856 research outputs found
Experimental investigation into an ORC-based low-grade energy recovery system equipped with sliding-vane expander using hot oil from an air compressor as thermal source
No full textCompressed air production is an energy-intensive sector, thus compressor manufacturers are constantly looking for enhancing the efficiency, by acting on several technological aspects. In an air compressor, about 80-90% of the input electric power used is wasted into the environment through the oil circuit, continuously cooled by ambient air blown via a fan. An interesting way to optimize the overall system efficiency is to exploit this waste heat to produce electrical power. Organic Rankine Cycles (ORCs) are a suitable solution for recovering energy from low-grade heat source. In this paper, an experimental analysis of two low-grade ORC-based recovery systems is presented. The thermal source is the hot lubricant of a mid-size air compressor, while the thermal sink is tap water. The first system is tested in a simple cycle configuration while the second in a recuperative one. An extensive experimental campaign is carried out on a test bench composed by sliding-vane expander, pump and plate heat exchangers. The expander differs in terms of geometry and aspect ratio between the two cycles. R236fa is used as working fluid in both the systems. The expander operating conditions are deeply investigated by using piezoelectric pressure transducers to determine the expansion indicated diagram and the expander mechanical efficiency. Experimental results show that the recuperative cycle has a better performance, in terms of cycle efficiency and expander mechanical efficiency, compared with the simple cycle. For this configuration, two off-design conditions are investigated, acting on the pump rotational speed. Finally, an exergy analysis is conducted, in order to evaluate the irreversible losses produced by each component
An intracooling system for a novel two-stage sliding-vane air compressor
No full textLube-oil injection is used in positive-displacement compressors and, among them, in sliding-vane machines to guarantee the correct lubrication of the moving parts and as sealing to prevent air leakage. Furthermore, lube-oil injection allows to exploit lubricant also as thermal ballast with a great thermal capacity to minimize the temperature increase during the compression. This study presents the design of a two-stage sliding-vane rotary compressor in which the air cooling is operated by high-pressure cold oil injection into a connection duct between the two stages. The heat exchange between the atomized oil jet and the air results in a decrease of the air temperature before the second stage, improving the overall system efficiency. This cooling system is named here intracooling, as opposed to intercooling. The oil injection is realized via pressure-swirl nozzles, both within the compressors and inside the intracooling duct. The design of the two-stage sliding-vane compressor is accomplished by way of a lumped parameter model. The model predicts an input power reduction as large as 10% for intercooled and intracooled two-stage compressors, the latter being slightly better, with respect to a conventional single-stage compressor for compressed air applications. An experimental campaign is conducted on a first prototype that comprises the low-pressure compressor and the intracooling duct, indicating that a significant temperature reduction is achieved in the duct
Modeling And Testing The Thermal Effect Of Lubricating Oil Sprayed In Sliding-Vane Air Compressors Using Pressure-Swirl Nozzles
No full textA number of studies report the benefit of proper oil spraying in positive-displacement compressors. This work presents a thermodynamic model for simulating sliding-vane air compressors that employ an injection system for the lubricating oil based on both plain orifices and pressure-swirl nozzles to exploit the thermal effect of sprayed oil inside the compression chambers. An experimental campaign on a large-size compressor is conducted measuring, among all, the pressure within a chamber. This measurement is used to validate the model. Oil droplet diameters depend strongly on the injection technology, nozzles generating a finer atomization than orifices, as well as the differential pressure. In any case, the proper positioning of the nozzles allows for an effective heat transfer from the air to the oil
Experimental investigation on materials and lubricants for sliding-vane air compressors
No full textAbstract. Positive-displacement compressors and, among them, sliding-vane rotary machines are widely used in the compressed air sector. As in many other industrial fields, the efficient utilization of energy has become a major goal also in this sector. The aim of the present activity is the experimental investigation on the influence of two vanes materials (cast iron and aluminium with anodized surface) and of four commercial lubricants (characterized by different formulations and additives concentrations) on the performance of a mid-capacity sliding-vane rotary compressor in a number of operating pressures. The performance is identified by both the volume flow rate and the absorbed mechanical power, evaluated according to the international standard ISO 5167 and ISO 1217. The campaign indicates that the considered lubricants do not affect appreciably the volumetric flow rate. On the other hand, the specific lubricants determine a variation of about 1% of the mechanical power for both materials, while the specific material a variation between 0.9% and 2.6%. The best performance is achieved by aluminium vanes and a synthetic poly-α-olefin lubricant
Fine morphology of the myrmecophilous larva of Paussus kannegieteri (Coleoptera: Carabidae: Paussinae: Paussini). Corresponding author
No full textFIGURES 13–18. Paussus kannegieteri third instar larva: 13, thorax, left lateral view; 14, thorax, dorsal view; 15, mesothoracic spiracle; 16, metathoracic spiracle-like structure; 17, mesothoracic leg, anterolateral view; 18, apex of metathoracic leg with lanceolate setae, posterolateral view. CO = coxa, ls = lanceolate setae, m = membrane, ME = mesonotum, MT = metanotum, pe = peritreme, PR = pronotum, un = claw. Scale bars: Figs. 13–14 = 500 µm; Fig. 15 = 10 µm; Fig. 16 = 20 µm; Fig. 17 = 200 µm; Fig. 18 = 50 µm.Published as part of Giulio, Andrea Di, 2008, Fine morphology of the myrmecophilous larva of Paussus kannegieteri (Coleoptera: Carabidae: Paussinae: Paussini), pp. 37-50 in Zootaxa 1741 on page 44, DOI: 10.5281/zenodo.18152
Modeling and Experimental Activities on a Small-scale Sliding Vane Pump for ORC-based Waste heat Recovery Applications
No full textPumping work in energy recovery units based on Organic Rankine Cycles (ORC) can severely affect the net power output
recovered. Nevertheless, in recent years scientific and industrial communities mainly focused on expanders’ development. In
order to address this lack of know-how and equipment, the current paper presents the development of a positive displacement
ORC pump based on the sliding vane rotary technology. The machine was installed in a power unit for low-medium grade
thermal energy recovery that operated with oil at 70-120°C as upper thermal source and tap water as lower one. Working fluid
was R236fa while cycle pressure ratio ranged from 2.8 to 3.7. The ORC pump was also tested at different revolution speeds such
that mass flow rate varied between 0.05 kg/s and 0.12 kg/s. These experimental data were further used to validate a
comprehensive one-dimensional model that takes into account fluid dynamic filling and emptying processes, closed vane
transformation and leakages at blade tip, rotor slots and end walls clearances. Viscous and dry friction phenomena occurring
between components in relative motion were additionally considered. A full operating map of the sliding vane pump was
eventually retrieved to explore multiple off-design operating conditions. The parametric and modular structure of the model will
act as a design platform to outline enhanced ORC sliding vane pump prototypes
Grid generation methodology and CFD simulations in sliding vane compressors and expanders
No full textThe limiting factor for the employment of advanced 3D CFD tools in the analysis and design of rotary vane machines is the unavailability of methods for generation of computational grids suitable for fast and reliable numerical analysis. The paper addresses this challenge presenting the development of an analytical grid generation for vane machines that is based on the user defined nodal displacement. In particular, mesh boundaries are defined as parametric curves generated using trigonometrical modelling of the axial cross section of the machine while the distribution of computational nodes is performed using algebraic algorithms with transfinite interpolation, post orthogonalisation and smoothing. Algebraic control functions are introduced for distribution of nodes on the rotor and casing boundaries in order to achieve good grid quality in terms of cell size and expansion. In this way, the moving and deforming fluid domain of the sliding vane machine is discretized and the conservation of intrinsic quantities in ensured by maintaining the cell connectivity and structure. For validation of generated grids, a mid-size air compressor and a small-scale expander for Organic Rankine Cycle applications have been investigated in this paper. Remarks on implementation of the mesh motion algorithm, stability and robustness experienced with the ANSYS CFX solver as well as the obtained flow results are presente
Numerical CFD simulations on a small-scale ORC expander using a customized grid generation methodology
No full textPositive displacement machines are the most suitable devices for small-scale waste heat to power conversion units based on an Organic Rankine Cycle (ORC) due to their capabilities of handling small mass flow rates and high pressure ratios. Among the technologies, sliding vane machines provide unique features such as low operating revolution speed, geometrical flexibility and uncomplicated manufacturing. Nonetheless, research and product development in this field have been constrained by the lack of interfaces between deforming and moving fluid domains that characterize sliding vane devices and the design tools at the state of the art. This research work tackles this challenge and presents the development of an analytical grid generation for sliding vane machines that is based on user defined nodal displacement. Through this approach, the numerical methodology discretizes the fluid domains enclosed between the cells and ensures conservation of intrinsic quantities by maintaining the cell connectivity and structure. Transient 3D single phase simulations on a small scale ORC expander were further set up in the ANSYS CFX solver and provided insights on the main flow field as well as in the leakage paths between rotor blade tips and casing. The numerical results were eventually validated with reference to an experimental dataset related to a waste heat to power conversion application in compressed air systems where the sliding vane ORC expander worked with R236fa, at a pressure ratio of 2.65 and at 1551 RPM
GIULIO TARRA TRADUTTORE DAL FRANCESE
No full textCon Il Libro pel bambino, Don Giulio Tarra risultò il vincitore di due concorsi indetti dal Congresso Pedagogico Italiano nel 1861: quello per un libro di lettura destinato ai bambini sordomuti e l’altro per un libro destinato alle scuole rurali. Fra le opere del Tarra pubblicate da Paolo Carrara è menzionato il volumetto “Lezioni in famiglia, versione da M. Carraud”. Questo contributo intende offrire alcuni elementi d’informazione su Zulma Carraud, autrice delle Historiettes véritables pour les enfants de quatre à huit ans, titolo originale della raccolta di racconti tradotta da Don Giulio. Il libro era uscito a Parigi nel 1864 per i tipi di Hachette. In precedenza lo stesso editore aveva accolto le prime opere di Zulma nelle collane destinate alla scuola primaria. A pochi anni di distanza l’uno dall’altra, la Carraud nella Francia del II Impero e il Tarra nell’Italia postunitaria, entrambi hanno contribuito con i loro “libri di lettura” allo sviluppo dell’editoria per la scuola e per l’infanzia.
Giulio Tarra translator from French
With the volume entitled Il Libro pel bambino, Don Giulio Tarra won two literary competitions held in 1861 by the Congresso Pedagogico Italiano: the first was dedicated to books for deaf-mute chidren, the second to books for rural schools. Among Tarra’s works published by Paolo Carrara we find “Lezioni in famiglia, versione da M. Carraud”. This article provides some information about Zulma Carraud, the author of the collection of novels entitled: Historiettes véritables pour les enfants de quatre à huit ans published by Hachette in 1864 and translated into Italian by Don Giulio. Previously the same publisher had collected Zulma’s first works in a series to be used in primary schools. Carraud, during the Second Empire period in France, and Tarra, in post-Unity Italy, both contributed to the development of the publishing industry for schools and children with their educational and entertaining books
- …
