Showing 9 results for Exergy Efficiency
Mahmood Chahartaghi, Ali Sarreshtehdari, Ali Mohammad Avatefinejad,
Volume 14, Issue 11 (2-2015)
Abstract
In this paper in order to study of effective parameters on energy and exergy efficiency, the modeling and analysis of fluidized bed dryer of Bandar Imam Petrochemical Complex is performed. For do this paper the commercial code with Euler-Euler two phase flow modeling has been used. Due to the importance of moisture content in the dryer system and method transfer between solid and gas phases, a numerical algorithm for estimating moisture content in each phase and exchange or transfer between phases in the proposed the mentioned, implement the code. With applying this algorithm in the code led to considerable correspondence between the results of modeling and the results from the actual performance of the dryer. The difference between the modeling and the experimental results is maximum 1% that represents significant fitness with similar works. The results also express that increase in inlet air and heat exchanger hot water mass flow rates, reduce efficiency while increment in the mass flow rate and temperature of products increase the efficiency. The results of this research for the mentioned petrochemical complex show that with the 15 % increase in mass flow rate of inlet product, overall efficiency of the dryer rises from 38.62 % to %42 and exergy efficiency increases from 35.16 % to 39.5 % while the product moisture decreases 18%.
Seyed Faramarz Ranjbar, Hossein Nami, Alireza Khorshid, Hamed Mohammadpour,
Volume 16, Issue 10 (1-2017)
Abstract
In order to power and hydrogen production, combination of Matiant cycle with an ORC cycle and PEM electrolysis have been analyzed from the viewpoint of energy and exergy. Waste heat of the Matiant cycle is used to run the ORC cycle. Effect of some decision variables i.e. evaporator temperature, minimum temperature difference in heat exchanger, degree of superheating in ORC turbine inlet and isentropic efficiency of ORC turbine on the rate of produced hydrogen, ORC produced power and exergy efficiency of the combined system have investigated. It is observed that, increasing minimum temperature difference leads to decrease in the rate of produced hydrogen, ORC produced power and consequently exergy efficiency of the combined system. Also change in the evaporator temperature makes an optimum value of rate of produced hydrogen, ORC produced power and therefore the exergy efficiency of the combined system. It is obtained that, rising the degree of superheating in the ORC turbine inlet decreases the rate of produced hydrogen, ORC produced power and the exergy efficiency of the combined system. As it was expected, increasing isentropic efficiency of ORC turbine leads to an increase in rate of produced hydrogen, ORC produced power and therefore the exergy efficiency of the combined system.
Mahmood Farzaneh Gord, Mohsen Jannatabadi,
Volume 17, Issue 2 (3-2017)
Abstract
Replacement of expansion valves which are used in natural gas pressure reduction stations, with expansion engine, to recycle wasted energy to generate electricity is the main objective of this study. In these engines, ports are used for inlet and outlet the gas. Control valve geometry set on these ports has a great impact on performance of this engine. In this research, simulation and optimization of the optimum opening and closing time of these valves according to two types of valve, piston and spool valves, to maximize the Exergy Efficiency has been done for the first time which Genetic Algorithm is used for this optimization. Simulation has been conducted with regard to the composition of gas stations which to calculate the thermodynamic properties of natural gas, AGA8 standard is used. For optimization constrain of having no back flow has been applied. Results showed that exergy destruction due to outlet processing in piston valve and due to inlet processing in cylinder valve is more than other destruction sources. Overall engine with cylinder valve has better performance than engine with piston valve. Variation of supply line pressure showed that engine with cylinder valve could not be used in inlet pressure of 30 bar, because engine doesn’t produce power.
Volume 17, Issue 106 (11-2020)
Abstract
In the present research, microwave drying process of potato slices were thermodynamically analyzed and evaluated. During the experiments, potato slices with thicknesses of 3.5, 5, 7 and 9 mm were dried using powers of 200, 400, 600 and 800 W. Specific energy consumption was obtained to be the range of 0.83‒3.29 MJ kg-1, and significantly increased (p < 0.05) with increasing samples thickness. Energy efficiency of the process (13.23‒35.59) was significantly (p < 0.05) improved with increasing microwave power and decreasing samples thickness. Average specific energy loss of the process varied from 0.69 to 2.71 MJ kg-1. Exergy efficiency and sustainability index of the process changed from 10.03 to 28.17 % and from 1.11 to 1.39, respectively. In General, according to the results obtained in this research, practicing higher microwave powers to dry thinner samples improved the thermodynamical performance and reduced the environmental footprints of the process.
Damoon Aghazadeh Dokandari, Ali Naseri, Mokhtar Bidi, Ramin Haghighi Khoshkhoo,
Volume 18, Issue 1 (3-2018)
Abstract
An ejector-expansion refrigeration cycle employing N2O is studied in this paper and thermodynamic and exergy analysis is carried out to find out the effect of some key factor within the system. The results show that Ejector-Expansion Refrigeration Cycle (EERC) obviously has the highest maximum coefficient of performance and exergy efficiency by about 12% and 14% more than Internal Heat Exchanger Cycle (IHEC); meanwhile these are about 15% and 16.5% higher than Vapor-Compression Refrigeration Cycle (VCRC) ones, respectively. Moreover, the total exergy destruction in N2O ejector-expansion cycle is 63.3% and 54% less than IHEC and VCRC and the exergy destructed in expansion process within EERC is 19.39% and 40.497% of total destruction less than IHEC and VCRC. Furthermore, the highest COP for vapor-compression refrigeration, internal heat exchanger and ejector-expansion refrigeration cycles is corresponding to the high side pressure of 7.328 Mpa, while this value for CO2 refrigeration cycle is about 8.5 Mpa.
Mehran Bozorgi, Maryam Karami, Shahram Delfani,
Volume 18, Issue 7 (11-2018)
Abstract
In this study, energy and exergy efficiency of residential-type direct absorption solar collector using PVP-coated silver nanofluid has been evaluated experimentally. First, stability and thermophysical and optical properties of nanofluid have been considered using the theoretical and experimental methods. Then, outdoor thermal performance of collector is investigated using the experimental setup based on EN12975-2. Results of energy analysis show that the collector efficiency is increased by increase of flowrate and concentration of nanofluid asymptotically. It is observed that exergy efficiency is firstly increased by nanofluid concentration and then, decreased after reaching the optimum value. The optimum concentration was 500 ppm for all flowrates. The variation of exergy efficiency by reduced temperature difference is similar to volume fraction. The optimum exergy efficiency is obtained at 0.01 m2K/W. The decrease of exergy efficiency by flowrate indicated that exergy losses due to pressure drop have the significant effect on the collector performance.
S.r. Kazemi Mazandarani, M. Farzaneh-Gord , M.m. Shahmardan ,
Volume 19, Issue 5 (5-2019)
Abstract
Prior to entering to the throttling valve of the City Gate Stations (CGS), high-pressure natural gas flow in pipelines is transmitted through Water Bath Indirect Heaters (WBIH), which is increasing its temperature to compensate for the temperature drop caused by the Joule-Thomson effect and preventing the occurrence of the hydration phenomenon, gas freezing, and subsequent blockage of the gas flow path. Because of feeding of processed gas of the network on a large scale, optimizing the WBIHs has a lot of significance. In the present study, each WBIH is simulated by a type of thermodynamic machine, consisting of two distinct thermal systems. According to the problem geometry and governing equations, the thermodynamic analysis of these two systems results in the formulation of a relationship between their thermal efficiencies together and the definition of a parameter was defined as the Thermodynamic Similarity Coefficient (TSC). Then, the results showed that always, a constant logarithmic relationship exists between of the Number of Heat Transfer Units (NTU) values difference of the fire tube and heat coil of the WBIHs with their TSC as well as a constant power relationship between their NTU values ratio with this coefficient too. Finally, by solving the equation system obtained from these two relations, it was possible to determine the optimal values of NTU for the fire tube and heat coil as functions of TSC of the WBIH and to achieve the relationship between their optimum geometric dimensions together in the most ideal heat transfer state with a maximum relative error of about 13%.
Mohammad Mazidi Sharfabadi, Mohammad Iman Ghiasi, Ali Seraj,
Volume 21, Issue 11 (9-2021)
Abstract
In this paper, the performance of a typical 190 W photovoltaic cell, located in Research Institute of Petroleum Industry, Tehran, Iran, has been studied and evaluated from the energy and exergy point of view. A computer code has been developed for modeling and determining the electrical characteristics of the system such as open circuit voltage, short circuit current, system resistances, maximum power point properties and characteristic curves. The operational and electrical parameters of the system and the environmental conditions such as solar radiation, wind speed and ambient temperature have been experimentally measured and logged on one typical day of May. For the validation of model, the results obtained from the model have been compared with the data reported by the manufacturer as well as the experimental data. The results show that the energy efficiency varies from 11.22 to 13.94 percent during the study period (7:30 AM to 5:30 PM) and its average is equal to 13.19 percent. The exergy efficiency also varies from 14.77 to 16.66 percent during the study period and its average is 15.62 percent.
Mohammad Saleh Barghi Jahromi, Vali Kalantar, Mohammad Hossein Dehestani Bafghi,
Volume 23, Issue 12 (12-2023)
Abstract
Among solar collectors, solar parabolic dishes have attracted the attention of researchers due to their high working temperature and high thermal performance. The purpose of this study is to compare two absorber receivers (normal-black color) for the solar parabolic dish. The analysis of energy and exergy was investigated for different conditions at different hours. Two-axis tracking system was applied to the outlet temperature in the solar parabolic dish system. The results show that the maximum temperature of the normal and black absorber is 101.52 and 115.53 ℃ , respectively, and the maximum energy and exergy efficiency of the black spiral absorber plate is 0.7 and 0.21. In addition, the designed parabolic solar container raised the temperature of 80 liters of water to 60 ℃ in 5 hours after sunlight, which is suitable for bathing and washing clothes in winter in backward and rural areas without electricity and fuel. Therefore, it is enough for four to five people.
