1,720,992 research outputs found
A thorough performance assessment of solar chimney power plants: Case study for Manzanares
No full textSolar chimney power plants (SCPPs) are promising systems for clean energy generation. SCPPs are ideal for the large-scale harnessing of solar energy. They operate efficiently without auxiliary energy and do not cause any environmental pollution. There are several theoretical, numerical and experimental attempts to date for performance assessment of SCPPs, however, there are still contradictions in the findings, and a thorough performance evaluation is still missing. Therefore, in this study, a novel three-dimensional axisymmetric computational fluid dynamics (CFD) approach is proposed by considering the pioneer plant in Manzanares region. For a realistic approach, actual geometric parameters of the pilot plant are utilised in the CFD model, and the performance assessments are done regardless of time. Pressure, temperature and velocity distributions within the SCPP from collector inlet to chimney outlet are numerically modelled with respect to changes in solar radiation and atmospheric temperature. For model validation, the numerical findings are compared with the typical experimental findings performed in pilot plant, and a good agreement is obtained. For a certain value of solar radiation (1000 W/m2), maximum air velocity in the pilot plant is found to be 14.24 m/s, which is compatible with the experimental data of 15.00 m/s. Static pressure is found to sharply decrease from chimney ground to turbine inlet, and then steadily rises to the chimney outlet. Minimum static pressure is observed to be −100.18 Pa at 21.92 m from the ground. Output power of SCPP linearly increases with the solar intensity whereas it steadily reduces with ambient temperature. Available power is determined to be 49059 W for the case of 1000 W/m2, and the atmospheric temperature of 293 K
Box type solar cookers with sensible thermal energy storage medium: A comparative experimental investigation and thermodynamic analysis
No full textBox type solar cookers with and without thermal energy storage are experimentally analysed within the scope of this research for characteristic continental climatic conditions of Bayburt, Turkey. For efficient and continuous cooking in such climates, thermal energy storage is required to be considered in solar cookers due to remarkable temperature differences between sunrise and sunset. Bayburt stone, a special natural stone with low density and notably high specific heat capacity, is utilised as a sensible thermal energy storage medium in a box type solar cooker, and thermal performance assessment of Bayburt stone cooker is compared with a conventional cooker without thermal energy storage through a comprehensive experimental research and thermodynamic analysis. For a typical late summer day, solar intensity, ambient temperature, absorber plate temperatures, internal air temperatures, internal and external glass temperatures, water temperatures, energy and exergy efficiencies are determined time-dependently for each solar cooker. the results clearly indicate that absorber plate temperature in conventional solar cooker has a notable decreasing tendency toward sunset, which totally affects the overall thermal performance of the system. on the contrary, Bayburt stone cooker enables an efficient, steady and continuous cooking till late evening owing to sensible thermal energy storage medium. in terms of thermo-dynamic performance figures, Bayburt stone cooker is observed to have considerably better energy and exergy efficiency. According to the results, energy efficiency of Bayburt stone cooker is determined to be in the range of 35.3-21.7% while it is found to be 27.6-16.9% for conventional solar cooker. on the other hand, exergy efficiency of Bayburt stone cooker is determined to be 21.2-14.1% whereas it is calculated to be 18.0-11.6% for conventional cooker. It can be concluded from the results that Bayburt stone as a thermal energy storage medium remarkably improves the thermal performance figures of box type solar cookers
Improving Electricity Production in Solar Chimney Power Plants with Sloping Ground Design: An Extensive CFD Research
Get PDFUnlike other solar energy systems, solar chimney power plants (SCPPs) allow power output even when there is no sun. SCPPs are promising with their simple structure and 24-hour electricity production potential. Massive pressure tower in the system maintains continuous energy generation irrespective of climatic conditions. Solar energy harnessed by the huge collector area is transmitted to the gorund material for sensible or latent heat storage purpose, and this stored energy during daytime yields to enhanced thermal and buoyant effects even after sunset. SCPPs are also in the centre of interest owing to their eco-friendly operation not causing any CO2 emission. Design aspects in SCPPs are widely studied numerically by researchers. However, geometric design factors are merely analysed for collector and chimney, and very few attempts are done for the ground design. In the present work, a new design for ground is proposed in order to improve the energy stored in the ground material, and the upward movement of the air flow in the system from collector to chimney by changing the ground geometry. The upward movement of the air under the collector is enhanced with the new design created by inclining the ground at a distance of 21 m from the chimney inlet to a certain distance from the collector inlet. ANSYS WORKBENCH based CFD analysis is carried out based on the geometric dimensions of the Manzanares pilot plant. Analyses are based on a 90° 3D CFD model for the purpose of time saving in iterations. The CFD model is supported by RNG k-? turbulence and DO (discrete ordinates) solar ray tracing models. After CFD results are verified with the experimental data, simulations are repeated for different designs and the ideal design is achieved. It is observed that the maximum air flow velocity, which is 14.202 m/s on the horizontal ground for the reference case, is improved by 34.1% in the new design to 19.046 m/s. In addition, it is seen that the power output of the reference case (54.333 kW) is enhanced by 23.04% to 66.855 kW
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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