1,720,995 research outputs found
Experimental investigation on micro-ORC system operating with partial evaporation and two–phase expansion
Full text linkThis paper presents an experimental analysis conducted on a low-temperature micro-ORC energy system, to assess its performance operating with partial evaporation (PE-ORC). Temperatures of the heat source in the range between 40 °C and 75 °C have been tested, and for each value, the vapour quality at the expander inlet has been varied by regulating the feed-pump rotating speed. The thermodynamic state of the working fluid in two-phase conditions has been estimated by means of a thermal balance at the heat exchangers, using the measured values of temperature, pressure and flow rate.
Detailed experimental results are provided, with special focus on the performance of evaporator, expander and feed-pump, highlighting the difference in their behaviour compared with the regular operation with dry expansion of the same micro-ORC system. Relevant improvements have been observed in the evaporator effectiveness, mainly due to the reduction of the pinch point temperature difference. Also, the volumetric and total efficiencies of the feed-pump are improved substantially.
On the other hand, the net power output and the expander efficiency resulted penalized by the operation with partial evaporation. The maximum power output obtained was close to 1.2 kW, with heat source temperature equal to 75 °C and fluid quality close to 1. The power output is reduced, at constant temperature, by decreasing the vapour quality at the expander inlet.
The results suggest that operating a small-scale ORC system with partial evaporation may lead to some improvements to the performance of the cycle, especially regarding the evaporator performance. Moreover, with values of fluid quality at the expander inlet between 0.8 and 1, the penalization on the expander performance, compared to the dry expansion mode, is limited. However, a proper redesign of the power plant for the specific purpose is required in order to make partial evaporation an effective solution. Specifically, the expander and pump geometry and control require to be optimized for the particular working conditions, the recuperator must be removed, and the evaporator should be designed for the optimal exploitation of the heat source
Performance Assessment of Smart District Heating Networks: The Influence of Distributed (Co)Generation on the Network Primary Energy Consumption
No full textInfluence of the Prosumer Allocation and Heat Production on a District Heating Network
Full text linkTo face the climate change and global warming issues, European countries have set new targets in order to reduce the CO2 emissions to 40% by 2030 and to 80% by 2050. The district heating networks, and in particular low-temperature networks, due to their efficient heat supply and distribution represent a key point for meeting these goals, as well as the renewable sources integration. Nowadays, in fact, about 40% of the energy consumed in Europe is for heating, most of which is provided by fossil fuels employment. This article concerns the smart district heating, namely, the possibility of a bidirectional energy exchange between the district heating network and the connected users. The main purpose of this study is to evaluate the possibility of including a prosumer-that is, a customer who can both consume and produce heat-in an existing small/medium district heating network. To this purpose, an in-house-developed software has been applied to analyze whether and which user of the district heating network is more suitable to be set as prosumer and the effect of the installed distributed generation system on the network. The results show how the choice of a prosumer over another and how the amount of exchanged thermal power affect the performance of the network, with a consequent need of a modification in its operation and management
Overall performance evaluation of small scale LNG production processes
Full text linkThe liquefied natural gas (LNG) is considered a viable solution to replace oil-based engines (common in heavy-duty truck and naval industry) reducing the environmental impact in the transport sector. Since liquefaction plants represent energy intensive processes, the best configurations/operation assessment is of primary importance. In this paper, a novel general procedure for the thermodynamic design and optimization, engineering design and off-design evaluation for small-scaleLNGproduction systems is presented. The procedure can be used for the complete design and performance evaluation of plug&play facilities at filling stations for vehicles/boats, with the contemporary benefits of reducing pollutant emission in the city/port area and operating as electrical storage, coupled with renewable generators. Furthermore, the procedure has been applied to a case study (ferry boat operating at the main canal in the port of Ravenna, Italy), evaluating the optimal size for the integrated wind plant by minimizing the electricity introduction into the grid. The obtained results show 78 kW as optimal wind size, allowing the LNG plant to operate 187 h/year in design and 4720 h/year in off-design conditions, with electricity surplus around 33 MWh/year. A prototype will be installed to reduce pollutant emissions and test this technology as a storage option for renewable sources
Modelling a Prototype of Bidirectional Substation for District Heating with Thermal Prosumers
Full text linkThe performance of the innovative configurations of the “efficient” thermal networks is a key topic in scientific research, focusing on distribution temperatures and integration with high-efficiency plants and renewable sources. As it already happens for the electricity prosumers, a thermal prosumer may feed the district heating network through a bidirectional exchange substation with the excess of the locally produced thermal energy (e.g., by means of solar thermal plant) or with the waste heat recovered in the industrial processes. The Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) and the Alma Mater Studiorum University of Bologna (UNIBO) designed a bidirectional substation prototype, based on a return-to-supply configuration, and tested steady-state and dynamic conditions to evaluate performances and optimization measures. In this paper, the Modelica language and Dymola software were used to run a multi-domain simulation and model-based design of the substation, starting from a new heat exchanger model featuring variable efficiency, based on the thermal resistance scaling method. Control systems and components were customized from models in standard libraries in order to reproduce the substation behavior under defined operating settings, and the model was validated on the abovementioned experimental tests. Numerical results in terms of exchanged powers, temperatures and flow rates were systematically compared to experimental data, demonstrating a sufficient agreement. In particular, the absolute mean deviation—in terms of temperature—between experimental and numerical data assessed over the entire tests remains contained in +/−1 °C. As further step of the analysis, an optimized model could be included as a component in a district heating network for further investigations on the prosumers’ effects on an existing traditional grid (e.g., in case of deep renovation of urban areas connected to district heating and/or creation of micro energy communities)
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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