Sharif Digital Repository

Performance of polymer electrolyte membrane fuel cells (PEMFC) at high current densities is limited to transport reactants and products. Furthermore, large amounts of water are generated and may be condensed due to the low temperature of the PEMFC. Development of a two-phase flow model is necessary in order to predict water flooding and its effects on the PEMFC performance. In this paper, a multiphase mixture model (M2) is used, accurately, to model two-phase transport in porous media of a PEMFC. The cathode side, which includes channel, gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL), is considered as the computational domain. A multidomain approach has been used... 

Due to increase of per capita water usage, water supply costs and population growth rate; optimal usages of available resources are vital. This is especially important in developing countries. If we add water resource deficits to the above problems, its importance duplicates. One of the ways of using resources optimally is utilizing transferred water in distribution systems properly and preventing its loss. Unaccounted for water (UFW) is an indicator of water loss in most cities. A big part of UFW is due to leakage of pipeline in distribution systems. Researchers have found direct relation between leakage and pressure in distribution systems. Earlier works have shown a series of laboratory... 

Analysis of multi dimensional interactions of flow of energy in passenger vehicle is a complex task that necessitates development and utilization of analytical tools. Development of analytical tools with high complexity is usually based on conclusions of many concepts and theories from different scientific disciplines. In this approach, Passenger vehicle is supposed to be organized in the form of a firm and appears in the market that oriented towards establishing an effective energy supply system which may be identified as delivering the product (person per mileage removable) with minimum operation costs. To this end, an optimization model named POWER software founded on theory of firm of... 

The present study employs Discrete Element Method (DEM) to establish a rheological model that relates the apparent viscosity of a granular material to shear rate, normal stress, and water saturation. In addition, a theoretical model was developed to determine water distribution and water-induced forces between particles for different saturations. The resulting forces were embedded in a 3D shear cell as a numerical rheometer, and a wet specimen was sheared between two walls. A power law rheological model was then obtained as a function of inertia number and saturation. It was found that up to a critical saturation, the apparent viscosity increased with saturation that was higher than that of... 

In this paper, a two-dimensional, two-phase, isothermal model is presented to investigate the water transport characteristic and water distribution in a direct methanol fuel cell (DMFC) with emphasis on exploring the water distribution in different layers of DMFC. The liquid-gas two-phase mass transport in the porous anode and cathode is formulated based on multi-fluid model in porous media and water and methanol crossover through the membrane are considered with the effect of diffusion, electro-osmotic drag, and convection. The modeling results agree well with the three different experimental data in an extensive range of operation conditions. A parametric study is also performed to examine... 

Demands growth and water resources limitation, enforce water sector policy makers to integrate water supply-demand interactions in a coherent framework for efficient water allocation. Water supply-demand interaction, changes long-term trend of water demands, which in turn has a substantial influence on water allocation. Researches on water allocation modeling lack adequate projection of relationship between water supply and demand. Socio-economic factors representing water allocation stakeholders' benefits, account for the main share of water supply-demand interaction. Identification, representation and consideration of these factors in a water allocation model, is the main limitation of... 

A detection technique for extraction of total harmonics, individual harmonics, and reactive current components is introduced and its performance is evaluated. The detection algorithm is then adopted as part of the control system of a single-phase active power filter (APF) to provide the required signals for harmonic filtering and reactive power compensation. Performance of the overall system is evaluated based on digital time-domain simulation studies. The APF control system including the signal processing algorithms are implemented in Matlab/Simulink Fixed-Point Blockset to accommodate bit-length limitation which is a crucial factor in digital implementation. The power system including the... 

Despite the abundant renewable energy sources, the Iranian energy sector relies almost entirely on fossil fuel energy resources. Power sector is dominant source of CO2 emissions and responsible for about 35% of total CO2 emissions in the country. Additionally, long-term electricity demand of Iran is expected to grow quickly, which in turn requires extensive investment to meet the growing demand over the next decades. On the other hand, increasing domestic fossil fuel consumption had been a serious challenge due to high costs of oil and gas. Current study pays particular attention to the possible penetration rates of renewable electricity technologies and their implications for fossil fuel... 

A deterministic energy supply model with bottom-up structure has limited capability in handling the uncertainties. To enhance the applicability of such a model in an uncertain environment two main issues have been investigated in the present paper. First, a binomial lattice is generated based on the stochastic nature of the source of uncertainty. Second, an energy system model (ESM) has been reformulated as a multistage stochastic problem. The result of the application of the modified energy model encompasses all uncertain outcomes together and enables optimal timing of capacity expansion. The performance of the model has been demonstrated with the help of a case study. The case study has... 

Iranian water authority has recently announced that one of the effective ways to avoid unprecedented high water consumption in Iran's agriculture sector is to increase water price. This paper analyzes the feasibility of this policy by using a hydro-economic approach with the aim to consider the role of water pricing in agricultural water management. Such an analysis was conducted through comparing price of water consumed for producing selected agricultural crops (i.e. wheat, sugar beets, onion, tomato, barley, potato, corn, alfalfa hay and watermelon) in a case study on two provinces (East Azarbaijan and West Azarbaijan) in Iran to that in the state of California (CA) in the USA. According... 

The energy supply system of Uzbekistan is not well positioned to meet the rapidly rising domestic energy demand of this country. Uzbekistan's current energy supply system is outdated and has very low diversity, as most of its energy comes from natural gas. In addition to producing immense amounts of greenhouse gas and environmental pollution, this situation is untenable considering the eventual depletion of fossil fuel reserves of this country. Uzbekistan's renewable energy sector is highly undeveloped, a situation that can be attributed to the lack of coherent policies for the advancement of renewable power and the low price of natural gas. However, this country has significant untapped... 

In order to achieve a hydrogen economy, developing widespread hydrogen supply systems are vitally important. A large number of technological options exist and are still in development for hydrogen production, storage, distribution., which cause various pathways for supplying hydrogen. Besides the technical factors, there are other effective parameters such as cost, operability, reliability, environmental impacts, safety and social implications that should be considered when assessing the different pathways as optimal and viable long-term alternatives. To aid this decision-making process, we have developed a generic optimization-based model for the long-range energy planning and design of... 

To attain an ongoing electricity economy, developing novel widespread electricity supply systems based on diverse energy resources are critically important. Several photovoltaic (PV) technologies exist, which cause various pathways to produce electricity from solar energy. This paper evaluates the competition between three influential solar technologies based on photovoltaic technique to find the optimal pathways for satisfying the electricity demand: (1) multicrystalline silicon; (2) copper, indium, gallium, and selenium (CIGS); and (3) multijunction. Besides the technical factors, there are other effective parameters such as cost, operability, feasibility, and capacity that should be... 

In the natural gas transmission network, from supply points to demand nods there are various technological options that include processing, transportation, conversion and gas distribution. Comprehensive analysis of natural gas network requires evaluation of different chains of gas flow through various levels based on economical and environmental criteria subject to technical and operational constraints such as feasibility, operability and reliability of different alternatives. To aid decision-making process in the sector of natural gas, a generic optimization-based model has been developed for assessing long term energy issues related to planning and design of natural gas supply systems. The... 

Energy Return on Investment (EROI) is an indicator of how efficient is an energy supply system. In the present study, the conventional approach of EROI assessment is extended to include the equivalent energy investment needed for offsetting the life cycle environmental impacts. Moreover, the issue of allocation of the invested energy among different by-products is addressed. The EROI of multiple products has been specified using different benchmarks of price, energy content, exergy content, and exergy costs. The application of the concept is demonstrated through a case study of an Iranian oil production unit. The overall conventional and environmentally-extended EROI values of the produced... 

The paper presents further experiments with an extended version of a comprehensive model for assessment of energy technologies and research and development (R&D) planning to evaluate the impact of innovation programs on development of Iranian electricity-supply system. This analytical instrument is a model of energy R&D resource allocation with an explicit perspective of developing countries which has been linked to a bottom-up energy-systems model. Three emerging electricity generation technologies of solar PV, wind turbine and gas fuel cell are considered in the model and the impact of innovation programs on cost-reducing innovation for them is examined. The main results provided by the... 

The sustainable retrofit options may significantly improve the energy consumption and the environmental impacts of the existing buildings. This paper presents a multi objective optimization framework to reach the minimum economic costs and Global Warming Potential (GWP) impact of existing buildings. New energy-efficient technologies for the supply side of the energy system are considered which may minimize life cycle environmental impacts of buildings. Two educational buildings in the campus of Sharif University of Technology are studied. The results show that utilizing reciprocating engine and exhaust-fired absorption chiller reduce the GWP to 133 tons (17.79% of reduction) and 190 tones... 

The integration of water demand management measures using a multi-criteria decision making model is discussed. The demand management measures include leakage detection, water metering and distribution network rehabilitation. A Compromise Programming method is used for integration of criteria including economic efficiency, public health and sustainability. The model is found to be efficient for long-term plans for implementation and usage of resources and is capable of being employed by decision makers in comprehensive urban water management studies  

The city of Zahedan, in South-eastern Iran, has high population growth, limited local freshwater resources and inadequate water distribution system resulting in water supply failures in recent years. This paper will investigate integration of several demand management measures such as leakage detection on water distribution network, water metering and low volume water fixtures as well as the conjunctive use of surface and groundwater resources of this city. For integration of water management criteria, compromise programming will be used as a multi-objective decision making method. The criteria include minimizing the cost, maximizing water supply and minimizing the social hazards due to the...