1,720,971 research outputs found
Setup and characterization of a multi-purpose test rig for R744 refrigerating cycles and equipment
No full textFollowing a widespread trend in international research on R744 cooling applications, the authors have developed a test rig for investigating refrigerating cycles and equipment which operates with such refrigerant. The facility was designed aiming to a compact layout and to a high flexibility in terms of cycles and pieces of equipment to be tested. The test rig can operate stand-alone thanks to a passive load management system which works with water as secondary fluid. The paper gives some useful data, based on direct experience, for the realization and management of a multi-purpose test rig that allows the analysis of several cycle layouts over wide operating ranges. Some of the main critical issues related to proper plant and component design, a correct choice of the measurement equipment and a suitable system management are shown and discussed. The paper also includes experimental data obtained while testing a reciprocating compressor and a single-stage cycle layout both with and without using an internal heat exchanger
Suitability of coupling a solar powered ejection cycle with a vapour compression refrigerating machine
No full textThe most commonly employed technology for cold production is vapour compression, mainly due to the high efficiency of such devices. However, a major operating issue is the strong dependency of system efficiency and capacity on ambient temperature, which in turn leads to low yearly performance and to a low capacity factor. On the other hand, solar cooling is gaining an increasing appeal as a way to locally exploit renewable energy sources and reducing carbon footprint. Many thermally driven systems are being currently studied, among these the ejection reverse cycle is being proposed as an interesting alternative due to its simplicity, low cost and reliability. The present paper aims to analyse a complex system in which the solar powered ejection machine is used to increase the efficiency of a traditional vapour compression machine by subtracting heat from the condenser. By means of a transient analysis, performed with a reference building and with climate data corresponding to four different system locations worldwide, the year-round performance of such a system in a space cooling application is estimated in terms of energy balance and savings on power costs with respect to the traditional solutions, in order to evaluate its potential benefits and to highlight some issues related to system design and operation. A sensitivity analysis is also performed with respect to solar collector area and equipment sizing, showing how the latter is an important optimisation parameter when designing the system
Experimental analysis of R744 parallel compression cycle
No full textA diffuse interest on cycle modifications for R744 applications that allow to achieve better CO2 cycles performance can be inferred from the literature. The parallel compression cycle in flash tank configuration seems to be an interesting solution and the authors conducted an experimental campaign to estimate the critical parameters that influence its performance in an actual cycle. Previous to that a thermodynamic analysis was lead to investigate the expectable performance of the cycle and the influence of key parameters such as compressors volumetric flow ratio and separator efficiency. The thermodynamic model designed also allowed the definition of the limit conditions for an optimal operability of the cycle of interest. The experiments showed that the theoretically reachable improvements in terms of refrigerating capacity and coefficient of performance are threatened by several phenomena which may occur in a real system. These detrimental effects are described and commented in the paper. The paper also includes experimental data obtained during the experimental activity for operating conditions typical of commercial refrigeration applications
Influence of the heat storage size on the plant performance in a Smart User case study
No full textThe increasing diffusion of renewable energy sources are posing new challenges to the power grid due to their intrinsic unpredictability causing poor power quality, line congestion and unreliable and unsecure grid operations. In the future, power grid operators may require to the customers/producers a prescribed exchange profile, leading to a diffusion of storage systems or prime movers (especially small combined heat and power for distributed resources) able to balance renewable sources fluctuations. In this latter case, one of the major issue is the efficient use of the heat co-generated: the adoption of thermal storages appears to be necessary. In this paper, the energy performance of a Smart User, i.e. a dwelling with renewable energy sources, a combined cooling, heat, and power system, and heat and cooling back-up generators, is estimated by means of a purposely developed TRNSYS unsteady model. A virtual stand-alone operating condition is imposed for the analysed building as an arbitrary profile of power exchange with the grid. The balancing of renewable sources fluctuations imposes a non-negligible part of the heat from the prime mover to be wasted and a sensible consumption for auxiliary devices (i.e. the auxiliary boiler and the compression chiller). By applying a thermal storage, and increasing its capacity, the fraction of heat wasted and the supply from other devices is remarkably changed, showing different plant performance and efficiencies. The Smart User primary energy consumptions of the different configurations are compared to several options, showing appreciable differences in the performance. © 2013 Elsevier Ltd
Analysis of a solar assisted vapour compression cooling system
No full textExploitation of solar energy is becoming increasingly popular thanks to the potential saving on energy costs and to widespread environmental friendly policies. In this context, solar cooling is particularly interesting since greater cooling loads are usually needed in areas where the solar radiation is more abundant and during sunny seasons. The present work aims to evaluate the potential benefits of integrating a traditional vapour compression cycle with a solar powered ejection cycle, in order to take advantage of solar energy without prejudicing the possibility of cold production during night or cloudy days. A numerical model is implemented in order to simulate the behaviour of solar capitation circuit, ejection cycle and traditional cycle. Considering weather data and global plant performance, the model is thereafter used to estimate a set of global performance parameters
Feasibility of small-size biomass-fueled Hirn-cycle cogeneration plants
No full textBiomass utilization seems to be the easiest way to increase the exploitation of renewable energy sources for small and medium scale energy production. In particular, ligneous biomass, thanks to its availability, appears to be the most suitable for cogeneration applications. Among the several technologies available for energy conversion, the most frequently utilized system to generate electric power is still a process based on a Rankine or Hirn cycle with water as a working fluid. This solution seems quite interesting particularly for small size cogeneration plants because of its availability on the market and the analogy with typical applications involving fossil fuels. Many investors (e.g. Energy Service Companies, ESCOs) might be interested in the installation of this type of cogeneration plants in order to reduce the environmental impact of the system and therefore to benefit from governmental incentives. In order to assess the feasibility of this type of plants, it is important to investigate the possible thermodynamic, economic and technologic constraints. An analysis of these factors has been carried out in the present study
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
- …
