bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas Turbine Inlet Air Fogging Systems: Application of Psychrometric Principles to Study Cooling and Humidification Processes
Authors: Mahapatra Sanjay , Gilstrap Jeffrey K.
Published: December 2008

Gas turbine inlet air-cooling utilizing a high pressure fogging system is theoretically based on the thermodynamic principle of adiabatic saturation. The dry bulb temperature of inlet air decreases by losing its sensible heat to the liquid water droplets generated by the fogging system. This sensible heat is enough to provide the latent heat necessary to evaporate and diffuse these droplets into the surrounding air stream. As a result of this heat interchange accomplished through a complex mechanism of heat transfer and fluid dynamics, the temperature and moisture content of inlet air is decreased & increased respectively resulting in an increase in its density. Neglecting the enthalpy of liquid water, which is insignificant compared to the water’s latent heat of vaporization, the total heat, i.e. enthalpy of the air stream remains unchanged. The net heat exchange outside of this control volume is zero because the droplets, which subsequently diffuse into the air stream, gain the sensible heat lost by inlet air. Therefore, the theoretical concept of adiabatic saturation is valid in this case. However, in real systems, the cooling and humidification process is seldom adiabatic. This paper applies psychrometric principles in conducting a detailed mathematical analysis of various cooling and humidification processes accomplished by fogging systems. The measurement of actual moisture content of air upstream and downstream of a fogging system is vital to gas turbine inlet air-cooling. The moisture content of air and its dry bulb temperature can provide accurate information on the system path and how well it approximates the adiabatic saturation process and determining system efficiency. The deviation from the adiabatic saturation process is attributed to several factors, such as external heat gain or loss, water temperature, etc. The measurement of moisture content can enable the fogging system control logic to control the required water flow rate through the system to obtain maximum performance without over spraying excessive water or under cooling inlet air. This paper presents possible scenarios of deviation from an adiabatic process and methods to determine fogging system total effectiveness.
Power Systems Development Facility: Demonstration of the Transport Reactor for Use in Advanced Integrated Combined Cycle Power Plants
Authors: Powell Charles A. , Vimalchand P. , Guan Xiaofeng , Wheeldon John M. , Smith Peter V. , Longanbach James R.
Published: December 2008

The Power Systems Development Facility (PSDF) is an engineering scale demonstration of advanced coal-fired power systems and high-temperature, high-pressure gas filtration systems that would be integral to an improved coal-fired power plant having efficiencies well over 40%, while exceeding all current emission standards for coal-fueled plants. The paper will describe such a plant before expanding the discussion on the operational experiences of the Kellogg Brown & Root, Inc. (KBR) Transport Reactor and the Siemens Westinghouse Power Corporation (SWPC) high-temperature gas filter system currently being demonstrated at the PSDF. A short survey of the process advantages (capital, operational, efficiency, and reliability) over current Integrated Gasification Combined Cycle (IGCC) plant designs, including hot gas clean-up, air-blown gasification, non-slagging gasifier operation and equipment commonality with existing pulverized coal power plants, will be highlighted; as will the potential of the power plant to be retrofitted in response to future carbon capture requirements.
Application of Rough Set Theory to Data Mining of Condenser Diagnosis in Power Plants
Authors: Fu Zhongguang , Jin Tao , Yang Kun
Published: December 2008

Rough set theory is a powerful tool in deal with vagueness and uncertainty. It is particularly suitable to discover hidden and potentially useful knowledge in data and can be used to reduce features and extract rules. This paper introduces the basic concepts and fundamental elements of the rough set theory. A reduction algorithm that integrates a priori with significance is proposed to illustrate how the rough set theory could be used to extract fault features of the condenser in a power plant. Two testing examples are then presented to demonstrate the effectiveness of the theory in fault diagnosis.
On the Aerodynamics of Wind Turbine
Authors: Liu Rui , Ting David S.-K.
Published: December 2008

The history and background of modern wind turbine technology were reviewed. The most widely used wind turbine airfoil shapes were presented. The previous studies on rotor-wind interaction emphasizing on the velocity deficit of the wake region of the wind turbine, the aerodynamics and structural dynamics of wind turbine airfoil were presented and followed with proposed direction on future study.
Advanced Aerodynamic Sealing System for Thermo Turbo Machinery
Authors: Uth Karl E. , Dong Edward G.
Published: December 2008

This paper presents the feasibility of using advanced aerodynamic sealing systems to replace aged labyrinth seals in gas & steam turbines for the electric power generating and aerospace industry. Focus is on promoting new technologies in the power generating industry to reduce pollutant emissions.
Design Intricacies of Fire Tube Heat Recovery Boiler for Large Utility IGCC Power Plants
Authors: Rao J. S. , Neelima J. , Srikanth G.
Published: December 2008

In the IGCC system, HRB is one of the critical equipments which need further development. The design of HRB was not very successful in the early stages of IGCC development using entrained bed gasification process. The first IGCC Plant of 100MWe Cool Water Plant located in California adopted Texaco Gasification Process having radiant boiler followed by convection boiler. In view of the failure of radiant section this plant was operated in quench mode resulting in a lower overall efficiency. The syngas cooler is very prone to operation failure because of slagging due to the high temperature dirty gas service. Hence a need araised to develop the appropriate HRB taking into account dusty coal gas environment. Later designs of Texaco, Shell process and Noell have improved the HRB design by correcting the flow path geometry thus avoiding the ash deposits at the raw gas inlet. The paper highlights the intricacies in the design of HRB with a program developed to optimise the same for use in large utility IGCC plants. A novel approach for improving the gas side heat transfer coefficient while handling hot particulate laden raw gases in HRB of pressurised fluidised bed gasifier is presented and the results validated from available experimental plant.
Developing Turbulence on the Propagation of Flames in Methane-Air Premixture
Authors: Haq M. Z.
Published: December 2008

In spark ignition engines, initial flame kernel is wrinkled by a progressively increasing bandwidth of turbulence length scales until eventually the size of the flame kernel is sufficient for it to experience the entire turbulence spectrum. In the present study, an effective r.m.s. turbulence velocity as a function of time, estimated by integrating the non-dimensional power spectrum density function for isotropic turbulence, is utilized in the analysis of the statistical distribution of flame front curvatures and turbulent burning velocities of flames propagating in methane-air premixtures. The distribution of flame front curvatures shows these to become more dispersed as the effective turbulence velocity increases, and results in increased burning of premixtures. A decrease in the Markstein number also results in a further increase in curvature dispersion and enhanced burning, in line with the flame stability analysis.
A Stage Efficiency Prediction Method and Related Performance Aspects of Retrofits on Disc/Diaphragm Steam Turbines
Authors: Hesketh Alan , Hogg Simon , Stephen Don
Published: December 2008

A general and well established ‘loss-debit’ method of stage-efficiency prediction, based on detailed physical blade-path modelling is described and reviewed in this paper. The continuous evolution of this process within the authors company with R&D support is also described. In particular, and through recent years, the method has been applied in Retrofit Projects, where ‘hardware is changed to improve turbine performance’. Initial retrofit applications have been on our Company’s own machines where we are the OEM (Original Equipment Manufacturer). Later this involved ‘upgrading’ part of non-OEM turbines, where dimensional and operational restraints have to be properly accommodated and the consequences on design have to be correctly accounted-for in performance prediction. The accuracy of the method is also examined with respect to application to individual component replacements, such as a specific turbine cylinder in a multi-cylinder steam turbine. It is here that ‘section’ efficiency may have more direct relevance than, say, overall heat rate and the method needs to be more discerning in this respect. Efficiency trends from possible design variants need to be accurately predicted in ‘optimisation studies’ that lead to the final ‘bespoke’ design giving the best techno-economic solution. Accurate trend prediction is, therefore, vital for the success of the method. Verification testing of the ‘performance improvement’ actually achieved in a Retrofit, by a ‘new’ component installed in an otherwise ‘old’ machine, has many special aspects and these are also reviewed in the paper.
Possibilities of Formaldehyde Removal by Discharge Plasma
Authors: Hensel Karol , Pawlat Joanna , Takashima Kazunori , Mizuno Akira
Published: December 2008

Removal of formaldehyde by streamer corona discharge was studied experimentally. It was shown the removal efficiency as well as the by-products of the chemical process in the non-thermal plasma of the discharge depend on the initial concentration, gas flow rate, carrier gas, discharge polarity and discharge mode. A combined effect of plasma and catalytic pellets of various materials placed in the discharge reactor was investigated too.
Recent New Combined Cycle and Gas Turbine Plant Acceptance Test Experience
Authors: McClintock Michael , Gwin Eric C. , Grace Harold P. , Burcham Ira R.
Published: December 2008

In the past year, Constellation Power Source Generation (CPSG) has commissioned (or is commissioning) four new combined cycle and simple cycle gas turbine plants. Each of these plants involved different equipment, vendors and architect engineers. Acceptance testing was done for these plants in accordance with ASME PTCs 46 and 22 with support from Fossil Consulting Services, Inc. (FCS). The Performance Test Codes provided the framework for the testing done, but considerable work was required to apply the codes in accordance with relevant contracts. Problems in acceptance testing can result in costly delay and retesting. This paper describes the lessons learned in resolving issues and problems that can help others in planning for and executing similar tests. These lessons learned can also help in writing effective contracts between owners, vendors and architect engineers.
Development of a Thermal Approach to Optimize the Waste Heat Utilisation From an Existing Gas Turbine Station Without Heat Recovery System
Authors: Ngoma Guyh Dituba , Sadiki Amsini
Published: December 2008

The present work deals with a numerical simulation of a flow in finned tube banks arranged behind a gas turbine. Three models of dual-pressure tube systems are developed and analyzed in order to predict the static system performances by optimizing the utilization of the exhaust gas from an existing gas turbine without heat recovery system. For more precise modeling, the theoretical analysis of finned tube banks systems is based on the non-linear conservation equations of mass, momentum and energy. Simulations are accomplished to prove the effectiveness of the present work in performance prediction of the dual-pressure tube systems. The obtained results clearly show the necessity to take into account all relevant physical phenomena in the simulation of flows in and across finned tube banks installed behind a gas turbine. The results also reveal the different operating behavior of the developed models considering combined effects of the exhaust gas parameters and the tube geometries.
Multi-Criteria Optimization of Pulverized Fuel Coal-Fired Power Generation System Load Dispatching
Authors: Li Hongtao , Burer Meinrad , Marechal Franc¸ois , Favrat Daniel , Hou Guolian , Zhang Bao-Heng , Song Zhi-Ping
Published: December 2008

With a given power demand pattern supplied by a set of pulverized fuel coal-fired (PC) power generation units at various locations, different power dispatching solutions will result in different fuel consumptions, CO2 emissions, and power generation costs. This is due to the performance differences of their shut-down and start-up processes as well as those under the operational conditions, and to fuel prices differences between different power stations. In this paper, a methodology characterized with a multi-objective optimization approach based on a fast evolutionary algorithm is employed to optimize the daily total power generation operating cost and the daily total CO2 emissions. The shut down and start-up processes are divided into 7 sub-operations: load-decreasing, shutdown, boiler ignition preparation, ignition-warming up, connecting to grid, load-increasing and stabilization process, according to their characteristics in order to calculate the fuel consumptions, the CO2 emissions and the cost. Available data have been used to derive the models that characterize the emission and cost performances of typical PC units as well as their rating and partial load performances [1]. From the results of the multi-objective optimization, the so called Pareto Optimal Frontiers (POFs) are used to evaluate the effect of CO2 tax on the optimal power dispatching solutions. The influence of SO2 tax on the CO2 abatement marginal cost is also analyzed.
Control of Rotating Stall in the Diffuser of a Low Speed Centrifugal Compressor
Authors: Ahmed Saad A. , Gadalla Mohamed A.
Published: December 2008

An experimental investigation to delay the onset of the rotating stall in the radial diffuser of a centrifugal blower was carried out. The method involved reducing the flow area by 50% at the diffuser exit using throttle rings attached to either diffuser shroud wall, or the diffuser hub wall. Simultaneous attachments of the throttle rings to both the diffuser’s shroud and the hub walls were also made. The following blockage ratios were used: 25% from both walls, 50% from the diffuser shroud and 0% from the diffuser hub and vice versa. The preliminary results suggest that the onset of the flow instability in the diffuser (stall) could be delayed (i.e., lower flow coefficient) when throttle rings were attached to the diffuser walls to reduce its exit flow area. The results also confirmed that the throttle rings could be an effective method to control/delay the stall in the vaneless radial diffuser.
Flexible Heat-to-Power Ratio Co-Generation System With Ammonia-Water Mixture Cycles at Bottoming
Authors: Takeshita Keisuke , Amano Yoshiharu , Hashizume Takumi , Usui Akira , Tanzawa Yoshiaki
Published: December 2008

This paper presents the experimental study of a unique cogeneration system which the authors call the “Advanced Co-Generation System (ACGS)”. It mainly consists of three turbine systems and an ammonia absorption refrigerator (AAR). The specialty of the ACGS is the bottoming stage employing an ammonia-water mixture (AWM) as the working fluid. First, the overall system configuration and some experimental results at the steady state are shown. The experimental investigation shows that the AWM bottoming cycles contribute to a higher efficiency of the system. An increase of 5–10% in electric power compared to a conventional co-generation system (CGS) is confirmed. Next, a hybrid configuration of the AWM turbine (AWMT) cycle and the AAR is investigated. A simulation model is constructed. The results of the simulation show that the hybrid configuration performs at about 14% higher efficiency.
Test and Operation of a PEM Fuel Cell Power System
Authors: Chen F. C. , Fiskum R. J.
Published: December 2008

The fuel cell power system is an emerging energy technology. It promises high energy conversion efficiency and cleaner emissions than many of the available power conversion technologies. It is amenable to co-generation that would result in even better total energy utilization. This paper describes the initial testing and operating experience of a 5-kWe natural gas-powered PEM fuel cell technology development unit with waste heat recovery for grid-parallel residential applications.
Hot Gas Filtration in Co-Generation Power Plants
Authors: Al-Hajeri M. H. , Al-Ajmi M. R.
Published: December 2008

This paper reports a computational study using CFD on a hot gas filter in cross flow arrangement. The filter generally operates with the dirty gases passing through the filter elements, the particulate material being deposited on the outside of the filter. However, in power co-generation plants, hot gas filtration is needed to allow the hot exhaust gases to be fed to a turbine without causing any physical damage to the blades. The aim of this work is to increase understanding of the deposition process and the factors that affect the build up of the filter cake. A parametric investigation is undertaken with particular emphasis on the effects of the ratio of the approach cross flow velocity to filter face velocity on the deposition pattern as a function of the particle size (1 to 100 microns). Velocity fields and particle tracks are presented, in addition to the radius of convergence which is a parameter that characterizes the deposition process for each flow regime.
Fluid Particles Straightly Forward and Circularly Forward Movements in the Direction of Tangent at Trailing Edge of Impeller Outlet in Centrifugal Turbomachinery
Authors: Tanaka Takaharu
Published: December 2008

Flow rate, which is caused in the direction radial outward in pump and radial inward in water turbine, is caused by the fluid particles straightly forward tangential movement in the direction of acting force perpendicular to impeller blades rotational radius. Impeller blades rotational motion is caused under the radial balance of centrifugal and centripetal forces. Centrifugal force is caused by the transferred energy from mechanical to hydraulic energy in pump and from hydraulic to mechanical energy in water turbine. Centripetal force is equivalent to discharge head in pump and equivalent to suction head in water turbine.
Large Outdoor Fire Model Analysis
Authors: Vidmar Peter , Petelin Stojan
Published: December 2008

The idea behind the article is how to define fire behavior. The work is based on an analytical study of fire origin, its development and spread. Mathematical fire model called FDS (Fire Dynamic Simulator) in used in a presented work. CFD (Computational Fluid Dynamic) model using LES (Large Eddie Simulation) is used to calculate fire development and spread of combustion products in the environment. The fire source is located in the vicinity of the hazardous plant, power, chemical etc. The article present the brief background of the FDS computer program and the initial and boundary conditions used in the mathematical model. Results discuss output data and check the validity of results. The work also presents some corrections of physical model used, which influence the quality of results.
Improved Plant Performance and Reduced CO2 Emission Through State-of-the-Art Condenser Cleaning and Air In-Leakage Detection
Authors: Saxon G. E. , Putman R. E.
Published: December 2008

Efficient condenser operation is critical to minimizing the operating costs and improving the performance of a turbogenerator unit or power plant. Efficient condenser performance is recognized by an improvement in heat rate and generation capacity, less fuel is consumed and a significant reduction in CO2 emissions can be achieved. Condenser tube fouling, fouled external surfaces of Air-Cooled Condensers (ACC) and condenser air-inleakage have been found to have a significant impact on condenser performance and subsequently plant performance. State-of-the-Art technologies have been developed to effectively remove fouling and deposits from condenser tubes, finned external surfaces of ACC’s and to identify the location of air and water in-leakage into the condenser, providing a longer useful life cycle. In addition, application of these technologies results in improved condenser backpressure, a decrease in plant heat rate and a decrease in yearly fuel consumption. Overall, plant performance is improved and CO2 emissions are reduced. Technology and cases are presented.
Case Studies of Distributed Generation Projects With Microturbines in Brazil
Authors: Batista Gomes Eli Eber , Rosa do Nascimento Marco Antoˆnio , Silva Lora Electo Eduardo
Published: December 2008

Microturbines have showed good perspectives for the distributed generation of the electricity in low capacity range, because they have high reliability and simple design (high potential for a cheap manufacture and in large scale). Besides, this technology must have a great application in systems of cogeneration of the public service (malls, hotel, hospital, etc.) and in the distributed generation of the electricity in the developing countries in order to get a reliable operation system, in a range of power compatible with the isolated communities. In Brazil, The Thermal Systems Study Group (NEST) of Federal University of Itajuba´ (UNIFEI) sponsored by The Energy Company of Minas Gerais (CEMIG), are developing a project of experimental valuation of the system with microturbines for electricity generation fueled with natural gas and diesel. The objective of this paper is to show an economic evaluation which presents the generation costs and the payback period with the Capstone 30 kW natural gas microturbines business in three cases: microturbines operating on base load in gas station, microturbines operating on peak shave in the industry and a microturbine cogeneration system operating in the residential segment. It was considered the cost of microturbines at this moment and the projection for the future, as well as the cost of electricity and natural gas in Brazil. An economical analysis was carried out for different variables involved and the results show the Capstone 30 kW natural gas microturbines business are feasible firstly in cogeneration cases which is possible to get until 3 years of payback period. Besides, the return on the investment have shown improvements with the incentive of the natural gas distributing companies and with the rises in the electricity price of Brazilian utilities.
A CFD Model Based Evaluation of Cost Effective NOx Reduction Strategies in a Roof-Fired Unit
Authors: Valentine James , Cremer Marc , Davis Kevin , Letcavits J. J. , Vierstra Scott
Published: December 2008

To meet aggressive NOx reduction requirements, a range of NOx reduction strategies are currently available for application to pulverized coal fired furnaces. Utilities must assess the benefits and drawbacks of each viable NOx control technology to develop the best strategy for unit specific NOx control that fits within the utilities’ overall compliance plan. The installation of high capital and operating cost NOx reduction technologies, such as selective catalytic reduction, is cost prohibitive on many units. Lower cost technologies, although not capable of SCR level NOx reductions, can provide a more cost-effective approach and still achieve compliance over the fleet. This paper describes how computational fluid dynamic (CFD) modeling has been utilized by an experienced group of combustion engineers to evaluate and design cost effective NOx reduction strategies applied to a relatively unique PC fired unit, a B&W 150 MW roof-fired furnace. The unit fires bituminous coal through 10 multi-tip burners and is equipped with 10 NOx ports located below the burners. A baseline CFD model was first constructed and the predicted model results were compared with available data including NOx and CO emissions, as well as unburned carbon in fly ash. Upon completion of the baseline model, combustion alterations, including deeper staging, were evaluated. Specific burner adjustments were evaluated to allow for the deeper staging without significantly increasing unburned carbon in the fly ash, CO emissions, or near burner slagging. The CFD model was also utilized to evaluate the impact of water injection. AEP has previously utilized water injection to reduce peak combustion temperatures and thermal NOx formation rates in coal fired units for incremental NOx reductions. It is crucial that the NOx production zones in the downstream portion combustion field be identified, since these regions are most likely to produce NOx that will not be subsequently reduced prior to exiting the furnace. The CFD model was utilized to identify the most appropriate regions for water injection combined with the other combustion alterations. The results showed that NOx emissions could be reduced in this unit by approximately 37% from baseline full load emissions with no associated increase in unburned carbon in the fly ash or furnace exit CO. Burner alterations and water injection equipment based on the CFD model evaluation are currently being installed. Comparisons between the model predictions and the post retrofit performance will be provided.
Influence of Variations in the Natural Gas Properties on the Combustion Process in Terms of Emissions and Pulsations for a Heavy-Duty Gas Turbine
Authors: Nord Lars O. , Andersen Helmer G.
Published: December 2008

The natural gas supply can vary significantly on a day-to-day or even hour-to-hour basis for a power plant equipped with gas turbines. The influence of such variations could potentially have an adverse effect on the combustion process in terms of emissions and acoustic pulsations, even if the fuel properties are within the original equipment manufacturer (OEM) guidelines. Since the operation of a gas turbine typically requires steady emissions within the air permit as well as low pulsations to limit mechanical damage on the unit, fuel variations could significantly affect how the unit can be operated. To investigate this matter, data from an ALSTOM GT11N1 gas turbine was collected and studied during a 6-month period. The data acquired included on-line gas chromatograph readings, frequency-analyzed combustion instabilities, various process data, as well as ambient conditions. The collected data shows the magnitude of the changes in the emissions and combustion noise with changes in the fuel. The conclusion is that normal day-to-day variations in the natural gas properties do not have a significant effect on the emissions and combustion instabilities; however, larger sudden changes, as exemplified in the paper, could lead to considerable changes in the combustion behavior of the unit.
Repair of Rotor Journals
Authors: Moore William G. , Eder Ralph
Published: December 2008

Correct size, roundness, concentricity and surface finish of rotor journals are critical to the proper operation of a rotor. Some typical defects that occur in damaged rotor journals include pitting, presence of grooves, presence of hard areas, cracks from overheating, deposit of babbitt from the bearing and uneven wear. These imperfections can impair the proper lubrication of the journal, creating a higher probability of additional journal damage progressing and leading to failure, including a forced outage. In most cases, journals can be repaired by tooling, grinding, honing, and/or super-finishing to close tolerances for improving lubrication and restoring performance. The techniques for repairing rotor journals vary, depending on the size of the journal and the weight of the rotor. Large journals can, in most instances, be refurbished without rotor rotation, and therefore can be done right at site, or in the case of other repairs, at the repair facility. This and other repair techniques will be discussed in this paper. Readily achievable size tolerances and micro-finishes will be discussed, as well as limiting conditions. Photos and experiences from recent rotor journal repairs will be discussed. This paper will be valuable to plant personnel when evaluating the condition of their rotor journals and selecting methods of repair of damaged journals. A discussion of these options, expected improvement, and other issues will add value to the readers ability to make educated decisions regarding journal refurbishment.
Conversion of a GE 7FA From 60 Cycle to 50 Cycle Generation
Authors: Sutherland Andrew W. , Barnes Samuel R. , McCourtie William E.
Published: December 2008

This paper examines the conversion of a GE 7FA from generating 60 Cycle power to 50 Cycle power. The turbine is nominally rated for a 60-cycle ISO output of 175 MW. With the gas turbine boom of the late 1990s and then the cancellation of several GT based projects, a surplus of GTs has been created. Owners of these GTs have been reviewing alternative options for installation at another of their plants or resale of their GTs to another user. One potential solution is the conversion of a GT into a 50-cycle machine for installation in other markets around the world. If this type of conversion proves feasible, it also opens the door for the 60-cycle designed GTs to be marketed overseas to compete with original 50-cycle equipment. Three potential options for creating 50 Cycle power with a 7FA were identified: 1. Operate the Combustion Turbine Generator (CTG) at 3000 RPM to generate energy at 50 Hz. 2. Operate the CTG at 3600 RPM to generate energy at 60 Hz with the installation of an invertor, external to the CTG, to convert 60 Hz potential to 50 Hz. 3. Operate the turbine at 3600 RPM and the generator at 3000 RPM by installing a gearbox (speed reducer) between the turbine and the generator. These three options were researched and pricing was obtained on those that were considered feasible. The turbine OEM, GE, was also contacted to provide input on each of the scenarios. The results for each of the options are as follows.
Value Analysis of Building Energy Conservation Options
Authors: Kumpanon Arpakorn , Boehm Robert
Published: December 2008

The purpose of this work was to determine the possible optimal cost effectiveness of various energy conservation options for new buildings in the local climate. The building energy analysis code Energy-10 was used for this purpose. Three types of savings have been evaluated: energy savings, operating cost savings, and Life-Cycle Cost (LCC) savings. To complete this study, a parametric analysis was performed on the influence on LCC savings due to variations of various individual components (including window characteristics, wall, floor, and roof constructions) and the whole-composite buildings. The initial part of the study focused on examining the impacts of individual components within the capabilities of Energy-10. For example, the impacts of a single window size, orientation, and construction were analyzed. While doing this, all of the other heat loss/heat gain paths were made negligible. Results of this aspect of the work were used to define a shorter list of components and building construction options to evaluate in the following composite-house studies. Then two general categories for the whole-composite buildings were evaluated to assist in analyzing the potential cost-effectiveness and benefits of buildings’ energy conservation options. In these studies, various energy cost escalation rates, economic life times, and replacement costs were considered. Building orientations relative the areal placement of fenestrations were also evaluated. Conclusions are given about combinations of construction elements that make the most economic sense for this rapidly growing population area. While Las Vegas climatic data are considered in this work, the conclusions are more generally applicable in the desert Southwest portion of the US.
Thermal Analysis of a Concentrating Photovoltaic Receiver
Authors: Mahderekal Isaac , Boehm R. F.
Published: December 2008

This paper presents the theoretical and computational analysis for a photovoltaic (PV) receiver for the Science Applications International Corporation (SAIC) dish concentrator. During photovoltaic energy conversion, thermal energy is also generated which results in increases in cell temperature. However, as the cell temperature increases, the efficiency of the PV cells drops—a 40°C increase in temperature for this unit cuts performance by 25%. An algorithm has been developed to predict the maximum cell temperature and working fluid temperature as a function of channel size, mass flow rate, cooling configuration, fluid-to-tube heat transfer coefficient and other parameters. To evaluate the transient characteristics of the system, a dynamic model of the concentrating PV collector has been developed. The model describes the change in temperature of the cells and the coolant in the receiver as a function of time, taking into account the: solar insolation, change in energy content of the element, energy transfer by the fluid flow, and temperature dependent energy flow between the element and the surroundings. Five energy balance differential equations have been solved simultaneously to examine the transient nature of the system. Computational fluid dynamics flow modeling (CFD) software has also been utilized to compare the temperature distribution along the module with the analytical results. The flow model is built and applied mesh using the preprocessing tool, GAMBIT, and the CFD analysis has been done by using Fluent. The model quantifies temperature, velocity and pressure profiles of the module.
Numerical and Experimental Analysis of Convection Heat Transfer in a Lean-To Type Greenhouse
Authors: Chen Wei , Liu Wei
Published: December 2008

In this paper, heat transfer and flow in a lean-to passive solar greenhouse has been studied. A mathematical model based on energy equilibrium and a one-dimensional mathematical model for the unsaturated porous medium have been founded and developed to predict the temperature and moisture content in soil and the enclosed air temperature in the greenhouse. On the condition that plant and massive wall is neglected, the air is mainly heated by the soil surface in the greenhouse, which absorbs the incident solar radiation. With increase in depth, the variation of the temperature and moisture content in soil decreases on account of ambient, and the appearance of the peak temperature in soil postpones. Solar irradiation absorber, heat storage and insulation are the main effects of the north massive wall on greenhouse, which is influenced by the structure and the material. The specific heat capacity and thermal conductivity of wall material have a remarkable effect on the north wall temperature. The build-up north wall with thermal insulation material may be chosen for greenhouse. The temperature distribution and gas flow in greenhouse is influenced by the cover material of the inside surface of the north wall. All results should be taken into account for a better design and run of a greenhouse.
Simulation of Thermal and Chemical Processes in Annular Layer of ZnO-C Mixtures
Authors: Vishnevetsky Irina , Epstein Michael , Rubin Rahamim
Published: December 2008

A special setup, electrically heated, is described, enabling the simulation of the process conditions encountered in a solar chemical reactor. The setup allows studying of the thermal and chemical processes in different solid (powder or granules) reactant layers from the beginning of the heating until the reaction is completed, in heating condition typical for indirectly, externally heated solar reactors. Tests were executed with ZnO carboreduction process, using different powder mixtures of ZnO-C to demonstrate the layer-wise character of the reaction. The results show that the reactivity and the behavior of mixtures strongly depend on their components structures, impurities and stoichiometry. This method can be generally applied for studying endothermic chemical reactions involving other solid reactants.
Parametric Study of an Evacuated Multi-Stage Solar Still
Authors: Abakr Yousif A. , Ismail Ahmad F. , Ahmed Mirghani I.
Published: December 2008

On this work a practical design to utilize the multistage evacuated solar still concept was developed. The mathematical model of the system was developed based on the energy and mass balance equations of the system. The system components were fabricated and the overall system was assembled. A prototype was constructed and tested at outdoor real solar radiation conditions. The experimental results show a significant improvement of the overall productivity relative to other systems.
Simulation of Concentrated Photovoltaic Cooling System
Authors: Halford Christopher , Boehm Robert F.
Published: December 2008

This paper reports work underway in converting a dish-Stirling system to a dish-PV system at UNLV. The existing SAIC dish–Stirling system is being retrofitted with new fixed-focus facets and an Amonix photovoltaic receiver to replace the Stirling engine/generator package. As is the case with photovoltaic systems generally, the Amonix cells being used in this application lose efficiency as their temperatures increase. To combat this effect, cooling is provided by circulating liquid through channels in the backing plate. The liquid is then pumped through an array of automotive type radiators and the excess heat is rejected to the ambient air. Reported here is the development of a numerical model for the cooling system, with specific attention being paid to the transient response. Experimental data is taken to determine the various properties of the individual components to be used in the system and this data is used in a MatLab-based simulation. The cooling system model can then be linked to a similar model for the receiver and cell assembly and the optimization functions included in MatLab can be used to select the input parameters (pump size, number of radiators, fan speed, etc.) that maximize the overall efficiency of the system. The predictions of the model can be used in the selection of the final cooling system design and the validity of the model can be checked against the actual performance of the unit.
“Back to the Roofs”: The Solarchemical Production of Fine Chemicals With Sunlight
Authors: Oelgemo¨ller Michael , Jung Christian , Ortner Ju¨rgen , Mattay Jochen , Schiel Christian , Zimmermann Elmar
Published: December 2008

Three photochemical reactions were performed successfully under solar irradiation conditions: the photoacylation of quinones with aldehydes and the rose bengal sensitized photooxygenations of citronellol or 1,5-dihydroxynaphthalene. All reactions were easily performed on multigram to kilogram scales using cheap and commercially available starting materials, and yielded important key-intermediates for industrial applications.
Incorporating Thermal Storage Into a SEGS Plant Using TRNSYS: A Status Report
Authors: Braithwaite Jade D. , Boehm Robert
Published: December 2008

Two new preliminary component types were developed for the transient simulation program TRNSYS with IISiBat that models three different types of sensible thermal storages for analysis with use in a solar electric generating system (SEGS) simulation. One component containing a fully mixed, a stratified and a plug flow tank model options has been developed such that the input and parameter specifications are similar so that all three models could be easily placed into one component type. A single, cylindrical direct storage tank with one inlet and one outlet that evaluates fluid properties as a function of temperature is representative for all three models. The second component is a storage controller that passes along pertinent charging, dwell or discharging information to the storage and integrates the storage into a given SEGS model. Results were generated for each storage tank integrated into a SEGS VI simulation model for temperature distribution and power generation.
Thermal Characterization of Prototypical ICS Systems With Immersed Heat Exchangers
Authors: Liu Wei , Davidson Jane H. , Kulacki F. A.
Published: December 2008

Natural convection is measured in an enclosure that represents an integral collector storage solar system with an immersed heat exchanger. The enclosure has an aspect ratio of 9.3:1 and is inclined 30 deg to the horizontal. Heat transfer coefficients for bundles of 240 tubes are obtained for a range of transient operating modes and pitch-to-diameter ratios of 1.5, 2.4, and 3.3. Results for isothermal and stratified enclosures yield a correlation for the overall Nusselt number, NuD=(2.45±0.03)RaD0.188,230≤RaD≤9800. Nusselt numbers are three times larger than those for a similarly configured single-tube and an eight-tube bundle. This increase is attributed to stronger fluid motion within the bundle and greater overall circulation rates in the enclosure.
Monte Carlo Radiative Transfer Modeling of a Solar Chemical Reactor for the Co-Production of Zinc and Syngas
Authors: Kra¨upl Stefan , Steinfeld Aldo
Published: December 2008

Radiation heat transfer within a solar chemical reactor for the co-production of zinc and syngas is analyzed by the Monte Carlo ray-tracing method. The reactor is treated as a 3D non-isothermal cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar irradiation and undergo endothermic reduction by CH4 at above 1300 K. The analysis includes coupling to conduction/convection heat transfer and chemical kinetics. Calculation of the apparent absorptivity indicates the cavity’s approach to a blackbody absorber, for either diffuse or specular reflecting inner walls. Numerically calculated temperature distributions, zinc production rates, and thermal efficiencies are validated with experimental measurements in a solar furnace with a 5-kW prototype reactor. At 1600 K, the zinc production rate reached 0.12 mol/min and the reactor’s thermal efficiency exceeded 16%. Scaling up the reactor to power levels of up to 1 MW while keeping constant the relative geometrical dimensions and the solar power flux at 2000 suns results in thermal efficiencies of up to 54%.
Modeling and Design of Direct Solar Steam Generating Collector Fields
Authors: Eck M. , Steinmann W.-D.
Published: December 2008

The direct steam generation (DSG) is an attractive option regarding the economic improvement of parabolic trough technology for solar thermal electricity generation in the multi megawatt range. According to [1] and [2] a 10% reduction of the LEC is expected compared to conventional SEGS like parabolic trough power plants. The European DISS project has proven the feasibility of the DSG process under real solar conditions at pressures up to 100 bar and temperatures up to 400°C in more than 4000 operation hours [3]. In a next step the detailed engineering for a pre-commercial DSG solar thermal power plant will be performed. This detailed engineering of the collector field requires the consideration of the occurring thermohydraulic phenomena and their influence on the stability of the absorber tubes. A design tool has been developed at DLR calculating all relevant process parameters including pressure drop, temperature field and stress in the absorber tubes. The models implemented in this design tool have been validated in detail at the DISS test facility under real DSG conditions for pressures between 30 and 100 bar and inner diameters between 50 and 85 mm. The models have been implemented into a MATLAB® program to allow for a first quick determination of critical process conditions. Once critical process conditions have been identified the FEM package ANSYS® is used for a detailed investigation. This article summarises the models used and shows the design procedure for a DSG collector field. The design program has proven to be a reliable tool for the detailed design of DSG collector fields.
Comparative Evaluation of Indoor Thermal Comfort for Green and Conventional Office Buildings
Authors: Nunez Alex , Krarti Moncef
Published: December 2008

A comparative analysis was conducted between two office buildings, one constructed using green design and the other erected using traditional building construction methods. As part of the analysis, thermal comfort indicators (using the Predicted Mean Value of Fanger model) were monitored by recording equivalent temperature, air temperature, and relative humidity at each site. The study tests whether office buildings constructed using different design approaches have significantly different indoor thermal environment. The results of the comparative analysis indicate that the green building provides better thermal comfort than the conventional building.
Building-Integrated Photovoltaics for Low-Slope Commercial Roofs
Authors: Miller William A. , Brown Ed , Livezey Rita Jo
Published: December 2008

A photovoltaic (PV) distributed energy resource (DER) was established to support the Tennessee Valley Authority’s Green Power Switch program, which allows utility customers to purchase blocks of electricity generated by solar resources. The PV DER was also used to study the potential shading benefits of roof-mounted PV systems for commercial buildings. Test data derived by monitoring an offset-mounted PV array shading a built-up low-slope roof system shows that the annual savings per square foot of low-slope roof can be as high as $0.18 ($1.95 per square meter) in Phoenix, AZ.
Solar Energy Applications on Military Bases
Authors: Kolb Greg , Black Bill , Moss Tim
Published: December 2008

The goals of the DOD-solar study were to identify potentially economic solar-energy projects on specific military bases and to define the necessary steps to install solar projects in the near term. Five classes of mature solar technologies were investigated: crystalline photovoltaics, solar hot water, transpired collectors (solar wall), pool heaters, and daylighting. Approximately 500 military bases/facilities were screened using simple payback models that used site-specific data for insolation, conventional energy prices, and financial incentives for solar. One or more economically viable projects appear to exist at nearly every base analyzed. Most projects are for solar daylighting and solar walls. Several pool and domestic water heating opportunities exist and a number of large photovoltaic projects also appear to be possible. Approximately 30 business-case analyses (BCAs) were performed which represent the larger project potential. Government and private ownership of the solar systems were investigated in the BCAs. Though the potential is large, it appears that a new multi-year DOD program that promotes private ownership needs to be launched before the full potential can be realized.
Optimization of Hybrid Power System Operation
Authors: Tupper Kendra , Jensen Rob , Cloyd Joe , Wills Rob , Sullivan Charles
Published: December 2008

In developing countries, half of the world’s population lives without electric power. Hybrid power systems, consisting of photovoltaic (PV) modules, battery banks, and backup diesel generators, have the potential to become a cost-effective solution for delivering power to many of these remote villages where grid extension is cost-prohibitive. In this paper, we show that improved dispatch strategies can significantly decrease the cost of a hybrid power system. We propose using a genetic algorithm (GA) in combination with novel load and insolation predictive strategies to reduce the operating costs over the present state-of-the-art methods. Realistic simulations demonstrate that this technique provides an average cost savings of 20.9% over the Set Point Strategy and 13.8% over the Load Following Strategy. We show that this strategy is a viable means of reducing the cost of hybrid power system operation.