bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Combined Cycle and Conventional Steam Power Plant Through Energy Level and Thermoeconomic Analysis
Authors: Khoshgoftar Manesh Mohammad Hasan , Amidpour Majid , Jalal Abadi Hasan Khodaei
Published: September 2009

Exergy, exergoeconomic and combined pinch and exergy analysis are beneficial methods that can be applied for design or performance evaluation of process systems or thermal power plants; however, these methods are usually applied individually. In this paper, these methods have been applied for 423 MW NEKA combined cycle power plant located in NEKA at north of Iran and 315-MW RAMIN steam power plant located in Ahvaz at south of Iran as real cases to evaluation and comparison of performance of each component in different load conditions simultaneously. To perform these analysis for both plants, a computer program is developed from thermodynamic modeling of the plant as simulator. With the thermodynamic properties of the most significant mass and energy flow stream being obtained from the plant, the simulator can reproduce the cycle behavior for different operating conditions with relative errors less than 4.2%. The models of computer program are refined using data from designed performance test in these plants. After thermodynamic simulation, this program can calculate exergy of the flows. In addition, it can perform exergoeconomic analysis using thermoeconomic model of both plants that are defined based on the functionally of each component by the fuel-product definition. The costs of all flows in production structure can be calculated by solving a set equation including thermoeconomic modeling of each plant. Furthermore, it is helpful to display the system information graphically for one to visualize the performance of system in different conditions by applying combined pinch-exergy analysis. Meanwhile, due to importance of exergy destruction cost and better understanding plant performance, the new variables have been defined as Exergy Destruction Level (EDL) and Exergy Cost Destruction Level (ECDL). In this respect, new graphical representation has been developed for showing performance of each component based on exergoeconomic analysis. In this regard, this computer program can generate improved combined pinch-exergy and EDL/ ECDL representation.
Electrolytic Reactors for High Pressure Hydrogen Generation: Design and Simulation
Authors: Albers Albert , Lauretta Juan Ricardo , Leslabay Pablo
Published: September 2009

The implementation of hydrogen as a mass scale energy vector requires the development of simple, cheap and efficient technologies for its production, storage and transportation. Generating hydrogen through electrolysis of alkali solution directly under pressures up to 700bar without the intervention of any mechanical gas compression systems and the direct storage of the gases in appropriate tanks is a viable example of such a technology. The present study introduces the advantages of this production scheme and the major technical difficulties to be overcame on the design of a high pressure operating electrolytic reactor. In order to study the general system’s behavior, a numerical simulation method that includes all the relevant components is developed. To reduce the complexity of the initial model, the details of the electrochemical reaction taking place on each electrolytic cell is not covered and its effect is replaced with an energy efficiency curve derived from experimental observations. Despite this simplification, the characteristics of the system remain very complex and require the use of multi-physics simulation tools to describe the interactions between solids, liquid and gas, the temperature distribution and pressure, and the production of gas and heat in the reactor. In spite of the multiple coupling possibilities within the multiphysics software, the interaction of the modules proved challenging and required the manual introduction of further differential equations and physical expressions, along with auxiliary routines, to allow the convergence of the solution. The simulation method developed is validated by modeling a test reactor designed and constructed in the Instituto Tecnolo´gico de Buenos Aires for its installation in the Argentinean Antarctic, for which different test-run results are available for comparison.
Optimization of the Operation of a Complex Combined-Cycle Cogeneration Plant Using a Professional Process Simulator
Authors: Vieira Leonardo S. , Matt Carlos F. , Guedes Vanessa G. , Cruz Manuel E. , Castello˜es Fernando V.
Published: September 2009

Thermoeconomic optimization is a relatively modern technique to analyze and design more efficient energy systems, leading to a better compromise between energetic efficiency and cost. Thermoeconomic optimization can be parametric (plant configuration is fixed), applicable both at the design phase or the operation phase of an energy system, or structural (plant configuration may vary). In practice, mathematical thermoeconomic optimization may be accomplished in two ways: (i) the conventional way, which manipulates all pertinent equations simultaneously, or (ii) integrated with a professional process simulator, such that the equations are manipulated separately. In the latter case, the simulator deals with the thermodynamic property and balance equations, while an external optimization routine, linked to the simulator, deals with the economic equations and objective function. In this work a previous implementation of an integrated approach for parametric mathematical thermoeconomic optimization of complex thermal systems is applied to an actual combined-cycle cogeneration plant located in the outskirts of the city of Rio de Janeiro, in Brazil. The simulator is the Thermoflex software, which interfaces with the MS-Excel program. Thus, the Powell’s method for optimization integrated with Thermoflex is written in the VBA language. The plant contains more than 60 thermal components, including two gas turbines, one steam turbine, and two heat recovery steam generators. Simulation of one operational condition of the plant requires several hundred variables. The plant produces nominally 380 MW of power, and exports a mass flow rate between 200 and 400 ton/h of superheated process steam, at 45 bar and 404°C, to a neighboring refinery. The cogeneration plant operates subjected to an economic scenario, which changes with time, because of varying fuel, electricity, and steam prices. Therefore, to manage the plant, it is important to know the minimum operational cost, when a fixed contracted hourly-rate of process steam has to be exported, while a variable amount of electrical power is produced. An optimization problem can thus be formulated, for which the objective is to minimize the cost of consumed resources per unit electrical power generated. Results of optimization exercises to determine the optimal operational conditions of the plant for various exported mass flow rates of process steam are presented and discussed.
Thermodynamic Estimate of Minimal Dissipation for Heat Exchange System
Authors: Akhremenkov Andrei A. , Tsirlin Anatoliy M. , Kazakov Vladimir
Published: September 2009

In this paper we consider heat exchange system from point of view of Finite-time thermodynamics. At first time the novel estimate of the minimal entropy production in a general-type heat exchange system with given heat load and fixed heat exchange surface is derived. The corresponding optimal distribution of heat exchange surface and optimal contact temperatures are also obtained. It is proven that if a heat flow is proportional to the difference of contacting flows’ temperatures then dissipation in a multi-flow heat exchanger is minimal only if the ratio of contact temperatures of any two flows at any point inside heat exchanger is the same and the temperatures of all heating flows leaving exchanger are also the same. Our result based on those assumptions: 1. heat transfer law is linear (17); 2. summary exchange surface is given; 3. heat load is given; 4. input tempretures for all flows are given; 5. water equivalents for all flows are given.
A General Exergy-Based Method for Combining a Cost Analysis With an Environmental Impact Analysis: Part I — Theoretical Development
Authors: Tsatsaronis G. , Morosuk T.
Published: September 2009

This paper deals with integrated conventional and advanced exergetic, exergoeconomic and exergoenvironmental analyses. Such an advanced analysis evaluates the interactions among components of the overall system, and the real potential for improving a system component. Splitting the exergy destruction, the capital investment cost and the component-related environmental impact associated with each single component of an energy conversion system into endogenous/exogenous and avoidable/unavoidable parts enhances these analyses and improves the quality of the conclusions obtained from them. The paper consists of two parts. In the first one, the theoretical development is presented, whereas in the second part an application to a gas-turbine-based cogeneration system is discussed.
A General Exergy-Based Method for Combining a Cost Analysis With an Environmental Impact Analysis: Part II — Application to a Cogeneration System
Authors: Tsatsaronis G. , Morosuk T.
Published: September 2009

This paper deals with integrated conventional and advanced exergetic, exergoeconomic and exergoenvironmental analyses. Such an advanced analysis evaluates the interactions among components of the overall system, and the real potential for improving a system component. Splitting the exergy destruction, the capital investment cost and the component-related environmental impact associated with each single component of an energy conversion system into endogenous/exogenous and avoidable/unavoidable parts enhances these analyses and improves the quality of the conclusions obtained from them. The paper consists of two parts. In the first one, the theoretical development is presented, whereas in the second part an application to a gas-turbine-based cogeneration system is discussed.
Performance Evaluation of Combined Cycles for Cruise Ship Applications
Authors: Emmanuel-Douglas Ibiba
Published: September 2009

The flexibility of the Gas Turbine to be configured to meet the requirements of various applications is outstanding. The basic engine cycle can be modified in a number of ways to enhance performance in chosen applications. This paper presents a performance analysis procedure for the choice of optimum combined gas and steam turbine power plants for cruise ships. Performance of various arrangements of gas turbine based plants in terms of combined generation capacity of propulsion power, electricity and heat are analyzed and matched with the demands of the vessel at various operating modes to determine the most suitable plants for given cruise ship type. In particular, cycles with integrated electric propulsion systems were evaluated in various combinations of conventional prime movers for ship power plants namely; diesel engines, gas turbines and steam turbines. Key evaluation criteria are fuel economy, effectiveness of operation, investment and profitability and emissions control. Results of the analyses are summarized and presented for direct assessment of the relative merits of the plants.
Net Energy Analysis for Concentrated Solar Power Plants in Chile
Authors: Escobar Rodrigo , Larrai´n Teresita
Published: September 2009

The Chilean Energy Policy calls for 15 percent of new power generation capacity to come from renewable energy sources from 2006 to 2010, and then a 5% of electric energy generated from renewable energy sources with gradual increases in order to reach 10% by 2024. Concentrated solar power is an interesting alternative to help achieving those objectives, as it is estimated that northern Chile has high radiation levels, coupled with high values of the local clearness index and availability of flat terrain. The present report investigates the net energy attributes of parabolic trough plants installed in the Atacama Desert. Monthly means of solar radiation are used in order to estimate the solar fraction for a 100 MW plant at three different locations. Our analysis considers three cases: operation during sunlight hours only, with and without fossil fuel back-up, and continuous operation during 24 hours a day. The net energy analysis for concentrated solar power (CSP) plants is then performed, considering the energy costs of manufacturing, transport, installation, operation and decommissioning. The results indicate that the CSP plants are a net energy source when operating in sunlight-only mode and that the energy payback time is a linear function of the total operation time when utilizing fossil fuel back-up. In the continuous operation mode, the CSP plants become fossil fuel plants with solar assistance, and therefore all locations display negative net energy. Based on this result, the back-up fraction required for the plants to be net energy sources is estimated from the EROEI as function of the back-up fraction. It is estimated that the net energy analysis is a useful tool for determining under which conditions a CSP plant becomes a net energy source, and thus can be utilized in order to define geographical locations and operation conditions where they can be considered renewable energy sources.
On the Benefits of Separating the Heat Transfer Section and Analyzing Elementary Thermodynamic Cycles in Energy Systems Analysis
Authors: Morandin Matteo , Toffolo Andrea , Lazzaretto Andrea
Published: September 2009

The search for increasing performance and efficiency in energy system analysis leads to complex and highly integrated systems configurations. In a wide variety of energy systems the high integration among components derives from the need of correctly exploiting all the internal heat sources by a proper matching with the internal heat sinks. To address this problem in a general way, in previous works it was suggested to extract from the system flowsheet a “basic configuration” including the components different from the heat exchangers (named “basic” components) and a set of hot and cold thermal flows (without considering the heat exchangers that realize the heat transfer among them). It was also shown how the comprehension of the processes occurring within the system can be strongly facilitated by analyzing separately the elementary thermodynamic cycles involved in the system processes. In this paper, a further step is done by considering the overall efficiency as a baseline efficiency, obtained from the contributions of the separate elementary cycles, with the additional contribution given by the thermal coupling (i.e. the internal heat transfer) among the cycles themselves. The advantages of this analysis are shown using the evolution of the STIG cycle towards more complex system configurations as an example of application.
Impact Performance of Natural Fique-Fiber Reinforced Composites
Authors: Maranon Alejandro , Sanabria Yan , Contreras Mari´a F. , Hormaza Wilson
Published: September 2009

Laminated composites made of natural fiber and polymeric resins have a strong potential for engineering applications as they offer an attractive combination of mechanical and physical properties together with their environmental friendly character. Among structural applications, hybrid ballistic systems made of natural fiber composites have attracted the attention of engineers and scientists because of their excellent energy absorption compared to mild steel. In this paper, the impact and tensile properties of fique fibers (fucraea) reinforced composites are investigated. Plain woven fique-fabrics were embedded in polyester resin to produce five ply laminated panels. It was found that fique composites exhibited similar energy absorption than other natural composites reported in the literature.
Evaluation of Efficiency in Compressible Flow Ejectors
Authors: Bulusu Kartik V. , Gould David M. , Garris Charles A.
Published: September 2009

A steady-flow ejectors are fluid dynamic flow induction devices that directly transfer energy and momentum from a high energy primary fluid to a low energy secondary fluid through the work provided by entrainment and turbulent mixing. A variety of applications from refrigeration systems that are thermally energized and capable of using environmentally friendly refrigerants such as water and air, to desalination of water are currently being explored with this technology. The potential benefit of using environmentally friendly refrigerants makes it extensively useful for commercial air conditioning and refrigeration, particularly in applications where a source of waste heat is readily available. While steady-flow ejectors operate on entrainment and turbulent mixing between the primary (driving) flow, and the secondary (driven) flow, eliminating mechanically moving parts, the turbulent entrainment mechanism itself, is inherently dissipative of energy and little can be done to improve it. The process of mixing, which is irreversible is not accounted for explicitly in the existing definitions of ejector efficiency. Moreover, efficiency of ejectors is based on the concepts of a indirect flow induction viz., turbine-compressor analogy and compressor efficiency, and entrainment ratio. An experimental steady flow ejector with compressed air as the motive fluid and ambient air as suction fluid was fabricated and tested in this study. Comparisons of efficiency are made with the assumption of adiabatic and complete mixing of primary and secondary fluids before fluid discharge from the ejector. An important goal in our research is the definition of a proper measure of ejector efficiency which is appropriate for non-dissipative, non-steady ejectors. Such a definition would enable a more systematic methodology for evaluating ejector performance. There are three proposed methods that will be presented and compared.
Multi- Versus Single-Level Dynamic Synthesis/Design and Operation/Control Optimizations of a PEMFC System
Authors: Wang Meng , Kim Kihyung , von Spakovsky Michael R. , Nelson Douglas J.
Published: September 2009

As primary tools for the development of energy systems, optimization techniques have been studied for decades. However, for large-scale synthesis/design and operation/control optimization problems, it may turn out that it is impractical to solve the entire problem as a single optimization problem. In this paper, a multi-level optimization strategy, dynamic iterative local-global optimization (DILGO), is utilized for the synthesis/design and operation/control optimization of a 5 kWe PEMFC (Proton Exchange Membrane Fuel Cell) system. The strategy decomposes the system into three subsystems: a stack subsystem (SS), a fuel processing subsystem (FPS), and a work and air recovery subsystem (WRAS) and, thus, into three optimization sub-problems. To validate the decomposition strategy, the results are compared with a single-level dynamic optimization, in which the whole system is optimized together. In addition, for the purpose of comparison between different optimization algorithms, gradient-based optimization results are compared with those for a hybrid heuristic/gradient-based optimization algorithm.
Exergy Analysis of a Solid Oxide Fuel Cell-Gas Turbine Hybrid Power Plant
Authors: Amati Valentina , Sciubba Enrico , Toro Claudia
Published: September 2009

The paper presents the exergy analysis of a natural gas fuelled energy conversion process consisting of a hybrid solid oxide fuel cell coupled with a gas turbine. The fuel is partly processed in a reformer and then undergoes complete reforming in an internal reforming planar SOFC stack (IRSOFC). The syngas fuels in turn a standard gas turbine cycle that drives the fuel compressor and generates excess shaft power. Extensive heat recovery is enforced both in the Gas Turbine and between the topping SOFC and the bottoming GT. Two different configurations have been simulated and compared on an exergy basis: in the first one, the steam needed to support the external and the internal reforming reactions is completely supplied by an external Heat Recovery Steam Generator (HRSG), while in the second one that steam is mainly obtained by recirculating part of the steam-rich anode outlet stream. The thermodynamic model of the fuel cell system has been developed and implemented into the library of a modular object-oriented Process Simulator, Camel-Pro®; then, by means of this simulator, the exergetic performance of the two alternative configurations has been analyzed. A detailed analysis of the exergy destruction at component level is presented, to better assess the distribution of irreversibilities along the process and to gain useful design insight.
Hydrogen Use in an Urban District: Environmental Impacts in a Possible Scenario Based on Coal
Authors: Gambini Marco , Vellini Michela
Published: September 2009

Hydrogen technology is becoming ever more relevant because hydrogen use can help containing greenhouse gas emission if CO2 capture and storage techniques are implemented in the hydrogen production technology (when hydrogen is produced from fossil fuels). For this reason this work aims at carrying out a comparative analysis of possible energy scenarios in urban districts: a medium-small Italian city is taken into consideration, and its energy consumptions, both for domestic and industrial use, are evaluated. The current situation, in which conventional technologies meet the energy needs, is compared to a hypothetical scenario where clean energy vectors, namely hydrogen and electricity, are utilized together with traditional primary energy supply. Hydrogen production by means of coal decarbonization is investigated, as well as hydrogen use in advanced energy systems for transport and for electric and thermal energy generation.
Strontium-Doped Lanthanum Manganate Cathode Degradation Due to a Decomposed Hydrogen Peroxide Oxidant Feed Stream
Authors: Izzo John R. , Grew Kyle N. , Chiu Wilson K. S.
Published: September 2009

Decomposed hydrogen peroxide (H2O2) contains excess moisture and stabilizers that can deteriorate SOFC performance and durability markedly in the cathode. A numerical study is performed for a strontium-doped lanthanum manganate and yttria stabilized zirconia (LSM-YSZ) composite cathode using an oxidant stream consisting of a 20% O2 and 80% H2O mixture to study the detailed reaction mechanism and local transport and polarization phenomena. Specifically the 1-D cathode model couples multi-component gas and charge transport with an oxygen reduction mechanism. The model is validated with data from the literature and used to study the transport effect only of H2O in the cathode. Future work will consider the effect of H2O on the electrochemical reaction mechanism.
Thermodynamic and Thermoeconomic Analysis of a MCFC Power Generation Unit Coupled With Hydrogen Production
Authors: Verda Vittorio , Nicolin Flavio
Published: September 2009

In this paper, a biogas fuelled power generation system is considered. The system is based on a molten carbonate fuel cell stack for electricity generation, coupled with a PSA for hydrogen production. The power generation system is about 500 kW and consists of a fuel cell integrated with a micro gas turbine and a steam reformer. A design model of the system is presented. A thermoeconomic analysis is performed with the objective of highlighting the critical processes in terms of low efficiencies or high cost of components and to improve the initial design. The main design parameters affecting the critical process are identified and a system optimization is performed in order to minimize the unit cost of electricity produced by the system. The analysis presented here is the first result of a three year project (BIOH2POWER), which aims to produce and test the system.
Modeling Biomass Gasification: A New Approach to Utilize Renewable Sources of Energy
Authors: Vaezi M. , Passandideh-Fard M. , Moghiman M. , Charmchi M.
Published: September 2009

Thermochemical equilibrium modeling is the basis of the numerical method implemented in this study to predict the performance of a biomass gasifier. To validate the model, a close agreement is shown between numerical and experimental results. The model is then used in order to optimize the selection procedure of a specific biomass for a certain application. For this purpose, the minimum and maximum amount of carbon, hydrogen, and oxygen for 55 different biomass materials are extracted to calculate the range of variation of oxygen content and carbon/hydrogen ratio. The influences of such variations on syngas characteristics are then studied. Syngas characteristics are comprised of syngas calorific value, outlet gas temperature, gasification efficiency, and the volume of syngas obtained. The results are plotted in a generalized format that may be used for a wide range of biomass materials. These plots can be used for the selection of a biomass material based on desired conditions. Therefore, the developed model in this study provides a tool for design optimization of a biomass downdraft gasifier.
Thermoelectric Heat Recovery From a Tankless Water Heating System
Authors: LeBlanc S. A. , Gao Y. , Goodson K. E.
Published: September 2009

Thermoelectric cogeneration promises to recover waste heat energy from a variety of combustion systems. There is a need for computationally efficient simulations of practical systems that allow optimization and illustrate the impact of key material and system parameters. Previous research investigated thermoelectric material enhancement and thermoelectric system integration separately. This work connects material parameters and system integration. We develop a thermal simulation for a 15kW tankless, methane-fueled water heater with thermoelectric modules embedded within a cross-flow heat exchanger. The simulation employs a finite volume method for the two fluids. It links external convection with a surface efficiency of 85%, internal convection for laminar flow, and conduction through the system in order to determine power generation within the thermoelectric. For a single pipe in the water heater system, 126 W of electrical power can be generated, and a typical system could yield 370 W. Realization of effective cogeneration systems hinges on investigating the impact of thermoelectric material parameters coupled with system parameters, so the impact of varying flow rate, convection coefficient, TEM thermal conductivity, Seebeck coefficient, and thermal interface materials are investigated. While varying parameters can improve thermoelectric output by over 50%, thermal interface materials can severely limit cogeneration system power output.
3D CFD Electrochemical and Heat Transfer Model of an Integrated-Planar Solid Oxide Electrolysis Cell
Authors: Hawkes Grant , O’Brien James
Published: September 2009

A three-dimensional computational fluid dynamics (CFD) electrochemical model has been created to assess high-temperature electrolysis performance of an Integrated Planar porous-tube-supported Solid Oxide Electrolysis Cell (IP-SOEC). The model includes ten integrated planar cells in a segmented-in-series geometry deposited on a flattened ceramic support tube. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) module adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, activation over-potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Contour plots of local electrolyte temperature, current density, and Nernst potential indicated the effects of heat transfer, endothermic reaction, Ohmic heating, and change in local gas composition. Results are discussed for using this design in the electrolysis mode. Discussion of thermal neutral voltage, enthalpy of reaction, hydrogen production is reported herein. Predictions show negative pressure in the H2 electrode, indicating a possible limit of H2O diffusion through the ceramic tube. Minimum temperatures occur in the fuel and air downstream corner of the ceramic tube for voltages below the thermal neutral point.
Entropy Generation Minimization in a Tubular Solid Oxide Fuel Cell
Authors: Sciacovelli Adriano , Verda Vittorio
Published: September 2009

The aim of the paper is to investigate possible design modifications in tubular solid oxide fuel cell (SOFC) geometry to increase its performance. The analysis of the cell performances is conducted on the basis of the entropy generation. The use of this technique makes it possible to identify the phenomena provoking the main irreversibilities, understand their causes and propose changes in the system design and operation. The different contributions to the entropy generation are analyzed in order to develop new geometries that increase the fuel cell efficiency. To achieve this purpose, a CFD model of the cell is used. The model includes energy equation, fluid dynamics in the channels and in porous media, current transfer, chemical reactions and electrochemistry. The geometrical parameters of the fuel cell are modified to minimize the overall entropy generation.
Design of a Compact Heat Exchanger for Heat Recuperation From a High Temperature Electrolysis System
Authors: Housley G. K. , O’Brien J. E. , Hawkes G. L.
Published: September 2009

Design details of a compact heat exchanger and supporting hardware for heat recuperation in a high-temperature electrolysis application are presented. The recuperative heat exchanger uses a vacuum-brazed plate-fin design and operates between 300 and 800°C. It includes corrugated inserts for enhancement of heat transfer coefficients and extended heat transfer surface area. Two recuperative heat exchangers are required per each four-stack electrolysis module. The heat exchangers are mated to a base manifold unit that distributes the inlet and outlet flows to and from the four electrolysis stacks. Results of heat exchanger design calculations and assembly details are also presented.
Comparison of a Multi-Megawatt High Temperature Fuel Cell System With Reciprocating Engines and Aero-Derivative Gas Turbines
Authors: Karvountzi Georgia C. , Duby Paul F.
Published: September 2009

High temperature fuel cells can be successfully integrated in a simple cycle or in a combined cycle configuration and achieve lower heating value (LHV) efficiencies greater than gas turbines and reciprocating engines. A simple cycle fuel cell system reaches 50 to 51% LHV efficiencies. A fuel cell system integrated with gas and steam turbines in a hybrid system could lead to LHV efficiencies of 70% to 72%. An aero-derivative gas turbine that is the most efficient simple cycle gas turbine achieves 40% to 46% thermal efficiency and a new generation reciprocating engine 39% to 42%. Upon integration in a combined cycle configuration with steam injection, aero-derivative gas turbines potentially reach LHV efficiencies of 55% to 58%. The purpose of the present paper is to compare initially the performance of a stand alone fuel cell with a stand alone gas turbine and a stand alone reciprocating engine. Then the fuel cell is integrated in a hybrid system and it is compared with a gas turbine combined cycle plant. The system sizes explored are 5MW in the stand alone case, and 20MW, 30MW, 60MW, 100MW and 200MW in the hybrid / combined cycle case. The performance of the hybrid system was reviewed under different ambient temperatures (0° F–90° F) and site elevations (0 ft–3000 ft). High temperature fuel cells are more efficient and have lower emissions than gas turbines and reciprocating engines. However fuel cells cannot be used for peak power generation due to long start-up time or load following applications.
A 150Kw Integrated Solar Combined Cycle (ISCC) Power Plant
Authors: Teets Jon W. , Teets J. Michael
Published: September 2009

With the soaring price of oil and the global push toward reduction in carbon emissions, renewable energy is treated by many as a solution to the economic and environmental cost of consumption of fossil fuels. With the power plant reviewed in this paper use of Solar and Bio-fuels will be attained. During the day power needs can be met with Solar energy and when that energy supply is not adequate can use bio-fuels or fuel of choice (gaseous or liquid). If there is a need for use only with Solar energy (i.e. peak power demand) can shut down and restart when desired. Due to the size of the unit, start up is not a long labor intensive task and can be accomplished within the hour. The 150 Kw Integrated Solar Combined Cycle (ISCC) power plant is for commercial and residential use. The unit will produce 150 Kw electrical power output to customer with Solar Thermal Energy (STE). Solar Thermal energy is attained from parabolic trough concentrator(s). Working fluid in the STE system is Syltherm 800 (Silicone Heat Transfer Fluid) is acceptable use from –40F to 750 F. This fluid is heated and passes through a heat exchanger to transfer energy to the closed rankine cycle (where the liquid is changed to vapor stage. Steady state analysis performed on the rankine cycle, with ammonia / water mixture (50/50) used NIST standard reference database 23 for the thermodynamic and transport properties REFPROP [1]. A unique feature with the combined cycle unit, is the rankine cycle turbine wheel is directly attached to the power producing gas turbine spool, thus share a common high speed permanent magnet alternator assembly. The core gas turbine engine used in the combined cycle is a two spool, high pressure ratio (11:1) simple cycle microturbine with cycle efficiency of 20%, at 70Kw output electrical power (sea level standard day). The latter is defined as model TMA 70SC. In addition to the gas turbine engine and rankine turbine stage, the combined cycle incorporates a gas turbine waste heat boiler, economizer, condenser and economizer fluid preheater. The combined cycle unit, without thermal energy, will produce 145Kw (sea level standard day) with an electrical output efficiency of 40%. The gas turbine exhaust to atmosphere will be less than 240 F. The ISCC unit power producing spool / rotor will operate at 100% N regardless of gas turbine power demand. Whereas, spool number one will vary with gas turbine power demand. When the available solar thermal energy decreases the gas turbine fuel flow will increase to maintain electrical power, pending day conditions. The ISCC power plant, can be used for main power plants in [stand alone] communities, business, industrial or distributed energy (D.E.). Also, will provide electrical power to the customer at lower rate than traditional power companies.
On Application of the Second Law to Heat Exchangers
Authors: Fakheri Ahmad
Published: September 2009

The application of entropy minimization to heat exchangers leads to inconsistent results and does not yield much useful design information. In this paper it is shown that in applying the second law to heat exchangers, three assumptions are typically made that are incorrect and that once they are removed, useful and consistent results are obtained from the second law. In addition, a new performance measure, entropy flux is introduced and it is shown that the objective in heat exchanger design should be the maximization of the entropy flux.
Statistics of normal mode amplitudes in an ocean with random sound-speed perturbations: Cross-mode coherence and mean intensity
Authors: Colosi John A. , Morozov Andrey K.
Published: September 2009

In this paper Creamer’s [(1996). J. Acoust. Soc. Am. 99, 2825–2838] transport equation for the mode amplitude coherence matrix resulting from coupled mode propagation through random fields of internal waves is examined in more detail. It is shown that the mode energy equations are approximately independent of the cross mode coherences, and that cross mode coherences and mode energy can evolve over very similar range scales. The decay of cross mode coherence depends on the relative mode phase randomization caused by coupling and adiabatic effects, each of which can be quantified by the theory. This behavior has a dramatic effect on the acoustic field second moments like mean intensity. Comparing estimates of the coherence matrix and mean intensity from Monte Carlo simulation, and the transport equations, good agreement is demonstrated for a 100-Hz deep-water example.
Possible occurrence of signature whistles in a population ofSotalia guianensis(Cetacea, Delphinidae) living in Sepetiba Bay, Brazil
Authors: Duarte de Figueiredo Luciana , Simão Sheila Marino
Published: September 2009

According to the “signature whistle” hypothesis, dolphins emit stereotypic sequential whistles whose function is to transmit the identity and location of the whistling animal. However, it has also been proposed that the information signature may be expressed by distinct acoustical features within a single type of whistle shared by a population of dolphins. In an attempt to detect signature whistles from Sotalia guianensis living in Sepetiba Bay, Rio de Janeiro, Brazil, 12 h of vocalizations were recorded. Following analysis of the spectrograms, the whistles were classified according to visual inspection and the contour similarity method. Although the identities of the whistling animals were not established, 202 whistle sequences were selected and classified by visual inspection into 27 different types of potential signature whistles. However, there was a large discrepancy between this classification method and that obtained using the quantitative contour similarity method. The arguments in support of the premise that S. guianensis produces signature whistles are discussed and the limitations of the classification systems employed are examined.
Tracking blue whales in the eastern tropical Pacific with an ocean-bottom seismometer and hydrophone array
Authors: Dunn Robert A. , Hernandez Olga
Published: September 2009

Low frequency northeastern Pacific blue whale calls were recorded near the northern East Pacific Rise (9 °N latitude) on 25 ocean-bottom-mounted hydrophones and three-component seismometers during a 5-day period (November 22–26, 1997). Call types A, B, C, and D were identified; the most common pattern being ∼130–135 s repetitions of the AB sequence that, for any individual whale, persisted for hours. Up to eight individual blue whales were recorded near enough to the instruments to determine their locations and were tracked call-by-call using the B components of the calls and a Bayesian inversion procedure. For four of these eight whales, the entire call sequences and swim tracks were determined for 20–26-h periods; the other whales were tracked for much shorter periods. The eight whales moved into the area during a period of airgun activity conducted by the academic seismic ship R/V Maurice Ewing. The authors examined the whales’ locations and call characteristics with respect to the periods of airgun activity. Although the data do not permit a thorough investigation of behavioral responses, no correlation in vocalization or movement with airgun activity was observed.
A perceptual equivalent of the labial-coronal effect in the first year of life
Authors: Nazzi Thierry , Bertoncini Josiane , Bijeljac-Babic Ranka
Published: September 2009

Several studies have investigated infants’ acquisition of the phonological (prosodic or phonotactic) regularities of their native language at the lexical level, by showing that infants around 9∕10months of age start preferring lists of words that have a more versus less frequent phonological structure. The present study investigates whether a similar acquisition pattern of preferences can be found for labial-coronal (LC) words over coronal-labial (CL) words, a bias classically interpreted in terms of production constraints but that could also be explained in terms of relative frequency of frequent LC and less frequent CL words in many languages including French, the language used here. Results show that a preference for bisyllabic LC words emerges between 6 and 10months of age in French-learning infants (Experiment 1), and that the non-preference at 6months is not due to the infants’ inability to discriminate the two lists of words (Experiment 2). The present study thus establishes an early perceptual equivalent of the LC bias initially found at the onset of word production. Implications of this finding for an understanding of the perception-production relationship are discussed.
Efficient estimation of decay parameters in acoustically coupled-spaces using slice sampling
Authors: Jasa Tomislav , Xiang Ning
Published: September 2009

Room-acoustic energy decay analysis of acoustically coupled-spaces within the Bayesian framework has proven valuable for architectural acoustics applications. This paper describes an efficient algorithm termed slice sampling Monte Carlo (SSMC) for room-acoustic decay parameter estimation within the Bayesian framework. This work combines the SSMC algorithm and a fast search algorithm in order to efficiently determine decay parameters, their uncertainties, and inter-relationships with a minimum amount of required user tuning and interaction. The large variations in the posterior probability density functions over multidimensional parameter spaces imply that an adaptive exploration algorithm such as SSMC can have advantages over the exiting importance sampling Monte Carlo and Metropolis–Hastings Markov Chain Monte Carlo algorithms. This paper discusses implementation of the SSMC algorithm, its initialization, and convergence using experimental data measured from acoustically coupled-spaces.
Seasonal changes in the vocal behavior of bowhead whales (Balaena mysticetus) in Disko Bay, Western-Greenland
Authors: Tervo Outi M. , Parks Susan E. , Miller Lee A.
Published: September 2009

Singing behavior has been described from bowhead whales in the Bering Sea during their annual spring migration and from Davis Strait during their spring feeding season. It has been suggested that this spring singing behavior is a remnant of the singing during the winter breeding season, though no winter recordings are available. In this study, the authors describe recordings made during the winter and spring months of bowhead whales in Disko Bay, Western-Greenland. A total of 7091 bowhead whale sounds were analyzed to describe the vocal repertoire, the singing behavior, and the changes in vocal behavior from February to May. The vocal signals could be divided into simple (frequency-modulated) calls (n=483), complex (amplitude-modulated) calls (n=635), and song notes (n=5973). Recordings from the end of February to middle of March were characterized by higher call rates with a greater diversity of call types than recordings made later in the season. This study is the first description of bowhead song from the stock in Western-Greenland during both the winter and spring months, and provides support for the hypothesis that song during the winter months contains more song notes than song from the spring making the winter song more variable.
Modeling source-filter interaction in belting and high-pitched operatic male singing
Authors: Titze Ingo R. , Worley Albert S.
Published: September 2009

Nonlinear source-filter theory is applied to explain some acoustic differences between two contrasting male singing productions at high pitches: operatic style versus jazz belt or theater belt. Several stylized vocal tract shapes (caricatures) are discussed that form the bases of these styles. It is hypothesized that operatic singing uses vowels that are modified toward an inverted megaphone mouth shape for transitioning into the high-pitch range. This allows all the harmonics except the fundamental to be “lifted” over the first formant. Belting, on the other hand, uses vowels that are consistently modified toward the megaphone (trumpet-like) mouth shape. Both the fundamental and the second harmonic are then kept below the first formant. The vocal tract shapes provide collective reinforcement to multiple harmonics in the form of inertive supraglottal reactance and compliant subglottal reactance. Examples of lip openings from four well-known artists are used to infer vocal tract area functions and the corresponding reactances.
A generalized statistical Burgers equation to predict the evolution of the power spectral density of high-intensity noise in atmosphere
Authors: Menounou Penelope , Athanasiadis Aristotelis N.
Published: September 2009

The present work is a theoretical/numerical investigation of the combined effect of nonlinearity, geometrical spreading, and atmospheric absorption on the evolution of the power spectral density of a noise field, when only the power spectral density is known at source, not the signal itself. This is often the case in aircraft noise measurements. The method presented here is based on and extends previous work [P. Menounou and D. T. Blackstock, J. Acoust. Soc. Am. 115, 567–580 (2004)], where a recursion equation [statistical Burgers equation (SBE)] describing the evolution of the joint moments of the noise source was derived. The SBE is restricted to plane waves, thermoviscous fluids, and short propagation distances (preshock region). In the present work, the SBE is extended to include the effects of geometrical spreading and arbitrary absorption, in order to be applicable to propagation of high-intensity noise through atmosphere. A new equation is derived and termed generalized SBE, and a method for its numerical implementation is presented. Results are in good agreement with time domain calculations for propagation in atmosphere of (i) sinusoidal signals (benchmark case) and (ii) Gaussian processes with known power spectral densities at source.
Contribution of crosstalk to the uncertainty of electrostatic actuator calibrations
Authors: Shams Qamar A. , Soto Hector L. , Zuckerwar Allan J.
Published: September 2009

Crosstalk in electrostatic actuator calibrations is defined as the ratio of the microphone response to the actuator excitation voltage at a given frequency with the actuator polarization voltage turned off to the response, at the excitation frequency, with the polarization voltage turned on. It consequently contributes to the uncertainty of electrostatic actuator calibrations. Two sources of crosstalk are analyzed: the first attributed to the stray capacitance between the actuator electrode and the microphone backplate, and the second to the ground resistance appearing as a common element in the actuator excitation and microphone input loops. Measurements conducted on 1/4, 1/2, and 1 in. air condenser microphones reveal that the crosstalk has no frequency dependence up to the membrane resonance frequency and that the level of crosstalk lies at about −60 dB for all three microphones—conclusions that are consistent with theory. The measurements support the stray capacitance model. The contribution of crosstalk to the measurement standard uncertainty of an electrostatic actuator calibration is therewith 0.01 dB.