1,720,962 research outputs found
Two-phase fluid compressors – A review
No full textAbstract. Two-phase fluid compressors in the scientific and patent literature are briefly
reviewed. Early theoretical and empirical studies date back to the ‘80s, but currently no device
is commercially available. This technology has a significant feature respect to the traditional
circulation pumps and vapor compressors: in fact a two-phase fluid compressor is able to work
with chemical species in the wet vapor phase (consisting of two phases liquid and vapor) in
order to increase simultaneously their pressure employing the mechanical energy provided by a
motor. Different types of two-phase fluid compressor have been conceived and analyzed. In the
first part of this paper, principle of operation and main construction features are described for
each class of two-phase compressors. In the second part, the applications of this technology in
some related thermodynamic cycles are presented. In the third part advantages and critical
aspects of two-phase compressors are analyzed. These devices can be employed in lieu of the
traditional technology in order to pressurize a fluid in the wet vapor phase with less mechanical
power, absence of complex pressure control systems, absence of a liquid-vapor separator and
lower condenser size. Critical aspects of this technology are the two phases thermal
equilibrium (related to the compressor performances), high mechanical pressures on the
surfaces, lubricating oil washing, emulsions or foams, slugging and flashing liquid
A novel mathematical model for the performance assessment of diabatic compressed air energy storage systems including the turbomachinery characteristic curves
No full textIn this work, a novel detailed mathematical model for the performance assessment of diabatic compressed air energy storage (D-CAES) systems with underground storage site is proposed. The model was implemented in Matlab environment and it was validated using the D-CAES Huntorf plant data, demonstrating a close agreement with the data reported in literature. The analysis of some case studies of the D-CAES plant showed that the characteristic curves of the compressors, that were assumed for the operation in steady state conditions, are not suitable for modeling the operation in time-dependent conditions. Thus, different characteristic curves of the compressors and turbines were identified in such a way that the operation points of turbomachinery lay within the admissible range during the entire process sequence, in steady state or time-dependent conditions. Furthermore, the analysis demonstrated that the presence of the throttling valves in the charging and discharging circuits is preferable due to a higher simplicity of construction and regulation despite a low increase of the fuel consumption in the combustion chambers
Thermodynamic sensitivity analysis of a novel trigeneration thermodynamic cycle with two-phase expanders and two-phase compressors
No full textA novel Combined Cooling, Heating and Power (CCHP) cycle, operating with two-phase devices for the compression and expansion processes and a single-component wet working fluid, is proposed. A detailed sensitivity analysis of the novel CCHP cycle has been investigated in order to evaluate, in terms of energy performance indicators, its potentiality to serve typical trigenerative tertiary and industrial end-users with different fixed operating temperatures. In general, the novel CCHP cycle is characterized by higher energy performance indicators than a separated energy production system. The comparison between the novel CCHP cycle and several commercialized CCHP systems has been performed in the case studies related to tertiary and industrial end-users. The novel CCHP cycle shows a trigenerative capability in wide ranges of the end-users demands without surplus or deficit of the electric or thermal powers. Furthermore, the maximum allowable capital cost of the whole novel CCHP plant (BEPCC), that will assure the profitability of the investment, is calculated in the tertiary and industrial end-users case studies. For the tertiary end-user, the capital costs of the commercialized CCHP are between the minimum and maximum BEPCC values. On the contrary, for the industrial end-user, they are lower than the minimum and maximum BEPCC values
Theoretical investigation of a novel high-temperature heat pump exploiting low-temperature waste heat and using two-phase machines with zero electric consumption
No full textA novel high-temperature heat pump (HTHP) exploiting low-temperature waste heat is presented, which is enabled by two-phase compressors and expanders without the need for any requirement of external electric power. The investigation involves a sensitivity analysis at the design point, considering the concurrent variation of five independent variables. The aim is to identify the best-performing conditions for a rubber manufacturer and a canning industry which have different temperatures of waste heat and required heating power. The COP of the overall HTHP system, which is the ratio between the output heating power and the input thermal power (coming from the heat source) is evaluated. The maximum COP values are 0.258 for the rubber manufacturer and 0.452 for the canning industry. The primary energy saving is assessed in terms of equivalent fuel consumption. For the rubber manufacturer, the resulting yearly cost saving is in the range of 129 & DIVIDE; 646 euro/kWth of HTHP installed capacity, and 140 euro/kWth for the canning industry. The economic viability of the HTHP is contingent upon achieving isentropic efficiencies of the expanders and compressors higher than 0.59 and 0.55, respectively, for the rubber manufacturer, and both higher than 0.45 for the canning industry
Sensitivity analysis for the energy performance assessment of hybrid compressed air energy storage systems
No full textA detailed mathematical model was developed for the complete Hybrid Compressed Air Energy Storage (H-CAES) configuration with underground storage site and liquid thermal energy storage, operating with a sequence of processes (charging, holding and discharging with respective duration) in arbitrary order. A sensitivity analysis was carried out in order to calculate several performance indicators of the complete H-CAES configuration, in relation to the simultaneous change of several process parameters. The methodology âDesign of Experimentsâ was applied to the results of the sensitivity analysis in order to calculate the main effects of each process parameter on each performance indicator. The influence of the storage site volume on each performance indicator is negligible. The reduction of the compressor group outlet pressure and of the turbine group power allows a more effective thermodynamic utilization both of the energy stored by the compressors and of the overall energy supplied to the plant. Furthermore, the former utilization is more effective by an increase of the gas temperature in the combustion chambers, whereas the latter utilization is worsened. Moreover, as case study, the existing diabatic CAES plant of Huntorf was modified by introducing a diathermic oil thermal storage. This plant is suitable to operate according to a partial hybrid configuration by the deactivation of the heat exchanger located upstream of the low pressure turbine. The thermodynamic utilization of the overall energy supplied to the plant in the partial hybrid configuration increases in percentage by 9.1% with respect to the diabatic configuration
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
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