1,721,110 research outputs found
On the reliability of thermoeconomic diagnosis of fouled evaporators: assessing the influence of geometries, operating conditions and reference state
No full textThermoeconomic diagnosis of refrigeration systems is a pioneeristic approach, which has been proven to achieve good performances (under favorable conditions) for the detection of specific faults such as condenser and evaporator fouling and compressor valve leakage. In this paper the sensitivity of performance in detecting fouled Direct Expansion (DX) coils is investigated; the examined parameters are the temperature and relative humidity of coil inlet air and the sensible/latent heat ratio of the coil (varied by considering different numbers of rows). As the thermoeconomic model requires splitting the specific exergy of cooling air into “mechanical”, “thermal” and “chemical” fractions, and since under fouled conditions the evaporator strongly modifies its exergetic performance, it is worthwhile discussing the possible existence of “optimal performance” regions for the use of this diagnostic technique
Experimental characterization of variable-speed packaged rooftop units in presence of evaporator fouling
No full textVariable-speed packaged rooftop units have been increasingly adopted in the commercial sector. If not properly maintained, the fouling of heat exchangers and the improper refrigerant charge could increase energy consumption. In this work, the response of variable-speed rooftop units to evaporator fouling is investigated based on experiments on a variable-speed 17.5 kW rooftop unit. A novel testing procedure is proposed, aimed at covering a broad range of operating conditions by a reduced number of tests. Two opposite cases were investigated: (i) even in presence of fouling, the controller can restore the required cooling capacity, and (ii) the intensity of the fouling does not allow the controller to restore the cooling capacity. While in the former case an increase in the indoor fan rotating speed is observed, with no variations in the evaporating pressure and the inlet temperature of cooled air, in the latter one the mismatch between the cooling load and the capacity induces a deviation of the indoor air condition from the setpoint. A regression model is proposed to quantify these deviations. Experimental results showed that in a faulty scenario, the maximum cooling capacity deliverable could decrease up to 15-20 %, and the indoor fan consumption increased up to 40%. In case of heavy faults involving cooling capacity shortage, a 2.3 °C deviation from the indoor setpoint temperature was estimated by the proposed regression model
A Novel solar trigeneration system integrating Photovoltaic/Thermal solar collectors and seawater desalination: dynamic simulation and economic assessment
No full textCoupling salinity gradient heat engines with power generation systems and industrial processes
No full textThe rising concern about global warming and the increasing trend in energy consumption have been pushing the need for efficient use of energy and intensive adoption of renewable energy sources. In general terms, energy efficiency means using less energy to perform the same task. Action aimed at improving the energy conversion efficiency of processes are the cheapest and the most immediate ways to reduce the consumption of fossil fuels and contain greenhouse gas emissions
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
Exergetic and exergoeconomic analysis of a renewable polygeneration system and viability study for small isolated communities
No full textA great interest has recently arisen for the sustainable supply of energy and fresh water, due to the
growing demand from developing countries. Facing this demand by traditional technologies implies
evident risks related with the high cost of fossil fuels and their environmental impact. Then, alternative
solutions based on the use of renewable sources and innovative technologies must be considered. In this
paper a renewable polygeneration system is examined, which includes a solar field based on parabolic
trough photovoltaic/thermal collectors, a biomass heater, an absorption chiller and a Multiple Effect
Distillation desalination unit.
Plant operation under dynamic conditions has been analysed in previous papers; in this paper an
exergetic and exergoeconomic analysis is carried out. The exergetic analysis is intended to identify the
steps that mostly affect the overall plant exergy efficiency, so as to propose possible improvements. The
exergoeconomic cost accounting is aimed at assigning a monetary value to each energy or material flow,
thus providing a rational basis for price assignment. Both the exergetic and exergoeconomic analyses are
applied to integral values of energy flows, comparing the results obtained in the summer and winter
season. Finally, economic viability of the system in different context scenarios is discussed
Thermoeconomic Analysis Under Dynamic Operating Conditions for Space Heating and Cooling Systems in Small Residential Buildings
No full textDue to the social concern for energy savings and ecological improvement necessity in the performance of buildings, new analysis tools emerged.
Thermoeconomics connects the physics and economics of energy conversion processes through the second law of thermodynamics. A limited number of thermoeconomic applications in buildings have been proposed, due to the difficulties in dealing with very irregular energy load profiles and unsteady plant operating conditions, which require the use of dynamic approaches that increase the complexity of the method. The present study highlights the potential of thermoeconomics as a support for decision making, due to the capability to identify trade-offs between cost and efficiency. Dynamic thermoeconomic analysis is performed for a school dwelling, supplied with space heating and cooling integrated with a mechanical ventilation Air Handling Unit.
The different sources of irreversibility are evaluated and the main targets for system improvement are identified, calculating exergetic, exergoeconomic and exergoenvironmental costs
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