1,720,961 research outputs found
Trasporto di fluidi organici e di fluttuazioni di pressione: un approccio numerico alla termofluidodinamica.
No full textI temi affrontati nella ricerca in ambito termofluidodinamico richiedono spesso un approccio multidisciplinare e tecniche di indagine non tradizionali. Una delle strategie più utilizzate, vista anche la sempre crescente disponibilità di risorse computazionali, è quella di operare con modelli numerici per la simulazione di fenomeni complessi, multifisici e multiscala. Una tematica di forte interesse ingegneristico è lo studio delle fluttuazioni di pressione derivanti dall’interazione tra un corpo e una corrente d’aria che lo investe: tale disturbo può ricadere nel campo dell’udibile e la sua diffusione può contribuire all’aumento dell’inquinamento acustico. Ne è un esempio il rumore prodotto dalle turbine eoliche di grande taglia per le quali sono state già state adottate tecniche di abbattimento del rumore, come l’impiego di bordi di uscita dentellati (trailing edge serration). Un altro tema di estrema rilevanza è quello del trasporto di fluidi organici veicolanti virus o batteri: la recente pandemia da SARS–CoV–2 ha messo in evidenza quanto sia importante valutare accuratamente la dinamica delle micro–gocce di saliva e la loro interazione termofluidodinamica con l’ambiente al fine di fornire corrette linee guida sulla distanza sociale e sulle buone pratiche da seguire nella quotidianità all’interno del contesto pandemico. In questo lavoro di tesi viene utilizzato un approccio numerico per lo studio dell’emissione aeroacustica prodotta da oggetti investiti da un flusso d’aria e della diffusione aerea di micro–particelle di fluido organico veicolanti virus. Viene sviluppato un solutore in grado di condurre simulazioni dirette (Direct Numerical Simulation – DNS) del campo aeroacustico, utilizzando condizioni al contorno non riflettive e schemi di integrazione temporale Runge–Kutta espliciti di alto ordine, e indagata la possibilità di adottare il riscaldamento localizzato quale tecnica di smorzamento delle fluttuazioni di pressione caratteristiche di un’onda sonora. Viene, inoltre, presentato un modello con approccio Euleriano–Lagrangiano multiscala, che permetta di valutare la diffusione in ambiente di particelle di fluido muco–salivare, nonché il processo di cristallizzazione della quota–parte salina delle droplet accoppiando il metodo Particle–Source–In–cell (PSI–cell) alla Population Balance Equation (PBE). Viene indagata anche la possibilità di ridurre la trasmissione di SARS–CoV–2 utilizzando la radiazione ultravioletta di tipo C quale tecnica di disinfezione real–time. I modelli sono sviluppati adottando il metodo di discretizzazione ai volumi finiti non strutturati e co–locati disponibile all’interno della libreria OpenFOAM.The new issues addressed in scientific research in the thermal and fluid dynamic field often require a multidisciplinary approach and non–traditional investigation techniques. One of the most used strategies, also because of increasing availability of computational resources, is to operate with numerical models that allow the simulation of complex, multiphysics and multiscale phenomena. A cutting-edge topic is certainly the study of fluctuating pressure resulting from a body and air interaction: this disturbance can be such that to be in the hearing range and its diffusion can contribute to the increase in noise pollution and have a significant impact on our daily life. As an example, we can refer to the noise produced by multi–megawatt wind turbines that are often equipped with trailing edge serration in order to reduce the aeroacouistic emission. Another crucial topic in this moment is related to the organic fluids, carrying viruses or bacteria, diffusion: SARS–CoV–2 pandemic has highlighted how important is to understand and rigorous study saliva droplets dynamics and their interaction with the environment in order to provide guidelines on social distance and good practices to be followed in daily life. In this PhD thesis a numerical approach is used to study the aeroacoustic emission radiated by objects in a flow as well as to investigate airborne diffusion of organic fluid micro - particles carrying viruses. A new solver is developed in order to perform Direct Numerical Simulation of the aeroacoustic fields. Explicit high–order Runge–Kutta schemes are employed for time integration and non–reflective boundary conditions are adopted. The local wall heating effect fluctuating pressure is also investigated, in order to give an insight on a new method for active controlling the noise emission. Furthermore, a new computational model, developed in a multiscale Eulerian - Lagrangian framework, is presented. This approach allows to evaluate the spreading of micro–droplets emitted in respiratory activities, as well as their thermal and fluid dynamic interaction with the surrounding environment, taking also into account the droplet dry nuclei formation. Saliva sodium chloride crystallization kinetics is modelled by coupling Particle–Source–In–cell (PSI–cell) method with Population Balance Equation (PBE). Moreover, a real–time disinfection strategy is studied: biological inactivation of SARS–CoV–2 using ultraviolet–C radiation is addressed. The aforementioned models are developed adopting the unstructured, co–located, finite volume method available in the well-known OpenFOAM library
Thermal Behaviour of a Cylindrical Li-Ion Battery
Get PDFThis paper presents an experimental evaluation of thermal and electrical performances of a 26650 cylindrical Lithium Iron Phosphate/graphite battery cell. Thermal management of Lithium batteries is a fundamental issue of electric mobility, where batteries are subjected to severe operating conditions. Therefore, battery heat generation is a very important characteristic to be studied. In this work cell performances were assessed during battery discharge at ambient temperature over a wide range of discharge rates. The cell surface temperature was measured both with thermocouples and infrared thermography. Furthermore, also the open circuit potential and entropic heat coefficient were experimentally measured. Based on this experimental data, a simplified battery thermal model was used to evaluate the battery heat generation. The results show a substantial increase of battery surface temperature especially at high discharge rates. During discharge, the heat generated is greater at low battery state of charge due to the sudden decrease of cell potential. The contributions to heat generation are also carefully evaluated
Impact of Sodium Chloride Crystallization on Saliva Droplets Spreading
No full textIt is well known that SARS–CoV–2, can be transmitted through airborne diffusion of saliva droplets which travels into atmospheric air through a thermo-fluid dynamic interaction with it.
In order to limit SARS-CoV-2 spread, social distancing is crucial. However, in this context is really important to emphasize that available knowledge is largely inadequate to make predictions on the airborne spreading of infectious droplets emitted during a cough and/or sneezing.
The main aim of our research activity is to provide a contribution to thermo-fluid dyamic modeling of saliva droplets diffusion produced by coughing. In particular in this paper, several efforts were devoted to the analysis of impact of saliva chemical composition on the their spreading in space
Infrared Thermography Study of Thermal Footprints Generated by Ordinary and Extraordinary Respiratory Activities in Persons Wearing Face Masks
Get PDFThe airborne diffusion of saliva droplets during respiratory activities is one of the major factors in the spread of infections. During the COVID-19 pandemic, the use of protective face masks was essential to reduce the risk of infection and spread of SARS-CoV-2. The face mask is able to significantly reduce the saliva droplet emission in front of the person. However, the use of masks also produces a particle leakage towards the back of the person, which could increase the infection risk of people behind the subject. Most of the experimental investigations applied invasive and/or complex experimental techniques to evaluate the face masks leakage. The primary objective of this study is to develop a novel, non-invasive methodology for assessing rearward droplet emission associated with the use of protective face masks. Specifically, a thermographic analysis of the thermal footprint released during ordinary and extraordinary respiratory activities is presented, evaluating the maximum temperature, the detection time, and the spread area of the thermal footprint. Both surgical and FFP2 face masks were tested. Two different subjects were involved in the experimentation to evaluate the influence of face conformation. The findings indicate that the area influenced by droplet dispersion is larger when wearing a surgical mask compared to an FFP2 mask, with the highest recorded temperatures observed for the surgical mask. The thermal footprint was found to be strongly dependent on individual facial morphology and mask fit. Notably, the FFP2 mask also altered the position of the thermal footprint, which was primarily confined to the region near the neck
Wall heating effects on aeroacoustic fields radiated by rigid bodies at different flow regimes
Get PDFThis study presents several direct numerical computations concerning wall heating effects on aeroacoustic fields derived from flow-rigid body interaction. Both laminar and turbulent flow configurations involving isolated and multibody arrangements have been addressed. Some insights into the physical mechanisms concerning these problems are addressed and discussed. In particular, we observed that the aeroacoustic fields produced by laminar flows can be more easily controlled and practically suppressed in terms of acoustic emission by wall heating. By contrast, in turbulent flows, the effectiveness of the analysed technique is more limited. Indeed, wall heating produces a slight increase in overall emissions. However, at the tonal peak frequency derived from adiabatic configuration, the acoustic contribution is considerably reduce
A semi-empirical correlation for the estimation of the second virial coefficients of refrigerants
No full textA low—storage Runge—Kutta OpenFOAM solver for compressible low—Mach number flows: aeroacoustic and thermo—fluid dynamic applications
No full textA solver for compressible Navier–Stokes equations is presented in this paper. Low-storage RungeKutta schemes were adopted for time integration; on the other hand the finite volume approach available within OpenFOAM library has been adopted for space discretization. Kurganov-Noelle-Petrova approach was used for convective terms, while central schemes for diffusive ones. The aforementioned techniques were selected and tested in order to allow the possibility of solving a broad range of physical phenomena with particular emphasis to aeroacoustic and thermo-fluid dynamic problems. Indeed, that standard OpenFOAM solution techniques produce an unacceptable dissipation for acoustic phenomena computations. Non–reflective boundary treatment was also considered to avoid spurious numerical reflections. The reliability and the robustness of the solver is proved by computing several benchmarks. Lastly, the impact of the thermal boundary conditions on the sound propagation was analyzed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
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