1,721,058 research outputs found
Development and validation of an advanced simulation model for ORC-based systems
No full textLow-grade heat recovery from solar or geothermal energy may be an eco-friendly resource for electric and thermal energy recovery. The Organic Rankine Cycle (ORC) is one of the main candidates to exploit low-temperature heat sources, otherwise difficult to access using conventional power generation systems. In this paper, an advanced thermodynamic model of an ORC is developed, with the final aim to optimize ORC conversion efficiency, especially for micro-CHP applications. First, a thorough review of issues related to ORC system modeling is presented by analyzing the state-of-the-art experience and advancements. Subsequently, an advanced simulation model is developed, by taking advantage of all the key characteristics of the models presented in the literature. The simulation model is developed in Matlab®/AMESim® environment, which allows system modeling both for steady and transient analysis. The heat source is coupled with the system through a plate heat exchanger, which is modeled using an iterative sub-heat exchanger modeling approach. A scroll expander, modeled in detail by decomposing the behavior of the fluid stream into several steps, is used to extract the useful work. Finally, model predictions for the evaporator and the expander are validated against both numerical and experimental data published in literature. The simulation model of the entire ORC system is also validated against literature data taken on a test bench. Copyright © 2012 by ASME
Experimental analysis of a novel Savonius based spline geometry with flexible blades for Vertical Axis Wind Turbines (VAWT)
No full textCurrently, the wind-power market is dominated by Horizontal Axis Wind Turbines (HAWT) owing to
their high efficiency. Vertical Axis Wind Turbines (VAWT) are far behind in popularity. However, the
interest for future applications of vertical axis wind rotors is increasing because of the simple geometry,
low cost, low sensitivity to turbulent flow conditions and simple and affordable maintenance. Thus, an
improvement in the efficiency of vertical rotors could close the existing gap and make HAWT more
attractive as wind energy conversion devices. In this paper, a new blade spline concept of Savonius
rotor with flexible blades is studied experimentally. The idea is to check the performance improvements
previously achieved by computational CFD simulations. Two Savonius rotors were built using fiber
glass: a rigid rotor with a spline blade shape and a flexible one with the same blade shape but with a
morphing section located at the blade’s tips. Important improvements were registered using the flexible
rotor compared to the same but rigid rotor, in a large working conditions range, validating the CFD
simulation results. The low speed wind tunnel at San Diego State University was utilized for the tests
considering a wind speed in the range of 3.5 to 9.5 m/s. A combined analysis of performance and
flexibility was also performed to find the deformation associated with the best performance for this kind
of rotor. Finally, a comparison was made between the energy conversion of the rigid and flexible rotors
at low wind speed for a possible urban application. Results show a 50% power coefficient improvement
for the flexible rotor compared to the rigid one at the most optimum working condition. A 90% increase
of energy produced by the flexible rotor during one year in the city of San Diego was calculated.
Eventually the most productive wind speed for the flexible rotor was found to be 9m/s. Thus, the
deformation angle obtained at that value (22°- 32°) was considered as the best deformation for this
kind of rotor
Application of an advanced simulation model to a micro-CHP ORC-based system for ultra-low grade heat recovery
No full textThis paper presents the results of the application of an advanced thermodynamic model developed by the authors for the simulation of Organic Rankine Cycles (ORCs). The model allows ORC simulation both for steady and transient analysis. The expander, selected to be a scroll expander, is modeled in detail by decomposing the behavior of the fluid stream into several steps. The heat source is coupled with the system through a plate heat exchanger, which is modeled using an iterative sub-heat exchanger modeling approach. The considered ORC system uses solar thermal energy for ultra-low grade heat recovery. The simulation model is used to investigate the influence of ORC characteristic parameters related to the working medium, hot reservoir and component efficiencies for the purpose of optimizing the ORC system efficiency and power output. Moreover, dynamic response of the ORC is also evaluated for two scenarios, i.e. (i) supplying electricity for a typical residential user and (ii) being driven by a hot reservoir. Finally, the simulation model is used to evaluate ORC capability to meet electric, thermal and cooling loads of a single residential building, for typical temperatures of the hot water exiting from a solar collector. Copyright © 2012 by ASME
Performance Evaluation of a Savonius Wind Turbine with Morphing Blades
No full textAnalysis of a novel flexible blade with the ability to morph and adapt to changing flow conditions is presented in this paper. The concept is applied to a novel rotor geometry with spline function, which is derivative of the traditional S-shape Savonius blade, explored in a previous study by the authors. A Fluid Structure Interaction algorithm, implemented in ANSYS CFX 12.1 and ANSYS Mechanical 12.1, is used to estimate the turbine performance by varying Young’s modulus and monitoring blade tip displacement. Since the Savonius wind turbine has a vertical axis of rotation, the centrifugal forces are an issue because of their high magnitude. Therefore, an effective morphing process is simulated in this study by first neglecting inertia forces. It was registered that, when inertia forces are considered, centrifugal forces tend to overwhelm aerodynamic forces bending both blade tips outward. Alterations to the design are proposed in this paper to account for this negative effect of centrifugal forces, thus validating the initial hypothesis regarding the superior performance of adaptive blades
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Modelling and simulation of waste heat recovery systems for marine applications
No full textWaste heat recovery systems have assumed an important role in the last decade as an effective way to improve fuel utilization in thermal engines, since they provide an opportunity to produce eco-friendly electrical power from an otherwise wasted energy source, leading to a reduction of the pollution and an increase of the overall system efficiency. In this scenario, Rankine cycle technology, based on simple Rankine cycle or Organic Rankine cycle (ORC), earned a good market position, thanks to its ability of producing additional electric power from relatively low- Temperature heat sources (80 to 350°C); this feature makes these cycles a very suitable solution as bottomers to Internal Combustion Engines (ICE), geothermal sources, solar thermal modules and micro-gas turbines. This paper presents a waste heat recovery system specifically designed as a bottomer to ICE of different power range for marine applications, using a simple Rankine cycle or a Rankine cycle with ORC further bottoming. The particular application considered shows several advantages for the installation of a waste heat recovery system; in particular, the basically infinite availability of the cooling medium represented by the water sea, avoids any issues in the condenser design. A steady state model of the system is developed via the process simulator CAMEL-ProTM, in order to identify the most convenient configuration, from a thermodynamic point of view. A most interesting feature of this study with respect to previous works, is the comparison of the organic fluids R245fa and R600, widely recognized as two of the best candidate ORC fluids, within a configuration analysis that critically and analytically compares the improvements regeneration can possibly bring in the low grade regime. To this scope, different cycle configurations have been modeled, simulated and comparatively assessed, in order to figure out whether the more expensive Rankine bottoming ORC brings substantial improvements over the simpler Rankine cycle configuration and to investigate system behaviors in bottoming applications to atmospheric intake or turbo-charged marine Diesel engines. The paper shows how adding a bottoming ORC to the Rankine cycle improves the WHR system performance both in terms of recovered electric power (up to 8.11% and 2.67% respectively in small and large application size) and heat source utilization rate, since the heat source temperature could reach values as low as 70 °C when considering a Sulphur free fuel. In addition, R 245fa is to be preferred over the R 600 since it allows for the production of the same power considering lower values for the ORC top pressures
Performance Evaluation of Novel Spline-Curved Blades of a Vertical Axis Wind Turbine Based on the Savonius Concept
No full textIn this study, we present the results of a two-dimensional fluid-dynamic simulation of novel rotor geometry with spline function which is derivative of the traditional S-shape Savonius blade. A Computational Fluid Dynamic (CFD) analysis is conducted using the Spalart-Allmaras turbulent model, validated using experimental data released by Sandia National Laboratory. Results are presented in terms of dimensionless torque and power coefficients, assuming a wind speed of 7 m/s and height and rotor diameter of 1 m. Furthermore, analysis of the forces acting on the rotor is conducted by evaluating frontal and side forces on each blade, and the resultant force acting on the central shaft. A qualitative representation of the vorticity around the traditional and spline rotor is shown to prove that the novel blade is more “flow-friendly”, thus the air flow is less turbulent through the rotor. Finally, energy conversion capability of the Savonius turbines is estimated in parametric form for both the traditional and spline-curved geometry.</jats:p
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