1,721,095 research outputs found
Optimization of the Adsorption/Desorption Contribution from Metal‐Organic‐Heat‐Carrier Nanoparticles in Waste Heat Recovery Applications: R245fa/MIL101 in Organic Rankine Cycles
Full text linkThe efficient recovery of low temperature waste heat, representing from 25% up to 55% of the energy losses in industrial processes, still remains a challenge and even Organic Rankine Cycles (ORCs) experience a strong efficiency decay in such a low temperature operating range (T < 150 °C). In similar heat transfer processes, several nanofluids have been proposed as a solution for increasing heat transfer efficiency, but they produced only moderate enhancements of the heat transfer efficiency in comparison with pure fluids. This paper aims at numerically assessing the potential gain in efficiency deriving from the application of an unconventional type of nanoparticles, the metal‐organic heat carriers (MOHCs), in the ORC field. In comparison with standard nanoparticles, these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption, with a theoretically high potential for boosting the heat transfer capacity of ORC systems. In this paper a numerical model was developed and customized for considering the adsorption/desorption processes of the pure fluid R245fa (pentafluoropropane) combined with a crystal structure for porous chromium terephthalate (MIL101). The R245fa/MIL101 nanofluid behavior was experimentally characterized, defining proper semi‐emipirical correlations. Then, an optimization procedure was developed, combining the numerical model with a PSO algorithm, to optimize the thermodynamic conditions in the ORC so as to maximize the contribution of desorption/absorption processes. The results confirm the increase in net power output (+2.9% for 100 °C) and in expander efficiency (+2.4% for 100 °C) at very low heat source temperature. The relevance of tuning the operating cycle and the nanofluid properties is also demonstrated
Gram-negative flora of horticulture products prevalently to be consumed fresh. II, Acinetobacter calcoaceticus
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Von Karman Vortex Induced Vibration in a Francis Turbine: a reduced numerical model for estimating the shedding frequency
No full textThe present paper presents a numerical analysis of the von Karman vortex shedding at the blades trailing edge of a recently installed small hydro Francis turbine manifesting very loud and high frequency acoustic pulsation when operating close to the rated discharge. A reduced single passage numerical model is developed to reduce the computational effort of the simulation while ensuring high accuracy in the assessment of fluid flow. The potentials of the numerical model are investigated by comparing the frequency spectrum of the experimentally acquired acoustic frequency and the numerical pressure signals allowing to confirm the nature of the vibrations affecting the machine. Thanks to the so demonstrated ability in the evaluation of the fluid flow, the proposed numerical model represents a valid alternative to the traditional correlation-bases approach for the evaluation of the von Karman shedding frequency with a less computational effort compared with a transient simulation of the entire machine
Von Karman Vortex Induced Vibration in a Francis turbine: as reduced numerical model for estimating the shedding frequency.
No full textThe present paper presents a numerical analysis of the von Karman vortex shedding at the blades trailing edge of a recently installed small hydro Francis turbine manifesting very loud and high frequency acoustic pulsation when operating close to the rated discharge.
A reduced single passage numerical model is developed to reduce the computational effort of the simulation while ensuring high accuracy in the assessment of fluid flow.
The potentials of the numerical model are investigated by comparing the frequency spectrum of the experimentally acquired acoustic frequency and the numerical pressure signals allowing to confirm the nature of the vibrations affecting the machine. Thanks to the so demonstrated ability in the evaluation of the fluid flow, the proposed numerical model represents a valid alternative to the traditional correlation-bases approach for the evaluation of the von Karman shedding frequency with a less computational effort compared with a transient simulation of the entire machine
Studio sulla profondità di cristallizzazione e messa in posto dei plutoni di Rensen, Vedrette di Ries e Polland (Alpi Orientali).
No full textOptimal assets management of a water distribution network for leakage minimization based on an innovative index
No full textLeakage reduction in water distribution networks is an absolute priority and several pressure management
strategies have been proposed in the literature to tackle this issue. However, the definition of an effective relationship
between leakage and relevant and measurable parameters still represents a challenge.
This paper presented a novel performance parameter, the Leakage Performance Index (LPI), to minimize
leakages starting from pressure and flow rate measurements. This parameter creates a ranking among the different
nodes in the network, by properly weighting the pressure of each node with the output flow from the node
in order to focus the pressure management strategy on those nodes whose impact, in terms of leakage, is expected
to be greater.
To verify the effectiveness of the proposed LPI, a model of an existing water distribution district in Italy was
developed in EPAnet and validated by comparison with experimental results. The valve settings of the model
were then used as variables of time-dependent optimization procedures aimed at minimizing different objective
functions. Different scenarios were considered by varying the minimum guaranteed pressure at the customer
points.
The LPI minimization strategy was efficient insofar as it indirectly minimized the leakages, achieving the
same results of the leakage minimization strategy
Gram-negative flora of horticultural produce destined for consumption mainly in the raw state
No full textA survey has been carried out to evaluate the recovery of Enterobacteriaceae in freshly consumed horticultural products. 64 samples of these vegetables random chosen in different stores in the General Vegetable Market of Ferrara have been examined among the families of Compositae (lettuce, prickly lettuce, cabbage lettuce, common chicory, artichoke), Umbrelliferae (curly parsley, carrot, celery, fennel), Cruciferae (garden cabbage, red radish), Liliaceae (onion), and Solanaceae (tomato). 654 bacterial lines were isolated, of which 92.5% were Enterobacteriaceae, found in all kinds of horticultural products, the more contaminated being celery, followed by fennel, onion, common chicory, curley parsley, tomato; less contaminated were the other vegetables. Serratia was found in 29.6% of the samples, Escherichia in 28%, Enterobacter in 21.6%, Hafnia in 8.3%, citrobacter in 4.9%, Klebsiella in 2.3% and Yersinia enterocolitica in 1.5%. The importance of horticultural products as source of cont..
Three-dimensional evolution of the flow unsteadiness in the S-shape of pump-turbines and its correlation with the runner geometry
No full textPump-turbines (RTP) are the most common mechanical equipment adopted in pumped-hydro power plants and, for grid balancing purposes, are required to sharply switch from pumping to generating mode, and to extend their operative, jeopardizing not only the machine operability but also its life. New design approaches to avoid the onset of unstable behaviours are still far from being defined, and control strategies for accelerating start-up/shut-down procedures are still not effective since these are based on semi-empirical approaches, due to the lack of identification of precursors of the unstable behavior. In this paper, a numerical analysis of the unstable behavior of an RPT during the transition from partial load up to the turbine-brake area was carried out. The fluid-dynamics in different operating points (partial load, run-away condition, turbine brake) was deeply investigated, identifying the rotor-stator mechanisms causing the 3D evolution of the flow field leading to the development of the unstable behavior. Three evolution phases (inception, growth and consolidation) were identified and clearly correlated with the runner geometry and with the S-Shape of the RPT characteristic curve. Customized signal processing strategies were adopted for spectrally characterizing each phase so as to identify potential triggers for new monitoring and control strategies. Moreover, for the first time, a clear fluid-dynamic explanation of the empirical results found in literature on the influence of the runner geometry is provided
Admiralty intrusives in the southern Bowers terrane: the Collins Peak Pluton. Comparisons with the Salamander Granite Complex, Northern Victoria Land, Antarctica
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