فهرست مطالب

  • Volume:7 Issue:1, 2019
  • تاریخ انتشار: 1397/12/27
  • تعداد عناوین: 8
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  • Milad Charmchi, Saadat Zirak * Pages 1-10

    The flow behavior inside the shrouded disk system is of importance in appropriate design of turbomachinery cavities and turbine test cell hydraulics dynamometer. The turbulent incompressible flow is analyzed for the shrouded disk system with axial clearance. The flow core behaves as a Batchelor type structure when a weak inflow is imposed on the disk cavity. By increasing the inflow, the central core disappears and the tangential velocity distribution is changed to Stewartson type structure. The central core again reappears by increasing the Reynolds number. The moment coefficient of rotary disk depends on superimposed flow rate coefficient and dimensionless geometrical parameters. Moment coefficient increases with increasing inflow rate while the other parameters remain constant. The coefficient is reduced by increasing the Reynolds number. Moreover, it increases with both increasing rotary and stationary disks axial distance, and decreasing clearance ratio. The experimental results of a cavity with radial clearance are used to validate the accuracy of the simulation. The results of this analysis and its development can be used in the design of turbine test cell hydraulics dynamometers.

    Keywords: Rotary - Stationary Disk, Batchelor - Stewartson Flow, Incompressible, Cavity Flow, Dynamometer, Moment Coefficient
  • Milad Zare Mahmoudabadi, Mohammad Mahdi Heyhat * Pages 11-22

    Application of nanofluid and coiled tubes are two passive methods for increasing the heat transfer. In the present study, the turbulent flows of water and nanofluid in coiled tubes heat exchanger were numerically studied. CuO-water nanofluid containing 1 vol% copper oxide nanoparticles was used and single-phase approach was considered for nanofluid flow. The effect of different geometrical parameters on Nusselt number was also investigated for both helical and conical coiled tubes. Water properties were defined as temperature dependent function, and constant wall temperature was employed as wall boundary condition. Simulation results were validated by available experimental and numerical data of heat transfer coefficient and pressure drop inside the helically coiled tube. The results show that for the helically coiled tubes, Nusselt number increased by tube diameter enhancement, while the increase of pitch circle diameter resulted in its decline. However, the variation of helical pitch exhibited a slight effect on the heat transfer. Moreover, for conical coiled tubes, increase helical pitch and cone angle reduced Nusselt number; while this parameter increased as the tube diameter increases. Addition of 1% copper oxide to water led to 8% heat transfer augmentation in the helically coiled tube. Also, using CuO-water nanofluid, the performance index was enhanced by 3.5 and 5% for helical and conical coiled tubes, respectively.

    Keywords: Single-Phase Approach, Conical -Helical Coiled Tubes, Nanofluid, Heat Transfer, Turbulent
  • Ali Habibollahzade, Ehsan Houshfar *, Mehdi Ashjaee, Ehsan Gholamian, Amirmohammad Behzadi Pages 23-39

    In this paper, a novel integrated system is proposed to improve the performance of a conventional low-grade geothermal-based organic Rankine cycle (ORC). The main idea is to utilize two TEG units to recover the waste heat of the condenser and geothermal brine. The proposed model is investigated and compared with simple ORC from the energy, exergy, and exergoeconomic viewpoints through the parametric study. Furthermore, the payback period of the systems is calculated to investigate the economic aspects of the model in more details. Results show that the exergy efficiency of the proposed system would be 56.81% at the base case (4.67% higher than the simple geothermal-based ORC system) and the total product cost of the proposed integrated system is 24.55 $/GJ at the base case (5.5% lower than simple ORC), while the payback period of the suggested system is 2.422 years (15 days lower than the simple ORC cycle). Furthermore, the net power output of the novel proposed system is 75.24 kW (9% higher than the simple ORC cycle). Comprehensive paramedic study and comparison of the exergy and exergoeconomic aspects reveal that the proposed system is a promising method to optimize such systems from exergy/exergoeconomic viewpoints.

    Keywords: Exergy, Exergoeconomic, ORC, Geothermal, Thermoelectric Generator
  • Hossein Yousefi, Younes Noorollahi, Mojtaba Tahani *, Roshanak Fahimi Pages 41-56

    Pressure Reducing Valves (PRV) are being used for decreasing the existing extra pressure in the water distribution network. however, they dissipate a considerable amount of energy. Therefore, the idea of application of Soft Pressure Reducing Systems (SPRS) is proposed, where a PRV is replaced by a hydropower station. The heart of An SPRS is the turbo-generator. One of the advantages of this type of hydropower plants is the opportunity of application of reverse pumps as the turbine. The performance of PATs is very susceptible to the flow amount and geometrical parameters. Therefore, the performance optimization of PATs is essential. In this research study, the performance of a PAT is investigated using computational fluid dynamics and four geometrical modifications are applied in order to improve its performance. The investigated geometrical parameters are volute type and diameter, beveling the impeller blade tip, deviation of the blade inlet angle. Results indicated that the utilization of radial volutes would be suitable when the flow is less than its BEP value most of the time and tangential volutes are suitable for the opposite situation. Decreasing the diameter would increase both the produced power and the efficiency but its influence is more significant for flows less than BEP. moreover, the results indicate that at a forward deviation equal to 5 degrees, the optimum performance of the turbine will be achieved.

    Keywords: Pump as Turbine, Geometrical Modification, Hydropower Plant, CFD
  • Amin Nikkhah, Mehdi Khojastehpour *, Mohammad Hossein Abbaspour, Fard Pages 57-65

    Iran is a developing country with a population of over 80 million. The total daily MSWs production in Iran is about 50 million kg. Most of the MSWs in this country is being disposed of in the landfills. Some of the landfills are located in the urban area or near to sea, river, and forest. In this regard, the management of MSWS becomes a concern in Iran. One solution to manage MSWs and mitigate their environmental impacts is to capture the biogas production. Thus, this research presents the potential biogas generation from MSWs in Iran. The findings of this study illustrated that Iran's daily energy generation potential from MSW is equal to 31,676 barrels of crude oil. The yearly biogas potential generation from MSWs resources is equal to 13.4 million barrels of crude oil equivalent. Overall, the results of this research show that there is a tremendous potential to generate energy and reduce the environmental impact of MSWs in Iran through converting them to the biogas.

    Keywords: Energy Production, Environmental Impacts, Renewable Energy, Resource Conservation
  • Maryam Khademi* Atefeh Behzadi Forough, Ahmad Khosravi Pages 67-79

    In this research study, energy, exergy and economic analyses is performed for a combined cycle power plant (CCPP) with a supplementary firing system. The purpose of this analyses is to evaluate the economic feasibility of a CCPP by applying an optimization techniques based on Evolutionary algorithms. Actually, the evolutionary algorithms of Firefly, PSO and NSGA-II are applied to minimize the cost function and to optimally adjust the operating design variables of a CCPP. The input parameters are measured in real case study (i.e., Yazd city, Iran) and they are used to model and optimize the system performance. The cost objective function is formed from several parts: Operating cost, capital cost and exergy destruction cost. In following of optimization procedure, a thermo-economic method is employed to compare the impact of operating parameters from an economic standpoint by COMFAR III (Computer Model for Feasibility Analysis and Reporting) software. The economic analysis consists of determination of NPV, sensitivity analysis and calculation of break-even point. The results showed that the optimization results are economically more feasible than the base case. In addition, among different optimization techniques, Firefly algorithm improves the economic justification of CCPP. At the end, the results of sensitivity analysis show that by decreasing the operation costs, fixed assets and sales revenue by 40%, the IRR increases by 6.7%, 42.8% and decreases by 41.4%, respectively. Furthermore, the lowest sensitivity of IRR is related to operation cost, while the highest sensitivity of IRR is corresponding to variations of fixed assets.

    Keywords: Techno-Economic Analysis, Firefly Algorithm, PSO, NSGA-II, COMFAR, CCCP
  • Nasim Hashemian, Alireza Noorpoor *, Parisa Heidarnejad Pages 81-98

    In this study, a new proposed multi-generation system as a promising integrated energy conversion system is studied, and its performance is investigated thermodynamically. The system equipped with parabolic trough collectors and biomass combustor to generate electricity, heating and cooling loads, hydrogen and potable water. A double effect absorption chiller to provide cooling demand, a proton exchange membrane electrolyzer to split water into hydrogen and oxygen and a multi-effect desalination system to provide potable water by recovering the waste heat of biomass combustion is combined with a steam Rankine cycle. The results of the thermodynamic analysis indicate that thermal efficiency of 82.5% and exergy efficiency of 14.6% is achievable for the proposed system. Hydrogen and potable water production rates are 88.1 kg/h and 3.9 m3/h, respectively. The proposed system generates 26.3 MW electricity, 26.3 MW heating load, and 137.2 MW cooling load. Parabolic trough solar collector, double effect absorption chiller and biomass combustor are the primary sources of thermodynamic irreversibilities in comparison to other components. The mass flow rate of biomass fed to the system and aperture area of parabolic trough solar collector is calculated to be 6.2 ton/h and 188,000 m2. Besides conventional analyses, to conclude the concept of multiplicity six different cases for the studied multi-generation system are modeled and evaluated regarding thermal and exergy efficiencies. Finally, the parametric study is performed to identify the consequential parameters on the thermodynamic performance of the system.

    Keywords: Exergy, Multi-Generation, Desalination, Hydrogen Production, Double Effect Absorption Chiller
  • Mohammad Mahdi Rastegardoost, Forooza Samadi Pages 99-108