nasim nayebpashaee

For high-voltage transmission lines near industrial plants and in areas with coastal weather conditions, insulation contamination strongly affects the reliability of the transmission network. Due to the great importance of insulation in power transmission, it is necessary to increase the reliability of these equipment through various methods. Common methods include regular washing and lubrication and use of room temperature vulcanized (RTV) silicone rubber polymer coatings. In the meantime, application of polymer coatings perform have been proposed as an efficient method worldwide, due to their very good performance in polluted environmental, resistant to weathering and suspended particles, as well as prolonging the life and reducing the cost of repairing and replacing insulators. In recent years, several reports have been published on the use of nanotechnology to improve the properties of insulators. Today, the use of RTV-based nanocoatings is common in many countries and has brought good results. Therefore, it seems necessary to assess the feasibility, optimization and selection of the appropriate coating to be applied on the insulators installed in different regions of the country are appropriate according to the weather conditions specific to that region. In this article, the solution of adding nanomaterials to solve the problems of silicone rubber polymer coatings applied on high-pressure insulators in the electrical industry is reviewed. The most common nanoparticles used to improve the properties of the coatings, the role of this filler in improving the properties of the coating, and the existing challenges in the uniform distribution of nanoparticles in the polymer matrix are also explained.

This work involves an experimental study of the thermophysical properties of hybrid nanofluids of TiO2 and graphene in a binary mixture of water and ethylene glycol. Hybrid nanofluid samples with different volume fractions (0.05-2.5%) were prepared by dispersing equal volumes of TiO2 and graphene nanoparticles in a binary mixture of water and ethylene glycol in the ratio of 50-50% by volume. The thermal conductivity, surface tension, and dynamic viscosity of the hybrid nanofluids were measured at temperatures ranging from 253 K to 303 K. The experimental results showed that the low concentration samples exhibited shear thinning non-Newtonian behavior, while the high concentration samples exhibited shear thickening non-Newtonian behavior. The measurements showed that the thermal conductivity of the nanofluids increases by up to 41.93% with increasing nanoparticle concentration and temperature. The surface tension improves by 43.61%, 39.77%, and 51.98% at concentrations of 2.5%, 2%, and 2% by volume at temperatures of 258.15 K, 268.15 K, and 283.15 K, respectively. In terms of aircraft deicing fluid performance, the addition of TiO2 and graphene nanoparticles at less than 0.5% by volume contributes to the improvement of aircraft deicing fluid performance.

A nanofluid is a fluid in which particles with a size between 1 and 100 nm are permanently suspended in the base fluid. The addition of nanoparticles affects the thermophysical properties of the liquid. In this study, the effect of temperature and concentration of alumina and titanium dioxide nanoparticles on the thermal conductivity and dynamic viscosity of a base fluid comprised of water and ethylene glycol was investigated. The volume fraction of the nanoparticles was 0.05, 0.1, 0.5, and 1 %vol. and the test temperatures were chosen to be between 260 and 305 K. SEM and TEM were used to examine the nanoparticles' morphology and microstructure. XRD analysis was used to detect phases in nanoparticles. BET analysis was also used to determine the specific area and porosity of the nanoparticles. The hybrid nanofluids' thermal conductivity and dynamic viscosity were measured and compared to the base fluid. The results showed that the thermal conductivity of the Al2O3-TiO2/ethylene glycol-water hybrid nanofluid depended on the concentration of nanoparticles and temperature. The findings revealed that the thermal conductivity of hybrid nanofluids increases with temperature and nano-additive concentration. Moreover, the viscosity increases with the increasing volume fraction of nanoparticles. As the results show, the viscosity changes with temperature are more pronounced at higher concentrations.

In the present study, the effect of nano Al2O3 and nano graphene ceramic additives in optimizing performance and improving thermophysical properties of aircraft anti-icing/de-icing fluids was investigated. Nanoparticles were characterized by TEM, SEM and XRD methods. The thermal conductivity, surface tension and dynamic viscosity of the hybrid nanofluids were experimentally assessed for temperatures between 253 and 303K and results were compared with some existing theoretical models. Results revealed that the thermal conductivity properties and thus the efficiency of aircraft anti-icing/de-icing fluids are improved by the addition of nanoparticles. Considering the performance of the aircraft anti-icing/de-icing fluids, increasing the surface tension of the fluid helps to improve its performance in covering the aircraft surfaces against the precipitation of super cooled raindrops and snow, resulting in better performance of aircraft anti-ice/de-ice fluid. Based on the results of measuring the dynamic viscosity of graphene-Al2O3/ aircraft anti-icing/de-icing -water hybrid nanofluid, the addition of nanoparticles in the volume fraction ranges from 0 to 0.5%, in addition to increasing the viscosity, show non-newtonian behavior Shear-thinning nanofluid the base, which is the main requirement for the performance of the aircraft anti-icing/de-icing fluid. However, at higher concentrations, the hybrid nanofluid shows a tendency to non-Newtonian shear-thickening behavior. Therefore, the addition of these two types of nanoparticles in volume fractions below 0.5% helps to enhance the performance of aircraft anti-icing/de-icing fluid.

Nanofluid is a suspension obtained by adding nanoscale particles (100 nm) to a base fluid to improve heat transfer. In this study, the effect of temperature and concentration of nanoparticles consisting of Alumina nanoparticles and Graphene nanosheets on the thermal conductivity of a base fluid consisting of water and ethylene glycol was studied. Also, 0.2% by volume of oleic acid (OA) and 0.2% by weight of sodium dodecyl sulfonate (SDS) were added to the base fluid as a surfactant to stabilize and disperse the nanoparticles. The volume fraction of nanoparticles of 0.05, 0.1, 0.5, 1, 1.5, 2 and 2.5% by volume and the tested temperatures were selected in the temperature range of 260-305 K. The morphology and microstructure of the nanoparticles were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermal conductivity of hybrid nanofluids was measured and compared with the base fluid. Results showed that thermal conductivity of water-ethylene glycol / nano Graphene-nano Alumina hybrid nanofluid depends on nanoparticle concentration and temperature. The thermal conductivity measurements of water-ethylene glycol / nano Graphene-nano Alumina hybrid nanofluid were compared with the thermal conductivity prediction models of nanofluids but there was no acceptable agreement. The results showed that increasing the temperature and volumetric concentration of nanoparticles increases the thermal conductivity of hybrid nanofluids. The maximum increase in thermal conductivity of hybrid nanofluid was 44.02% which was obtained in solid volume fraction of 2.5% and at temperature of 303 K.

Nanofluids are a new generation of fluids with very high potential in industrial applications. In this study, the effect of temperature and concentration of nanoparticles consisting of Al2O3 nanoparticles and graphene nanoplates on the rheological behavior of the base fluid consisting of water and ethylene glycol was studied. Also, 0.2%vol. of oleic acid and 0.2%wt. of sodium dodecyl sulfonate were added to the base fluid as a surfactant to disperse the nanoparticles. The volume fraction of nanoparticles in this study was considered 0.05, 0.1, 0.5, 1, 1.5, 2, and 2.5% by volume, and also to investigate the effect of temperature, the tested temperatures were selected in the temperature range of 263-293K. The morphology and microstructure of the nanoparticles were investigated by scanning and transmission electron microscopy. Detection of phases in nanoparticles was performed by X-Ray Diffraction analysis. Also, the specific area and porosity of nanoparticles were determined. The dynamic viscosity of hybrid nanofluids was measured and compared with the base fluid. The results showed that the rheological properties of nanofluid were dependent on temperature and nanoparticle concentration, especially at sub-zero temperatures. Hybrid nanofluid samples with solid volume fraction less than 0.5% showed Newtonian behavior, while samples with higher solid volume fractions showed non-Newtonian shear thinning behavior.

In this study, a finite element numerical method was developed to simulate the stress distribution in the conventional and functionaly graded NiCrAlY / YSZ (GZ) plasma sprayed thermal barrier coating on the Inconel 738 substrate. Residual stress was measured using the nanoindentation method and the results used for verification of the numerical results. The results showed that with increasing the amplitude of the interface, the maximum stress decreases and then increases with further amplitude increment. The maximum residual stress increases with increasing thickness. Comparison of stress distribution in YSZ and GZ coatings showed that the use of GZ coating increases residual stress.

In this study, the effect of the wire cut machining parameters on the surface quality of superalloy718 was investigated. For the first time, the Inconel 718 superalloy machining was performed by wire cut method with spraying suds. This method of machining has had many advantages over the previous methods, which were immersed and cooled distilled water. The regulatory parameters were the intensity of the current, pulse lighting time, pulse power offset; forward speed and wire feed speed. Roughness and material removal rate were the Output characteristic of this process. Two methods of Taguchi design and experimental design (DOE) were used to determine the effect of the parameters on the performance of the wirecut output. Using the design of experiments in Taguchi method, the minimum roughness of the surface was 4.97 μm and the maximum roughness of the surface was 9.65 μm. The results showed that the parameters of the lighting time, the forward speed and the feeding rate of the wire increased the surface roughness and it decreased with increasing roughness time. With the analysis of the dispersion of the concentration of alloying elements on the surface, it was determined that the surface with maximum surface roughness, in addition to being sensitive to stresses and mechanical factors, has less resistance to chemical agents.

In this study, a finite element-based numerical method was developed to simulate stress distribution in conventional and functionally graded thermal barrier coatings YSZ/NiCrAlY plasma spayed on the Hastelloy-x. The coatings were characterized using optical microscope and Scanning Electron Microscopy (SEM). Moreover, thermal shock resistance of the coatings was determined. Comparisons of simulation model results with experimental results of nano-indentation stress measurement method showed good agreement. Thermal shock results show that conventional thermal barrier coating is less thermal shock resistant than functionally graded coating. The results of simulation showed that in samples after thermal shock without oxidation time (without Thermally Grown Oxide layer-TGO), the average value of the maximum stress is 29 MPa in duplex TBC (interface of top coat /bondcoat), 3.15 MPa in three-layer FG-TBC system (interface of 50% NiCrAlY - 50% YSZ / YSZ) and 1.8 MPa in five-layer FG-TBC system (interface of 25% NiCrAlY- 75% YSZ / YSZ). Also, the stress distribution is more uniform in five-layer FG-TBC system that helps to increase the performance and extend the life time of thermal barrier system.

In this study, a set of possible conditions for the addition of alumina to the thermal barrier coating system was considered,
taking into account the experimental results reported by other researchers, from the point of view of the optimal state of adding the alumina to the thermal barrier coating system, in terms of increasing oxidation resistance and hot corrosion. The heat transfer and distribution of stress have been discussed and studied in a comparative and absolute manner. The results showed that in alumina-containing samples, the critical area of concentration of stress is in the interface of the layers containing alumina. Also, the maximum stress values in alumina-containing samples are higher than those with no alumina. Due to the higher thermal conductivity of alumina than YSZ, the addition of alumina to the thermal barrier coating system weakens the thermal insulation property.

Thermal barrier coatings are used to insulate the components in the hot turbine parts to increase the working temperature and efficiency of these components. In this study, conventional and functionally graded thermal barrier coatings of NiCrAlY / YSZ were applied by plasma spraying on Hastelloy-x. The specimens were subjected to thermal shock with a defined cycle. The coatings were characterized using optical microscope, Scanning Electron Microscopy (SEM), Energy Dispersive x-ray Spectrometry (EDS), map analysis and X-Ray Diffraction (XRD). Moreover, thermal shock resistance of the coatings was determined. The thermal shock stress was measured by a new method. In this research, nano-indentation stress measurement method was used to measure the residual stress in thermal barrier coatings. The results of scanning electron microscopy analysis showed that microstructure, porosity and chemical composition changed gradually through the functionally graded coating. Surveying the surface of the samples after applying thermal shock showed that the separation of layers in the two-layer thermal barrier coatings occurred more than the graded coatings. The results of stress measurement by nano-indentation method indicated that the designed method for measuring stress, in contrast to other conventional methods, can measure stresses along the coating depth with acceptable accuracy, without damaging the sample.

An attempt was made to investigate the thermal and residual stress distribution in a novel three layer (La2Zr2O7/ 8YSZ/ NiCrAlY) during a real-like heating regime. The technique of reduction of solving time like mass scaling leads to a considerable reduction in running time while satisfying and not violating accuracy and converging criteria and constrains. Simulation results indicated that, most of damaging and harmful distortion and residual stress concentrate on ceramic top coats and this lead less harm and life time reduction in substrate.

An attempt was made to investigate the thermal and residual stress distribution in a novel three layer (La2Zr2O7/ 8YSZ/ NiCrAlY) during a real-like heating regime which includes heating, service time and final cooling. For achieving maximum accuracy and consistency in calculation of thermal and mechanical properties of hybrid coating system, all related andrequired properties were introduced to the software in temperature- dependent mode. Element modification approaches like mass scaling leads to a considerable reduction in running time while satisfying and not violating accuracy and converging criteria and constrains. Applying adaptive hybrid meshing techniques which applies both mesh – part dependency and independency during numerical iterative solution avoids element distortion and diverging in coupled problem. Heat flux and nodal temperature contours indicated that, most of damaging and harmful thermal load and residual stress concentrate on ceramic top coats and this lead less harm and life time reduction in substarte.

In this study، pulsed plasma nitriding treatment was performed on hot work tool steel AISI H11 samples and plastic mould steel AISI P20 samples at different process temperatures of 500ºC and 550ºC for 5 and 10 h in gas mixture of 75% N2 - 25% H2. Diffusion zones and compound layers were studied by optical and scanning electron microscopy and the surface phases were determined by X-ray diffraction analysis. Moreover، micro hardness changes from surface to core of the samples were determined. Results have shown that، at any specific plasma nitriding temperature and time، due to the microstructure and appropriate paths for diffusing of nitrogen in AISI H11 in comparison with AISI P20، the diffusion and compound layers of AISI H11 are thicker than that of AISIP20. Regarding the results of EDS، upward diffusion of carbon occurred during the ion nitriding of AISI P20، but EDS analysis of diffusion zone of AISI H11 does not show carbon. XRD results have shown that nitriding layer in AISI H11 is composed of γ-nitride and ε-nitride،while ε-nitride was the most forming phase in AISI P20 at all the process parameters. The results of micro hardness profiles at the same depth، have shown that AISI H11 is harder than AISI P20.

Plasma nitriding could improve the lifecycle of plastic mould steels by modifying the surface layers. In this study, the effects of time and temperature of plasma nitriding on plasma nitriding behavior of plastic injection moulding steel P20 were studied. In this regard, pulsed plasma nitriding treatment was performed on P20 samples at different processing temperatures such as 450, 500 and 550 ºC for 2.5, 5, 7.5 and 10 h at gas mixture of 75% N2 - 25% H2. Diffusion zone and compound layer were studied by optical and scanning electron microscopy and the crystallographic phases on surface were determined by X-ray diffraction analysis. Also, micro hardness changes from surface to core of the samples were determined. Results have shown that by increasing treatment temperature and time, nitrided layer thickness and hardness were increased respectively. The SEM results showed that the interface of the compound layer and the diffusion layer formed on the sample treated at higher temperatures were more uniform than those treated at lower temperatures. Regarding the results of EDS, during the ion nitriding of P20 upward diffusion of the carbon and the downward diffusion of the nitrogen have been occurred. XRD results have shown that in all the process parameters ε-nitride was the most forming phase.