1,720,974 research outputs found
Start-up timing behavior of single-loop oscillating heat pipes based on the second-order dynamic model
No full textOscillating heat pipes have the potential to combine with the grinding wheel to enhance heat transfer in grinding process to avoid thermal damage of workpiece and grinding wheel. Since the time of grinding process is short, it raises a requirement for a good start-up behavior of oscillating heat pipes inside grinding wheel. In order to understand the start-up behavior, a new method is proposed based on the second-order dynamic theory to represent and evaluate start-up process. Several parameters (i.e., rising and settling time, percent-overshoot) are defined to value quantitatively the start-up process. Accordingly, three start-up modes are discovered with respect to the evaporator temperature, which are over-damped, under-damped and transient start-up modes. The start-up behavior is discussed with both pure fluids and nanofluids. Results show that as the heating power increases, the start-up speed enhances, and over-damped start-up mode develops to under-damped or transition start-up mode. The start-up speed of DI water is faster at low heating power, while acetone and nano-diamond solution without dispersant show faster start-up speed at high heating power. This methodology will help to compare the start-up timing of the OHP experiments in literatures, providing a more robust way to analyze start-up data.</p
Heat transfer and temperature characteristics of single-loop oscillating heat pipe under axial-rotation conditions
Full text linkThermal management is important for rotating machinery, such as spindles, grinding wheels or drillers, etc. If the heat cannot be dissipated in time, high temperatures will be generated, and abnormal operations or even destruction of the machinery may occur. Oscillating heat pipes (OHP) have attracted attention in thermal management and also have a demonstrated potential to transfer heat under rotation conditions. Research on OHPs under rotation is still insufficient: For example, the heat transport capacity and the temperature characterization of OHP under axial-rotation are not investigated, and also the motion of the working fluid is not yet recorded and analyzed. The thermal performance of a single-loop OHP under axial-rotations is here experimentally investigated. The temperature characteristics of the evaporator and condenser are analyzed. The inside flow is also visualized to better understand the heat transfer process. The results show that the heat transfer capacity of OHPs filled with acetone and methanol improves with the increase of centrifugal acceleration; while the thermal performance of an OHP filled with water peaks at rotation centrifugal acceleration of 30 m/s2. The centrifugal acceleration promotes movements of the working fluid and improves the heat transport capacity. Besides, the OHP shows a chaotic state under the axial-rotation based on nonlinear dynamic analysis.</p
Thermal performance analysis of axial-rotating oscillating heat pipe and its prediction model based on grey system theory
No full textOscillating heat pipes (OHP) have attracted much attention in thermal management due to its high heat transport capacity and simple structure. OHP also have the potential to transfer heat under rotational conditions, while research on OHP heat transfer performance under a system rotation is still insufficient. The thermal performance of a single closed loop OHP under a centrifugal acceleration due to an axial rotation is here experimentally investigated. This OHP is then treated as a grey system, since the complexity of the internal physical processes is very high and only a limited amount of experimental data is available. The grey system theory, which analyzes an uncertain system with small samples and poor information, is used to provide a novel path of modeling the thermal performance of two-phase systems. The results show that the heat transfer characteristics of an OHP filled with methanol improve with the increase of centrifugal acceleration and heat flux. The data are then modeled by a GM(1,1) grey model to simulate and predict the heat transfer coefficient. The errors range from 3.36% to 16.6%, and the prediction of the performance is satisfying. A case study of applying the prediction model in designing abrasive-milling tool with OHP inside to enhance heat transfer is conducted. It shows that the grey system prediction model provides a reliable guidance for the engineering application of the OHPs.</p
Heat transport capacity of an axial-rotating single- loop oscillating heat pipe for abrasive-milling tools
Full text linkIn order to enhance heat transfer in the abrasive-milling processes to reduce thermal damage, the concept of employing oscillating heat pipes (OHPs) in an abrasive-milling tool is proposed. A single-loop OHP (SLOHP) is positioned on the plane parallel to the rotational axis of the tool. In this case, centrifugal accelerations do not segregate the fluid between the evaporator and condenser. The experimental investigation is conducted to study the effects of centrifugal acceleration (0-738 m/s2), heat flux (9100-31,850 W/m2) and working fluids (methanol, acetone and water) on the thermal performance. Results show that the centrifugal acceleration has a positive influence on the thermal performance of the axial-rotating SLOHP when filled with acetone or methanol. As for water, with the increase of centrifugal acceleration, the heat transfer performance first increases and then decreases. The thermal performance enhances for higher heat flux rises for all the fluids. The flow inside the axial-rotating SLOHP is analyzed by a slow-motion visualization supported by the theoretical analysis. Based on the theoretical analysis, the rotation will increase the resistance for the vapor to penetrate through the liquid slugs to form an annular flow, which is verified by the visualization.</p
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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