bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Adverse Environmental Conditions on Rotorcraft Operational Performance and Pollutant Emissions
Authors: Ortiz-Carretero Jesus , Castillo Pardo Alejandro , Goulos Ioannis , Pachidis Vassilios
Published: August 2017

It is anticipated that the contribution of rotorcraft activities to the environmental impact of civil aviation will increase in the future. Due to their versatility and robustness, helicopters are often operated in harsh environments with extreme ambient conditions. These severe conditions not only affect the performance of the engine but also affect the aerodynamics of the rotorcraft. This impact is reflected in the fuel burn and pollutants emitted by the rotorcraft during a mission. The aim of this paper is to introduce an exhaustive methodology to quantify the influence adverse environment conditions have in the mission fuel consumption and the associated emissions of nitrogen oxides (NOx). An emergency medical service (EMS) and a search and rescue (SAR) mission are used as case studies to simulate the effects of extreme temperatures, high altitude, and compressor degradation on a representative twin-engine medium (TEM) weight helicopter, the Sikorsky UH-60A Black Hawk. A simulation tool for helicopter mission performance analysis developed and validated at Cranfield University was employed. This software comprises different modules that enable the analysis of helicopter flight dynamics, powerplant performance, and exhaust emissions over a user-defined flight path profile. For the validation of the models implemented, extensive comparisons with experimental data are presented throughout for rotorcraft and engine performance as well as NOx emissions. Reductions as high as 12% and 40% in mission fuel and NOx emissions, respectively, were observed for the “high and cold” scenario simulated at the SAR role relative to the same mission trajectory under standard conditions.
Integrated Approach for Steam Turbine Thermostructural Analysis and Lifetime Prediction at Transient Operations
Authors: Moroz Leonid , Doerksen Glenn , Romero Fernando , Kochurov Roman , Frolov Boris
Published: August 2017

In order to achieve the highest power plant efficiency, original equipment manufacturers continuously increase turbine working parameters (steam temperatures and pressures), improve components design, and modify start-up cycles to reduce time while providing more frequent start-up events. All these actions result in much higher levels of thermostresses, a lifetime consumption of primary components and an increased demand for accurate thermostructural and low cycle fatigue (LCF) simulations. In this study, some aspects of methodological improvement are analyzed and proposed in the frame of an integrated approach for steam turbine components thermostructural analysis, reliability, and lifetime prediction. The full scope of the engineering tasks includes aero/thermodynamic flow path and secondary flows analysis to determine thermal boundary conditions (BCs), detailed thermal/structural two-dimensional and three-dimensional (3D) finite element (FE) models preparation, components thermal and stress–strain simulation, rotor–casing differential expansion and clearances analysis, and finally, turbine unit lifetime estimation. Special attention is paid to some of the key factors influencing the accuracy of thermal stresses prediction, specifically, the effect of “steam condensation” on thermal BC, the level of detailing for thermal zones definition, thermal contacts, and mesh quality in mechanical models. These aspects have been studied and validated against test data, obtained via a 30 MW steam turbine for combined cycle application based on actual start-up data measured from the power plant. The casing temperatures and rotor–stator differential expansion, measured during the commissioning phase of the turbine, were used for methodology validation. Finally, the evaluation of the steam turbine HPIP rotor lifetime by means of a LCF approach is performed.
Experimental and Computational Study of the Effect of Momentum-Flux Ratio on High-Pressure Nozzle Guide Vane Endwall Cooling Systems
Authors: Ornano Francesco , Povey Thomas
Published: August 2017

High-pressure (HP) nozzle guide vane (NGV) endwalls are often characterized by highly three-dimensional (3D) flows. The flow structure depends on the incoming boundary layer state (inlet total pressure profile) and the (static) pressure gradients within the vane passage. In many engine applications, this can lead to strong secondary flows. The prediction and design of optimized endwall film cooling systems is therefore challenging and is a topic of current research interest. A detailed experimental investigation of the film effectiveness distribution on an engine-realistic endwall geometry is presented in this paper. The film cooling system was a fairly conventional axisymmetric double-row configuration. The study was performed on a large-scale, low-speed wind tunnel using infrared (IR) thermography. Adiabatic film effectiveness distributions were measured using IR cameras, and tests were performed across a wide range of coolant-to-mainstream momentum-flux and mass flow ratios (MFRs). Complex interactions between coolant film and vane secondary flows are presented and discussed. A particular feature of interest is the suppression of secondary flows (and associated improved adiabatic film effectiveness) beyond a critical momentum flux ratio. Jet liftoff effects are also observed and discussed in the context of sensitivity to local momentum flux ratio. Full coverage experimental results are also compared to 3D, steady-state computational fluid dynamics (CFD) simulations. This paper provides insights into the effects of momentum flux ratio in establishing similarity between cascade conditions and engine conditions and gives design guidelines for engine designers in relation to minimum endwall cooling momentum flux requirements to suppress endwall secondary flows.
Effect of Uneven Wall Heating Conditions Under Different Buoyancy Numbers for a One Side Rib-Roughened Rotating Channel
Authors: Wang Zhi , Corral Roque
Published: August 2017

This paper investigates the impacts of uneven wall heating conditions under different buoyancy numbers on flow field and heat transfer performance of a rotating channel with one side smooth and one side roughened by 45 deg inclined ribs. Parametric Reynolds-averaged Navier–Stokes (RANS) simulations were conducted under two different wall heating conditions: only ribbed wall heated, as in experiment setup, and all walls heated, under three different buoyancy numbers. Results are compared, when available, with experimental results. Numerical results show that uneven wall heating has only a minor impact on nonrotating cases and very low buoyancy rotating cases. However, it has a significant influence, on both, the heat transfer behavior and the flow field, when the buoyancy number is large. In the ribbed trailing rotating tests, the all walls heated cases show significantly higher heat transfer rate than only the ribbed wall heated cases. The discrepancy is enlarged as buoyancy number increases. The heat transfer in the all walls heated case increases monotonically with the buoyancy number, whereas in the ribbed wall, heated case is slight reduced. In the ribbed leading rotating tests, the heat transfer sensitivity to the heating conditions is not conspicuous, and for both cases, the heat transfer level slightly reduced as the buoyancy number increased. The flow field investigation shows that there is a significant displacement of main flow in the all walls heated cases than only the ribbed wall heated cases under high buoyancy numbers. This displacement is due to the buoyancy effect and responsible for the heat transfer differences in uneven heating problems. According to the results obtained in the paper, we conclude that when buoyancy effects are relevant, the heating settings can play a significant role in the heat transfer mechanisms and therefore in the experimental and numerical results.
Modeling of Dive Maneuvers for Executing Autonomous Dives With a Flapping Wing Air Vehicle
Authors: Roberts Luke J. , Bruck Hugh A. , Gupta S. K.
Published: August 2017

This paper is focused on design of dive maneuvers that can be performed outdoors on flapping wing air vehicles (FWAVs) with a minimal amount of on-board computing capability. We present a simple computational model that provides accuracy of 5 m in open loop operation mode for outdoor dives under wind speeds of up to 3 m/s. This model is executed using a low power, on-board processor. We have also demonstrated that the platform can independently execute roll control through tail positioning, and dive control through wing positioning to produce safe dive behaviors. These capabilities were used to successfully demonstrate autonomous dive maneuvers on the Robo Raven platform developed at the University of Maryland.
Transmission Error Due to Resonance in Synchronous Belt Drive With Eccentric Pulley
Authors: Kagotani Masanori , Ueda Hiroyuki
Published: August 2017

In synchronous belt drives, it is generally difficult to eliminate pulley eccentricity, because the pulley teeth and shaft hole are produced separately and the pulley is installed on an eccentric shaft. This eccentricity affects the accuracy of rotation transmission, so that the belt tension changes during a single rotation of the pulley. This in turn affects the occurrence of resonance in the spans. In the present study, the transmission error in a synchronous belt drive with an eccentric pulley in the absence of a transmitted load was experimentally investigated for the case in which the spans undergo first-mode transverse vibration due to resonance. The transmission error was found to have a component with a period equal to the span displacement, in addition to a component with a period of half the span displacement. During a single rotation of the pulley, the magnitude of the transmission error increased, and its frequency decreased, with decreasing belt tension. The transmission error exhibited the large value when two frequency conditions were satisfied: one was that the meshing frequency was within the range of span frequency variations due to the eccentricity, and the other was that the minimum span frequency was close to an integer multiple of the pulley rotation frequency. Even if both of these conditions occurred, if the range of span frequency variations due to the eccentricity was larger than 13 Hz, the transmission error could be eliminated by adjusting the belt tension, so that the average span frequency corresponded to the meshing frequency.
Periodic Response of a Timing Belt Drive System With an Oval Cogged
Pulley and Optimal Design of the Pitch Profile for Vibration
Reduction
Authors: Zhu Hao , Zhu Weidong , Hu Yumei , Wang Xuefeng
Published: August 2017

A complete dynamic model of a timing belt drive system with an oval cogged pulley and an auto-tensioner is established in this work. Periodic torsional vibrations of all accessory pulleys and the tensioner arm are calculated using a modified incremental harmonic balance (MIHB) method based on the complete dynamic model. Calculated results from the MIHB method are verified by comparing them with those obtained from Runge–Kutta method. Influences of tensioner parameters and oval pulley parameters on torsional vibrations of camshafts and other accessory pulleys are investigated. A sequence quadratic programing (SQP) method with oval pulley parameters selected as design variables is applied to minimize the overall torsional vibration amplitude of all the accessory pulleys and the tensioner arm in the timing belt drive system at different operational speeds. It is demonstrated that torsional vibrations of the timing belt drive system are significantly reduced by matching belt stretch with speed variations of the crankshaft and fluctuating torque loads on camshafts. The timing belt drive system with optimal oval parameters given in this work has better performance in the overall torsional vibration of the system than that with oval parameters provided by the kinematic model and the simplified dynamic model in previous research.
Prediction of Diesel Combustion and Emission Characteristics in CI Engine Using Computational Fluid Dynamics Simulations
Authors: Hawi Meshack , Abdel-Rahman Ali K. , Bady Mahmoud , Ookawara Shinichi
Published: August 2017

Computational Fluid Dynamics (CFD) study of compression ignition (CI) engines provides invaluable insights into in-cylinder conditions and processes, which greatly expands on the very limited detail provided by engine output measurements, fuel consumption measurements, and engine-out measurements of exhaust emissions. CFD modeling and simulation has therefore become an attractive alternative for engine analysis in place of full experimental testbed study in recent years. In this research work, the performance of a single cylinder four stroke diesel engine was investigated. Commercial simulation software ANSYS Forte was used to study the combustion and emission characteristics of a diesel engine, in order to establish strategies for improvement of in-cylinder combustion and emission control. Normal heptane (n-heptane) was used as the surrogate fuel to represent diesel. Simulation results are compared against data from experimental testbed studies in terms of in-cylinder pressure profiles, heat release rate and exhaust emission of oxides of nitrogen (NOx), soot and unburned hydrocarbon (UHC) levels. The pressure trace from the simulations is found to be within a reasonable error limit of 10%. The combustion process is simulated with special focus on exhaust emissions of soot, NOx and unburned hydrocarbon. Graphical plots for mass fraction of soot, NOx and UHC are presented and discussed to elucidate the formation of these emissions. Graphics contours of temperature, NO mass fraction and oxygen concentration within the combustion chamber are also presented and discussed. The effects of injection timing on engine in-cylinder pressure, heat release rate and exhaust emissions are also studied by varying the injection timing and maintaining constant injection duration. Results are compared for the three different injection timings investigated, namely start of injection (SOI) 18° bTDC, 15° bTDC and 12° bTDC. Emissions of soot and NOx are found to decrease with retarded injection timing. However, the peak in-cylinder pressure is greatly reduced and hence the output power is low. Injection timing is found to have no significant effect on emissions of UHC. The optimum injection timing that gives high output power and relatively low emission is 15° bTDC.
Influence of Seasonal Heat Load Variation on Daily Optimal Scheduling of CHP System With Renewable Energy and Heat Storage
Authors: Hu Kang , Chen Qun , Zhang Meng-Qi , Chen Lei , Xu Fei , Min Yong
Published: August 2017

Due to fluctuation and intermittence, renewable energy sources (RESs) require high adjustability of power system. However, the existing combined heat and power (CHP) system has limited adjustability because of being controlled in the “heat-led” mode, which, consequently, hinders the development of the RESs. A solution of the problem is to introduce the heat storage (HS), which decouples heat supply from heat load. Although a number of researchers have studied in the design and the planning optimization of such CHP systems with RESs and HS, few people have paid attention to the seasonal variation of the heat load, which may vary the daily optimal planning of the systems. In this dissertation, we set up the model and optimize the planning of a CHP system with RESs and HS, with the consideration of the seasonal variation of the heat load. We find that in the beginning/ending of the heating season, the HS should store heat when the wind power is being abandoned and release heat in the rest of the days, while in the middle of the heating season, the HS should release heat when the wind power is being abandoned and store heat in the rest of the days.
Fluidized-Bed Heat Transfer Modeling for the Development of Particle/Supercritical-CO2 Heat Exchanger
Authors: Ma Zhiwen , Martinek Janna
Published: August 2017

Concentrating solar power (CSP) technology is moving toward high-temperature and high-performance design. One technology approach is to explore high-temperature heat-transfer fluids and storage, integrated with a high-efficiency power cycle such as the supercritical carbon dioxide (s-CO2) Brayton power cycle. The s-CO2 Brayton power system has great potential to enable the future CSP system to achieve high solar-to-electricity conversion efficiency and to reduce the cost of power generation. Solid particles have been proposed as a possible high-temperature heat-transfer medium that is inexpensive and stable at high temperatures above 1,000°C. The particle/heat exchanger provides a connection between the particles and s-CO2 fluid in the emerging s-CO2 power cycles in order to meet CSP power-cycle performance targets of 50% thermal-to-electric efficiency, and dry cooling at an ambient temperature of 40°C. The development goals for a particle/s-CO2 heat exchanger are to heat s-CO2 to ≥720°C and to use direct thermal storage with low-cost, stable solid particles. This paper presents heat-transfer modeling to inform the particle/s-CO2 heat-exchanger design and assess design tradeoffs. The heat-transfer process was modeled based on a particle/s-CO2 counterflow configuration. Empirical heat-transfer correlations for the fluidized bed and s-CO2 were used in calculating the heat-transfer area and optimizing the tube layout. A 2-D computational fluid-dynamics simulation was applied for particle distribution and fluidization characterization. The operating conditions were studied from the heat-transfer analysis, and cost was estimated from the sizing of the heat exchanger. The paper shows the path in achieving the cost and performance objectives for a heat-exchanger design.
Effect of the Working Fluid on Performance of the ORC and Combined Brayton/ORC Cycle
Authors: Javanshir Alireza , Sarunac Nenad
Published: August 2017

This study focuses on the power cycles such as organic Rankine cycle (ORC) and combined regenerative Brayton/ORC. The selection of working fluids and power cycles is traditionally conducted by trial and error method and performing a large number of parametric calculations over a range of operating conditions. A methodology for selection of optimal working fluid based on the cycle operating conditions and thermophysical properties of the working fluids was developed in this study. Thermodynamic performance (thermal efficiency and net power output) of a simple subcritical and supercritical ORC was analyzed over a range of operating conditions for a number of working fluids to determine the effect of operating parameters on cycle performance and select the best working fluid. New expressions for thermal efficiency of a simple ORC are proposed. In case of a regenerative Brayton/ORC, the results show that CO2 is the best working fluid for the topping cycle. Depending on the exhaust temperature of the topping cycle, Isobutane, R11 and Ethanol are the preferred working fluids for the bottoming (ORC) cycle, resulting in highest efficiency of the combined cycle. Finally, a performance map is presented as guidance for selection of the best working fluid for specific cycle operating conditions.
Impact of Utilizing PV Surplus Electricity on CO2 Emissions From the Residential Energy Systems
Authors: Nagai Toshiyuki , Yoshida Akira , Amano Yoshiharu
Published: August 2017

In order to reduce CO2 emissions in the residential sector, the installation of photovoltaics (PV) has been increasing extensively. However, such large-scale PV installations cause problems in the low-voltage distribution grid of the residential sector, such as PV related voltage surges. In this study, the utilization of suppressed PV output through energy storage devices was proposed. Using demand side energy storage devices reduces voltage surge, transmission loss, and CO2 emissions from the residential buildings. The objective of this study was to add voltage constraints of the low-voltage distribution grid to an operational planning problem that we developed for the residential energy systems, and to quantitatively evaluate the potential of heat pump water heater (HP) to utilize the PV surplus electricity, while considering the electrical grid constraints based on the minimization of CO2 emissions. We found that when a 4.5 kW HP with 370 L storage, which utilizes PV output, was added to the system, the reduction in CO2 emissions was more than twice compared with that in the case of adding 4 kWh battery (BT) to a PV and gas fired water heater configuration. Further, the effect of utilizing the suppressed PV electricity by HP was almost equivalent to that by the BT. Therefore, the potential of HP in utilizing PV surplus electricity is higher than that of the BT in terms of CO2 emissions reduction in the residential sector.
Heat Transfer Models of Moving Packed-Bed Particle-to-SCO2 Heat Exchangers
Authors: Albrecht Kevin J. , Ho Clifford K.
Published: August 2017

Particle-based concentrating solar power (CSP) plants have been proposed to increase operating temperature for integration with higher efficiency power cycles using supercritical carbon dioxide (sCO2). The majority of research to date has focused on the development of high-efficiency and high-temperature particle solar thermal receivers. However, system realization will require the design of a particle/sCO2 heat exchanger as well for delivering thermal energy to the power-cycle working fluid. Recent work has identified moving packed-bed heat exchangers as low-cost alternatives to fluidized-bed heat exchangers, which require additional pumps to fluidize the particles and recuperators to capture the lost heat. However, the reduced heat transfer between the particles and the walls of moving packed-bed heat exchangers, compared to fluidized beds, causes concern with adequately sizing components to meet the thermal duty. Models of moving packed-bed heat exchangers are not currently capable of exploring the design trade-offs in particle size, operating temperature, and residence time. The present work provides a predictive numerical model based on literature correlations capable of designing moving packed-bed heat exchangers as well as investigating the effects of particle size, operating temperature, and particle velocity (residence time). Furthermore, the development of a reliable design tool for moving packed-bed heat exchangers must be validated by predicting experimental results in the operating regime of interest. An experimental system is designed to provide the data necessary for model validation and/or to identify where deficiencies or new constitutive relations are needed.
Exhaust Systems: CO2 Emission Reduction Using Zeolite Catalyst
Authors: Menon Shruti Mohandas , Goudarzi Navid
Published: August 2017

Air pollution is a leading public health concern that needs to be tackled. About 30% of the total greenhouse gas emissions, such as CO, HC and NOx are due to automobiles. By 2030, the US Department of Transportation aims to reduce light duty vehicle emissions by 18%. This can be achieved by public policy approaches such as implementing emission control norms and performance improvements such as exhaust system design.

In this work, the implementation of a pure Zeolite catalyst to reduce the exhaust CO2 emission of a SI engine is studied theoretically and experimentally. The complete exhaust system including the catalytic converter, muffler, and pipes is modeled in a 3D CAD modeling software, using the engine specifications. Current expensive precious metals in the catalytic converter are replaced with a binding agent along with Zeolite catalyst. The exhaust system is fabricated and the experimental tests are performed at the maximum engine RPM to obtain threshold emission reduction values. The results showed obtaining an emission reduction of CO2 at a lower cost. Furthermore, it is found that employing Zeolite sieves can further reduce the pollutant emission at a similar cost.
Parametric Study of Vertical Axis Wind Turbine Rotor Configurations Using CFD
Authors: Difuntorum John Keithley , Danao Louis Angelo M.
Published: August 2017

Vertical axis wind turbines present several advantages over the horizontal axis machines that make them suitable to a variety of wind conditions. However due to the complexity of VAWT aerodynamics, available literature on VAWT performance in steady and turbulent wind conditions is limited. This paper aims to numerically predict the performance of a 5kW VAWT under steady wind conditions through computational fluid dynamics modeling by varying turbine configuration parameters. Two dimensional VAWT models using a cambered blade (1.5%) were created with open field boundary extents. Turbine configuration parameters studied include blade mounting position, blade fixing angle, and rotor solidity. Baseline case with peak Cp of 0.31 at tip speed ratio of 4 has the following parameters: mounting position at 0.5c, zero fixing angle, 3 blades (solidity = 0.3). Independent parametric studies were carried out and results show that a blade mounting position of 0.7c from the leading edge produces best performance with maximum Cp = 0.315 while worst case is a mounting position of 0.15c with peak Cp = 0.273. Fixing angle study reveals a toe-out setting of −1° producing the best performance with peak Cp of 0.315 and the worst setting at toe-in of 1.5° with peak Cp of 0.287. The solidity study resulted in a best case of 4 blades (solidity = 0.4) with peak Cp = 0.316 and worst case of 2 blades (solidity = 0.2) with peak Cp = 0.283.
Effects of Philippine Coconut Methyl Ester on the Performance and Emissions of a Heavy Duty CRDI Engine
Authors: Encarnacion Job Immanuel B. , Quiros Edwin N.
Published: August 2017

The Philippine Department of Environment and Natural Resources (DENR) has issued Department Order 2015-04 (DAO 2015-04) or the “The Implementation of Vehicle Emission Limits for EURO 4/IV, and In-Use Vehicle Emission Standards”. This policy, coupled with the Philippine Biofuels Act of 2016 (RA 9367) should greatly reduce the environmental impact of local automobile emissions. Commercial fuel is a mix of local coconut methyl ester (CME) and neat diesel blend. However, commercial diesel fuel is still at 2% v/v as of 2016 in contrast to the 5% v/v set by the policy, part due to the fact that only few local studies are done to show the effects of higher percentage of CME, with most recent studies showing results against increased CME usage. The study shows the effects of the usage of higher CME percentage in accordance to the set schedule of RA 9367. Five fuel blends with varying CME percentages v/v (2%, 5%, 10%, 15%, and 20%) are used in a heavy duty turbocharged common rail direct injection (CRDI) engine. The engine is run on an eddy current dynamometer with steady state measurements at 50 to 500Nm with 50Nm intervals. Each fuel is tested at three pedal positions, alpha, (25%, 50%, and 60%) controlled directly from the engine control unit (ECU). Results show that higher CME usage does not result in reduction of power and achieved torque. There is, however, a significant increase in brake specific fuel consumption at higher percentages of CME. No significant change in carbon monoxide (CO) and unburned hydrocarbons of diesel (HCD) is observed but there is a significant increase in Nitrous Oxides (NOx) concentration as CME percentage is increased. However, brake specific CO and HCD were found to be out of standard for near no load and near full load operations. A similar trend is observed for brake specific. Brake specific NOx is particularly more problematic since all measurements were observed to be out of standard with maximum values of 1350% of the set EURO 4/IV standard. However, it is also seen that the performance of each blend does not significantly differ from each other. Nevertheless, there is still some potential in the usage of CME due to the fact that power and torque requirements are still met at the expense of higher fuel consumption; but with the opportunity of being self-sufficient as coconut-producing country.
Evaluation of a Model Helical Bladed Hydrokinetic Turbine Characteristics From In-Situ Experiments
Authors: Talukdar Parag K. , Kulkarni Vinayak , Dehingia Dipankar , Saha Ujjwal K.
Published: August 2017

Hydro power has always been a major source of electricity generation among different renewable energy technologies. However, due to the construction of dams, the conventional hydro energy extraction techniques cause disturbance to the ecology by diverting the natural flow of water and migrating population from their native land. Of late, energy extraction from the natural flow of water is considered as potential source of renewable power since it is clean and reliable. In view of this, the present study deals with the development and performance characterization of a vertical-axis helical-bladed hydrokinetic turbine. Considering the various design parameters, a NACA 0020 bladed vertical-axis turbine of solidity ratio 0.38 and aspect ratio 1.0 has been developed. In-situ experiments have been carried out at an irrigation sluice having a water velocity of 1.1 m/s. Further, its performance characteristics are evaluated at different mechanical loading conditions with the help of a mechanical dynamometer. It has been observed that the developed helical-bladed turbine demonstrates a peak power coefficient of 0.16 at a tip-speed ratio of 0.85. The present experimental investigation has clearly demonstrated the usefulness of the hydrokinetic turbine. It has also been logged that the average water velocity at the concerned site has a great importance on the turbine design.
Design and Testing of a Novel Bladed Receiver
Authors: Ortega Jesus D. , Christian Joshua M. , Ho Clifford K.
Published: August 2017

Previous research at Sandia National Laboratories showed the potential advantages of using light-trapping features which are not currently used in direct tubular receivers. A horizontal bladed receiver arrangement showed the best potential for increasing the effective solar absorptance by increasing the ratio of effective surface area to the aperture footprint. Ray-tracing analyses using SolTrace were performed to understand the light-trapping effects of the bladed receivers, which enable re-reflections between the fins that enhance the effective solar absorptance. A parametric optimization study was performed to determine the best possible configuration with a fixed intrinsic absorptivity of 0.9 and exposed surface area of 1 m2. The resulting design consisted of three vertical panels 0.584 m long and 0.508 m wide and 3 blades 0.508 m long and 0.229 m wide with a downward tilt of 50 degrees from the horizontal. Each blade consisted of two panels which were placed in front of the three vertical panels. The receiver was tested at the National Solar Thermal Test Facility using pressurized air. However, the receiver was designed to operate using supercritical carbon dioxide (sCO2) at 650 °C and 15 MPa for 100,000 hours following the ASME Boiler and Pressure Vessel Code Section VIII Division 1. The air flowed through the leading panel of the blade first, and then recirculated toward the back panel of the blade before flowing through one of the vertical back panels. The test results of the bladed receiver design showed a receiver efficiency increase over a flat receiver panel of ∼5 – 7% (from ∼80% to ∼86%) over a range of average irradiances, while showing that the receiver tubes can withstand temperatures > 800 °C with no issues. Computational fluid dynamics (CFD) modeling using the Discrete Ordinates (DO) radiation model was used to predict the temperature distribution and the resulting receiver efficiencies. The predicted thermal efficiency and surface temperature values correspond to the measured efficiencies and surface temperatures within one standard deviation. In the near future, an sCO2 flow system will be built to expose the receiver to higher pressure and fluid temperatures which could yield higher efficiencies.
Dynamic Model of Supercritical CO2 Brayton Cycles Driven by Concentrated Solar Power
Authors: Berthet Couso Gregory , Barraza Vicencio Rodrigo , Vasquez Padilla Ricardo , Soo Too Yen Chean , Pye John
Published: August 2017

Supercritical carbon dioxide (sCO2) Brayton cycle is an emerging technology to be used as a power block with concentrated solar power (CSP) systems, tower type, sCO2 Brayton cycle has the potential to be competitive with traditional Rankine steam cycle. Most of the studies have been focused on the steady state analysis of this technology.

This research has developed numerical models for five configurations of sCO2 Brayton cycles operating under quasi steady state conditions. The studied cycles are connected directly to the solar central receiver tower, which is used to provide heat input to the cycles; consequently, the heat addition is changing over time as a function of solar radiation. During the off load operation, the mass flow rate of the cycle is changing with the goal of keeping the turbine inlet temperature at 700°C. The compressor and turbine use a partial load model to adjust velocities according to the new mass flow rate. Also, the heat exchangers effectiveness are adjusted as they present off-design operation. In the recompression cycle, the model permits to explore the relationship between recompression fraction and the ambient temperature. It is demonstrated that the power generated by the cycle may be improved more than 6 % if the recompression fraction is continuously changed and controlled as a function of the ambient temperature.
Dispatchable Solar Combined Cycle
Authors: Conlon William M.
Published: August 2017

Successful deployment of large amounts of renewable solar and wind energy has created a pressing need for significant additions of grid connected energy storage. Excess renewable generation is increasingly necessitating curtailment or derating of renewable or conventional generators. The CAISO Duck Curve [8] illustrates the challenge caused by very large quantities of solar generation. Both large scale energy storage and flexible ramping are needed for renewable resources to be financially sustainable and to meet CO2 reduction goals.

The Dispatchable Solar Combined Cycle (DSCC) integrates Concentrating Solar Power (CSP) with Thermal Energy Storage (TES) in a holistic combined cycle configuration to meet the challenges of the CAISO Duck Curve by delivering flexible capacity with dispatchable solar power. Energy cost from DSCC is comparable to that from a Combined Cycle Power Plant (CCPP), and substantially below the alternatives: Photovoltaic plus battery or Photovoltaic plus combustion turbine. DSCC also enable far higher integration of renewable power and far larger renewable capacity factors than the Integrated Solar Combined Cycle (ISCC), which typically has no storage.

The innovative DSCC system:

• uses energy storage to deliver power when it is most valuable,

• increases the capacity factor to deliver more renewable energy,

• improves the power plant Heat Rate to reduce fuel consumption, and

• reduces the cost of power while addressing RPS and storage mandates.

In DSCC, the CSP and TES are used primarily for latent heat: the evaporation of steam, and the Combustion Turbine (CT) exhaust gas is used primarily for sensible heating, especially superheating steam. This simplifies the integration of low-cost storage media, such as paraffinic oils or concrete, instead of molten salt, since high temperature storage is not needed. A single pressure, non-reheat steam cycle suitable, allowing for simplicity of design and operation, reducing costs and facilitating faster startup and ramping.

With DSCC, the steam turbine generates about the same power as the CT, unlike a typical CCPP where about half the power comes from the steam cycle. The additional steam production reduces the Heat Rate about 25% compared to CCPP.

The DSCC approach is ideally suited for repowering existing CSP plants, to provide firm capacity that can dispatch at valuable evening peak periods, increase the power output, and reduce fossil fuel use compared with conventional CCPP or peaking plants.

This paper will outline the DSCC concept, and provide performance estimates for a reference plant.
Techno-Economic Comparison of Solar-Driven SCO2 Brayton Cycles Using Component Cost Models Baselined With Vendor Data and Estimates
Authors: Carlson Matthew D. , Middleton Bobby M. , Ho Clifford K.
Published: August 2017

Supercritical carbon dioxide (sCO2) Brayton power cycles have the potential to significantly improve the economic viability of concentrating solar power (CSP) plants by increasing the thermal to electric conversion efficiency from around 35% using high-temperature steam Rankine systems to above 45% depending on the cycle configuration. These systems are the most likely path toward achieving the Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE) SunShot targets for CSP tower thermal to electric conversion efficiency above 50% with dry cooling to air at 40 °C and a power block cost of less than 900 $/kWe. Many studies have been conducted to optimize the performance of various sCO2 Brayton cycle configurations in order to achieve high efficiency, and a few have accounted for drivers of cost such as equipment size in the optimization, but complete techno-economic optimization has not been feasible because there are no validated models relating component performance and cost.

Reasonably accurate component cost models exist from several sources for conventional equipment including turbines, compressors, and heat exchangers for use in rough order of magnitude cost estimates when assembling a system of conventional equipment. However, cost data from fabricated equipment relevant to sCO2 Brayton cycles is very limited in terms of both supplier variety and performance level with most existing data in the range of 1 MWe power cycles or smaller systems, a single completed system around 7 MWe by Echogen Power Systems, and numerous ROM estimates based on preliminary designs of equipment for 10 MWe systems. This data is highly proprietary as the publication of individual data by any single supplier would damage their market position by potentially allowing other vendors to undercut their stated price rather than competing on reduced manufacturing costs.

This paper describes one approach to develop component cost models in order to enable the techno-economic optimization activities needed to guide further research and development while protecting commercially proprietary information from individual vendors. Existing cost models were taken from literature for each major component used in different sCO2 Brayton cycle configurations and adjusted for their magnitude to fit the limited vendor cost data and estimates available. A mean fit curve was developed for each component and used to calculate updated cost comparisons between previously-reviewed sCO2 Brayton cycle configurations for CSP applications including simple recuperated, recompression, cascaded, and mixed-gas combined bifurcation with intercooling cycles. These fitting curves represent an average of the assembled vendor data without revealing any individual vendor cost, and maintain the scaling behavior with performance expected from similar equipment found in literature.
Volume Element Model for Modeling, Simulation, and Optimization of Parabolic Trough Solar Collectors
Authors: Sensoy Tugba S. , Yang Sam , Ordonez Juan C.
Published: August 2017

In this paper we present a dynamic three-dimensional volume element model (VEM) of a parabolic trough solar collector (PTC) comprising an outer glass cover, annular space, absorber tube, and heat transfer fluid. The spatial domain in the VEM is discretized with lumped control volumes (i.e., volume elements) in cylindrical coordinates according to the predefined collector geometry; therefore, the spatial dependency of the model is taken into account without the need to solve partial differential equations. The proposed model combines principles of thermodynamics and heat transfer, along with empirical heat transfer correlations, to simplify the modeling and expedite the computations. The resulting system of ordinary differential equations is integrated in time, yielding temperature fields which can be visualized and assessed with scientific visualization tools. In addition to the mathematical formulation, we present the model validation using the experimental data provided in the literature, and conduct two simple case studies to investigate the collector performance as a function of annulus pressure for different gases as well as its dynamic behavior throughout a sunny day. The proposed model also exhibits computational advantages over conventional PTC models-the model has been written in Fortran with parallel computing capabilities. In summary, we elaborate the unique features of the proposed model coupled with enhanced computational characteristics, and demonstrate its suitability for future simulation and optimization of parabolic trough solar collectors.
Wind Turbine Drivetrain Test Bench Capability to Replicate Design Loads: Part II — Case Study of a Multi-MW Drivetrain
Authors: Giguère Philippe , Wagner John R.
Published: August 2017

The systematic evaluation of wind turbine drivetrains using hardware-in-the-loop strategies (previously presented in Part I) is demonstrated using a state-of-the-art multi-MW drivetrain design and a 7.5-MW test bench. The test bench has the capability to apply both torque and non-torque loads to the electro-mechanical drivetrain. The proposed method to evaluate the capability of a test bench to impose the loads of interest uses design loads of the drivetrain and the test bench load application unit limits as inputs. The design loads are defined by stochastic time series of the longitudinal, lateral, and vertical forces as well as the yawing and nodding bending moments that the load application unit can concurrently apply to the drivetrain (i.e., combined loading). A total of 14 time series sets are considered to capture the minimum and maximum values of the longitudinal, lateral, vertical, and resultant forces as well as the yawing, nodding, and resultant moments. These time series are processed individually to calculate two metrics: the coverage and the capability ratio of the test bench. The former is a percentage of the time series that be applied by the test bench, and the latter indicates an excess (or deficit) in load application capability as compared with the selected design loads. The results are presented and interpreted using the previously described methodology. The findings suggest a good match between test bench capability and the loads of interest in general, and also points to challenges. These discoveries establish a basis for the experimental verification and the development of compensation methods to enhance test bench capabilities.
Evaluation of Heliostat Standby Aiming Strategies to Reduce Avian Flux Hazards and Impacts on Operational Performance
Authors: Ho Clifford K. , Wendelin Timothy , Horstman Luke
Published: August 2017

This paper presents a study of alternative heliostat standby aiming strategies and their impact on avian flux hazards and operational performance of a concentrating solar power plant. A mathematical model was developed that predicts the bird-feather temperature as a function of solar irradiance, thermal emittance, convection, and thermal properties of the feather. The irradiance distribution in the airspace above the Ivanpah Unit 2 heliostat field was simulated using a ray-trace model for two different times of the day, four days of the year, and nine different standby aiming strategies. The impact of the alternative aiming strategies on operational performance was assessed by comparing the heliostat slew times from standby position to the receiver for the different aiming strategies. Increased slew times increased a proxy start-up time that reduced the simulated annual energy production. Results showed that spreading the radial aim points around the receiver to a distance of ∼150 m or greater reduced the hazardous exposure times that the feather temperature exceeded the hazard metric of 160 °C. The hazardous exposure times were reduced by ∼23% and 90% at a radial spread of aim points extending to 150 m and 250 m, respectively, but the simulated annual energy production decreased as a result of increased slew times. Single point-focus aiming strategies were also evaluated, but these strategies increased the exposure hazard relative to other aiming strategies.
High dislocation density–induced large ductility in deformed and partitioned steels
Authors: He B. B. , Hu B. , Yen H. W. , Cheng G. J. , Wang Z. K. , Luo H. W. , Huang M. X.
Published: August 2017

A ductile steel shows its strength

Many industrial applications require materials to have high strength while remaining pliable, or ductile. However, the microstructure that increases strength tends to reduce ductility. He
et al.
used a processing mechanism to create a “forest” of line defects in manganese steel. This deformed and partitioned steel was produced by cold-rolling and low-temperature annealing and contained a dislocation network that improved both strength and ductility.

Science
, this issue p.
1029
Draft Genome Sequence of
Pacificimonas aurantium
Type Strain JLT2012, Isolated from the Seawater of the Pacific Ocean
Authors: Tang Guangrong , Cui Rong , Tian Yu , Lin Xiaopei
Published: August 2017

Type strain JLT2012 was isolated from the southeastern Pacific. Here, we report the draft genome sequence and the initial findings from a preliminary analysis of strain JLT2012, which represents a novel species and should be classified in the existing genus
Pacificimonas
.
Draft Genome Sequences of 10 Environmental Pseudomonas aeruginosa Strains Isolated from Soils, Sediments, and Waters
Authors: Shrestha Shailab D. , Guttman David S. , Perron Gabriel G.
Published: August 2017

Pseudomonas aeruginosa
is an important opportunistic pathogen that has the ability to grow in a range of environmental niches. Here, we report the draft genome sequences of 10 environmental strains of the bacterium isolated from soils, sediments, and waters in various locations in North America and South Africa.
Complete Genome Sequence of the Yogurt Isolate Lactobacillus delbrueckii subsp.
bulgaricus
ACA-DC 87
Authors: Alexandraki Voula , Kazou Maria , Pot Bruno , Tsakalidou Effie , Papadimitriou Konstantinos
Published: August 2017

Lactobacillus delbrueckii
subsp.
bulgaricus
is widely used in the production of yogurt and cheese. In this study, we present the complete genome sequence of
L. delbrueckii
subsp.
bulgaricus
ACA-DC 87 isolated from traditional Greek yogurt. Whole-genome analysis may reveal desirable technological traits of the strain for dairy fermentations.
Draft Genome Sequence of the Anoxygenic Phototrophic Bacterium Phaeospirillum fulvum MGU-K5
Authors: Ivanovsky Ruslan N. , Keppen Olga I. , Lebedeva Natalia N. , Beletsky Aleksey V. , Mardanov Andrey V. , Grouzdev Denis S.
Published: August 2017

Phaeospirillum fulvum
MGU-K5 is an anoxygenic, purple, photoheterotrophic, nonsulfur alphaproteobacterium. Unlike most purple nonsulfur bacteria, MGU-K5 is unable to grow aerobically under chemoorganotrophic conditions. Here, we present the draft genome sequence of
P. fulvum
to provide insights into its physiology.
Complete Genome Sequence of Vitreoscilla filiformis (ATCC 15551), Used as a Cosmetic Ingredient
Authors: Contreras Sandy , Sagory-Zalkind Pierre , Blanquart Hélène , Iltis Agnès , Morand Stanislas
Published: August 2017

We report the first complete genome sequence of a
Vitreoscilla filiformis
strain (ATCC 15551) that is used in the cosmetic industry as
Vitreoscilla
ferment. The assembled genome consisted of one chromosome and two plasmids. These data will provide valuable information and important insights into the physiology of this filamentous organism.