2,400 research outputs found
Droplet condensation in turbulent jets
No full textThe evaporation and condensation process of liquid droplets, advected by a turbu- lent flow is found in many technological applications - ranging from aeronautical/power- plants engines up to the rather new discipline of Particle Engineering in the biotech industry - and in many natural phenomena, such as cloud formation and meteorology. A better understanding of droplets nucleation, transport, evaporation/condensation and vapour mixing is crucial for the efficiency of these devices as well as it would be to improve weather forecasting.
The phase change is a multi-scale phenomena ranging from the nano scale, at which droplets nucleate, to the micro and macro scales where the turbulent flow advects both the droplets and their vapour. Although droplet laden flows have been extensively studied, several issues are still in place, especially when dealing with multi-phase turbulent flows. Many phenomena, such as small scales clustering of droplets (considered as inertial particles) or preferential spatial accumulation, have been observed and understood under the simplifying assumption of the one-way cou- pling regime, where the disperse phase does not modify the carrier fluid. Nonetheless, a deeper understanding of multiphase flows demands at least for two-way coupling effects, accounting for the inter-phase mass, momentum and energy exchanges. Homogeneous nucleation of liquid droplets occurs when a hot vapour stream mixes with a cooler and dry external flow. Even though many applications could benefit from a better understanding of droplet nucleation in turbulence, nowadays it has been investigated only experimentally, given all the aforementioned difficulties on modelling the multi-physics phenomena occurring in such a complex turbulent flow. In fact, the nonlinear interplay between turbulent fluctuations and homogeneous nucleation, immediately leads to non-trivial cross-coupling phenomena between the gas and the liquid phase. Their modelling reveals to be crucial for detailed numerical investigations to be reliable.
Classical Nucleation Theory (CNT) prescribes a rate for the homogenous nucleation of droplets, per unit time and volume. It also provides for an estimate of the critical radius at which – eventually – each droplet nucleates. The droplet nucleation itself basically occurs when a stable molecules cluster size is reached, thus everything strongly depends on the local thermodynamical state. While the equations describ- ing mass, momentum and energy exchange, between droplets and the turbulent flow are still formulated on phenomenological ground, a rigorous derivation of the fluid flow equations still lacks. In the present work a first attempt to tackle this challenging physical problem will be presented: modelling the mass, momentum and energy transfer, with appropriate boundary conditions, at the interface between the two phases. Starting from the low-Mach number formulation of the Navier-Stokes equations for the gaseous phase, an analytical decomposition of the flow field allows
– within the point particle approximation, for the disperse phase – to reallocate the boundary conditions at the droplets surface as equivalent source/sink terms on the carrier phase, without any ad-hoc assumption. However this methodology still needs an estimate for the fluxes at the droplet surface, at any length-scale. Two different models for the mass transfer, have been tested and employed here to be validated against the available experimental investigations found in literature.
In the present study a full description of the droplet nucleation in a vapour turbulent jet is provided by means of Direct Numerical Simulation (DNS). No turbulence model has been considered, since all the relevant scales of turbulent motion have been resolved on the computational grid. To capture the inter-phase exchanges the so-called Exact Regularised Point-Particle method (ERPP) has been adopted, proving again its suitability for High Performance Computing simulations (HPC) on massively parallel machines, handling billions particles. In the point-particle ap- proximation and within the Eulerian-Lagrangian approach, here adopted to describe respectively the carrier and disperse phase dynamics, each droplets is described as point mass. The relevance of the inter-phase coupling effects is thoroughly discussed, by comparing the results obtained accounting for the droplets back-reaction with those obtained neglecting it. It is already known how a disperse phase does affect the carrier phase dynamics, modulating turbulence, stretching the shape of the jet, but always preserving the (statuary) jet self-similarity found in the one-way coupling regime. Beyond turbulence modulation, the droplets back-reaction is mainly effective on the temperature and vapour fields of the carrier phase, heavily altering the local thermodynamical fluctuations, thus affecting the related droplet nucleation rate. This way, one is able to completely characterise the phase change process, to measure any droplet trajectory followed in a Lagrangian way and to fully characterise any observable from a statistical point of view.
Considerable effects of the droplets back-reaction on the nucleation rate emerged, by decreasing the amount of vapour – due to nucleation/condensation – and heating up, to a lesser extent, the dry environment. Both effects decrease the vapour saturation and the nucleation rate that strongly depends on it. The intensity of these effects is related to the number of back-reacting nucleated droplets, thus at lower concen- trations the nucleation rate is almost insensitive to it. However, for higher vapour concentration, it is not possible to neglect the particles back-reaction, especially being these an additional source of turbulent fluctuations that ultimately impacts on the mean nucleation rate. In fact, the droplets redistribute vapour through condensation/evaporation and temperature by releasing/absorbing heat, along their trajectory. In other words, the particles back-reaction serves as an additional source of fluctuations not to be disregarded. It is reasonable to hypothesise that it is not possible to effectively model the back-reaction effects, discussed so far, rather than to simply evolve each single droplet as it has been done in the present DNS simulations. Under this respect, the present contribution constitutes an absolute novelty in the aerosol community shedding light on the the two-way coupling effects that were revealed to be crucial in the overall nucleation process and turbulent transport of the droplets
Su di un modello Attuariale per la valutazione al Fair Value di contratti di assicurazione sulla vita
No full textFrancesco Cetta, Paolo De Angelis, Nicolino Ettore D'Orton
Voci dagli Stati Uniti. Prosa & Poesia & Teatro del secondo Novecento.
No full textIntroduzione - IX Caterina Ricciardi. 3 Zora Neale Hurston - Anna Scacchi. 15 Henry Roth - Mario Materassi. 25 Frederic Prokosch - Fedora Giordano. 35 Kenneth Patchen - Maria Anita Stefanelli. 45 Tillie Olsen - Anna Scacchi. 57 Walker Percy - Mattia Carratello. 65 Gwendolyn Brooks - Ugo Rubeo. 79 Charles Bukowsky - Daniela Daniele. 87 Henry Swados - Federico Siniscalco. 95 Richard Wilbur - Paola Loreto. 103 William Gaddis - Anna Scacchi. 117 Kurt Vonnegut - Biancamaria Pisapia. 131 Anthony Hecht - Francesco Rognoni. 147 Herbert Gold - Stefano Tani. 155 John Hawkes - Stefano Tani. 165 Frank O'Hara - Cristina Giorcelli. 183 John Ashbery - Francesco Rognoni. 203 William Stanley Merwin - Andrea Mariani. 215 Philip K. Dick - Salvatore Proietti. 231 Raymond Federman - Maria Vittoria D'Amico. 243 Cynthia Ozick - Mario Materassi. 265 John Barth - Clara Bartocci. 283 Stanley Elkin - Roberto Maria Dainotto. 293 Walter Abish - Salvatore Marano. 305 Edgar Lawrence Doctorow - Biancamaria Pisapia, Valerio Massimo De Angelis. 317 Toni Morrison - Chiara Midolo. 333 Tom Wolfe - Igina Tattono. 343 Robert Coover - Maria Anita Stefanelli. 353 Grace Paley - Gabriella Ferrugia. 365 John Gardner - Stefano Tani. 375 Cormac McCarthy - Luca Briasco. 387 Hugh Nissenson - Mario Materassi. 399 Susan Sontag - Luciana Piré. 417 Joan Didion - Paola Cabibbo. 429 Don DeLillo - Roberto Maria Dainotto. 443 Thomas Pynchon - Maria Vittoria D'Amico. 461 Raymond Carver - Riccardo Duranti. 475 Russell Banks - Francesco Pontuale. 485 Sam Shepard - Annalisa Goldoni, Alessandro Clericuzio. 499 Richard Ford - Francesco Rognoni. 513 August Wilson - Alessandro Clericuzio. 525 Paul Auster Luca Briasco. 539 Stephen King - Valerio Massimo De Angelis. 555 David MAmet - Maria Anita Stefanelli. 567 David Leavitt. 577 Bret Easton Ellis - Tatiana Petrovich Njegosh. 587 Letteratura Indiano Americana - Giorgio Mariani. 601 Letteratura Portoricana - Anna Scannavini. 613 Letteratura Appalachiana - Annalucia Accardo. 629 Postfazione - Valerio Massimo De Angelis. 647 Indici. 647 Indice Analitico. 661 Indice Generale
Per conoscere De Angelis con una poesia. La luce sulle tempie (Somiglianze)
No full textIl saggio commenta La luce sulle tempie, quinto testo della raccolta di esordio di Milo De Angelis, Somiglianze (1976); individua e discute i tratti formali e concettuali, ne segue le diramazioni nei testi vicini e lontani della raccolta. In primo piano: i modi, ellittici e metonimici, di rappresentare la scena e l’evento; le parole e i concetti chiave (come sorriso, abbraccio carezza, subito e adesso, spiegazioni e ragione) che compongono quello che De Angelis ha definito il dissidio tra «il rovello analitico e il desiderio di essere invasi dalla corrente della vita». Nel macrotesto e nel sistema dei valori della poesia di De Angelis La luce sulle tempie è una poesia imprescindibile e necessaria
Trata, tráfico y prostitución : aproximaciones conceptuales al debate
Get PDFFil: Pani, Mariaconcetta. Universidad de Buenos Aires. Facultad de Filosofía y Letras; Argentina.Fil: Gutiérrez De Angelis, Marina. Universidad de Buenos Aires. Facultad de Filosofía y Letras; Argentina
Especialización y complementación productiva en el MERCOSUR un enfoque de cadenas productivas de valor
Get PDFEl MERCOSUR ha mostrado un creciente interés por utilizar la integración regional como base para aumentar su competitividad internacional aludiendo a la complementariedad y especialización productiva entre sus socios. Este trabajo pretende realizar una contribución metodológica a la medición de este fenómeno, agregando productos para conformar cadenas productivas de valor, al mismo tiempo que realiza una primera medición de esta nueva metodología para el MERCOSUR durante el período 2003-2012. Los resultados arrojan algunos casos incipientes de integración productiva, fundamentalmente para los socios de mayor tamaño, y varias potencialidades interesantes para la aplicación de una política productiva para el bloque.Fil: Molinari, Andrea.Fil: De Angelis, Jesica
Efficient modeling of graphene based optical devices
No full textIn this paper we describe some basic issues in the numerical modeling of graphene devices at optical frequencies. In the first part of the paper we analytically describe the behavior of a graphene-based directional coupler; in the second part of the paper we introduce a novel formulation of the Beam Propagation Method to show how this powerful numerical technique can also be used to describe light propagation in graphene as well as in other new emerging two-dimensional materials
Supplemental_Material – Supplemental material for Image that Matters: News Media Consumption and Party Leader Effects on Voting Behavior
No full textSupplemental material, Supplemental_Material for Image that Matters: News Media Consumption and Party Leader Effects on Voting Behavior by Diego Garzia, Frederico Ferreira da Silva and Andrea De Angelis in The International Journal of Press/Politics</p
Supplemental Material, PPQ_supplemental_mat - From party to leader mobilization? The personalization of voter turnout
No full textSupplemental Material, PPQ_supplemental_mat for From party to leader mobilization? The personalization of voter turnout by Frederico Ferreira da Silva, Diego Garzia and Andrea De Angelis in Party Politics</p
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