78 research outputs found
A proposito di "Il perdono responsabile. Le alternative alla punizione e alle pene tradizionali" (di Gherardo Colombo), Ponte alle Grazie, 2011)
No full textPresentazione e recensione del volume di Gherardo Colombo di cui al titolo. L'occasione fornisce inoltre il giusto stimolo per riflettere sul significato costituzionale della pena e sull'opportunità di adottare soluzioni alternative alla mera detenzione. Ciò anche alla luce di una serie di paradossi che riguardano gli effetti stessi delle pene tradizionali: a esempi di tal genere messi in luce nel volume recensito se ne aggiungono così di ulteriori
PERFORMANCE ASSESSMENT OF A MICROTURBINE-BASED COGENERATIVE PLANT
No full textThis paper presents the results of an experimental analysis performed on a microturbine-based small cogenerative plant. The aim of the experimental campaign was to verify behavior and performances of the microturbine at both full and partial load. Attention was particularly paid to the energy saving indexes defined in the AEEG 42/02 Directive (Italian Authority for electrical energy and gas) and EU Directive 2004/8/EC, which is more strict. Such indexes are the energy saving index IRE, the thermal limit LT (AEEG 42/02) and the primary energy saving PES (EU 2004/8/EC). The results of the experimental campaign show that a cogenerative plant equipped with a microturbine as a prime mover can easily exceed the minimum values of the energy saving index imposed by the current directives during operation at full load. On the contrary, very accurate design of the plant and prediction of the load profiles are required to get acceptable results if operation at partial load becomes necessary
A detailed characterization of viscous oil-water flows downward sudden contractions in horizontal pipes
No full textTwo-phase flows of viscous oil and water through singularities such as sudden area contractions/expansions have been taken into limited consideration in the relevant scientific literature. Nevertheless, they play a role of primary importance in industrial systems, for instance, but not only, in the exploitation of oil wells and pipelines. The proposed work is based on the comparison of photographic images of the flow patterns taken from three points of view, i.e. upper, lower and frontal, thanks to a couple of mirrors ???45° inclined with respect to the horizontal plane. Oil-water flow regimes have been observed both upward and downward of five horizontal test sections with area contractions d/D = 40/50, 30/50, 30/40, respectively. The observed structures of the oil-water interface, especially for core-annular flows, has suggested also detecting flow patterns in a 30 mm straight pipe for sake of comparison. Actually, the shape of the oil-core interface appears significantly influenced by the sharp-edged area change as well as by the expected momentum variation
SEMI-EMPIRICAL ANALYSIS OF THE CRITICAL TRANSITION FROM ANNULAR TO WAVY-STRATIFIED OIL-WATER ADIABATIC FLOW WITHIN HORIZONTAL AND SLIGHTLY INCLINED PIPES
No full textThe main subject of this paper concerns the critical transition from annular to wavy-stratified oil-water adiabatic flow within horizontal and slightly inclined pipes. The transition is referred to as critical because it occurs suddenly, giving rise to a sharp and strong increase in the pressure drop due to the contact of the high-viscosity oil with the pipe wall. This could be a dangerous accident, e.g. in pipelines operation, because the peak-wise increase in the pressure drop might give rise to a “chugging” phenomenon in the flow.
Experimental runs were performed on eight test sections of both Plexiglas® and Pyrex® pipes with internal diameters ranging from 21.5 mm to 50 mm, using tap water and viscous oil (ρo=890 kg/m^3, μo=0.9 Pa s at 20°C). Inclination angles from 0 to 6 deg upward were tested. Water and oil superficial velocities were varied in their proper range and the pressure drop was measured for several combinations of these quantities. Flow pattern visualizations were also taken by a CCD photo-video camera in order to draw flow pattern maps.
Based on these findings, the transition boundary between annular and wavy-stratified flow was analytically determined and compared with the data reported in the existing flow pattern maps
Characterization of the critical transition from annular to wavy-stratified flow for oil-water mixtures in horizontal pipes
No full textThe transition from annular to wavy-stratified oil-water adiabatic flow within horizontal pipes is experimentally analysed and a semi-empirical model is proposed. The transition is referred to as critical because it occurs suddenly, giving rise to a sharp and strong increase in the pressure drop due to the contact of the high-viscosity oil with the pipe wall. This could lead to a dangerous accident in pipelines. Experimental runs were performed on eight test sections of both Plexiglas® and Pyrex® pipes with internal diameters ranging from 21.5 mm to 50 mm, using tap water and oil with viscosity about 880 times higher than that of water. On the basis of pressure drop measurement and flow pattern visualization, the transition boundary between annular and wavy-stratified flow was analytically determined and compared with flow pattern maps
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On rules /
No full textJustice is simultaneously a practical and an ideal concept: when we think of justice, we refer to its day-to-day administration, involving police, lawyers, judges, and politicians-but we also refer to a larger ideal, a set of basic values that guide our attempts to live together and balance competing interests, obligations, and freedoms. If we lose sight of the practical, the ideal will fail-but if we forget the ideal, the practical becomes pointless. On Rules is the culmination of decades of thinking about and working within the law as both ideal and realm of practical action. Gherardo Colombo brings to his rich philosophical analysis of the culture of justice thirty years of experience in the Italian judiciary, which saw him head up numerous important and sensitive commissions and inquiries. His exploration of the concept and application of rules of justice is powerful and clear: if we don't root our experience in a fundamental respect for rules, we cannot have a functioning, just society
CFD simulation with experimental validation of oil-water core-annular flows through Venturi and Nozzle flow meters
No full textIn the present study, Volume of Fluid (VOF) multiphase flow model by ANSYS Fluent 16.2 is used to characterize core-annular flow patterns of highly-viscous oil-water flows through a Venturi Flow Meter (VFM) and a Nozzle Flow Meter (NFM) in a 40 mm i.d. horizontal pipe. Numerical simulations are compared with experiments, for oil superficial velocities in the range 0.25–0.75 m s−1 and water superficial velocities in the range 0.44–1.32 m s−1. Eight cases were considered for numerical runs. Two turbulence models were considered, namely realizable k−ε and Shear Stress Transport ((SST)k−ω. Two phase pressure drop, instantaneous radial velocity and holdup profile, cross-sectional time-averaged holdup and slip ratio were extracted from CFD simulations. Flow patterns were also compared to actual images taken by a Olympus E-M10 mirrorless camera. In terms of concentrated pressure drop and mean water holdup, the results of CFD simulations are consistent with the experimental data. Prediction of the total mass flow rate, computed by homogeneous model, for both the VFM and NFM also gave very satisfactory results
Concentrated pressure drop across sudden diameter contractions of oil-water flows in horizontal pipes: an experimental investigation
No full textTwo-phase flows of liquid (water) – gas (air, vapor, steam) throughout singularities have been widely investigated both by experimental and theoretical approaches. On the contrary, there are very few works dealing with liquid – liquid mixtures, such as water – light/heavy hydrocarbons, even though their industrial interest is not negligible. In particular, both experimental data and numerical models are available for oil-water flows almost only in horizontal straight pipes. To extend the knowledge in such a field, an experimental investigation was carried out about tap water and high viscosity oil (density 890 kg/m3, viscosity 0.838 Pa s at 20 °C, surface tension 0.035 N/m) two-phase flows within pipes including sudden area contractions. Flow pattern, pressure gradient and concentrated pressure drop were analyzed for two test sections, with a sudden contraction 50/40 mm i.d. and with a
50/30 mm i.d. respectively. Models and correlations for the prediction of the pressure variations were tested, both developed for oil-water and gas-water flows. No one gave good agreement with the experimental data, and particularly the gas-liquid ones heavily failed. Therefore, the need of deepening the experimental database appears of utmost importance also in order to formulate appropriated flow models
Influence of sudden contractions on in situ volume fractions for oil–water flows in horizontal pipes
No full textOil–water two-phase flow experiments were conducted in horizontal ducts made of Plexiglas® to determine the in situ oil fraction (holdup) by means of the closing valves technique, using mineral oil (viscosity: 0.838 Pa s at 20 °C; density: 890 kg m−3) and tap water. The ducts present sudden contractions from 50 mm to 40 mm i.d. and from 50 mm to 30 mm i.d., with contraction ratios of 0.64 and 0.36, respectively. About 200–320 tests were performed by varying the flow rates of the phases. Flow patterns were investigated for both the up- and downstream pipe in order to assess whether relevant variations of the flow patterns across the sudden contraction take place. Data were then compared with predictions of a specific correlation for oil–water flow and some correlations for gas–water flow. A drift-flux model was also applied to determine the distribution parameter
Measurement of the oil holdup for a two-phase oil-water flow through a sudden contraction in a horizontal pipe
No full textOil-water two-phase flow experiments were conducted in a horizontal duct made of Plexiglas to determine the holdup of oil by means of the quick closing valves technique, using mineral oil (viscosity: 0.838 Pa s at 20 °C; density: 890 kg m-3) and tap Water. The duct presents a sudden contraction, with contraction ratio of 0.64. about 200 tests were performed by varying the flow rates of the phases. Flow patterns were investigated for both the up- and downstream pipe. Due to the relatively high value of the contraction ratio, it was not observed any relevant variation of the flow patterns across the sudden contraction. Data were then compared with predictions of a specific correlation for oil-water flow and some correlations for gas-water flow. A drift-flux model was also applied to determine the distribution parameter. The results agree quite well with flow pattern visualization
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