1,720,985 research outputs found
A new generation of centrifugal pumps for high conversion efficiency
No full textCentrifugal pumps are fundamental machines in our daily life. Indeed, they can be found everywhere, for instance, in domestic, civil, industrial, and agricultural fields. In the last years, the pump market has newly gained a boost coherently with the world demographic growth. Pumps are among the main responsible for electric energy consumption, therefore even a slight efficiency improvement (+1%) can be effective in contrasting the growth of the global Greenhouse Gas Emissions (at least −570 tCO2/day in Europe). For this reason, a new generation of centrifugal pumps is here proposed. In particular, the impeller has been redesigned improving the flow guidance inside the vanes and simultaneously reducing the number of blades, with the aim to increase the blade loading, reducing manufacturing costs, and enhancing the conversion efficiency with respect to conventional configurations. Furthermore, the new impeller design respects all the geometrical constraints of the corresponding conventional configuration, allowing its retrofit with a boost of performance. To reach these goals, a 1D in-house code has been developed implementing a Harmony Search Algorithm (HSA) for the selection of the most suitable design point (H and Q), and introducing two parameters for the blade loading evaluation, namely, the blade pressure coefficient (Cp,blade), computed locally along the impeller blade walls, and the blade lift coefficient (CL), achieving an optimal vane arrangement. Starting from a baseline centrifugal pump, the novel impeller has been designed, manufactured, and finally experimentally tested. The resulting new generation of centrifugal pumps actually proves to have a higher performance (maximum efficiency at BEP +1%), a flatter efficiency curve, and a monotone bending characteristic curve, while keeping unchanged the required Net Positive Suction Head (NPSH3%)
Performance analysis of double suction centrifugal pumps with a novel impeller configuration
Full text linkPumps are largely used in domestic, civil, industrial and agricultural systems. It is estimated that they are responsible of about 10% of the world energy consumption. To favor sustainability and reduce carbon footprint of pumps, it is required to improve their efficiency. In recent years, the authors proposed a novel impeller configuration (cross-vaned, with a completely new design of the vanes) for double suction centrifugal pumps with higher efficiency and reduced blade loading compared to conventional back-to-back impellers. Given the good results, herein a second version of the prototype has been designed by means of a one-dimensional (1D) in-house code with the purpose to increase the blade loading by reducing the number of blades. The new 5-bladed crossed-vaned prototype was studied numerically, then constructed and experimentally tested showing a good agreement between numerics and experiments in terms of head coefficient and efficiency. Through numerical simulations, pressure, velocity and vorticity fields at the outlet of the impeller have been investigated; besides, a new slip factor correlation is proposed for this new generation of pumps. Moreover, the new configuration confirms its benefit in term of reduction of the slip factor and increase of the global efficiency, proving to be useful for retrofitting of old impellers, with a higher efficiency and smaller overall dimensions. Finally, an example of conventional impellers retrofitting in a real pumped-storage system is presented and its impact in terms of global efficiency and carbon footprint is discussed
Innovative impeller design for double suction centrifugal pumps
Full text linkWorld’s energy consumption is increasing year by year driven by the industrial and the tertiary sector, where most of the electrical energy is consumed by electrical motors (65%). The latter drive pumps (22%), most of which are centrifugal pumps (73% - world market = 20 billion euro per year).
Due to their wide use, a great effort has been spent in the last decades in trying to improve the selection and the efficiency of pump systems with the aim to reduce their energy consumption. Besides, it has been found out that among all the rotating devices in a process plant, centrifugal pumps typically have the best overall potential for energy savings.
In this work, a variety of activities has been carried out in order to introduce innovation in the field of the hydraulic turbomachinery.
Firstly, an innovative impeller for double suction centrifugal pumps will be presented and the techniques and methodology adopted to make this geometry feasible will be described.
The novel geometry embodiment includes an innovative arrangement of the impeller vanes. The novel impeller has been designed with the purpose of retrofitting the impeller of a conventional pump, preserving its initial size and specific speed.
Comparing the baseline and the novel geometry, the latter shows an improvement of the hydraulic efficiency (+1.2%) and a remarkable reduction of the slip phenomenon at the outlet of the impeller (sigma- slip factor +8.5%). Thus, it is possible to provide a larger pressure rise with the same size of the pump or alternatively to choose a more efficient and compact system.
Moreover, two different prototypes with different number of blades have been designed and their performance has been studied numerically, by means of 3D URANS simulations. Thereafter, they have been manufactured using the lost-foam casting technique, and tested experimentally thanks to the collaboration with the Hydraulic test rig of Nuovo Pignone, Bari (Italy). The novel design is now protected by a patent application.
Furthermore, given the increasing use of centrifugal pumps as turbines (PaT) in water distribution systems, the baseline and the novel geometry have been simulated as turbines with the aim to investigate their performance in reverse mode. This allowed a description of the slip phenomenon at the outlet of centripetal runners. This parameter has proved to be helpful for a 1D performance prediction model based on loss analysis, which works starting from the machine geometrical information; indeed, it allows to minimize the error in predicting the characteristic curve at part-load (-8\% error compared to Busemann and Stodola formulation) and at the best efficiency point (-6\% error compared to models which neglect this phenomenon).
Finally, in order to enlarge the operative range of hydraulic pumps and turbines working under cavitating conditions, a passive cavitation control system (PCS) has been proposed. The aim is to guarantee a high performance level, comparable to the single-phase conditions, for these machines in the regions where they usually are affected by performance degradation. The system proposed has been applied to a symmetric 2D hydrofoil which is an archetype of the leading edge of a blade. Even though it appears to induce a loss of performance in terms of lift and drag, it is shown to be helpful for reducing the vapour volume cavity up to 93%. Thus, the introduction of this system to a real impeller (e.g., a centrifugal pump or a turbine) shall be positive to enlarge their operative field towards low suction pressure providing at the same time acceptable level of losses
Analysis of the Influence of the Mean Flow Field Mach Number on Thermo-Acoustic Combustion Instability
No full textGas-dynamic and mixing analysis of under-expanded hydrogen jets: effect of the cross section shape
No full textGreen hydrogen is expected to have a key role in the transition towards a carbon-neutral society, particularly in the transportation sector. Exploration of novel solutions for the direct injection of hydrogen in internal combustion engines (ICEs) is a main topic for both academia and industry. Here, the authors explore the gas-dynamic and mixing features of hydrogen under-expanded jets exiting from non-axisymmetric cross-sections, with the aim to provide guidelines for designing novel generations of ICE hydrogen injectors. Triangular and star shapes have been compared with elliptical and rectangular sections with different aspect ratios. Differences in the shock wave systems are reported, and explanations of the gas-dynamic mechanisms developed by each section are proposed. Non-uniformity in the radial expansion of the jet boundary has been noticed in all of the non-axisymmetric sections, leading to an axis switching of the jet in some cases. Differences in the radial mixing and axial jet penetration have been reported too, and a robust correlation with the vorticity distribution along the jet boundary has been observed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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