Search

Electrohydrodynamic processing including electrospinning and electrospraying is suitable for depositing controllable structures in fiber or film form. In this work, the electrohydrodynamic approach was used to prepare poly(vinylidene fluoride)/polyaniline composite film. Scanning electron microscopic analysis was performed to show the morphology of the film on soft tissue paper. Self-poling of the film was found due to the high voltage application in the electrohydrodynamic process. The addition of polyaniline into PVDF improves the conductivity of the film significantly. Mechanoelectrical response of the film was demonstrated by measuring the open circuit voltage of the specimens under bending. The peak voltage generated is over 1.2 V due to the bending deformation of the film. The film has ultrafast response to the deformation. It is concluded that the film has multiple functions for mechanoelectrical energy conversion, vibration sensing, and structural integrity monitoring applications.

The thermodynamic performances of the two different integrated solar combined cycle (ISCC) systems are compared in this paper. Different from the previous comparison researches of ISCC systems based on different solar energy collecting technologies, the goal of this paper is to compare the integration characteristics of two different configurations of integrating concentrated solar energy into a gas turbine combined cycle (GTCC) system based on the same solar collector system. For the first kind of integrated solar gas-steam combined cycle system (ISCC1), the solar energy is introduced to the topping cycle of the gas-steam combined cycle system, while for the second kind of integrated solar gas-steam combined cycle system (ISCC2), the solar energy is introduced to the bottoming cycle of the GTCC system. The detailed system models are developed and their thermal performances are compared under different conditions. For ISCC1, the solar-to-electricity efficiency is higher than that of ISCC2 at the design condition when both the direct normal irradiation and ambient temperature are high due to more efficient energy conversion to electricity. However, the ISCC2 offers the advantages of higher solar-to-electricity efficiency and more solar power output when both the direct normal irradiation and ambient temperature are low. Two ISCC systems are good for energy saving, the ISCC1 consumes 4.412 × 108 kg of fuel a year, which is 2.803 × 106 kg less than that of ISCC2, and the ISCC1 has an annual solar-to-electricity efficiency of 23.93%, 0.88% higher than that of ISCC2. Detailed daily and monthly simulation results show that two systems have advantages of saving energy, and the simulations results show the obvious effects of different solar energy integration modes on the overall IGCC system performance. The achievements of this paper can offer valuable references for the design and operation optimization of ISCC system.

In this paper, the electrical-to-thermal energy transfer efficiency of the transistor coil ignition system for spark-ignition engines is investigated using both electrical and calorimetry measurements. The gap voltage and discharge current are measured to determine the electrical energy supplied to the spark gap. A pressure-rise calorimeter is used to estimate the thermal energy transferred from the plasma channel to the gas. Firstly, this paper studies the influences of spark gap size, electrode geometry and background pressure on the energy transfer efficiency. To further investigate the effectiveness of increasing breakdown energy on the energy transfer process, a direct-capacitor is paralleled to the spark gap to redistribute the spark energy in both breakdown and glow phases. The varying of the capacitance enables the investigation of the energy transfer efficiency under different breakdown energy level. Results show that the electrical-to-thermal energy transfer efficiency is strongly dependent on gap size, electrode geometry and background pressure. Increasing the breakdown discharge energy is beneficial for the electrical to thermal energy transfer process.

This paper puts forward a new kind of SOFC - GT distributed energy system with methanol as fuel, through the absorption refrigeration (AR) and heat exchanger (HE) to recover the waste heat of GT. Based on thermodynamic analysis model, the performances, especially the exergy losses of the unit as well as its subsystems mainly including eight parts were obtained. The chemical energy of the fuel will directly be changed into electricity. Energy conversion efficiency can be as high as 85% above. The theoretical value has been paid attention by the researchers from all over the world. Comparative study in this paper, the simulation calculation and thermal performance analysis of the performance of two kinds of SOFC - GT is conducted. The results show that the total power generation efficiency of pure SOFC system, Case A and Case B are 19.28%, 55.79% and 52.26% respectively. The total thermal efficiency of Case A and B are 83.44 % and 82.79 % respectively. Additionally, the changing laws of total exergy loss, energy and exergy efficiency of integrated system at different loads also were studied. The results provide not only theory basis and scientific support for the design of the SOFC - GT distributed energy system with absorption refrigeration and heat exchanger recovering waste heat, but also a new scheme of energy saving and optimization for the units.

Closed Brayton cycle (CBC) coupled with High Temperature Gas-cooled Reactor (HTGR) has potential application due to its compact configuration, high power generation efficiency and inherent safety. It is also one of the major power conversion methods for Generation IV advanced nuclear power systems. The typical CBC has several helium-water heat exchangers, including pre-cooler and inter-cooler. These helium-water heat exchangers have important influence on the performance of power conversion system, especially in loss-of-flow accidents (LOFAs). A system model including the reactor and the energy conversion system was established in this paper. The 10MW High Temperature Gas-cooled reactor-test Module helium Gas Turbine (HTR-10GT) was taken as the example to show the consequences of LOFAs. The results showed that LOFAs led to the rising of water temperature out of heat exchangers. With the reduction of water flow rate, the maximum water temperature would increase sharply, and the water temperature in pre-cooler was higher than that in inter-cooler. At low water flow rate, the water temperature would exceed the boiling point. LOFAs also made the rising of helium temperature. It had impacts on the performance of helium compressors. The elevated inlet temperature of helium compressors changed the corrected speed and corrected flow rate, therefore caused the deterioration of compressor’s performance. Furthermore, the LOFAs caused the reactor inlet temperature increasing. In low water flow rate, it would make the reactor inlet temperature beyond the temperature limitation of reactor pressure vessel and influence the safety of reactor. And the LOFAs also reduced the output work of cycle. This paper provides insights of features of CBC in LOFAs and will be helpful to the design and safety operation of closed Brayton cycle coupled with HTGR.

Coiled tube air heaters (CTAH) are heat exchangers currently under investigation at the University of California, Berkeley for application to Reheat Air-Brayton Combined Cycles (RACC). In a CTAH, molten fluoride salt on the tube side heats air on the shell side in a cross-counterflow arrangement, leading to high heat exchange effectiveness, while the coiled geometry provides good transient mechanical performance during thermal transients. This paper describes the important phenomenology involved in CTAH design and operation, such as salt freezing, flow induced vibration, start-up and shut-down control, and air circulating power requirements. The THEEM simulation tool used in the design of CTAHs and its validation against simple water to air test sub-bundles is presented. Finally, an initial design for a demonstration 370 kWth CTAH closed air test loop is presented. This test loop design, when constructed, would enable demonstration of salt-to-air heating under conditions relevant to RACC power conversion (air pressures from 4 to 20 atm and air temperatures from 400 to 650°C).

This paper describes the ongoing work on modeling and simulation of energy conversion processes. The efficiency of the supercritical carbon dioxide (SCO2) power cycles are higher than steam Rankine cycle and helium Brayton cycle in the mild turbine inlet temperature region, and the compact structure and the less restraint of the environment make the SCO2 a promising alternative power conversion system for the next-generation nuclear reactors. In this paper, a SCO2 Brayton cycle steady state simulation program in a small modular reactor is developed. The model is implemented in Modelica language and simulated in Openmodelica environment. The studied process is a high-efficient heat transfer system working in the SCO2 Brayton cycle (SBC). And it is used to analyze the performance of recuperated and recompression cycle configurations. The mathematical models for cooler, heat exchanger are formulated by using the mass and energy conservation equations. The CO2 fluid properties adopted the Reference Fluid Thermodynamic and Transport Properties Database distributed by NIST. Using the SCO2 Brayton cycle model, the design-point operation parameter of the SCO2 Brayton cycle was analyzed, including the outlet pressure and the pressure ratio of compression, the pressure drop and temperature of the heat source. In order to study the 10MW SCO2 Brayton cycle, the equipment selection, numerical modeling has been proceeded under the water-cooled and air-cooled condition. The results show that both the two loops are able to achieve the highest thermal efficiency by adjusting the operation. The modeling language Modelica and the CO2-library is given and the modeling of CO2-recuperator is presented.

While renewable energy is generally considered to be a well-researched field, wave energy converters (WECs) are still in early industrial stages, for example due to high costs, even though the potential of WECs in countries such as the UK is very high. Apart from the power plant location, the amount of power generated by a wave energy converter is also highly influenced by the efficiency of both the energy transfer from the wave to the plant’s generator and the power take-off (PTO) itself. Improving on any of these aspects therefore increases the power output and economic attractiveness. Based on a commercial development project by the NEMOS GmbH in Germany, this paper presents a more efficient means of connecting a floater and a rotary PTO based on a free traction mechanism consisting of a custom belt and matching pulley. In addition to regular longitudinal forces, the belt system can transfer transversal forces of up to 14 % of its pulling force and allowing run-in angles up to 8°. First tests show an average efficiency to 99.6 % in wet conditions. The paper lays out the theoretical background of the new design and discusses existing alternatives, before detailing the taken approach to design and optimization. The results are validated and compared to an existing rope design and a benchmark flat belt.

As a kind of unconventional gas reservoirs, shale gas reservoirs are full of potential to develop and have attracted global attention. Accompanying the exploiting of shale gas, a large amount of drilling cuttings contaminated by the oil-based drilling fluid are generated inevitably. How to deal with the drilling cuttings in a environmental-friendly way is tough especially for offshore oilfield. So it is important to investigate this aspect deeply and develop methods to clean the contaminated drilling cuttings. As is known to all, the thermal desorption technology has outstanding performance in oily cuttings cleaning. This paper bases on a kind of mechanical-thermal cuttings cleaning apparatus where the contaminated drilling cuttings are heated up by friction heat produced by the friction between the cuttings and the agitating vanes. And the harmful substance is separated from the cuttings in the agitated and high temperature flow field. This thesis investigates the fundamental of the energy conversion in the frictional process, infer formulas analyzing the thermo-physical phenomena and quantitatively model the energy conversion and thermal transmission accompanying the friction. Firstly, the principle of heat transfer and the law of conservation of energy are employed to investigate the natural law of the energy conversion in the frictional process. Based on the investigation, taking the liquid bridge between the oily cuttings and the agitating vane into account, this paper deduces the physical equations and the frictional energy model to calculate the total frictional heat, heat density and temperature distribution. Following up the frictional model, in the Eulerian-Lagrangian coupling framework, this paper develops a parallel numerical platform of computational fluid dynamics combined with discrete element method (CFD-DEM). In the coupling approach, the gas motion is solved at the computational grid level while the solid motion is resolved at the particle-scale level. Furthermore, the coupling approach is extended with the frictional energy model. The numerical platform can calculate the dense gas-solid motion in the fluidizing apparatus, the convective heat transfer between gas and solid phase, and the conductive heat transfer between particles. Based on the platform, the mechanical-thermal energy conversion and the convective heat transfer between gas and oily cuttings, and the conductive heat transfer between cuttings and the agitating vanes are investigated. Meanwhile an experiment is conducted. By comparing the numerical results with the experiment data, the paper can come to the conclusion that how to dispose the nonlinear parameters such as the friction contact area, the friction coefficient and the normal pressure is the key to accurately model the energy conversion and the heat transmission. What’s more, it can be understood that the convective heat transfer between gas and solid phase play an important role in the heat transmission.

Small Modular Reactor (SMR) technologies have been recently deemed by the DOE as clean energy, a low carbon-dioxide emitting “alternative energy” source. Recent UN Sustainability Goals and Global Climate Talks to reduce the anthropomorphic Carbon-Dioxide atmospheric concentrations signal a renewed interest and need for nuclear power. The objective of this paper is to present an improved approach to the evaluation of “Hybrid Nuclear Energy Systems”. A hybrid energy system is defined as an energy system that utilizes two or more sources of energy to be used in single or multiple applications. Traditional single sourced energy or power systems require the amount of energy creation and the production of usable power to be carefully balanced. With the introduction of multiple energy sources, loads, and energy capacitors, the design, simulation, and operation of such hybrid systems requires a new approach to analysis and control. This paper introduces three examples of “Hybrid Nuclear Energy Systems”, for large scale power, industrial heat, and electricity generation. The system component independence, reliability, availability, and dynamic control aspects, coupled with component operational decisions presents a new way to optimize energy production and availability. Additional novel hybrid hydro-nuclear systems, concentrated solar-nuclear power desalination systems, and nuclear-insitu petroleum extraction systems are compared. The design aspects of such hybrid systems suitable for process heat, electricity generation, and/or desalination applications are discussed. After a multiple-year research study of past hybrid reactor designs and recent system proposals, the following design evaluation approach is the result of analysis of the best concepts discovered. This review of existing literature has summerized that postulated benefits of Hybrid Nuclear Sytems are; reduced greenhouse gas emissions, increased energy conversion efficiency, high reliability of electricity supply and consistent power quality, reduced fossil fuel dependence, less fresh water consumption, conversion of local coal or shale into higher value fuels, while lowering the risks and costs. As these proposed hybrid systems are interdisciplinary in nature, they will require a new multidisciplinary approach to systems evaluation.

A rapid development in wind turbine technology took place during the Second World War and oil crisis of 1973. It continued during twentieths century, which resulted in turbines with bigger size and more advanced technology. Today, large wind turbines are becoming more competitive in the field of electricity generation because of economical production of electricity and availability at rural and remote locations. They have occupied remarkable share in world renewable power generation among various renewable energy sources. On the other hand small wind turbines are not accepted well because of lack of assured performance, cost, efficiency, etc. Therefore some researchers are trying to develop new wind turbine systems to convert wind energy in to electricity. Innovations in the design wind turbine to make them compatible for household use and also to favor their installations by building more eye-catching, efficient and economical wind turbine. To increase acceptability of wind turbines, wind turbine should satisfy the most of the criteria listed in the present study such as, ability to catch the wind from all the direction, self starting, light weight, inexpensive, maintenance free, low weight tower-top system and hence supporting structure, light weight and efficient generator, efficient wind to mechanical energy conversion and manufacturing simplicity at affordable cost and reliable performance. Present study focused on the innovative wind turbines that installed as an offshore and onshore technology. There are more than one hundred of different innovative wind turbine designs listed research papers, books, magazines and internet. In present paper, innovative design aspects of some of these turbines discussed with the technological challenges. Innovations are in the area of blade profile design, aerodynamic shape of the wind turbine, reduction of noise and vibrations, the material of the blade, mechanical and electronic instruments such as gearbox and electronic power circuit, suitability to the application, etc. The aims of these innovations are improvement in the efficiency of the wind turbine; increase in power output and to lower the overall cost. At the end of paper the technological challenges that these innovations overcome, innovative concept and feasibility of the concept are discussed. These innovations include spiral wind turbine, VAWT with accelerator, Windpax-Collapsible portable wind turbine, multi-rotor wind turbines, diffuser augmented wind turbines and floating wind turbines.Copyright © 2015 by ASME

This paper considers the use of a chain of springs and masses to reduce the transmission of shock and vibration through the system. The masses are equipped with internally rotating masses that absorb some of the axial vibration into internal kinetic energy of the masses. The internal masses have viscous damping, but no elastic or gravitational restraint. Previous research has shown that a single cart system attached to a vibrating structure can help mitigate shock through targeted energy transfer. This paper examines the potential for shock isolation provided by a chain of such systems. Through numerical simulations, tradeoffs are examined between displacement and transmitted force.Copyright © 2015 by ASME

Concentrating solar power (CSP) plants can provide dispatchable power with the thermal energy storage (TES) capability for greater renewable-energy grid penetration. To increase the market competitiveness, CSP technology needs to increase the solar-to-electric efficiency and reduce costs in the areas of solar collection from the heliostat field to the receiver, energy conversion systems, and TES. The current state-of-the-art molten-salt systems have limitations regarding both the potential for cost reduction and improvements in performance. Even with significant improvements in operating performance, these systems face major challenges to satisfy the performance targets, which include high-temperature stability (>650°C), low freezing point (650°C) at a reduced cost. The fluidized-bed CSP (FB-CSP) plant being developed by the National Renewable Energy Laboratory (NREL) has the potential to overcome the above issues with substantially lower cost. The particle receiver is a critical component to enable the FB-CSP system. This paper introduces the development of an innovative receiver design using the blackbody design mechanism by collecting solar heat with absorber tubes that transfer the radiant heat to flowing particles. The particle and receiver materials can withstand temperatures of >1000°C because the receiver can use low-cost materials, such as ceramics and stainless steel, and the solid particles can be any low-cost, stable materials such as sand or ash for particle containment and TES. The heated particles can be stored in containers for TES or supply heat for power generation. This study investigated the performance of convection, reflection, and infrared (IR) re-radiation losses on the absorber solar receiving side. We developed a flux model to predict the reflection losses from the absorber tubes based on the NREL SolTrace program, and conducted thermal modeling by using the Fluent Software. This paper presents the thermal modeling and results on the receiver performance. The receiver configuration may have broad applications for different heattransfer fluids (HTFs), including gas, liquid, or the solid particle-based system in our receiver development.

It is foreseen that distributed power generation, using biogas and natural gas as fuel, will play increasingly important role in the future European energy market. These technologies are presenting controllable power generation capacity as complementary to the installed intermittent renewable power generation in terms of wind and solar. A nationally funded project was initiated in Stavanger, Norway in 2010, led by the Center for Sustainable Energy Solutions (cenSE), to investigate use of existing small scale energy conversion technologies developed for natural gas, using as much as possible biogas mixed with natural gas without any hardware modifications to the energy conversion units. Three test setups with a micro gas turbine (100 kWe), a gas engine (11 kWe) and a short stack of solid oxide fuel cell consisting of six cells (30–40 We) were installed for experimental studies, providing necessary data for model validation and development of data driven models for engine performance monitoring. This paper reports the results of the project, concerning mapping the operational window for use of mixture of simulated biogas (50% methane, 50% CO2) and natural gas for each technology as an enabler of biogas utilization with natural gas as fallback solution. The CO2 reduction potential, when natural gas is replaced with biogas, is also presented. Moreover, the capability of using data driven models based on artificial neural network for online monitoring and control of the engine performance at various operational conditions is shown. Detailed reporting on various aspects of fuel composition and technology impact has been conducted earlier. This paper provides a total overview and a comparison of performance of the technologies tested in this study.

This paper studies a targeted energy transfer (TET) mechanism for a two-degree-of-freedom (TDOF) model in free vibration. The model comprises a primary linear system and a secondary system in the form of an energy sink which can be nonlinear. The free vibrations are considered subject to an impulsive excitation exerted on the primary system, leading to a nonzero initial velocity. The goal is to obtain the spring parameters in the nonlinear energy sink (NES) so as to maximize an energy dissipation measure (EDM) representing the percentage of impulsive energy that is absorbed and dissipated in the NES. A global optimization algorithm is used for this purpose. The optimal performance is assessed for the purely linear, linear-cubic, and purely cubic configurations of the spring connecting the primary and secondary systems. The corresponding results are compared with each other. The optimization process is performed for the EDM averaged over given ranges of the initial impulse and natural frequency in the primary system. It is shown that the type of the optimal configuration can vary depending on these ranges.

The small break loss of coolant accident (SBLOCA) is a typical accident in the nuclear power plant, and the diagnosis of accident parameters in a small break loss of coolant accident (SBLOCA) is a very important research direction in the field of nuclear safety. The timely and accurate judgment of the break parameters can help the operator understand the serious situation of the SBLOCA and avoid more serious consequences. In this study, a physical model of the blowdown process during SBLOCA was established by using the theory of two-phase critical flow, flash evaporation, and energy conversion. Then a diagnostic model for the break diameter of SBLOCA was established by combining the NSGA-II and the physical model, and the experimental results obtained by the blowdown experiment of simulated pressurizer under a low pressure condition were used to verify the accuracy of results obtained by the diagnostic model. The results show that the diagnosis model can be used to obtain the break diameter during the blowdown process of SBLOCA. In different conditions of the blowdown process, the errors between the diagnosis results and the experiment results do not exceed 20%. The calculation time of the diagnostic model is less than 400s.

This two-part paper describes a new approach to determine the effect of surface waviness, arising from manufacture of composite fan blades, on transition onset location movement and hence fan profile losses. The approach includes analysis and computations of unsteady disturbances in boundary layers over a wavy surface, assessed and supported by wind tunnel measurements of these disturbances and the transition location. An integrated framework is developed for analysis of surface waviness effects on natural transition. The framework, referred to as the extended eN method, traces the evolution of disturbance energy transfer in flow over a wavy surface, from external acoustic noise through exponential growth of Tollmien-Schlichting (TS) waves, to the start and end of the transition process. The computational results show that surface waviness affects the transition onset location due to the interaction between the surface waviness and the TS boundary layer instability, and that the interaction is strongest when the geometric and TS wavelengths match. The condition at which this occurs, and the initial amplitude of the boundary layer disturbances that grow to create the transition onset is maximized, is called receptivity amplification. The results provide first-of-a-kind descriptions of the mechanism for the changes in transition onset location as well as quantitative calculations for the effects of surface waviness on fan performance due to changes in surface wavelength, surface wave amplitude, and the location at which the waviness is initiated on the fan blade.

This paper presents a radio frequency (RF) energy harvesting (RFEH) system with a multiband antenna configuration that can simultaneously harvest energy from the sub-6 GHz and 5G millimeter-wave (mm-Wave) frequency bands. The performance of the RFEH system is studied from −25 dBm to 5 dBm input power levels underlying the maximization of the overall efficiency and possible optimization strategies. The maximum achievable power conversion efficiency (PCE) is formulated as a mathematical programming problem and solved by optimizing the design factors including antenna geometry, operational frequencies, rectifier topologies, and rectifier parameters. An array of broadband high gain patch antennas with reconfigurable rectifiers, an impedance matching network, and a voltage-multiplier circuit are employed in the system to maximize the PCE. The voltage standing wave ratio (VSWR) and reflection coefficient (S11) of the antenna are estimated and optimized by numerical method. Simulations are conducted to evaluate the performances of the rectenna and the voltage-multiplier circuit. Results for radiation pattern, wave absorption, input impedance, voltage, and power across the load resistance as a function of frequency are obtained for the optimized configuration. The overall efficiency of the optimized RFEH system is measured at various power inputs and load resistances.

Piezoelectric transduction has received great attention for vibration-to-electric energy conversion in the last ten years. A typical PZT harvester is a cantilever subject due to its easy implementation. It has been investigated in regard to its harvesting capacity under various conditions. However, its electro-mechanical properties hasn’t gotten involved enough, which is in fact crucial for comprehending the intrinsic properties. Given that, this paper set out to explore the electro-mechanical characteristics of a cantilever beam from a laminated PZT patch by means of experiment and modeling studies. In the test, the PZT cantilever is magnetize by a tip mass, then connected into a circuit with a resistor and vibrated by an exciter. Through tuning excitation frequency, mass weight and resistances load, an optimal settings are summarized for obtaining more harvested energy in the system. Besides, the electro-mechanical behavior is investigated that demonstrates nonlinear hysteretic. On the basis, electromechanical model is presented to accurately mimic the aforementioned nonlinear behavior of the PZT harvester. The presented study has revealed that a proper choice of harvesting system with an accurate model can further exploit energy potentiality in piezoelectric material so as to apply its energy harvesting capability into much more extensive engineering fields.

This paper presents a high-fidelity numerical wave tank simulation for Variable Geometry Wave Energy Converters (VG-WECs). Typically, wave energy converters require reactive power to optimize the energy conversion, which significantly jeopardizes the economic index of the system. The proposed VGWECs allows comprehensive shape-changing not only in response to ocean climate but also to reduce the reactive power requirements on the power take-off (PTO) unit. This design aims at eliminating reactive power with minimal impact on optimality in terms of energy production. To investigate the dynamic behavior of the VGWEC, this model is simulated in a Computational Fluid Dynamics (CFD) based Numerical Wave Tank (CNWT) using ANSYS 2-way Fluid Structure Interaction (FSI) tool. The interaction between irregular waves and the VGWEC is simulated. The numerical results show that the proposed VGWEC has large deformation and motion in response to the incoming wave. This highly nonlinear interaction between waves and VGWEC can be leveraged to eliminate reactive power.

Savonius wind turbines are drag-type vertical axis wind turbines. Their blades experience less drag while moving against the wind flow and more drag while moving in the wind direction. The drag difference rotates Savonius wind turbines and produces electrical power. Savonius wind turbines can catch wind from any direction. No yaw motion mechanism is needed for them to be pointed in the wind direction. Savonius wind turbines have simple structures and are convenient to install and maintain. They can operate on low wind speed and have good starting characteristics. Compared with horizontal axis wind turbines and lift-type vertical axis wind turbines such as Darrieus and Giromill wind turbines, Savonius wind turbines have relatively low power conversion efficiency. This is because of their drag-type nature which generates positive and negative torque on their advancing and returning blades, respectively. Savonius wind turbines are suitable for locations where power conversion efficiency can be compromised for the sake of low cost and high reliability. One major drawback from Savonius wind turbines is the negative static torque which lowers their self-starting ability. Although the negative static torque of Savonius wind turbines can be mitigated by adding additional components such as curtains, nozzles and ducts to them, these additional components make them complex and lose omnidirectional performance. In this paper, Savonius wind turbines are designed based on their geometric parameters to remove their negative static torque and improve their performance. Savonius wind turbines with different numbers of blades and other geometric parameters are designed, analyzed and simulated.

In this paper, a non-traditional variant nonlinear energy sink (NES) is developed for simultaneous vibration suppression and energy harvesting in a broad frequency band. The non-traditional variant NES consists of a cantilever beam attached by a pair of magnets at its free end, a pair of the so-called continuous-contact blocks, and a pair of coils. The beam is placed between the continuous-contact blocks. The constraint of the continuous-contact blocks forces the beam to deflect nonlinearly. Each of the magnet-coil pairs forms an electromagnetic energy harvester. Different from a traditional way that attaches the coils to the primary mass, the developed setup has the coils fixed to the base. First, the developed apparatus is described. Subsequently, the system modeling and parameter identification are addressed. The performance of the apparatus under transient responses is examined by using computer simulation. The results show that the proposed apparatus behaves similarly as the NES with the following features: 1:1 resonance, targeted energy transfer, initial energy dependence, etc.

Nonlinear energy harvesters have been widely studied in the last decade. Their broad bandwidth and relatively high power output contribute to energy harvesting applications. However, the coexisting multiple orbits brought by the nonlinearity weaken the performance of nonlinear energy harvesters. This paper proposes to achieve orbit jumps of monostable energy harvesters by a bidirectional energy conversion circuit. Changing the switch control sequence in the bidirectional energy conversion circuit facilitates it with both the energy harvesting and vibration exciting functions. Thus, a nonlinear energy harvester in connection with the circuit can harness ambient energy as well as excite itself, through energy harvesting and vibration exciting modes separately. Based on the concept of vibration exciting, the energy saved in the storage is used to stimulate the piezoelectric transducer for a larger vibration amplitude, which enables orbit jumps. The working mechanism of the circuit is introduced. Experimental setup of a monostable energy harvester has been developed to validate the proposed method. The monostable system can be stimulated to high-energy orbit from a small vibration amplitude by the vibration exciting mode of the circuit. It is also revealed that the method can achieve orbit jumps in a wide frequency range within the hysteresis area. Evaluations on energy consumption and energy gain show that the sacrificed energy can be quickly recovered. A novel approach for orbit jumps of monostable energy harvesters is performed so as to open new opportunities for monostable energy harvesters.

A “33” mode (mechanical stress being in parallel to the electric dipole moment direction) piezoelectric lead zirconate titanate (PZT) multilayer stack-based piezoelectric flextensional energy harvester (PZT-Stacked-FEH) has been developed. Interdisciplinary approaches had been taken to increase the performance of the PZT-Stacked-FEH. First, an elastic flextensional frame for force amplification has been optimally designed to capture more mechanical energy with high energy transition efficiency into the PZT-Stacked-FEH. Second, a “33” mode piezoelectric PZT multilayer stack (PZT-Stack) was employed instead of “31” mode (stress being in perpendicular to the dipole moment direction) single layer piezoelectric component to increase mechanical to electrical energy conversion efficiency and to generate more electrical charges in order to improve energy storage efficiency. With these approaches, the PZT-Stacked-FEH demonstrates excellent performance: 1) a 19% of overall mechanical to electrical energy conversion efficiency was achieved, 2) 48.6 times more mechanical energy was transited into PZT-Stacked-FEH and 26.5 times more electrical power was generated than directly applying force to the PZT-stack, and 3) energy storage efficiency was significantly improved. In this paper, we are focusing on the investigations for the off-resonance mode performance of the PZT-Stacked-FEH through theoretical modeling, prototype development, and experimental studies. A prototype PZT-Stacked-FEH of weight 18 grams was able to generate 666 mW electrical power under 52 Nrms force at 250 Hz, which is much lower than the resonant frequency (936 Hz). At this condition, a 6,600 μF super-capacitor was charged from 0 to 7 V in 1.6 second, at an average rate of 100 mW. Furthermore, 70% of generated appear electrical powers were delivered to matched resistive loads in the investigated regime of frequencies. Finally, the experimental results matched well with theoretical predictions which verified the developed theoretical models.

Supercritical carbon dioxide (S-CO2) Brayton power cycle has attracted a lot of attention around the world in energy conversion field. It takes advantage of the high density of CO2 near the critical point while maintaining low viscosity to reduce compressor power and achieve high cycle efficiency. However, as CO2 approaches to its critical point, the thermodynamic properties of CO2 vary dramatically with small changes in temperature or pressure. As a result, the density of the working fluid varies significantly at the compressor inlet in the practical cycle if operating near the critical point, especially for small-scale cycles and air-cooled cycles, which leads to compressors operating out of the flow range, even being damaged. Concerns of large density variations at the inlet of the compressor result in S-CO2 compressor designers selecting compressor inlet conditions away from the critical point, thereby increasing compressor power. In this paper, a criterion to choose inlet pressure and inlet temperature of compressors as the design inlet condition is proposed, which is guaranteeing ±50% change in inlet specific volume within ±3 °C variation in inlet temperature. By the criterion, 8 MPa and 34.7 °C is selected as the design inlet condition. According to design requirements of the cycle, a S-CO2 centrifugal compressor is designed through 1-D design methodology. Based on the two-zone model, the effects of compressor inlet condition including inlet pressure and inlet temperature on the compressor performance are analyzed in detail. In practical operation, the compressor inlet condition is varied. Thus, an accurate prediction of compressor performance under different inlet conditions is necessary. The traditional correction method is not suitable for S-CO2 compressor. Dimensionless specific enthalpy rise is used to correct pressure ratio by the real gas table. And the S-CO2 compressor performance can be predicted correctly under different inlet conditions.

In this paper, we conducted a three-dimensional investigation of flow past a cylinder undergoing forced oscillation. The flow configuration is similar to the work of Blackburn & Henderson (1999) [1], in which Reynolds number equals to 500 and a fixed motion amplitude of A/D = 0.25. The oscillation frequencies are varied in the range near to the natural shedding frequency of a stationary cylinder. The flow dynamics are governed by Navier-Stokes equations and the solutions are obtained by employing high-order spectral/hp element method. It is found that the flow dynamics are significantly distinguished from the study of two-dimensional flow by Blackburn & Henderson (1999) [1]. The values of hydrodynamic forces are smaller compared to that in the two-dimensional study. However, lock-in boundary we identified is broader. In addition, a different type of hysteresis loop of energy transfer coefficient is obtained.

Most low-frequency AC single-phase railway grids have both power-electronic based Static Frequency Converters (SFCs) and electrical-machine based Rotary Frequency Converters (RFCs) connecting them to the three-phase public grid. Already today, in some such grids, a majority of the power conversion is from SFCs. As railway traffic (and thus power demand) increases, more SFCs are installed for capacity increase, while the number of RFCs remains (almost) constant. Thus, the share of SFCs is expected to increase, and the ratio of installed rotational inertia over installed power to decrease. This paper investigates how different shares of SFCs affect the transient stability of low-frequency AC railway grids when having a mix of RFCs and SFCs converting three-phase AC power to single-phase AC power. Results from numerical simulations of the interactions that occur between converters when and after the grid is subject to a fault are presented. The numerical studies show that with an increased share of SFCs there is an increased oscillatory behavior, for example in the voltage magnitude and active power after fault clearance.

During the past few decades, significant interest in applying linear and nonlinear dynamical vibration absorbers for energy transfer and dissipation has significantly arisen. The existing studies of employing dynamical absorbers with small and large-scale dynamical structures have been mostly focusing on suppressing the oscillations for structures that move in one direction only. However, most of these structures are vulnerable to different sources and types of excitations that could induce two-dimensional oscillations into these structures. Consequently, this paper presents an application of a vibration absorber to suppress the two-dimensional vibration induced into the structure caused by a two-dimensional impulsive loading. The system description and the governing equations are firstly introduced and then followed by an optimization process to maximize vibration suppression. The response of the system under various combinations of longitudinal and lateral impulsive loadings is presented and the capability of the proposed absorber to suppress the induced vibration is evaluated.

Nuclear reactor severe accidents can lead to the release of a large amount of radioactive material and cause immense disaster to the environment. Since the Fukushima nuclear accident in Japan, the severe accident research has drawn worldwide attention. Based on the one-dimensional heat conduction model, a DEBRIS-HT program for analyzing the heat transfer characteristics of a debris bed after a severe accident of a sodium-cooled fast reactor was developed. The basic idea of the DEBRIS-HT program is to simplify the complex energy transfer process in the debris bed to a simple one-dimensional heat transfer problem by solving the equivalent thermal conductivity in different situations. In this paper, the DEBRIS-HT program code is prepared by using the existing model and compared with the experimental results. The results show that the DEBRIS-HT program can correctly predict the heat transfer process in the fragment bed. In addition, the heat transfer characteristics analysis program is also used to model the core catcher of the China fast reactor. Firstly, the dryout heat flux when all of molten core dropped on the core catcher was calculated, which was compared with the result of Lipinski’s zero dimensional model, and the error between two values is only 11.2%. Then, the temperature distribution was calculated with the heat power of 15MW.

Supercritical CO2 (S-CO2) Brayton cycle has been identified as a promising power conversion method for the next generation of nuclear reactors due to its high efficiency and compactness. The heat exchanger is one of the most important components for S-CO2 Brayton cycle, and the printed circuit heat exchanger (PCHE) is supposed to be one of the promising candidates for the heat exchangers in S-CO2 Brayton cycle. It should be noted that the fluid maldistribution would induce heat transfer deterioration, especially for heat exchangers with micro- or mini-scale channels like PCHE. The thermal-physical properties of S-CO2 change violently during the heat transfer process, which makes the flow inside PCHE more complex. In this paper, the distribution of S-CO2 flow inside PCHE would be studied by 2-D CFD simulations. For the working fluids with constant properties, the flow nonuniformity increases with the mass flow rate. For the working fluid with S-CO2, the thermal-physical properties change significantly with temperature, and there exist a minimum value in the flow nonuniformity-mass flow rate curves (1.64 × 105 ≤ Rein ≤ 1.31 × 106). Insertion of baffles at manifolds could significantly improve the flow distribution uniformity and reduce the pressure drop. And it has been found that insertion of baffles at the collecting manifold has better performance compared with that at the distributing manifold or both.

Internal waves in the ocean occur in stably stratified fluids when a water parcel is vertically displaced by some external forcing and is restored by buoyancy forces. A specific case of such internal waves is internal tides and their associated currents. These currents can be significant in areas where internal waves degenerate into nonlinear solitary waves, known as solitons. Solitons are potentially hazardous for offshore engineering constructions, such as oil/gas pipelines and floating platforms. The most efficient mechanism of soliton generation is the tidal energy conversion from barotropic to baroclinic component over large-scale oceanic bottom obstructions (shelf breaks, seamounts, canyons and ridges). In this paper, a methodology is provided to compute diagnostics and prognostics for soliton generation and propagation, including the associated currents. The methodology comprises a diagnostic tool which, through the use of a set of theoretical and empirical formulations, selects areas where solitons are likely to occur. These theoretical and empirical formulations include the computation of the integral body force (1), the linear wave theory to compute the phase speed and the empirical model proposed by (2). After the selection procedure, the tool provides initial and boundary conditions for non-hydrostatic numerical models. The numerical models run in 2D-V configuration (vertical slices) with horizontal and vertical resolutions ranging from 50 to 200 m and 5 to 10 m, respectively. Examples are provided for an open ocean location over the Mascarene Plateau in the Indian Ocean. Validation of diagnostics and prognostics are provided against ADCP and satellite data.

The supercritical CO2 (sCO2) Brayton cycle has been attracting much attention to produce the electricity power, chiefly due to its higher thermal efficiency with the relatively lower temperature at the turbine inlet compared to other common energy conversion cycles. Centrifugal compressor operating conditions in the supercritical Brayton cycle are commonly set in vicinity of the critical point, owing to smaller compressibility factor and eventually lower compressor work. This paper investigates and compares different centrifugal compressor design methodologies in close proximity to the critical point and suggests the most accurate design procedure based on the findings. An in-house mean-line design code, which is based on the individual enthalpy loss models, is compared to stage efficiency correlation design methods. Moreover, modifications are introduced to the skin friction loss calculation to establish an accurate 1-D design methodology. Moreover, compressor performances are compared to the experimental measurements.

This paper focuses on the rotor forced response behavior in a 3.5-stage compressor rig. The aim is to provide an accurate prediction of forced response with the less computational effort. Previous research indicates that by reducing the computation domain from 7-row to a 3-row stator-rotor-stator (S1-R2-S2) configuration, the forcing function is over-predicted by 60%. To address this over prediction, an investigation of boundary conditions and a study with additional rows are conducted. The influence of reflecting boundary conditions on the blade modal force is studied by preventing wave reflection. Additionally, a 5-row simulation is studied to take an extra source of excitation force, the IGV row with the same blade count as the other stators, into consideration. Three conclusions were drawn from this study: 1) boundary reflection has a significant influence on unsteady simulation and the modal force, thus should be avoided by using mesh treatment up and down stream; 2) the IGV wake contributes to the forcing function and cannot be ignored; 3) the clocking feature of IGV, S1, and S2 leads to a transfer of energy from 1st harmonic to other higher harmonics. This research provides a guidance of forced response modeling and can be employed for industrial forced response analysis.

Further reduction of vibratory stresses of blades and vanes using an appropriate damping system is required whenever the total damping of the stage is insufficient to avoid High Cycle Fatigue during the life of the blades. An alternative to standard friction based damping systems are impulse mistuning systems — a kind of vibration impact induced non-linear energy sink. Previous publications introduced impulse mistuning systems for avoidance of HCF caused by forced synchronous vibrations of blades and vanes. This included the development of the system, analytical predictions of the effectiveness as well as experimental validation. The effectiveness of the impulse mistuning systems in the case of self-excitation (e.g. flutter) has not been investigated yet to the knowledge of the authors. In this paper, a numerical study of the dynamic phenomena taking place in lumped-parameter models with negative damping and different impulse mistuning systems is presented. One of the results shown is that energy transfer takes place, whereby the vibration initiates at one mode and after some time gets transferred into higher vibration at another mode.

The fundamental challenge in the synthesis/design optimization of energy conversion systems is the definition of the system configuration and design parameters. The traditional way to operate in system engineering practice is to follow the previous experience, starting from design solutions that already exist. A more advanced strategy consists in the preliminary identification of a superstructure that should include all the possible solutions to the synthesis/design optimization problem, and in the selection of the system configuration starting from this superstructure through a design parameter optimization. This top-down approach cannot guarantee that all possible configurations could be predicted in advance and that all the configurations derived from the superstructure are really feasible. To solve the general problem of the synthesis/design of complex energy systems a new bottom-up methodology is proposed, based on the original idea that the fundamental nucleus in the construction of any energy system configuration is the elementary thermodynamic cycle (compression, heat transfer with the hot source, expansion, heat transfer with the cold source). So, any configuration can be built by generating, according to a rigorous set of rules, all the combinations of the elementary thermodynamic cycles operated by different working fluids that can be identified within the system, and selecting the best resulting configuration through an optimization procedure. In this paper a deep analysis of the major features of the methodology is presented to show, through different examples of applications, how an artificial intelligence is able to generate system configurations of various complexity using preset logical rules without any “ad hoc” expertise.

Hydraulic-electromagnetic Energy-regenerative Shock Absorber (HESA) has been proposed recently, with the purpose of mitigating vibration in vehicle suspensions and recovering vibration energy traditionally dissipated by oil dampers simultaneously. The HESA is composed of hydraulic cylinder, check valves, accumulators, hydraulic motor, generator, pipelines and so on. The energy conversion from hydraulic energy to mechanical energy mainly depends on the hydraulic motor between two accumulators. Hence, the dimension match and parameter settings of hydraulic motor for the HESA are extremely important for efficiency of the whole system. This paper studies the methods and steps for dimension matching and parameter settings of the hydraulic motor in a case of a typical commercial vehicle. To evaluate suspension’s vibration characteristics, experiments on the target tour bus have been done. Simulations are conducted to investigate the effects of the hydraulic motor in different working conditions. The simulation results verify that the methods and steps adopted are accurate over a wide range of operating conditions and also show that appropriate matching and parameter settings of the hydraulic motor attached in the HESA can work with high efficiency and then effectively improving energy conversion efficiency for the whole system. Therefore, the theory of the matching progress can guide the future design of an HESA.

The present work augments vertical-axis unidirectional wave energy converter (WEC) designs with a new approach. The enabling technique is the hydrodynamic design of a special rotor, which consists of a series of uniquely shaped blades in a certain formation. Specifically, individual blades are realized by revolving a two-dimensional symmetric hydrofoil about its chord line. Then the blades are arranged around a vertical shaft in a desired formation to form the rotor. When driven by an approaching flow through interaction, the rotor naturally rotates about the vertical shaft in a predefined direction. The approaching flow could be from any spatial direction, and could have changing speed and direction in any fashion, but the unidirectional behavior of the rotor never changes. Such a behavior guarantees a unidirectional performance of the rotor in waves, where the water flow is omnidirectional and constantly evolving. In validating the proof of concept and characterizing the rotor’s unidirectional performance, experiments were carried out under various flow conditions. Specifically, three types of flows were employed: horizontally oscillating flow, vertically oscillating flow, and orbital flow along a circular path in a vertical plane. The three flows were actually created by translating the rotor in still water, with the first two to characterize the rotor’s responsiveness to the flow direction and the third one to simulate rotor interaction with deep waves. For each flow type, different rotor configurations/blade formations were examined under various testing parameters. For all the cases, the rotor shaft was kept vertically all the time. The experimental results are discussed in details in the paper.

As an important kind of energy source, radioisotope batteries are attracting more and more academic researchers and people from industry due to the high power density, long lifetime (equal to half life of the radioisotope source), outstanding reliability, without maintenance, miniaturization and wide application compared with traditional dry batteries, chemical batteries, fuel batteries and solar batteries. Radioisotope batteries have been developed for more than 15 species since the first β battery invented by Henry Mosley in 1913. Based on a Brayton cycle Radioisotope Power System and a PZT-5H (Pb(ZrxTi1-x)O3, 0≤x≤1) unimorph, the piezoelectric nuclear battery driven by the jet-flow (PNBJ) is demonstrated in this work. The PZT-5H unimorph replaces turbine and utilizes high speed nitrogen jet-flow heated by the decay energy of radioisotope to output electrical energy. Over 0.34% energy conversion efficiency for the PNBJ is obtained at the flow of 2.26 × 10−3 m3/s and room temperature on half plane. The PNBJ can be used in low power microelectronics and microsystems, like electronic watch, AC-LED (alternating current light-emitting diode), and sensors. We believe that the researches and applications of PNBJ will be much attractive with the breakthroughs of preparation technology made by academic and industrial world.Copyright © 2017 by ASME

Supercritical CO2 cycles is a promising technology for the next generation power conversion cycles. Supercritical CO2 Brayton cycles offer equivalent or higher cycle efficiency when compared with steam cycles at similar temperatures. This paper presents an investigation of the sCO2 recompression cycle, where recompressing a fraction of the flow without heat rejection, results in an increase in thermal efficiency. A thermodynamic analysis of a 600 MWth power cycle has been carried out, in order to study the effect of the most significant design parameters on the components performance and cycle efficiency, using two different simulation tools to model the recompression system. An iterative model using basic thermodynamic equations describing the system’s components was employed in this direction. The system was also modeled by means of commercial process modeling software for comparison. Hence, useful results regarding the operating pressures and temperatures of the cycle and how they affect the recuperators, the compressor and the turbine performance have been derived. Finally, a comparative analysis of the results of the two simulation tools and those of a reference cycle from the bibliography is carried out, showing deviations in the range of 2.8 to 4%.

Energy resources of offshore wind and ocean wave are clean, renewable and abundant. Various technologies have been developed to utilize the two kinds of energy separately. This paper presents the principle of an integrated generation unit for offshore wind power and ocean wave energy. The principle of the unit includes that: The wind rotor with retractable blades and the 3-DOF (degrees of freedom) mechanism with the hemispherical oscillating body are used to collect the irregular wind and wave power, respectively; The energy conversion devices (ECDs) are utilized to convert mechanical energy from both the wind rotor and the 3-DOF mechanism into hydraulic energy; The hydraulic energy is used to drive the hydraulic motors and electrical generators to produce electricity. Some analyses and experiments of the unit is conducted.

This paper discusses results from an experiment where forces on a rigid cylinder are measured during prescribed oscillations both in-line with and transverse to a constant flow. Two “figure of eight” oscillation patterns with identical shape but opposite orbital direction, relative to the flow, have been tested at a Reynolds number of 24000. Results show that the hydrodynamic force acting on the cylinder is significantly different for the two orbital directions. The force in phase with velocity, which represents the energy transfer between the fluid and the cylinder, has opposite sign and different magnitude for the two orbital directions. Flow visualization by particle image velocimetry (PIV) reveals that the two orbits leads to different vortex shedding modes. Hydrodynamic forces at multiples of the oscillation frequency, known as higher harmonics, are seen for both orbital directions. Comparison with pure in-line and pure transverse oscillations indicates that the higher harmonics are related to oscillations in in-line direction. A three-dimensional Large Eddy Simulation numerical simulation with equivalent experiment parameters has been conducted. It is very encouraging to see a good agreement between numerical results and observations with respect to global forces, vortex shedding modes and hydrodynamic co-efficients.

When there is a two to one internal resonance ratio between the natural frequencies of the pitch motion and the roll motion of a ship, a nonlinear energy transfer occurs between the modes. If the ship is excited near the pitch natural frequency and at a large enough excitation amplitude, the pitch mode transfers energy to the roll mode. We use this interesting phenomenon to develop a wave power device for off-shore purposes. In this paper, we experimentally show that we can use a horizontal pendulum and use the quadratic nonlinear coupling between the pitch and the roll mode to get full rotation of the pendulum inside the ship. A rotating pendulum will generate orders of magnitude more power than a locally oscillating one when connected to a DC generator. This article measures the angle of the pendulum at the pitch frequency excitation of the ship to experimentally confirm the expected theoretical results on this phenomenon.

International audience; Energy use optimization of systems is traditionally done by looking for the best thermodynamic operating conditions of the process and heat integration solutions such as networks to redistribute intelligently the heat between different sources and sinks. Hence, there are two emerging situations in industrial parks that call for new methodologies: first, the flow exchanges are not limited to the plant boundaries, and incoming and outgoing flows could generate economic and environmental gains. Second, material such as waste can no longer be neglected in this optimization. Not only the energy conversion potential of material could be investigated, but other conversion options would bring the possibility of turning the non-usable waste into another usable material through chemical processes. This paper present a conceptual framework of optimization for an energy and mass system, and proposes a methodology for integrating conversion processes, with a case demonstration on wooden waste in an industrial activity zone.

In developing numerical code for interfacial evaporation problems, 1st Stefan problem is generally used for validation. In this paper, both 1st and 2nd Stefan problems are used for validating a numerical code that utilizes volume of fluid method and is based on ANSYS-Fluent along with user defined functions (UDFs) to account for the mass and energy transfer at the interface. The 2nd Stefan problem incorporates heat transfer in both phases and provides a more realistic representation of an evaporating interface. Emphasis is put on the vapor-liquid heat transfer, which takes into account the sensible heat transfer in the liquid phase where liquid conduction effects are important. The mass transfer model takes into account the temperature gradients in both phases at the interface. Analytical solutions for the two Stefan problems are reported and used for validation purposes. Results show that the interface displacement and temperature distributions are simulated accurately. The current approach utilizes the robust platform of ANSYS-Fluent while allowing an accurate representation of the phase change processes at the interface.

In this work, we investigated the reflection properties of artificial opals composed of submicron silica spheres with diverse structural parameters and under the effect of light in different states. Furthermore, the primary rules how the reflection properties of artificial opals convert as these factors changing have been revealed clearly. These factors can take effects in changing the shape, value, and position of the peak of the hemispherical reflectance of artificial opals. Then we got the distribution and propagation process of the Poynting vectors corresponding to the positions of the diffraction peak and the low reflectance in the artificial opals at normal and oblique incidence of P-polarization. Comparing with the theoretical interpretation which is a little complicated and nonobjective, this paper will provide a visual result to explain the reason why the structure has high reflectance in some spectral ranges.Copyright © 2016 by ASME

The targeted energy transfer (TET) phenomenon has been observed in the field of acoustics, which provides a new approach to passive sound control in low frequency domain. The TET phenomenon has been investigated firstly inside one tube (1D acoustic system) with a membrane nonlinear energy sink (NES) or a loudspeaker nonlinear absorber, then inside an acoustic cavity (3D acoustic system) with a membrane NES. 3D acoustic cavities have been considered as more general geometry for the acoustic medium in view of applications in the acoustic field and the membrane NES is mounted directly on the wall of the acoustic cavity. The placement of a membrane NES on the wall involves a weak coupling between the membrane NES and a considered acoustic mode, which constitute the two degrees-of-freedom (DOF) system. The beginning of TET phenomenon of the two DOFs system has been analyzed and the desired working zone for the membrane NES has also been defined. The two thresholds of the zone have been determined by an analytical formula and semi-analytically, respectively. The parametric analysis of the membrane NES by using the two DOFs system has been investigated to design the membrane NES. In order to enhance the robustness and the effective TET range in acoustic cavities, a three DOFs system with two membranes and one acoustic mode is studied in this paper. We consider two different membranes and two almost identical membranes to analyze the TET phenomenon, respectively. The desired working zone for the membrane NES and the value of the plateau which are obtained by the two DOFs system are applied to analyze the three DOFs system. We observe that two membranes can enlarge the desired working zone of the NES.Copyright © 2015 by ASME

Thermophotovoltaic (TPV) devices are popular energy converters due to providing low noise, low thermal-mechanical stresses and portability. The conversion efficiency of TPVs is still low due to mistuned spectral properties between thermal selective emitters and the TPV cell. Using thermal selective emitters that are well-matched to the TPV cell spectrum enhances the conversion efficiency of TPVs. Several thermal selective emitters, composed of 1-D complex multilayer structures with rectangular gratings, have been proposed. Cost, fabrication and stability factors have been major problems for their application on TPV modules. In this paper, a 1-D tungsten thermal emitter is optimized which exhibits close to blackbody emittance near the band-gap of a GaInAsSb TPV cell and sharp cutoff for longer wavelengths. The emitter is at 1200K, and is designed and optimized by modeling triangular grooves to excite localized groove modes which are well-matched to the GaInAsSb TPV cell external quantum efficiency (EQE) for high efficiency energy conversion. We suggest that a quasi-monochromatic, narrow-band and coherent emitter at a frequency near the energy band-gap of the converter is an ideal source to achieve high conversion efficiency.

Gas turbines are one of the most important energy conversion methods in the world today. This is because using gas turbines, large scale, high efficiency, low cost and low emission energy production is possible. For this type of engines, low pollutants emissions can be achieved by very lean premixed combustion systems. Numerical simulation is foreseen to provide a tremendous increase in gas turbine combustors design efficiency and quality over the next future. However, the numerical simulation of modern stationary gas-turbine combustion systems represents a very challenging task. Several numerical models have been developed in order to reduce the costs of flame simulations for engineering applications. In the present paper the Flamelet-Generated Manifold (FGM) chemistry reduction method is implemented and extended for the inclusion of all the features that are typically observed in stationary gas-turbine combustion. These consist of stratification effects, heat loss and turbulence. The latter is included by coupling FGM with the Reynolds Averaged Navier Stokes (RANS) model. Three control variables are included for the chemistry representation: the reaction evolution is described by the reaction progress variable, the heat loss is described by the enthalpy and the stratification effect is expressed by the mixture fraction. The interaction between chemistry and turbulence is considered through a presumed probability density function (PDF) approach, which is considered for progress variable and mixture fraction. This results in two extra control variables: progress variable variance and mixture fraction variance. The resulting manifold is therefore five-dimensional, in which the dimensions are progress variable, enthalpy, mixture fraction, progress variable variance and mixture fraction variance. A highly turbulent and swirling flame in a gas turbine model combustor is computed in order to test the 5-D FGM implementation. The use of FGM as a combustion model shows that combustion features at gas turbine conditions can be satisfactorily reproduced with a reasonable computational effort. The implemented combustion model retains most of the physical accuracy of a detailed simulation while drastically reducing its computational time, paving the way for new developments of alternative fuel usage in a cleaner and more efficient combustion.

Demand of secondary energy is ever increasing. Presently, fossil fuels supply majority of it. Energy technologists are currently facing the formidable challenge of meeting this demand with minimum environmental impact, specifically reduced CO2 emission to minimize ‘climate change’. Also new technology development for efficient energy conversion is needed for renewable resource (e.g. biomass) utilization. Rice straw is an agricultural residue and has good calorific value to be used as an energy resource. For the efficient utilization of rice straw, combined cycle gas turbine (CCGT) based polygeneration is a possible option to deliver multiple utilities. In this paper, a polygeneration plant is proposed to deliver power, cooling, heating and desalinated water. It was simulated by Aspen Plus®. Results show that polygeneration has good potential in power generation as well as for various other utilities. Effects of gasification parameters and gas turbine compression ratio are also studied. Results show that optimum equivalence ratio is 3.5–4 for maximum fuel energy savings ratio and for maximum exergy efficiency. Higher GT-cycle compression ratio results more power output but other utility outputs decrease with increase in compression ratio.Copyright © 2014 by ASME

This paper presents a novel energy storage and recovery architecture for speed-controlled hydraulic actuation in hydraulic elevators. The study is motivated by a need to increase efficiency in the fluid power industry, in general, and hydraulic elevators, in particular. In contrast to previously employed systems, the proposed architecture eliminates the need for throttling and inefficient energy conversions in electric motor/generators. The system has 6 main components: 1 actuator, 1 hydraulic transformer composed of 2 pump/motors, 2 accumulators, a reservoir or small auxiliary accumulator, and a small auxiliary electric motor to recharge accumulators. By operating in 3 different modes, the system is always able to recapture energy when decreasing actuation speed, and return energy if needed when increasing actuation speed. Assessment of the proposed architecture is accomplished through high-fidelity simulations and a simplified analytical model. The analytical model is derived with the pump/motor displacements as a single input. A heuristic rule-based control is developed to control the high-fidelity simulation through an operation cycle and a comparison to a counterweighted elevator simulation is done to validate energy advantages of the novel system. Preliminary results demonstrate the ability of the system to follow a velocity profile using a single input. Comparison with a conventional counterweighted hydraulic elevator shows a large increase in energy efficiency. It is believed the architecture may have additional applicability to a wide range of hydraulic machines, such as heavy equipment used in construction, manufacturing, forestry, etc.Copyright © 2014 by ASME