1,720,978 research outputs found
Greenhouse gas reductions and primary energy savings via adoption of hybrid plants in place of conventional ones
No full textWith the Kyoto agreement, there has been a greater emphasis on lowering energy waste and supporting low-emissions systems such as fuel cells (FC), photovoltaic (PV) systems or solar thermal systems (STS). These technologies produce environmental benefits since non-renewable energy can be preserved and environmental pollution can be drastically reduced. In addition to this, the decentralization of the electricity production plants mitigates the grid distribution losses. This paper developes a theoretical analysis focused on the environmental benefits achievable through a shift from the conventional systems, normally operating in hospitals, to different hybrid plants. The model site is a hospital located near Ferrara (Italy). At first, a numerical procedure has been adopted in order to calculate the energy requirements of the existing plant. Then several hybrid schemes have been investigated and compared: PAFCs (phosporic acid fuel cells), STS, PV systems. An energy analysis is developed for each option assuming the conventional systems, operating in the medical center, as the reference. At the same time, an economic study is developed for all the retrofit scenarios in terms of annual return, simple payback period and IRR. The results are presented with reference to the primary energy requirements and the pollutant emissions; it is demonstrated that in the case the existing conventional systems would be upgraded with these hybrid plants, overall greenhouse emissions could be abated with a significant reduction in primary fossil energy consumptions
Experimental Analysis of non-Newtonian Droplets Generated in Silicone Oil Flows through a Micro Cross-Junction
No full textExperimental Characterization of a Generator of Non-Newtonian droplets based on a Micro Cross-Junction
Full text linkMicro Droplets of non-Newtonian Solutions in Silicone Oil Flow through a Hydrophobic Micro Cross-Junction
Full text linkIn this paper the generation of non-Newtonian droplets of aqueous Xanthan gum solution (0.3, 0.5 wt%) in a silicone oil flow through a micro cross-junction is experimentally analyzed. A commercial glass cross-junction microchip with hydrophobic walls has been employed to study the droplet generation mechanism. The cross-section of the channel is stadium-shaped, the width of the junction varies between 195 to 390 mu m while the height of the channel is fixed at 190 mu m. Tween 20 (2 wt%), as a surfactant, has been added to the dispersed phase to avoid the coalescence of the droplets and to enhance the droplet formation. With the aim to follow the time evolution of the droplets inside the channel a specific experimental setup has been implemented. The post-processing of the recorded images has been carried out by means of an "in-house" Matlab code. The typical flow patterns obtained by imposing different flow rates at the inlets of the cross-junction have been observed. The effect of the continuous and dispersed phase flow rates as well as the concentration of Xanthan gum solution on the main droplet characteristics has been studied in detail
Experimental Investigation of Dripping and Jetting Regimes in a Micro Cross-Junction with Newtonian and Non-Newtonian Dispersed Phases in Silicon Oil
No full textEffect of Aspect Ratio of Rectangular Microchannels on Laminar-to-turbulent Transition for Compressible Flows
No full textExperimental measurements of thermal-hydraulic performance of aluminum-foam water-to-air heat exchangers for a HVAC application
Full text linkIn this paper, thermal and hydraulic performance of in-house made prototypes of water-to-air heat exchangers are experimentally investigated and compared to those of a compact heat exchanger, used in a commercial fan coil. The prototypes are built replacing the fins with aluminum foam surfaces characterized by a large porosity, higher than 96%. In order to evaluate the performance of the foam-based heat exchangers in a real-scale application, the geometry of the prototypes was based on that of the reference model and, moreover, experimental tests were performed placing the heat exchangers within the commercial cabinet, under the same fan power. Different bonding techniques were also tested to couple metal foams to copper tubes. Results show that similar hydraulic performance can be obtained with the foam-based heat exchangers, if compared to the commercial device. However, the large foam porosity accounts for a lower value of the surface-to-volume ratio of the aluminum foam media, thus yielding a strong penalty, up to 60%, of the heat transfer rate with respect to that of the conventional finned surface. Moreover, experimental results highlight how the bonding technique and the foam packaging have a strong influence on the contact thermal resistance and, consequently, on the overall heat transfer coefficient. Epoxy bonding allows to increase the thermal performance of the heat exchanger, if compared to press fitting, between 15% and 110%. In conclusion, results presented in this paper suggest that metal foams can be considered as a potential alternative to fins in water-to-air heat exchangers only if the foam tube bonding is obtained by welding or brazing
Squeezing Droplet Formation in a Flow-Focusing Micro Cross-Junction
Full text linkMotivated by the increasing need of optimised micro-devices for droplet production in medical and biological applications, this paper introduces an integrated approach for the study of the liquid-liquid droplet creation in flow-focusing micro cross-junctions. The micro-junction considered is characterised by a restriction of the channels cross-sections in the junction, which has the function of focusing the flow in the region of the droplet formation. The problem is studied numerically in the OpenFOAM environment and validated by a comparison with experimental results obtained by high-speed camera images and micro-PIV measurements. The analysis of the forces acting on the dispersed phase during the droplet formation and the diameter of the droplets obtained numerically are considered for the development of a model of the droplet breakup under the squeezing regime. On the basis of energy balancing during the breakup, a relation between interfacial tension, the size of the cross-sections in the junction, and the time interval needed for droplet creation is obtained, which yields a novel correlation between the dimensionless length of the droplet and the dimensionless flow rate. This research expands our knowledge of the phenomenon of drop creation in micro-junctions with restrictions providing new aid for the optimal design of micro-drop generators
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
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