فهرست مطالب

Energy Equipment and Systems - Volume:6 Issue:2, 2018
  • Volume:6 Issue:2, 2018
  • تاریخ انتشار: 1397/04/20
  • تعداد عناوین: 9
  • Ghazanfar Shahgholian * Pages 117-130
    Local renewable resources such as wind and solar are often available in remote locations. Wind farms consist of many individual wind turbines which are connected to the electric power transm­iss­i­o­n ne­tw­o­r­k­. A wind farm can use the wind resources from a certain area efficiently. Double-fed induction generator (DFIG) is a gene­rating principle widely used in wind turbine (WT). DFIG are able to generate active and reactive powers in an independent way. The objective of this paper is to study the imp­rovement in dynamic performance conurbation from wind farms. Simulation studies were carried out in a two-machine power system. Different operating scenarios have been considered. Finally, some simulations are shown to support the imp­rovement in dynamic performance of the DFIG based WT.
    Keywords: DFIG, Wind Farm, Dynamic Performance
  • Milad Babadi Soultanzadeh *, Mojtaba Haratian, Mohammadsaleh Teymouri Pages 131-141
    In this case study, exergy analysis is applied to a mini two-shaft gas turbine which is located in Islamic Azad University Khomeini Shahr Branch`s Thermodynamics laboratory and a proposal presented to make exergy destruction less using a Heat Recovery Water Heater (HRWH). Calculations were done for N2=20000 (rpm) constant and various N1 and after that for N1=60000 (rpm) constant and various N2. Results revealed that the highest exergy destruction rate occurs in combustion chamber in all conditions and a huge part of exergy destruction through the turbine exhaust. Increase in N1 leads to increases in all component exergy destruction rates. On the other hand, power turbine is the only component which is affected by changes in N2 and the exergy destruction rate increases with increase in N2. Moreover, exergy gained rate within HRWH increased with increase in N1 and is almost constant with changes in N2. In the same vein, exergetic efficiency of HRWH and exergy gained rate within HRWH are increased with decrease in water outlet temperature of HRWH.
    Keywords: Gas Turbine, Exergy Analysis, Second Law Efficiency, Exergy Recovery
  • Amireh Nourbakhsh *, Morteza Bayareh Pages 143-154
    Finite-volume procedure is presented for solving the natural convection of the laminar nanofluid flow in a Γ shaped microchannel in this article. Modified Navier-Stokes equations for nanofluids are the basic equations for this problem. Slip flow region, including the effects of velocity slip and temperature jump at the wall, are the main characteristics of flow in the slip flow region. Steady state equations were solved by using time marching method. In provided FORTRAN code, the finite volume method and an explicit fourth-order Runge–Kutta integration algorithm were applied to find the steady state solutions. Also an artificial compressibility technique was used to couple the continuity to the momentum equations as it is simpler and converges faster. The Grashof numbers from to were considered. The results showed that Nusselt number increases with the Grashof number and the parameter R (the ratio of minimum diameter of nanoparticles and maximum one).. As the parameter R increases, the distortion of the isotherm lines increases to some extent.
    Keywords: Microchannel, Velocity Slip, Temperature Jump, Grashof Number, nanoparticle
  • Mohammad Ahmadzadehtalatapeh *, Yat Huangyau Pages 155-165
    In the present research, performance validation of a Heating, Ventilation, and Air Conditioning (HVAC) system operating in a library building was conducted. The operating HVAC system was studied in terms of the provided indoor air conditions and energy consumption level. The fieldwork measurements showed that the HVAC system is not capable of providing the desired indoor air conditions based on the ASHRAE standards. Therefore, two deciding design and operating parameters namely, chilled water cooling coil number of rows and chilled water temperate were investigated to achieve possible improvement in the system performance. For this purpose, different numbers of rows for cooling coil design at different chilled water temperatures were examined. TRNSYS software was employed to investigate the hourly effect of the variables on the system for a whole year of operation.Based on the simulation results, the provided indoor air conditions were appropriate and within the comfort area with the two-row configuration cooling coil. However, the energy performance of the system indicated that the two-row configuration with 10 chilled water temperature was superior in terms of energy consumption, and could provide the desired indoor air conditions, thus it was recommended to be implemented in the existing system.
    Keywords: Energy Consumption, HVAC System, Indoor Air Conditions, TRNSYS
  • Davoud Jafari, Alireza Shateri *, Afshin Ahmadi Nadooshan Pages 167-179
    In the past, wind towers were applied as the main architectural part of building construction in the desert areas of Iran. These almost high structures were used as cooling load suppliers at residential buildings. In the present study, the effect of symmetric four-sided wind tower in flow induction to the bottom space has been analysed by using a wind tunnel and numerical simulations. In the numerical simulation, the flow is assumed to be three-dimensional, unsteady, compressible and turbulent. The experimental studies have been performed by placing a model of these structures at a laboratory wind tunnel. At this state, crossing airflow through every channel is measured for analysing the induction performance of wind tower at different angles of wind blowing. Moreover, the turbulence effect is analysed by adding horizontal and vertical blades and crowns at the top and bottom of the internal gate of traps for attaining better performance. Two different geometries are used for simulations. The results showed that inserting the blade and crown at the bottom and topaffect on the flow rate have effect on the flow rate. For instance, inserting horizontal blades and crown at the top of the model leads to 8 and 16% increase in the flow rate, respectively. The results of the numerical simulations have shown acceptable agreement with experimental results.
    Keywords: Wind Tower, Wind Tunnel, Natural Ventilation, Numerical simulation
  • Shahram Derakhshan, Mahdi Moghimi *, Hadi Motawej Pages 181-200
    Fossil Fuels are always considered as environmental pollutants. On the other hand, the political and economic situations highly affect the price of these fuels. Offshore wind and wave, as renewable energy sources, represent the better alternatives for electricity generation. Therefore, it is necessary that wind speeds effectively be estimated due to the absence of field measurements of the wind speed above the surface of the sea in many regions. In this paper, the annual-average wind speed above the sea is calculated mathematically. Wind data obtained from onshore monitoring stations were analyzed to obtain wind power density above the sea. In addition, this study provides information on the variation of the wave energy using Beaufort scale and wind speeds. This allows an approximate estimation of energies corresponding to various wave heights in that region. Besides, a mathematical model was developed to assess wave and wind hybrid energy system. Thus, using a mathematical model, wind-wave hybrid system components were: wind turbine, wave converter and foundation. The wave energy converter (WEC) selected for the hybrid device is Wavestar prototype which was combined with a wind turbine. As for case study, the wind speed as well as the resulting wind and wave power potential in the area of Eastern Mediterranean Sea and the North Sea were determined and the assessment were done for the designed hybrid system. It can be concluded that the annual energy production from hybrid wind-wave device in the North Sea is 64.3% more than its value in the Mediterranean Sea.
    Keywords: Offshore Wind Energy, Wind Power Density, Mean Wind Speed, Wave Energy, Hybrid Energy System
  • Saeed Hadipour Zimsar, Saeed Firouzi *, Mohammad Sadegh Allahyari Pages 201-209
    The cost reduction of green tea processing, the control of fossil fuel resources, and the curbing of corresponding greenhouse gases emission depend on the energy efficiency of tea processing units. Therefore, it is imperative to identify and analyze factors determining energy efficiency of these agro-industrial units. To this end, the present descriptive survey was carried out on 40 managers of tea factories in Guilan Province, Iran. At the first phase of the study, the experts and managers of the tea manufacturing units were given an open-response question to identify the factors affecting energy productivity of tea industry. Then, the factors were divided into three broad categories of technical, managerial-policy, and knowledge-skill. The statistical analysis of final questionnaire data showed that “the correct and sound design of the new hot air furnaces”, “the enhancement of technical knowledge of technicians in withering, fermentation, drying and storage units”, and “optimum scheduling of withering operation with respect to the final status of green tea leaf” were found to be the most important technical, managerial-policy, and knowledge-skill factors determining the improvement of energy productivity in tea factories of Guilan Province, respectively. Accordingly, it is recommended to hold training courses to enhance energy productivity knowledge of tea factory managers, to improve the technical knowledge of technicians in withering, rolling, fermentation, drying, and storage units, to renew machinery and equipment of tea factories, to enforce manufacturing units to comply with relevant quality standards, and to allocate financial supports through low-interest loans for mounting tea processing machinery and equipment with high energy efficiency.
    Keywords: Electricity, Fuel, Energy Use Efficiency, Tea Industry
  • Mohammad Rasoul Omidvar, Amir Homayoon Meghdadi Isfahani * Pages 211-219
    Glucose is a 6-carbon carbohydrate compound present in plants and the ingredient for hemicellulose which makes up 30% of plants’ total mass. The current study uses glucose as reactant and evaluates hydrogen generation at different temperatures and different amounts of input flow of glucose – water mixture. Hydrothermal gasification method is used for hydrogen generation in an open system with controlled volume with temperature changing in the range of 375 to 1000ºC, water intake flow of 800 kg/h and biomass intake flow of 2000 kg/h.
    Keywords: Hydrogen, Temperature, Supercritical Water, Methane, Carbon Dioxide, Biomass, Gibbs Reactor
  • Mehdi Mahmoodi *, Mofid Gorji Bandpy Pages 221-233
    When a natural gas pipeline ruptures, the adjacent automatic line control valves (ALCVs) should close quickly to prevent leakage or explosion. The differential pressure set point (DPS) at each valve location is the main criteria for value setting in ALCV action. If the DPS is not properly adjusted, the ALCV may mistakenly close or it may not take any action at proper time. This study focused on the DPS values prediction for setting ALCV installed on a gas pipeline with 1mm orifice diameter. The effect of characteristic parameters such as pipeline operational pressure (POP) and pipeline pressure drop rate (ROD) due to rupture or major leak was experimentally investigated on DPS. Twenty-five different conditions with double set of typical mentioned characteristic parameters were chosen. For each condition, the differential pressure (DP) was measured over 180 seconds by analyzing the experimental values. Therefore, 25 maximum DP values (DPSs) were obtained. The DPS increases by increase in ROD or decreasing POP parameters. Because of using nitrogen gas instead of natural gas due to safety reasons, the DPS results can be practically applied by adding a safety factor of 15%. The diagram of DPS with respect to ROD and non-dimensional DPS (DOP) versus non-dimensional ROD (RTP) was provided for different POPs.
    Keywords: Automatic Control Valve, Operating Pressure, Adjusting Values, Pressure Drop Rate, Gas Pipeline