1,720,961 research outputs found
Full-scale experiments of fire control and suppression in enclosed car parks: A comparison between sprinkler and water-mist systems
Full text linkRecent efforts to investigate car-park fires and understand the related mechanisms have fostered the need for analyses of suppression performance against this type of fire scenario. This work aims at providing an insight into the ability of sprinklers and water-mist systems to control and extinguish a fire within an enclosed car park through a series of real-scale experiments. Three cars were employed in each test: the central one was ignited by a heptane pool fire and the adjacent ones served as targets. Two configurations were explored: in the first one, a nozzle was placed directly at the vertical axis of the ignition source, whereas the ignition source was located between the area coverage of four nozzles in the second one. The sprinkler system mainly served as a reference; two values of discharge density were evaluated for water mist at high operative pressure and a biodegradable surfactant was also tested against the most challenging configuration. A quantitative analysis of free-burn and discharge phases by temperature measurements was coupled with radiant heat-flux measurements and an assessment of post-fire damage. Sprinkler and water-mist systems were capable of containing the fire spread and thermally controlling the fire, thus preventing structural damage. The water mist’s ability to overpower the plume and reach the burning surfaces proved more effective than that of sprinklers, especially as no nozzles were located right above the ignition surface. The higher discharge density showed better capability of preventing re-ignition phenomena and suppression was attained in both the investigated configurations, which suggests that a certain amount of flux is also needed to achieve flame cooling. The additive had promising impact on suppression performance; however, more tests are required to specifically explore its ability to enhance thermal control
Multi-droplet cooling: Experimental tests on infrared-transparent media
No full textThe present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid droplets. In particular, the study is focused on the comparison between the cooling effects obtained with multiple droplets and sparse spray configurations.A new, non-intrusive measurement of the transient contact temperature between impinging droplets and hot solid surfaces is used and described. An experimental apparatus was built and set up in order to approach the non-trivial problem of the measurement of a solid-liquid interface temperature after droplet impingement. The solid-liquid interface temperature was monitored from below through a transparent-to-infrared material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below.The paper reports the main results that have been collected to date, with particular regard to the approaches used to coat the transparent solid. Some considerations are also expressed about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements
Confronto fra tecniche PIV e UPDV per misure di velocità in convenzione naturale in una cavità chiusa contenente una sorgente termica
No full texttecniche PIV e UPDV, per la determinazione dei campi di velocità nei fluidi in moto, vengono per la prima volta comparate nell’ambito di uno stesso esperimento relativo ai moti di convezione naturale indotti da una sorgente termica all’interno di una cavità chiusa. L’esperimento viene condotto utilizzando una resistenza termica cilindrica orizzontale in una cavità allungata a sezione quadrata, contenente acqua. Il caso analizzato è caratterizzato da numeri di Rayleigh modificato e Prandtl rispettivamente pari a Ra=17400 e Pr=8.03. Il confronto tra tecniche PIV e UPDV è svolto sia in termini quantitativi, determinando l’accuratezza e la precisione di misura, che evidenziando parametri qualitativi, quali la complessità d’uso della strumentazione nel particolare caso di studio. L’accuratezza delle tecniche di misura è anche stimata in riferimento alla risoluzione numerica del problema ottenuta mediante tecnica di simulazione numerica (DNS). Si descrivono l’apparato sperimentale, le procedure di rilevazione della velocità e gli esiti sulla comparazione tra le due tecniche di misura. L’indagine mostra che, nell’ambito dell’esperimento svolto, la tecnica PIV dimostra maggiore precisione, mentre la stima dell’accuratezza porta a risultati analoghi per le due tecniche; entrambe denunciano limiti in prossimità delle pareti solide
Full-scale experiments of water-mist systems for control and suppression of sauna fires
Full text linkSauna is a common fixture in many facilities; a specific fire-protection system is typically designed and installed for this application, as short circuits or direct contact with incandescent materials may result in a fire. Water mist has been recently considered as a promising option for this purpose; so, assessing its control and suppression capability in a sauna configuration has become of paramount importance for designers and engineers. To this end, an unprecedented real-scale test rig was built and instrumented with thermocouples and a hot-plate thermometer towards the evaluation of water-mist performance against various fire scenarios and, ultimately, to provide guidelines to designers. Timber benches were employed as target materials, while the fire was initiated in a wood crib. Design parameters, such as initial room temperature, location of the ignition source, nozzle-to-wall distance, and air gap between benches and wall, were varied, also including natural ventilation in a dedicated experiment. The system proved successful in controlling and containing the fire: bench damage ratio—selected as a quantitative parameter to assess water-mist performance—was consistently lower than 5%. However, extinction was not always achieved, especially under the most challenging configuration in terms of ventilation, initial room temperature, and nozzle-to-wall distance
Experimental Assessment of the Acoustic Performance of Nozzles Designed for Clean Agent Fire Suppression
Full text linkDischarge through nozzles used in gas-based fire protection of data centers may generate noise that causes the performance of hard drives to decay considerably; silent nozzles are employed to limit this harmful effect. This work focuses on proposing an experimental methodology to assess the impact of sound emitted by gaseous jets by comparing various nozzles under several operating conditions, together with relating that impact to design parameters. A setup was developed and repeatability of the experiments was evaluated; standard and silent nozzles were tested regarding the discharge of inert gases and halocarbon compounds. The ability of silent nozzles to contain the emitted noise—generally below the 110 dB reference threshold—was proven effective; a relationship between Reynolds number and peak noise level is suggested to support the reported increase in noise maxima as released flow rate increases. Hard drives with lower speed were the most affected. Spectral analysis was conducted, with sound at the higher frequency range causing performance decay even if lower than the acknowledged threshold. Independence of emitted noise from the selected clean agent was also observed in terms of released volumetric flow rate, yet the denser the fluid, the lower the generated noise under the same released mass flow rate
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
COVID-19 as an effect modifier of the relationship between age and in-hospital survival in older patients admitted to an Italian Emergency Department
No full textBackground: The SARS-CoV-2 pandemic modified how persons got into contact with emergency services, particularly during the first wave. Aim: The aim is to describe the characteristics of older persons with and without COVID-19 visiting the Emergency Department of a tertiary hospital and to investigate the impact of age on in-hospital survival in the two groups. Methods: Patients older than 70 years were followed-up till discharge or in-hospital death. Cox regression models stratified by COVID-19 diagnosis were used to investigate survival. Results: Out of 896 patients, 36.7% had COVID-19. Those without COVID-19 were older and affected by a higher number of chronic conditions but exhibited lower mortality (10.5 vs 48.1%). After the adjustment, age was associated with mortality only among those with COVID-19. Discussion: COVID-19 modified the relationship between older age and in-hospital survival: whether this finding is explained by other biological vulnerabilities or by a selection of treatments based on age should be further investigated
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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