Original Article
Fuel Cells
M. Rostami; A. H. Farajollahi; F. Bagherpor; V. Sfandiyar
Abstract
Polymer electrolyte membrane fuel cells (PEMFCs) produce high power density efficiently and in a pollution-free way. Therefore, it is employed in UAVs. Flow fields play key role in the performance of PEMFC-powered UAVs. In this study, a novel flow field named modified combined was introduced and investigated ...
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Polymer electrolyte membrane fuel cells (PEMFCs) produce high power density efficiently and in a pollution-free way. Therefore, it is employed in UAVs. Flow fields play key role in the performance of PEMFC-powered UAVs. In this study, a novel flow field named modified combined was introduced and investigated by a three-dimensional and two-phase PEMFC model. In the flow field main channels are tapered aiming to reinforce the performance. The study consists of two steps. In the first stage, modified combined was compared with parallel, serpentine, interdigitated, and combined. The results showed that in the modified combined compared with simple combined, pressure drop decreased 22.6%. Modified combined demonstrated suitable oxygen distribution and appropriate management and the specific power of modified combined is the highest value among all flow fields. Finally, the effect of atmospheric conditions on the performance of the PEMFC with modified combined flow field was studied and two equations were presented to predict the performance at 0.4V and 0.7V at the different altitudes of flight. The findings unveiled the point that in the cruise phase of the flight, low voltage is more suitable for PEMFC-driven UAV with modified combined flow field. All in all, modified combined flow field and low voltage are recommended to be utilized in PEMFCs as propulsion system of UAVs.
Original Article
Systems with Low Energy Consumption
Seyed E. Hoseini; M. Simab; B. Bahmani-Firouzi
Abstract
The argument of power systems planning in home microgrids has become one of the burning topics in optimization studies today among the researchers. Since the installation and use of high-capacity energy sources in power systems have many limitations and constraints, so part of the perspective of power ...
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The argument of power systems planning in home microgrids has become one of the burning topics in optimization studies today among the researchers. Since the installation and use of high-capacity energy sources in power systems have many limitations and constraints, so part of the perspective of power systems studies tends to operate residential microgrids. For this purpose, in this paper, operation planning is based on a residential microgrid consisting of combined heat and power (CHP), heat storage tank and boiler, and when possible, surplus electricity is sold to the upstream network to generate revenue. One of the innovations of this paper is the use of the exergy function to complete the optimization and, in practice, combine energy with economics. Other objective functions of this paper are to discuss the reduction of carbon dioxide in the air and the cost of operation. Energy management and planning in this home microgrid is tested with different capacities and types of CHPs, so that the home operator can choose the best mode to use. The multi-stage decision based dynamic programing (MSD-DP) optimization approach is used to minimize the operation costs of proposed framework. The most important innovation of this paper is the use of exergy function for energy management in a residential complex where CHP can also be used to generate electricity and heat simultaneously. Therefore, determining the capacity of CHP and the possibility of exchanging electricity with the upstream network can be mentioned as other innovations of this research.
Original Article
Photovoltaic Systems
M. Mirzaei Omrani; M. Mirzaei Omrani
Abstract
Solar energy as renewable and clean energy has a remarkable share in improving the water-energy-food nexus. However, due to occupying a vast area of land, the development of large-scale photovoltaic systems is a serious challenge, particularly in regions with land restrictions. As a solution, it is argued ...
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Solar energy as renewable and clean energy has a remarkable share in improving the water-energy-food nexus. However, due to occupying a vast area of land, the development of large-scale photovoltaic systems is a serious challenge, particularly in regions with land restrictions. As a solution, it is argued that the installation of the floating photovoltaic systems on the water reservoirs can save land as well as reduce the evaporation rate. The aim of this study is to economically and environmentally evaluate the feasibility of the installation of a 10-megawatt floating photovoltaic power plant on a water reservoir. Results show that the payback period of investment and internal rate of return are achieved at 5.2 years and 20.4%, respectively. It is also found that if only 0.3% of the water reservoir surface is covered, evaporation volume will be decreased from 441.2 up to 515.2 thousand cubic meters. Moreover, environmental assessment demonstrates that 8470 to 15311 tons of CO2 and 27 to 52.3 tons of NOx are not released into the atmosphere. Ultimately, sensitivity analysis proves that if the capital cost is reduced by 30%, the payback period will be shortened to 3.6 years. Furthermore, such a project in Chah-nimeh will be profitable as long as the electricity purchasing tariffs are more than US$ 0.096/kWh.
Original Article
Energy Policy
M. Ansari Manesh; E. Sarkardehee; S. Jafarian
Abstract
Human beings spend most of their time in indoor environments. A large part of people around the world work and live in urban areas. Economic productivity is an important goal of different buildings, especially office buildings. Various factors play a role in economic productivity, including reducing ...
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Human beings spend most of their time in indoor environments. A large part of people around the world work and live in urban areas. Economic productivity is an important goal of different buildings, especially office buildings. Various factors play a role in economic productivity, including reducing energy consumption, managerial programs, and increasing the personnel’s efficacy. Increasing attention to efficiency see day by day. Efficiency is a dependent variable i.e., it depends on the individual, environmental, and work conditions. In recent years, most offices pay attention to indoor environmental quality. Because the cost of hiring staff is higher than the cost of operating and maintaining a building. Thus, spending on improving the workplace is the most effective strategy to improve efficiency. This research seeks to study the effective factors on the efficiency of the employees through field studies. Environmental measurements of temperature, humidity, and carbon dioxide were measured in office buildings (from February 4, 2012, to March 5, 2012). Physical measurements showed that, as these parameters increased, efficiency decreased.Then employees fill out the questionnaires (N=328) in the offices of Kermanshah city. An indoor environment is effective for public health. Having healthy indoor environments is a definite right of people. The results of this research showed that satisfaction with the thermal condition, thermal comfort, optimal thermal condition, suitable workplace, and high quality of the workplace are factors influencing efficiency. Providing desired thermal conditions and increasing the quality of the workplace have the highest and lowest effects on the efficiency of employees.
Original Article
Tide, Wave and Hydro Power
A. Abazari
Abstract
The combination of offshore wind turbines and wave energy converters has recently been the focus of researchers. Many types of converters have been installed on the offshore platform in the design step, and the performance of these hybrid systems has been investigated. The oscillating water column converter ...
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The combination of offshore wind turbines and wave energy converters has recently been the focus of researchers. Many types of converters have been installed on the offshore platform in the design step, and the performance of these hybrid systems has been investigated. The oscillating water column converter is one of the most favorite and commercialized systems due to its efficiency and low maintenance cost. In the present study, a new design including the array of the oscillating water column in a circular arrangement around the spar-type platform is considered. The coupled governing equations are solved based on the simplified analytical approach through frequency domain analysis. The results show that the increase in the number of energy converters increases the total generated power, and consequently, the converters capture the vibrational energy of the spar platform. Therefore, the dynamic response of the spar decreases in the case with an array of energy converters which is one of the main objects of this hybrid system.
Original Article
Electricity Generation by Green Energy Sources
S. Poursheikhali
Abstract
In this paper, an energy harvesting assisted wireless network is considered where a source, contrary to the conventional networks, harvests its required energy via two independent energy channels. In addition, we assume a destination terminal, which receives interference signals along with the data transferred ...
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In this paper, an energy harvesting assisted wireless network is considered where a source, contrary to the conventional networks, harvests its required energy via two independent energy channels. In addition, we assume a destination terminal, which receives interference signals along with the data transferred by the source. In this model, the source is considered to scavenge energy from the destination's broadcasted signal and ambient interference signal. We model the energy and data channels via Rayleigh-Racian channel model. Then, the system outage probability is obtained after analyzing the outage probability of energy and data channels. Moreover, another scenario in which the source is assumed to harvest energy from only the destination terminal is investigated. Computer simulations are conducted to evaluate the effectiveness of the proposed approach, and the impacts of different system parameters on the system outage probability are investigated. The results indicate the outperformance of the scenario in which energy harvests via two channels compared to the case where only one energy harvesting channel exists. In addition, the overall system outage highly degrades when outage in energy channels decreases, especially in the first scenario.
Original Article
A. Abazari; M.M. Aziminia
Abstract
Flap-type wave energy converter is one of the oscillating surge devices for generating electricity from the ocean wave source. It comprises a vertical plate pivoted on a hinged base that oscillates rotationally due to the exciting wave. Splitting a single flap into two separated flaps in a double arrangement ...
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Flap-type wave energy converter is one of the oscillating surge devices for generating electricity from the ocean wave source. It comprises a vertical plate pivoted on a hinged base that oscillates rotationally due to the exciting wave. Splitting a single flap into two separated flaps in a double arrangement may cause different dynamic characteristics. This can improve the output extracted power versus the excitation period. Therefore, this effect is investigated in the present study through a dynamic mathematical model. The hydrodynamic coefficients and exciting torques in the equation are calculated based on the Boundary Element-based software of ANSYS AQWA. In the next step, the rotational displacement is calculated through the frequency domain approach based on the assumption of the regular monochromatic and head-on waves, and consequently, the maximum power is computed regarding the optimum power take-off damping strategy. Finally, in the same procedure as the single flap, the output power for the double arrangement is derived. The results show that decreasing the natural period for each flap can potentially cause a wideband response of the total power for the double configuration compared to the single one.
Original Article
Biomass Energy Sources
Moslem Akbari Vakilabadi; Alireza Binesh; Mostafa Monfared
Abstract
A mathematical model has been investigated to predict the effect of hydrodynamic forces, especially thermophoretic forces on micro organic particles in counter-flow combustion in this research. Hydrodynamic forces change the velocity and concentration of evaporative organic particles moving toward the ...
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A mathematical model has been investigated to predict the effect of hydrodynamic forces, especially thermophoretic forces on micro organic particles in counter-flow combustion in this research. Hydrodynamic forces change the velocity and concentration of evaporative organic particles moving toward the flame and they make a particle-free distance above the flame surface. Particle evaporation creates a thrust force that affects the velocity of the particles, which can be ignored compared to other hydrodynamic forces. Also, the temperature difference between the particles, the interaction of the particles on each other is neglected.The distance between the inlet nozzle and the flame surface is divided into four zones to investigate the dynamic behavior of particles in the flame front that in each case, the dynamic particles equations are written and the effect of thermophoretic force, weight force, drag force and buoyant force are analyzed on the particles and as a result, the velocity and concentration profiles of the particles are obtained in terms of distance from the flame front at different strain rates and with different particle diameters. The particles concentration of above the flame front increases with the balance of these forces, which the increasing the particles accumulation above the flame decreases the combustibility of particles in the flame front. Then, the length of the particle-free zone is extracted under the influence of different strain rates at different temperatures. As the flame surface approaches, the temperature gradient rises and the thermophoretic force increases. Accordingly, heavier particles accumulate closer to the flame surface.
Original Article
Mohammad Akhlaghi; Farzad Ghafoorian
Abstract
Unacceptable air pollution leads to a remarkable increase in the consumption of renewable energy. Wind energy is known as one of the conventional renewable sources, therefore installation of wind turbines has increased over the past three decades. Savonius wind turbine is one of the types of vertical ...
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Unacceptable air pollution leads to a remarkable increase in the consumption of renewable energy. Wind energy is known as one of the conventional renewable sources, therefore installation of wind turbines has increased over the past three decades. Savonius wind turbine is one of the types of vertical axis wind turbines. This type has many advantages namely low noise, self-start capability and closer spacing. Some studies has been carried out to increase the efficiency of wind turbines by optimizing the geometry. In the present study, the arc angle of Savonius turbine blades and its effects as one of the geometric parameters affecting the efficiency of the turbine have been investigated within a CFD method. The amount of arc angle, also called camber angle, is very effective in the optimal efficiency of Savonius wind turbine. To investigate this issue, three different arc angles in the different tip speed ratios have been evaluated. The values of power and torque coefficients which play a vital role in the efficiency of the above turbine have been considered with respect to the changes in the amount of three different arc angle. The results of three-dimensional numerical solution show that the highest power and torque coefficients are obtained with values (0.0261) and (0.501) at a 180 degree arc angle, respectively. Adopting values other than the above value will cause a significant drop in efficiency.
Original Article
arman zare; Mohsen Simab; mehdi nafar
Abstract
Due to the growing demand in the electricity sector and the shift to the operation of renewable sources, the use of solar arrays has been at the forefront of consumers' interests. In the meantime, since the production capacity of each solar cell is limited, in order to increase the production capacity ...
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Due to the growing demand in the electricity sector and the shift to the operation of renewable sources, the use of solar arrays has been at the forefront of consumers' interests. In the meantime, since the production capacity of each solar cell is limited, in order to increase the production capacity of photovoltaic (PV) arrays, several cells are arranged in parallel or in series to form a panel in order to obtain the expected power. Short circuit (SC) and open circuit (OC) faults in the solar PV systems are the main factors that reduce the amount of solar power generation, which has different types. Partial shadow, cable rot, un-achieved maximum power point tracking (MPPT) and ground faults are some of these malfunctions that should be detected and located as soon as possible. Therefore, effective fault detection strategy is very essential to maintain the proper performance of PV systems to minimize network interruptions. The detection method must also be able to detect, locate and differentiate between SC and OC modules in irradiated PV arrays and non-uniform temperature distributions. In this paper, based on artificial intelligence (AI) and neural networks (NN), neutrons can be utilized, as they have been trained in machine learning process, to detect various types of faults in PV networks. The proposed technique is faster than other artificial neural networks (ANN) methods, since it uses an additional hidden layer that can also increase processing accuracy. The output results prove the superiority of this claim.
Original Article
Masoud Taghavi; Hesamoddin Salarian; Bahram Ghorbani
Abstract
The present study economically evaluates a combined hydrogen liquefaction configuration using combined heat and power system, photovoltaic cells unit and liquid air energy recovery for precooling under climatic states of Yazd, Iran. The LAC recovery is used to precool hydrogen. Moreover, the cascade ...
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The present study economically evaluates a combined hydrogen liquefaction configuration using combined heat and power system, photovoltaic cells unit and liquid air energy recovery for precooling under climatic states of Yazd, Iran. The LAC recovery is used to precool hydrogen. Moreover, the cascade refrigeration systems with helium and hydrogen refrigerants are employed to supply refrigeration and liquefaction. The rest of the power required for refrigeration cycles to liquefy hydrogen is supplied by PVC unit. This integrated structure generates liquid hydrogen by receiving 5559 kW of power from PVC unit, 60.79 kg/h of natural gas, 8000 kg/h of liquid air and 1028 kg/h of gaseous hydrogen as inputs. The annualized cost of the configuration is applied to economically evaluate the hydrogen liquefaction system using renewable energies. The developed integrated structure is economically evaluated by HYSYS V10 software and m-file code in the MATLAB package. The economic research results of the hybrid cycle indicate the period of return, prime price of liquid hydrogen production and additive value are 4.249 years, 5.432 USD/kg LH2 and 1.567 USD/kg LH2, respectively. The economic sensitivity examination of the combined system reveals POR increases from 2.295 to 13.97 years and net annual profit decreases from 32.66 to 5.366 MMUSD/year by increasing the gaseous hydrogen cost from 1.4 to 3.4 USD/kg LH2. Moreover, POR increases from 2.753 to 25.07 years and levelized cost of product increases from 5.02 to 7.488 US$/kg LH2 by increasing the capital cost from 52.5 to 217.5 MMUSD.
Original Article
Degnechew Genene Demisu; Daniel Gebeyehu Wondifraw
Abstract
Biodiesel has been considered as biodegradable, green, cleaner, alternative, renewable and eco-friendly energy source. It can supersede petrol-diesel and help to solve challenges accompanied with energy crisis, socio-economic, environmental pollution, climate change and global warming. Hybridization ...
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Biodiesel has been considered as biodegradable, green, cleaner, alternative, renewable and eco-friendly energy source. It can supersede petrol-diesel and help to solve challenges accompanied with energy crisis, socio-economic, environmental pollution, climate change and global warming. Hybridization of vegetable oils to synthesize biodiesel while improving fuel quality has not been studied extensively. Thus, the aim of this study was hybridization of M. stenopetala and A. indica seed oil to synthesize biodiesel and thereby improving the fuel quality. Response Surface Methodology, Box-Behnken Design, was employed in experimental design and result analysis. Oil mixing composition, reaction time and catalyst dose were selected as factors of study with three levels: low (-1), medium (0) and high (+1). Other parameters, temperature, alcohol to oil molar ratio and mixing speed were kept constant. The oil hybrid compositions were: M75N25 (75%v/v M. stenopetala oil and 25%v/v A. indica oil), M50N50 (50%v/v M. stenopetala oil and 50%v/v A. indica oil) and M25N75 (25%v/v M. stenopetala oil and 75%v/v A. indica seed oil) with their corresponding biodiesel, BM75N25, BM50N50, BM25N75 respectively. The catalyst dose of: 1, 1.5 and 2 %w/v potassium hydroxide flake; and reaction time of 20 min, 40 min and 60 min were considered as variables of study. Fifteen experimental runs were conducted with three levels for each factor. Quadratic model was developed with statistical significance, P - value < 0.0001. Analysis of variance (ANOVA) and determination of coefficients were used to evaluate the model quality, where the main comparison was conducted at 5% Least Significant Difference.
Original Article
Alireza Babaie Pirouziana; Abolfazl Ahmadi
Abstract
Recent studies have shown that the integration of power generation, seawater desalination, and industrial gas production can significantly reduce costs and generate clean energy on a large scale. On the other hand, by the growth of population, transportation has been known as a major consumer of fuel ...
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Recent studies have shown that the integration of power generation, seawater desalination, and industrial gas production can significantly reduce costs and generate clean energy on a large scale. On the other hand, by the growth of population, transportation has been known as a major consumer of fuel and energy leading to higher energy demand, increased total costs and, more pollutant components. In this study, the effect of merging the transportation sector to the integration system on energy production and total costs by 2050 in 5-year time steps has been investigated based on an optimization method and a linear model simulation. The modeling was under three senarios :a) Integrated scenario, b) Current Policy Scenario and c) Combined integrated scenario. Renewable systems are considered to be the energy suppliers of power generation, seawater desalination, industrial gas and, transportation sectors. The results showed that the addition of the transportation sector had a significant effect on reducing the final cost from 41 €/MWh to 36 €/MWh which was attributed to the increased generated energy and the severe price drop of power generation technologies as a result of this merging. Also, the share of various renewable technologies in energy generation showed that in the Combined-Integrated scenario, the share of revenues especially solar PV was increased 2% from the Integrated scenario. The results revealed that the installation capacity had a 32% growth compared to the Integrated scenario and 90% compared to the CPS scenario.
Original Article
Seyyed Ali Sina; B. Balanian
Abstract
Multi-Megawatt wind turbines have long, slender and heavy blades that can undergo extremely wind loadings. Good understanding of the modal dynamics of these large machines is of great priority. In this paper, modal dynamics of NREL 5 MW wind turbine is investigated. To this aim, FAST software has been ...
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Multi-Megawatt wind turbines have long, slender and heavy blades that can undergo extremely wind loadings. Good understanding of the modal dynamics of these large machines is of great priority. In this paper, modal dynamics of NREL 5 MW wind turbine is investigated. To this aim, FAST software has been implemented. Vibration characteristics of blades, tower and whole wind turbine machine is extracted. To examine the effects of wind velocity, two operating conditions of machine have been considered. Namely: normal operating condition at rated wind velocity and rated rotor speed and the other, parked condition with fixed rotor at the wind velocity equal to rated wind velocity. Blades root bending moments (both in plane and out of plane) and tower bending moments (both longitudinal and lateral) are extracted. Frequency spectrum of the results is utilized as a tool to study the effects of each vibration mode on wind turbine dynamics in each of aforementioned operating conditions. It is shown that tower vibration during normal operation is highly influenced from blade edge-wise bending mode. On the other hand, during parked condition the effects of flap-wise bending modes become more dominant. The results are expected to offer better predictions of the vibrational behavior of large wind turbines.