Sharif Digital Repository

From a thermal point of view, zeotropic mixtures are likely to be more efficient than azeotropic fluids in low-temperature power cycles for reduction in exergy destruction occurring during heat absorption/rejection processes due to their suitable boiling characteristics. In this study, comprehensive energetic and exergetic analyses are mathematically performed for an organic Rankine cycle (ORC) system employing a potential binary zeotropic working fluid, namely R717/water. For this purpose, initially mass, energy, and exergy balance equations are derived. With regard to the similarity in molar mass of R717 (17.03 g mol −1 ) and water (18.01 g mol −1 ), there is no need to alter the size of... 

Improvement of energy efficiency in Software Defined Networking (SDN) is a challenging problem. In order to achieve higher energy efficiency, the routing and scheduling in software defined networks should be planned robustly based on the topological specifications of the SDN. The topological specifications of the SDN depends on the size of the network graph which changes rapidly as the virtualized network devices in the network turned on and off by the controller. Therefore, modelling the SDN graph is an important issue in designing a reliability aware energy efficient SDN. In this paper we propose a new algorithm for reliable energy efficient traffic engineering in SDN. In the proposed... 

Recently, energy harvesting systems that utilize hybrid NVM-SRAM memory in their designs are introduced as a promising alternative for battery-operated systems. Since the ambient input power of an energy harvesting system fluctuates as the environmental conditions change, the system may stop the execution of programs until it receives enough energy to continue the execution. Resuming the execution of a program after the suspension may lead to data inconsistency in an energy harvesting system and threatens the correct functionality of the programs. In this paper, we propose COACH, an energy-efficient consistency-aware memory scheme which guarantees the correct functionality and consistency of... 

In this paper, exergy analysis of a steam power plant located in southern Iran named Zarand power plant has been studied. In order to optimize the performance of the Rankine cycle and achieve higher exergy efficiency, several parameters have been considered as decision variables. Knowing that there is the ability to change some of the parameters in the specific range in the process of electricity production in power plant, temperature and output pressure of the boiler and output pressure of four steps of extraction turbine have been selected as six decision variables. Also, exergy efficiency has been considered as the objective function. For this purpose, the exergy efficiency of the system... 

Recently, energy harvesting systems that utilize hybrid NVM-SRAM memory in their designs are introduced as a promising alternative for battery-operated systems. Since the ambient input power of an energy harvesting system fluctuates as the environmental conditions change, the system may stop the execution of programs until it receives enough energy to continue the execution. Resuming the execution of a program after the suspension may lead to data inconsistency in an energy harvesting system and threatens the correct functionality of the programs. In this paper, we propose COACH, an energy-efficient consistency-aware memory scheme which guarantees the correct functionality and consistency of... 

Despite several different measures of efficiency that are applicable to the photosynthetic systems, a precise degree of efficiency of these systems is not completely determined. Introducing an efficient model for the dynamics of light-harvesting complexes in biological environments is a major purpose in investigating such systems. Here, we investigate the effect of macroscopic quantum behavior of a system of two pigments on the transport phenomena in this system model which interacts with an oscillating environment. We use the second-order perturbation theory to calculate the time-dependent population of excitonic states of a two-dimensional Hamiltonian using a non-master equation approach.... 

Presence of sulfur components in liquid fuels should be controlled due to environmental issues and process considerations. In order to decrease the level of sulfurous compounds in crude gas-oil with 5750 ppmw sulfur, electrochemical oxidative desulfurization has been investigated over electrodes of copper and stainless steel because of their easy operation and mild process conditions. In this research, the effects of stirring rate, temperature, applied potential, sodium hydroxide addition as electrolyte media and water volume have been examined on the sulfur removal efficiency. The results show that electrical conductivity of gas-oil sharply increases with addition of electrolyte up to 613... 

Heaters are one of the central parts of natural gas reduction stations using turboexpanders to prevent the formation of hydrate and corrosion failure. This study intends to design a fired heater by applying a combustion sub-model to derive an optimal model for this kind of application. This model is developed to accurately consider all subsections of the fired heater namely radiation, convection, and shield sections, as well as flue gas composition, and its volume. Within this context, a multi-objective optimization is employed to identify the optimal design of the gas-fired heater in the natural gas reduction station for the Ramin power plant case study. The total economic and environmental... 

Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed,... 

A new high step-up boost converter with an active clamp circuit to eliminate voltage spike caused by leakage inductor is introduced in this paper. The introduced power converter has a high voltage gain for variable input voltage from 48V to 80V. Since both main and auxiliary switches turn on with zero voltage switching (ZVS) and all the diodes turn off under zero current switching (ZCS) condition, switching losses and EMI noises are strongly degraded. Therefore, the converter's efficiency is improved significantly. Simulation results show a 96.4% peak efficiency and 95.4% average efficiency. The proposed topology is suitable for low-input-voltage and low-output power applications such as... 

Delta-orthogonal multiple access (D-OMA) has been recently investigated as a potential technique to enhance the spectral efficiency in the sixth-generation (6G) networks. D-OMA enables partial overlapping of the adjacent sub-channels that are assigned to different clusters of users served by non-orthogonal multiple access (NOMA), at the expense of additional interference. In this paper, we analyze the performance of D-OMA in the uplink and develop a multi-objective optimization framework to maximize the uplink energy efficiency (EE) in a multi-access point (AP) network enabled by D-OMA. Specifically, we optimize the sub-channel and transmit power allocations of the users as well as the... 

To reduce the sulfur content of crude diesel, several sets of experiments have been conducted using electrochemical oxidative desulfurization technique using electrolyte of NaOH at different applied voltages. Due to impacts of operating parameters on desulfurization, kinetic study is pursued and it is found that the kinetic follows a second order reaction rate with a high accuracy. The reaction of desulfurization was modeled using COMSOL and followed by coupled electrochemical oxidation-extraction, while the extraction process was particularly performed using process simulator. The effects of different solvents on extraction performance were studied and dimethyl sulfoxide was selected for... 

This work concerns a fundamental understanding of how heterogeneities induced by flow barriers and connate water affect the displacement efficiency of polymer floods, which has rarely been studied in the available literature. Here, a series of water/polymer injection experiments to heavy oil performed on five-spot glass micromodels containing randomly distributed shale structures is presented. It has been found that macroscopic efficiency of polymer flooding majorly depends on flow barriers distribution/configuration; shale content and geometrical characteristics; presence of connate water and wettability of medium. Microscopic pictures revealed that the main parts of connate water were... 

Many high performance steganographic schemes work at a limited or sparsely distributed set of embedding rates. We have shown that some steganographic changes will be wasted as these schemes are utilized individually for messages of various lengths. To measure the wasted changes and compare different schemes in this respect, we have built a framework based on two new criteria: the Relative Change Waste (RCW) and the Expected Changes per Pixel (ECP). To decrease the wasted changes a systematic combination of schemes is introduced and proved to be equivalent to nonlinear interpolation of points in a two-dimensional space. We have proved that a special case which leads to a linear interpolation... 

Multi-layer schemes have been proposed for steganography. Also some authors have combined these methods with the idea of wet paper codes and gained higher embedding efficiency. This paper proposes a generalized multi-layer method for wet paper embedding. First, the cover bits are divided into blocks and, by combining these bits in groups of 3, a pyramid is formed. Next, the secret message is embedded through a layer-by-layer procedure. The proposed method has higher embedding efficiency in some cases and provides more flexibility for choosing the embedding payload, especially in lower payload conditions  

Direction-of-arrival (DOA) estimation algorithms usually impose high computation burden and most of them are incapable of facing the coherent sources. In this paper, a new computationally efficient algorithm that is robust against the coherent sources is proposed. This method is based on a combination of the Maximum Likelihood (ML) and Orthogonal-Matching-Pursuit (OMP) algorithms. Simulation results show that the proposed algorithm has good performance in the small sample size cases and the coherency does not affect its performance  

In this study a system for real-time analysis of some involving factors in the efficiency of gas-liquid separators is developed based on the weighing method. An ultrasonic atomizer generates water drops in a size range of 1-10 μm with the same frequency during the test. A cyclone separator is selected and effect of the developing flow rate and shape of the mini-riser as a part of connecting assembly to the cyclone separator is investigated. Further an efficient electrostatic precipitator (ESP) with outcome of single-phase airflow is employed in the downstream of the cyclone to separate remaining droplets and produce the same pressure loss during the test. Circular, triangular, rectangular... 

In this paper we consider the content distribution to a set of mobile users interested in the same content. We use the concept of mobile clouds, which exploits cooperation between mobile terminals over the low-power short-range links. We propose, formulate and investigate the energy efficiency and delay of four realistic cooperative content delivery strategies. The derived results, through analysis of mathematical models and simulations, demonstrate around 65% to 95% energy saving gain in mobile cloud strategies compared to conventional multicasting. We also show that using mobile clouds, content distribution delay can be reduced for up to 85%