1,720,959 research outputs found
Numerical Heat Transfer Study of Turbulent Tube Flow through Winglet-pairs
No full textAbstractA numerical investigation on heat transfer behaviors in a constant heat-fluxed round tube inserted with winglet vortex generators is conducted. Air as the working medium flows through the tube for Reynolds numbers (Re) between 4000 and 20,000. The effect of using the rectangular-winglet tape (RWT) on heat transfer characteristics in the tube is numerically examined. For comparison purpose, the trapezoidal-winglet tape (TWT) and delta-winglet tape (DWT) are also offered. The RWT parameters in this work include four relative winglet-to-tube heights or blockage ratios (BR=b/D= 0.1, 0.15, 0.2, and 0.25) while the TWT and DWT are only at BR= 0.2. All the winglet pairs are at a single attack angle (α= 45°) and pitch ratio (p/D=PR=4). The numerical results show that the Nusselt number (Nu) and friction factor (f) of the tube inserts are enhanced with increasing BR values. The Nu for the inserted tube is about 1.8-2.7 times above that for the smooth tube while the f is around 4.5-11 times higher. For the studied BR ranges, the highest thermal performance is 1.48 for the RWT with BR= 0.1 at lower Reynolds number
Review of Ranque-Hilsch effects in vortex tubes
No full textThe vortex tube or Ranque-Hilsch vortex tube is a device that enables the separation of hot and cold air as compressed air flows tangentially into the vortex chamber through inlet nozzles. Separating cold and hot airs by using the principles of the vortex tube can be applied to industrial applications such as cooling equipment in CNC machines, refrigerators, cooling suits, heating processes, etc. The vortex tube is well-suited for these applications because it is simple, compact, light, quiet, and does not use Freon or other refrigerants (CFCs/HCFCs). It has no moving parts and does not break or wear and therefore requires little maintenance. Thus, this paper presents an overview of the phenomena occurring inside the vortex tube during the temperature/energy separation on both the counter flow and parallel flow types. The paper also reviews the experiments and the calculations presented in previous studies on temperature separation in the vortex tube. The experiment consisted of two important parameters, the first is the geometrical characteristics of the vortex tube (for example, the diameter and length of the hot and cold tubes, the diameter of the cold orifice, shape of the hot (divergent) tube, number of inlet nozzles, shape of the inlet nozzles, and shape of the cone valve. The second is focused on the thermo-physical parameters such as inlet gas pressure, cold mass fraction, moisture of inlet gas, and type of gas (air, oxygen, helium, and methane). For each parameter, the temperature separation mechanism and the flow-field inside the vortex tubes is explored by measuring the pressure, velocity, and temperature fields. The computation review is concentrated on the quantitative, theoretical, analytical, and numerical (finite volume method) aspects of the study. Although many experimental and numerical studies on the vortex tubes have been made, the physical behaviour of the flow is not fully understood due to its complexity and the lack of consistency in the experimental findings. Furthermore, several different hypotheses based on experimental, analytical, and numerical studies have been put forward to describe the thermal separation phenomenon.Vortex tube Ranque-Hilsch vortex tube Temperature separation Ranque-Hilsch effects
Numerical Heat Transfer Investigation in a Heat Exchanger Tube with Hexagonal Conical-ring Inserts
No full textAbstractThe hexagonal conical rings (HCR) modified from the typical conical ring (CR) are used as a turbulence promoter for producing the vortex flows to enhance the heat transfer rate in a heat exchanger tube. To reduce the pressure loss, the V-shaped HCR (V-HCR) obtained by cutting both symmetric plane of the cone-tip of HCR at 30°, 45° and 60° is offered in the present work. The tube fitted with V-HCR elements having a fixed inlet and outlet diameter is numerically investigated. The computation is carried out for Reynolds number in a range of 3000 to 20,000 in a uniform heat-fluxed test tube. The numerical results show that the V-HCR insert leads to much higher heat transfer than the typical CR/HCR insert or the smooth tube alone and also provides lower friction factor. The 30° V-shaped HCR gives the highest heat transfer and thermal performance due to the lowest friction loss, indicating the promising device of the V-HCR
Behaviors of hydrogen sulfide removal using granular activated carbon and modified granular activated carbon
No full textAn experimental study on hydrogen sulphide (H2S) adsorption behaviours using amine-impregnated solid adsorbent (GAC/PEI) was carried out for H2S concentration in the range of 200 and 400 ppm. The dynamic adsorptions of GAC and modified GAC (2.0 and 1000 g/L PEI) in a fixed-bed column were investigated by determining the breakthrough curves and adsorption capacities of various adsorbents. The adsorbent exhibits an excellent adsorption capacity of 106.87 and 231.45 mgH2S/g-adsorbent for 200 ppm and 400 ppm H2S, respectively. The H2S breakthrough capacity is found to relate to the surface adsorption and chemical adsorption
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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