1,721,055 research outputs found
Theoretical analysis of mixed open-circuit potential for high temperature electrochemical cells electrodes
Full text linkThe Nernst equilibrium potential calculates the theoretical OCV, which estimates the best performance achievable by an electrochemical cell. When multiple semi-reactions (or multiple ionic species) are active in one of the electrodes, the calculation of the theoretical OCV is not straightforward, since different Nernst potentials are associated to each semi-reaction. In this paper, analytical equations for calculation of the theoretical OCV are developed, using the mixed potential theory. The case of H2 and CO co-oxidation (or H2O and CO2 co-reduction) in solid oxide cells is used as a reference case, but similar conclusions can be drawn for other equivalent cases. OCV data from literature are used to calibrate and validate the model. The relative reaction rate of H2 and CO semi-reactions is estimated within the calibration process, and the result is in line with assumptions and suggestions given by other authors. The validation procedure shows predicted OCV values in line with experimental literature data, except for mixtures with relatively large CH4 concentration (e.g., 8%), for which the OCV is significantly underestimated. This is expected when thermochemical reactions, in parallel to electrochemical reactions occur, since the additional H2 produced by internal steam methane reforming is not accounted within the local mixed potential model. A fuel cell polarization model is developed based on the results from the calibration procedure, and it is used to predict the polarization behavior of an SOFC fed with a H2-H2O-CO-CO2 fuel mixture. It is found that either H2 or CO may be reduced rather than oxidized via an equivalent electrochemical water-gas-shift reaction
Interoperability standards and educational projects: some case studies in Politecnico of Milan
No full textTailoring nanoscale friction in MX2 transition metal dichalcogenides
No full textThe lattice dynamics of MX2 transition metal dichalcogenides can be controlled at the atomic scale to improve the frictional behavior. The electro-structural features of the M?X atomic pair are found to determine the lattice frequencies of those phonons affecting the macroscopic friction; the relative contributions are isolated through a new metric, named cophonicity, formulated at the quantum mechanical level. A new protocol to design new tribologic materials is thus propose
SIMULATION OF THE HIPOWAR GAS-STEAM POWER GENERATION SYSTEM USING AMMONIA AS FUEL
Full text linkThis work presents a simulation activity on an innovative power generation cycle, developed within the EU Horizon 2020 project HiPowAR, using ammonia as fuel for an oxy-combustion process in a membrane reactor. The key advantages of the system are the low compression requirement, typical of steam cycles, and the large expander inlet temperature, typical of gas turbine cycles. The analysis explores the options of cooled or uncooled expander, either adopting a steam-cooled turbine made of conventional Ni-based alloys or using high temperature-resistant ceramic matrix composite (CMC) materials. The simulations show that, with a reactor outlet temperature of 1350°C, a cooled system could reach up to 48.2% efficiency, with limited additional advantages when further increasing the temperature. At the same temperature level, the uncooled system could instead achieve 52.5% efficiency, allowing also a substantial system simplification. However, since the expanded mixture contains nearly 90%mol steam, the use of CMC materials is made difficult by degradation issues and would require the development of suitable barrier coatings
On the dynamic isotropy of mechanisms with two degrees of freedom
No full textThe comparison of mechanisms with different topology or with different geometry, but with the same topology, is a necessary operation during the design of a machine sized for a given task. Therefore, tools that evaluate the dynamic performances of a mechanism are welcomed. This paper deals with the dynamic isotropy of 2-dof mechanisms starting from the definition introduced in a previous paper. In particular, starting from the condition that identifies the dynamically isotropic configurations, it shows that, provided some special cases are not considered, 2-dof mechanisms have at most a finite number of isotropic configurations. Moreover, it shows that, provided the dynamically isotropic configurations are excluded, the geometric locus of the configuration space that collects the points associated to configurations with the same dynamic isotropy is constituted by closed curves. This results will allow the classification of 2-dof mechanisms from the dynamic-isotropy point of view, and t..
Evaluation of bronchial hyperreactivity using a multiparametric method in FEV1--non-responder asthmatic patients
No full textPreliminary results of the use of multiple functional parameters during tests of bronchial provocation
No full text
- …
