bluuebunny/crossref_metadata_2025 huggingface dataset:
Out-of-Lab Solar Photocatalytic Hydrogen Production in the Presence of Methanol Employing the Solar Concentrator SoCRatus
Authors: Wullenkord Michael , Jung Christian , Sattler Christian
Published: November 2016

Hydrogen production from water via efficient solar based photocatalytic or photoelectrochemical processes could play a major role in the energy regimes of the future. Here, intermittent solar energy is converted into the promising energy vector hydrogen for later carbon free use on demand. Although much effort has been made in the last years photocatalytic/photoelectrochemical systems with acceptable solar-to-hydrogen-efficiency for economic operation could not be introduced, yet. Within the project DuaSol simultaneous hydrogen generation and water treatment in a photoelectrochemical tandem cell is investigated as a potentially economic process. Organic contaminants are oxidised by interaction with photo-generated electron holes at the photoanode. Produced protons approach the photocathode to react with photo-generated electrons to form hydrogen. Experiments with photocatalytic systems employing DLR’s 2-axis tracking modified linear Fresnel solar concentrator SoCRatus (Solar Concentrator with a Rectangular Flat Focus) were carried out in order to set a reference for the further experimental assessment. Diverse photocatalysts based on titanium dioxide (TiO2) and tin niobate (SnNb2O6) were tested in a planar suspension reactor with two parallel reaction chambers irradiated in the focal plane of the SoCRatus. The evolution of hydrogen was measured and correlated to the overall solar input and to spectral quantities. Three temperature levels, mostly 25°C, 37.5°C, and 50°C, were considered and maintained during the experiments in order to study temperature related effects. Methanol as a sacrificial reagent or rather a model substance for organic contaminants formed part of the suspension with a volume fraction of 10% at 20°C. As expected regarding the band gaps of the considered TiO2 based photocatalysts the hydrogen output is predominately affected by the applied UV portion. The UV fraction of solar light varies significantly in the course of a day and coherently also the production of hydrogen. Hydrogen was generated at rates as high as 7386 μmol/h. Regarding the SnNb2O6 based photocatalysts the generation of hydrogen rather corresponds with the irradiance in the visible range. The solar-to-hydrogen efficiency as well as the photon efficiency in different spectral ranges could be calculated. In addition an extensive analysis of the uncertainty of experimental results was conducted. It could be confirmed that the SoCRatus is an excellent platform for the experimental assessment of photocatalytic / photoelectro-chemical systems under practical conditions.
Solar Net Metering Increases Utility-Supplier Profit Margins
Authors: Flarend Richard
Published: November 2016

Net metering is an incentive that is essential to most solar photovoltaic systems. Recently the burden placed upon local utilities is an issue some regulators have been asked to address. This research uses actual 2013 and 2014 solar production data from nearly 200 sites, wholesale electricity day-ahead pricing data, and utility-wide demand data. This is all analyzed by the hour for two full years for a western Pennsylvania based utility and an eastern Pennsylvania based utility and their wholesale generators. Results show electricity is 15% more valuable when solar PV systems are generating power and feeding the grid during good weather conditions than at night or cloudy days when solar customers get energy back from the grid.

Solar energy generation is highly predictable in the day-ahead market, and leads to suppression in market prices for electricity. Thus to reveal the true impact of this market suppression, an increased solar renewable portfolio standard (RPS) fraction of 0.2 to 10% was simulated. This caused a decrease in demand resulting in a corresponding reduction in the price of electricity yielding savings to the utility. The maximum rate of increase and decrease in the utility-wide load did not change significantly until the solar RPS exceeded 5%. Additionally, the demand for electricity was reduced during the highest load hours of the year that corresponded to the most expensive hours of the year. The minimum base-load of the year was decreased substantially for solar RPS of 5% or greater and the base load reaches zero for solar RPS over 10%.

From the data of these two years, it is demonstrated that an increased use of solar energy would lead to savings that are larger than the loss in revenue due to having fewer traditional non-solar customers. Thus electricity suppliers and utilities stand to have both higher profits and higher profit margins when customers adopt net-metered solar energy compared to the non-adoption of solar energy.
Volumetric Particle Receivers for Increased Light Trapping and Heating
Authors: Ho Clifford K. , Mills Brantley , Christian Joshua M.
Published: November 2016

This paper evaluates novel particle release patterns for high-temperature falling particle receivers. Spatial release patterns resembling triangular and square waves are investigated and compared to the conventional straight-line particle release. A design of experiments was developed, and a simulation matrix was developed that investigated three two-level factors: amplitude, wavelength, and wave type. Results show that the wave-like patterns increased both the particle temperature rise and thermal efficiency of the receiver relative to the straight-line particle release. Larger amplitudes and smaller wavelengths increased the performance by creating a volumetric heating effect that increased light absorption and reduced heat loss. Experiments are also being designed to investigate the hydraulic and thermal performance of these new particle release configurations.
Informing Low Carbon HVAC Systems Modelling and Design, Using a Global Sensitivity Analysis Framework
Authors: Chatzopoulou Maria-Anna , Keirstead James , Fisk David , Markides Christos N.
Published: November 2016

Buildings are widely recognised as key contributors to global energy use and emissions. Approximately 50% of the energy consumption of the non-domestic buildings is due to Heating Ventilation and Air-Conditioning (HVAC) systems. Therefore, there is great potential in improving the energy performance of buildings, by investigating the deployment of low-carbon HVAC technologies. HVAC system selection is usually performed in early design stages, when there is high uncertainty associated with the system’s requirements. To deal with these uncertainties, Global Sensitivity Analysis (GSA) can be deployed. GSA can systematically identify the most important variables, in terms of their impact on system performance. This study considers the usefulness of GSA in designing HVAC systems with an office building case study. GSA identifies the heat pump and heat recovery efficiencies as the most significant uncertain parameters. These, account for more than 90% of the observed variation in the energy consumption. Additionally, the results reveal that by selecting a heat pump capacity at 80% of the potential annual peak load point estimate, there is 95% probability for the system to satisfy the peak demand at any given hour. The analysis demonstrates the potential of GSA in informing the design of novel HVAC and power generation technologies.
Mapping Energy Storage Physics to Application Economics
Authors: Berry Irene , Merfeld Glen , Riley Patrick
Published: November 2016

The success of grid scale energy storage hinges on our ability to solve real problems economically. By mapping energy storage physics to application economics, this paper offers a technology neutral look at how energy storage can solve real problems.

A value analytics methodology was developed that combines the physics of energy storage, application power commands, and market-specific economic constructs. This approach evaluates and optimizes the value of energy storage for specific projects by providing insight into the tradeoffs between the lifecycle costs and revenues. These analytics calculate the net present value (NPV) and internal rate of return (IRR) of select energy storage assets, markets, and applications by considering these key factors:

• Duty profiles and control strategies

• Market economics and revenue streams

• Asset performance at cell, module, and system levels

• Price projections including balance of plant (BOP)

• Cycle and calendar life

• Project length and financing terms

The value analytics methodology combines three model streams. The first takes a high fidelity load profile (for example, the power output of a building, wind turbine, or solar farm), imposes a specific control strategy, and calculates revenue streams in a selected market. From this first model stream a storage power command is generated. This power command is fed into the second model stream that calculates the required size and price of a given storage type. Finally, a third model stream uses empirical life models to calculate degradation rates, replacement intervals, and maintenance costs. These are rolled up into a project specific financial analysis that forecasts project NPV and IRR.

The underlying engine for this methodology is a large performance and price database of over 100 commercial and emerging energy storage assets that spans a wide range of technologies from ultracapacitors and flywheels to lead acid and lithium-ion batteries. The physics based performance of each asset is captured as an equivalent circuit model. These models are exercised to create performance envelops that describe the rate dependent power capability as a function of the type, amount, and age of installed storage.

The energy storage value analytics described in this paper can be used to test key sensitivities. This methodology has been applied to standalone energy storage systems as well as the combination of energy storage with renewables and distributed power generation. As shown, the methodology is relevant for an even wider range of applications. Several solution maps will be shared that reveal, by market segment, the energy storage type, amount, and application that create the greatest customer value. This type of informed design and dispatch will solve real problems, create new value streams, and open new markets for grid scale energy storage.
Operation of a Porous Membrane Photobioreactor
Authors: Anderson Gary A. , Katuwal Sarmila , Kommareddy Anil , Gent Stephen
Published: November 2016

A unique photobioreactor (PBR) constructed with acrylic sheet was used to grow S. Leopoliensis in 3.36 litters of Scully’s growth media. The PBR width was 51mm with a 273mm length and a growth media depth of 271mm. One of the PBR unique features was that it used a plenum and a porous membrane to inject air enriched with carbon dioxide into the growth medium. The HDPE (high-density polyethylene sintered beads) porous membrane served as the barrier between the reactor volume and the mixing plenum of the PBR. The air bubbled up through the porous membrane into the reactor volume with the growth medium mixing the contents of the reactor volume and transfer oxygen and carbon dioxide between the growth media and the bubbles. The second unique feature of the PBR is that it incorporated light guides in the design. The light guides were acrylic rods 9.5mm in diameter and a length projecting into the reactor volume of 38.1mm. The guides did not touch the opposite PBR wall. The light guides were abraded with sand paper on the outer to enhance light transfer from the guide to the growth medium. There were eight rows of light guides on each of the two PBR walls that were 273mm in length. Each row consisted of eight light guides space 34.1mm apart and 17.1mm from the side (short) walls of the PBR. Light was provided by two LED panels with 384 LED lights on each panel. The light from the panels had a wavelength of 650nm. The Light guides protruded through the PBR wall and light from the LED panels entered the light guide ends or transferred through the wall directly into the PBR reactor volume. The light guide ends occupied approximately 16% of the PBR wall area lit by the LED panels. The PBR produced 7.1g per litter of algal biomass in a 14 day growth cycle which encompassed a 3 day lag phase. The light guides disrupted the bubble flow pattern not allowing an obvious riser and/or downcomer to develop in the reactor volume. The disrupted flow pattern enhanced mixing and gas transfer. The enhanced mixing rotated the algal cells from more to less areas of the reactor volume more often aiding photosynthesis in a manner similar to flashing lights.
Synthesis and Performance Evaluation of a Solid Electrolyte and Air Cathode for a Rechargeable Lithium-Air Battery
Authors: Das Susanta K. , Sarkar Abhijit
Published: November 2016

A tri-layered solid electrolyte and an oxygen permeable solid air cathode for lithium-air battery cells were synthesized in this investigation. Detailed fabrication procedures for solid electrolyte, air cathode and the assembly of real-world lithium-air battery cell are described. Fabrication of real-world lithium-air button cells was performed using the synthesized tri-layered solid electrolyte, an oxygen permeable air cathode, and a metallic lithium anode. The lithium-air button cells were tested under dry air with 0.1mA∼0.2mA discharge/charge current at different temperatures. It was found that interfacial contact resistances play an important role in Li-air battery cell performance. Experimental results suggested that the lack of robust interfacial contact among solid electrolyte, air cathode and lithium metal anode were the primary factors for the cell’s high internal resistances. It was also found that once the cell internal resistance issues were resolved, the discharge curve of the battery cell was much smoother and the cell was able to discharge at above 2.0V for up to 40 hours. It indicated that in order to have better performing lithium-air battery cell, interfacial contact resistances issue must be resolved very efficiently.
Electrohydrodynamic-Jet Deposition of Pt-Based Fuel Cell Catalysts
Authors: Hollinger Adam S. , Kenis Paul J. A.
Published: November 2016

Fuel cell electrodes are traditionally fabricated by hand-painting or spraying a catalyst ink onto a gas diffusion electrode or membrane. However, electrodes prepared via these techniques do not always have a uniform distribution of catalyst. Recently, electrohydrodynamic-jet (e-jet) printing has been developed as a method to deposit a variety of chemical and biological materials with excellent precision for various applications in electronics, biotechnology, and microelectro-mechanical systems. Here we demonstrate e-jet deposition of Pt-based fuel cell catalysts as a technique for achieving uniform catalyst distribution on microelectrodes. E-jet deposition is studied as a function of applied potential, and at 450 V, printed catalyst lines are very uniform at ∼10 μm in width. For electrode areas less than 1 mm2, deposition times are on the order of a few hours, which compares well with traditional hand-painting deposition times. Uniform catalyst distribution is important to reducing catalyst loading, and the deposition technique presented here shows significant possibility to produce electrodes with high uniformity.
Multi-Functional Electrolyte for Thermal Management of Lithium-Ion Batteries
Authors: Westhoff Kevin , Bandhauer Todd M.
Published: November 2016

The high thermal conduction resistances of lithium-ion batteries severely limits the effectiveness of conventional external thermal management systems. To remove heat from the insulated interior portions of the cell, a large temperature difference is required across the cell, and the center of the electrode stack can exceed the thermal runaway onset temperature even under normal cycling conditions. One potential solution is to remove heat locally inside the cell by evaporating a volatile component of the electrolyte. In this system, a high vapor pressure co-solvent evaporates at a low temperature prior to triggering thermal runaway. The vapor generated is transported to the skin of the cell, where it is condensed and transported back to the internal portion of the cell via surface tension forces. For this system to function, a co-solvent that has a boiling point below the thermal runaway onset temperature must also allow the cell to function under normal operating conditions. Low boiling point hydrofluoroethers (HFE) were first used by Arai to reduce LIB electrolyte flash points, and have been proven to be compatible with LIB chemistry. In the present study, HFE-7000 and ethyl methyl carbonate (EMC) 1:1 by volume are used to solvate 1.0 M LiTFSI to produce a candidate electrolyte for the proposed cooling system. Copper antimonide (Cu2Sb) and lithium iron phosphate (LiFePO4) are used in a full cell architecture with the candidate electrolyte in a custom electrolyte boiling facility. The facility enables direct viewing of the vapor generation within the full cell and characterizes the galvanostatic electrochemical performance. Test results show that the LFP/Cu2Sb cell is capable of operation even when a portion of the more volatile HFE-7000 is continuously evaporated.
Lightweight System Design Optimization of High Reliability Compact Air Independent PEMFC Power Systems for Aerial and Space Vehicles
Authors: Utz Robert , Wynne Bob , Ferguson Scott , Miller Mike , Sievers Bob , Song Ying
Published: November 2016

Demand has increased for high reliability mobile power systems for space and aerial vehicles in military, scientific, and commercial applications. Batteries have traditionally supplied power in these applications, but the desire to extend mission duration and expand vehicle capabilities would require an energy density increase that is difficult for batteries to achieve. The use of pure hydrogen and oxygen reactants with high efficiency membrane electrode assemblies and novel design concepts for the fuel cell stack bipolar plates and balance of plant (BOP) components has the potential to meet the desired system energy density.

This paper reviews subsystem and integrated testing of a lightweight PEM fuel cell system design for implementation into an aerial vehicle or space mission. The PEM fuel cell stack is designed for optimum efficiency at 2 kWe of power during standard operation with the capacity to provide over 5 kWe of continuous power. The passive flow control and water management subsystems provide the gas flow and humidification necessary for efficient operation and remove excess water produced by the stack under all operating regimes. Work is in progress to test the fully integrated system under expected operating conditions for potential lightweight PEMFC applications.
Robust PID Controller Design of a Solid Oxide Fuel Cell Gas Turbine
Authors: Emami Tooran , Tsai Alex , Tucker David
Published: November 2016

The performance of a 300 kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) pilot power plant simulator is evaluated by applying a set of robust Proportional Integral Derivative (PID) controllers that satisfy time delay and gain uncertainties of the SOFC-GT system. The actuators are a fuel valve (FV) that models the fuel cell thermal exhaust, and a cold-air (CA) valve which bypasses airflow rate from the fuel cell cathode. The robust PID controller results for the uncertain gains are presented first, followed by a design for uncertain time delays for both, FV and CA bypass valves. The final design incorporates the combined uncertain gain parameters with the time delay modeling of both actuators. This Multiple-Input Multiple-Output (MIMO) technique is beneficial to plants having a wide range of operation and a strong parameter interaction. The practical implementation is presented through simulation in the Matlab/Simulink environment.
Guidelines and Techniques for the Effective Control of Condensate Dissolved Oxygen in Steam Surface Condensers
Authors: Nightingale Darren M.
Published: November 2016

Low levels of dissolved oxygen for the condensate produced within steam surface condensers is highly desirable and an increasingly important performance metric related to the efficient operation of today’s power plants. The presence of high levels of dissolved oxygen within condensate can quickly contribute to; accelerated corrosion, the need for additional treatment requirements, increased maintenance, operational challenges and even early equipment failure.

Under certain operating conditions, steam surface condensers can be expected to produce condensate with defined and/or guaranteed levels of dissolved oxygen. However, these levels can only be achieved provided certain guidelines are maintained and operational limitations are not exceeded. This is not always the case.

This paper includes the latest design guidelines, operational limitations, general considerations and practical techniques for controlling and minimizing condensate dissolved oxygen levels produced within steam surface condensers.
Simulation and Validation of Hydrogen Production From Hydrogen Sulfide Pyrolysis
Authors: Commenges J. , El-Melih A. M. , Gupta A. K.
Published: November 2016

Pyrolysis of hydrogen sulfide has been studied for the treatment of hydrogen sulfide with simultaneous production of hydrogen and sulfur. This novel treatment method has been studied experimentally to provide fundamental information on the overall kinetic parameters. Numerical simulation of thermal pyrolysis of hydrogen sulfide is studied and the results obtained from the modified detailed chemical reaction mechanism are validated with the experimental data. The simulation results agreed favorably well with the experimental data for all examined temperatures up to 1473K. The thermal pyrolysis of hydrogen sulfide has been studied at residence times of 0.4 to 1.5 seconds and at temperatures of 1273–1473K. Experiments and simulations were also conducted using hydrogen sulfide diluted with 95% nitrogen using a heated quartz plug flow reactor to avoid any catalytic effects and excessive build of sulfur during experimentation. Numerically plug flow type reactor model was used to simulate the hydrogen sulfide thermal pyrolysis. The available mechanism in the literature provided poor match with the experimental data at temperatures higher than 1273 K. A modified mechanism is proposed and validated with our experimental data. Both simulations and experimental results showed increased conversion of H2S to hydrogen at increased temperatures. The increase in temperature reduced the residence time required to reach a steady asymptotic equilibrium value. Based on the qualitative agreement between simulations and experimental data under the investigated conditions, the reaction pathways as well as the most dominant reactions on hydrogen sulfide thermal pyrolysis are also presented. These results assist our efforts in the development of new technologies for hydrogen sulfide treatment.
Hydraulic Model Calibration of a Nuclear Plant Service Water System
Authors: Onat Erin A. , Walters Trey W. , Mobley David M. , Mead James J.
Published: November 2016

As pipe networks age, build-up [scaling] and corrosion decrease pipe diameter and increase pipe roughness, leading to significant pressure drops and lower flow rates. When modeling the hydraulics of these systems, calibrating the pipes to account for additional scaling and/or fouling can be vital to accurately predicting the hydraulic behavior of the system.

An automated, multi-variable goal-seeking software was used to calibrate the raw water system of the Duke McGuire Nuclear Station (MNS). This calibration process involved three phases. The first phase was the testing of the automated, multivariable goal-seeking software on a previously calibrated system. The second phase was the calibration of a partial data set. The third phase was the calibration of a complete data set. The automated goal-seeking software was found to have varying degrees of success in each phase.

At the conclusion of the calibration process, the partial data calibration of two parallel systems at MNS yielded average overall calibration accuracies of 2.1% and 1% for flow rates, and 1.2 psig (8.4 kPa-g) and 1.7 psig (11.9 kPa-g) for pressures. The complete data calibration of one of these systems at MNS yielded an average overall calibration accuracy of 2.3% for flow rates, and 1.4 psig (9.5 kPa-g) for pressures.
Integrating Isolation Valve Specifications Into Supercritical Power Plant Piping Design Specifications
Authors: Bose Rana
Published: November 2016

Clean and cost effective super critical power plants (SCPP) require “whistle clean” conditions, low emissions, low noise, higher velocities and flow rates. A majority of the specification packages for valves are developed by experienced piping engineers, assigned to EPCs and the valve section comprises a relatively small element where references to industrial standards like ASME B16.34 or ANSI B31.1 are made for design and stress parameters. The specific valve data sheets then provide some more information as to operating and boundary conditions for the specific valves. With the increasing prevalence of SCPP requirements, the current specifications made available by EPCs, make it somewhat enigmatic for valve designers and manufacturers to address the concerns of the power plant designers and engineers. This is in terms of valve bores, pressure drops, velocities, thermal fatigue, lowered valve weights and acceptable sound levels that are intrinsic to valve design, sizing and optimization. This paper presents some specific examples where flows, velocities, pipe ID and valve bore are compared to enable a better integration of piping characteristics in relationship to safe valve design, without unnecessarily over-specifying. In addition, suggestions have been made for an understanding of the relatively newer piping and valve materials for high temperature, high pressure applications, where alternative design methods would enable lower costs and greater resilience to thermal binding and fatigue.
Challenges in Meeting the Electricity Needs of South Africa
Authors: Roy-Aikins Joseph
Published: November 2016

The state-owned power utility, Eskom, generates about ninety five percent of the electricity produced in South Africa. Plans by the government of South Africa in the mid-nineteen nineties to restructure the electricity industry in the country prevented Eskom from embarking on capacity expansion activities when it was necessary. Load growth, as a result of economic growth and a national electrification programme, caused an erosion of the electricity reserve margin, which was quite massive in the early nineties. The large reserve margin then caused Eskom to reduce operating capacity by mothballing some generating plants and putting them in reserve storage.

The current situation is that the reserve margin has dropped to about 17,4 percent and a capacity expansion programme is underway. Though the apparent reserve margin is within the desired range, plant unavailability has diminished the reserve margin in real terms and this does not leave Eskom with much room for planned maintenance and a buffer to manage unplanned maintenance, the result being that plant incidents and technical problems cannot easily be absorbed within the power system to avoid interruption of supply. Also, the new environmental legislation does not help the situation, as it has the potential to shut down generating plants that do not meet the new emissions standard. In addition, there have been problems with the New Build Programme that caused a delay, of over three years, in the delivery of new power, and to compound the problem the Energy Regulator refused recently Eskom’s application for additional tariff increase, which was requested to enable the company provide the finances to cover the shortfall in funding for operational expenses and the New Build Programme. As such, Eskom faces many challenges in meeting its obligation to South Africa, and interventions are in place to manage the situation. In the short term, the key to generation sustainability is improved plant health, brought about by on-time maintenance and correctly-scoped and no-slip outages.

This paper presents an overview of the power situation in South Africa, explaining where the country has come from, the plan for long term security of supply, and the challenges faced by Eskom from the generation supply side in meeting the demand load in the short term. Trends in the performance indices indicative of plant health are examined and it is argued that executing planned plant maintenance will improve plant health and, hence, plant availability, which can bring about a turnaround in the short term power supply situation, as Eskom awaits new capacity from the New Build Programme.
Producing the World’s Finest Heat Engine
Authors: Koff Bernard L.
Published: November 2016

The gas turbine is the World’s most complex and versatile heat engine used worldwide for aircraft propulsion, marine applications and power generation. The technology evolution developed since Whittle’s first successful demonstration in 1937 is an exciting story of design innovation using many engineering disciplines. This paper, from a designer’s perspective, covers key design and manufacturing innovations that were developed to produce today’s engines with high specific power, efficiency and durability.
Simulation of Tethered Underwater Kites: Three Dimensional Trajectories for Power Generation
Authors: Ghasemi Amirmahdi , Olinger David J. , Tryggvason Gretar
Published: November 2016

In this paper, a numerical simulation of three dimensional motion of tether undersea kites (TUSK) for power generation is studied. TUSK systems consist of a rigid-winged kite, or glider, moving in an ocean current. One proposed concept uses a tethered kite which is connected by a flexible tether to a support structure with a generator on the ocean surface. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. A two-step projection method along with Open Multi-Processing (OpenMP) is employed to solve the flow equations. In order to track the rigid kite, an immersed boundary method is used. A NACA 0021 airfoil is used for the cross section shape of the kite, and the tension forces in the elastic tethers are modeled by a simple Hooke’s law. A grid refinement study has been carried out to ensure the independence of the numerical results on the grid mesh resolution. Also, the Reynolds number independency has been studied. PID control methods are used to adjust the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases to obtain desired kite trajectories. During the reel-out phase the kite moves in successive cross-current motions in a figure-8 pattern, the tether length increases and power is generated. During reel-in the kite motion is along the tether, and kite hydrodynamic forces are reduced so that net positive power is produced. Kite trajectories, hydrodynamic forces on the kite, kite tether tension and output power are determined and analyzed for a baseline TUSK simulation.
Dry Air Turbo-Compression Cooling
Authors: Bandhauer Todd M. , Garland Shane D.
Published: November 2016

Electric power plants in the U.S. dissipate 4.3 billion gallons of water per day into the atmosphere through evaporative cooling. As freshwater resources become constrained, it will be essential for power plants to transition from evaporative cooling to dry air cooling. One of the major problems associated with dry air cooling is the large size and associated cost of the dry air heat exchangers due to the large surface area required to overcome the low convective heat transfer coefficient of air. This study investigates using low-grade waste heat available in the combustion exhaust gases (106°C inlet, 86 MW dry waste heat available) of a 565 MW Natural Gas Combined Cycle Power Plant (NGCC) to drive a supplemental high efficiency turbo-compression cooling (TCC) system that decreases the size of the dry air heat exchangers. In this system, both a recuperative Rankine cycle and a supercritical system were considered to drive a turbo-compressor. The low-grade waste heat is supplied to a flue gas heat exchanger in either the recuperative Rankine or supercritical cycle to generate power that drives a vapor compression cycle to supply supplementary cooling for the power plant condenser water. For the TCC system to operate at a high COP, both the turbine and compressor must operate at isentropic efficiencies exceeding 80%. This high efficiency has been demonstrated for centrifugal turbomachines for a wide variety of applications over small ranges of specific speed: from 45 to 100 for turbines, and from 80 to 140 for compressors. In the present study, a wide range of possible fluids was considered to perform a complete system level thermodynamic analysis combined with a turbo-compressor dimensional scaling analysis. The results of the analyses show that the total UA required for both the primary dry air coolers and the dry air condensers in the supercritical TCC system with a COP of 2 is 26% less than the UA required for dry air cooling alone (from 150.7 to 111.5 MW K−1). As a result, using the supercritical TCC cooling system has the potential to reduce the overall cost of dry air cooling relative to the state of the art.
Dynamic Modeling and Experimental Analysis of Induced Draft Cooling Tower
Authors: Languri Ehsan M. , Patil Pallavi P. , Cunningham Glenn , Welch Albert , Loftis Anthony
Published: November 2016

A dynamic modeling study and field validation of a cooling tower serving a chiller are performed in this study to evaluate the efficiency of the cooling tower under various conditions. The dynamic model examines the losses and thermal capability of the cooling tower. The cooling tower used in this study for field validation is located at Cookeville, Tennessee, USA. The whole setup is fully instrumented to record the water and air flow rates and temperature; make-up water and blow down water flow rates; power consumption of pump; fan and chiller; weather data; etc. with one-hour resolution. The outcomes of the model are validated with the recorded data of the cooling tower and the test condition data. Furthermore, the effects of using Variable Frequency Drive (VFD) on the cooling tower’s fan power consumption are investigated. Additional recommendations on improving the energy efficiency and reducing the water losses are suggested based on the modeling data.
Effect of Novel Swirling Perforated Distributor on Fluid Dynamic Characteristics of Circulating Fluidized Bed Riser
Authors: Kalola M. G. , Dasar Mahesh , Shete K. P. , Patil R. S.
Published: November 2016

The present work is associated with Circulating Fluidized Bed (CFB) technology, related to the energy sector. The applications of CFB technology span across wide range of areas i.e. boiler, gasifier, combustor, dryer, etc. In the present paper, CFD simulations using ANSYS-Fluent 14.5 were performed to study the effect of novel swirling perforated distributor on fluid dynamics characteristics like pressure drop along the riser and distributor, suspension density variations along the riser of the Circulating Fluidized Bed (CFB). The simulation results were also used to compare qualitatively and quantitatively the dead-zone formations in the four corners of riser just above the distributor plate for swirl and normal distributor plates. The riser alongwith distributor was modeled using Pro-E 5.0, and it was meshed in ICEM CFD 14.5. Post processing simulations were performed using Fluent 14.5. 3D CFD simulations were performed on the CFB riser of cross section 0.15 m × 0.15 m and height 2.85 m. RNG k-ε model was used for turbulence modeling. Eulerian model with Syamlal-O’Brien phase interaction scheme was used to simulate the two phase flow (air + sand mixture flow). RNG k-ε model was used for turbulence modeling of the flow inside the riser. The RNG turbulence model has a calculation for effective viscosity. Modeling and simulations were performed for normal perforated distributor plate and results obtained were compared with available experimental data. In this way, after validation of computational results, further CFD simulations were performed for novel geometry of swirl distributor plate. It is observed that suspension density (particles’ concentration) was more in the middle and upper region of the riser in case of swirl distributor plate. However, pressure drop across the distributor plate increased in the case of novel swirl distributor plate. The objective of significant reduction in the dead-zone formation just above the normal distributor plate was achieved through novel swirl distributor, which in-turn is expected to increase particles’ participation in combustion which takes place in oxygen rich middle portion of CFB riser and subsequently increases heat transfer rate in the CFB riser.
Increasing Load Flexibility and Plant Dynamics of Thermal Power via the Implementation of Thermal Energy Storages
Authors: Steiner Peter , Schwaiger Karl , Haider Markus , Walter Heimo , Hämmerle Martin
Published: November 2016

The significant increase of fluctuating renewables leads to great challenges for the power grids and for the power suppliers: the flexibility of their power plants has to rise to be sufficiently competitive. For thermal power plants the integration of thermal energy storages (TES) seems to be a promising approach. Therefore the so called sandTES technology, an active particle based TES system, is introduced. In a second step it is used to demonstrate the flexibility enhancement via TES integration. Thereby a novel concept for integrating this type of TES is presented and afterwards discussed. The results give an overview about the chances and restrictions of this implementation concept.
Rapid H2 Purge With CO2 for Safer Plant Operations: Test Run Results
Authors: Warren Ted , Morris Larry , McPhearson John
Published: November 2016

Hydrogen cooled generators need to undergo carbon dioxide (CO2) purging before being placed into service and when taken offline. This process typically takes 4 to 12 hours, and can take as long as 36 hours in extreme cases, to fully and safely purge a generator. Reducing the volume of hydrogen gas in these generators is essential for reducing the risks of explosions. If these purge times could be shortened, improvements in safety, shorter outages, and increased production could be realized. This paper describes plant testing of a CO2 Fast Degas purging system for hydrogen cooled generators. Results from eight test runs at two different plants are presented in tabular and graphical form. Mean reduction from pure hydrogen to less than 4% hydrogen was 39.8 minutes, while maintaining CO2 temperatures above 80°F (27°C). This eliminates the possibility of CO2 freeze up, and reduces the stress on the piping and the detrimental effects on the generator from extreme temperature swings that occur when CO2 is de-pressurized. These rapid purge rates were accomplished while maintaining the generator pressure within a set range. In order to achieve the minimum purge time, it is critical that mixing of the two gases be minimized during the purge operation. By utilizing the slope of the graphs provided, the system was optimized to minimize purge times to reach safe levels. Tests were performed on both purging operations, replacing hydrogen with CO2 and replacing air with CO2. Samples to analyze the generator gas purity were taken from the vent line using multiple thermal conductivity purity instruments to assure accurate results. The system was tested in both automatic and semi-automatic modes of operation. The fast degas system was found to significantly reduce generator purge times, reducing down time, and improve operator efficiency, positively affecting the overall safety profile of the plant.
Design Optimization of T-Root Geometry of a Gas Engine HP Compressor Rotor Blade for Lifing the Blade Against Fretting Failure
Authors: Gowda Kumar K. , Ajit Prasad S. L. , Nagarajaiah Vinayaka
Published: November 2016

Stress Concentration Factor (SCF) is significant in machine elements as it gives rise to localised stresses which lead to peak stresses introducing cracks which propagate further and hence the component fails before the desired design life. Turbine blades are subjected to high centrifugal stresses and vibratory stresses in a Gas Engine HP Rotor. The vibratory stresses arise due to air wake flow excitations called Nozzle Passing Frequency (NPF). Hence, Turbomachinery industry calls for an optimum structurally rigid blade root geometry. An optimum blade root was defined, as a root with practical geometry, which when loaded returns the minimum fillet SCF. In the present work an approach has been done for design optimization of fillet stresses at sharp edges of T-root blade, optimization of platform dimensions, shank dimensions, root land dimensions and to ensure that stress distribution is uniformly spread along the filleted width of the root land on both sides of the blade, which otherwise will lead to crack initiation, propagation and hence, fretting failure at blade root lands. This may further lead to blade lift and effect on stage and overall gas engine failure over a period of cycles. Hence, a special attention is made on SCF of the T root -blade which fails and to guarantee for safe and reliable operation under all possible service conditions. Finite Element Analysis (FEA) is used to determine the fillet stresses and Peterson’s SCF chart is effectively utilized to modify the blade root. The root is modified due to the difficulty in manufacturing the butting surface of the tang which grips the blade to the disk crowns having small contact area. The blade height is suitably designed using Campbell diagram by ensuring the working frequency is well within 6e excitations for the specified operating speeds. Hence, increasing the life of the HP compressor blade.
Pool Boiling Heat Transfer Enhancement With Structured Surfaces
Authors: Dikici Birce , Al-Sukaini Basim Q. A.
Published: November 2016

With the increasing power of electronic devices in recent years, thermal management has become an obstacle in scaling down chip designs. Direct liquid cooling is a great option for heat dissipation from high powered electronic systems due to its ability to remove large amounts of heat [1–2].

The aim of this study is to investigate pool boiling performance of water under atmospheric pressure by using structured surfaces. Surfaces with rectangular channels, holes, and mushroom fins are manufactured and tested. The results showed that boiling heat transfer can be enhanced by macroscopically structured surfaces.

Heat transfer coefficient (h) enhancement ranged between 23–44% for structured surfaces compared to plain surface. Heat flux is varied in the range of 16–18kW/m2. The maximum enhancement in heat transfer coefficient is ranged between 39–44.4% measured by 405 holed surface compared to the plain surface. The measured excess temperature drops ranged between 12–34% for different surfaces compared to plain surface. The excess temperature dropped around 29–34% for 405-holed surface compared to the plain surface.

As the spacing between channels or holes is decreased, the heat transfer coefficient is increased. Base temperature measurements are carried out using an Infrared Camera. A digital camera was used to record pool boiling phenomena and evaluate bubble dynamics. The bubbles with holed surfaces and mushroomed surface observed to have almost spherical shape, while in plain and grooved surfaces they have an irregular shape.
Nash Equilibrium of a Retail Electricity Market With a High Penetration of Small Renewable Suppliers
Authors: Azad Saeed , Ghotbi Ehsan
Published: November 2016

Increasing the level of the competition, a worldwide trend in the evolution of electricity markets, has made game theory a notably popular approach to find the market equilibrium. This paper models a retail electricity market with a high penetration of renewable resources. Using game theory, the clearing electricity prices, as well as the optimum behavior of market participants are obtained. In this model, which is inspired by the “Energy Internet” concept, consumers play an active role in managing their load demands. This highly dynamic model allows us to analyze consumers’ reaction to price fluctuations. Spot pricing, which is employed here to model the electricity market, can make consumers react to the high electricity prices. This is particularly important in the demand side management, where consumers should modify their demand through financial incentives. Two types of active players are considered in this electricity market, small electricity suppliers and consumers. Electricity grid, while present in the market, only takes the responsibility to compensate for the deficiency of power from small and mid-size suppliers. The problem is formulated mathematically, subject to a number of local and global constraints to find the Nash equilibrium.
Fundamentals of a Babbitted Bearing Repair Assistant
Authors: Branagan L. A. , Hesler S. H.
Published: November 2016

Fluid film bearings provide critical support for the rotors in gas turbines, steam turbines, generators, exciters and other machines through the generation and support of a hydrodynamic film. Industrial bearings are lined with a babbitt material which serves as a sacrificial element during operation and may need to be refurbished depending on the past operating and maintenance history. After inspection, engineering judgment is typically used during a machine overhaul to determine whether a bearing requires refurbishment. This engineering judgment is developed through an understanding of the principals of bearing design, machine operation, machine monitoring and babbitt wear / damage characteristics. This paper describes the criteria to serve as a basis for a decision support tool relative to the refurbishment of a babbitted, fluid-film bearing. Those criteria start with key descriptors of any damage to the bearing and evaluate the remaining load capacity, repairability, bearing support, rotordynamics influence, journal conditions and pivot conditions. The descriptors focus on visual examinations of the condition of the babbitt and seek to be intuitive, yet remaining comprehensive; to this end a graphical interface is used where feasible.

Evaluations include specific load capacity calculations, determination of damage factors for the principal modes of babbitt damage and data from lookup tables whose input is based on experience. These evaluations are combined to provide the basis for the refurbishment decision. Scaling efforts are incorporated into the evaluations to allow their combination into a single bearing condition index. Initial experience suggests that discrete ranges of the bearing condition index are preferable to numerical value.

One goal of the tool is to allow use by inexperienced engineers as a support to their technical development. Another goal is to better document the decision process for particular bearings. The preliminary tool was applied to a cylindrical, radial bearing in a horizontal orientation and to a bumper thrust bearing. Initial results have confirmed the general strategy employed and have suggested areas requiring refinement.