فهرست مطالب

  • Volume:7 Issue: 1, 2020
  • تاریخ انتشار: 1399/02/07
  • تعداد عناوین: 6
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  • AmirReza Khedmati, Mohammad Behshad Shafii * Pages 1-11

    The humidification-dehumidification system is one of the desalination technologies that can utilize non-fossil thermal sources and requires insignificant input energy. This system is usually suitable for rural areas and places far from the main sources of energy. The purpose of this study is to obtain the most suitable working conditions and dimensions of this system. In this research, thermodynamic modeling was first performed for a simple type of the system (water-heated); then, the effect of parameters on the system performance was investigated. Modeling was conducted through a numerical simulation; furthermore, the assumption of the saturation of exhaust air from the humidifier was also considered in the mentioned code. Afterward, a comparison was made between two different forms of the system, and the proper form was chosen for the rest of the research. Moreover, through heat transfer equations, the dimensions of the two main parts of the system, i.e., humidifier and dehumidifier, were calculated. Besides, multi-objective optimization was carried out for two objective functions, i.e., gained output ratio (GOR) and the system volume, to reduce the space occupied by the system and reach the desired efficiency simultaneously. The optimization was performed using a simulation program, and results were obtained for different weights in order to optimize each objective function. For instance, 379 liters of freshwater can be produced in a day with a total volume of 48 liters for the humidifier and the dehumidifier in the optimized system.

    Keywords: Humidification-dehumidification, Desalination, Gained Output Ratio, multi-objective, optimization
  • Hasan Huseyin Coban * Pages 12-17
    This paper focuses on the short-term cascade hydro scheduling problem, especially in a competitive environment, namely in market conditions. A nonlinear stochastic optimization method is proposed to take into consideration the hydroelectric energy production as a function of hourly electricity market prices and water release rates. In order to solve a case study based on one of the Turkish cascaded hydropower facilities, the proposed method has been successfully applied to a wide variety of problems at a negligible computation time while providing a higher profit. The paper shows the benefits that could be achieved by applying a model based on the Quasi-Newton Method, which finds zeroes or local maxima and minima of solving a certain type of optimization functions because it can better handle the uncertainty, constraints, and complexity of the problem. Ten-year hourly water inflow data and electricity market prices were used as inputs, and the results of the cascade and single optimization were compared. A comparison study with the operation of each hydropower plant (HPP) separately showed that 18 % higher income was obtained with a cascade variant.
    Keywords: Optimization based electricity market, cascaded reservoir operating rule, hydroelectric producer, short-term hydro scheduling, Nonlinear Optimization
  • Ali Mostafaeipour *, Afsaneh Nasiri Pages 18-32
    In hot and dry regions, air conditioning is used for many different applications like residential, industry, and agriculture and dairy products. This research studies the applicability of wind and solar energies for cooling fruit storage warehouse in the hot and dry region of Yazd in Iran. The studied case is a fruit warehouse with an area of 4240 m2 resulting in a storage capacity of about 1000 tons. For this purpose, the heat gain of the warehouse is determined, and the obtained cooling load is then used to examine the solar and wind energy to power a conventional warehouse system. Different scenarios are examined for this research such as solar air conditioner, solar absorption chiller, wind catcher, and a combination of solar air conditioners and solar absorption chiller for cooling the fruit warehouse. Comparison and economic evaluation of different scenarios show that the solar air conditioning ranks first for this purpose. Results are then validated using value engineering methodology. Solar air conditioning with the highest net present value (NPV) of 4,865,040,418 Rials and the best internal rate of return (IRR) value of 182.98 % was determined to be the best approach among the studied methods. The results of this research can be applied to other regions with similar climatic conditions too.
    Keywords: Renewable Energy, Energy efficiency, fruit storage warehouses, solar air conditioner, Economic Evaluation
  • Alireza Shirneshan *, Mohammad Mostofi Pages 33-39
    The determination of the optimum engine working conditions plays an important role in increasing engine performance and reducing exhaust emissions. The main objective of this study is to optimize the performance and emission characteristics of a CI engine fueled with aviation fuel-biodiesel-diesel blends at various engine speeds and loads using Mixture-RSM. According to the experimental tests carried on a 4-cylinder engine, the mathematical models were developed. Then, the optimization processes were defined as the six scenarios containing the consideration of performance or emission parameters or both of them. Scenario 1 shows that the higher percentage of diesel and jet fuel can improve the performance parameters of the engine; however, Scenario 2 shows that only higher percentage of diesel can improve the engine emission due to negative effect of biodiesel on the NOx emissions and negative impact of aviation fuel on the CO and HC emissions that limit the amount of biodiesel and aviation fuel in the fuel mixture. The results also show that Scenario 3 does not vary compared to Scenario 2. The optimized point for both of engine performance and emission parameters presented in Scenario 6 was calculated as D48.9B32.7J18.4 at 2526 RPM and full engine load to obtain 88.4 (kW), 337 (N.m), 255 (gr/Kw.hr), 0.0268 (%), 469 (ppm), 7.7 (%) brake power, torque, BSFC, CO, NOx, and HC emission, respectively.
    Keywords: optimization, Aviation Fuel, Emission, performance, Diesel engine
  • Sadegh Safaria, HassanAli Ozgoli * Pages 40-50

    In this paper, an electrochemical model was developed to investigate the performance analysis of a Solid Oxide Fuel Cell (SOFC). The curves of voltage, power, efficiency, and the generated heat of cell have been analyzed to accomplish a set of optimal operating conditions. Further, a sensitivity analysis of major parameters that have a remarkable impact on the economy of the SOFC and its residential applications has been conducted. The results illustrate that the current density and cell performance temperature have vital effects on the system efficiency, output power and heat generation of cell of the SOFC. The best system efficiency is approached up to 53.34 % while implementing combined heat and power generation might be further improved up to 86 %. The economic evaluation results indicate that parameters such as overall efficiency, natural gas price and additional produced electricity that has prone to be sold to the national power grid, have a significant impact on the SOFC economy. The results indicate the strong reduction in the purchasing cost of the SOFC, i.e. not more than $2500, and improving the electrical efficiency of SOFC, i.e. not less than 42 %, can be the breakeven points of investment on such systems in residential applications. Also, it is found that the target of this SOFC cogeneration system for residential applications in Iran is relying on considerable technological enhancement of the SOFC, as well as life cycle improvement; improvement in governmental policies; and profound development in infrastructures to mitigate legal constraints.

    Keywords: solid oxide fuel cell, Electrochemical model, Sensitivity analysis, Economic Evaluation
  • Bahram Hosseinzadeh Samani *, Marziyeh Ansari Samani, Rahim Ebrahimi, Zahra Esmaeili, Ali Ansari Ardali Pages 51-61
    Due to limited oil reserves, the rising world fuel prices and environmental problems caused by the use of fossil fuels increase the tendency to use alternative fuels such as biodiesel and bioethanol. In this study, the evaluation of energy and exergy flow from seed planting to final production of biodiesel from rapeseed oil was carried out. Biodiesel production from rapeseed was made in three main phases: farm, oil extraction, and industrial biodiesel production. Initially, the input and output variables for rapeseed production were collected through questionnaires from 30 rapeseed farms in Khuzestan province, Iran. Thus, the amount of energy input and output to the field for rapeseed was estimated to be 12826.98 and 22195 MJ/ha, respectively. The highest energy consumption is related to chemical fertilizers with 65 % share of other inputs. Input and output exergy rates were obtained as 3933.494 and 22603.39 MJ/ha, respectively, and the highest exergy consumption related to diesel fuel with 58 % share of other inputs. At the biodiesel production stage, the input energy and output energy were 156.95 MJ and 41.88 MJ, respectively, and the highest amount of electricity consumed was 91.02 MJ. The total amount of exergy in the production of biodiesel and the output exergy was 48.412 MJ and 64.568 MJ, respectively. In this study, the effects of alcohol-to-oil molar ratio, ultrasound power (W), catalyst concentration (w/w %), and the reaction time (min) on methyl ester yield using response surface methodology based on Box Behnken experimental design in the Design Expert software were investigated. Finally, gas emissions were studied at the planting and biodiesel production stages, and the resultsshowed that the highest greenhouse gas emissions at the planting stage were related to chemical fertilizers and alcohol production.
    Keywords: Exergy, energy consumption, Rapeseed, Biodiesel, Renewable Energy