1,720,970 research outputs found
An Experimental Study on Heterogeneous Porous Stacks in a Thermoacoustic Heat Pump
No full textGrowing evidence suggests that research must be done to develop energy efficient systems and clean energy conversion technologies to combat the limited sources of fossil fuel, its high price, and its adverse effects on environment. Thermoacoustic is a clean energy conversion technology that uses the conversion of sound to thermal energy and vice versa for the design of heat engines and refrigerators. However, the efficient conversion of sound to thermal energy demands research on altering fluid, operational, and geometric parameters. The present study is a contribution to improve the efficiency of thermoacoustic devices by introducing a novel stack design. This novel stack consists of alternative conducting and insulating materials or heterogeneous materials. The author examined the performance of eight different types of heterogeneous stacks (combination 1–8) that are only a fraction of the displacement amplitude long and consisted of alternating aluminum (AL) and Corning Celcor or reticulated vitreous carbon (RVC) foam materials. From the thermal field measurements, the author found that combination eight performs better (12% more temperature difference at the stack ends) than all the other combinations. One interesting feature obtained from these experiments is that combination 7 produces the minimum temperature at the cold end (17% less than other combinations). The thermal performance of the heterogeneous stack is compared to that of the traditional homogeneous stack. Based on the study, the newly proposed stack design provides better cooling performance than a traditionally designed stack.</jats:p
Measurements of thermal field at the stack extremities of a standing wave thermoacoustic heat pump
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Modeling and Analysis of Flow, Thermal, and Energy Fields Within Stacks of Thermoacoustic Engines Filled With Porous Media: A Conjugate Problem
No full textAbstract
In this paper, an analytical study has been conducted on the flow and energy transfer of an unsteady compressible oscillating flow through channels filled with porous media representing stacks in thermoacoustic engines and refrigerators. The flow in the porous material is described by the Darcy momentum equation. The thickness of the channel wall is considered to be nonzero, and the entire problem is treated as a conjugate heat transfer problem, i.e., by considering conduction heat transfer inside the channel walls. Analytical expressions for the oscillating temperature, complex Nusselt number, and energy flux density are obtained after linearizing and solving the governing differential equations with long wave, short stack, and small amplitude oscillation approximations. To verify the present study, the energy flux density expression derived in this paper is compared with the expression available in the existing thermoacoustic literature. The two expressions match quantitatively for the limiting case of infinitely large pores. For infinitely large pore limits, the Nusselt number (nondimensional heat transfer between the porous media and the channel wall) obtained in the present study also agrees quantitatively with the nonporous medium expression reported in the literature. The present study indicates that refrigeration performance comparable to that of a traditional plastic parallel plate stack is achievable using reticulated vitreous carbon foam (ϕ=0.95, Lck=2.11) as a porous medium, which is also supported by other researchers. The system of equations developed in the present study is a helpful tool for thermal engineers and physicists to design porous stacks for thermoacoustic devices.</jats:p
Thermal Field Measurements of a Thermoacoustically Driven Thermoacoustic Refrigerator
No full textThermoacoustic refrigerator is a device that transfers heat from a low temperature medium to a high-temperature medium by using sound energy as work input. We have designed and tested a simplified thermally driven thermoacoustic refrigerator. Our refrigerator is easy to make, uses no moving parts, and has proved to be an impressive illustration of simplicity, an inherent attribute of thermoacoustic engines. At the same time it can be used as a working demonstration of a thermoacoustic refrigerator. Also, in this paper we have reported the results of measurements of temperature gradients and maximum cooling temperature in a thermally driven thermoacoustic refrigerator. The present research shows that the magnitude and position of the maximum cooling temperature depend on the position of the prime mover stack from the nearest pressure antinode. Based on the design of this simplified thermally driven thermoacoustic refrigerator, the design of a complete thermally driven thermoacoustic refrigerator is in progress.</jats:p
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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