1,720,984 research outputs found
Effect of the choice of the balance point on the mean seasonal COP of electric air-to-water heat pumps without inverter
No full textA MATLAB numerical code to determine the effects of the choice of the balance point and of the thermal storage (puffer) volume on the mean seasonal COP of an on-off electric air-to-water heat pump is presented. The heat pump is used to heat a building and is provided with a puffer and a back-up system (electrical resistances). The code employs as main input parameters: the hourly values of the external air temperature, the heat loss coefficient of the building, the volume and the imposed maximum and minimum temperature of the storage water, the technical data of the heat pump as functions of the source temperatures. The code evaluates the hourly values of the energy lost by the building, of the average temperature of the water in the puffer, of the energy supplied to the building by the heat pump and by the back-up system. By varying the selected values of the balance point and of the storage volume, it is possible to calculate their optimal values in order to maximize the seasonal COP. The results show that a correct choice of the balance point yields a significant increase of the mean seasonal COP of the system, while the effect of the puffer volume is less considerable
Considerations on the thermal performances of ribbed channels by means of a novel dynamic method for hierarchical clustering
Full text linkThe investigation of ribbed surfaces for the enhancement of heat transfer in forced convection allowed to observe that different geometries may lead to comparable performances. Due to the lack of an underlying structure of the data, a novel method for data clustering is introduced here, to assess to what extent comparable performances can be achieved using
different rib geometries. The clustering method is an agglomerative technique, based on the inclusion of each configuration in another ones bounding box, whose size depends dynamically on the Nusselt number and the pumping power. The method is applied to a large database experimentally obtained at ThermALab of Politecnico di Milano, in order to identify the Nusselt number and the friction factor for diverse-rib configurations in a large-aspect ratio channel with low-Reynolds flows. The clusters are determined, and the resulting families of configurations are used to assess the possible effects of the rib eometry on the thermal and fluid-dynamic performances. The clustering analysis results suggest interesting considerations
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
Heat transfer characteristics in forced convection through a rectangular channel with 60° tilted in line, staggered and crossed rib
No full textIn this paper we present new experimental results of investigation on average heat transfer characteristics of a forced air-flow through a rectangular channel with the lower and upper surfaces roughened by ribs; data for a rectangular channel with flat surfaces are presented for comparison as well. The channel cross-section is 120 mm wide and 12 mm high; the channel is operated with the lower and upper walls at fixed temperature whereas the side ones are adiabatic. Ribs have a square cross section and are mounted in three different arrangements: in-line, 60° parallel-tilted (the angle is respect to main stream); staggered, 60°
parallel-tilted; 60° cross-tilted. The tested configurations differ each other for the rib side dimension, namely, 2 or 4 mm, and for their pitch-to-side ratio equal to 10, 20 and 40. Upstream the test channel, there is an entry-section consisting of a 800 mm long, rectangular duct with the same transverse dimensions as the test section but with flat and adiabatic walls.
Air flow rates have been varied in order to have Reynolds numbers, based on the duct hydraulic diameter, ranging between 700 and 7500. The average Nusselt numbers are evaluated on the basis of the air-flow bulk-temperature at entrance and exit from the heated zone, as well
as of the surface temperature measured by eight T-type thermocouples plugged into the heated walls. The test section is also equipped with static pressure taps placed at the heated zone ends. Results show an increase of the average Nusselt number, calculated as the ratio Nu/Nu_0 , for the
all tested ribbed channels ranging between 1.0 and 5.0
Control of Natural Circulation Loops by Electrohydrodynamic Pumping
No full textThe paper analyses the effect of electrohydrodynamic (EHD) pumping on the stabilization and control of natural circulation loops (NCLs). In the initial experimental set-up, we measured the static pressure rise given by an EHD pump made of three consecutive modules of point-ring electrodes for different dielectrics fluids and electrode materials. When switching the polarity of the applied voltage, we observed opposite pumping directions, suggesting the presence of two distinct EHD phenomena, inducing motion on opposite directions: ion-drag pumping and conduction pumping. Based on these preliminary experiments, we built an NCL, operating with the fluid HFE-7100. Two oppositely mounted pumping sections could be alternately activated, to promote clockwise or anticlockwise motion. In the first series of tests, alternately, the pumping sections were triggered prior to the heat input. In any case, the circulation followed the EHD pumping direction. In other tests, the electric field was applied when natural circulation was already present and the flow was reversed by means of opposite EHD pumping, at both polarities. Simply inverting the polarity of the applied voltage, we could alternate ion-drag and conduction pumping; in this way, we easily controlled the direction of motion by means of a single pumping section
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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