to minimize mechanical components, such as gears or cams in the system.
Dry Cooling in Solar Thermal Power Plants
Authors: Goswami Jaya
Published: March 2012

The purpose of this study is to evaluate the performance metrics of a solar thermal power plant with dry cooling and further implement a method to increase the cycle efficiency, using passive cooling techniques within the dry cooling cycle. Current methods implementing dry cooled condensation use an air-cooled condenser for heat rejection. While this reduces the water consumption of the plant, it results in performance penalties in the overall plant between 5–10% [1]. Passive cooling methods can be used to alleviate the performance penalties. While passive cooling methods have been studied and used on a small scale, this model explores the possibilities of applying these methods to large-scale solar thermal power plants. Based on the model developed, it was found that underground-cooling techniques can improve the performance of the overall dry cooled solar thermal power plant by up to 3% at peak dry bulb temperatures. This study finds that there is a possibility to apply these passive cooling techniques on a large scale to yield positive results.
Performance of the Southern Nevada Water Authority of Amonix’s High Concentration Multi-Junction System
Authors: Wood Gary , Sahm Aaron , Hurt Rick , Boehm Robert , Stone Kenneth W.
Published: March 2012

The Southern Nevada Water Authority contracted with Amonix, Inc. in 2008 to procure 220 kWdc of their latest generation multi-junction cell High Concentration Photovoltaic systems (HCPV). This paper discusses the performance of the six HCPV systems that started operating in mid 2009. Data sets included show: a. Daily power performance; b. Power performance compared to the specified performance; c. Effect of field shading upon the daily power performance. What is demonstrated is the system power performance has not degraded during this initial period of operation and continues to meet or exceed the specified performance levels.