Sharif Digital Repository

A thermodynamic model considering flame propagation is presented to predict SI engine characteristics for hydrogen-methane blends. The partially charge stratification approach which involves micro direct injection of pure fuel or a fuel-air mixture, to create a rich zone near the spark plug, is proposed as a method to improve engine performance. Presented approach was validated with experimental data for the natural gas at lean condition. The model was generalized to predict the performance of engine for a variety of hydrogen contents in hydrogen-methane blends. Hydrogen molar concentrations of 0%, 15%, 30%, and 45% were used in the simulations. Results showed that partially charge... 

In this study, interfacial tension measurement (IFT) is utilized to assess the impact of temperature, pressure, and paraffin type on a nitrogen injection process as an efficient enhanced oil recovery method. The pure and equilibrium densities of oil in contact with nitrogen are examined to find IFT behavior and gas solubility in oil. The minimum miscible pressure (MMP) of different systems has been measured using the vanishing interfacial tension technique. The experimental results show that IFT decreases linearly with pressure, with two different slopes. The results indicate that IFT values decrease linearly with temperature at different pressure conditions. The obtained IFT values for... 

This paper presents a control strategy for an islanded medium voltage microgrid to coordinate hybrid power source (HPS) units and to control interfaced multilevel inverters under unbalanced and nonlinear load conditions. The proposed HPS systems are connected to the loads through a cascaded H-bridge (CHB) multilevel inverter. The CHB multilevel inverters increase the output voltage level and enhance power quality. The HPS employs fuel cell (FC) and photovoltaic sources as the main and supercapacitors as the complementary power sources. Fast transient response, high performance, high power density, and low FC fuel consumption are the main advantages of the proposed HPS system. The proposed... 

Microbial enhanced oil recovery (MEOR) refers to the process of using bacterial activities for more oil recovery from oil reservoirs mainly by interfacial tension reduction and wettability alteration mechanisms. Investigating the impact of these two mechanisms on enhanced oil recovery during MEOR process is the main objective of this work. Different analytical methods such as oil spreading and surface activity measurements were utilized to screen the biosurfactant-producing bacteria isolated from the brine of a specific oil reservoir located in the southwest of Iran. The isolates identified by 16S rDNA and biochemical analysis as Enterobacter cloacae (Persian Type Culture Collection (PTCC)... 

In the present study, we developed a multi-component one-dimensional mathematical model for simulation and optimisation of a commercial catalytic slurry reactor for the direct synthesis of dimethyl ether (DME) from syngas and CO2, operating in a churn-turbulent regime. DME productivity and CO conversion were optimised by tuning operating conditions, such as superficial gas velocity, catalyst concentration, catalyst mass over molar gas flow rate (W/F), syngas composition, pressure and temperature. Reactor modelling was accomplished utilising mass balance, global kinetic models and heterogeneous hydrodynamics. In the heterogeneous flow regime, gas was distributed into two bubble phases: small... 

Reduction in ship resistance, in order to decrease fuel consumption and also achieve higher speeds, has been the topic of major research over the last three decades. One of the most attractive ideas in this field is micro bubble drag reduction, which attempts to obtain optimum injection flow rate based on ship specifications. The model test results of a 70 cm catamaran model was used to quantify the effect of air injection rate on drag reduction, and to estimate a simple formulation for calculating an efficient injection rate by considering the main parameters of the ship, such as: length, width and speed. The test results show that excessive air injection decreases the drag reduction... 

The aim of this research is the optimisation of full-toroidal continuously variable transmission (CVT) in conjunction with the fixed ratio (FR) mechanism, while the optimisation objective is to minimise fuel consumption (FC) of the vehicle in the new European driving cycle. After the dynamic analysis of the power train, a computer model is developed to simulate contact between CVT elements and consequently calculate its efficiency. Then an algorithm is presented to calculate FC of the vehicle in the driving cycle. Then, an optimisation using particle swarm optimisation on the CVT geometry and FR mechanism (which is embedded between CVT and final drive) is carried out to minimise FC. It is... 

MnCo oxide spinels have received recent interest as surface coatings on ferritic stainless steel (FSS) interconnects in solid oxide fuel cell (SOFC) stacks, where they provide relatively stable electrical conductivity and reduced Cr volatility compared to uncoated FSS interconnects. In this study, sol-gel deposited MnCo surface coatings on FSS, with post-deposition treatments, were investigated in laboratory air at up to 750°C for up to 750h. The protective coating formed and evolved isomorphic crystallites, (Mn,Co,Fe,Cr)3O4, following fifteen (15) fifty hour (50h) cycles in air up to 750°C. Relative to the surface oxide on the uncoated FSS, the coating was dense, crack-free and exhibited... 

This paper proposes a control strategy for an islanded microgrid to effectively coordinate hybrid power source (HPS) units and to robustly control individual interfaced inverters under unbalanced and nonlinear load conditions. Cascaded H-bridge (CHB) multilevel inverters are flexibly deployed in order to enhance the power quality and redundancy. The HPS employs fuel cell (FC) as the main and supercapacitors (SC) as complementary power sources. Fast transient response; high performance; and high power density are the main characteristics of the proposed HPS system. The presented control strategy consists of a power management strategy for the HPS units and a voltage control strategy for the... 

In present study, the neutron noise source is reconstructed using three different unfolding techniques in a typical VVER-1000 reactor core. In first stage, the neutron noise calculation based on Galerkin finite element method (GFEM) is performed; in which the neutron noise in two energy group due to the noise sources of type absorber of variable strength and vibrating absorber is calculated. The neutron noise due to inadvertent loading of a fuel assembly in an improper position (ILFAIP), as a new defined noise source in the neutron noise studies, is calculated as well. In the second stage, the inversion, zoning and scanning methods are applied for reconstruction of the noise source of type... 

Polyaniline fiber (PANI) was synthesized by chemical interfacial method and doped with para toluene sulfonic acid (PTSA) through a sequential doping-dedoping-redoping process resulting in PANI-PTSA. The doped material was utilized to fabricate Vulcan-polyaniline composite of C-PANI-PTSA. Next, through reduction, Pt particles were deposited on to this composite to produce a Pt/C-PANI-PTSA electrocatalyst. To investigate the PANI-PTSA interaction with the carbon support as well as, to consider its effect upon the catalytic activity of Pt/C-PANI-PTSA, electrocatalysts with different ratios of 10, 15, 20, 25 and 30 wt% were synthesized and their activity was compared with the Pt/C (Electrochem).... 

Natural gas has widely been used as a fuel in conventional Diesel and spark ignition engines. The better understanding of injector parameters on the jet structure is helpful for the combustion optimization. This paper presents an experimental and numerical study on the jet structure of gaseous fuel injector in spark ignition direct injection engine by Schlieren technique and numerical procedure. Helium was injected through a gaseous injector at the different pressure ratios and nozzle diameters to understand the effects of nozzle geometry and pressure ratio for a dedicated correlation of CNG-SIDI injector. It was found that higher pressure ratio and exit nozzle diameter led to more tip... 

The High-Performance Light Water Reactor (HPLWR) is the European version of the Supercritical-pressure Water Cooled Reactor (SCWR). Light water reactors at supercritical pressure, being currently under design, are the new generation of nuclear reactors. The present article is a thermal-hydraulic analysis of the HPLWR fuel assembly cluster. The existing thermal hydraulic codes are not capable of analyzing and designing the HPLWR fuel assembly. It is necessary to introduce a new thermal-hydraulic code that can incorporate the parameters and specifications of the HPLWR fuel assembly. The governing equations include energy, mass and momentum equations beside thermal-hydraulic equations are... 

In this paper, the concentrations of fission products and fuel isotopes as well as the changes of the thermo-neutronic parameters of the Bushehr's VVER-1000 reactor were studied during the initial startup and the first cycle. In order to perform the time-dependent cell calculations and obtain the concentration of fuel elements, the WIMSD5-B code was used. Besides, by utilizing the CITATION-LDI2 code, the effective multiplication factor and the thermal power distribution of the reactor were calculated. A computer program (WERL code) was designed in order to perform accurate calculation of the temperature distribution of the reactor core. For this purpose, the Ross-Stoute, Weisman, and... 

The prospects of the Clean Development Mechanism (CDM) and for carbon income, up to and beyond 2012, in the industrial sectors of Iran and five other Asian countries are investigated. The attractiveness and suitability of each host country, the status of their industrial sectors (based on four post-2012 scenarios), and the post-2012 potential of the CDM (or similar carbon projects) in these sectors are all examined. A multi-criteria analysis of Iran, Saudi Arabia, the UAE, Qatar, China, and India, based on seven sets of criteria (institutional, regulatory, economic, political, social, CDM experience, and energy production/consumption), is conducted, and the post-2012 potential carbon incomes... 

In this paper, numerical and analytical approaches are presented to evaluate the effect of catalyst loading gradient in the catalyst layer (CL) of a polymer electrolyte membrane (PEM) fuel cell. The model is developed based on agglomerate catalyst and accounts for reactant spices and charge (ion and electron) transport in the cathode side of a PEM fuel cell. The special variation of catalyst loading is considered in two direction, "across the layer" from membrane/CL interface to gas diffusion layer (GDL) and "in catalyst plane" under the channels and land areas in the channel direction. A fuel cell test stand is designed and built to facilitate experimental validation of the model. The... 

This paper presents a fuzzy based modified artificial bee colony (MABC) algorithm to solve discrete optimal power flow (OPF) problem that has both discrete and continuous variables considering valve point effects. The OPF problem is formulated as a multi-objective mixed-integer nonlinear problem, where optimal settings of the OPF control variables for simultaneous minimization of total fuel cost of thermal units, total emission, total real power losses, and voltage deviation are obtained. The proposed approach is applied to the OPF problem on IEEE 30-bus and IEEE 118-bus test systems. The performance and operation of the proposed approach is compared with the conventional methods. The... 

Highly porous nanocrystalline alumina was synthesized using two different precipitation processes and precipitating agents, which were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and porosimetry analyses. Different precipitating agents yielded nanocrystalline alumina catalysts with different morphologies and textural properties. Batch precipitation using sodium bicarbonate at constant pH resulted in a highly porous nanocrystalline γ-alumina catalyst, having surface area of 351.47 m2 g-1, total pore volume of 1.68 cm3 g -1 and mean pore diameter of 19.17 nm. The mean crystallite size was also determined to be 3.8 nm, based on the XRD results. Catalytic... 

This work deals with waste heat recovery from a proposed direct internal reforming molten carbonate fuel cell (DIR-MCFC), including an integrated pre-reformer. In this regard, some advantages are attainable over exhaust gas recycling. For instance, due to low temperature in the pre-reformer, carbon deposition and coke formation resulting from higher hydrocarbons can be eliminated. In this study, the cathode outlet provides the heat requirement for the pre-reforming process. After partial heat recovery from the cathode outlet, the stream still has a considerable energy and exergy (352.55 °C and 83.687 kW respectively). This study investigates waste heat recovery from the proposed DIR-MCFC,... 

In this study, the effect of adding walnut shell-based powdered activated carbon (WS) to a bench-scale dissolved air flotation (DAF) column on oil removal was investigated. All experiments were conducted using synthetically prepared wastewater containing low but stable concentrations of heavy fuel oil. After comparing the effect of different WS doses from 0 (blank) to 40 mg/L at the saturator pressure of 5 bar and 10 min flotation time, 20 mg/L WS was chosen as the optimal concentration. In order to find the best flotation time for efficient use of WS capacity, experiments were repeated with and without 20 mg/L WS at longer flotation times. According to the obtained results, by adding WS,...