Lucian Pîslaru-Dănescu

By Lucian Pîslaru-Dănescu, Gabriela Telipan, Floriana D. Stoian, Sorin Holotescu and Oana Maria Marinică

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

By Lucian Pîslaru‐Dănescu and Lipan Laurențiu Constantin

This study presents an apparatus for the measurement of the electrical volume resistivity of concrete structures in civil and industrial constructions in 2.5 accuracy class, which operates at 500 Hz, for measuring the in situ resistivity of concrete in the range of 5–100 Ωm that is immune to errors due to the polarization phenomena at the interface probe/concrete sample. Also, a quench protection active system (QPS), which works in tandem with a superconducting coil structures (SCSs), in order to prevent the damaging effects when the coil structures pass from the superconducting state into normal conduction state (quench), is presented. An SCS made of YBCO tape high‐temperature superconductor (HTS) type, with a critical temperature of 92 K, has been experimented. In order to minimize the heat transfer influx by convection, the SCSs are confined to a cryostat, which is vacuumed at about 0.001 mbar. The working temperature of the HTS coil structures is about 77 K, ensured by liquid nitrogen as cryogenic agent. Finally, the measurement of the electrical resistance of the sensing element (SE) as part of the resistive‐type gas sensor is shown. The SE is placed on a Wheatstone bridge. The electrical resistance of the SE is variable by an amount ΔR, on when all the resistances of a Wheatstone bridge are nominally equal.

Part of the book: Electrical Resistivity and Conductivity

By Lucian Pîslaru-Dănescu and Lipan Laurențiu Constantin

This study starts with the ZnO nanostructured materials used for improve the efficiency of polycrystalline solar cells operation under low solar radiation conditions. The ZnO nanowires were prepared using the hydrothermal method of deposition on the seed layer by a new and complex process, with controllable morphological and optical properties. The analysis of the XRD patterns, scanning electron microscopy images (SEM) of the ZnO nanowires and a lot of tests made Pasan Meyer Burger HighLight 3 solar simulator, confirm the advantages of using the ZnO nanowires in solar cells applications for antireflection coatings. Then, piezoelectric structures based on new modified PZT zirconate titanate designed for energy harvesting applications is presented. Based on their piezoelectric characteristics, modified PZT zirconate titanate ceramics made of Pb(Zr0.53Ti0.47)0.99Nb0.01O3 ceramic have efficient applications in energy harvesting devices. A piezoelectric transducer, consisting of a thin plate of this piezoceramic material, with dimensions (34 mm × 14 mm × 1 mm), is illustrated. A multiphysics numerical simulation further illustrates such piezoelectric transducer operation. Finally, the miniature planar transformer with circular spiral winding and hybrid core—ferrite and magnetic nanofluid, designed for new energy harvesting systems is presented. We purpose now that the magnetic nanofluid be used both as a coolant and as part of the hybrid magnetic core.

Part of the book: Advanced Electronic Circuits

By Lucian Pîslaru-Dănescu and Laurențiu Constantin Lipan

The continuity of power supply to users is considered to be one of the main problems in the design and implementation of low-voltage smart microgrid configurations. Switching to the backup power supply, when using two frequency converters, one of which is alternately maintained in cold reserve, is presented. Switching to the backup power supply, in the case of low-voltage symmetrical smart microgrids, is another highlighted aspect. In the case of modern residential buildings, the automatic switching is necessary between two or more types of users, critical and noncritical ones to the available sources, like the public grid, photovoltaic panels, power generator, etc. Also, in this study, the implementation of smart power microgrids, featuring auto-reconfiguration, is proposed. It is considered the conversion of the public grids to active (distribution/using) smart power microgrids, which have the autoconfiguration option and use high-tech smart devices, like recloser type. Thus, the faults and contingencies will be limited or even removed, creating the frame for the supplied equipment (in a continuously increasing number due to the local and regional expansion) to operate until the removal of the fault.

Part of the book: Smart Microgrids

By Lucian Pîslaru-Dănescu, Gabriela Telipan, Ioana Ion and Virgil Marinescu

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