Browsing by Author "Coelho, M.F."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- An approach to characterize the nanolayer for a nanofluid: Thickness, density and molar massPublication . Iglesias, T.P.; Queirós, A.; Coelho, M.F.The aim of this work is to develop a theoretical approximation to calculate the effective thickness, density and molar mass of the interfacial nanolayer around nanofluid particles. These properties of the nanolayer depend, in general, on temperature, on the nature of the base fluid, the nature of nanoparticles, their geometry and their concentration. The model takes into account all these parameters. This is presented for a general geometry and it is shown that the effective nanolayer molar mass is equal to that of the base fluid. Then, this is particularized for a spherical geometry, which is one of the most usual in literature, and is numerically applied to the aqueous alumina (15 nm) nanofluids at different temperatures and nanoparticle concentrations. The obtained results together with those from the application of the model to some nanofluids from literature, at different temperatures and nanoparticle concentrations, allow providing a general insight into the effective behavior of those nanolayer properties. Finally, it is shown that the model, under its hypothesis, does not support the equation of Pak and Cho except as an approximation.
- Antibacterial activity study of copper oxide nanofluids for infection control in hospital environmentPublication . Queirós, Â.; Martins, A.; Domingues, V.F.; Iglesias, T.P.; Coelho, M.F.[Introduction] Coronavirus disease appears. Due to its antibacterial potential, copper and its alloys attracted the attention of the scientific community. The use of nanoscale materials with antimicrobial properties is another approachthat has been considered.
- Permittivity and electrical conductivity of copper oxide nanofluid (12 nm) in water at different temperaturesPublication . Coelho, M.F.; Rivas, M.A.; Vilão, G.; Nogueira, E.M.; Iglesias, T.P.The effective permittivity and electrical conductivity of copper oxide (12 nm) nanofluids in water are studied. The measurements were carried out at various concentrations (up to 2% in volume) and at six temperatures (from 298.15 K to 348.15 K). Empirical equations were used for describing the conductivity and the permittivity of the experimental data. The study shows the influence of the volume fraction, the temperature on relative permittivity and electrical conductivity. When compared with the previously published values for alumina (15 nm) in water, present results show the influence of the nanoparticle’s nature. The enhancement of both permittivity and electrical conductivity were calculated and their behaviour was analysed. It is discussed whether their positive values can be considered greater than what would be expected. The contributions to permittivity from volume, contrast and interactions are separated. Theoretical models are applied in the study of permittivity and electrical conductivity. The poor predictions of classical models for permittivity are attributed to the positive behaviour of the permittivity change on mixing for these nanofluids. The contributions to electrical conductivity from water and nanoparticles are separated.