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

Key issues in processing metal-supported proton conducting anodes for SOFCs applications

BaCe0.65Zr0.2Y0.15O3-δ(BCZY) have been recently proposed for IT-SOFCs due to its high proton conductivity. A the same time considerable efforts are directed towards the development of metal-supported cells. The combination of the potential advantages offered by either proton conductors based cells and metal supported configuration has never been explored before. In this work the technological issues to produce proton conducting BCZY-Ni anodes stainless steel-supported were carefully investigated. A tailored porous metal support was produced by tape casting. Afterwards the anode was deposited by screen printing and the resulting bilayer sintered in reducing atmosphere. Each step of the production process was throughly investigated. A cations interdiffusion between the metallic support and the anodic layer was observed in all the range of temperatures considered. The influence of a CeO2 barrier layer and anode thickness on the cations diffusion and a successful production of planar crack-free anode was deeply analyze

Densification behaviour of screen printed Gadolinia doped Ceria films: effect of CuO

The effect of CuO on the densification of a Gadolinia doped Ceria (Ce0.8Gd0.2O2-d, GDC) deposited by screen printing on a GDC/NiO anode produced by tape casting was considered aiming to a complete co-firing of the anode-electrolyte half cell. A comparative study on a CuO-doped and undoped GDC revealed that the effect of CuO is strongly dependent on the thickness of the deposited layer and can lower of more than 100?C the temperature of co-firing of the anode-electrolyte half-cell. Chemical analysis did not reveal traces of CuO on the sintered GDC layer indicating that the oxide should evaporate from the electrolyte layer during sintering not affecting in this way its electrochemical propertie

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

The contact angle of nanofluids as thermophysical property

Droplet volume and temperature affect contact angle significantly. Phase change heat transfer processes of nanofluids – suspensions containing nanometre-sized particles – can only be modelled properly by understanding these effects. The approach proposed here considers the limiting contact angle of a droplet asymptotically approaching zero-volume as a thermophysical property to characterise nanofluids positioned on a certain substrate under a certain atmosphere. Graphene oxide, alumina, and gold nanoparticles are suspended in deionised water. Within the framework of a round robin test carried out by nine independent European institutes the contact angle of these suspensions on a stainless steel solid substrate is measured with high accuracy. No dependence of nanofluids contact angle of sessile droplets on the measurement device is found. However, the measurements reveal clear differences of the contact angle of nanofluids compared to the pure base fluid. Physically founded correlations of the contact angle in dependency of droplet temperature and volume are obtained from the data. Extrapolating these functions to zero droplet volume delivers the searched limiting contact angle depending only on the temperature. It is for the first time, that this specific parameter, is understood as a characteristic material property of nanofluid droplets placed on a certain substrate under a certain atmosphere. Together with the surface tension it provides the foundation of proper modelling phase change heat transfer processes of nanofluids

Development and thermophysical profile of cetyl alcohol-in-water nanoemulsions for thermal management

This study focuses on the preparation, thermophysical and rheological characterization of phase change material nanoemulsions as latent functionally thermal fluids. Aqueous dispersions with fine droplets of cetyl alcohol (with a melting temperature at ~321 K) were prepared by means of a solvent-assisted method, combining ultrasonication with non-ionic and anionic emulsifiers. Eicosyl alcohol (melting at ~337 K) and hydrophobic silica nanoparticles were tested as nucleating agents. Droplet size studies through time and after freeze–thaw cycles confirmed the good stability of formulated nanoemulsions. Phase change analyses proved the effectiveness of eicosyl alcohol to reduce subcooling to a few Kelvin. Although phase change material emulsions exhibited thermal conductivities much larger than bulk cetyl alcohol (at least 60% higher when droplets are solid), reductions in this property reached 15% when compared to water. Samples mainly showed desirable Newtonian behavior (or slight shear thinning viscosities) and modifications in density around melting transition were lower than 1.2%. In the case of phase change material nanoemulsions with 8 wt.% content of dispersed phase, enhancements in the energy storage capacity overcome 20% (considering an operational temperature interval of 10 K around solid–liquid phase change). Formulated dispersions also showed good thermal reliability throughout 200 solidification–melting cycles.European Commission | Ref. SOE2 / P1 / P0823Ministerio de Ciencia e Innovación | Ref. ENE2017-86425-C2-1-RMinisterio de Ciencia e Innovación | Ref. PID2020-112846RB-C2

Electrochemical preparation of nanostructured CeO2-Pt catalysts on Fe-Cr-Al alloy foams for the low-temperature combustion of methanol

Pt-based structured catalysts for the low-temperature combustion of methanol have been prepared by electrochemical methods, using Fe-Cr-Al alloy (Fecralloy) foam supports. Among the strategies investigated, pulsed electrodeposition of Pt nanoparticles from an H2PtCl6solution, followed by cathodic electrodeposition of CeO2thin films from a nitrate bath was the most successful. Pt loading and surface area were measured by ICP-MS and cyclic voltammetry, respectively. Although the presence of a CeO2film decreased the Pt surface area accessible to electrolyte it enhanced the performance of the catalysts towards methanol combustion, without affecting the activation energy of the process, due to the formation of additional active sites along the interface of CeO2-coated Pt nanoparticles

New Sustainable Multilayered Membranes Based on ZrVTi for Hydrogen Purification

Some metals belonging to groups IV and V show a high permeability to hydrogen and have been studied as possible alternatives to palladium in membranes for hydrogen purification/separation in order to increase their sustainability and decrease their costs. However, to date, very few alloys among those metals have been investigated, and no membrane studies based on 4-5 element alloys with low or zero Pd content and quasi-amorphous structure have been reported so far. In this work, new membranes based on ZrVTi- and ZrVTiPd alloys were tested for the first time for this application. The unprecedented deposition of micrometric-based multilayers was performed via high-power impulse magnetron sputtering onto porous alumina substrates. Dense Pd/ZrxVyTizPdw/Pd multilayers were obtained. The composition of the alloys, morphology and structure, hydrogen permeance, selectivity, and resistance to embrittlement were tested and analyzed depending on the deposition conditions, and the membrane with the enhanced performance was tuned. The environmental impact of these membranes was also investigated to ascertain the sustainability of these alloys relative to more common Pd77Ag23 and V93Pd7 thin-film membranes using a life cycle assessment analysis. The results showed that the partial substitution of Pd can efficiently lead to a decrease in the environmental impacts of the membranes