1,721,328 research outputs found
Advanced exergy analysis of a R744 booster refrigeration system with parallel compression
Full text linkIn this paper, the advanced exergy analysis was applied to a R744 booster refrigeration system with parallel compression taking into account the design external temperatures of 25 degrees C and 35 degrees C, as well as the operating conditions of a conventional European supermarket. The global efficiencies of all the chosen compressors were extrapolated from some manufactures' data and appropriated optimization procedures of the performance of the investigated solution were implemented.According to the results associated with the conventional exergy evaluation, the gas cooler/condenser, the HS (high stage) compressor and the MT (medium temperature) display cabinet exhibited the highest enhancement potential. The further splitting of their corresponding exergy destruction rates into their different parts and the following assessment of the interactions among the components allowed figuring out the real achievable improvements. The avoidable irreversibilities of the HS compressor and that of the MT evaporator were mainly and completely endogenous, respectively. On the other hand, the gas cooler/condenser could be predominantly improved by decreasing the inefficiencies of the MT evaporator. As regards the auxiliary compressor, large enhancements were attainable through the drop in the irreversibilities occurring in the remaining components. (C) 2016 Elsevier Ltd. All rights reserved
The potential of heat pumps in the electrification of the Danish industry
No full textReaching the goals set by the Paris Agreement (UNFCCC, 2015) requires the energy sector to have netzero CO2-emissions the latest by 2060 (Philibert, 2017). The power sector changes from fossil fuels to renewable energy sources, providing increasing amounts of clean energy. The decarbonisation of the industry sector is however often overseen, despite the industry accounting for 21 % of the direct global greenhouse gas emissions in 2010 (IPCC, 2014). A decarbonisation of the industry can happen on a large scale following three main technology options, (i) the replacement of fossil fuels with bioenergy, (ii) the electrification of processes and (iii) the implementation of carbon capture and storage technologies (Åhman et al., 2012). Electrification of processes reduces energy-related CO2-emissions, but it can also reduce the final energy use by integrating heat pumps (HP). The choice of Power-to-Heat technologies generally depend on process and temperature requirements. Some promising electrification technologies, such as high temperature heat pumps (HTHP) or heat pump-assisted distillation, have currently a low technology readiness level (den Ouden et al., 2017), while other available technologies, such as electric boilers and Mechanical Vapour Recompression (MVR), can be infeasible under current economic conditions. The potential for HTHPs was investigated for the European industry (Kosmadakis, 2019), where it was found that HTHP can cover about 1.5 % of the industries heat consumption. This work derives an overview of the potential of heat pump-based process heat supply for the electrification of thermal processes in the Danish industry
Analysis of technologies and potentials for heat pump-based process heat supply above 150 °C
Full text linkThe transition of the manufacturing industry towards carbon neutrality requires a reduction of the emissions from combustion for the supply of process heat. Heat pumps are an efficient alternative technology for supplying heat while improving the overall efficiency and shifting to potentially carbon neutral electricity. The state-of-the-art technology is limited to supply temperatures between 100 °C and 150 °C because of lower efficiency and component limitations. This paper has therefore analyzed two promising concepts for higher supply temperatures and found technically and economically feasible solutions for process heat supply of up to 280 °C. These solutions are using large-scale equipment from oil and gas industries for applications in energy-intensive industries. The suggested systems benefitted from the economy of scale and access to low electricity prices. The concepts outperformed a biogas-based solution, and they were competitive with biomass or natural gas systems with respect to economic performance. It was concluded that an electricity-based heat supply is possible for a wide range of industrial applications and accordingly represents an important contribution to fulfilling the objectives of lower climate impact of energy supply in industry.</p
Energy and environmental performance assessment of R744 booster supermarket refrigeration systems operating in warm climates
Full text linkThis paper presents a theoretical comparison among different commercial refrigeration systems in terms of annual energy consumption and environmental impact. Eight configurations were studied: a R744/R134a cascade refrigeration system (baseline), a conventional and an improved R744 booster system, two R744 booster solutions with dedicated mechanical subcooling, a R744 booster with parallel compression and two solutions which combined the parallel compression and the mechanical subcooling. The evaluation was based on the weather data in Valencia (Spain) and in Athens (Greece), as well as on the running modes of a conventional European supermarket. A transition zone, which occurred between sub critical and transcritical operations, was adopted.The results showed that all the enhanced configurations may achieve a comparable energy saving to the one of the baseline in both the selected locations. Furthermore, they allow reducing the Total Equivalent Warming Impact (TEWI) by at least 9.6% beside the cascade solution. (C) 2016 Elsevier Ltd and IIR. All rights reserved
Energy saving in breweries
No full textProyecto confidencialRamada Correa, CJ. (2008). Energy saving in breweries. https://riunet.upv.es/handle/10251/34321.Archivo delegad
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
Where is the money ? A decomposition of monetary flows behind fossil fuels
No full textTransition from fossils to renewables is leading to radical societal changes. Shifting the capital from fossils to renewables is commonly accompanied with political concerns, such as energy autonomy, domestic employment etc. Despite a decreasing trend in recent decades, energy cost remains the major bottleneck for a massive penetration of renewables, resulting in diverse policies with respect to carbon taxes and renewable subsidies. This study focuses on analysing the opportunities for Switzerland within the energy transition, through a systematic assessment on the curent petroleum supply chain with associated cost decomposition. By modeling a fossil fuels supply chain, it is within reach to estimate the final price decomposition of petroleum products. To be more precise, the aim of this study, based on open source data, is to highlight how the money spent in fossil fuels is distributed in the industry and to examine opportunities an energy transition could offer to the country in question. Applied to Switzerland, but applicable to any other country, the results show that more than 30% of the final price is spent and invested outside the country. For instance, the Swiss net import of fossil fuels alone amounted to 7.2 billions CHF in 2019. If this capital had been invested in PV, Switzerland could have produced 33.5 TWh/year, constituting 60% of Swiss electric production in 2020. In the near future, this reinvestment in PV would contribute more generally to the full development of solar energy, whose walls and roofs potential in the Swiss context is estimated to be around 67 TWh/year.SCI-STI-F
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
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