356 research outputs found
Performance and rangeability enhancement of a pump as turbine embedding variable Inlet Guide Vanes
No full textPumps as Turbines (PaTs), also referred to as Hydraulic Power Recovery Turbines
(HPRTs) in several industrial applications, are emerging as a viable solution for smallscale
hydropower applications. However, their efficiency at part-load conditions remains
a significant drawback due to the lack of an inlet flow control mechanism. Therefore, this
work, in collaboration with the industrial partner Nuovo Pignone srl, investigates the
feasibility of enhancing the operational range of a HPRT by embedding Variable Inlet
Guide Vane (VIGV). For this study, a low-specific-speed centrifugal pump is selected.
This machine has been retrofitted by embedding the VIGV between the volute cutwater
and the impeller while keeping the original pump body. To accommodate this modification,
the impeller has been trimmed to make place to the VIGV and its kinematics in
order to obtain a compact solution. A design methodology for the VIGV is presented,
surveying the best practices in Francis turbine guide vane design. Computational Fluid
Dynamics (CFD) analyses are conducted to evaluate the flow characteristics before and
after the VIGV installation, providing insight into loss mechanisms and performance
variations. The results highlight a 25% improvement in part-load efficiency. Additionally,
the VIGV increased the rangeability of the machine by 0.25 of the flow rate at the
best efficiency point (BEP). Furthermore, a cycle-based analysis of variable operating
conditions demonstrates a 25% increase in harvested power. These findings confirm that
embedding a Variable IGV substantially improves PaT performance, making them a
more efficient and adaptable solution for energy recovery applications
La Torre Velasca e il suo restauro
No full textL'articolo analizza la costruzione e il restauro della Torre Velasca a Milano, in particolare il tema della struttura in cemento armato
Il ruolo dell'idrogeno nella transizione energetica verso la decarbonizzazione
No full textL’evoluzione del quadro energetico nazionale, con una sempre maggiore incidenza delle rinnovabili, pone l’attenzione allo sviluppo di tecnologie che permettano
un migliore e più flessibile dispacciamento dell’energia. In questo senso, l’idrogeno può rivelarsi uno strumento valido per l’accumulo di energia in eccesso (power
to gas) per un suo successivo utilizzo diretto o miscelato al gas naturale in centrali termiche. Questo utilizzo dell’idrogeno, com’è facile intuire, può portare
benefici in termini di riduzione delle emissioni di gas serra (CO2), ma necessita di studi approfonditi in termini di stabilità della fiamma ed emissioni di NOx
Injection and combustion modelling in hydrogen internal combustion engines
No full textThis thesis focuses on the numerical analysis of the injection, mixing, and combustion
in direct injection internal combustion engines fueled by hydrogen.
Most likely, the current transition towards a sustainable mobility will be achieved only
through a combination of different technologies. For specific applications, such as heavyduty
road transport, hydrogen-powered internal combustion engines—particularly those
based on direct injection — represent a competitive powertrain solution in terms of cost
and reliability compared to more innovative alternatives like fuel cells.
Although internal combustion engines have been in use for over a century, the unique
chemical and physical properties of hydrogen necessitate a renewed analysis of the fundamental
processes governing engine operation, such as injection, fuel-air mixing, and
combustion.
For this reason, the first step of this thesis is the characterization of the fluid dynamics
of high-pressure hydrogen direct injection into the combustion chamber. The study analyzes
the fluid-dynamic structures characterizing these flows, with particular attention
to the numerical setup required to accurately resolve them. With respect to the state of
art, the analysis focuses on the effect of the typical combustion chamber conditions on
the jet phenomenology. More specifically, an analysis is proposed by varying the cylinder
pressure over time to determine the possible presence of dynamic phenomena that
could alter the flow configuration compared to what is observed under constant pressure
ratios.
As a second step, focus has been posed on the influence of the injector exit section geometry,
to determine whether specific configurations are more suitable for use in internal
combustion engines. Although the injector outlet sections are primarily circular or annular,
new geometries (triangular, star-shaped, rectangular, and elliptical) have been
studied to understand their effect on the mixing between the jet and the surrounding
environment. While some of these geometric configurations have already been analyzed
in the aerospace field, their applicability in the automotive sector has been tested in
this thesis work. Significant differences have been observed in the shock and expansion
system characterizing these flows, for which a detailed explanation has been provided.
Subsequently, the analysis has been extended to the design space of key variables affecting
the mixing process, such as the injection pressure, timing, and nozzle geometry.
The goal has been to extend the engine operability under increasingly lean mixtures
compared to the current state of the art. More specifically, focus has been placed on
mixtures featured by an equivalence ratio of 0.25, which help to reduce wall heat losses
while limiting nitrogen oxide emissions. It has been demonstrated that the mixture
stratification under these conditions is the key to increasing the combustion process
speed. In particular, multi-injection strategies have been tested, showing the potential
to optimize the combustion speed and NOx emissions.
Finally, in an effort to improve internal combustion engine modeling, a procedure has
been developed to account for the effects of thermodiffusive instabilities in hydrogen
flames within the framework of the G-equation combustion model. Preliminary results
show the potential to effectively capture pressure trends with a single preliminary calibration
process regarding the interaction between the flame front and the in-cylinder
turbulence
Un progetto "invisibile" per Sassari: il progetto preliminare di restauro di Sergio Poretti (2007)
No full text
Rascacielos a la italiana. Construcción de gran altura en los años cincuenta y sesenta
No full textIn the fifties and sixties, while Italian engineering was receiving important international awards, the theme of the tall building attracted the attention of the best architects. They made it a field of design experimentation, immediately sensing how the strategic use of the structure could revolutionize the already stereotyped image of the all-steel and glass towers proposed by the International Style. Gio Ponti, Luigi Moretti and the BBPR thus created formidable partnerships with Pier Luigi Nervi and Arturo Danusso, the most active engineers in the field of skyscraper design. The result was at least three masterpieces, among the works created in those years: the Velasca tower and the Pirelli skyscraper in Milan and the Stock Exchange tower in Montreal, which, at the time of its completion, also marked the record for the highest reinforced concrete building in the world.En los años cincuenta y sesenta del siglo XX, mientras la ingeniería italiana recibía importantes premios internacionales, el diseño de los edificios en altura atraía la atención de los mejores arquitectos. Estos entendieron inmediatamente lo mucho que el empleo estratégico de la estructura habría podido revolucionar la ya de por sí estereotipada imagen de la torre de acero y vidrio propuesta por el Estilo Internacional, y lo convirtieron en un campo de experimentación. De esta forma Gio Ponti, Luigi Moretti y la BBPR desarrollaron extraordinarias colaboraciones con Pier Luigi Nervi y Arturo Danusso, los ingenieros más activos en el campo del diseño de rascacielos. De entre los proyectos realizados en esos años, este proceso de colaboración dió como resultado a al menos tres obras maestras: la torre Velasca, el rascacielos Pirelli y la torre de la Bolsa de Valores de Montreal. Esta última, en el momento de su finalización, además significó el récord del edificio de hormigón armado más alto del mundo
Systemic and intestinal chronic inflammation, diet and cancer: an unbreakable bond
No full textIdiopathic intestinal inflammatory diseases (IID) include two types of chronic intestinal disorders: Crohn’s disease and ulcerative rectocolitis. Evidence suggests that the IID is derived from the loss of immune tolerance in normal enteric bacteria diners in a genetically susceptible host. In humans, the initial intestinal immune response to intestinal microbiota is closely regulated; this regulation determines if there is a condition of immune tolerance or an inflammatory defensive response. The alteration of the balance of this immune response can lead to IID. In healthy people, the intestinal lamina contains a complex population of cells of the immune system that secrete cytokines with the function of modulating the immune response, both in anti-inflammatory direction that reduce immune response [transforming growth factor β (TGF-β) and interleukin-10] and pro-inflammatory direction. All these mediators are produced by innate and adaptive immune cells, which limit the excessive entry of intestinal microbiota and defend themselves from pathogens. The balance of the immune response is maintained between regulatory T cells and effector T cells (Th1, Th2 and Th17). In IID, innate cells increase the production of tumor necrosis factor alpha (TNF-α), interleukin-1β, interleukin-6, interleukin-12, interleukin-23 and chemokines. There is a marked increase in the thickness of the lamina propria, with an increase in the number of CD4+ T cells, in particular proinflammatory subgroups of T cells, which also produce cytokines and chemokines in high quantities. This increase in the production of cytokines determines the recruitment of further leukocytes, thus determining a vicious circle that maintains the state of inflammatio
Velasca tower: an italian-style structure unveiled in a new light through the BBPR archive
No full textThis paper expands on the study of the relationship between the construction and architecture of Torre Velasca in Milan, concerning the solutions adopted for the supporting structure. It evaluates records from the BBPR architects, presently kept at Rome’s MAXXI Museo Nazionale delle Arti del XXI secolo, loaned by the Belgiojoso family in 2022 and now accessible to researchers for the first time. The research delves into unpublished documents related to the project’s execution, particularly emphasizing the interactions between various participants involved in the building’s construction. This study scrutinizes BBPR’s drawings, project papers,meeting reports, and communicationwith the SGI - Società
Generale Immobiliare technical office. The paper elucidates the key factors influencing structural decisions by comparing the new data with information from previous research. Furthermore, it sheds light on the underlying rationale behind
the design choices implemented throughout the tower’s construction. It illustrates how the structural framework was strategically utilized to redefine its architectural identity, distinct from the conventional North American skyscraper model. Additionally, the study uncovered the unique contributions of individuals who played pivotal roles in shaping this globally acclaimed architectural masterpiece
Design and CFD performance analysis of a novel impeller for double suction centrifugal pumps
No full textDouble suction centrifugal pumps are the main devices involved in the feedwater system of nuclear power plants and they are responsible for a significant share of their energy consumption (by affecting the balance of both the gross and net electrical energy production), hence even an efficiency increase of only a few percentage points could be substantial in their economy. Herein a novel impeller designed for low-medium specific speed double suction centrifugal pumps (nq<60) is proposed showing an efficiency improvement with respect to conventional designs in the order of 1–2% associated to a slip factor increase, secondary losses reduction and impeller outflow homogeneity improvement. The novel double suction impeller is characterized by a new arrangement of its flow channels, which come up alternately on the same circumferential exit even if they start from the two different sides. The flow field through the impeller is investigated via numerical simulations run by means of the open source CFD code OpenFOAM and its performance is compared against experimental results. The CFD model set-up, in terms of grid size and discretization schemes, has been previously assessed against results of consolidated CFX simulations on a conventional centrifugal pump
- …
