1,720,964 research outputs found
Scale-resolving CFD modeling of a thick wind turbine airfoil with application of vortex generators: Validation and sensitivity analyses
No full textExperimental investigation of two-phase flow in Chevron-type compact plate heat exchangers: A Study on pressure drops and flow regimes visualization
Full text linkCompact plate heat exchangers are a very promising technology and lately they are being considered for potential use as steam generators in Small Modular Reactors. However, there is a lack of scientific literature on their operation with two-phase flows, especially with non-refrigerant fluids. In this study, we conducted experiments to visualize and measure the pressure drop of a two-phase flow in a Chevron-type Plate Heat Exchanger. An air–water mixture was used in adiabatic conditions as the operating fluid in upward-flow configuration. Visualization was achieved through high-framerate videos. This study covers a wide range of operating conditions, surpassing those documented in existing literature by specifically analyzing also the region of very low mass flux for both phases. The tested conditions ranged from 6 to 365 kg/m^2s of water and from 0.02 to 5 kg/m^2s of air. Single-phase pressure drops were measured to establish a correlation for the Darcy friction factor. Instead, measurements of the pressure drop in two-phase conditions were processed and presented using a non-dimensional form referred to as the two-phase multiplier. The adoption of a void-fraction model played a crucial role in accurately extrapolating the frictional component of the pressure drop from the measurements, resulting in less scattered data on the Lockhart–Martinelli plot. In addition, the observed flow structures were categorized into distinct regimes (fine-coarse bubbly, Taylor-like bubbly, heterogeneous, partial film, and film flow) based on visual observation and were represented on a flow map. Finally, these data were used to develop new criteria for predicting flow pattern transitions
Flow pattern visualization and definition of transition criteria for two-phase flow in Chevron-type corrugated channels
Full text linkThis study aims to highlight the factors influencing flow patterns in Plate Heat Exchangers (PHEs) operated with two-phase flows. Our focus is on providing precise definitions of flow regimes and proposing transition boundaries by comparing diverse experimental datasets. To accomplish this, we designed an experimental apparatus for flow visualization through high-speed videos. The videos clarify flow patterns in an upward-flowing air-water mixture within a chevron-type plate heat exchanger. We introduce a new, clearly defined nomenclature and present the results in the form of a flow regime map. Moreover, we reclassify previously documented flow patterns in the literature using our established nomenclature, creating a unified and comparable database of visualization data. Subsequently, we explore semi-theoretical transition criteria and establish new transition boundaries based on the compiled experimental data. These newly determined transition lines are integrated into a comprehensive global flow regime map, advancing our understanding of two-phase flow behavior in PHEs
INTEGRATED NUMERICAL APPROACH FOR WIND ENERGY AERODYNAMICS AND ENERGY OUTPUT ESTIMATION
No full textThe wind energy source is playing a leading role in the worldwide power generation, with a high yearly growth of installed wind power capacity and a continuous technological development to reduce the cost of energy and to promote a higher penetration of wind energy. In this scenario, a better comprehension of the fluid dynamics becomes necessary to increase the wind turbines efficiency and related energy output in both small and large size devices. For this purpose, the use of experimental campaigns in wind tunnel are still largely used, requiring important investment and limiting the tested operating conditions. In last years, the Computational Fluid Dynamics (CFD) approach is used more and more for both design and optimization to investigate the single blade geometrical configuration up to whole wind farm, for single wind turbines positioning and interaction. Specifically, the CFD approach can be used with advantages and limits to support the design of flow control devices, such as the vortex generators (VGs), to define the local fluid dynamics and to carry out a detailed analysis of VGs geometrical effects up to the modeling of wind farm through the use of Actuator Line Method (ALM) approach to limit the computational costs. Both analysis can be coupled with traditional methods such as BEM (Blade Element Momentum) theory to evaluate the effects on the turbine Annual Energy Output (AEP) and related economical consequences
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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