Sharif Digital Repository

Ti4Ni2O, Ti4Ni2N, TiC and Ti2Ni are brittle compounds usually formed during production and processing of the Ti-Ni SMA alloys. These compounds adversely affect on workability and shape memory properties of the alloy. This paper presents most recent findings related to the morphologies of various inclusions and Ti-Ni phases formed during and after vacuum induction melting and casting of Ti-45wt.% Ni material. Cast samples were mechanically and/or electrolytically polished and etched. Extensive optical and scanning electron microscopic studies were carried out to characterize the composition and microstructure of the as cast Ti-Ni alloys. Results indicated that mechanical polishing followed by... 

The concentration distribution and microstructure of NiTi shape memory alloys produced in vacuum induction furnaces operating at high and medium frequencies are compared with those of materials melted in vacuum resistance furnaces. The production procedure consisted of charging pure metals into a graphite crucible; raising the temperature to 1450°C under vacuum; holding the materials in high and medium frequency induction and resistance furnaces for 3, 5, and 120 min under vacuum; and allowing alloys to solidify in the crucibles under the same vacuum. The procedures in each of the three furnaces were made as similar as possible. Chemical composition, microstructure, and surface hardness of... 

NiTi shape memory alloy (SMA) ingots were produced by vacuum induction melting/casting unit. The effect of microstructure on the hot (1000C) and cold (room temperature) rolling workability of cast samples was investigated. Microstructure of the cast samples was related to the type of crucible which used for melting and the average vacuum pressure of VIM furnace. Optical microscope, scanning electron microscope (SEM), and energy dispersive technology (EDS) methods were used to inspect the origins of observed cracks after rolling processes. The results showed that the formation of both Ti4Ni2O and TiC impurities formed due to inappropriate melting conditions had detrimental effects on... 

Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal surface of the crucible. The results indicated that the major sources of the losses were (a) evaporation of the metals, (b) formation of the NiTi scalp and (c) the sprinkling drops splashed out of the melt due to the exothermic reactions occurring between Ni and Ti to form the NiTi parent phase. Quantitative evaluations were made for the metallic losses by holding the molten alloy for 0.5, 3, 5, 10 and 15 min at around 100°C above the melting point inside the crucible. Chemical... 

Attempts have been made to quantify the amount of contaminants absorbed by liquid metal from commercial ZrO2-, Al2O3-, and SiC-base crucibles used for vacuum melting of Ni-45 wt pet Ti alloy. The molten alloy was held under vacuum for 90 minutes at 1450°C to become homogenized. Reactions between the liquid metal and the crucible were investigated by visual observation, chemical analysis, scanning electron microscopy (SEM) image processing, and X-ray mapping. The relative degree of contamination declined in the following sequence: commercially pure SiC > SiC-5 wt pct Al2O3-5 wt pet SiO2] > slurry cast alumina > recrystallized alumina > zircon type A > oxygen deficient high-purity zirconia.... 

This paper provides a novel bad data detection processor to identify false data injection attacks (FDIAs) on the power system state estimation. The attackers are able to alter the result of the state estimation virtually intending to change the result of the state estimation without being detected by the bad data processors. However, using a specific configuration of an artificial neural network (ANN), named nonlinear autoregressive exogenous (NARX), can help to identify the injected bad data in state estimation. Considering the high correlation between power system measurements as well as state variables, the proposed neural network-based approach is feasible to detect any potential FDIAs.... 

There is a global tendency towards using Distributed Generation (DG) and renewable energy resources. Considering low utilization cost and low undesirable environmental effects, wind farms have become a considerable resource for producing electrical energy in many countries. Since Wind farms are not programmable and their power output which depends on weather and wind speed is uncertain, they create problems for utilizing electricity system. There are different methods for preserving system stability against the uncertainty of wind power plants. Optimal utilization of pumped storage and gas resources is one of the approaches for reducing production risk of wind farms. In this paper, it is... 

Reduction of aromatics implies that the gasoline pool would suffer both quantitatively and qualitatively. Alkylates (highly branched paraffinic hydrocarbons) are ideal substitutes because of their high octane numbers, and environmental friendly characters. Alkylates have played significant roles in US gasoline pool, while in Europe alkylates have a lesser important role. The phase out of lead and the increased capacity of FCC units for making more gasoline from heavier petroleum cuts have enhanced the validity of alkylation processes in petroleum refineries. Based on the data obtained in the laboratory using a new developed catalyst, it is predicted to behave as a successful catalyst for C4... 

Dimensional analysis of the governing equations in liquid-phase, solid-acid-catalyzed alkylation was used to develop an empirical model for the catalyst lifetime in terms of important operating variables. It was found that the dimensionless catalyst lifetime in a continuous stirred tank reactor was a function of four dimensionless groups, incorporating all important kinetic and operating variables. A power-law correlation was found to be adequate in representing the available experimental data. Because the alkylation reactions are highly diffusion-limited, it was shown that only three of the four exponents in the power-law correlation were independent. As such, the fourth exponent was... 

Photovoltaic energy is one of the clean and efficient energies which has been developing quickly in the last years. As the penetration of solar plants is increasing in the electricity network, new problems have arisen in network operation. This paper models a high penetration factor of solar energy in the electricity network and investigates the impact of solar energy growth on both the generation schedule of different power plants and in the natural gas transmission network. Fuel management of gas power plants is modeled through simulation of the natural gas transmission network. To this end, an increase in the penetration of solar energy in the electricity network inevitably leads to a... 

Demand response (DR) is known as a key solution in modern power systems and electricity markets for mitigating wind power uncertainties. However, effective incorporation of DR into power system operation scheduling needs knowledge of the price–elastic demand curve that relies on several factors such as estimation of a customer’s elasticity as well as their participation level in DR programs. To overcome this challenge, this paper proposes a novel autonomous DR scheme without prediction of the price–elastic demand curve so that the DR providers apply their selected load profiles ranked in the high priority to the independent system operator (ISO). The energy and reserve markets clearing... 

This paper presents a formulation of fuzzy optimization for uncertainties in natural gas in fuel constraints for hourly individual unit and total unit fuel consumptions. Security Constrained Unit Commitment (SCUC) is usually a mixed integer programming and gas load flow has a non-linear equation a genetic algorithm is proposed to solve natural gas transmission network. A fuzzy mixed integer programming optimization is briefly discussed and adapted to deal with security constrained unit commitment schedule. Finally, two case studies are investigated (IEEE 6-bus system with 7-node natural gas transmission grid and the IEEE 118-bus power system linked with 14-node gas transmission test system)... 

Gas injection into reservoirs can be used to increase oil recovery. However, reservoir heterogeneity and high gas mobility reduce sweep efficiency and decrease recovery. Using foam can reduce gas mobility and therefore increase sweep efficiency. Foam is thermodynamically unstable, so it is important to predict the foam stability. In order to understand the influence of oil presence on foam stability, static experiments performed on foam by varying the type and amount of added oil and molecular weight of added alkane. Also static foam properties have been investigated by varying the surfactant concentration, ionic strength, composition of different salts in the sample, and addition of polymer... 

The interdependencies of power systems and natural gas networks have increased due to the additional installations of more environmental-friendly and fast-ramping natural gas power plants. The natural gas transmission network constraints and the use of natural gas for other types of loads can affect the delivery of natural gas to generation units. These interdependencies will affect the power system security and economics in day-ahead and real-time operations. Hence, it is imperative to analyze the impact of natural gas network constraints on the security-constrained unit commitment (SCUC) problem. In particular, it is important to include natural gas and electricity network transients in... 

Beside their worldwide abundance, oil recovery from fractured carbonate reservoirs is commonly low. Such reservoirs are usually oil-wet, thus, waterflooding leads into early breakthrough and low recovery due to the high conductivity of the fracture network, negative capillary pressure of the matrix and, consequently, the poor spontaneous imbibitions of water from fractures into the matrix during the course of waterflooding. In such problematic reservoirs, changing the wettability of the matrix toward water-wetness can improve spontaneous imbibition by changing the sign and, thus, the direction of capillary forces, resulting in an improvement of waterflood efficiency and, consequently, oil... 

Power generation consumes a substantial amount of water in the power industry. In order to address the impact of water consumption restriction on the power generation, this paper proposes a security-constrained unit commitment (SCUC) formulation considering water consumption impact as an additional constraint. To this end, the water consumption in power plants is formulated. Consequently, the SCUC is extended to consider the consumed water volume as a restricting factor. A procedure is introduced to investigate the most appropriate point of power generation operation to save a vital amount of water by raising reasonable generation costs. The objective of the proposed model is to minimize the... 

Several corrosion inhibitors, such as, HEDP, sodium molybdate and zinc ions, were added to an aqueous corrosive media containing different concentrations chloride ions, and the corrosion rates (CRs) of carbon steel were measured at various temperatures. It was shown that, in the presence of more than 1,200 ppm of chloride ions, and temperatures greater than or equal to 42.5°C, the combination of HEDP, molybdate and zinc could not control the corrosion in a cooling water system. Then four different models were designed to represent the CR of carbon steel in presence of various corrosive parameters  

The deactivation of solid acid catalysts in liquid-phase alkylation of isobutane with butenes was investigated. The role of pore mouth plugging, in particular, was studied and it was found that it had a significant effect on the deactivation behavior. Simple explicit correlations were developed for catalyst lifetime in a CSTR, both in terms of time-on-stream and butene turnover per catalyst weight. The correlations were tested using available experimental data from the literature and a reasonable agreement was observed. It was shown that for a zeolitic catalyst the butene turnover per catalyst weight was proportional to the square root of catalyst loading, while it was inversely proportional...