bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar Water Detoxification: Novel TiO2 Powders as Highly Active Photocatalysts
Authors: Lindner M. , Bahnemann D. W. , Hirthe B. , Griebler W.-D.
Published: February 2008

The photocatalytic activity of a novel anatase titanium dioxide powder, namely Sachtleben Hombikat UV 100, has been investigated and compared with that of a well-studied material (i.e., Degussa P25). Laboratory experiments using dichloroacetate (DCA) as the model pollutant have been carried out showing a very high photonic efficiency (ζ) reaching almost unity at low-light intensities. The effect of pH, substrate concentration, catalyst concentration, and addition of various inorganic salts has been thoroughly investigated. The inhibiting effect of anions such as chloride, nitrate, sulphate, and phosphate was completely reversible upon washing the catalyst powder with pure water or diluted base, respectively. The overall photonic efficiency of the DCA degradation was found to decrease with increasing illumination intensity. Various kinetic and mechanistic models are proposed to explain this effect as well as the results of the other experiments. Implications of these laboratory results for “real world” applications, e.g., for the design of appropriate photoreactors, are discussed.
A Photovoltaic Solar Water Heating System
Authors: Fanney A. H. , Dougherty B. P.
Published: February 2008

A novel solar water heating system was patented in 1994. This system uses photovoltaic cells to generate electrical energy that is subsequently dissipated in multiple electric resistive heating elements. A microprocessor controller continually selects the appropriate heating elements such that the resistive load causes the photovoltaic array to operate at or near maximum power. Unlike other residential photovoltaic systems, the photovoltaic solar water heating system does not require an inverter to convert the direct current supplied by the photovoltaic array to an alternating current or a battery system for storage. It uses the direct current supplied by the photovoltaic array and the inherent storage capabilities of a residential water heater. A photovoltaic solar hot water system eliminates the components most often associated with the failures of solar thermal hot water systems. Although currently more expensive than a solar thermal hot water system, the continued decline of photovoltaic cell prices is likely to make this system competitive with solar thermal hot water systems within the next decade. This paper describes the system, discusses the advantages and disadvantages relative to solar thermal water heating systems, reviews the various control strategies which have been considered, and presents experimental results for two full-scale prototype systems.
Solar Power Output Correlation With Utility Demand in Southern Nevada
Authors: Frei J. A. , Chen Y.-T. , Boehm R. F.
Published: February 2008

Various solar electric system performance codes are used to predict the power generated by different solar power systems in the Southern Nevada area during 1990 by using the National Solar Radiation Data Base (NSRDB) for Las Vegas. The system types evaluated along with the prediction codes (shown in parenthesis) are as follows: a central receiver or a power tower system with various amounts of storage (SOLERGY), a Luz-type SEGS parabolic trough system without fossil fuel backup or storage (LUZERGY), a dish-Stirling system (DISH2, a conversion of direct beam radiation with constant collector/engine efficiency was used for this), and various arrangements of nonconcentrating photovoltaic devices (PVFORM). Comparisons of these results are made with the daily variations of load requirements of an electrical utility operating in the same geographical area. These comparisons are made for summer and winter periods. It is shown that several of the power generation schemes have summer peak outputs that occur at times very near to, but not coincident with, the peak utility load requirements. The power tower with a relatively small amount of thermal storage was the only scheme able to provide full power output at the times of summer peak demands. Winter peaks in this region occur during the night. Two comparisons are made that illuminate the summer load serving capability of solar generation in addition to simply showing time-variations of outputs. Included in these comparisons are the determination of the difference in time between the peak power output and the peak demand, as well as the normalized fraction of the peak power generated at the peak demand times.
The Operating Strategy and Its Impact on the Performance of a 30 MWe SEGS Plant
Authors: Lippke F.
Published: February 2008

The part-load behavior of a typical 30 MWe SEGS plant was studied using the detailed thermodynamic model EASY. In this model, a detailed solar field model was directly included, which was based on measurement results of an LS-2 collector and accounts for various conditions of receiver tubes, lost mirrors, and measured reflectivity. For the first time, the overall plant performance of a solar electric generating system could he compared with this tool, and the influence of changing operating conditions could be analyzed. Both, the solar field and the complex EASY model were first compared to measured plant data. This showed that, although the results of the solar field model agreed quite well with test loop data, there are still little differences between the plant model results and real plant conditions. Finally, the effects of different plant operating strategies were studied for summer, fall, and winter days. This clearly demonstrates that, depending on the insolation conditions, different superheating temperatures should be chosen to maximize the net output. With a reduced solar field pressure drop due to using rotating joints in the field, the lowest possible superheating temperature maximizes the net output in any case.
Modeling and Optimum Design of a Wire Mesh Solar Volumetric Air Receiver
Authors: Hellmuth T. E. , Matthews L. K.
Published: February 2008

This paper describes the development of a computer model to predict the performance of a discrete layer wire mesh solar volumetric air receiver. The model accounts for all important energy transfer processes within the absorber and allows for the use of two different types of wire mesh screens. Model predictions are compared to experimental results for validation purposes. An optimum design analysis is performed to determine optimum receiver characteristics and performance. Results show a predicted efficiency in the range of 89 percent to 87 percent when the outlet air temperature is between 700°C and 820°C, respectively.
In-Situ FT-IR Monitoring of a Solar Flux Induced Chemical Process
Authors: Markham J. R. , Cosgrove J. E. , Nelson C. M. , Bonanno A. S. , Schlief R. E. , Stoy M. A. , Glatzmaier G. C. , Bingham C. E. , Lewandowski A. A.
Published: February 2008

The capability to perform in-situ, on-line monitoring of processes induced by concentrated solar flux will enhance the development and utilization of solar technologies. Temperature measurements and chemical concentration measurements provide an understanding of the ongoing chemistry, process limits, and process reproducibility. A Fourier transform infrared (FT-IR) spectrometer was optically coupled to a quartz flow reactor at the High Flux Solar Furnace of the National Renewable Energy Laboratory in Golden, CO. In-situ emission/transmission spectroscopy was utilized to simultaneously monitor steam temperature and the concentration of formed hydrogen bromide during the solar flux induced reaction of steam and bromine. The photochemical process is being investigated for the production of industrial quantities of hydrogen and oxygen, where downstream electrolysis of the formed hydrogen bromide provides the hydrogen and regenerates bromine. Steam temperature was measured to increase upon the addition of bromine to the reactor. Gas temperature increases of 200°C to 400°C were observed. Hydrogen bromide concentrations up to ten percent of the reactor gas volume were measured. The FT-IR system provided quantitative information of two critical parameters of the measured process and serves to accelerate this technology area.
Photogrammetry: An Available Surface Characterization Tool for Solar Concentrators, Part II: Assessment of Surfaces
Authors: Shortis M. , Johnston G.
Published: February 2008

In a previous paper, the results of photogrammetric measurements of a number of paraboloidal reflecting surfaces were presented. These results showed that photogrammetry can provide three-dimensional surface characterisations of such solar concentrators. The present paper describes the assessment of the quality of these surfaces as a derivation of the photogrammetrically produced surface coordinates. Statistical analysis of the z-coordinate distribution of errors indicates that these generally conform to a univariate Gaussian distribution, while the numerical assessment of the surface normal vectors on these surfaces indicates that the surface normal deviations appear to follow an approximately bivariate Gaussian distribution. Ray tracing of the measured surfaces to predict the expected flux distribution at the focal point of the 400 m2 dish show a close correlation with the videographically measured flux distribution at the focal point of the dish.
Wind Tubine Cost of Electricity and Capacity Factor
Authors: Cavallo A. J.
Published: February 2008

Wind turbines are currently designed to minimize the cost of electricity at the wind turbine (the busbar cost) in a given wind regime, ignoring constraints on the capacity factor (the ratio of the average power output to the maximum power output). The trade-off between these two quantities can be examined in a straightforward fashion; it is found that the capacity factor can be increased by a factor of 30 percent above its value at the cost minimum for a ten percent increase in the busbar cost of electricity. This has important implications for the large-scale integration of wind electricity on utility grids where the cost of transmission may be a significant fraction of the cost of delivered electricity, or where transmission line capacity may be limited.
Advanced Wind Turbine Design
Authors: Jamieson P. M. , Jaffrey A.
Published: February 2008

Garrad Hassan have a project in progress funded by the U.K. Department of Trade & Industry (DTI) to assess the prospects and Cost benefits of advanced wind turbine design. In the course of this work, a new concept, the coned rotor design, has been developed. This enables a wind turbine system to operate in effect with variable rotor diameter augmenting energy capture in light winds and shedding loads in storm conditions. Comparisons with conventional design suggest that a major benefit in reduced cost of wind-generated electricity may be possible.
Optimization of a Class of Latent Thermal Energy Storage Systems With Multiple Phase-Change Materials
Authors: Aceves S. M. , Nakamura H. , Reistad G. M. , Martinez-Frias J.
Published: February 2008

This paper presents an analysis of a class of latent thermal energy storage (LTES) system. The analysis is based on a simplified model that allows the system performance to be evaluated in terms of a small set of parameters, while still retaining the main thermodynamic aspects associated with their operation. This analysis therefore permits the broad-based application potential of these systems to be viewed. The paper also discusses the applicability of the model to practical systems. This paper analyzes LTES with multiple energy storage cells and multiple phase-change materials (PCMs). The most general case of infinite energy storage cells and PCMs is solved, for the charge process only, as well as for the overall charge-discharge process. The results yield the optimum phase change temperature, expressed as a continuous function of position along the LTES. The method is equally applicable to the case of a finite number of storage cells. An example of the application of the method to this case is also included. The results show the optimum phase change temperatures for each of the problems being considered, along with the corresponding optimum exergetic efficiencies. The solutions to the optimization problems are surprisingly simple to express, considering the difficulty of the problems, and indicate the potential advantages of using LTES with multiple PCMs.
A Transient Heat and Mass Transfer Model of Residential Attics Used to Simulate Radiant Barrier Retrofits, Part I: Development
Authors: Medina M. A. , O’Neal D. L. , Turner W. D.
Published: February 2008

This paper describes a transient heat and mass transfer model of residential attics. The model is used to predict hourly ceiling heat gain/loss in residences with the purpose of estimating reductions in cooling and heating loads produced by radiant barriers. The model accounts for transient conduction, convection, and radiation and incorporates moisture and air transport across the attic. Environmental variables, such as solar loads on outer attic surfaces and sky temperatures, are also estimated. The model is driven by hourly weather data which include: outdoor dry bulb air temperature, horizontal solar and sky radiation, wind speed and direction, relative humidity (or dew point), and cloud cover data. The output of the model includes ceiling heat fluxes, inner and outer heat fluxes from all surfaces, inner and outer surface temperatures, and attic dry bulb air temperatures. The calculated fluxes have been compared to experimental data of side-by-side testing of attics retrofit with radiant barriers. The model predicts ceiling heat flows with an error of less than ten percent for most cases.
Performance of a Heat Pipe Solar Collector
Authors: Ismail K. A. R. , Abogderah M. M.
Published: February 2008

This paper presents a comparative study between theoretical predictions and experimental results of a flat-plate solar collector with heat pipes. The theoretical model for the heat pipe solar collector is based upon the method by Duffie and Beckman(1980), modified to use heat pipes for energy transport. The methanol filled heat pipes are self-contained devices whose evaporators are inserted under pressure in the flat plate of the solar collector and the heat exchange is carried out at their condensers. The evaporators contain a wick of one mesh layer to ensure a better distribution of the working fluid. The condensers are wickless and inclined 15 deg more than the inclination of the evaporators to facilitate the return of the condensate to the evaporators. The time constant of the heat pipe solar collector was calculated and found to be about 23 minutes. Also presented in this paper are comparative experimental results of the proposed solar collector and a conventional commercial solar collector. The two collectors were tested simultaneously. The instantaneous efficiencies of the heat pipe solar collector are lower than the conventional collector in the morning and higher when the heat pipes reach their operating temperatures.
Wind Turbine Performance Under Icing Conditions
Authors: Jasinski W. J. , Noe S. C. , Selig M. S. , Bragg M. B.
Published: February 2008

The effects of rime ice on horizontal axis wind turbine performance were estimated. For typical supercooled fog conditions found in cold northern regions, four rime ice accretions on the S809 wind turbine airfoil were predicted using the NASA LEWICE code. The resulting airfoil/ice profile combinations were wind tunnel tested to obtain the lift, drag, and pitching moment characteristics over the Reynolds number range 1−2 × 106. These data were used in the PROPID wind turbine performance prediction code to predict the effects of rime ice on a 450-kW rated-power, 28.7-m diameter turbine operated under both stall-regulated and variable-speed/variable-pitch modes. Performance losses on the order of 20 percent were observed for the variable-speed/ variable-pitch rotor. For the stall-regulated rotor, however, a relatively small rime ice profile yielded significantly larger performance losses. For a larger 0.08c-long rime ice protrusion, however, the rated peak power was exceeded by 16 percent because at high angles the rime ice shape acted like a leading edge flap, thereby increasing the airfoil Cl,max and delaying stall.
Numerical Investigation of Airfoil Dynamic Stall in Simultaneous Harmonic Oscillatory and Translatory Motion
Authors: Ekaterinaris J. A. , So̸rensen N. N. , Rasmussen F.
Published: February 2008

Wind turbine blades are subject to complex flow conditions. For operation in yaw and turbulent inflow, the blade sections appear to execute a motion more complex than a harmonic blade oscillation, which causes dynamic stall. Predictions of dynamic stall caused by simple harmonic oscillation are crucial to efforts in understanding and improving wind turbine performance. Investigation of dynamic stall development caused by a combined oscillatory and translatory motion contributes to better understand blade loading under complex flow conditions. In this paper, numerical predictions of light and deep stall caused by simple oscillatory motion are obtained first. The ability of the numerical solution to predict dynamic stall loads caused by a combined motion is further investigated. The numerical solution is obtained with a factorized, upwind-biased numerical scheme. The turbulent flow region is computed with a one-equation turbulence model. A transition model is used to simulate the transitional flow effects, which play an important role to the overall unsteady flowfield development. The computed results are compared with available experimental data.
Dynamic Response of a Feedback Thermoresistive Electrical Substitution Pyranometer
Authors: Freire R. C. S. , Deep G. S. , Lobo P. C. , Lima A. M. N. , Rocha Neto J. S. , Oliveira A.
Published: February 2008

Calorimetric pyranometers use plane black thermal sensors which absorb solar radiation. If a thermoresistive transducer (sensor-detector combination) is used, the temperature measured is nearer the true value than for thermoelectric transducers. More importantly, the measurement of electrical power is much more accurate than the measurement of temperature. In commercial platinum (thermoresistive), thin film thermometers, the substrate produces transducer time constants an order of magnitude larger than for the best thermoelectric transducers. Use of an electronic amplifier with the thermoresistive sensor, forming one arm of a Wheatstone bridge and arranged in a negative feedback configuration, can reduce the overall response time considerably. Theoretical formulations of instrument response, taking into account the amplifier input offset voltage, are presented and the response time is estimated.
A Perspective on Methods for Analysis of Measured Energy Data from Commercial Buildings
Authors: Claridge D. E.
Published: February 2008

This paper provides a historical perspective on the methods used to analyze measured energy use in commercial buildings. It summarizes the capabilities and uncertainties of the regression methods used in most M&V applications today and the calibrated simulation approaches used for M&V, commissioning, and end-use disaggregation. The need for graphical indices is introduced and applications of artificial neural networks, Fourier series and spectral analysis methods for M&V and data acquisition are described.
Multivariate Regression Modeling
Authors: Katipamula S. , Reddy T. A. , Claridge D. E.
Published: February 2008

An empirical or regression modeling approach is simple to develop and easy to use compared to detailed hourly simulations of energy use in commercial buildings. Therefore, regression models developed from measured energy data are becoming an increasingly popular method for determining retrofit savings or identifying operational and maintenance (O&M) problems. Because energy consumption in large commercial buildings is a complex function of climatic conditions, building characteristics, building usage, system characteristics and type of heating, ventilation, and air conditioning (HVAC) equipment used, a multiple linear regression (MLR) model provides better accuracy than a single-variable model for modeling energy consumption. Also, when hourly monitored data are available, an issue which arises is what time resolution to adopt for regression models to be most accurate. This paper addresses both these topics. This paper reviews the literature on MLR models of building energy use, describes the methodology to develop MLR models, and highlights the usefulness of MLR models as baseline models and in detecting deviations in energy consumption resulting from major operational changes. The paper first develops the functional basis of cooling energy use for two commonly used HVAC systems: dual-duct constant volume (DDCV) and dual-duct variable air volume (DDVAV). Using these functional forms, the cooling energy consumption in five large commercial buildings located in central Texas were modeled at monthly, daily, hourly, and hour-of-day (HOD) time scales. Compared to the single-variable model (two-parameter model with outdoor dry-bulb as the only variable), MLR models showed a decrease in coefficient of variation (CV) between 10 percent to 60 percent, with an average decrease of about 33 percent, thus clearly indicating the superiority of MLR models. Although the models at the monthly time scale had higher coefficient of determination (R2) and lower CV than daily, hourly, and HOD models, the daily and HOD models proved more accurate at predicting cooling energy use.
Modeling Hourly Energy Use in Commercial Buildings With Fourier Series Functional Forms
Authors: Dhar A. , Reddy T. A. , Claridge D. E.
Published: February 2008

Hourly energy use in commercial buildings shows periodic variation in daily and annual cycles. Moreover, the pattern of variation is such that Fourier series functional forms provide one of the best approaches for modeling this behavior. Results from numerous case studies have demonstrated the power of Fourier series as a modeling tool to represent hourly energy use in commercial buildings. This paper describes the Fourier series approaches that have been developed for modeling energy use in commercial buildings and presents the results of application to data collected from many sites.
Application of Measured Loads to Wind Turbine Fatigue and Reliability Analysis
Authors: Veers P. S. , Winterstein S. R.
Published: February 2008

Cyclic loadings produce progressive damage that can ultimately result in wind turbine structural failure. There are many issues that must be dealt with in turning load measurements into estimates of component fatigue life. This paper deals with how the measured loads can be analyzed and processed to meet the needs of both fatigue life calculations and reliability estimates. It is recommended that moments of the distribution of rainflow-range load amplitudes be calculated and used to characterize the fatigue loading. These moments reflect successively more detailed physical characteristics of the loading (mean, spread, tail behavior). Moments can be calculated from data samples and functional forms can be fitted to wind conditions, such as wind speed and turbulence intensity, with standard regression techniques. Distributions of load amplitudes that accurately reflect the damaging potential of the loadings can be estimated from the moments at any wind condition of interest. Fatigue life can then be calculated from the estimated load distributions, and the overall, long-term, or design spectrum can be generated for any particular wind-speed distribution. Characterizing the uncertainty in the distribution of cyclic loads is facilitated by using a small set of descriptive statistics for which uncertainties can be estimated. The effects of loading parameter uncertainty can then be transferred to the fatigue life estimate and compared with other uncertainties, such as material durability.
Mixed Convection Heat Transfer and Pressure Drop Correlations for Tube-ln-Shell Thermosyphon Heat Exchangers With Uniform Heat Flux
Authors: Dahl S. D. , Davidson J. H.
Published: February 2008

An important issue arising from prior studies of thermosyphon heat exchangers for use in solar water heaters is the need for heat transfer and pressure drop correlations for the laminar, mixed-convection regime in which these many of these heat exchangers operate. In this paper, we present empirical correlations for tube-in-shell heat exchangers with the thermosyphon flow on the shell side. The correlations are determined for uniform heat flux on the tube walls. Ranges of Reynolds and Grashof numbers are 130 to 2,000 and 4 × 105 to 8 × 107, respectively. Nusselt number correlations are presented in a form that combines the contributions of forced and natural convection. Mixed convection dominates forced convection heat transfer in these geometries. Pressure drop is not significantly affected by mixed convection.
Analysis of a Load-Side Heat Exchanger for a Solar Domestic Hot Water Heating System
Authors: Smith T. R. , Burns P. J. , Hittle D. C.
Published: February 2008

Testing is done of an unpressurized drainback system with a load-side heat exchanger. Analytical calculations for the heat exchanger effectiveness and three models for convective heat transfer coefficients from correlations are compared against the experimental data. TRNSYS simulations were performed using the average effectiveness of 0.78 (the calculated effectiveness varies from 0.68 to 0.95); the results compare favorably with experimental results, indicating that a constant effectiveness is an adequate model for the system.
Performance Prediction of a Sub-Slab Heat Exchanger for Geothermal Heat Pumps
Authors: Den Braven K. , Nielson E.
Published: February 2008

A large portion of the installation cost of a ground-coupled heat pump system is for the excavation necessary for ground coil placement. One possible method of reducing this cost is to place the ground coils beneath the slab floor of the building. This configuration of ground coil placement has not been specifically addressed in previous research. Freezing of the soil must be avoided in such a system. To simulate the temperature response of the surrounding soil to heat pump operation, a computer model was developed which incorporates line source theory in the form of a system of rings. The fluid temperature change along the length of the coil was used to determine the distribution of the ground load throughout the ring system. The model includes an adiabatic upper boundary, seasonal soil temperature variation, and thermal interference throughout the system. Using these results, the minimum soil temperature over a season was predicted. Based on these results, design recommendations for ground coil installation are provided based on available area, soil type, heat extraction rate, depth of coil beneath the slab floor, and depth of slab floor below grade. These include recommendations for pipe spacing, flow direction, and a method to determine whether this type of system is feasible for installation in a particular location.
Experimental Study of the Heat and Mass Transfer in a Packed Bed Liquid Desiccant Air Dehumidifier
Authors: O¨berg V. , Goswami D. Y.
Published: February 2008

Desiccant cooling systems have the ability to provide efficient humidity and temperature control while reducing the electrical energy requirement for air conditioning as compared to a conventional system. Naturally, the desiccant air dehumidification process greatly influences the overall performance of the desiccant system. Therefore, the effects of variables such as air and desiccant flow rates, air temperature and humidity, desiccant temperature and concentration, and the area available for heat and mass transfer are of great interest. Due to the complexity of the dehumidification process, theoretical modeling relies heavily upon experimental studies. However, a limited number of experimental studies are reported in the literature. This paper presents results from a detailed experimental investigation of the heat and mass transfer between a liquid desiccant (triethylene glycol) and air in a packed bed absorption tower using high liquid flow rates. A high performance packing that combines good heat and mass transfer characteristics with low pressure drop is used. The rate of dehumidification, as well as the effectiveness of the dehumidification process are assessed based on the variables listed above. Good agreement is shown to exist between the experimental findings and predictions from finite difference modeling. In addition, a comparison between the findings in the present study and findings previously reported in the literature is made. The results obtained from this study make it possible to characterize the important variables which impact the system design.
A Continuous Heat Regenerative Adsorption Refrigerator Using Spiral Plate Heat Exchanger as Adsorbers: Improvements
Authors: Wang R. Z. , Wu J. Y. , Xu Y. X.
Published: February 2008

Spiral plate heat exchangers as adsorbers have been proposed, and a prototype heat regenerative adsorption refrigerator using activated carbon-methanol pair has been developed and tested. Various improvements have been made, at last we get a specific cooling power for 2.6 kg-ice/day-kg adsorbent at the condition of generation temperature lower than 100°C. Discussions on the arrangements of thermal cycles and influences of design are shown.
Dehumidification and Simultaneous Removal of Selected Pollutants from Indoor Air by a Desiccant Wheel Using a 1M Type Desiccant
Authors: Popescu M. , Ghosh T. K.
Published: February 2008

Solid-desiccant dehumidifiers are increasingly becoming an integral part of desiccant based air-conditioning systems because of their effective handling of latent heat loads compared to conventional vapor compression units. In these units, either a silica gel or a molecular sieve is used for dehumidification of air. Both of them have the capability to co-adsorb various chemical pollutants during dehumidification of air. However, the shape of the isotherm for water vapor on these materials is not favorable for desiccant cooling applications. A mixture (IM desiccant) containing a silica gel, a molecular sieve, and a hydrophobic molecular sieve that was coated on an aluminum foil was studied for its capability for simultaneous removal of moisture and some selected pollutants from air. Experimental data were obtained in a fixed bed adsorber that simulated the operation of a rotary desiccant wheel. Air to be dehumidified and cleaned and the hot regeneration air were cycled in a specific time interval through this bed. The shape of the water isotherm on IM desiccant was found to be in between that of silica gel and molecular sieve 13×, but its uptake capacity was significantly lower than that of either silica gel or molecular sieve. A flow rate of about 100 L/min that provided a face velocity of about 132 cm/s was used in the adsorption step. The flow rate during regeneration was about 50 L/min. The temperature of the inlet air was about 23°C and its relative humidity was varied between 20 percent and 80 percent. The concentrations of pollutants were as follows; carbon dioxide: 1050 and 2300 ppm; toluene: 32 ppm; 1,1,1-trichloroethane: 172 ppm, and formaldehyde: 0.35 ppm. A complete breakthrough of all the pollutants was observed during an adsorption cycle. However, a removal efficiency greater than 50 percent for these pollutants was observed if the adsorption cycle time was about 1 minute.
Optical Fiber Reflectometer Coupled With a Solar Concentrator to Determine Solar Reflectivity and Absorptivity at High Temperature
Authors: Hernandez D. , Antoine D. , Olalde G. , Gineste J. M.
Published: February 2008

Devices and methods are presented in which an optical fiber reflectometer and a solar concentrator are used to determine solar reflectivity and absorptivity for opaque and diffuse materials. The measurements can be taken at high temperature, the final aim is to reach 2500°C. Firstly we will present the specific reflectometer and its measurement principles. We will then describe the whole experimental hardware (solar concentrator, associated devices) and the method used to determine solar reflectivity and absorptivity. Finally, we will present examples of results obtained on a metallic sample.
Prediction Uncertainty of Linear Building Energy Use Models With Autocorrelated Residuals
Authors: Ruch D. K. , Kissock J. K. , Reddy T. A.
Published: February 2008

Autocorrelated residuals from regression models of building energy use present problems when attempting to estimate retrofit energy savings and the uncertainty of the savings. This paper discusses the causes of autocorrelation in energy use models and proposes a method to deal with autocorrelation. A hybrid of ordinary least squares (OLS) and autoregressive (AR) models is developed to accurately predict energy use and give reasonable uncertainty estimates. Only linear models are considered because both the data and the physical theory for many commercial buildings support this choice (Kissock, 1993). A procedure for model selection is presented and tested on data from three commercial buildings participating in the Texas LoanSTAR program. In every case examined, the hybrid OLS-AR model provided the best estimate of energy use and the most robust estimate of uncertainty.
Analysis of the Working Process and Mechanical Losses in a Stirling Engine for a Solar Power Unit
Authors: Makhkamov Kh. Kh. , Ingham D. B.
Published: February 2008

In this paper a second level mathematical model for the computational simulation of the working process of a 1-kW Stirling engine has been used and the results obtained are presented. The internal circuit of the engine in the calculation scheme was divided into five chambers, namely, the expansion space, heater, regenerator, cooler and the compression space, and the governing system of ordinary differential equations for the energy and mass conservation were solved in each chamber by Euler’s method. In additional, mechanical losses in the construction of the engine have been determined and the computational results show that the mechanical losses for this particular design of the Stirling engine may be up to 50% of the indicated power of the engine.
Applicability of Uniform Heat Flux Nusselt Number Correlations to Thermosyphon Heat Exchangers for Solar Water Heaters
Authors: Dahl S. , Davidson J.
Published: February 2008

Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under morerealistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.
Correlations for Surface Temperatures of the Glass Cover for Estimation of Heat-Transfer Coefficients in Upward Heat-Flow in Solar Collectors with Single Glazing
Authors: Akhtar N. , Mullick S. C.
Published: February 2008

A set of correlations for predicting the temperatures of inner and outer surfaces of the glass-cover of flat-plate solar collectors with single glazing is developed, enabling estimation of the heat-transfer coefficients. The temperatures of the inner surface of the glass-cover (Tgi) and outer surface of glass-cover (Tgo) are computed using the proposed relations and the results are compared with those obtained by numerical solution of heat balance equations. Using the proposed relations maximum computational errors in Tgi and Tgo are within 1.5 degrees and 3.0 degrees respectively: for the range of glass-cover thicknesses 3 mm to 5 mm.(Using the previously available relation in the literature computational error in glass-cover temperature is 9 to 11 degrees.) As a result the maximum errors in calculation of convective and radiative heat-transfer coefficients between the absorber-plate and the glass-cover are reduced from about 8.8 percent to 1.1 percent and from 3.7 percent to 0.5 percent respectively. With such low errors in computation of the heat-transfer coefficients, numerical solution of heat balance equations is not required. The proposed method can also take into account absorption in the glass-cover.
Two-Dimensional Model of the Air Flow and Temperature Distribution in a Cavity-Type Heat Receiver of a Solar Stirling Engine
Authors: Makhkamov Kh. Kh. , Ingham D. B.
Published: February 2008

A theoretical study on the air flow and temperature in the heat receiver, affected by free convection, of a Stirling Engine for a Dish/Stirling Engine Power System is presented. The standard k-ε turbulence model for the fluid flow has been used and the boundary conditions employed were obtained using a second level mathematical model of the Stirling Engine working cycle. Physical models for the distribution of the solar insolation from the Concentrator on the bottom and side walls of the cavity-type heat receiver have been taken into account. The numerical results show that most of the heat losses in the receiver are due to re-radiation from the cavity and conduction through the walls of the cavity. It is in the region of the boundary of the input window of the heat receiver where there is a sensible reduction in the temperature in the shell of the heat exchangers and this is due to the free convection of the air. Further, the numerical results show that convective heat losses increase with decreasing tilt angle.
Aluminum Nitridation in a Solar-Heated Vibrating Fluidized Bed Reactor
Authors: Lock John P. , Peterson Brennan L. , Weimer Alan W. , Pitts Roland J. , Bingham Carl E. , Lewandowski Allan A.
Published: February 2008

A vibrating fluidized bed reactor was constructed and interfaced with the High-Flux Solar Furnace at the National Renewable Energy Laboratory in Golden, CO. Various precursor mixtures of aluminum and aluminum nitride were heated for approximately 10 to 15 minutes using focused sunlight with an intensity as high as 2000 kW/m2. Particles ranging in size from 2 μm to 10 μm were produced with the heating and fluidization process. X-ray diffraction and chemical composition analyses of the product indicate virtually complete conversion of aluminum to aluminum nitride for some precursor mixtures. High conversion was also achieved using multi-pass processing.
Dynamic Behavior of a Drill-String: Experimental Investigation of Lateral Instabilities
Authors: Berlioz A. , Der Hagopian J. , Dufour R. , Draoui E.
Published: February 2008

This paper focuses on laboratory tests concerned with the lateral behavior of a rod representative of part of a drill-string in the area of rotary oil drilling. The original experimental set-up takes into account the curvature of the rod, mud, stabilizers and rotation speed. The lateral behavior of the drill-string subjected to the axial excitations of the bit is governed by time varying parameter equations due to torsion-lateral and longitudinal-lateral couplings. The experimental results highlight the different kinds of lateral instabilities and they are compared either with existing experimental, or theoretical results. The experimental investigation described in this paper is included in a wide ranging study which also involves theory and the development of a computer code, both briefly presented here.
Active Vibration Control of the Axially Moving String Using Space Feedforward and Feedback Controllers
Authors: Ying S. , Tan C. A.
Published: February 2008

Active vibration control of an axially moving string using space feedforward and feedback controllers is presented. Closed-form results for the transverse response of both the uncontrolled and controlled string are given in the s domain. The space feedforward controller is established by employing the idea of wave cancellation. The proposed control law indicates that vibration in the region downstream of the control force can be cancelled. With the space feedforward control, the mode shapes of the axially moving string are changed such that the free response tends to zero in the downstream region. An interesting physical interpretation is that the control force acts effectively as a holder (active support) which limits the vibration of the string to the upstream region and eliminates any vibration in the downstream region. Simulation results show that the response of the string to both sinusoidal and random excitations is suppressed by applying the space feedforward control. The feedback controller is introduced to attenuate the response of the string due to undesired disturbances in the downstream.
A Method for Calculating the Dynamics of Rotating Flexible Structures, Part 2: Example Calculations
Authors: Segalman D. J. , Dohrmann C. R. , Slavin A. M.
Published: February 2008

The problem of calculating the vibrations of rotating structures has challenged analysts since the observation that use of traditional modal coordinates in such problems leads to the prediction of instability involving infinite deformation when rotation rates exceed the first natural frequency. A method using a system of nonlinearly coupled deformation modes to analyze rotating general, linear (unjointed) structures that addresses the problem of erroneously predicting infinite deformations has been presented in a preceding paper (Segalman and Dohrmann, 1995). This technique is employed to address several types of problems ranging from simple beams to an inflated membrane structure. Some of the details of exploiting existing finite element codes to evaluate the relevant matrices are also developed.
The Dynamic Stiffness Method for Linear Rotor-Bearing Systems
Authors: Raffa F. A. , Vatta F.
Published: February 2008

The behavior of linear rotor-bearing systems is investigated by using the exact approach of the dynamic stiffness method, which entails the use of continuous rather than lumped models. In particular, the theoretical formulation for rotor systems with anisotropic bearings is developed by utilizing the complex representation of all the involved variables. The proposed formulation eventually leads to the 8 × 8 complex dynamic stiffness matrix of the rotating Timoshenko beam; this matrix proves to be related, by a simple rule, to the 4 × 4 dynamic stiffness matrix, which describes rotor systems with isotropic bearings. The method is first applied to the critical speeds evaluation of a simple rotor system with rigid supports; for this case, the exact results of the dynamic stiffness approach are compared to the usual convergence procedure of the finite element method. Successively, the steady-state unbalance response of two rotor systems with anisotropic supports is analyzed; for these examples, the dynamic stiffness results compare favorably with the results of the finite element and the transfer matrix analysis performed by other authors.
Stability and Limit Cycles of Parametrically Excited, Axially Moving Strings
Authors: Mockensturm E. M. , Perkins N. C. , Ulsoy A. Galip
Published: February 2008

Tension fluctuations are the dominant source of excitation in automotive belts. In particular designs, these fluctuations may parametrically excite large amplitude transverse belt vibrations and adversely impact belt life. This paper evaluates an efficient discrete model of a parametrically excited translating belt. The efficiency derives from the use of translating string eigenfunctions as a basis for a Galerkin discretization of the equations of transverse belt response. Accurate and low-order models lead to simple closed-form solutions for the existence and stability of limit cycles near parametric instability regions. In particular, simple expressions are found for the stability boundaries of the general nth-mode principal parametric instability regions and the first summation and difference parametric instability regions. Subsequent evaluation of the weakly nonlinear equation of motion leads to an analytical expression for the amplitudes (and stability) of nontrivial limit cycles that exist around the nth-mode principal parametric instability regions. Example results highlight important conclusions concerning the response of automotive belt drives.
Dynamic Responses of Plates With Viscoelastic Free Layer Damping Treatment
Authors: Yi Sung , Ahmad M. Fouad , Hilton H. H.
Published: February 2008

Dynamic transient responses of plates with viscoelastic free damping layers are studied in order to evaluate free layer damping treatment performances. The effects of forcing frequencies and temperatures on free-layer viscoelastic damping treatment of plates are investigated analytically. Young’s modulus ratio of structures to viscoelastic damping materials and the damping layer thickness effects on the damping ability are also explored.
Detecting Parameter Changes Using Experimental Nonlinear Dynamics and Chaos
Authors: Chancellor R. S. , Alexander R. M. , Noah S. T.
Published: February 2008

A method of detecting parameter changes using analytical and experimental nonlinear dynamics and chaos is applied to a piecewise-linear oscillator. Experimental data show the chaotic nature of the system through phase portraits, Poincare´ maps, frequency spectra and bifurcation diagrams. Unstable periodic orbits were extracted from each chaotic time series obtained from the system with six different parameter values. Movement of the unstable periodic orbits in phase space is used to detect parameter changes in the system.
The Derivatives of Repeated Eigenvalues and Their Associated Eigenvectors
Authors: Friswell M. I.
Published: February 2008

This paper considers the calculation of eigenvalue and eigenvector derivatives when the eigenvalues are repeated. An extension to Nelson’s method is used to calculate the first order derivatives of eigenvectors when the derivatives of the associated eigenvalues are also equal. The continuity of the eigenvalues and eigenvectors is discussed, and the discontinuities in the eigenvectors, when they are regarded as functions of two or more design parameters, is demonstrated. The validity of Taylor series for the eigenvalues and eigenvectors is examined and the use of these series critically assessed.
Exact Perturbation for the Vibration of Almost Annular or Circular Plates
Authors: Parker R. G. , Mote C. D.
Published: February 2008

A perturbation solution is presented to analytically determine the eigensolutions for self-adjoint plate vibration problems on nearly annular or circular domains. The irregular domain eigensolutions are calculated as perturbations of the corresponding annular or circular domain eigensolutions. These perturbations are determined exactly. The simplicity of these exact solutions allows the perturbation to be carried through third order for distinct unperturbed eigenvalues and through second order for degenerate unperturbed eigenvalues. Furthermore, this simplicity allows the resulting orthonormalized eigenfunctions to be readily incorporated into response, system identification, and control analyses. The clamped, nearly circular plate is studied in detail, and the exact eigensolution perturbations are derived for an arbitrary boundary shape deviation. Rules governing the splitting of degenerate unperturbed eigenvalues at both first and second orders of perturbation are presented. These rules, which apply for arbitrary shape deviation, generalize those obtained in previous works where specific, discrete asymmetries and first order splitting are examined. The eigensolution perturbations and splitting rules reduce to simple, algebraic formulae in the Fourier coefficients of the boundary shape asymmetry. Elliptical plate eigensolutions are calculated and compared to finite element analysis and, for the fundamental eigenvalue, to the exact solution given by Shibaoka (1956).