Exploring ways to efficiently and inexpensively exploit and transport high-viscosity and high-pour-point crude oil is very important, and use of silica nanoparticles (nano-SiO 2 ) to reduce the pour point and viscosity of this oil is promising. For this purpose, we modified nano-SiO 2 in two ways. First, we used the coupling agent KH570 to replace hydroxyl groups in nano-SiO 2 with organic groups. Next, we used four monomers (octadecyl methacrylate, styrene, maleic anhydride, and acrylamide) for graft copolymerization of the modified nano-SiO 2 to obtain a nano-SiO 2 composite. This method of modifying the nano-SiO 2 surface reduces the agglomeration tendency of unmodified nano-SiO 2 and disperses the composite material in the organic solvent. A synthetic nanocomposite material could reduce the viscosity of heavy oil with different viscosities and pour points by more than 60%. It could also reduce the pour points of heavy oil by more than 10 °C, thus showing superiority over the traditional ethylene−vinyl acetate flow modifier.
Large-scale voltage collapse incidences, which result in power outages over large regions and extensive economic losses, are presently common occurrences worldwide. Therefore, the voltage stability analysis of power systems has become a topic of increasing interest. This paper firstly presents a comprehensive evaluation method for conducting static and transient voltage stability analysis in electric power systems. To overcome the limitations associated with single-index systems in the evaluation of voltage stability, the analysis approach employs a multi-index system with four primary criteria based on separate analysis methods with ten sub-criteria based on individual indices. In addition, this paper proposes a comprehensive method for establishing index weights, which combines the subjective analytic hierarchy process weighting method and the objective entropy weighting method. An innovative index-weight optimization method based on the Lagrange conditioned extreme value is presented and sensitivity analysis is applied to test the robust of the proposed method. Finally, Fuzzy-TOPSIS is employed to rank the voltage buses of a power system as the final results, considering system functionality and proportionality. The results obtained for an actual power grid in Hami City, China demonstrate that the proposed method represents an effective approach for determining the weakest bus in power systems.
Carbon fiber reinforced carbon matrix composites (C/C) have received much attention due to their excellent high-temperature strength, high thermal conductivity, low coefficient of thermal expansion (CTE), good thermal shock resistance. However, the poor ablation resistance of the C/C restricts its high temperature ablating applications. Making a thin anti-ablation coating on the C/C has been proved to improve the performance effectively. In order to improve the anti-ablation property of the composite, MoSi2 coatings were deposited by Atmosphere Plasma Spraying (APS) on the SiC covered C/C matrix. The SiC coatings were prepared by pack cementation. Oxyacetylene flame torch was selected to simulate the ablation situation. The ablation temperature was 1800°C. XRD and SEM were employed to discover the diversification of the coatings structure and composition. And the mechanism of anti-ablation of the MoSi2 coatings system was investigated in this paper.
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