Experimental stability analysis of different water-based nanofluids

In the recent years, great interest has been devoted to the unique properties of nanofluids. The dispersion process and the nanoparticle suspension stability have been found to be critical points in the development of these new fluids. For this reason, an experimental study on the stability of water-based dispersions containing different nanoparticles, i.e. single wall carbon nanohorns (SWCNHs), titanium dioxide (TiO2) and copper oxide (CuO), has been developed in this study. The aim of this study is to provide stable nanofluids for selecting suitable fluids with enhanced thermal characteristics. Different dispersion techniques were considered in this study, including sonication, ball milling and high-pressure homogenization. Both the dispersion process and the use of some dispersants were investigated as a function of the nanoparticle concentration. The high-pressure homogenization was found to be the best method, and the addition of n-dodecyl sulphate and polyethylene glycol as dispersants, respectively in SWCNHs-water and TiO2-water nanofluids, improved the nanofluid stability

Optical characterisation of oxidised carbon nanohorn nanofluids for direct solar energy absorption applications

Carbon nanohorns and oxidised carbon nanohorns-based nanofluids were characterised by taking one step forward. The advantage of studying oxidised carbon nanohorns is that they are surfactant-free. The stability of both nanofluids was checked after a 3-month preparation period at high temperature, which comes closer to real applications. Two different dynamic light scattering (DLS) systems were used to measure stability at high temperature before being compared. A deep optical analysis was run. An integrating sphere was attached to the classic spectrophotometer to determine the scattering of nanofluids. After obtaining the experimental values of the optical parameters for both nanofluids, the Kubelka-Munk Theory was applied to obtain optical coefficients. Finally, the scattering albedo was calculated to facilitate comparisons with the literature. Studying both nanofluid types provided us with new knowledge about their potential use as direct solar absorbers in solar thermal collectors

Absorption and scattering properties of carbon nanohorn-based nanofluids for direct sunlight absorbers

In the present work, we investigated the scattering and spectrally resolved absorption properties of nanofluids consisting in aqueous and glycol suspensions of single-wall carbon nanohorns. The characteristics of these nanofluids were evaluated in view of their use as sunlight absorber fluids in a solar device. The observed nanoparticle-induced differences in optical properties appeared promising, leading to a considerably higher sunlight absorption with respect to the pure base fluids. Scattered light was found to be not more than about 5% with respect to the total attenuation of light. Both these effects, together with the possible chemical functionalization of carbon nanohorns, make this new kind of nanofluids very interesting for increasing the overall efficiency of the sunlight exploiting device

Relevance, benefits, and problems of software modelling and model driven techniques—A survey in the Italian industry

Context Claimed benefits of software modelling and model driven techniques are improvements in productivity, portability, maintainability and interoperability. However, little effort has been devoted at collecting evidence to evaluate their actual relevance, benefits and usage complications. Goal The main goals of this paper are: (1) assess the diffusion and relevance of software modelling and MD techniques in the Italian industry, (2) understand the expected and achieved benefits, and (3) identify which problems limit/prevent their diffusion. Method We conducted an exploratory personal opinion survey with a sample of 155 Italian software professionals by means of a Web-based questionnaire on-line from February to April 2011. Results Software modelling and MD techniques are very relevant in the Italian industry. The adoption of simple modelling brings common benefits (better design support, documentation improvement, better maintenance, and higher software quality), while MD techniques make it easier to achieve: improved standardization, higher productivity, and platform independence. We identified problems, some hindering adoption (too much effort required and limited usefulness) others preventing it (lack of competencies and supporting tools). Conclusions The relevance represents an important objective motivation for researchers in this area. The relationship between techniques and attainable benefits represents an instrument for practitioners planning the adoption of such techniques. In addition the findings may provide hints for companies and universitie

Progettazione di un motore monofase Line Start Permanent Magnet

L’ elaborato descrive i criteri necessari per la progettazione di un motore monofase Line Start Permanent Magnet (LSPM). I motori LSPM combinano l’ elevata efficienza dei motori a magneti permanenti (Brushless) con la capacità, da parte dei motori asincroni, di avviarsi autonomamente collegandosi direttamente alla rete, senza la necessità di un inverter. Rispetto ai motori asincroni, i motori LSPM presentano una struttura dello statore identica mentre sul rotore rimane la gabbia, ma vengono aggiunti i magneti permanenti all’ interno. La trattazione viene focalizzata prima sulla determinazione di un algoritmo di dimensionamento che sia in grado di ricavare i parametri geometrici ed elettromagnetici per un motore Brushless monofase a magneti superficiali, considerato come sistema di partenza. In seguito all’ implementazione su MagNet di un modello con magneti superficiali ad una coppia polare e di verifiche sul funzionamento dei magneti e sulla coppia nominale, si introduce un modello a magneti interni equivalente e capace di erogare la medesima coppia elettromagnetica. Il modello completo del motore monofase LSPM è costituito da due avvolgimenti statorici alimentati alla tensione nominale, dalla gabbia rotorica e da magneti permanenti all’ interno del rotore. L’ obiettivo finale della trattazione è quello di verificare la capacità del motore progettato di avviarsi autonomamente collegandosi direttamente alla rete, senza la necessità di un inverter, e di agganciare il sincronismo durante il funzionamento a regime

Hydrogen Storage in Metal and Complex Hydrides: from Possible Niche Applications towards Promising High Performance Systems

A promising alternative to hydrogen storage in high pressure cylinders and cryogenic tanks is the hydrogen storage in solid form as metal hydrides or complex metal hydrides. However, much research is still necessary in this direction. In particular, the optimal pressure and temperature of operation for the use of a hydride-based tank in a PEM fuel cell-powered vehicle should remain in the of 1-10 atm and 25-120 °C, respectively. The further difficulty is related to the weight of the storing materials, which is still too high for efficient mobile applications compared to the amount of stored hydrogen. The work reported in this thesis deals with systems belonging to several hydride classes such as complex hydrides, interstitial metal hydrides and magnesium-based hydrides. Improvements from the point of view of thermodynamic and kinetic properties are proposed and discussed on systems almost ready for niche applications and on other very promising systems but still far from hydrogen storage applications. Among the classical interstitial hydrides-forming alloys, the interaction of hydrogen with TiCr1.78-xMnx alloys, one of the most promising for the use in high pressure-solid state hybrid tanks, has been studied. Among the Mg-based hydrides, a compacted Mg-Al-based material is proposed in order to overcome the degradation problems found during the scaling up of MgH2 as hydrogen storage medium. Concerning the complex hydrides, the kinetics improvement of the Li-Mg-N-H system by high energy ball milling processing is discussed and the problem of reversibility and slow decomposition kinetics of LiBH4 has been faced.Una promettente alternativa allo stoccaggio dell’idrogeno in bombole ad alta pressione e in contenitori criogenici è lo stoccaggio dell’idrogeno allo stato solido utilizzando idruri metallici o idruri complessi. In ogni caso, molta ricerca è ancora necessaria in questa direzione. In particolare, la pressione e la temperatura di lavoro ottimali per un serbatoio da utilizzare in una vettura basata su celle a combustibili PEM dovrebbero rimanere rispettivamente negli intervalli 1-10 atm e 25-120 °C. L’ulteriore difficoltà è legata al peso dei materiali assorbenti, che è ancora troppo elevato rispetto alla quantità di idrogeno stoccata per applicazioni veicolari efficienti. Il lavoro riportato in questa tesi riguarda sistemi appartenenti a diverse classi di idruri come idruri complessi, idruri metallici interstiziali, idruri a base di magnesio. Vengono proposti e discussi miglioramenti dal punto di vista termodinamico e cinetico apportati a sistemi ormai quasi pronti ad applicazioni di nicchia e ad altri molto promettenti ma ancora lontani da applicazioni per lo stoccaggio dell’idrogeno. Per quanto riguarda i classici idruri interstiziali, è stata studiata l’interazione dell’idrogeno con le leghe TiCr1.78-xMnx, tra le più promettenti per l’utilizzo in serbatoi ibridi ad alta pressione. Riguardo gli idruri a base di magnesio, un materiale basato su Mg-Al compattato in pastiglie viene proposto per ovviare ai problemi legati allo “scaling-up” del MgH2. Per quanto riguarda la classe degli idruri complessi, viene discusso il miglioramento delle cinetiche di assorbimento/desorbimento di idrogeno grazie al trattamento con macinazione ad alta energia e vengono affrontati i problemi della reversibilità e della lenta cinetica di decomposizione del LiBH4

Pellets of MgH2-based Composites as Practical Material for Solid State Hydrogen Storage

Hydrogenation properties and mechanical stability of pellets made starting from compressed ball-milled MgH2 powders mixed with catalysts (Nb2O5 and graphite) and a binding agent (aluminium powder) have been investigated. Structural characterization with X-ray diffraction and gas\u2013solid reaction kinetic and thermodynamic tests with a Sievert's apparatus have been done on the samples up to 50 hydrogen absorption/desorption (a/d) cycles. The best cycling behaviour and mechanical strength stability have been observed for pellets of catalysed MgH2 powders added with 5 wt% aluminium annealed in vacuum at 450 \ub0C before starting the a/d cycles. This mechanical stability to cycles has been attributed to the formation of a solid solution of aluminium in magnesium

The problem of solid state hydrogen storage

Abstract A short review of the materials under investigation suitable for solid state hydrogen storage is presented, with particular reference to the experimental activity carried out at the laboratory of Hydrogen Group of Padova University

Ball-milling and AlB2 addition effects on the hydrogen sorption properties of the CaH2+MgB2 system

Among the borohydrides proposed for solid state hydrogen storage, Ca(BH4)2 is particularly interesting because of its favourable thermodynamics and relatively cheap price. Composite systems, where other species are present in addition to the borohydride, show some advantages in hydrogen sorption properties with respect to the borohydrides alone, despite a reduction of the theoretical storage capacity. We have investigated the milling time influence on the sorption properties of the CaH2 + MgB2 system from which Ca(BH4)2 and MgH 2 can be synthesized by hydrogen absorption process. Manometric and calorimetric measurements showed better kinetics for long time milled samples. We found that the total substitution of MgB2 with AlB2 in the starting material can improve the sorption properties significantly, while the co-existence of both magnesium and aluminum borides in the starting mixture did not cause any improvement. Rietveld refinements of the X-ray powder diffraction spectra were used to confirm the hypothesized reactions