bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Simulation Study of n-Heptane Adsorption on Rutile
Authors: Rakhmatkariev G.U. , Carvalho A.J. Palace , Ramalho J.P. Prates
Published: April 2010

The adsorption of n-heptane on microcrystalline rutile has been studied experimentally by thermodynamic techniques (adsorption isotherms and microcalorimetry) over a wide range of coverage at 303 K and complemented by Grand Canonical Monte Carlo simulations. The differential heat of adsorption exhibited three descending segments corresponding to the adsorption of n-heptane on three types of surfaces. The mean molar adsorption entropy of n-heptane in the monolayer was less than the entropy of the bulk liquid by ca. −23 J/(mol K), thus revealing a hindered state of motion for the n-heptane molecules on the surface of rutile. Simulations of the adsorption of n-heptane were performed on the three most abundant crystallographic faces of rutile. The adsorption isotherm obtained from the combination of the isotherm for each face weighted by the respective abundance was found to be in good agreement with experimental data. A structural characterization of n-heptane near the surface was also conducted which indicated that the substrate strongly perturbed the distribution of the n-heptane conformations relative to the situation found for the gaseous phase. Adsorbed molecules are predominantly orientated with their long axes, with the zig-zag planes of their backbones parallel to the surface and preferentially aligned along the five-fold cus Ti4+ ions of the faces. Fewer gauche conformations were observed for molecules near the surface than was characteristic of the bulk phase.
Functionalization of Carbon and Silica Gel by Phosphoric Acid
Authors: Puziy A.M. , Poddubnaya O.I. , Gawdzik B. , Sobiesiak M. , Tsyba M.M.
Published: April 2010

Functionalization of polymer-based carbon (SCS-3) and silica gel (SG60) by phosphoric acid at 800°C was investigated. It was shown that heat treatment of carbon and silica gel in the presence of phosphoric acid at 800°C provides a way of functionalizing materials with phosphorus-containing surface groups. Functionalization of the finished carbon occurs as a surface reaction while destruction of the silica gel structure was observed. Functionalization with phosphoric acid creates new acid surface groups — phosphorus-containing and oxygen-containing in the case of carbon and only phosphorus-containing in the case of silica gel. Enhancement of the amount of acid surface groups by functionalization improves the metal-ion binding properties of both carbon and silica gel.
Surface Heterogeneity at the Solid-Gas Interface of Hydrophilic Solids Modified by Water-Repellent Molecules
Authors: Villiéras F. , Chamerois M. , Yvon J. , Cases J.M.
Published: April 2010

The surface heterogeneity of a hydrophilic calcium carbonate (calcite) at the solid-gas interface was studied before and after modification by the adsorption of different amounts of a water-repellent molecule (WRM). The surface heterogeneity was analysed using nitrogen, argon and water as molecular probes. Low-pressure adsorption techniques coupled with derivative isotherm summation (DIS) analysis of the experimental curves gave quantitative information on the decrease in the calcite surfaces and the increase in the WRM surfaces. The modelling results enabled the monolayer capacity for WRMs as measured by argon adsorption to be correlated with the disappearance of calcite surfaces and the disappearance of high-energy adsorption sites as measured by nitrogen adsorption. In addition, the argon results suggested that WRMs first adsorb on argon low-energy carbonate faces and then on low- and high-energy faces. With water, the adsorption energy distribution remained unchanged in shape, indicating that this molecule can diffuse into the adsorbed layer between and around the adsorbed hydrophilic heads of the WRMs and thereby interact directly with the carbonate surface.
Electronic Properties of the Active Sites Present at the (011) Surface of MoO2
Authors: Tokarz-Sobieraj Renata , Witko Malgorzata
Published: April 2010

The DFT method was used to describe the electronic structure of the catalytically interesting (011) surface of molybdenum dioxide, with attention being particularly focused on the properties of the active sites, both molybdenum and oxygen, present at this surface. In addition, a comparison of (011)MoO2 and (100)MoO3 surfaces was undertaken since both surfaces contain not only differently coordinated oxygen sites but also the bare molybdenum centres. The electronic structures of both surfaces were obtained using the cluster method and DFT approach. The local properties of the different surface sites exposed at the (011)MoO2 surface, viz. five- and six-fold coordinated Mo atoms and nucleophilic O sites with different coordination numbers, have been discussed using charge densities, bond-order indices and molecular orbital diagrams.
Validation of Simple Equations Describing the Adsorption of Binary Gas Mixtures onto Surfaces with an Asymmetric Distribution of Adsorption Energy
Authors: Szabelski Paweł , Nieszporek Krzysztof , Drach Mateusz
Published: April 2010

The Monte Carlo simulation method was used to test the accuracy of approximate equations derived for binary gas adsorption onto a heterogeneous surface characterized by a Dubinin-Astakhov adsorption energy distribution (AED) function. In particular, the Condensation Approximation (CA) was applied to obtain simple equations for the partial adsorption isotherms and phase diagrams in the system for which a separate AED was assumed for each component of the mixture. A few cases involving different relationships between the AEDs associated with the adsorbing components were discussed. Additionally, the results of the proposed theory were compared with exact numerical solutions obtained using the Integral Equation method. From both simulations and numerical calculations, it follows that, in general, the CA is not appropriate for the prediction of binary adsorption equilibria when the individual AEDs are of an entirely different shape. On the other hand, when the AEDs were microscopically correlated, i.e. when the adsorption energy of one component on every site was shifted by a constant value compared to that of the other, the phase diagrams obtained were found to be in a very good agreement with their simulated counterparts.
Role of Electrostatic Effects in the Pure Component and Binary Adsorption of Ethylene and Ethane in Cu-Tricarboxylate Metal-Organic Frameworks
Authors: Nicholson Timothy M. , Bhatia Suresh K.
Published: April 2010

The interaction of ethane and ethylene with a Cu-tricarboxylate complex was investigated, showing that at low loadings the lighter molecule has a higher binding energy as a result of interaction with framework Cu and H-bonding with basic framework oxygen atoms. This leads to the selective adsorption of ethylene at low pressure by a factor of ca. 2. This is overcome by the stronger van der Waals interaction of ethane at high loadings, explaining recent literature data. Both experimental data and single-component Grand Canonical Monte Carlo (GCMC) simulations were fitted well with the Unilan model and mixture isotherms were satisfactorily predicted by the Ideal Adsorbed Solution Theory when compared with binary simulation results. Both binary GCMC simulations and Ideal Adsorbed Solution Theory predictions yielded separation factors of ca. 2 and a difference in isosteric heat of 3 kJ/mol. The results suggest that the Cu-BTC framework offers a possible route for the separation of ethane and ethylene, a Holy Grail of adsorption.
One-Step Steam Pyrolysis Preparation and Characterization of Spherical Carbon Adsorbents Obtained from Ion-Exchange Resins
Authors: Wiśniewski Marek , Pacholczyk Agnieszka , Rychlicki Gerhard , Terzyk Artur P. , Gauden Piotr A.
Published: April 2010

Using the single-set steam pyrolysis of Dowex 50 WX-2 (a polystyrene–divinylbenzene resin), Spherical Carbon Adsorbents (SCAs) were prepared. The porous structure of the materials obtained was easily controlled by varying the heating rate, allowing carbons having a controlled ratio of micropores to mesopores to be obtained. These materials are promising for the adsorption of phenol from aqueous solutions. Moreover, due to the relatively small amount of irreversibility exhibited in such adsorption, they could find potential use in environmental protection.
On the Adsorption of Chiral Propylene Oxide onto Pd(111): A DFT Study
Authors: Gil-Rebaza A. , Linares D. , Zgrablich G.
Published: April 2010

The adsorption of chiral propylene oxide onto a Pd(111) single crystal was studied via ab initio calculations based on plane-wave Density Functional Theory. Different adsorption sites and different molecular configurations, both tilted and flat, have been analyzed. The on-top site is the preferred one for all configurations. The adsorption energy varies over a wide range of values spanning the range from ca. 10–20 kcal/mol for both the inclination of the molecule with respect to the surface and the coverage.
Thermo-Responsivity of the Polyacrylate-Adsorbed Metal Cation and its Hydration Structure
Authors: Seida Yoshimi , Imai Takahiro , Murata Kiyoshi , Nakano Yoshio
Published: April 2010

The thermo-responsive phase behaviour of the sodium salt of poly(acrylic acid) (PAA) was studied when its counter-ion was exchanged for a series of metal cations (PAA–metal cation complexes). The thermo-responsivity of such PAA–metal cation complexes appeared greatest for divalent metal cations capable of interacting weakly with PAA carboxylates. The thermo-responsivity was correlated with the adsorption behaviour of PAA towards such cations and the hydration structure of the complexes. The effect of metal cations on the thermo-responsivity followed the Irving–Williams order of stability. The condition of such complexes allowing the generation of thermo-responsivity was discussed.
Use of the [Copper(II)/MAA-nylon] Complex for the Adsorption of Residual Acid Dyes
Authors: Makhlouf Chahira , Baouab Mohamed Hassen V , Roudesli Sadok
Published: April 2010

Nylon fibres were converted into a strong ion-exchange polymer by grafting with methacrylic acid (MAA). The modified nylon fibres were monitored for their ability to remove copper(II) ions and dyes from aqueous solutions. Evidence for the grafting of MAA onto nylon was provided by weight uptake experiments and atomic force microscopy (AFM). The exchange capacity of MAA–nylon was evaluated by potentiometric titration of the grafted acidic groups. Due to complexation, the acidic grafted groups immobilize Cu(II) ions from Clark–Lub's buffered solution at a pH value of 8. The formation of a 1:1 complex was demonstrated by the values of the adsorption limits.

The binary [Cu(II)/MAA–nylon] system was then tested for the adsorption of two Acid dyes, i.e. Acid Blue 25 (AB 25) and Calmagite (Calma), as ligands in the metal-coordinating process. The adsorption of Cu(II) onto MAA–nylon and of the dyes onto Cu(II)/MAA–nylon was followed spectrometrically. The observed stoichiometries of the ternary [dye/Cu(II)/MAA–nylon] complex formed were [[Formula: see text]] for AB 25 and [[Formula: see text]] for Calma at 20°C.

Theoretical modelling of the adsorption process was performed employing the Langmuir, Freundlich and Jossen equations. Thermodynamic parameters such as the free energy change (ΔG0), the enthalpy change (ΔH0) and the entropy change (ΔS0) for adsorption were also investigated. The adsorption process is exothermic, which leads to a reduction in the extent of dye adsorption with increasing temperature.
A New Pb2+ Ion-selective Hybrid Cation-exchanger — EDTA–Zirconium Iodate: Synthesis, Characterization and Analytical Applications
Authors: Nabi Syed Ashfaq , Ganai Sajad A. , Naushad Mu.
Published: April 2010

An amorphous sample of the new hybrid cation-exchanger EDTA–zirconium iodate was synthesized by the combination of the inorganic ion-exchanger zirconium iodate with the organic EDTA molecule, thereby providing a new class of organic–inorganic hybrid ion-exchangers with better mechanical and granular properties, good ion-exchange capacity (e.g. 2 mequiv Na+/g dry exchanger), good reproducibility, a higher stability and demonstrating selectivity towards heavy metal ions.

The physicochemical properties of this material were examined by instrumental analyses, viz. FT-IR spectroscopy, X-ray diffraction studies and TGA/DTA investigations. Assessments of the elution and distribution behaviour were made and pH titrations undertaken to obtain an understanding of the ion-exchange behaviour of the material. On the basis of the distribution studies, the material was found to be highly selective towards the Pb2+ ion, a highly toxic environmental pollutant. Its selectivity was assessed by examining its use for some important binary separations such as Mg2+–Pb2+, Cd2+–Pb2+, Hg2+–Pb2+, Zn2+–Pb2+, Cu2+–Pb2+ and Al3+–Pb2+ on a packed column of the material. The practical potential of EDTA–zirconium iodate was explored by separating Mg2+ and Al3+ ions quantitatively from a commercially available pharmaceutical formulation, viz. Digene.01.
Preparation and Characterization of Sulpho-Functionalized Ordered Mesoporous Silica
Authors: Yeoh Fei-Yee , Matsumoto Akihiko , Iwase Yoshiyuki , Baba Toshihide
Published: April 2010

Sulpho groups have been successfully embedded in mesoporous silica with an ordered two-dimensional hexagonal structure. The sulpho-functionalized mesoporous silica was prepared by the oxidation of a thiol-functionalized mesoporous silica which was obtained via the hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples exhibited an ordered two-dimensional hexagonal pore array up to 30 mol% MPTMS loading. The large surface area of MCM-41 (ca. 1000 m2/g) was maintained after incorporation of the mercaptopropyl group and oxidation of its thiol group. Solid-state 29Si NMR spectra showed the existence a mercaptopropyl group in a silica framework and 13C NMR studies further proved that treatment with hydrogen peroxide led to oxidation of the sulpho groups. High ammonia uptakes with high differential heats of adsorption revealed the strong acidity of sulpho-functionalized mesoporous silica. The amounts of acid sites may be controlled by regulating the amount of MPTMS employed in the synthesis. The sulpho-functionalized mesoporous silica behaved as an acid catalysis for the isomerization reaction of but-1-ene to cis- and trans-but-2-ene.
Performance of Asymmetric Electric Double Layer Capacitors — Predominant Contribution of the Negative Electrode
Authors: Wang Lihong , Toyoda Masahiro , Inagaki Michio
Published: April 2010

Asymmetric capacitors with a non-aqueous electrolyte were constructed by using various carbons as negative and positive electrodes in order to study their performance. For asymmetric capacitors where the ratio of the BET surface area, SBET, of the negative carbon electrode to that of the positive carbon electrode was less than 1.7, the capacitance of the electric double layer was strongly governed by the negative carbon electrode. Their rate performance, as evaluated from the ratio of the capacitance at 200 mA to that at 20 mA, C200/C20, was determined by the mesoporous surface area of the negative carbon electrode. What is important, however, is that the negative carbon electrode in capacitors governs their characteristics, viz. their capacitance and rate performance. This conclusion was arrived at by constructing asymmetric electric double layer capacitors employing carbons with different pore structures as the negative and positive electrodes. The present result provides information which is important in the design of electrodes for electric double layer capacitors.
Study of Nitrogen-Modified Titanium Dioxide as an Adsorbent for Azo Dyes
Authors: Janus Magdalena , Choina Julia , Kusiak Ewelina , Morawski Antoni W.
Published: April 2010

The removal of two azo dyes from aqueous solution was investigated using a highly active nitrogen-modified titanium dioxide (TiO2/N). This photocatalyst was prepared by pressure modification of a commercial sample of anatase, TiO2 (supplied by Zaklady Chemiczne Police SA, Poland). The adsorption of two azo dyes (Reactive Red 198 — a monoazo dye and Direct Green 99 — a polyazo dye) onto the unmodified and nitrogen-modified TiO2 surface was determined. Adsorption onto unmodified TiO2 led to an isotherm which could be described by the Freundlich model, whereas that onto the nitrogen-modified TiO2 surface was best described by the Langmuir model. The adsorption isotherms of Direct Green 99 onto TiO2/N from aqueous solutions at various pH values were compared with those onto unmodified TiO2 during dye removal under UV irradiation. Such a comparison is important since it provides information as to how solutes interact with adsorbents.

Zeta potential measurements of TiO2 provided an explanation for the observed behaviour in terms of the surface charge. The IR spectrum of the photocatalyst obtained exhibited new absorption bands at 1430–1440 cm−1 which were attributed to the bending vibrations of NH+4 and at 1535 cm−1 associated with NH2 groups or NO2 and NO groups.
A Correlation between the Kinetic and Thermodynamic Adsorption Characteristics of an Optical Brightener on a Pulp Surface
Authors: Radeva Greta , Veleva Stefka , Valcheva Eva
Published: April 2010

An attempt to find a correlation between the kinetic and thermodynamic terms (e.g. activation energy, pre-exponential factor, isosteric heat, entropy, etc.) of the chemisorption process involved in a commercial optical brightener/pulp system is presented. A linear inter-relationship between the kinetic and thermodynamic characteristics of the system was found. Based on the coefficients obtained in the thermodynamic investigation of the adsorption process, it was possible to calculate the kinetic coefficient of the surface inhomogeneity. The use of both a model employing uniformly inhomogeneous surfaces and an approach involving all the kinetic and thermodynamic data was confirmed by the results obtained.
Preparation of Activated Carbons from Sawdust by Chemical Activation
Authors: Zhang Huiping , Yan Ying , Yang Lichun
Published: April 2010

Activated carbons were prepared from sawdust by chemical activation with H3PO4. The effects of various parameters such as the impregnation ratio, activation temperature and time on the nitrogen adsorption isotherms, specific surface areas and pore volumes of the activated carbons were measured and analyzed in order to optimize the operational conditions. The nitrogen adsorption capacity of the activated carbons was significantly affected by the impregnation ratio and the activation temperature. The most important operational parameter in chemical activation with H3PO4 was found to be the H3PO4/sawdust impregnation ratio. The specific surface area of the activated carbon prepared with a 1:1 H3PO4/sawdust ratio and activated at 500°C for 90 min attained the relatively high value of 1642 m2/g. The experimental results show that, under the experimental conditions studied, an activated carbon containing well-developed micropores and mesopores exhibiting improved nitrogen adsorption properties can be obtained via a H3PO4 activation process under the optimum operation conditions, viz. activated with an impregnation ratio of 1.0–1.5H3PO4/sawdust at 500°C for 60–90 min.
Creating the Dataset for the Western Wind and Solar Integration Study (U.S.A.)
Authors: Potter Cameron W. , Lew Debra , McCaa Jim , Cheng Sam , Eichelberger Scott , Grimit Eric
Published: April 2010

The Western Wind and Solar Integration Study (WWSIS) is one of the world's largest regional integration studies to date. This paper discusses the creation of the wind dataset that will be the basis for assessing the operating impacts and mitigation options due to the variability and uncertainty of wind power on the utility grids. The dataset is based on output from a mesoscale numerical weather prediction (NWP) model, covering over 4 million square kilometers with a spatial resolution of approximately two-kilometers over a period of three years with a temporal resolution of 10 minutes. The mesoscale model dataset includes all the meteorological variables necessary to calculate wind energy production. Individual time series were produced for over 30 thousand locations representing more than 900 GW of potential wind power generation.
Using Standard Deviation as a Measure of Increased Operational Reserve Requirement for Wind Power
Authors: Holttinen Hannele , Milligan Michael , Kirby Brendan , Acker Tom , Neimane Viktoria , Molinski Tom
Published: April 2010

The variability inherent in wind power production will require increased flexibility in the power system, when a significant amount of load is covered with wind power. Standard deviation (σ) of variability in load and net load (load net of wind) has been used when estimating the effect of wind power on the short term reserves of the power system. This method is straightforward and easy to use when data on wind power and load exist. In this paper, the use of standard deviation as a measure of reserve requirement is studied. The confidence level given by ±3–6 times σ is compared to other means of deriving the extra reserve requirements over different operating time scales. Also taking into account the total variability of load and wind generation and only the unpredicted part of the variability of load and wind is compared. Using an exceedence level can provide an alternative approach to confidence level by standard deviation that provides the same level of risk. The results from US indicate that the number of σ that result in 99% exceedence in load following time scale is between 2.3–2.5 and the number of σ for 99.7% exceedence is 3.4. For regulation time scale the number of σ for 99.7 % exceedence is 5.6. The results from the Nordic countries indicate that the number of σ should be increased by 67–100% if better load predictability is taken into account (combining wind variability with load forecast errors).
The Impact of Balancing Area Size and Ramping Requirements on Wind Integration
Authors: Milligan Michael , Kirby Brendan
Published: April 2010

Balancing area reserve sharing2 may significantly reduce wind integration costs. It also reduces utility costs without wind. Some recent studies indicate that large balancing areas can integrate wind more easily than small ones. The “hockey stick” pattern of dramatically increasing wind integration cost above some threshold wind penetration may not be as pronounced as expected. The existence and location of this threshold could have important implications regarding the cost of integrating significant wind penetrations. We examine wind integration impacts as a function of balancing area size to determine if the larger system size mitigates wind integration impacts at high penetrations. Using data from Minnesota, we show that ramping requirements can be reduced by balancing area consolidation. In a companion paper3, we examine electricity market data in the United States that show how ramping capability is provided at low or no cost, and discuss its relevance to wind integration.
The Impact of Balancing Area Size, Obligation Sharing, and Energy Markets on Mitigating Ramping Requirements in Systems with Wind Energy
Authors: Kirby Brendan , Milligan Michael
Published: April 2010

Balancing area reserve sharing2 holds the promise of significantly reducing wind integration costs. In a companion paper3 we examine wind integration costs as a function of balancing area size to determine if the larger system size helps mitigate wind integration cost increases. In this paper we turn to an examination of the NYISO sub-hourly energy market to understand how it incentivizes generators to respond to ramping signals without having to explicitly pay for the service. Because markets appear to have the ability of bringing out supply response in sub-hourly energy markets, and because existing thermal resources appear to have significant untapped ramping capability, we believe that a combination of fast energy markets and combined balancing area operations can increase the grid's ability to absorb higher wind penetrations without experiencing significant operational problems or costs.
Yaw Behavior of Horizontal-Axis Small Wind Turbines in an Urban Area
Authors: Nishizawa Yoshifumi , Tokuyama Hideki , Nakajo Yuichi , Ushiyama Izumi
Published: April 2010

This paper reports the experimental study on passive yaw behavior of a horizontal axis small wind turbines.

The yaw angle velocity in a small wind turbine is one of the significant design values and IEC61400-2 Ed.2 prescribes its maximum value should be less than 3 rad/s. However, in practice, in the case of small wind turbines with diameters under 2 m, the yaw angular velocity may exceed the limit of 3 rad/s.

The authors conducted a theoretical evaluation as well as a wind tunnel test to examine the possible maximum yaw velocity. The model wind turbine has a diameter of 1 m, blade number of 5, solidity of 0.26 and 2 types of tail fins (large and small). For each tail fin size, the yaw behavior was studied for a range of rotational speeds and wind speeds.

The results show that the yaw angular velocity becomes larger with increasing wind velocity and tail fin area. The larger the rotor rotational speed, the smaller the yaw angular velocity. Furthermore, a maximum yaw angular velocity of 3.84 rad/s was observed at a wind speed of 10 m/s, which exceeds the conventional design value of 3 rad/s.
A Regulation-Caused Bottleneck for Regulating Power Utilization of Balancing Offshore Wind Power in Hourly- and Quarter-Hourly- Based Power Systems
Authors: Akhmatov Vladislav , Gleditsch Morten , Gjengedal Terje
Published: April 2010

In Denmark, the operation experience from the Horns Rev I offshore windfarm (160 MW) located in the North Sea showed that power output of the windfarm was characterised by intense, rapid and repeating fluctuations due to unsteady wind conditions. In certain wind conditions, the power output from the offshore windfarm changes between zero and rated power levels in faster than a quarter of an hour, introducing power fluctuations of a repeating character to the Danish transmission grid. Such intense power fluctuations may last for several hours, introducing a power-balance challenge to the Danish transmission system. Many transmission systems, including the Nordic system which Denmark is part of, are hourly- and quarter-hourly- based regarding the power generation plans, power balance and agreed power transmission between the countries. Applying the Nordel1 cooperation regulations and a simplified grid equivalent of a hydro-power-based transmission system with the main generation and consumption figures of Norway, this paper shows that such hourly- and quarter-hourly- system operation regulations may introduce a bottleneck for efficient utilization of available regulating power with increasing grid-integration of large offshore windfarms.
Optimal Design and Economic Evaluation of a Battery Energy Storage System for the Maximization of the Energy Generated by Wind Farms in Isolated Electric Grids
Authors: Koutroulis E. , Kolokotsa D. , Stavrakakis G.
Published: April 2010

In this paper, a methodology for the optimal sizing of a Battery Energy Storage System (BESS) targeting to supply a predefined and constant (guaranteed) amount of power to an isolated electric grid during the peak load-demand hours is presented. The BESS battery bank is charged using that part of the energy produced by wind parks interconnected with the power system, which is rejected by the electric network due to grid stability limitations. Thus, using the proposed BESS configuration results in increment of the wind energy penetration in the isolated power system and reduction of the air pollution caused by the thermal power stations. The economic viability of the optimally sized BESS configuration is investigated by calculating the investment discounted payback period and internal rate of return. The proposed method has been applied for the optimal design of a BESS supporting the isolated electric network of a remote island with significant wind potential. According to the economic analysis results, the installation of the proposed BESS is economically beneficial for both the BESS investor and the local electric network operator.
Evaluation of the Wind Shear at a Site in the North-West of the Yucatan Peninsula, Mexico
Authors: Soler-Bientz Rolando , Watson Simon , Infield David
Published: April 2010

Extrapolations from 10m above the ground up to the wind turbine hub height are frequently made to the data available for wind power assessments. Because of its simplicity, the power law profile has been one of the most popular mathematical formulations to predict the vertical wind shear. This paper presents an analysis of wind speed and wind shear in terms of the directional, diurnal and seasonal patterns for a site at the Autonomous University of Yucatan which experiences the tropical conditions of the Yucatan Peninsula in Mexico. This analysis takes a detailed look at frequency distributions to facilitate a comprehensive understanding of the local climatic conditions. Diurnal wind speed variations are shown to be affected in particular by the differing wind conditions associated with fetches over two distinct offshore regions. Seasonal behaviour suggests some departure from the oscillations expected from temperature variation. In addition, the use of rate of change of temperature at one height is proposed as an alternative to vertical temperature gradient inferred from two heights as an indicator of atmospheric stability which will affect the wind shear. The work presented is part of a regionally funded research program to evaluate the onshore and offshore wind potential in the north of the Yucatan Peninsula.
Short Term Forecasting for Utility-Scale Wind Farms — The Power Model Challenge
Authors: Collins Jonathan , Parkes Jeremy , Tindal Andrew
Published: April 2010

To date, many studies have focused on the mathematical modelling techniques for forecasting the production from wind farms, looking predominantly at the task of predicting the meteorological conditions at the site. This paper focuses on the final stage of the forecasting process-conversion from a meteorological forecast to a power production forecast. This challenge is particularly significant for utility-scale (>100MW) wind farms, where the simple application of a turbine manufacturer's power curve is insufficient to capture the true behaviour and interaction of the wind turbines over the whole site. This paper shows that the errors introduced by this power conversion process can be significantly reduced through the use of more advanced power modelling methods. A market trading scenario is considered and the increase in annual trading revenue for an example 100MW wind farm when using an advanced power model is estimated to be €180,000.
Power Law Extrapolation of Wind Measurements for Predicting Wind Energy Production
Authors: Lubitz William David
Published: April 2010

This study investigates the level of uncertainty that would be expected if anemometer data from a short tower (less than 40 meters) was used to predict wind speeds and power production at typical utility-scale wind turbine hub-heights. Data from five tall towers was used to predict wind speeds at levels above 70 m based on anemometer data from levels below 40 meters. 1/7 power law, two level power law fit, and hybrids of these methods were applied. Predicted wind speeds were compared to the measured wind speeds at the higher levels to assess the level of error in the predictions. Accuracy of predicting upper level winds varied considerably between sites. Predicting this accuracy at a site without upper level wind measurements or prior knowledge of the upper level wind climate is very difficult, and significant uncertainty in the predicted results must be accepted.
Factors Influencing Design of Dynamic Reactive Power Compensation for an Offshore Wind Farm
Authors: Perdana Abram , Carlson Ola
Published: April 2010

This paper investigates factors that influence the design of dynamic reactive power compensation (DRPC) for an offshore wind farm consisting of fixed-speed wind turbines. Several influencing factors are considered including DRPC device types and locations, network strength, and fault ride-through (FRT) capability of individual wind turbines in the wind farm. The DRPC alternatives discussed in this paper comprise of a STATCOM and an SVC. It is found that the exclusion of wind turbine FRT capability results in too large DRPC size estimation. In the case of wind turbines equipped with FRT capability, it was found that the investment cost for both STATCOM and SVC options are comparable. The study also emphasizes the necessity of performing dynamic analysis to correctly design the size and location of the DRPC device.
Solving the Turbine Positioning Problem for Large Offshore Wind Farms by Simulated Annealing
Authors: Rivas Rajai Aghabi , Clausen Jens , Hansen Kurt S. , Jensen Leo E.
Published: April 2010

The current paper is concerned with determining the optimal layout of the turbines inside large offshore wind farms by means of an optimization algorithm. We call this the Turbine Positioning Problem. To achieve this goal a simulated annealing algorithm has been devised, where three types of local search operations are performed recursively until the system converges. The effectiveness of the proposed algorithm is demonstrated on a suite of real life test cases, including Horns Rev offshore wind farm. The results are verified using a commercial wind resource software indicating that this method represents an effective strategy for the wind turbine positioning problem. The findings enable the comparison of the optimized and the grid layouts and the study of the wake differences between these configurations. It is seen that for very large offshore wind farms the difference in wake losses is negligible while, as the wind farm's size reduces, the differences start becoming significant. A sensitivity analysis is also performed showing that greater density of turbines in the perimeter of the optimized wind farm reduces the wake losses even if the wind climate changes.
The Shape and Performance of Hand-Carved Small Wind Turbine Blades
Authors: Clausen P. D. , Freere P. , Peterson P. , Wilson S.V.R. , Wood D.H.
Published: April 2010

This paper describes measurements of the shape of a 900 mm long, hand-carved timber blade for a 500 W three-bladed horizontal axis wind turbine. Four blades were hand-carved in Nepal by reference to a master blade cut in Australia on a numerically controlled milling machine. A high definition three-dimensional scanner was used to determine the surface of one hand-carved blade as a series of profiles at 50 mm intervals along the blade's length. A surface model generated from these profiles was compared to the designed blade shape in terms of the three fundamental blade design parameters: chord, twist, and profile shape. The measured twist and chord were less that the design values, particularly in the hub region. This is consistent with the poor starting performance of the turbine when mounted with the remaining hand-carved blades. Assessment of the differences in profile shape would require a detailed computational analysis, which has not been undertaken.
Optimally Sensitive and Efficient Compact Loudspeakers for Low Audio Frequencies
Authors: Aarts Ronald M.
Published: April 2010

Conventionally, the ultimate goal in loudspeaker design has been to obtain a flat frequency response over a specified frequency range. This can be achieved by carefully selecting the main loudspeaker parameters such as the enclosure volume, the cone diameter, the moving mass and the very crucial “force factor”. For loudspeakers in small cabinets the results of this design procedure appear to be quite inefficient, especially at low frequencies. This paper describes a new solution to this problem. It consists of the combination of a highly non-linear preprocessing of the audio signal and the use of a so called low-force-factor loudspeaker. This combination yields a strongly increased efficiency, at least over a limited frequency range, at the cost of a somewhat altered sound quality. An analytically tractable optimality criterion has been defined and has been verified by the design of an experimental loudspeaker. This has a much higher efficiency and a higher sensitivity than current low-frequency loudspeakers, while its cabinet can be much smaller.
Coupling Misalignment in Rotating Machines: Modelling, Effects and Monitoring
Authors: Sudhakar G.N.D.S. , Sekhar A.S.
Published: April 2010

After unbalance, coupling misalignment is the most common fault present in rotating machines. However, limited research has been carried out on coupling misalignment and its effects. The present study aims to explore the research on coupling misalignment by briefly summarizing the research work done so far on different modelling techniques, effects on the system behaviour, fault identification and condition monitoring techniques.
Temperature Trends in the Lower Atmosphere
Authors: Gray Vincent
Published: April 2010

A new publication by NOAA (US National Oceanic and Atmospheric Administration) claims to have removed the previously evident discrepancies between mean global temperature anomalies measured on the surface and those measured in the lower troposphere. It claims that a combination of attention to inaccuracies and the use of linear regression equations on selected climate sequences have removed these discrepancies.

This paper shows that these claims are untrue. The apparent agreement of the two sets of records for the chosen sequences is dependent on the enhanced influence of volcanoes and El Niño events in the lower troposphere, compared with an additional warming factor on the surface. If a temperature sequence comparatively free from these influences, (1979–1997) is chosen, there is no significant warming in the lower atmosphere for six of the seven records, and for the seventh, no significant warming between 1988 and 1997; whereas warming still prevails on the surface over these periods. The supposed enhanced greenhouse effect is thus currently undetectable in the lower atmosphere, where it is supposed to be most prominent, for extended periods, so the warming on the surface over these periods must have some other cause.
Environmental Assessment Procedures for Wind Power Projects in Australia
Authors: Hall Andrew , Harvey Nick
Published: April 2010

Australia currently has significantly less wind power capacity than Germany, the world leader, but has a much larger land area with considerable untapped wind energy resources. Australia like the rest of the world has experienced a rapid increase in its wind power industry over the last decade, particularly in the southern states, South Australia, Western Australia and Victoria. However, the rapidity in the development of wind power projects has caused controversy and criticism of inadequate planning and inconsistency in environmental impact assessment. This paper examines the implications of the rapid growth in Australian wind power in terms of the need for a strategic approach to environmental assessment.
Aircraft Cruise Nitrogen Oxides (NOx) Emissions Prediction and Environmental Pollution Factor
Authors: Tsague Louis , Tatietsé Thomas Tamo
Published: April 2010

Nitrogen oxides (NOx) emitted at low altitude increase ozone formation, thus potentially affecting local air quality. On the other hand supersonic aircraft NOx emitted in the lower stratosphere deplete the ozone layer, which represents a serious health concern according to Richard Miake Lyea and Ulrich Schumannb). The necessity to evaluate aircraft NOx production at cruise is urgent, since ICAO standard on NOx limitations has not yet taken into account cruise NOx emissions. The purpose of this work is to solve the problem of aircraft cruise NOx emissions regulation. The evaluation of nitrogen oxides production according to operational time in mode is realized with the ICAO data bank from different types of aircraft engines. Cruise NOx production is compared to LTO NOx production. A predictive correlation linking cruise NOx production to flight distance is developed and evaluated with good accuracy. Although cruise NOx production prediction is very important, alone it may not be enough to settle a limitation regulation on cruise NOx emissions, then the maximum flight range and the maximum take off weight, as those important factors influencing the NOx emissions are taken into account to develop a specific NOx production parameter which can enable the commercial aircraft classification according to their pollution factor, by so doing, ICAO NOx emissions regulation can be completed using the approach we propose to set up a limit value on aircraft cruise NOx emissions.
Energy Diversification Choices for Nigeria
Authors: Nwofor O.K. , Chineke T.C. , Akujor C.E. , Okoro U.O.
Published: April 2010

This paper reviews the diverse energy options available to Nigeria, and presents some popular arguments for choosing certain energy options above others for large-scale development. These popular methods of making energy policy decisions may be prone to faulty reasoning and may not be quantitatively assessable. Using the criteria of availability, economy of energy conversion and environmental sustainability, a procedure of preference ranking based on expert opinions is suggested for optimizing decisions on the most suitable candidates for energy diversification in Nigeria in the coming decades. A test case utilizing three opinions on the criteria for nine energy options is used to show how the method works.
The Status of Bioenergy in the Sharavathi River Basin, India
Authors: Ramachandra T. V. , Sreekantha  , Purnima G. B.
Published: April 2010

Most of the developing countries including India depend heavily on bioenergy and it accounts for about 15% of the global energy usage. Its role in meeting a region's requirement has increased the interest of assessing the status of biomass availability in a region. The present work assess the status of bioenergy in the Linganamakki reservoir catchment of the Sharavathi river basin, Western Ghats, India, by assessing the energy supply and sector wise energy consumption. The study reveals that majority of the households (92.17%) depend on fuelwood for their domestic energy needs with the per capita fuelwood consumption of 1.2 tonnes/year, which is higher than the national average (0.7 tonnes/year). This higher dependence on fuelwood has contributed to the degradation of forests, resulting in scarcity of bioresources necessitating exploration of viable energy alternatives to meet the growing energy demand.
On Setting Near-Term Climate Policy While the Dust Begins to Settle
Authors: Yohe Gary , Tol Richard S.J. , Murphy Dean
Published: April 2010

We review the explosion of commentary that has followed the release of the Stern Review: The Economics of Climate Change, and agree with most of what has been written. The Review is right when it argues on economic grounds for immediate intervention to reduce emissions of greenhouse gases, but we feel that it is right for the wrong reasons. A persuasive case can be made that climate risks are real and increasingly threatening. If follows that some sort of policy will be required, and the least cost approach necessarily involves starting now. Since policy implemented in 2007 will not “solve” the climate problem, near term interventions can be designed to begin the process by working to avoid locking in high carbon investments and providing adequate incentives for carbon sequestration. We argue that both objectives can be achieved without undue economic harm in the near term by pricing carbon at something on the order of $15 per ton as long as it is understood that the price will increase persistently and predictably at something like the rate of interest; and we express support for a tax alternative to the usual cap-and-trade approach.
Computational Study of Aero- and Acoustic Performance of a Small Axial-Flow Fan
Authors: Cao Renjing , Lee Duck-Joo
Published: April 2010

This study aims to predict the overall aerodynamic performance, unsteady forces and the tonal noise radiation from a small axial flow fan. The computation is divided into two stages: (a) the computation of the unsteady flow field at design and off-design working conditions, and (b) detailed analysis of the acoustic field. A dual-time scheme for dealing with rotor-stator or wake-struts interactions in turbomachinery environments by introducing a pseudo-time to represent the time variation of source terms and the finite volume control method are applied for the unsteady solutions involving the whole flow passages of the axial flow fan, and the pressure rise against volume flow rate is obtained and shown to be in good agreement with experimental data. The interaction of the rotor wake and the downstream struts has been simulated by investigating the effects of source distribution over the whole blades. And the tonal noise is then predicted based on Lowson's theory.

The unsteady force is divided into thrust in the rotational axis direction and drag in the rotational direction for the rotor and struts. It is demonstrated that the unsteady forces acting on the rotor and struts are produced by the interaction between them, and has a close relationship with the rotor wake structure and the strut alignment. In the rotor near wake, both the viscous and potential flow is dominant not only to aerodynamic forces but also to interaction noise. The present study shows that the higher lean angle of struts can gain about 4 dB reduction of overall sound power level compared to the smallest one.
Suppression of Jet Noise by Staged Water Injection during Launch Vehicle Lift-Off
Authors: Ignatius Jopaul K. , Sankaran S. , Kumar R. Ashok , Satyanarayana T. N. V. , Chakravarthy Satyanarayanan R.
Published: April 2010

Jet noise during the lift-off of a launch vehicle is complicated by the simultaneous flow of multiple jets, and their deflection by jet deflectors. Further, the presence of the launch pedestal, the service structure, and the moving vehicle itself, act as reflecting surfaces, which contribute to the noise environment. The present work involves the suppression of noise as measured at different parts of the launch vehicle in a small-scale replica of a full launch pad, for different locations of the vehicle along its vertical lift-off trajectory. The primary source of noise is the two jets emerging from the base of the launch vehicle at a Mach number of 3.38. Noise is suppressed by water injection at different locations in the launch pad such as the upstream and downstream edges of the jet deflector cover-plate, bottom and top of the launch pedestal, and at two different locations on the service structure. The effect of staged injection of water, i.e., without and with injection at different heights relative to the position of the jets, as the vehicle is at different locations in its trajectory, is examined. It is found that sustained suppression of noise is obtained only with injection of water in successive stages closer to the nozzle exit, as the jet position is moved up. The effect of angle of injection of water is investigated to verify previously reported results that an injection angle of 60°, i.e., along the flow, is superior to injection at 90° to the jet. The effect of injection pressure shows an optimum that supports the effective atomization of the injected water jets into droplets due to shear by the gas jet flow. Investigation with hot jets shows increased noise levels by at least ~2 dB relative to cold jets of nearly the same nozzle-exit Mach number. However, an increased reduction of noise by water injection is apparent with hot jets. The reduction is nearly independent of the jet temperature in the 600-900 K range. The present results collectively confirm the qualitative applicability of different previous studies on single free jets to the complicated launch vehicle noise scenario.