1,720,964 research outputs found
Numerical investigation of heat transfer enhancement in plate-fin heat sinks: effect of flow direction and fillet profile
No full textMany researchers have studied the thermal performance of heat sinks, however to the best knowledge of the authors, the effect of flow direction (place of fan) on the thermal performance of plate-fin heat sinks with fillet profile have not yet been investigated. In this paper, the investigation develops a computational fluid dynamics (CFD) model, validated through comparison with an experimental data from the literature, which demonstrates the effect of flow direction and fillet profile on the thermal performance of plate-fin heat sinks. In particular, a plate-fin heat sink with fillet profile subject to parallel flow has been compared with the conventional design (plate-fin heat sink without fillet profile subject to an impinging flow) and satisfactory results have been perceived. The results of this study show that the base temperature along with the thermal resistance of the heat sink is lower for the proposed design. Therefore, the developed approach has strong potential to be used to improve the thermal performance of heat sinks and hence to develop more advanced effective cooling technologies
Design, development and optimisation of a novel thermo-syphon system for domestic applications
No full textIn order to decrease reliance on fossil fuels, renewable energy has become an important topic of research in recent years. The development in the renewable energy source will help in meeting the requirements of limiting greenhouse-gas effects, and conserve the environment from pollution, global warming, ozone layer depletion, etc. There are various naturally available renewable energy sources. One of these sources is solar energy. Solar energy is available in abundance throughout the world and is the cleanest of all known energy sources. There are various devices that can be used to harness solar energy. One of such devices is a thermo-syphon. Thermo-syphon converts the solar energy obtained from the Sun into thermal energy of a working fluid. This thermal energy in the working fluid can be used for various industrial and household activities. In a closed loop thermo-syphon system, the working fluid circulates within the thermo-syphon loop via natural convection phenomenon and does not need any external devices, such as a pump. Therefore, it is considered to be one of the most efficient devices for the heat transfer. Moreover, the absence of a pumping device reduces the manufacturing and maintenance costs of a thermo-syphon system.
The heat exchange process in the thermo-syphon is a complicated process, which considers the heat convection phenomenon. Therefore, to understand the natural convection process in the thermo-syphon and their effect on the thermal performance of the system a Computational Fluid Dynamics (CFD) based techniques have been used. Numerical results obtained have been verified against the experimental results, and they match closely with each other. The comparison between the CFD and experimental result, suggest that CFD can be used as an effective tool to analyse the performance of a thermo-syphon with reasonable accuracy. In order to investigate the flow structure within the thermo-syphon system, detailed qualitative and quantitative analyses have been carried out in the present study. The qualitative analysis of the flow field includes descriptions of the velocity magnitude and the static temperature distributions contours within the closed loop thermo-syphon system. Furthermore, the variation in the temperature of water within the storage tank, temperature of the working fluid, heat transfer coefficient, wall shear stress, and local velocity and temperature distribution of the working fluid within thermo-syphon loop have been quantified as a function of time. In addition, numerical studies have been conducted to identify the effects of various geometrical parameters, which include the number of the riser pipes, length-to-diameter ratio of the riser pipe on the thermal performance of a closed loop thermo-syphon system. Moreover, a further investigation has been carried out to analyse the effect of various heat flux conditions and different transient thermal loadings on the thermal performance of a closed loop thermo-syphon system. Based on these analyses some novel semi-empirical relations have been developed to predict the thermal performance of the thermo-syphon, which is one of the focal points of this research.
Another goal of the current study is to improve the thermal performance characteristic of thermo-syphon solar water heating system using an enhancement device to improve the heat transfer. This aspect of the work focuses on the increasing energy conversion from the riser pipes to the working fluid within the thermo-syphon loop. This is accomplished by increasing the surface area of riser pipes by employing several design modifications, such as straight, wavy and helical pipes, within the riser pipes, while maintaining the amount of the working fluid constant within the closed loop thermo-syphon system. In this study, a comparative analysis has been carried out for these new design modifications to identify the best in terms of heat transfer coefficient, heat gain in collector etc., as an indication of thermal performance. According to the findings of this analysis, the model comprising of pipe inside the riser pipe depict better thermal performance as compared to other models. After defining the best design modification, a further detailed investigation has been carried out between the traditional and modified design (straight pipe inside the riser pipe) using experimental and numerical method.
Established methods regarding the design process of thermo-syphons are very limited, and they are severely limited in estimating important design parameters, such as useful heat gain and heat transfer coefficient, which have a significant impact on the thermal performance of thermo-syphon system/loop. A design methodology has been developed to enrich the design process of a closed loop thermo-syphon solar water heating system. The developed methodology is more efficient and reliable since it is capable of estimating various geometrical and thermal parameters, such as collector area, diameter and length of the riser pipes, distance between the centers of the riser pipes, heat transfer coefficient, temperature of the working fluid and the mass flow rate. This design methodology is user friendly and robust
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
Effects of condenser volume on the performance of a solar thermo-syphon
No full textOne of the alternative sources of energy is solar energy which is available in abundance throughout
the world. The energy contained within the solar rays is capable of starting natural convection within
closed mechanical systems containing a suitable working fluid. One such system is commonly known
as a Thermo-syphon which transfers solar energy into internal energy of the working fluid, commonly
water. In the present study, an attempt has been made towards better understanding of the flow
structure within a thermo-syphon by analysing the natural convection phenomenon using
Computational Fluid Dynamics based techniques. A commercial CFD package has been used to
create a virtual domain of the working fluid within the thermo-syphon, operating under no-load
condition. The effects of the condenser volume, on the performance of the thermo-syphon, have been
critically analysed in this study. The results depict that as the condenser volume increases, the
average temperature of water within the condenser decreases. Hence, CFD can be used as a tool to
design, analyse and optimize the performance of a thermo-syphon with reasonable accurac
Computational fluid dynamics based analysis of a closed thermo-siphon hot water solar system.
Get PDFOne of the alternative sources of energy is solar energy which is available in abundance throughout the world. The energy contained within the solar rays is capable of starting natural convection within closed mechanical systems containing a suitable working fluid. One such system is commonly known as a Thermo-Siphon which transfers solar energy into internal energy of the working fluid, commonly water. In the present study, an attempt has been made towards better understanding of the flow structure within a thermo-siphon by analysing the natural convection phenomenon using Computational Fluid Dynamics techniques. A commercial CFD package has been used to create a virtual domain of the working fluid within the thermo-siphon, operating under no-load condition. The effects of the length to diameter ratio of the pipes connecting the condenser and the evaporator, number of connecting pipes, angle of inclination of the thermo-siphon and the heat flux from the solar rays to the working fluid, on the performance of the thermo-siphon, have been critically analysed in this study. The results depict that the heat flux and the length to diameter ratio of the pipes have significant effects on the performance of a thermo-siphon, whereas, the angle of inclination has negligibly small effect. Furthermore, an increase in the number of connecting pipes increases the temperature of the working fluid by absorbing more solar energy. Hence, CFD can be used as a tool to analyse, design and optimise the performance output of a thermo-siphon with reasonable accuracy
- …
