In this study, we propose a new type of a cooling agent based on magnetic nanofluid for the purpose of replacing the classical cooling fluids in electrical power transformers. The magnetite (Fe3O4) nanoparticles were synthesized by the co-precipitation method from an aqueous medium of salts FeCl3x6H2O and FeSO4x7H2O in the molar ratio Fe3+/Fe2+ = 2:1, by alkalization with 10% aqueous solution of NaOH at 80°C, for 1 h. The size of the magnetite nanoparticles, as measured by X-ray diffraction method, was 14 nm and by scanning electron microscopy (SEM), they are between 10 and 30 nm. Magnetite powder was placed in oleic acid as a surfactant to prevent agglomeration of nanoparticles. The resulting mixture was dispersed in transformer oil UTR 40, with the role of carrier liquid. The magnetic, rheological, thermal and electrical characteristic properties of the obtained Fe3O4 transformer oil-based nanofluid were determined. A mathematical model and numerical simulation results are very useful for investigating the heat transfer performances of the magnetic nanofluid. Based on this study, it was tested the cooling performance of this magnetic nanofluid for two types of electrical power transformers as compared to classical methods. We also presented a microactuator based on the same magnetic nanofluid.
Part of the book: Nanofluid Heat and Mass Transfer in Engineering Problems
In this chapter, two important aspects of using CeO2 in the field of gas sensors are presented. Firstly, for CO2 detection in the range of 0–5000 ppm, a binary semiconductor oxides CeO2-Y2O3 was used. Secondly, as a dopants, in oxide semiconductor systems, used to detect the NO2. In this case, CeO2 is used as a dopant in hybride composite, consisting of reduced graphene oxide/ZnO, in order to increase the sensibility in NO2 detection at low concentration in the range of 0–10 ppm. The structural and morphological characterization of sensitive materials by X-ray diffraction, SEM, adsorption desorption isotherms, thermal analysis and RAMAN spectroscopy are presented. Also, the sensing element of the sensor that detects the NO2 is achieved by depositing the nanocomposite material on the interdigital grid. The electronic conditioning signal from the sensing element is achieved by using a Wheatstone bridge together with an instrumentation operational amplifier.
Part of the book: Cerium Oxide