bluuebunny/crossref_metadata_2025 huggingface dataset:
Phonon Transport Across Mesoscopic Constrictions
Authors: Singh Dhruv , Murthy Jayathi Y. , Fisher Timothy S.
Published: January 2011

Phonon transport across constrictions formed by a nanowire or a nanoparticle on a substrate is studied by a numerical solution of the gray Boltzmann transport equation (BTE) resolving the effects of two length scales that govern problems of practical importance. Predictions of total thermal resistance for wire/substrate and particle/substrate combinations are made for the entire range of Knudsen number, with an emphasis on resolving transport in the mesoscopic regime where ballistic-diffusive mechanisms operate and analytical expressions are not available. The relative magnitudes of bulk and constriction resistance are established, and a correlation for overall thermal resistance spanning the range of practical Knudsen numbers is provided.
Scaling of Natural Convection of an Inclined Flat Plate: Sudden Cooling Condition
Authors: Saha Suvash C. , Patterson John C. , Lei Chengwang
Published: January 2011

The natural convection boundary layer adjacent to an inclined plate subject to sudden cooling boundary condition has been studied. It is found that the cold boundary layer adjacent to the plate is potentially unstable to Rayleigh–Bénard instability if the Rayleigh number exceeds a certain critical value. A scaling relation for the onset of instability of the boundary layer is achieved. The scaling relations have been developed by equating important terms of the governing equations based on the development of the boundary layer with time. The flow adjacent to the plate can be classified broadly into a conductive, a stable convective, or an unstable convective regime determined by the Rayleigh number. Proper scales have been established to quantify the flow properties in each of these flow regimes. An appropriate identification of the time when the instability may set in is discussed. A numerical verification of the time for the onset of instability is also presented in this study. Different flow regimes based on the stability of the boundary layer have been discussed with numerical results.
Thermodynamic Basis of Dual-Phase-Lagging Heat Conduction
Authors: Xu Mingtian
Published: January 2011

The thermal vibration phenomenon occurring in the dual-phase-lagging heat conduction violates the second law of thermodynamics under the local equilibrium assumption. In order to resolve this paradox, two types of the extended irreversible thermodynamics are developed in the present work, which make the dual-phase-lagging heat conduction model compatible with the second law of thermodynamics. It is also shown that these extended irreversible thermodynamics can give rise to the Maxwell model for the viscoelastic fluid flow.
Reflections on the Motive Power of Heat II
Authors: Mahl George J.
Published: January 2011

This paper explores and challenges the underlying basis of the Second Law of Thermodynamics. The second law of thermodynamics and its related equations define the relationship between thermal energy and its conversion into mechanical work. The second law of thermodynamics and its equations are based on theory developed by analysis of the Carnot cycle, then with a leap of faith, applies this theory and these equations to the Rankine cycle and to the general conversion of thermal energy into mechanical energy. This paper explores the original analysis, which forms the basis of the second law of thermodynamics, and offers new analysis which may form a new understanding of thermodynamics. If proven correct, this new understanding may unlock tremendous resources for the production of mechanical and electrical energy.
Solar Syngas Production From H2O and CO2 via Two Step Thermochemical Cycles Based on FeO/Fe3O4 Redox Reactions: Kinetic Analysis
Authors: Stamatiou Anastasia , Loutzenhiser Peter G. , Steinfeld Aldo
Published: January 2011

Syngas production via a two-step H2O/CO2-splitting thermochemical cycle based on FeO/Fe3O4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of Fe3O4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO2 and H2O with FeO to CO and H2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with FeO in the range 973–1273 K and CO2/H2O concentrations of 15–75%. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir-Hinshelwood type was formulated to describe the competitiveness of the reaction based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.
Thermal Computational Model to Analyze PV Modules: Preliminary Results
Authors: Soler-Bientz Rolando , Go´mez-Castro Fernando , Ricalde-Cab Lifter
Published: January 2011

A computational model of a PV module was implemented to describe its thermal behaviour considering the geographical conditions of the Yucatan Peninsula, Mexico. In order to analyze the effects of non uniform illumination on the thermal profiles of a PV module, a reflecting surface was added adjacent to a PV module edge. A finite difference formulation was used to represents the thermal patterns of each PV describing the thermal conditions of each particular solar cell within the PV module. The mathematical model and the preliminary results obtained for two time instants are presented using real meteorological data to reflect the effect of the wind patterns.
Water Impacts of the American Clean Energy and Security Act of 2009 on Texas
Authors: Grubert Emily A. , Webber Michael E.
Published: January 2011

Complex environmental systems are frequently broken into politically manageable pieces, and a policy focusing on a single environmental issue can undermine other policy priorities. It is a nontrivial concern that domestic and international legislation focused on reducing emissions of climate-related pollution have not adequately considered policy effects on related systems like water. The goal of this work is to assess the possible effects of the American Clean Energy and Security Act of 2009 (ACES, passed by the House of Representatives in June) on water resources in Texas.
Combustion Emissions Modeling and Testing of Neat Biodiesel Fuels
Authors: Liu Hsing-Pang , Strank Shannon , Werst Mike , Hebner Robert , Osara Jude
Published: January 2011

This paper presents emissions modeling and testing of a four-stroke single cylinder diesel engine using pure soybean, cottonseed, and algae biodiesel fuels. A system level engine simulation tool developed by Gamma Technologies, GT-Power, has been used to perform predictive engine combustion simulations using direct-injection jet modeling technique. Various physical and thermodynamic properties of the biodiesel fuels in both liquid and vapor states are required by the GT-Power combustion simulations. However, many of these fuel properties either do not exist or are not available in published literatures. The properties of the individual fatty esters, that comprise a biofuel, determine the overall fuel properties of the biofuel. In this study, fatty acid profiles of the soybean, cottonseed, and algae methylester biodiesel fuels have been identified and used for fuel property calculations. The predicted thermo-physical properties of biodiesels were then provided as fuel property inputs in the biodiesel combustion simulations. Using the calculated biodiesel fuel properties and an assumed fuel injector sac pressure profile, engine emissions of the conventional diesel and biodiesel fuels have been predicted from combustion simulations to investigate emission impacts of the biodiesel fuels. Soybean biodiesel engine emissions, which include NOx, HC, CO and CO2, measured at various engine speeds and loads in actual combustion emissions tests performed in this study were also compared to those predicted by the combustion simulations.
A New Oscillating-Foil Power Generator for Sailingship-Based Renewable Energy Generation
Authors: Platzer Max F. , Sarigul-Klijn Nesrin
Published: January 2011

The wind energy available over the globe’s vast ocean areas offers the opportunity to make a decisive contribution to the solution of the energy and climate crisis. In this paper we propose the use of sailing ships equipped with hydropower generators to convert the ocean wind energy into electricity. We describe a new oscillating-foil hydropower generator to achieve this objective. Our preliminary performance estimates indicate the feasibility of generating at least one megawatt of electrical power output per ship for electrolytic conversion of sea water into hydrogen and oxygen. Tests of a small-scale prototype confirmed the expected operational characteristics of the new generator.
Finite Element Modeling of Concentrating Solar Collectors for Evaluation of Gravity Loads, Bending, and Optical Characterization
Authors: Christian Joshua M. , Ho Clifford K.
Published: January 2011

Understanding the effects of gravity and wind loads on concentrating solar power (CSP) collectors is critical for performance calculations and developing more accurate alignment procedures and techniques. This paper presents a rigorous finite-element model of a parabolic trough collector that is used to determine the impact of gravity loads on bending and displacements of the mirror facets and support structure. The geometry of the LUZ LS-2 parabolic trough collector was modeled using SolidWorks, and gravity-induced loading and displacements were simulated in SolidWorks Simulation. The model of the trough collector was evaluated in two positions: the 90° position (mirrors facing upward) and the 0° position (mirrors facing horizontally). The slope errors of the mirror facet reflective surfaces were found by evaluating simulated angular displacements of node-connected segments along the mirror surface. The ideal (undeformed) shape of the mirror was compared to the shape of the deformed mirror after gravity loading. Also, slope errors were obtained by comparing the deformed shapes between the 90° and 0° positions. The slope errors resulting from comparison between the deformed vs. undeformed shape were as high as ∼2 mrad, depending on the location of the mirror facet on the collector. The slope errors resulting from a change in orientation of the trough from the 90° position to the 0° position with gravity loading were as high as ∼3 mrad, depending on the location of the facet.
Analytical Methods to Evaluate Flux Distributions From Point-Focus Collectors for Solar Furnace and Dish Engine Applications
Authors: Ho Clifford K. , Khalsa Siri S. , Siegel Nathan P.
Published: January 2011

This paper introduces a new analytical “stretch” function that accurately predicts the flux distribution from on-axis point-focus collectors. Different dish sizes and slope errors can be assessed using this analytical function with a ratio of the focal length to collector diameter fixed at 0.6 to yield the maximum concentration ratio. Results are compared to data, and the stretch function is shown to provide more accurate flux distributions than other analytical methods employing cone optics.
Applicability of Nanofluids in Concentrated Solar Energy Harvesting
Authors: Taylor Robert A. , Phelan Patrick E. , Otanicar Todd P. , Tyagi Himanshu , Trimble Steven
Published: January 2011

Concentrated solar energy is becoming the input for an increasing number of thermal systems [1]. Recent papers have indicated that the addition of nanoparticles to conventional working fluids (i.e. nanofluids) can improve heat transfer and solar collection [2–4]. Thermal models developed herein show that nanofluid collectors can be more efficient than conventional concentrating solar thermal technology. This work indicates that power tower schemes are the best application for taking advantage of potential nanofluid efficiency improvements. This study provides a notional design of how such a nanofluid power tower receiver might be built. Using this type of design, we show a theoretical enhancement in efficiency of up to a 10% by using nanofluids. Further, we compare the energy and revenue generated in a conventional solar thermal plant to a nanofluid one. It was found that a 100MWe capacity solar thermal power tower operating in a solar resource similar to Tucson, AZ could generate ∼$3.5 million more per year by incorporating a nanofluid receiver.
Towards a Definition and Metric for the Survivability of Ocean Wave Energy Converters
Authors: Brown Adam , Paasch Robert , Tumer Irem Y. , Lenee-Bluhm Pukha , Hovland Justin , von Jouanne Annette , Brekken Ted
Published: January 2011

Survivability is a term that is widely used in the ocean wave energy industry, but the term has never been defined in that context. The word itself seems to have an intrinsic meaning that people understand; this fact often leads to the term’s misuse and its confusion with “reliability”. In order to design systems that are capable of long term survival in the ocean environment, it must be clear what “survivability” means and how it affects the design process and ultimately the device being deployed. Ocean energy is relatively predictable over the span of months, days, and even hours, which makes it very promising as a form of renewable energy. However, the variation of the energy content of ocean waves in a given location is likely high due to the effect of storms and the seasons. Wave energy converters must be built to be reliable while operating and survivable during severe conditions. Therefore, probabilistic design practices must be used to insure reliability and survivability in conditions that are constantly changing. Reliability is used to numerically express the failures of a device that occur while the system is operational, and it is usually expressed in terms of the mean time between failure (MTBF). However, in the context of ocean wave energy converters, the devices are likely to be continuously deployed in conditions that push them beyond their operating limits. During these times it is likely that wave energy converters will be placed in some sort of “survival mode” where the device sheds excess power, reducing system loading. Survivability is focused specifically on failures that occur during these times, when the device is experiencing conditions that surpass its operational limits. Developing a highly survivable wave energy converter is an outstanding goal, but without a standard definition of the term survivability, progress towards that goal cannot be measured. The purpose of this paper is to provide an initial definition for survivability, and to introduce a simple metric that provides an objective comparison of the survivability of varying wave energy converter technologies.
Distributed Industrial Scale Hybrid Solar Concentrator Photovoltaics and Thermal Energy
Authors: Borton David N.
Published: January 2011

While solar photovoltaic (PV) panels have been used successfully to produce electricity for quite some time, it has been technically difficult to capture their heat because of the large area of a flat-plate photovoltaic panel. Likewise it has been difficult to manufacture solar concentrator systems that are of the same physical scale, about one square meter, as successful commercial flat-plate photovoltaic panels and incorporate them into a commercializable and easily manufactured solar energy system. This paper addresses the two problems by considering the feasibility of a single design of a one square meter plastic nonimaging solar concentrator that focuses sunlight on a heat-capturing, dense array of high-intensity photovoltaic chips. The individual one square meter modules are designed to be mounted on a 2-axis tracking system which could have a double polar-axis support for energy and cost efficiency. When coupled with an existing electronic control, these three components create a commercial-scale solar electricity device that also provides heat in quantities suitable for heating or cooling. Preliminary contacts with electric utilities and commercial/industrial businesses have found interest in procurement of the proposed technology for widespread harvesting and use of solar energy in the US and abroad.
3D FEM Model to Improve the Heat Transfer in Concrete for Thermal Energy Storage in Solar Power Generation
Authors: Selvam R. Panneer , Castro Marco
Published: January 2011

Solar thermal energy has been shown to be a viable alternative resource. At this time, the concentrating solar power systems costs are 13–17 cents/kWh. The goal of DOE is to reduce the cost to 5 cents/kWh by 2015 using energy storage techniques. Several storage schemes and materials have been developed over the past two decades. Concrete is an inexpensive storage medium for sensible heat. Research has been done lately using concrete blocks which are heated up by circulating synthetic oil at a maximum temperature of 390 °C through a series of pipes embedded in the concrete. However, the efficiency of the storage unit can be improved by increasing the operating temperature, which is in turn limited by the materials used. A 3-D finite element computer model was written in order to perform parametric studies during the thermal charging and discharging of concrete. The program allows modifying the physical properties of the heat transfer fluid and storage material. A feature to add fins attached to the flow line was developed to evaluate improvements in heat transfer. Several fin configurations were studied. The increase in energy stored in the system, and the corresponding cost increase are reported.
Solar Assisted Household Clothes Dryer
Authors: Luttrell Jeff , Agonafer Dereje
Published: January 2011

Energy savings for domestic appliances have been an emphasis for several years. The efficiencies of several appliances have improved dramatically as a result of this attention. Refrigerator, water heater, and washing machine energy consumptions have been reduced. One appliance has not experienced significant improvement, the clothes dryer. Typical household clothes dryers use large amounts of electricity or natural gas to heat air that is circulated with the clothes. The energy to heat the air is a function of the amount of air and heat needed to remove moisture from the clothes. Using solar heat to augment or replace the other energy sources can provide significant energy savings. Conventional house construction includes features which collect and concentrate solar energy in the air occupying the attic space. Typical home design provides a roof which functions as a large area solar energy collector. Many roofing materials have solar absorption of 80% or more. Insulation of the roof decking is uncommon so that absorbed solar heat conducts through and heats the attic air. Through simple, low-cost ducting and minor modification of a clothes dryer air inlet, this energy resource becomes available for use. This study evaluates the potential energy savings of using solar-heated attic air as a clothes dryer air source. Considering house construction as well as seasonal and regional climate variations, attic air can augment and may fully replace utility energy as the heat source for drying air during daylight hours when solar energy is incident on the roof. The energy savings can be up to 3.5 kilowatt hours (or the heating equivalent for natural gas) for each dryer load.
A System-Level Simulation Model of Poly-Generation Plant Based on Gasification Technology With Methanol and Power Generation
Authors: Chen Po-Chuang , Chiu Hsiu-Mei , Chyou Yau-Pin , Yu Chiou-Shia
Published: January 2011

This study presents a system-level simulation model with the commercial chemical process simulator, Pro/II® V8.1.1, for poly-generation applications, based on gasification technology. The feedstock is coal and the products are electricity and methanol. There are five major blocks in the simulated polygeneration plant, i.e. air separation unit (ASU), gasification unit, gas clean-up unit, combined cycle, and methanol synthetic unit. The first four blocks can be combined for electricity generation, i.e. integrated gasification combined cycle (IGCC). The study performs two analyses of basic case and polygeneration. The basic case is the benchmark case which is verified with the reference data from United States Environment Protection Agency. The poly-generation case is based on the basic case model, and to simulate a feasible case with actual parameters in Taiwan. The simulated outcome shows that the power output is 262.35 MW and the methanol production is 1,768.8 ton per day. The gross and net efficiency (HHV) of the integrated gasification poly-generation case are 52.75% and 46.42%, respectively. The latter is higher than the counterpart of traditional IGCC plants by over 4% points. In conclusion, integrated gasification poly-generation process provides an alternative choice to reduce the dependence on fossil fuels, especially crude oil, in Taiwan.
CFD Simulation of the Supersonic Steam Ejector
Authors: Li Zhiming , Wang Jinli , Zheng Hongtao , Cailin  , Li Yajun
Published: January 2011

The supersonic steam ejector is widely used in many industries which are steam powered such as oil, thermoelectric, refrigeration and so on. Many scholars analyzed the steam ejector by using ideal gas model and they ignored phase change, this may bring some errors for the flowing field of the ejector. In this study, the supersonic steam ejector was simulated using CFD (Computational Fluid Dynamics). Flowing field of the ejector was analyzed by using different state equations. The results shows that performance of the ejector was underestimated under the ideal gas model, and the entrainment ratio is 20%–40% lower than using real gas model. When phase changing was considered under real gas state equations, influences of working fluid pressure and back pressure were investigated. The results illustrates that working critical pressure and back flow critical pressure exist in the flow, and the entrainment ratio reaches its peak at working critical pressure. The performance of the ejector was almost the same when the outlet pressure was lower than critical back pressure. Effects of ejector geometries were also investigated in this paper. It shows that there are optimums of the relative position of the steam nozzle and the taper of the mixing section, length of mixing chamber and diameter of throat according to mass flow rate of second fluid. There are also critical length of diffuser and throat. Mass flow rate stayed the same when the length of diffuser or throat grows. This paper will provide a theoretical basis for ejector’s energy-saving and geometry optimization.
The Structure Design and Numerical Simulation of Dual-Fuel Gas Turbine Nozzle
Authors: Yang Honglei , Zheng Hongtao , Li Zhiming , Li Yajun
Published: January 2011

This paper designed several dual-fuel nozzle structures for the chemically recuperated gas turbine (CRGT) combustor and then the numerical simulation in regard to the combustion flow fields of the combustors with these nozzle structures was carried out with the aid of CFD method and finally the contrastive analysis was made. Realizable k-ε turbulence model, PDF combustion model and the SIMPLE algorithm method were applied in the numerical simulation. According to the contrast of these nozzle structure models’ flame length, position of the high temperature zone, wall temperature and the evenness of exit temperature field as the key influencing factors of the combustor, we could know that the gas swirling dual-fuel nozzle with oblique holes, on the one hand, can produce preswirl flow in the gas channel to enable a better mixing of the pyrolysis gas and air; on the other hand, can protect the nozzle and the wall of flame tube from fire and keep the exit temperature in a moderate level.
Modeling of a SOFC-GT Hybrid Power Plant With Anode Recycling
Authors: Cheddie Denver , Murray Renique
Published: January 2011

Power generation using gas turbine power plants operating on the Brayton cycle suffers from low efficiencies and high irreversibilities. In this work, a solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% electrical efficiency (13.7% second law efficiency). The SOFC system entails anode recycling to enable self sustaining reformation reactions, thus alleviating the need for an external water supply and steam generation unit. It also utilizes turbine outlet heat recovery to ensure a sufficiently high SOFC operating temperature. The power output of the hybrid plant is 26.2 MW at 63.4% efficiency (35.3% second law efficiency). The hybrid plant performs best when 70–80% anode recycling is used. A thermo-economic model predicts a payback period of 4.6 years, based on future projected SOFC cost estimates.
Low Capital Cost Renewable Energy Conversion With Liquid Piston Stirling Engines
Authors: Stevens James W.
Published: January 2011

Since many renewable energy technologies use low cost or free primary energy sources such as solar insolation or wind, the capital cost of conversion equipment can become the dominant factor in determining economic feasibility. A natural approach to lowering the capital cost per unit of electricity is to strive for high efficiency equipment, i.e., increase the amount of electricity produced. Another approach is to seek out low cost conversion technologies, i.e., lower the capital cost. Capital equipment costs must be significantly lower than currently available off-the-shelf technologies to make solar power generally attractive economically for small-scale electricity generation. One potential low capital cost energy conversion technology is the liquid piston Stirling engine. A necessary design component for liquid piston Stirling engines is estimation of the frictional losses in the oscillating liquid columns. While frictional losses for fully developed laminar and turbulent pipe flow are characterized quite completely, average frictional loss factors for the continually starting and stopping liquid flow in oscillating columns are less complete. Direct measurements of frictional loss using a log-decrement method are reported in the paper. Measurements were completed for a variety of piping and tubing sizes and configurations. It was found that liquid volume correlated damping coefficient data well. A comparison with an equivalent fully developed laminar flow damping coefficient is presented.
Evaluation of H.R. 2454’s Potential Impacts on Texas’s Electricity Profile Using the Rosenfeld Effect as a Basis for Evaluation
Authors: Lott Melissa C. , Webber Michael E.
Published: January 2011

The American Clean Energy and Security Act of 2009 (H.R. 2454) introduces a combined federal standard for efficiency and renewable electricity. This standard requires utilities to supply a portion of their customer’s demand using energy efficiency measures and renewable electricity generation. (1) This manuscript discusses an analysis conducted on the effect of H.R. 2454 on Texas’s electricity generation mix. In order to benchmark the net opportunity for energy efficiency, this analysis includes the historical trends in electricity consumption by sector and per capita for two states, Texas and California. This manuscript contains discussion on findings in two key areas. First, the overall consumption patterns seen historically in Texas compared to California including key differences found in each sector: residential, industrial and commercial/other. Second, the factors that contributed to these patterns including policy mechanisms, technological advances, and shifts in industry that contributed to these patterns. These findings are then applied to electricity consumption and generation mix projections in Texas. Evaluating these projections reveals the potential environmental impacts of H.R. 2454 on Texas.
Tool for Small Office Buildings Energy Consumption Estimation
Authors: Fumo N. , Mago P. J.
Published: January 2011

Building energy consumption analysis is a difficult task because it depends on the characteristics and interaction among the building, the heating/cooling system, and the surroundings (weather). Since building energy profiles are usually required on an hourly basis, which often is not available for existing buildings, the hourly energy consumption must be estimated or predicted. The dynamic behavior of the weather conditions and building operation makes computer simulations a good practice for reliable solutions. However, energy building computer simulations require considerable amount of detailed input data and user time, which is a drawback for a cost-effective solution. Therefore, simplified models based on statistics or a combination of statistics and simulations may be a better solution with reasonable uncertainty. This paper presents the tool Small Office Hourly Energy Consumption Estimator (SOHECE). The tool estimates hourly building energy consumption for small office buildings. The proposed tool has been developed in Microsoft Excel and it uses simulation data from EnergyPlus benchmark models to convert monthly energy consumption from utility bills into hourly energy consumption. Since benchmark models were developed by the U.S. government to provide a consistent baseline of comparison, energy consumption data from simulations of the benchmark models are considered reasonable representations of energy consumption profiles. Results account for baseline and variable energy consumption for electricity and fuel. The site weather conditions, for which the energy consumption is estimated, are considered using the sixteen climate zones of the U.S. benchmark models. The tool has been applied to a hypothetical building placed in Meridian, MS, and errors obtained for the estimated hourly energy consumption are mainly lower than ten percent.
Second-Law Analysis in a Steam Power Plant for Minimization of Avoidable Exergy Destruction
Authors: Ray Tapan K. , Ekbote Pankaj , Ganguly Ranjan , Gupta Amitava
Published: January 2011

Performance analysis of a 500 MWe steam turbine cycle is performed combining the thermodynamic first and second-law constraints to identify the potential avenues for significant enhancement in efficiency. The efficiency of certain plant components, e.g. condenser, feed water heaters etc., is not readily defined in the gamut of the first law, since their output do not involve any thermodynamic work. Performance criteria for such components are defined in a way which can easily be translated to the overall influence of the cycle input and output, and can be used to assess performances under different operating conditions. A performance calculation software has been developed that computes the energy and exergy flows using thermodynamic property values with the real time operation parameters at the terminal points of each system/equipment and evaluates the relevant rational performance parameters for them. Exergy-based analysis of the turbine cycle under different strategic conditions with different degrees of superheat and reheat sprays exhibit the extent of performance deterioration of the major equipment and its impact to the overall cycle efficiency. For example, during a unit operation with attemperation flow, a traditional energy analysis alone would wrongly indicate an improved thermal performance of HP heater 5, since the feed water temperature rise across it increases. However, the actual performance degradation is reflected as an exergy analysis indicates an increased exergy destruction within the HP heater 5 under reheat spray. These results corroborate to the deterioration of overall cycle efficiency and rightly assist operational optimization. The exergy-based analysis is found to offer a more direct tool for evaluating the commercial implication of the off-design operation of an individual component of a turbine cycle. The exergy destruction is also translated in terms of its environmental impact, since the irretrievable loss of useful work eventually leads to thermal pollution. The technique can be effectively used by practicing engineers in order to improve efficiency by reducing the avoidable exergy destruction, directly assisting the saving of energy resources and decreasing environmental pollution.
Opportunities for CO2 Capture and Storage in Iranian Electricity Generation
Authors: Zabihian Farshid , Fung Alan S.
Published: January 2011

CO2 capture and storage (CCS) systems are technologies that can be used to reduce CO2 emissions by different industries where combustion is part of the process. A major problem of CCS system utilization in electricity generation industry is their high efficiency penalty in power plants. For different types of power plants fueled by oil, natural gas and coal, there are three main techniques that can be applied: • CO2 capture after combustion (post-combustion); • CO2 capture after concentration of flue gas by using pure oxygen in boilers and furnaces (oxy-fuel power plant); • CO2 capture before combustion (pre-combustion). More than 90% of electricity generation in Iran is based on fossil fuel power plants. Worldwide, electricity generation is responsible for 54% of GHG emissions. Thus, it is vital to reduce CO2 emission in fossil fuel-fired power plants. In this paper, it is shown that, by applying CO2 capture systems in power generation industry, very low CO2 emission intensity is possible but the energy and economic penalties are substantial. The analyses showed that for different technologies efficiency penalty could be as high as 25% and cost of electricity might increase by more than 65%. Two scenarios for Iranian electricity generation sector were investigated in this paper: installing CCS in the existing power plants with current technologies and replacing existing power plants by natural gas combined cycle plants equipped with CO2 capture system. The results revealed that the GHG intensity can be reduced from 610 to 79 gCO2eq/kWh in the first scenario and to 54 gCO2eq/kWh in the second scenario.
Performance of Biogas Fueled Hybrid Solid Oxide Fuel Cell (SOFC) and Gas Turbine Cycle
Authors: Zabihian Farshid , Fung Alan S. , Koksal Murat
Published: January 2011

The macro level model of a solid oxide fuel cell (SOFC) system was developed considering fundamental equations of thermodynamics, chemical reactions, and electrochemistry. The SOFC model was implemented in a hybrid SOFC-gas turbine (GT) cycle model using Aspen Plus® to simulate two configurations, system with and without anode recirculation. In order to monitor the performance of the system, parameters such as SOFC and system thermal efficiency; SOFC, GT, and cycle net and specific work; as well as air to fuel ratio, and air and fuel mass flow rate were investigated. The results of simulation for different types of fuel, namely, pure methane, natural gas, coal syngas, different types of biomass syngas, and farm and sewage biogas showed that system output and operation parameters were greatly influenced by changes in the fuel composition. Therefore, in feasibility study of a SOFC-GT hybrid cycle fueled by biogas, gasified biomass, and syngas, it is vital that possibility of variation of inlet fuel composition and its impacts on system performance to be considered and investigated.
A Method to Estimate Real-Time Energy Performance and Carbon Offsets in Residential Buildings
Authors: Escobar Sergio , Gonza´lez Jorge E. , Wong Adam , Aschheim Mark
Published: January 2011

A method is presented to determine energy performance of residential buildings. The method is based on an extended application of the degree-days basis to determine building thermal performance. The overall heat transfer coefficient and radiation shading factors are extracted from nightime and daytime readings of indoor and outdoor temperatures, solar radiation, and total energy usage of the building. It is shown that the overall heat transfer coefficient (thermal response) UA of the building is linear. Radiation shading factors can be represented as nonlinear functions of time. Application of the method to estimate real-time energy performance and carbon offsets of high performance buildings is discussed. The performance of the building is compared with an equivalent building with standard physical and thermal characteristics.
A Resource-Limited Approach to Estimating Algal Biomass Production With Geographical Fidelity
Authors: Wogan David M. , Webber Michael , da Silva Alexandre K.
Published: January 2011

This paper discusses the potential for algal biofuel production under resource-limited conditions in Texas. Algal biomass and lipid production quantities are estimated using a fully integrated biological and engineering model that incorporates primary resources required for growth, such as carbon dioxide, sunlight and water. The biomass and lipid production are estimated at the county resolution in Texas, which accounts for geographic variation in primary resources from the Eastern half of the state, which has moderate solar resources and abundant water resources, to the Western half of the state, which has abundant solar resources and moderate water resources. Two resource-limited scenarios are analyzed in this paper: the variation in algal biomass production as a function of carbon dioxide concentration and as a function of water availability. The initial carbon dioxide concentration, ranging from low concentrations in ambient air to higher concentrations found in power plant flue gas streams, affects the growth rate and production of algal biomass. The model compares biomass production using carbon dioxide available from flue gas or refinery activities, which are present only in a limited number of counties, with ambient concentrations found in the atmosphere. Biomass production is also estimated first for counties containing terrestrial sources of water such as wastewater and/or saline aquifers, and compared with those with additional water available from the Gulf of Mexico. The results of these analyses are presented on a series of maps depicting algal biomass and lipid production in gallons per year under each of the resource-limited scenarios. Based on the analysis, between 13.9 and 154.1 thousand tons of algal biomass and 1.0 and 11.1 million gallons of lipids can be produced annually.
Cogeneration System Modeling Based on Experimental Results
Authors: Marion Flore , Betz Fred , Archer David
Published: January 2011

A 25 kWe cogeneration system has been installed by the School of Architecture of Carnegie Mellon University that provides steam and hot water to its Intelligent Workplace, the IW. This cogeneration system comprises a biodiesel fueled engine generator, a steam generator that operates on its exhaust, a hot water heat exchanger that operates on its engine coolant, and a steam driven absorption chiller. The steam and hot water are thus used for cooling, heating, and ventilation air dehumidification in the IW. This cogeneration system is a primary component of an overall energy supply system that halves the consumption of primary energy required to operate the IW. This cogeneration system was completed in September 2007, and extensive tests have been carried out on its performance over a broad range of power and heat outputs with Diesel and biodiesel fuels. In parallel, a detailed systems performance model of the engine generator, its heat recovery exchangers, the steam driven absorption chiller, a ventilation and air dehumidification unit, and multiple fan coil cooling/heating units has been programmed making use of TRNSYS to evaluate the utilization of the heat from the unit in the IW. In this model the distribution of heat from the engine to the exhaust, to the coolant, and directly to the surroundings has been based on an ASHRAE model. While a computational model was created, its complexity made calculation of annual performance excessively time consuming and a simplified model based on experimental data was created. The testing of the cogeneration system at 6, 12, 18 and 25 kWe is now completed and a wealth of data on flow rates, temperatures, pressures throughout the system were collected. These data have been organized in look up tables to create a simplified empirical TRNSYS component for the cogeneration system in order to allow representative evaluation of annual performance of the system for three different mode of operation. Using the look up table, a simple TRNSYS module for the cogeneration system was developed that equates fuel flow to electricity generation, hot water generation via the coolant heat exchanger, and steam production via the steam generator. The different modes of operation for this cogeneration system can be design load: 25 kWe, following the thermal — heating or cooling — load, following the ventilation regeneration load. The calculated annual efficiency for the different mode is respectively 66% 68% and 65%. This cogeneration installation was sized to provide guidance on future cogeneration plant design for small commercial buildings. The new cogeneration TRNSYS component has been created to be applicable in the design of various buildings where a similar cogeneration system could be implemented. It will assist in selection of equipment and of operating conditions to realize an efficient and economic cogeneration system.
Evaluating the Cost of Food in a Carbon Constrained Economy
Authors: Twomey Kelly M. , Webber Michael E.
Published: January 2011

Although consensus has not been reached regarding the most efficient mechanism to curb anthropogenic greenhouse gas emissions, rising concern over the consequences of global climate change and consequent shifts in public and political sentiment suggest that carbon legislation will be instituted in the US in the near future. The recent climate change bill passed in the House of Representatives titled The American Clean Energy and Security Act of 2009 (HR 2454) includes provisions for a cap-and-trade system intended to reduce the nation’s greenhouse gas emissions 83% by 2050. Consequently, it is likely that some means of carbon pricing will take effect that will make it more expensive to emit greenhouse gases. In a carbon constrained economy, it will become increasingly important to consider every stage of food production and consumption in order to evaluate the potential opportunities for emission reductions. This analysis uses Life-Cycle Assessment to estimate the social cost of food production by quantifying the associated negative externalities under a range of potential carbon prices, using meat and grain as examples. It concludes that 0.42 and 16.0 kg of lifecycle CO2e are embedded in 1 kg of grain and beef production, respectively. Consequently, the marginal cost associated with the emissions caused by grain production under a carbon price range of $10 and $85 per t CO2e is estimated to be between $.004 and $0.036 per kg of grain. By comparison, the estimated marginal cost associated with beef production over the same range of carbon pricing is $0.16 and $1.36 per kg of beef. Considering that the US produces 12 billion kg of beef per year, this range indicates that the carbon cost of beef production alone might fall anywhere between $1.9 and $16.3 billion per year, depending on whether and how a carbon price is applied. This uncertainty and potential carbon price could significantly impact the cost of carbon-intensive foods.
Thermo-Economic Analysis of Microalgae Co-Firing Process for Fossil Fuel-Fired Power Plants
Authors: Ma Jian , Hemmers Oliver
Published: January 2011

A thermoeconomic analysis of microalgae co-firing process for fossil fuel-fired power plants is studied. A process with closed photobioreactor and artificial illumination is evaluated for microalgae cultivation, due to its simplicity with less influence from climate variations. The results from this process would contribute to further estimation of process performance and investment. The concept of co-firing (coal-microalgae or natural gas-microalgae) includes the utilization of CO2 from power plant for microalgal biomass culture and oxy-combustion of using oxygen generated by biomass to enhance the combustion efficiency. As it reduces CO2 emission by recycling it and uses less fossil fuel, there are concomitant benefits of reduced GHG emissions. The by-products (oxygen) of microalgal biomass can be mixed with air or recycled flue gas prior to combustion, which will have the benefits of lower nitrogen oxide concentration in flue gas, higher efficiency of combustion, and not too high temperature (avoided by available construction materials) resulting from coal combustion in pure oxygen. Two case studies show that there are average savings about $0.386 million/MW/yr and $0.323 million/MW/yr for coal-fired and natural gas-fired power plants, respectively. These costs saving are economically attractive and demonstrate the promise of microalgae technology for reducing greenhouse gas (GHG) emission.
Heat Flow Control and Energy Recovery Using CO2 in Double Glass Arrangements
Authors: Zevenhoven Ron , Fa¨lt Martin
Published: January 2011

The interaction of gases such as carbon dioxide (CO2) and other so-called participating gases with thermal infra-red (TIR) radiation is one of the mechanisms behind global warming and climate change. The noticeable effect this apparently gives at atmospheric concentrations of around 400 ppmv can be made use of in technical systems where pure (and pressurized) CO2 is confined in, for example, a double glass arrangement. Depending on pressure, temperature, gas composition and path length a certain “optical thickness” for TIR radiation is obtained that can be used to decrease or increase heat flows, or create temperature differences. The latter would allow for power production using, for example, a Stirling engine. Of great importance also is the temperature difference between ground-level surroundings and the sky. With significant amounts of electric power being used for air-conditioning, heating or cooling purposes a smart window set-up that makes use of the interference of TIR radiation with participating gases may result in significant reductions in energy use and costs. Typical applications can be found in residential and office building windows or a glass roof that covers large building structures like railway stations or parking areas. Besides glass, plastics may be used as window material. The purpose of this paper is to present the potential of energy recovery from TIR radiation using most importantly earth-to-space radiation of long wavelengths (> 4 μm), to be distinguished from incoming solar radiation at shorter wavelengths (< 4 μm). Most relevant here is the TIR absorption band for CO2 around a wavelength of 15 μm. Note also that unlike solar irradiation the earth-to-space radiation is not limited to daytime and cloudless skies. Finally, some examples for technical system lay-out and performance are given. This gives an introduction by the paper by Fa¨lt and Zevenhoven submitted to this conference (Fa¨lt and Zevenhoven, 2010).
Co-Design of Energy-Efficient Housing With the Pinoleville-Pomo Nation
Authors: Schultz Tobias C. , Shelby Ryan L. , Agogino Alice M.
Published: January 2011

The Pinoleville-Pomo Nation of northern California is seeking to implement sustainable technologies and best practices that will increase their self sufficiency and meet their housing, energy, and water conservation needs. Since 2008, the Tribe has worked with UC Berkeley on sustainable community projects, including the design of a prototype “roundhouse” design, to be constructed in 2010 in Ukiah, California. Using an energy-efficient architecture and an analysis tool for selection of the engineered systems (the Native American Energy Analysis Tool, or NAEPA), the new homes are predicted to emit less than 50% of the carbon emissions over their lifetime, and have lower lifetime energy expenditures. The design methodology, energy analyses and life cycle assessment used by NAEPA will be discussed. Extensions to community-based housing energy plans and an optimization will also be discussed.