This paper introduces a novel type of direct-drive electric generator, suitable for producing high-power at low rpm in wind applications. The proposed patented design eliminates the magnetic core based on the concept of circular flux and characteristics of Halbach Array. By using circular flux crossing through patented Folded Electromagnetic Coils (FECs) on the stator, an optimal design with maximum use of space will be gained. Furthermore, through special configuration of diametric and axial magnets on the rotor, a pattern of circular flux can be produced, which is magnified only on the side of the stator (where needed), based on characteristics of the Halbach array. By using such design, the need for using magnets on both sides of armature windings (devised in certain designs such as the Yokeless and Segmented Armature (YASA) topology), will be eliminated, resulting in further reduction of the magnetic materials in the machine design. In the paper, we show how the proposed design results in better no-load voltage per kg by a factor of 1.52 when compared to a YASA design of the same physical size. Furthermore, we show how our calculations are based on experimental results verified through tests on a prototype of the proposed design.

Islanded, renewably powered microgrids require energy storage or emergency generation to overcome intermittency. Batteries and fossil fuel generators have traditionally filled these roles. However, liquid air energy storage (LAES) is a promising alternative. Using power in excess of immediate demand, a LAES system can liquefy and cryogenically store ambient air. When renewable generation abates, the liquid air can be expanded through a turbine to provide power to the microgrid. This study explores energy recovery from a dual Stirling cycle LAES system. Liquid air is generated by a commercial Stirling cryocooler and stored in a vacuum dewar. A second Stirling engine utilizes the temperature difference between the liquid air and surroundings to run a small electric generator. This paper focuses on energy recovery from the cryogenic liquid air through the Stirling engine using a series of experiments. Liquid air volume as a function of time and power for varying loads were measured and used to quantify the energy recovered from the stored liquid air. Energy efficiency is calculated and recommendations for design improvements are presented. Follow-on work will include design and operation of an updated dual-Stirling LAES system. This work is part of a larger effort to determine the feasibility of different energy storage methods for small, mobile applications as well as fixed infrastructure energy storage systems.

Our recent progress on studying wave interaction with a lift-type rotor is discussed in this paper. The particular focus is on characterization of the rotor’s unidirectional responsiveness in waves. The rotor consists of six hydrofoil blades in two sets. One blade set has three blades laid out as a vertical-axis wind turbine of the Darrieus type. The other blade set has three blades configured like a Wells turbine. In combination, the formed rotor can be driven by flows in any direction to perform unidirectional rotation about its vertically mounted shaft. This unidirectional responsiveness of the rotor also holds in waves, making the rotor a valuable device for wave energy conversion. For parametric study of the rotor, hydrofoil blades using different cross sectional profiles and chord lengths have been employed to configure the rotor. The rotor was then tested in a wave flume under various wave conditions in a freewheeling mode. Experimental results were analyzed and discussed. The yielded research findings will greatly enhance the fundamental understanding on the rotor performance in waves, and effectively guide the prototype rotor development for practical applications.

Numerical models for the evaluation of cryo-adsorbent based hydrogen storage systems for fuel cell vehicles were developed and validated against experimental data. These models simultaneously solve the conservation equations for heat, mass, and momentum together with the equations for the adsorbent thermodynamics. The models also use real gas thermodynamic properties for hydrogen. Model predictions were compared to data for charging and discharging both MOF-5™ and activated carbon systems. Applications of the model include detailed finite element analysis simulations as well as full vehicle-level system analyses. The present work provides an overview of the compacted adsorbent MOF-5™ storage prototype system, as well as a detailed computational analysis and its validation using 2-liter prototype test system. The results of these validated computational analyses are then projected to a full scale vehicle system, based on an 80 KW fuel cell with a 20 kW battery. This work is part of the Hydrogen Storage Engineering Center of Excellence (HSECoE), which brings materials development and hydrogen storage technology efforts address onboard hydrogen storage in light duty vehicle applications. The HSECoE spans the design space of the vehicle requirements, balance of plant requirements, storage system components, and materials engineering. Theoretical, computational, and experimental efforts are combined to evaluate, design, analyze, and scale potential hydrogen storage systems and their supporting components against the Department of Energy (DOE) 2020 and Ultimate Technical Targets for Hydrogen Storage Systems for Light Duty Vehicles.

A supplemental main steam condenser cooling system is under development, which utilizes a phase change material (PCM). This PCM rejects heat to the cool atmosphere at night until it is fully frozen. The frozen PCM is available for condenser cooling during peak daytime electric demand. Three calcium chloride hexahydrate (CaCl 2 ·6H 2 O)-based PCMs were selected for development after being characterized using differential scanning calorimetry (DSC). Additives to minimize supercooling and phase separation have demonstrated good performance after long and short-term thermal cycling. Corrosion testing under both isothermal and cycling conditions was conducted to determine long-term compatibility between several common metals and the selected PCMs. Several metals were demonstrated to have acceptably low corrosion rates for long-term operation, despite continual immersion in the selected hydrated salts. A system optimization model was developed, which utilizes a 3D modeling approach called the Layered Thermal Resistance (LTR) model. This model efficiently models the nonlinear, transient solidification process by applying analytic equations to layers of PCM. Good agreement was found between this model and more traditional computational fluid dynamics (CFD) modeling. Next phases of the work includes prototype testing and a techno-economic analysis of the technology.

This paper describes a quantitative methodology to estimate the probability of blade failure modes resulting from typical wear mechanisms in nuclear turbines, which can be used to optimize maintenance. The approach used to model time and spatial dependence of wear mechanisms that affect blades involves the coupling of a Static Bayesian Network to a Dynamic Bayesian Network. This prototype model has been designed to use conditional and time dependent Weibull-like failure rates that can be computed from reliability data bases (failure times and modes, associated causes, row and blade part that failed) to quantify Markov matrixes contained within dynamic nodes. The model can be used to make inferences such as the most probable causes of failure in a row and blade part, and visualize the probability as a function of time. It can be also used to determine the riskier location given evidence such as failure mode or the wear mechanisms involved. Also, maintenance tasks acting over time dependent failure functions have been implemented to exemplify the effect of perfect and three kinds of imperfect actions and how they affect the mechanisms and failure mode evolution, given the conditional dependences among them.

Marine and hydrokinetic (MHK) energy resources with advantages such as predictability and less variability compared to other forms of renewable energies, have been drawing more interest in recent years. One important phase before commercialization of new MHK technologies is to conduct experimental testing and evaluate their performance in a real environment. In this work, a numerical computational fluid dynamics (CFD) method is used to study the fluid flow behavior within a designed water flume for MHK energy technologies. The water flume design parameters were given by the team collaborators at National Renewable Energy Laboratory (NREL) and Colorado School of Mines. The results from this simulation showed the flow characteristics within the test-section of the proposed water flume design. These results can be used for the follow on phases of this research that includes testing scaled MHK prototypes at different flow rates as well as optimizing either the water flume design to obtain more realistic flow characteristics within the test section or the MHK devices to obtain higher performance metrics at lower cost.

This paper addresses modeling, design, and experimental assessment of a Gamma type low-temperature differential free-piston Stirling engine. The most advanced third-order design analysis method is used to model, simulate and optimize the engine. Moreover, the paper provides an experimental parametric investigation of engine physical parameters and operating conditions on the engine performance. The experimental test results are presented for a model validation, which shows about a 5% to 10% difference in the simulation results. The aim of this study is to design a Stirling engine capable of harvesting low-temperature waste heat effectively and economically and convert it to power. The engine prototype is designed to increase the engine performance by eliminating the main losses occurred in conventional Kinematic engines. Thus, elastic diaphragm pistons are used in this prototype to eliminate the surface friction of the moving parts, the use of lubricant, and to provide appropriate seals. In addition, flat plate heat exchangers, linear flexure bearing, a stainless-steel regenerator and a polyurethane displacer are outlined as the main components of the engine. Experiments successfully confirm the design models for output power and efficiency. Furthermore, it is revealed that the displacer-to-piston natural frequency ratio is an important design point for free-piston Stirling engines and should be addressed in the design for optimum power output.

This paper aims at developing a mesoscale combustion based thermoelectric power generator as an alternate to the electrochemical batteries. Most of the micro and mesoscale combustors investigated till date are based on external fuel and air supply systems, which may not be beneficial for a practical system. The proposed design is a standalone system which makes use of the heat conducted through the combustor walls, as an energy source to evaporate the liquid fuel stored in a surrounding tank and supply the vaporized fuel to the combustor. The high momentum fuel (vapor) jet is designed to entrain the ambient air in appropriate proportion so as to form a combustible mixture. The partially mixed fuel/air mixture is fed to a mesoscale combustor and the flame is stabilized by facilitating hot gas recirculation regions. The heat conduction through the combustor walls is controlled by providing an air gap between two concentric, low thermal conductivity, ceramic tubes so as to transmit desirable amount of heat to the fuel tank. Note that the heat lost from the combustor, is recovered via increased enthalpy of the supplied fuel. The hot products then flow over the hot side of a thermoelectric module to generate electricity. The cold side of the module is maintained at relatively lower temperature and the rejected heat is used to boil the stored water. The prototype is designed to produce an electrical power output of 15 W with an overall efficiency of about 3% and endurance of 1 hour in a single fuel (and cold side water) refill. The paper presents detailed thermo-fluid and heat transfer analysis of the constituent components and evaluates the performance of the system.

A novel concept for shear flow driven gas compression that could enable next generation turbomachinery has been designed and experimentally demonstrated. In order to achieve this, a prototype proof-of-concept compliant foil-based bladeless turbo-compressor device was developed and used to conduct a gas compression parametric study. The principle underpinning the operation of this device is the conversion of shaft power into hydrodynamically generated pressure that occurs in the shear flow between a smooth rotating disk and a compliant surface. The present compliant foil bladeless turbocompressor (CFBT) is an evolutionary derivative of self-acting compliant foil bearings and seals, which operate in the hydrodynamic regime. Thus, as in these devices, the process of compression induced by shear flow is dominated by the balance between pressure and viscous forces, which are in turn enhanced and controlled by tribological effects arising between the shear layer and the deformable geometry of the compliant surface. The single shaft foil bearing based proof-of-concept CFBT presented is powered by a permanent magnet motor capable of reaching speeds up 360,000 rpm, and consists of two independent compression stages mounted on opposite ends of the shaft. Each compression stage consists of a smooth disk with the effective corresponding counterface of radii 7.6 mm < r < 14.1 mm, with one of each disk’s surfaces facing a four-pad compliant foil surface mounted on the housing. The nominal initial gap separating each of the disks from their corresponding compliant foils is nominally h 0 = 0.025 mm and 0.4 mm, respectively. In this configuration, air is entrained from opposite directions through axial intakes and turned 90° as it undergoes shear between the rotating disk and the compliant foil pads of each of the stages, inducing a net radially-oriented outward flow, which is then collected in the quasi-volute of the respective stage. The system is heavily instrumented, with each of the quasi-volutes fitted with thermocouples, pressure probes and a flow meter. An experimental parametric study was performed compressing standard temperature and pressure air for varying speeds up to 360,000 rpm. Performance curves reporting flow vs. pressure as well as compression power requirements vs. speed were obtained for the individual compression stages. The experimental results on the proof of concept turbocompressor are analyzed in the context of the theoretical foundations presented in a companion paper (Heshmat and Cordova, 2017), showing excellent correlation. It is anticipated that due to its simple bladeless geometry, application of this novel technology in conjunction with foil bearings will result in low cost, ultra-high speed, high efficiency, high specific power, miniaturized turbocompressors and high power density oil-free and maintenance-free machines, such as compressors, meso-scale gas turbines, or turbogenerators. Attractive applications for this technology range from military micro-UAV propulsion and portable power systems, to domestic combined heat and power (CHP) turboalternators and medical devices such as portable oxygen concentrators and CPAP (Continuous Positive Air Pressure) machines.

Ocean and wind energy require reliable, efficient electric conversion systems to be viable resources. Direct drive electric generators offer both benefits; however, it is difficult to generate the required torque at the low speeds typical of these resources. In this DOE sponsored project, ABB US Corporate Research partnered with Resolute Marine Energy (RME) and Texas A&M University to investigate the suitability of direct drive electric power generation for a paddle-type wave energy converter (WEC). This WEC provides high torque in a relatively chaotic, oscillating manner and requires a machine capable of handling high peak torques of approximately 40,000 N·m at speeds typically not exceeding 3 rpm. The baseline concept uses a hydraulic power take-off coupled with a generator and convertor; a direct drive electric solution may be beneficial. As a first step in designing a suitable direct drive generator for this application, we have begun with a smaller scale prototype targeting one tenth of the speed and torque, and we investigated a machine topology that may be promising in the operating regime of the full-scale machine. To this end, we designed and tested an integral generator and magnetic gear which is rated at 3,800 N·m at 30 rpm and completed a paper design for a machine of the required scale. This paper describes the mechanical design and testing of the prototype machine and provides some reflection on necessary design changes for the full-scale machine.

Clean gas turbine combustion research has gained popularity in power generation and propulsion industry in recent days. Present days, advanced efficient emission (NOx, CO and UHC) reduction combustion technologies are acknowledged for using the lean premixed combustion system. To support continuous development of eco-friendly combustion system, a 4 th generation dry low NOx prototype downscaled burner (designed and manufactured by Siemens Industrial Turbomachinery AB) has been researched experimentally and numerically. The research burner has multiple stages, which includes a central Pilot (named as RPL/Rich-Premixed Lean) stages, Pilot stage and Main stage. The RPL combustion chamber holds the primary flame, which produces the temperature and high concentration of radicals. The radicals and hot product is reached to the forward stagnation point of the Main flame anchoring point. Swirled reactant mixture is delivered to the Main combustion zone and a strong recirculation zone is developed. The recirculated product is moved to the Main flame root and ignites the fresh mixture. The Main flame was visualized by applying Chemiluminescence and 2D OH-PLIF imaging techniques. Emission measurement was performed to quantify the burner operability and emission competency. Burner stage fuel splits are varied and their effects on flame stability was monitored thoroughly. Computational fluid dynamic (CFD) analysis was performed to understand the flow field and compare the experimental results with numerical analysis. CFD simulation can help to identify the approximate NOx formation region and flame locations inside the burner. RPL flow and Pilot fuel split shows significant contribution towards flame stabilization as experienced from experiment and CFD. A high temperature B-type thermocouple was positioned at the liner exit to measure the exhaust gas temperature. Numerical calculation prediction and measured temperatures showed good qualitative agreement. From the present experimental and numerical research, it is evident that the downscaled prototype gas turbine burner demonstrates a wide flame stability for various operating condition. The fundamental physics behind the flame stabilization and flame dynamics were explored using numerical and experimental research.

This paper describes the design and testing of a high-efficiency turbo-generator for use in an Organic Rankine Cycles (ORC) with a power target of 30–100 kWe. The elegant yet simple design consists of a hermetically sealed, single piece rotor, with axial turbine and permanent magnet generator. The design employs compliant foil bearings (CFB), which eliminate the need for any external lubricates or dynamic seals and no contamination risk to the process fluid. A unique partial admission turbine concept is employed which provides better than 80% efficiency across a wide range of seasonal temperature variation, such as those occurring in northern latitudes, where summers can be hot (> 35°C) and humid and winters are extremely cold (< −20°C) and dry. We describe the design and prototype manufacturing as it pertains to micro and meso-scale turbines (< 100 kW) in terms of thermodynamic cycle considerations, turbine design, rotor-bearing dynamics, overall system design and scale-up considerations.

Electric generators and synchronous motors with static excitation use rotating slip rings (also known as collector rings) and stationary carbon brushes to transfer the field current from the stationary exciter to the rotating generator field. The carbon brushes experience wear from both mechanical friction and electrical contact with the rings. Therefore, the brushes need to be periodically inspected and replaced. This is often the most frequent maintenance activity for an electric generator. It is generally recognized that if brushes are not changed when worn down, this can result in a damaging condition called a flashover that will usually force the generator offline. Several collector flashovers were investigated to look for other common characteristics with the aim of reducing the risk of flashover occurrence and improving generator reliability. Some features of the generator collector brush holders were identified as significant contributors to collector flashovers and also to other, more common maintenance problems. Several brush holder designs were evaluated with regard to these features and also with regard to feedback received from operators. In addition, an in-house test rig was developed and used to compare multiple, existing brush holder designs and new prototype concepts for brush wear rate and current selectivity. This work led to a new brush holder design that addresses these concerns and has subsequently been successfully tested in a laboratory and at a customer site. That new brush holder design is being applied to both new units and as a retrofit to in-service aftermarket generators.

A prototype water-glycerol two tank storage system was designed to simulate the fluidic properties of a high temperature molten salt system while allowing for room temperature testing of a low cost, small scale pneumatically pumped thermal storage system for use in concentrated solar power (CSP) applications. Pressurized air is metered into a primary heat transfer fluid (HTF) storage tank; the airflow displaces the HTF through a 3D printed prototype thermoplate receiver and into a secondary storage tank to be dispatched in order to drive a heat engine during peak demand times. A microcontroller was programmed to use pulse-width modulation (PWM) to regulate air flow via an air solenoid. At a constant frequency of 10Hz, it was found that the lowest pressure drops and the slowest flowrates across the receiver occurred at low duty cycles of 15% and 20% and low inlet air pressures of 124 and 207 kPa. However, the data also suggested the possibility of slug flow. Replacement equipment and design modifications are suggested for further analysis and high temperature experiments. Nevertheless, testing demonstrated the feasibility of pneumatic pumping for small systems.

An investigation on the central-pilot stage of a Siemens Industrial Turbomachinery 4 th Generation DLE prototype test burner has been performed to understand the emission performance and operability. The core section, which is defined as RPL (Rich premixed lean) plays an important role for full burner combustion operation by stabilizing the main and pilot flames at different operating condition. Optimal fuel-air flow through the RPL is critical for multiple stages mixing and main flame anchoring. Heat and radical production from the central stage provides the ignition source and required heat for burning the main flame downstream of the RPL section. Surrounding the RPL outside wall cooling air has been blown through an annular passage. The cooling air protects the RPL wall from overheating and provides the oxygen source for the secondary combustion downstream of the RPL. At rich operation unburned hydrocarbon/radicals can pass the RPL and burns by the co-flow air entrainment. To determine the flame stabilization and operability, an atmospheric pressure test has been accomplished using methane as a fuel. Primary flame zone can be identified by a thermocouple placed outside the RPL wall and secondary combustion zone at the exit has been examined by chemiluminescence imaging. Emission measurement and LBO (Lean blow out) limits have been determined for different equivalence ratios from 1.8 to LBO limit. Co-flow air temperature was changed from 303 K to 573 K to evaluate the secondary combustion and RPL wall heat transfer effect on flame stability/emission. It is found that equivalence ratio has strong effect on the RPL flame stabilization (primary/secondary flame). Emissions/radical generation were also influenced by the chemical reaction inside the RPL. It can be noticed that co-flow air temperature has a significant role on emission, LBO and flame stabilization for the central-pilot stage burner due to the heat loss from the flame zone and RPL wall. A chemical kinetic network (Chemkin™) and CFD modelling approaches (Fluent) are employed to understand in detail the chemical kinetics, heat transfer effect and flow field inside the RPL (combustion and heat loss inside and emission capability). Experiment shows that the low CO and NOx levels can be achieved at lean and rich condition due to lower flame temperature. Present experimental results by changing equivalence ratio, residence time and co-flow temperature, creates a complete map for the RPL combustion, which is key input for full 4 th Generation DLE burner design.

A new concept of Thermal Energy Storage (TES) system based on current available technologies is being developed under the framework of the Masdar Institute (MI) and Massachusetts Institute of Technology (MIT) collaborative Flagship Program. The key feature of this concept lies on concentrating sun light directly on the molten salt storage tank, avoiding the necessity of pumping the salts to the top of a tower thereby avoiding thermal losses and pumping and electric tracing needs inherent in most conventional CSP plants. This Concentrated Solar Power on Demand (CSPonD) volumetric receiver/TES unit prototype will be tested in the existing MI heliostat field and beam down tower in Abu Dhabi (UAE) which will collect and redirect solar energy to an upwards-facing final optical element (FOE). These energy will be concentrated on the aperture of the prototype designed to store 400 kWh of energy allowing 16 hours of continuous production after sunset using Solar Salt (60%NaNO 3 + 40%KNO 3 ) as storage material. The tank is divided in two volumes: one cold in the bottom region, where Solar Salt is at 250 °C and another hot on the upper region, at 550 °C. A moving divider plate with active control separates both volumes. The plate includes mixing enhancement features to help with convection on the hot volume of salts. It’s expected that results will demonstrate the technical feasibility and economic viability of this concept allowing its scale up at commercial size.

Westinghouse Electric Company and Tranter Inc. are collaborating to develop the modular, low-pressure horizontal shell and plate feedwater heater (SPFWH™) heat exchanger product. This design utilizes easily removable modules of welded heat transfer plates within a pressure vessel instead of traditional tubes as the pressure boundary and heat transfer interface between the steam and feedwater. Design advantages include improved long-term performance, inspection and maintenance access. Each SPFWH™ heat exchanger will be designed to meet all plant-specific requirements and is ASME Section VIII compliant. A prototype SPFWH™ heat exchanger design (herein called the prototype or test unit) was fabricated and tested to validate the functionality of the design features and benchmark the correlations used to predict the performance. The test was performed in the Tranter Inc. laboratory facility using full temperature and pressure steam conditions over a broad operating range typical of low pressure feedwater heaters. Heat transfer coefficient characteristics have been evaluated and the prototype test data shows good agreement with established empirical correlations and other industry research. These results indicate that the SPFWH™ heat exchanger design is a viable alternative to a shell-and-tube type heat exchanger due to the performance, compactness, modularity, and robustness of the new design.

A gasketed plate heat exchanger that has a seal pressure of 6.5 MPa or more has been developed. This heat exchanger can be applied to heat exchangers (design temperature: 182°C, design pressure: 3.43 MPa) for the residual heat removal (RHR) systems of boiling water reactors (BWR). Practical use of gasketed plate heat exchangers under the condition of higher temperature and higher pressure has been achieved by developing a high-pressure-retaining plate and frame, as well as a heat- and radiation-resistant gasket. Various element tests related to strength and performance were conducted in the process of this development. A verification test using a prototype heat exchanger was also conducted, and pressure resistance, heat resistance, radiation resistance, endurance against thermal transients, and heat transfer performance have been confirmed. As a result of this development, gasketed plate heat exchangers can be applied for use under the condition of higher temperature and higher pressure, and various effects such as lower system flow, smaller footprint, easier maintenance, and lower cost for weld inspection are expected, compared to conventional shell & tube heat exchangers.

As noted in a Summer 2007 EPRI Journal article entitled Running Dry At The Power Plant , “Securing sufficient supplies of fresh water for societal, industrial, and agricultural uses while protecting the natural environment is becoming increasingly difficult in many parts of the United States. Climate variability and change may exacerbate the situation through hotter weather and disrupted precipitation patterns that promote regional drought.” Currently, in the United States, thermoelectric power production accounts for approximately 39% of freshwater withdrawals and 3% of overall fresh water consumption. The Electric Power Research Institute, EPRI, as part of its Technology Innovation (TI) program, is collaborating with Johnson Controls to conduct a feasibility study comparing the performance of a water saving Thermosyphon Cooler Hybrid System (TCHS) with other heat rejection systems for power plant applications. The TCHS employs a sensible heat rejection device, a thermosyphon cooler (TSC) in conjunction with an evaporative heat rejection device, an open cooling tower, to satisfy the annual cooling requirements of a given power plant. By reducing the evaporative heat load, the TCHS can significantly reduce the annual water consumed for cooling while still maintaining peak power plant output on the hottest summer days. Operational details of the Thermosyphon Cooler Hybrid System are presented. Additionally an overview of the cooling system simulation program, based on an 8,760 hourly analysis, used in the feasibility study is discussed. Results comparing the water use and additional fan power requirements between power plants employing a traditional all evaporative system and the TCHS are discussed for two different climatic locations. The concept of incorporating the cost of water, cost of power, the current plant operating conditions, and the current ambient dry bulb temperature into the TSC fan control strategy are also explored. The simulation program performance model is currently being validated with testing of a 1MW prototype TCHS at the Water Research Center near Cartersville, GA. Finally, a conceptual design for a power plant scale TCHS is presented.