Search

The oscillating-water-column (OWC) wave energy converter with air turbine has been object of extensive development. The spring-like effect of air compressibility in the chamber is related to the density–pressure relationship. It is known to significantly affect the power performance of the full-sized converter, and is rarely accounted for in model testing. A method is presented to correct results from physical model testing for effects of air compressibility. It combines linear theory in the frequency domain and hydrodynamic coefficients, together with air thermodynamics. A new concept of linear turbine simulator aerodynamically equivalent to the orifice simulator is introduced in the theory. Corrections for non-linear real-fluid effects may be accounted for from comparisons with data from wave tank testing. The method was validated in a case study involving published data from OWC model testing with regular waves of different periods and amplitudes in a wave flume. Theoretically based corrections were found to well predict the air compressibility effects upon power performance. Air compressibility may negatively or positively affect power conversion depending on whether the wave period is larger or smaller than a critical value accurately predicted by the theory. • A theory is developed to correct OWC model test results for air compressibility. • The theory is based on frequency domain analysis corrected for real fluid effects. • New concept of linear turbine simulator equivalent to orifice damping is introduced. • The theory is validated by comparisons with published physical model test results. • The compressibility effect may be positive or negative, depending on wave frequency. [ABSTRACT FROM AUTHOR]

In order to improve the performance of an air turbine starter，the aerodynamic performance and flow field details of the air turbine starter are studied by combining numerical simulation and experiment. The numerical simulation results show that there is obvious flow separation inside the inlet elbow，leading to poor uniformity of the downstream flow field. There is a certain boundary layer separation on the surface of the guide vane and rotor blade，and the flow field is relatively poor because the smooth flow is not fully considered in the exhaust frame. The comparison between the numerical simulation results and the experimental results shows that the air flow rate obtained by numerical simulation is about 1.90% lower than that of the experiment，and the turbine power is about 1.04% higher. Generally speaking，the numerical simulation is in good agreement with the experiment，and this numerical simulation method has a high accuracy to study the air turbine starter. The performance of the air turbine is significantly improved by the optimized design of the guide vane. The power of the air turbine is increased by 14.2% compared with the prototype. [ABSTRACT FROM AUTHOR]

A fully-submerged bottom-standing 1.5 MW wave energy converter (WEC) equipped with a membrane-pump system is under development for installation at a test site off the coast of Pembrokeshire, Wales, UK. The system comprises several flexible-membrane air cells that are compressed and sucked by the action of the waves, rectifying valves, low-pressure and high-pressure ducts, and a unidirectional air turbine that drives an electrical generator. This two-part paper reports the design and testing of an effective control law to be implemented into the programmable logic controller of the membrane-pump turbine-generator set, allowing efficient and safe operation for the wave climate at the Pembrokeshire test site. Part 1 of this paper concerns developing the design strategy of the control laws, the numerical model, and the performance evaluation of the WEC power take-off system. A genetic algorithm is used to design control laws to maximise each sea state's WEC time-average efficiency. An adaptive control algorithm is devised by cross-correlating the control laws parameters and the rotational speed. The final result is a control law that uses input the rotational speed signal and airflow density. It adapts to the sea state conditions while maximising the time-average total efficiency of the membrane-pump WEC for deployment off the Pembrokeshire coast. • A genetic algorithm used to design control laws. • Torque versus rotational speed control-laws studied using Bézier curves. • Adaptive control devised by correlating control parameters and rotational speed. • The control law uses as input the rotational speed and airflow density. • A one-parameter adaptive control law provides good performance. [ABSTRACT FROM AUTHOR]

The path to the World's energy system decarbonisation requires the contribution of a mix of renewable energy sources. In particular, wave energy and oscillating-water-column (OWC) devices can be significant contributors. However, they are still in an early stage of development, and their levelized cost of energy (LCOE) is still too high to compete in the utility market. The Wells turbine is an attractive solution to reduce the LCOE of OWC devices. Completing the available information in the literature on the performance of different Wells arrangements is a necessary step towards decision-making on which configuration is most cost-efficient given the hydrodynamic characteristics of a particular OWC wave energy converter (WEC). Furthermore, there is a research gap on these devices' acoustics, which needs to be filled, given the impact noise might have on surrounding ecosystems. This study investigated the aero-acoustics performance of four Wells turbine geometries, including monoplane and biplane turbines with and without guide vanes. Experimental tests of the turbine models were conducted in an open-circuit test rig under design and off-design flow conditions. The research provides accurate aerodynamic data on very high flow rate (pressure) coefficients, essential to turbine-generator control algorithms and OWC WECs wave-to-wire numerical models. A specific noise level definition was inferred by analysing the aerodynamic noise sources in Wells turbines. This allows the prediction of noise emission from geometrically similar turbines of different sizes and rotational speeds from the experimental noise data collected with the tested Wells turbines. • Aero-acoustic characterisation of Wells turbine in design and off-design conditions. • Rotor blade trailing edge noise emission is dominant in stall-free operation. • A sharp increase in noise emission is observed with the stall onset. [ABSTRACT FROM AUTHOR]

The concept of optimization of operating and design parameters of the regenerative air turbine cogeneration (RATC) system is proposed. To determine the energy efficiency indicators of this system, its thermodynamic analysis was performed. At the same time, it is shown that it is not correct to search for the optimal parameters of such a system only by energy indicators, and modern thermoeconomic methods should be more actively involved in pre-design practice, which allow a comprehensive evaluation of the efficiency and economy of the energy-technological system as a whole and its individual elements. Therefore, on the basis of the data obtained during the thermodynamic analysis, exergy destruction and losses in the main system elements were calculated. Then, using the structural-variant method in combination with the graphical apparatus of C-curves, the pre-project thermoeconomic optimization of the RATC system was performed. This made it possible to choose the optimal operating and design parameters of the system and determine the minimum cost for its creation and operation throughout the entire life cycle, taking into account the thermodynamic perfection of the main system elements. Each variable operating mode parameter of the system serves as a kind of navigator when searching for the option of system parameters that is optimal in terms of energy and economic indicators, which is accompanied by graphic visualization. Therefore, the proposed approach makes the optimization of the system being designed convenient and clear. It can be used in the optimal design of various types of thermal transformers and other energy-technological systems. [ABSTRACT FROM AUTHOR]

A fully-submerged bottom-standing 1.5 MW wave energy converter (WEC) equipped with a membrane-pump system is being developed for installation at a test site off the coast of Pembrokeshire, Wales, UK. The system comprises several flexible-membrane air-cells that are compressed and sucked by the action of the waves, a system of rectifying valves, low-pressure and high-pressure ducts and a unidirectional air turbine that drives an electrical generator. This two-part paper reports the design and testing of an effective control law to be implemented into the programmable logic controller of the membrane-pump turbine-generator set, allowing efficient and safe operation for the wave climate at the Pembrokeshire test-site. Part 2 of this paper focuses on the experimental investigation at the IST variable flow test rig of the real-time control algorithm described in Part 1 of this paper, using a 1:2.4 turbine scale model. Tests were performed for five sea-states and two turbine model average rotational speeds. Experimental results reveal that the control law proposed for the Pembrokeshire mWave turbine-generator set, based only on the turbine rotational speed and airflow density measurements, is effective and of a simple implementation. Fine fitting between the model testing results validates the performed scaling of the variables related to the time-dependent turbine-generator operation, as well as the numerical model of the system described in Part 1. • The turbine-generator set real-time control algorithm was experimentally studied. • Tests were performed for five sea-states and two turbine model average rotational speeds. • The control law based on the turbine rotational speed and airflow density is effective. • Model testing results validate the scaling of the turbine-generator operation time-dependent variables. [ABSTRACT FROM AUTHOR]

The oscillating-water-column (OWC) wave energy converter with air turbine has been object of extensive research and development effort, including the deployment of floating and fixed-structure full-sized prototypes into the sea. It consists of a hollow (fixed or floating) structure, open to the sea below the water surface. Wave action alternately compresses and decompresses the air trapped above the inner water free-surface in a chamber, which forces air to flow through a turbine coupled to an electrical generator. The spring-like effect of air compressibility in the chamber is related to the density-pressure relationship. It is known to significantly affect the power performance of the full-sized converter, and is rarely accounted for in theoretical modelling, and even more rarely in physical model testing at reduced scale, as appears from the literature review. Three theoretical models of increasing complexity are analysed and compared: (i) the incompressible air model; (ii) the isentropic process model; (iii) and the (more difficult and rarely adopted) adiabatic non-isentropic process model in which losses due to the imperfectly efficient turbine are accounted for. The air is assumed as a perfect gas. The hydrodynamic modelling of wave energy absorption is based on linear water wave theory. The validity of the various simplifying assumptions, especially in the aero-thermodynamic domain, is illustrated by a case study with numerical results for a fixed-structure OWC equipped with a Wells turbine. Results are shown for regular and irregular waves, and for a theoretical simulation of model testing in wave tank at small scale. • The air compressibility effect in the chamber of OWCs was revised and analysed. • Converter performance may be substantially affected by compressibility effects. • Isentropic model was found to give good results for the compressibility effect. • Rules were derived for the air chamber volume in physical model testing. • Physical model testing may provide good simulation of compressibility effects. [ABSTRACT FROM AUTHOR]

A 30 kW fixed-guide-vanes biradial turbine-generator set was designed by Instituto Superior Técnico (IST) and manufactured by Kymaner, within the framework of the H2020 European project OPERA, for open sea testing at the Mutriku breakwater oscillating water column (OWC) power plant and at the IDOM MARMOK-A-5 OWC spar-buoy, deployed at BiMEP, Basque Country, Spain. The paper reports the design and construction of the prototype, and its dry testing at IST, in a variable-flow test rig, simulating the oscillating flow induced by irregular waves. Results show that the turbine exhibits a peak efficiency of 70% under steady-state conditions and an average efficiency of 56% for the control laws tested. [ABSTRACT FROM AUTHOR]

The oscillating water column (OWC) device is one of the most reliable wave energy converters. The air turbine generator uses the pressure difference between the air chamber and the atmosphere to generate electricity. The design of OWC devices requires simultaneous consideration of the air turbine and its influence on the hydrodynamic process of wave energy absorption. Biplane-rotor Wells turbines are suitable for applications requiring high-pressure heads and have been investigated in only a few studies. This paper concerns the design and experimental testing of a high-solidity biplane Wells turbine with and without guide vanes. Turbines with a rotor diameter of 0. 590 m were tested on a unidirectional flow test rig to investigate turbine performance and flow characteristics. Considering a numerical stochastic Gaussian approach, data from the literature was used to compare the performance of the tested Wells turbines to other Wells turbine configurations under irregular bidirectional variable flow. The results show that introducing intermediate guide vanes on a 0. 96 solidity biplane Wells turbine increased the peak efficiency of the turbine by 6 % while reducing the damping of the OWC. The comparative analysis of different turbine configurations in variable flow shows that the high-solidity Wells turbine with guide vanes does not have the highest instantaneous nor the average peak efficiency. However, it can produce higher output power. In addition, the rotor diameter and rotational speed are lower than the lower solidity turbines, which provide similar damping. • Testing of biplane Wells turbine with and without guide vanes. • The guide vanes were found to decrease the turbine damping. • The presence of guide vanes increases the power output under variable flow. • High-solidity Wells turbines are suitable for high-pressure head applications. [ABSTRACT FROM AUTHOR]

Control algorithms for wave energy conversion technologies with air turbines require contingency tools to prevent the rated power and maximum rotational speed from being exceeded. Survival problems limit energy conversion when the available power is too large compared to the turbo-generator-rated power. Short-term predictions require information from local wave-measuring buoys, which raises reliability concerns. Wave groups in the ocean result in extremely high wave power peaks that cannot be smoothed by low-inertia power-take-off (PTO) systems, leading to survival problems. The most common strategy to cope with this situation is to set the rated power of the PTO several times more than the annual average produced electrical power. The PTO is shut-down when the available power is excessive. These two engineering decisions have a detrimental impact on the capacity factor and the energy cost. The paper shows a new control algorithm for wave energy oscillating-water-column (OWC) devices that can control the shutter position of a fast-acting valve to dissipate the pneumatic energy excess. Hence, the PTO can operate even when the available power is significantly larger than the generator's rated power. The algorithm was validated with the 30 kW biradial turbine prototype from the OPERA H2020 European project under real sea conditions at Mutriku's wave power plant. Results show the algorithm's effectiveness in real situations and during a generator failure simulated during the experimental campaign. This new concept may reduce the energy cost from wave energy and open a new field of design possibilities for OWC wave energy converters. • First-of-a-kind hardware to perform peak shaving in OWC wave energy devices. • Algorithm tested at Mutriku's wave power plant in real sea conditions. • Generator's rated power and maximum rotational speed are prevented from being exceeded. • The algorithm protects the power take-off system in the case of a generator failure. • Novel peak shaving control can reduce the OWC WECs energy costs. [ABSTRACT FROM AUTHOR]

Abstract The paper presents an experimental study of a novel self-rectifying twin-rotor air turbine to equip an oscillating water column wave energy converter. The turbine is based on a pair of conventional radial inflow rotors mounted on a common shaft, complemented by the corresponding inlet guide vane rows, by a curved-duct manifold arranged circumferentially in a periodic manner and by an axially-moving cylindrical valve. The valve ensures that the air flows alternately through one or the other of the two parts of the twin-rotor turbine, depending on the sign of the pressure head. Due to its symmetry, only one half of the twin-rotor turbine was constructed and tested in a relatively large-scale unidirectional flow at the blow-down test rig of Instituto Superior Técnico. Results are presented in dimensionless form for efficiency, power output, pressure head and flow rate. A comparison with self-rectifying turbines commonly used in wave energy converters is shown. Additionally, an approach of turbine efficiency in random waves was made using the stochastic model. Highlights • The twin-rotor turbine attains a peak efficiency of about 74%. • The turbine efficiency remains above 60% over a wide range of ow rates. • Most of the kinetic energy at the rotor exit is recovered by the manifolded diffuser. • Windages losses at the inactive rotor are more significant at the lower flow rates. [ABSTRACT FROM AUTHOR]

The oscillating water column (OWC) with an air turbine is a major class of wave energy converter that has been object of extensive research and development effort over many years, including the deployment of prototypes into the sea. In an OWC, the air alternately flows from the chamber to the atmosphere and back. Unless check valves are used, the turbines are self-rectifying, i.e. their rotational direction remains unchanged regardless of the direction of the air flow. The paper presents a comparative study of the performance of various types of self-rectifying air turbines and their suitability to different OWC applications and energy levels of the local wave climate. The study is based on available information on results from laboratory testing at Reynolds numbers high enough to make those results representative of full-sized machine performance under real operating conditions. Average values of flow rate, pressure head and efficiency are used in the comparisons, based on a stochastic approach in which the pressure oscillations in the OWC air chamber are assumed to be a random Gaussian process. [ABSTRACT FROM AUTHOR]

Global energy strategy has quickly shifted to a new paradigm. Countries understand the importance of a near-zero carbon energy mix and the need to reduce their energy imports and become energy independent. One immediate solution is the re-enforcement of renewable energy infrastructures such as wind, solar and hydro generation. However, certain sectors, particularly the Blue Economy, may need a different solution. The oscillating-water-column (OWC) wave energy converter is a proven concept, many prototypes of which are already being deployed on the open sea, and can help bridge this gap. Energy harvesting from this system will be improved if more efficient (and reliable) power take-off (PTO) systems and control algorithms are used. A novel control algorithm for a turbine–generator set was developed based on the physical interactions between the PTO and the OWC system. The results were compared with experimental data from real operation at sea. The algorithm does not need to predict the sea state conditions in order to maximise power generation. Additionally, it protects the PTO in extremely energetic sea states and minimises overspeeding and the use of a safety valve. Comparing the operating results of the 30 kW biradial turbine–generator set at the Mutriku wave power plant with the corresponding numerical results provided by the novel control algorithm showed a 6% increase in annual electricity production. • Increase of 6% in the mean annual electrical energy production was achieved. • The novel control law balances electrical generator and turbine efficiencies. • Prediction of sea state conditions is not needed, avoiding wave-measuring systems. • The novel control law needs the infrequent use of a low-speed safety valve. [ABSTRACT FROM AUTHOR]

The oscillating-water-column device equipped with an air turbine is regarded by many researchers and developers as the simplest and most reliable wave energy converter. It has been object of extensive development effort, including the deployment of prototypes into the sea. The maximization of the produced electrical energy involves the control of the rotational speed, which affects the hydrodynamic process of wave energy absorption, the turbine aerodynamics and the performance of the electrical equipment. In the paper, the overall performance of the plant is modelled as an integrated process, with the hydrodynamic modelling based on linear water wave theory. Special account is taken of the electrical efficiency dependence on the load factor and of the constraint introduced by electrical rated power as a power level that should not be exceeded. A case study was selected to investigate these issues: the existing bottom-standing plant on the shoreline of the island of Pico, in the Azores Archipelago. Results are presented for the control of the self-rectifying air turbine of biradial type and for the annually produced electrical energy as affected by turbine size and by electrical rated power. [ABSTRACT FROM AUTHOR]

A novel air turbine for bidirectional flows in oscillating-water-column wave energy converters is presented and its performance is analyzed. The turbine is based on a pair of conventional radial-inflow rotors mounted on the same shaft, complemented by the corresponding guide vane rows, by a curved-duct manifold arranged circumferentially in a period manner and by a two-position cylindrical valve. Numerical values of the performance of the whole machine were obtained from published experimental data of the flow through a conventional radial-inflow gas turbine, together with CFD (computational fluid dynamics) results for aerodynamic losses in the curved duct manifold. Four different geometries, combined with five different sizes, of the curved-duct manifold were numerically simulated. Windage losses, that occur at the inactive rotor and are inherent to the machine conception, were found to be a major loss. A peak value of about 86% was obtained for the overall efficiency of the machine. Comparisons are presented between the new turbine and the biradial turbine (sliding guide-vanes version), the latter being possibly the most efficient self-rectifying turbine model-tested so far. The new turbine was found to be more efficient, both in peak instantaneous efficiency and in maximum average efficiency in random waves, by a margin of about 8%. [ABSTRACT FROM AUTHOR]

This study presents the design and evaluation of a high-speed and precision microspindle used for micromechanical machining. A radial impulse turbine with two rows of nozzles was designed to realize the high-speed performance. A monolithic flexible coupling was used to decouple the turbine shaft and the tool, and then, the tool shank was directly supported by aerostatic bearings, which can minimize the run-out of the tool at high speeds. Additionally, a shape memory alloy (SMA)-based clamp was designed for tool clamping. It can avoid the assembly error caused by stack-up tolerances. The microspindle has simple configuration and compact design with a 30-mm outer diameter and a 95-mm length. The prototype microspindle has a maximum speed of over 240,000 rpm and a tool radial run-out of 2.79 μm. The evaluation results show the feasibility and potential application of the new design concept of the microspindle proposed in this study. [ABSTRACT FROM AUTHOR]

Under the circumstance of pursuing high speed and miniaturization, mini-type air turbines have been widely applied to high-speed dental handpieces in recent years. Among all the components of a mini-type air turbine, bearing is the most important part which significantly affects its efficiency. Friction, collision, and wear are the main causes to make the ball bearing unable to reach higher efficiency. Though very small sliding friction can be realized by the aerostatic bearing, its poor bearing capacity limits the application. This research combines the magnetic and aerostatic levitation principle to develop a magnetoaerostatic hybrid bearing for miniature air turbine. The aerostatic bearing undertakes the main function of the radial and the axial bearings. However, the air bearing also possesses a drawback, which is pneumatic hammer effect induced by the air compressibility. In order to eliminate the pneumatic instability, an axial passive magnetic bearing is integrated into the aerostatic bearing. With the magnetic bearing, not only the bearing capacity can be improved, but also the pneumatic hammer effect can be significantly damped. Both theoretical calculation and finite element method (FEM) are used to study the cause and elimination solution of the pneumatic instability. Through experimental testing, the performance of our developed magneto-aerostatic bearing is also verified. The magneto-aerostatic bearing suppresses the axial vibration over 57%, and also enhances its axial bearing capacity by 50%. [ABSTRACT FROM AUTHOR]

The Wells turbine is the most frequently used or proposed self-rectifying air turbine for oscillating-water-column wave-energy converter application, largely because of its conceptual and mechanical simplicity. Biplane Wells turbines allow a higher total blade solidity to be attained than monoplane turbines do, but this results in larger aerodynamic losses associated with the swirl kinetic energy loss at turbine exit. This may be overcome by the presence of a row of guide vanes between the two rotor planes, a solution that had been proposed and investigated theoretically or by numerical modelling. Results of turbine overall performance and flow details are reported from laboratory tests of a biplane Wells turbine without guide vanes and with specially designed guide vanes. The presence of the guide vanes was found to increase the peak efficiency by seven percentual points, while reducing (for fixed rotational speed) the damping provided by the turbine. Measured losses in the guide vane row were much smaller than in the rotors. Experimental results are compared with previously published numerical results. A stochastic theoretical transform was applied to obtain averaged results for the turbine performance subject to the irregular bidirectional air flow induced by real sea waves. • A biplane Wells turbine was tested with and without intermediate guide vanes. • The energy losses in the guide vanes were small compared with losses in the rotors. • The guide vanes were found to increase the peak efficiency by about seven percent. • The presence of guide vanes decreases the turbine damping effect. • The experimental results fairly well agree with published CFD results. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents results from model testing of a self-rectifying radial-flow air turbine, that is being developed as an alternative to the axial-flow self-rectifying turbines for applications in wave energy conversion. In the new machine, named biradial turbine, the flow into, and out of, the rotor is radial. The rotor is surrounded by a pair of radial-flow guide-vane rows. The downstream guide vanes are prevented from obstructing the flow coming out of the rotor by axially displacing the whole guide vane set. The turbine model, with a 0.488 m diameter rotor, was tested in unidirectional flow. Experimental results are shown, in dimensionless form, for efficiency, power and pressure head versus flow rate. They are compared with predictions from CFD computations. The results from model testing were used to estimate the time-averaged efficiency of the turbine subject to the irregular bidirectional air flow induced by random waves. [Copyright &y& Elsevier]

Abstract: The flow through the air turbine of an oscillating water column (OWC) wave energy converter is reciprocating and is random and highly variable. It is not surprising that the time-averaged efficiency of the air turbine is substantially lower than that of a conventional turbine working in nearly steady conditions. A new type of radial-flow self-rectifying turbine (named here biradial turbine) is described in the paper. The two inlet/outlet openings of the rotor are axially offset from each other and face radially the surrounding space. The turbine is symmetrical with respect to a plane perpendicular to its axis of rotation. The rotor blades are surrounded by a pair of radial-flow guide-vane rows. Each guide vane row is connected to the rotor by an axisymmetric duct whose walls are flat discs. A two-dimensional flow method is used first as a preliminary design tool for the turbine geometry. More detailed numerical results are then obtained with the aid of a commercial three-dimensional real-fluid CFD code, which allows a more refined geometry optimization to be carried out, and yields results for flow details through the turbine and for the turbine overall performance under several operating conditions. [Copyright &y& Elsevier]

Abstract: The paper concerns the hydrodynamic analysis and optimization of an OWC spar buoy, possibly the simplest concept for a floating oscillating water column (OWC) wave energy converter. It is an axisymmetric device consisting basically of a submerged vertical tail-tube-fixed to an axisymmetric floater that oscillates essentially in heave. The air flow displaced by the water motion inside the tube drives a self-rectifying air turbine. The possible advantages of using a tube of non-uniform inner cross section are investigated theoretically and numerically, especially as a way of reducing the draught of the device without significantly impairing its power performance. The unsteady water flow in the tube is modelled as one-dimensional. The frequency-dependent hydrodynamic coefficients of the tube-floater pair were computed with a boundary-element code. A linear air turbine is assumed. The hydrodynamics of the wave energy absorption is analysed in the frequency domain, including the effect of air compressibility in the chamber; special attention is devoted to optimization. Numerical results are presented for device''s performance in regular and irregular waves, including especially optimization of the tube geometry and of the turbine characteristic. Practical implications of these results are discussed. [Copyright &y& Elsevier]

Abstract: Remote areas around the world predominantly rely on diesel-powered generators for their electricity supply, a relatively expensive and inefficient technology that is responsible for the emission of 1.2million tons of greenhouse gas (GHG) annually, only in Canada . Wind–diesel hybrid systems (WDS) with various penetration rates have been experimented to reduce diesel consumption of the generators. After having experimented wind–diesel hybrid systems (WDS) that used various penetration rates, we turned our focus to that the re-engineering of existing diesel power plants can be achieved most efficiently, in terms of cost and diesel consumption, through the introduction of high penetration wind systems combined with compressed air energy storage (CAES). This article compares the available technical alternatives to supercharge the diesel that was used in this high penetration wind–diesel system with compressed air storage (WDCAS), in order to identify the one that optimizes its cost and performances. The technical characteristics and performances of the best candidate technology are subsequently assessed at different working regimes in order to evaluate the varying effects on the system. Finally, a specific WDCAS system with diesel engine downsizing is explored. This proposed design, that requires the repowering of existing facilities, leads to heightened diesel power output, increased engine lifetime and efficiency and to the reduction of fuel consumption and GHG emissions, in addition to savings on maintenance and replacement cost. [Copyright &y& Elsevier]

Abstract: An innovative air driven spindle for micro-milling applications is presented, in which a so-called viscous turbine is used to both drive and support the spindle. The viscous turbine drives the spindle by exerting viscous traction forces directly on the smooth surface of the spindle. It is even possible to use a standard milling tool directly as spindle, thereby rendering a tool holder, with its inherent inaccuracies, redundant. Furthermore the viscous turbine not only drives the tool, but also functions as an aerostatic radial bearing. In this paper the viscous turbine concept is presented, and an optimisation for the pertinent design dimensions is carried out using a simplified analytical model. A prototype spindle design is presented, and the results of the first experiments are analysed and improvements for the second prototype are proposed. [Copyright &y& Elsevier]

The aim of this study was to evaluate tooth vibration obtained with the Er:YAG laser and high-speed drills. The rotational apparatuses used were the air turbine and the quintuple speed handpiece. Five of the extracted upper first premolars were built up on the plaster box. Silicone impression material was selected as experimental periodontal tissue in this study. The vibration speed and frequency characteristics were measured by using a laser Doppler vibrometer, which has a high accuracy and reproducibility compared with acceleration pickup. We found that small vibration of the tooth occurred with the Er:YAG laser preparations. The rotational drill preparation caused greater tooth vibration with a frequency peak in or near the domain which had the high sensitivity of hearing compared to the Er:YAG laser, suggesting them to be the primary factors of provoking pain and discomfort during tooth preparation. [Copyright &y& Elsevier]

The method of wave energy conversion utilises an oscillating water column (OWC). The OWC converts wave energy into low-pressure pneumatic energy in the form of bi-directional airflow. Wells turbine with its zero blade pitch setting has been used to convert this pneumatic power into uni-directional mechanical shaft power. Measurements in OWC based wave energy plants in India and Japan show that the airflow velocity is not equal in both directions. The velocity is more when the airflows out to the atmosphere (exhalation) than in the reverse direction. It may be advantageous to set the rotor blade pitch asymmetrically at a positive pitch so as to achieve a higher mean efficiency in a wave cycle. Towards this objective, performance characteristics of a turbine with different blade setting angles in steady flow were found by experimentation. Quasi-steady analysis was then used to predict the mean efficiency for a certain variation of air velocity with time. This variation with time was taken as pseudo-sinusoidal wherein the positive part of the cycle was taken as a half sine-wave whose amplitude is greater than that of the negative half sine-wave. Such a variation is representative of what happens in reality. For exhalation velocity amplitude to inhalation velocity ratios 0.8 and 0.6, a rotor blade setting angle of 2° was found to be optimum. [Copyright &y& Elsevier]

[Display omitted] • A novel municipal solid waste fired combined cycle plant has been developed. • Exergy, economy and environmental assessments of the plant have been carried out. • Optimization is done to get lowest electricity price and highest exergy efficiency. • The proposed plant has an optimized exergy efficiency of 39%. • The plant has electricity price of 0.085 $/kWh at the optimal operating condition. This paper aims to design, analyze, and find the optimized performance of a novel municipal solid waste fired combined cycle power plant, to cater the utility electrical needs of an urban municipality. Performance of the plant is evaluated through energy, exergy, economy and environmental analyses. Response surface methodology is used as optimization tool for finding the optimal performance of the plant. Air compressor outlet pressure, air turbine inlet temperature, hot end temperature difference of the dual combustor and heat recovery unit, organic vapor turbine inlet temperature, and organic vapor turbine inlet pressure are considered as input parameters for finding out the optimal values of the response parameters such as exergy efficiency and levelized unit cost of electricity. This particular regression model offers extremely accurate results for the response parameters. The optimal values of exergy efficiency and cost of electricity are found to be about 39% and 0.085 $/kWh (5.3 INR/kWh), respectively at the air compressor outlet pressure of 4 bar, air turbine inlet temperature of 1100 °C, hot end temperature difference of 70 °C, and organic vapor turbine inlet temperature and pressure of 201.8 °C and 5 bar, respectively. At this optimal operating point, the plant can deliver 1810 kW electricity with an environmental damage cost savings of 270 $/year compared to the environmental damage cost associated with the conventional land-filling of municipal solid waste. Composite desirability for this model is found to be 1, indicating the fact that the model predicts the best suitable results for the proposed plant's performance optimization. [ABSTRACT FROM AUTHOR]

We here present and analyze a novel conceptual design of 550 MW-level, syngas-fueled intermediate-temperature solid oxide fuel cell (SOFC)/Air Turbine (AT) hybrid system with an oxy-fuel combustion. To decouple the operation of SOFC and AT and allow independent operation of each, an intermediate heat exchanger is implemented between SOFC and AT cycles to transfer only heat from SOFC to AT. To facilitate CO 2 separation and capture, the gas streams from both electrodes are separately operated and pure O 2 is used in the afterburner for combustion. A total of four scenarios has been analyzed to cover the effects of current density, pressure and staged SOFC design. The results show that by elevating the pressure to 10 atm and using two-stage SOFC design, the system can achieve an overall efficiency of 64% at a nominal power output. The work provides important engineering insights in SOFC staged design and operating conditions for the next-generation SOFC/turbine hybrid systems. • A MW-level syngas-fueled solid oxide fuel cell/Air Turbine hybrid system. • An intermediate heat exchanger between SOFC and AT. • Pressure and multi-stage SOFC design effects on the overall system efficiency. [ABSTRACT FROM AUTHOR]

Self-rectifying impulse turbines are a popular alternative to the Wells turbine for oscillating-water-column wave energy converters. Self-rectifying impulse turbines have two sets of guide-vanes, one set placed symmetrically on each side of the rotor, instead of a single set as in unidirectional turbines. The efficiency of self-rectifying turbines with fixed guide-vanes is known to be severely affected by the large aerodynamic losses due to the inherent misalignment between the outflow from the rotor and the downstream guide-vanes. The biradial turbine is an advanced, more efficient, version of the impulse self-rectifying turbine, as compared with the conventional axial-flow type. The paper presents a new topology for the radially-set guide-vane system arranged into multiple, rather than simple, rows, aiming to increase the turbine efficiency by reducing the losses by aerodynamic outflow stalling at the exit guide-vane system while ensuring the required inflow deflection by the inlet guide vanes. The design method combines an evolutionary optimisation algorithm with cascade-flow CFD RANS calculations. Experimental results are presented to validate the design method and to assess the performance and flow-losses of the single and double-row guide-vane system configurations. • Single-row stator configuration high blockage severely penalises turbine efficiency. • Multiple-row guide-vane systems reduce rotor outflow obstruction. • Turbine peak efficiency increased by using a novel double-row guide-vane system. [ABSTRACT FROM AUTHOR]

The self-rectifying biradial air turbine was proposed to equip wave energy converters of the oscillating-water-column type. There are two configurations: with fixed guide vanes and a radially more compact one with axially-sliding guide vanes. The added complexity of the movable guide-vane mechanism represents a drawback in offshore environments. The configuration with fixed guide vanes is the object of the present investigation using a novel stator design. The guide-vanes were radially shifted from the rotor and the single row of guide-vanes, located on each side of the rotor, was replaced by two concentric rows of guide-vanes, with wider circumferential spacing for the exit-flow. The work comprised the design, construction and experimental study of a 0.5 m rotor diameter turbine model tested under steady flow. Experimental results show that the new stator design provides significant reduction in the flow stagnation pressure losses at the exit guide vanes, while appropriately turning the flow admitted into the rotor. The measured efficiency reaches a peak of 0.728 and is above 0.6 over a wide range of flow coefficients. [ABSTRACT FROM AUTHOR]

Sustained power supply and thermal protection of electronic elements are two essential problems for developing long-endurance and reusable hypersonic aircrafts. In this study, a combined power and cooling (CPC) system is established between high temperature incoming air and low temperature fuel based on fuel cooling air turbine and organic Rankine cycle (ORC). The organic Rankine cycle is investigated based on thermodynamic analysis. The fuel rotating cooling air turbine is modeled with a mean diameter of 150 mm and investigated with 3D CFD simulation. The turbulence models for main flow and cooling channel are k-omega and SST, respectively. And the CFD method for air turbine is verified with land experimental test. Finally, the performance of the CPC system is theoretically researched. ORC can obviously increase the power output of the CPC system. With the designed air turbine, the real power output of the CPC system is 118.5 kW, higher by 20.7% than air turbine's power of 98.2 kW. The obtained mass flow rate of cooling air is 0.292 kg/s. The blade of the air turbine can be cooled with reasonable low mass flow rate of 5 g/s per blade. • The power of the CPC system is 118.5 kW, including AT 98.2 kW and ORC 20.3 kW. • Fuel with 5 g/s per blade is enough for cooling the air turbine. • The mass flow of cooling air obtained after ORC is 0.292 kg/s. • Air turbine land experimental test is carried out. [ABSTRACT FROM AUTHOR]

The Tupperwave device is a closed-circuit oscillating water column (OWC) wave energy converter that uses non-return valves and two large fixed-volume accumulator chambers to create a smooth unidirectional air flow, harnessed by a unidirectional turbine. In this paper, the relevance of the Tupperwave concept against the conventional OWC concept, that uses a self-rectifying turbine, is investigated. For this purpose, wave-to-wire numerical models of the Tupperwave device and a corresponding conventional OWC device are developed and validated against experimental tests. Both devices have the same floating spar buoy structure and a similar turbine technology. The models include wave-structure hydrodynamic interaction, air turbines and generators, along with their control laws in order to encompass all power conversion stages from wave to electrical power. Hardware-in-the-loop is used to physically emulate the last power conversion stage from mechanic to electrical power and hence validate the control law and the generator numerical model. The dimensioning methodology for turbines and generators for power optimisation is explained. Eventually, the validated wave-to-wire numerical models of the conventional OWC and the Tupperwave device are used to assess and compare the performances of these two OWC type wave energy device concepts in the same wave climate. The benefits of pneumatic power smoothing by the Tupperwave device are discussed and the required efficiency of the non-return valves is investigated. [ABSTRACT FROM AUTHOR]