1,720,962 research outputs found
Experimental evidence of non-ideal compressible effects in expanding flow of a high molecular complexity vapor
Full text linkSupersonic expansions of a molecularly complex vapor occurring within the non-ideal thermodynamic region in the close proximity of liquid-vapor saturation curve were characterized experimentally for the first time. Results for two planar converging–diverging nozzles in the adapted regime and at different inlet conditions, from highly non-ideal to dilute gas state, are reported. Measurements of upstream total pressure and temperature are performed in the plenum ahead of the nozzle, while static pressure and supersonic Mach number measurements are carried out along the nozzle centerline. The investigated expansions are of interest for both fundamental research on non-ideal compressible flows and industrial applications, especially in the energy field. Siloxane MDM (octamethyltrisiloxane, C8H24O2Si3), a high molecular complexity organic compound, is used. Local pressure ratio P/ PTand Mach number M measurements display a dependence on the inlet total state, a typical non-ideal feature different from dilute gas conditions
DESIGN AND COMMISSIONING OF A LASER DOPPLER VELOCIMETRY SEEDING SYSTEM FOR NON-IDEAL FLUID FLOWS
Full text linkPapers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016.The design, the construction and the commissioning of a seeding
system for Laser Doppler Velocimetry operating in non-ideal
conditions, namely in the close proximity of the liquid-vapor saturation
curve and critical point, is presented. The system is implemented
in the Test Rig for Organic VApors (TROVA), a facility
built at CREALab (Politecnico di Milano) with the aim of
characterizing non-ideal gas flows representative of those occurring
in Organic Rankine Cycle turbine passages. The tested fluid
is the siloxane MDM (Octamethyltrisiloxane – C8H24O2Si3), a
silicon oil of particular interest for high temperature ORC applications.
Depending on the test operating conditions, the fluid under
scrutiny expands in a convergent-divergent nozzle from total
pressure and total temperature ranging from 4 bar to 25 bar and
from 253:2 C to 310:3 C respectively, therefore the seeding has
to be injected in a high temperature and high pressure environment,
without altering the thermo-fluid dynamic behavior of the
fluid. A suspension of the tracer particles (titanium dioxide, TiO2
or silicon dioxide, SiO2) in the working fluid is atomized into the
flow, in a plenum ahead of the nozzle inlet. Since the surrounding
fluid is in superheated vapor (or supercritical) conditions, the
spray then evaporates leaving the solid particles free to follow
the flow. The designed system consists of a tank, pressurized
with nitrogen and containing the MDM-seeding suspension, of
a jet mixing system, to maintain the suspension stirred, and of a
drawing line ending with the atomizing nozzle. During normal
operation, the tank is pressurized at a pressure higher than the
plenum one and the fluid flows naturally through the atomizer.
The system has been commissioned and validated through the
verification of its operation. The system is suitable for all cases
where optical measurements (LDV, PIV, etc.) have to be applied
in high temperature, high pressure conditions similar to those
occurring in the TROVA and whenever the use of auxiliary fluids
different from the working one is not feasible. The reported test
proves the suitability of the system in properly seeding the flow
Experimental observation and thermodynamic modeling of non-ideal expanding flows of siloxane MDM vapor for ORC applications
Full text linkThis paper reports extensive experimental results characterizing the supersonic expansion of an organic vapor in non-ideal thermodynamic conditions typical of organic Rankine cycle (ORC) turbines. Data are also employed to assess the accuracy of different thermodynamic models used to describe non-ideal expansions. Experiments were carried out on a converging-diverging nozzle test section, where siloxane vapor MDM expanded in the proximity of the saturation curve, the typical operating region of ORC expanders, thus proving the importance of the present investigation for ORC technology. Indeed, detailed experimental data representative of ORC expansions, useful for design tool assessment, were lacking in the open literature up to date. Two nozzles, featuring exit Mach number of 2.0 and 1.5, were tested from highly non-ideal states to dilute gas conditions. The nozzle flow was characterized by measuring total pressure, total temperature and static pressure along the axis. The Mach number was measured at the centerline through schlieren imaging. Vapor expansion was found to be dependent on inlet conditions, thus proving the flow non-ideality. State-of-the-art thermodynamic models proved their capability of fully describing the flow non-ideality, while simpler and easier to implement equations of state, such as van der Waals, can be acceptable for preliminary expander calculations
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
Design and commissioning of a laser Doppler velocimetry seeding system for non-ideal fluid flows
No full textLAUREA MAGISTRALENel presente lavoro, viene presentato il progetto, la costruzione e la messa in opera di un sistema d’inseminazione per effettuare misure di velocimetria laser Doppler in flussi in condizioni non ideali, cioè nelle vicinanze del punto critico. Il sistema è stato implementato nel Test Rig for Organic VApors (TROVA), un impianto costruito al CREALab, presso il Politecnico di Milano, con l’obiettivo di caratterizzare flussi di gas non ideali rappresentativi delle condizioni che si ritrovano nelle schiere di turbina ORC. Il fluido testato è il silossano MDM (Ottametiltrisilossano – C8H24O2Si3), un fluido di particolare interesse per applicazioni ORC ad alta temperatura.
A seconda delle condizioni operative dello specifico test, il fluido in esame espande in un ugello convergente divergente, da una pressione totale e temperatura totale comprese rispettivamente tra 4 bar e 25 bar e tra 253.2 °C e 310.3 °C, quindi il tracciante deve essere iniettato in un ambiente ad alta temperatura e alta pressione, senza alterare il comportamento termo fluidodinamico del fluido. Una sospensione di particelle traccianti (biossido di titanio, TiO2 o biossido di silicio, SiO2) nel fluido di lavoro viene atomizzata nel flusso, nel plenum a monte dell’ingresso dell’ugello. Dato che il fluido circostante è in condizioni di vapore surriscaldato (o supercritiche), lo spray evapora, lasciando le particelle solide libere di seguire il flusso. Il sistema progettato è composto da un serbatoio, pressurizzato con azoto e contenente la sospensione di MDM e inseminante, da un sistema di miscelamento a getto, per mantenere una sospensione omogenea, e da una linea di prelievo che termina con l’atomizzatore. Durante il normale funzionamento, il serbatoio è pressurizzato ad una pressione maggiore di quella del plenum e il fluido fluisce naturalmente attraverso l’atomizzatore.
Il sistema è stato messo in opera e validato attraverso una verifica del suo funzionamento. Il presente lavoro è la parte iniziale di un processo di ottimizzazione, e i test fatti mostrano le migliorie che devono essere apportate per effettuare una misura LDV affidabile. Il sistema è adatto per tutti i casi in cui si devono effettuare misure ottiche (LDV, PIV, ecc.) in condizioni ad alta temperatura e pressione, simili a quelle che si ritrovano nel TROVA e in tutti quei casi dove fluidi ausiliari diversi da quello di lavoro non possono essere utilizzati. I test riportati provano l’idoneità del sistema ad inseminare correttamente il flusso.The design, the construction and the commissioning of a seeding system for Laser Doppler Velocimetry operating in non-ideal conditions, namely in the close proximity of the liquid-vapor saturation curve and critical point, is presented. The system is implemented in the Test Rig for Organic VApors (TROVA), a facility built at the CREALab (Politecnico di Milano) with the aim of characterizing non-ideal gas flows representative of those occurring in Organic Rankine Cycle turbine passages. The tested fluid is the siloxane MDM (Octamethyltrisiloxane – C8H24O2Si3), a silicon oil of particular interest for high temperature ORC applications. Depending on the test operating conditions, the fluid under scrutiny expands in a convergent-divergent nozzle from total pressure and total temperature ranging from 4 bar to 25 bar and from 253.2 °C to 310.3 °C respectively, therefore the seeding has to be injected in a high temperature and high pressure environment, without altering the thermo-fluid dynamic behavior of the fluid. A suspension of the tracer particles (titanium dioxide, TiO2 or silicon dioxide, SiO2) in the working fluid is atomized into the flow, within a plenum ahead of the nozzle inlet. Since the surrounding fluid is in superheated vapor (or supercritical) conditions, the spray then evaporates leaving the solid particles free to follow the flow. The designed system consists of a tank, pressurized with nitrogen and containing the MDM–seeding suspension, of a jet mixing system, to maintain the suspension stirred, and of a drawing line ending with the atomizing nozzle. During normal operation, the tank is pressurized at a pressure higher than the plenum one and the fluid flows naturally through the atomizer.
The system has been commissioned and validated through the verification of its operation. The presented work is the initial part of an optimization process, and the implemented tests show the developments that have to be carried out to perform a reliable LDV measurement. The system is suitable for all cases where optical measurements (LDV, PIV, etc.) have to be applied in high temperature, high pressure conditions similar to those occurring in the TROVA and whenever the use of auxiliary fluids different from the working one is not feasible. The reported test proves the suitability of the system in properly seeding the flow
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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