1,762 research outputs found
TUTELA DEL LAVORO E LIBERTA' D'IMPRESA NEI PROCESSI DI ESTERNALIZZAZIONE
No full textL’elaborato analizza le conseguenze lavoristiche della successione fra imprenditori, muovendo da una ricognizione delle varie tipologie di esternalizzazione con le relative esigenze e principali criticità.
L’indagine si concentra in primo luogo sul trasferimento d’azienda, esaminando la normativa e la giurisprudenza europee per passare poi alla disciplina di diritto interno, alle procedure sindacali e a uno specifico focus sul trasferimento delle aziende in crisi.
Successivamente l’autore si sofferma sull’appalto, prendendone in particolare considerazione gli indici di genuinità, i criteri di distinzione dalla somministrazione illecita di manodopera e la tutela delle maestranze in caso di avvicendamento fra imprese.
Da ultimo, la ricerca approfondisce le c.d. “clausole sociali”, sia di prima che di seconda generazione, valutandone la compatibilità con il diritto eurounitario e con la costituzione nonché riflettendo sui possibili rimedi in caso di loro violazione.The author analyzes the labour consequences of the succession between entrepreneurs, starting from a recognition of the various types of outsourcing with the related needs and main critical issues.
The survey focuses primarily on the transfer of businesses, examining European legislation and case-law and then moving on to internal legislation, trade union procedures and a specific focus on the transfer of companies in crisis.
The author then dwells on the contract, taking into account in particular the indications of authenticity, the criteria of distinction from the illicit administration of labour and the protection of workers in the event of turnover between companies.
Finally, the research deepens the "social clauses", both first and second generation, assessing their compatibility with European law and with the constitution and reflecting on possible remedies in case of their violation
Influence of Molecular Complexity on Nozzle Design for an Organic Vapor Wind Tunnel
No full textA novel blow-down wind tunnel is currently being commissioned at the Politecnico di Milano, Italy, to investigate real-gas behavior of organic fluids operating at subsonic-supersonic speed in the proximity of the liquid-vapor critical point and the saturation curve. The working fluid is expanded from a high-pressure reservoir, where it is kept at controlled super-heated or super-critical conditions, into a low-pressure reservoir, where the vapor is condensed and pumped back into the high-pressure reservoir. Expansion to supersonic speeds occurs through a converging-diverging Laval nozzle. Siloxane fluid MDM (octamethyltrisiloxane-C8H24O2Si3) is to be tested during the first experimental trials. A standard method of characteristics is used here to assess the influence of the molecular complexity of the working fluid on the design of the supersonic portion of the nozzle by considering different fluids at the same real-gas operating conditions, including linear and cyclic siloxanes, refrigerant R245fa, toluene, and ammonia. The thermodynamic properties of these fluids are described by state-of-the-art thermodynamic models. The nozzle length and exit area are found to increase with increasing molecular complexity due to the nonideal dependence of the speed of sound on density along isentropic expansion of organic fluids
Aerodynamics of Centrifugal Turbine Cascades
No full textThe centrifugal turbine architecture represents a promising solution for Organic Rankine
Cycle (ORC) Systems, in the small-to-medium power range. ORC expanders operate with
very high volumetric expansion ratios, which can be better accomplished in a centrifugal
machine thanks to the increase of passage area along the
ow path. Furthermore the
centrifugal arrangement allows for assembling a multiplicity of stages in a relatively
compact machine, thus reducing the expansion ratio per stage, with benecial eects on
the performances in both design and o-design operating conditions.
A preliminary design exercise proposed by the authors [1] has recently shown the po-
tential of multistage centrifugal turbines, composed by a succession of xed nozzles and
rotors, for medium power applications (about 1MWel). By limiting the
ow regime to
transonic or slightly supersonic conditions, purely converging ducts can be used with
a certain degree of post-expansion, if necessary; the resulting
ow conguration, char-
acterized by weak oblique shocks, leads to a promising design eciency above 85% ;
the absence of converging-diverging ducts allows to negotiate a certain degree of power
control without the onset of normal shocks which, instead, result in a dramatic increase
of aerodynamic losses in axial ORC turbines.
These promising features, however, were based on estimates performed with preliminary
design tools. In this perspective, the aerodynamic performances of centrifugal cascades
represent the most critical issue, since very few information are available in literature
for centrifugal turbines. In absence of experimental data on this kind of machines, the
correlations used to estimate the aerodynamic losses and the
ow deviation must be
assessed with high-delity computational methods.
In the present work the aerodynamics and performance of centrifugal turbine cascades
are studied by applying a three-dimensional CFD model. The study is focused on the
sixth stage of the transonic centrifugal turbine proposed in [1]. At rst a simple but
eective blade design technique, introduced by the authors in [2], is recalled and applied
to the present conguration. The resulting stage is then analyzed focusing on the
prole aerodynamics, considering both stator and rotor blade rows (in this latter case
discussing the eects of the Coriolis acceleration). Finally the morphology of secondary
ows and the three-dimensional eects of the channel
aring are investigated
Design, simulation, and construction of a test rig for organic vapors
No full textA blow-down wind tunnel for real-gas applications has been designed, validated by means of dynamic simulation, and then built. The facility is aimed at characterizing an organic vapor stream, representative of the expansion taking place in organic Rankine cycle (ORC) turbines, by independent measurements of pressure, temperature, and velocity.
The characterization of such flows and the validation of design tools with experimental data, which are still lacking in the scientific literature, is expected to strongly benefit the performance of future ORC turbines. The investigation of flow fields within industrial ORC turbines has been strongly limited by the unavailability of calibration tunnels for real-gas operating probes, by the limited availability of plants, and by restricted access for instrumentation. As a consequence, it has been decided to design and realize a dedicated
facility, in partnership with a major ORC manufacturer. The paper thoroughly discusses the design and the dynamic simulation of the apparatus, presents its final layout, and shows the facility “as built”. A straight-axis planar convergent-divergent nozzle represents
the test section for early tests, but the test rig can also accommodate linear blade
cascades. The facility implements a blow down operating scheme, due to high fluid density
and operating temperature, which prevent continuous operation because of the prohibitive
thermal power required. A wide variety of working fluids can be tested, with
adjustable operating conditions up to maximum temperature and pressure of 400 C and
50 bar, respectively. Despite the fact that the test rig operation is unsteady, the inlet nozzle
pressure can be kept constant by a control valve. In order to estimate the duration of
the setup and experimental phase, and to describe the time evolution of the main process
variables, the dynamic plant operation, including the control system, has been simulated.
Design and simulation have been performed with both lumped-parameter and 1D models,
using siloxane MDM and hydrofluorocarbon R245fa as the reference working fluids,
described by state-of-the-art thermodynamic models. Calculations show how experiments
may last from 12 seconds up to several minutes (depending on the fluid and test pressure),
while reaching the experimental conditions requires few hours, consistently with the performance
of daily-based experiments. Moreover, the economic constraints have been met
by the technical solutions adopted for the plant, allowing the construction of the facility
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