Abbas Rajabi Khanghahi; Mohammad Zamen; Mehdi Soufari; Majid Amidpour; Ali Abbas Nejad
Abstract
One of the subjects in solar water heater design is considering distribution of hot water consumption during the day. For example, each of the household, commercial, office, school, and industrial consumptions have a particular distribution of hot water consumption named pattern in this article. In solar ...
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One of the subjects in solar water heater design is considering distribution of hot water consumption during the day. For example, each of the household, commercial, office, school, and industrial consumptions have a particular distribution of hot water consumption named pattern in this article. In solar computation principles, the effect of longitude, latitude, and altitude on collector angle has been clearly presented. However, the effect of consumption pattern especially on the collector orientation has been rarely investigated. The aim of the current study is to survey the effect of various consumption patterns on the collector’s orientation and tilt angle and so calculation of related energy saving. So, five common patterns including office building, commercial building, afternoon and morning shift high school and a 15-unit apartment have been studied and optimal surface azimuth angle and tilt angle determined. It has been observed that 11 to 14 % energy saving can be archived by selecting the optimal angles with respect to hot water consumption pattern in comparison to a state that collectors are orientated for maximum reception of solar energy. Also effect of solar fraction, storage volume and amount of hot water consumption are studied and discussed.
Research Article
Zahra Hajabdollahi; Majid Sedghi Dehnavi; Hassan Hajabdollahi
Abstract
Thermal modelling and optimal design of a solar absorption cooling system are presented, and hourly analysis is performed over the period of a year. Three design parameters are considered, then the Real Parameter Genetic Algorithm (RPGA) is applied to obtain the minimum total annual cost. The optimization ...
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Thermal modelling and optimal design of a solar absorption cooling system are presented, and hourly analysis is performed over the period of a year. Three design parameters are considered, then the Real Parameter Genetic Algorithm (RPGA) is applied to obtain the minimum total annual cost. The optimization results show that the solar cooling optimum configuration needs 1630 square meter collectors, a storage tank with a 15000L capacity as well as an absorption chiller with 300kW capacity. The hourly analysis shows that the space temperature fluctuates on average every 62 minutes during June and decreases to 51 minutes in September. In addition, the optimum number of collectors increases 26.67% given a 50% increment in electricity price while it decreases 20% given a 50% decrement in electricity price. Finally a sensitivity analysis on RPGA parameters is performed and results are reported.
Ehsan Hosseini; Ghazanfar Shahgholian
Abstract
The most common controller in wind turbine is the blade pitch angle control in order to get the desired power. Controlling the pitch angle in wind turbines has a direct impact on the dynamic performance of the machine and fluctuations in the power systems. Due to constant changes in wind ...
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The most common controller in wind turbine is the blade pitch angle control in order to get the desired power. Controlling the pitch angle in wind turbines has a direct impact on the dynamic performance of the machine and fluctuations in the power systems. Due to constant changes in wind speed, the wind turbines are of nonlinear and multivariate system. The design of a controller that can adapt itself with the system, at any given time, is of crucial importance. To limit the aerodynamic power gained from the wind turbine in the high wind speed areas, different methods has are applied on pitch angle. In this paper an extensive literature review on pitch angle control technique in wind turbine has been highlighted. Classical and adaptive controllers, structure control, robust control and intelligent control are among the control methods adopted in this study. In comparison of the controllers, although adaptive and robust controllers, with less sensitivity to changes in environmental conditions, outperform the classic controller, the intelligent controller system presents the best performance of the wind turbines through estimating the system variables and appropriate adaptation to changes at the operating point.
Research Article
Rozita Asgari; Farida Iraji Asiabadi; Hadi Radnezhad
Abstract
The anaerobic digestion of organic waste for biogas production can be affected by some variables such as temperature; concentration of the biogas feed solution, bacteria populations, and pressure. This study investigated the effects of thermal pretreatment at 50, 75, and 100 ºC on the biogas produced ...
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The anaerobic digestion of organic waste for biogas production can be affected by some variables such as temperature; concentration of the biogas feed solution, bacteria populations, and pressure. This study investigated the effects of thermal pretreatment at 50, 75, and 100 ºC on the biogas produced by simultaneous anaerobic digestion of cow manure, mushroom waste, and wheat straw at thermophilic temperature. Moreover, the effects of a zeolite on reducing the salinity of the wastewater were evaluated. Cow manure, mushroom waste, and wheat straw were mixed to yield a mixture with an optimum carbon to nitrogen ratio of 20-30 and TS of 25-35%. Each thermal pretreatment was prepared in four replicates and placed in a steam bath with a temperature of 55 ºC. The amount of gas produced by each thermal pretreatment was measured every day for 15 days. On day 15, the electrical conductivity of the produced wastewater was measured and the wastewater was exposed to a modified zeolite. The results showed that the greatest level of biogas was produced by thermal pretreatment at 75 ºC, which gave the biogas yield of 0.197 L/gVS after 15 days observation while, the other thermal pretreatments at 50, and 100 ºC gave the biogas yield 0.147, and 0.169 L/gVS, respectively. The highest amount of biogas was achieved on the third day for every three thermal pretreatments. Moreover, the modified zeolite reduced the wastewater salinity by 25%. These results confirmed that thermal pretreatment at 75 ºC is an effective pretreatment for biogas production improvement from the mixture of cow manure, mushroom waste, and wheat straw, and the modified zeolite could be used for salinity reduction of wastewater discharged from the process.
Research Article
Siamak Azimi-Nam; Foad Farhani
Abstract
Effects of temperature on electrical parameters of polysilicon solar cells, fabricated using the phosphorous spin-on diffusion technique, have been studied. The current density–voltagecharacteristics of polycrystalline silicon solar cells were measured in dark at different temperaturelevels. For ...
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Effects of temperature on electrical parameters of polysilicon solar cells, fabricated using the phosphorous spin-on diffusion technique, have been studied. The current density–voltagecharacteristics of polycrystalline silicon solar cells were measured in dark at different temperaturelevels. For this purpose, a diode equivalent model was used to obtain saturation current densitiesmeasured at the required temperatures. The experimental results showed that the increase intemperature from 27 to 70˚C produced a rapid increase in the saturation current densities from 0.00003to 0.0005A. The changes in the open circuit voltage and the short circuit current density were found tobe linear with the temperature variations: about 3 mV/˚C reduction in the open circuit voltage wasobserved. Measurements of the short circuit current density revealed a very small dependency of thecurrent density on the temperature variations. Accordingly, the short circuit current density increasedfrom 17.8 to 18.4 mA with increase in temperature from 27 to 107˚C. Measurements of the outputpower versus load resistance were obtained at different temperature levels. The results showed that theoutput power dropped by 30% with temperature rise from 27 to 107˚C.
Research Article
Somayeh Sarirchi; S. Rowshanzamir
Abstract
Nowadays, proton exchange membrane fuel cells (PEMFCs) are the most promising green energy conversion devices for portable and stationary applications. Traditionally, these devices were based onperfluoro-sulfonic acid electrolytes membranes, given the commercial name Nafion. Nafion is the mostused electrolyte ...
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Nowadays, proton exchange membrane fuel cells (PEMFCs) are the most promising green energy conversion devices for portable and stationary applications. Traditionally, these devices were based onperfluoro-sulfonic acid electrolytes membranes, given the commercial name Nafion. Nafion is the mostused electrolyte membrane till now; because of its high electrochemical properties such as high protonconductivity, good mechanical and chemical stability at fuel cell conditions, and .... However, its high cost, reducing the performance at temperature higher than 80℃, and low humidity are the majorproblems. Hydrocarbon polymers are encouraging alternative to Nafion, since they show the same oreven superior performance than Nafion at high temperature and low humidity by some modifications. Numerous researches confirmed that Sulfonated poly ether ether ketone (SPEEK) is a promising PEMbecause of its low-cost, low fuel cross over, and acceptable thermo-mechanical stabilities. However,suitable proton conductivity in SPEEKs is depending on the high degree of sulfonation (DS), whichcould deteriorate the mechanical properties of SPEEK membranes progressively at the high level. Toovercome this dilemma, various SPPEK-based hybrid/blend membranes are synthesized, and theeffects of the introduced fillers on their performance are investigated. The introduced inorganicparticles to the polymer membranes might be silica, zirconia, titania, heteropolyacids, carbonnanotubes, and.... Enhanced proton conductivity, water retention at high temperatures, and higherelectrochemical properties are mentioned as some advantages of incorporating inorganic material intothe polymer matrix. High thermo-mechanical resistance and electrochemical activities are supplied byinorganic moieties, while the organic parts supply plasticity and easier ductility at the low temperature.Indeed, SPEEK blends have a good potential to alter Nafion at the high temperature and/or relativelylow humidity. In this paper, the last advances in progress of SPEEK-based organic/inorganiccomposite membranes that perform truly under fuel cell conditions are discussed.
Research Article
Shoeleh Vahdatpour; Shokoofeh Behzadfar; Leila Siampour; Elahe Veisi; Mehdi Jahangiri
Abstract
Renewable systems influence the process of supplying domestic electricity demands. It will be useful to replace the conventional energy generation system by renewable energy sources since the uncontrolled use of fossil fuels is accompanied by global warming and environmental hazards, in addition ...
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Renewable systems influence the process of supplying domestic electricity demands. It will be useful to replace the conventional energy generation system by renewable energy sources since the uncontrolled use of fossil fuels is accompanied by global warming and environmental hazards, in addition to the danger of their depletion, and because most of the energy derived from these fuels are used in buildings. Economical renewable energy systems have not yet been studied in each climate of Iran. Considering the historical background and the potential biomass of Iran, the potential of using a hybrid solar cell/wind turbine/biomass system for supplying the electricity demands of a residential building in each of the four climate regions of Iran has been studied by using HOMER software in this paper. HOMER software has been determined the most cost-efficient system for each region by using the solar radiation and wind speed data, which are acquired over 20 years. By considering economic issues, results indicate that usage of solar cells is the ideal option for the cold, hot dry and warm humid climates (Total net present cost (NPC) and cost of electricity (COE) are $11639 and 1.808 $/kWh, respectively). Also, usage of systems based on biomass is the best choice for the moderate and humid climates (total NPC and COE are $13211 and 2.052 $/kWh, respectively for Babol and $13075 and 2.031 $/kWh, respectively for Chalous).