Browsing by Author "Iglesias, T.P."
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- 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.
- Behavior of dielectric permittivity in squalane Graphene Nanofluid at 333.15KPublication . Vilão, G.; Ramos, C.A.; Iglesias, T.P.(Introduction) The global demand for energy is constantly growing, requiring the development of efficient systems to ensure sustainable consumption and prevent long-term environmental damage. Carbon-based materials, such as graphene, have been extensively studied due to their environmentally friendly properties, structure, and availability. Squalane is also a component with significant physiological effects in fields like nutrition, pharmacy, and medicine [1]. However, both graphene and squalane are relatively new in the field of nanofluids. While research on thermal conductivity has been prioritized, studies on permittivity and electrical conductivity remain limited. In this study, we analyzed the dielectric permittivity of graphene nanofluid at temperatures of 333.15K and 343.15K. The nanofluid was prepared using squalane as base fluid with a volumetric concentration of 0.75% of graphene nanoparticles, without adding surfactants to avoid interference.
- Experimental study on the density of graphene nanofluid: effects of concentration, temperaturePublication . Vilão, G.; Soares, F.; Ramos, C.A.; Iglesias, T.P.(Introduction) Thermal and physical properties of fluids are crucial factors in the design and development of heat transfer equipment that operates with high efficiency. These properties determine how effectively a fluid can transfer heat, how it behaves under different temperatures and pressures, and its overall performance in heat exchange processes. The density of fluids is an essential physical-chemical property that plays a vital role in mass and heat transfer. The experimental values of the density compared to the initial models existing in the literature present significant deviations, this difference increasing with the increase of the volume fraction. The most used model for calculating density is the mixture model of Pak and Cho [1], however, this equation is still an approximation. As the density of the nanofluid is affected by numerous factors, one of which is the shape and size of the nanoparticle, we will present the study considering this factor [2].
- 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.
- Permittivity of (40 nm and 80 nm) alumina nanofluids in ethylene glycol at different temperaturesPublication . Coelho, Maria de Fátima; Rivas, M.A.; Nogueira, Elisabete Maria; Iglesias, T.P.This article studies the effective permittivity of alumina nanofluids (aluminium oxide) in ethylene glycol. Two nanoparticle sizes (40 nm and 80 nm) were considered and the measurements were carried out at various concentrations (up to 2% in volume) and at six different temperatures (from 298.15 K to 348.15 K). An empirical equation is proposed that allows to obtain the permittivity value at any concentration or temperature in the studied ranges. The influence of the volume fraction, nanoparticle size and the temperature on relative permittivity is shown. When compared to the previous published values for alumina (40 nm) in water, current results show the influence of the base fluid. The enhancement of permittivity was calculated, and its behaviour was analysed. Smaller sized particles have the highest values of permittivity and enhancement. Theoretical models in the study of permittivity are applied. The poor predictions of classical models are attributed to the positive behaviour of the permittivity change on mixing for these nanofluids. The contributions to permittivity from ethylene glycol and nanoparticles are separated in two distinct terms in the variable index equation. The permittivity change on mixing calculated from this equation points out that the nanoparticles are the main responsible for the unusual permittivity increment in these colloids.