1,721,024 research outputs found
Near-Field Entrainment in an Impulsively Started Turbulent Gas Jet
No full textABSTRACT
The entrainment characteristics of an impulsively started gas jet injected into quiescent atmosphere was studied by means of 2-D visualisations and Laser Doppler velocimetry. The focus of the study was on the near field behaviour where the velocity profiles are not self-similar unlike that far downstream and the unsteady jet head structure plays a relevant role in the early jet development. Direct measurements of the size of the unsteady leading jet structure shows that its length is larger than 12 nozzle diameters, in the near field region investigated, and grows linearly with time. The present analysis indicates that early in the near field the jet volume becomes larger than the injected one, and suggests a possible mechanism for surrounding gas entrainment into the jet head, which differs significantly from the mechanism responsible of entrainment in the quasi-steady part of the jet. It follows that the frequently used model that assumes the head vortex growing due to the mass entrainment from the steady-state jet cone only should be modified when dealing with the initial part of the jet injection. A further result is that the attainment of the steady-state conditions is faster on the jet axis than at the edges, where the mixing mechanism requires larger times to reach equilibrium
Twin background subtraction technique: A novel infrared technique for simultaneous thickness and temperature measurements of micro films
Full text linkThe study proposes a novel non-intrusive infrared technique to measure simultaneously the thickness and temperature of a thin layer that is semi-transparent to infrared radiation. The measurement method has been called Twin Background Subtraction technique. The technique simultaneously exploits the mid-wave IR emission from the film to be measured and the radiation attenuation by the same film of the emission coming from two backgrounds at different constant temperatures. This study discusses the method theoretically and experimentally, focusing on the uncertainties and the dependence on different parameters of the set-up and fluid physical properties. The fluid adopted for the film is water, and various tests have been carried out by changing its temperature between 15 and 50 °C and its thickness from 0 to 500 μm. The TBS technique was proven to be of interest for studying micro to mini films both from a qualitative and quantitative point of view for water films ranging between 10 μm and 350 μm
Performance analysis and simplified modelling of a capillary jet loop heat pipe
No full textIn this study, a prototype Capillary Jet Loop Heat Pipe has been tested to investigate its performances, and a lumped parameters simplified model has been developed to study the key parameters of the device. The tested Capillary Jet Loop is composed of an evaporator, a fluid loop with an ejector and a condenser. The working fluid used is R1233zd(e); an electric resistor of 40x40 mm2, dimensionally similar to a CPU, provides the thermal load, and a water cooling circuit removes it. An experimental investigation on the thermal behaviour has been conducted, varying the orientation, the thermal load from 40 W to 160 W, and the condenser cooling water temperature from 15 °C to 30 °C. The temperatures measured in different locations of the device have been used to estimate the equivalent thermal resistances. The results show a strong relation between performances and orientation and low dependence on thermal load and condensing temperature. The lowest equivalent thermal resistance value is obtained in the horizontal configuration with a value of 0.104 ± 0.005 K/W (CI 64%) at 80 W (5 W/cm2) while it reached the maximum value of 0.202 ± 0.002 K/W at 160 W (10 W/cm2) in vertical bottom heated orientation. The simulation includes a lumped parameter model focused on the two-phase evaporation condensation and capillary phenomena coupled with the fluid dynamics in the loop and in the ejector. Steady-state conditions are simulated. Under some simplified hypotheses, a parametric analysis was performed to investigate the influence on the thermal performances of the different construction and operative variables of the Capillary Jet Loop: loop length, tube diameter, ejector diameter, pore diameter, filling ratio, the fluid temperature. The maximum stable thermal load is calculated, and a stability map is found as a function of the fluid temperature. The matching point between the Loop and the ejector curve identifies the operating system point as a function of the studied parameters
Performances Modelling of a Twin Fluid Internal Mixing Nozzles for Industrial Burners
Full text linkAt the Centro Combustione Ambiente facility, within the “BE4GreenS” R&D project, sponsored by Regione Puglia using European founds, a series of test is being performed to analyze the performances of different Heavy Fuel Oil burner guns and injection nozzles, by varying the operative conditions and some design parameters. With the aim of improving the parameters design, semi-empirical models are being developed to predict the system performance. The emission of NOx and CO are measured and displayed as a function O2, the residual oxygen content in the exhaust gasses, that depends on the tunable air excess being varied for each test series. The CO content data are then interpolated by an hyperbolic function under some hypotheses and simplifications, the first one being that air excess is always guaranteed, otherwise for an under-stoichiometric combustion the CO asymptote should be backward inclined instead of vertical but. So two parameters should be determined experimentally for each test series i: the position of each vertical asymptote O2lim,i, and the curvature of each hyperbole defined by the parameter Ki, in the function (O2 - O2lim,i) × CO = Ki . By assuming also that for similar combustion systems, e.g. the same furnace and the same gun with similar flame asset and burned fuel, the parameters Ki, specific for each test series i can be replaced by a unique parameter K for that set-up, only the specific O2Lim,i have to be determined for each series. This can help in reducing the total number of tests, and furthermore it allows to reverse the function, for example to calculate the air excess that will keep the CO content under a given limit.
A similar linear model for the NOx can then be used to complete the simulation and help in tuning-up the system operative parameter
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
Capillary Jet Loop performance in parabolic flight
Full text linkIn this study, a prototype Capillary Jet Loop Heat Pipe partially filled with R1233zd(E) has been tested to investigate its thermal behaviour on board of parabolic flights where gravity condition changes in the range from 0 to 1.8 g level with a 22 s window of microgravity. The device has been tested both in horizontal and vertical orientations, varying the thermal load provided to the evaporator from 40 W to 180 W. With power higher than 100 W, the device operated in stationary conditions during hypergravity and normal gravity periods. During the microgravity periods, the device has always shown a sharp increase in pressure and temperatures, reducing temporarily the transport capability of the CJL and fast recovery when gravity increases again. Each series of power level results is presented and discussed in terms of temperature, pressure, and temperature difference from the saturation temperature. The thermal power dissipated by the condenser and an estimation of the condensing flow rate have been calculated from the condenser cooling water inlet and outlet to highlight the Capillary Jet Loop operating phenomena. The temperature of the ejector's primary, secondary, and mixing flows (vapour jet pump) are compared for both configurations
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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