1,720,966 research outputs found
Thermally conductive polymer/graphene-related materials nanocomposites prepared by melt reactive processing
Full text linkPolymer nanocomposites containing graphene-related materials attracted a wide research interest thanks to the combination of the processability, lightweight and corrosion resistance typical of polymers, with the outstanding properties of graphene-related materials, including mechanical properties, thermal conductivity and electrical conductivity. Nanocomposites exploiting graphene-related materials are indeed showing interesting properties and several industrial applications for such nanomaterials are currently being developed, including structural materials, as well as functional materials, electrodes and conductors in flexible electronics, waste heat management, gas-barrier materials, etc., also taking into advantage of the large European initiative for graphene research, development and application called Graphene Flagship (http://graphene-flagship.eu/). This thesis aims to the preparation of polymer nanocomposites, exploiting graphene-related materials, by the development of industrially viable preparation methods, for the application as heat management materials. These are currently of interest in several application fields, including low temperature heat recovery, heat exchange in highly corrosive environments as well as heat dissipation in electronics and flexible electronics. Beside the thermal conductivity property, this PhD thesis was aimed at the fundamental understanding of phenomena controlling nanoparticle dispersion into the polymer matrix as well as the correlations between structure and properties of the prepared materials, including electrical conductivity, rheological properties and polymer crystallization phenomena. As the availability of graphene (i.e. a single layer of sp2 carbons) nanoflakes remains extremely limited and insufficient for the exploitation in large scale applications embedding graphene in the polymer bulk, different types of graphene-related materials were selected for exploitation in this PhD thesis, namely graphite nanoplatelets (GNP) and reduced graphene oxide (rGO). In particular, different grades of GNP and rGO were selected aiming at the correlation between their quality, mainly in terms of defectiveness and aspect ratio, and the properties of their corresponding polymer nanocomposite. For these reasons, the initial part of this thesis is focused on thorough characterization of nanoflake quality, i.e. defectiveness and aspect ratio, through electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. On the other hand, the second part is focused on the preparation and detailed characterization of nanocomposites prepared by ring opening polymerization of polyester oligomers (CBT) during melt mixing in presence of graphene-related materials. In particular, the effects of the exploitation of different graphene-related materials, of the polymerization during reactive mixing and of the processing parameters (processing temperature, time and shear rate) on the electrical and thermal properties of polymer nanocomposites is addressed. Thorough characterization of the effect of the exploitation of pristine and high temperature-annealed reduced graphene oxide on the nanocomposite properties is also reported, in terms of both of conductivities and modification in the crystallization of the polymer matrix. The results reported in this thesis demonstrate the viability of CBT polymerization during melt mixing with graphene-related materials to produce thermally and electrically conductive polymer nanocomposites aiming at possible industrial applications
Energy and exergy analysis of ground thermal energy storage: optimal charging time in different operating conditions
No full textSecond law analysis of horizontal geothermal heat pump systems
Full text linkThis paper presents an exergetic analysis of the operating conditions of a shallow horizontal groundsource heat pump. The analysis is conducted through theoretical evaluation of the exergy potential andthe evaluation of the main sources of unavoidable irreversibilities. This approach can be used to assessthe main causes of performance reduction and degradation, as well as to select the optimal installation(depth, position) or to modify the operating parameters.The analysis of a real installation in then considered. This is a horizontal ground heat exchanger, consti-tuted of a network of pipes installed 1 m below the surface, covering an area of about 210 m2. A comparisonof the current installation with a deeper installation, 2 m below the surface, shows that the exergy outputcan be increased of more than 60%. This improvement can be easily compared with the increase in theinstallation costs in order to evaluate the optimal depth
Second law analysis of horizontal geothermal heat pump systems
No full textThis paper presents an exergetic analysis of the operating conditions of a shallow horizontal ground source
heat pump. The analysis is conducted through theoretical evaluation of the exergy potential and the
evaluation of the main sources of unavoidable irreversibilities. This approach can be used to select the
optimal installation depth. A simple model is used for second law analysis. The model only considers a two
dimensional domain of a single pipe, instead of the full ground heat exchanger.
The analysis of a real installation in then considered. This is a horizontal ground heat exchanger, constituted
of a network of pipes installed 1 m below the surface, covering an area of about 210 m2. A comparison of the
current installation with a deeper installation, 2 m below the surface, shows that the exergy output can be
increased of more than 60%. This improvement can be easily compared with the increase of installation
costs in order to evaluate the optimal depth
Expanding the FDS Simulation Capabilities to Fire Tunnel Scenarios Through a Novel Multi-scale Model
Full text linkComputational Fluid Dynamics (CFD) is widely used to simulate tunnels and partially substitute on-site tests. As technology advances, new application opportunities appear; some examples are the optimal operation of ventilation and emergency systems, risk assessment of tunnels and training of the operators. Even when the computational capacity of computers has grown, CFD is still constrained by the large amount of computational resources needed in long tunnels. This introduces a need for methods able to reduce the amount of time required for simulations. To face this need, a novel 1D–3D multiscale model is presented in this paper. The model incorporates the code Whitesmoke into FDS (Fire Dynamics Simulator) through a direct coupling. Whitesmoke manages the fluid dynamics, temperature and concentration of species in the 1D portion, while FDS calculates these fields in the portion where fire occurs. Using this multiscale model, the computation time for long tunnels is reduced, proportionally to the 1D length in the domain. Also, additional simulation capabilities particularly useful for tunnel analysis are obtained. Some new characteristics are pressure boundary conditions can be easily imposed at the tunnel portals or at the ventilation shafts; the characteristic curves of the fans/jet-fans can be included, also considering the degradation effects due to smoke propagation; the piston effect can be properly considered. Our research verifies most of its capabilities, also clarifying its limitations and the criteria used to set the domain for the analysis. As a final step, the model is tested in a tunnel with a cross section of 4.8 m and 600 m of length with a 2 MW fire, comparing its performance with a full 3D FDS simulation. The difference in temperature and velocity is minimal for most of the domain, making It a good way to optimize resource usage in large simulations. Furthermore, the multiscale manages to reduce the computational time of more than a 50%
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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