1,720,983 research outputs found
Experimental investigation and development of Oil free absorption-compression heat pump
No full textThe industrial sector is a major contributor to global greenhouse gas emissions, with energy demand steadily increasing across various processes. Decarbonizing industrial heating systems presents a significant challenge due to the complexity and diversity of these processes. Addressing each heating application individually is a daunting task, yet the urgency for innovative, low-carbon heating technologies is undeniable. A holistic approach that enables substantial emission reductions across industries is essential to achieving sustainable energy goals.
Industrial heating primarily relies on fossil fuels such as oil and natural gas, which not only contribute to high CO₂ emissions but also result in considerable waste heat being discarded into the environment without being utilized. Waste heat from various industrial processes, often released to the ambient, represents an untapped energy resource that if recovered could significantly improve industrial energy efficiency. High-temperature heat pumps offer a sustainable solution by upgrading low-temperature waste heat into a high-temperature heat supply while utilizing significantly less primary energy. Replacing traditional oil or gas burners with heat pumps can help lower emissions, particularly in future energy systems with a higher share of renewable energy sources.
The combined absorption-compression heat pump, also known as the Osenbrück cycle, is a prominent example of a high-temperature heat pump utilizing natural working fluids. Osenbrück patented this concept in 1895. The use of a binary mixture as the working fluid distinguishes it from the conventional vapor compression cycle. This absorption-compression cycle integrates absorption and vapor compression technologies, employing a refrigerant absorbent mixture instead of pure components. The refrigerant and absorbent are characterized by a significant boiling point difference. Challenges arise when supplying heat sink temperatures above 100 °C. Many industries require heat within the 100–250 °C range, which presents a major barrier to current heat pump technology development.
A key challenge in improving system efficiency and extending applicability to thermally intensive industrial processes lies in achieving higher sink outlet temperatures or supply temperature. These conditions lead to increase refrigerant pressure levels and compressor discharge temperatures. One strategy to address this is to use oil-lubricated compressors and reducing compressor superheating.
However, this increases system complexity and cost due to the need for components such as oil separators. Moreover, excessive oil carryover into the heat exchanger at high discharge temperatures can significantly reducing heat transfer performance.
This study aims to experimentally evaluate the performance of a developed single-stage combined absorption-compression heat pump utilizing a standard oil-free compressor. The objective is to assess the effect of liquid injection on the compressor’s discharge temperature and perform parametric studies on the complete prototype system. At the beginning of the experimental phase, potential key failures and performance issues were investigated. After dismantling the compressor, modifications were made, and some parts were redesigned and installed to ensures continued testing. The system’s performance was assessed under varying operational conditions, focusing on parameters such as heat sink and source loads, temperature glides, and heat transfer coefficients.
The initial investigation emphasized optimizing the compressor and absorber, as well as evaluating overall system behavior. Preliminary results show that, with a constant inlet temperature of 60 °C for both the heat sink and heat source, the system achieves a temperature lift of 35 °C. The heat sink and source loads reach 60 kW and 30 kW, respectively, with corresponding temperature glides of 35 °C and 15 °C. While higher temperature lifts improve certain performance indicators, they reducing the Carnot and Lorenz coefficients of performance.
Increasing the weak solution mass flow rate from 0.024 kg/s to 0.036 kg/s decreases the temperature lift and heat sink capacity. Conversely, increasing the weak solution injection flow rate from 0 to 0.03 kg/s reducing the compressor discharge temperature from 140 °C to 126 °C. Absorber 1 (bubble mode) demonstrates superior performance over Absorber 2 (falling-film mode), achieving a maximum heat transfer coefficient of 1.39 kW/m²·K.
Further investigations focused on the influence of heat sink temperature glide on overall system performances. With constant inlet temperatures of 60 °C for both the heat sink and heat source, and a mass flow rate of 0.25 kg/s, the system delivers 50 kW of heating load and 26 kW of cooling load. Increasing the heat sink temperature glide from 28 °C to 48 °C reduces the Lorenz COP. To achieve optimal temperature glide performance, a weak solution mass flow rate between 0.015 and 0.025 kg/s at a minimum absorber pressure of 15 bar is recommended. Additionally, increasing the weak solution injection flow rate from 0 to 0.03 kg/s decreases the compressor discharge temperature from 139 °C to 122 °C, with a constant 0.0015 kg/s injection to the bearing and shaft seal side. The results also highlight significant differences in heat transfer characteristics between the two absorbers. Absorber 1 in bubble mode shows better performance in both test series.
Beyond compressor and absorber optimization, the role of the desorption process was also investigated using plate heat exchangers as desorbers for industrial waste heat recovery. Two vertically arranged desorbers operating in series were analyzed in the same prototype circuit. Experimental results showed that, by varying the strong solution mass flux from 4 to 35 kg/m²·s, the following performance changes occurred in Desorber 1: thermal load increased from 5 to 20 kW, the overall heat transfer coefficient improved from 1.1 to 1.7 kW/m²·K, and thermal efficiency increased from 66% to 86%. For Desorber 2, operating in falling film mode, the heat load decreased from 17 kW to 14 kW, the heat transfer coefficient varied from 1.1 to 1.5 kW/m²·K, and thermal efficiency increased from 66% to 80%. Additionally, the vapor mass fraction at the outlet of Desorber 2 ranged from 0.1 to 0.6 kg/kg. The highest-pressure drop was recorded in Desorber 1.
The findings of this research provide valuable insights into the optimization of absorptioncompression heat pump systems, outlining effective strategies to improve efficiency, lower compressor discharge temperatures, and evaluate heat exchanger performance in oil compression. These advancements contribute to the development of more efficient, cost-effective solutions for industrial high-temperature heat pump applications and waste heat recovery
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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