فصلنامه مهندسی و مدیریت انرژی
سال دهم شماره 4 (پیاپی 38، زمستان 1399)

In this paper, a series Z-source inverter based on a switched inductor cell is proposed for the first time. This inverter is able not only to increase the voltage gain, in comparison with the conventional Z–source inverters, but also to solve the ST (shoot-through) state’s problems. In this inverter, the value of the voltage gain is increased by an increase in the number of used diodes and inductors in the switched inductor cells. The low value of the capacitors’ voltage stress is another advantage of the proposed inverter. The voltage of the capacitors is increased from zero to the desired value by increasing the duty cycle of ST state from zero to the desired value. This leads to a soft start in the proposed inverter, which is impossible in conventional Z-source inverters. In this paper, in addition to investigating the operation of the proposed inverter in different operating modes, the value of voltage stress of the capacitors, current inductors, and the value of voltage gain are also calculated. Moreover, the proposed inverter is compared with the conventional Z-source inverters to investigate the advantages and disadvantages of it. Finally, the accuracy performance of the proposed inverter is verified through the simulation results in PSCAD/EMTDC software programs.

A double-cyclone is used as a gas-solid separator in the fluid bed-drying process to prepare dry HDPE powder from a wet feed rate of 56000 kg/hr. Particles’ behavior and flow pattern in the dryer affect the cyclones as effective equipment. In evaluation of this system, the numerical simulation of the fluid flow field and particle dynamics, presented by CFD technique, characterize cyclone pressure drop and turbulence parameters. Navier-Stoke equations through the Euelerian-Lagrangian framework by RNG k-ɛ turbulence model are used as mathematical methods and the calculated results are in an acceptable agreement with industrial parameters. The obtained carrier gas flow rates of 14040, 14011 and 14000 m3hr-1 as thermal energy for PE100, BL3, and EX5 respectively cause excellent flow regime, desired final volatile of 0.04%, 0.06% and 0.07% as well as high separation efficiency in different HDPE grades.  The created flow pattern in the dryer makes the efficient use of the immersed coils as another source of energy for drying the particles. Double-cyclones conduct the minimum escaped contents of 70.2, 75.8 and 76.2 for the distributor section and 69.3, 75.3, 75.9 gr in 1 hr for the scrubbing tower. These rates of dusts provide the optimized electrical energy consumptions with maximum saving value of 17%.

Air-Conditioning (AC) systems are responsible for a considerable portion of energy consumption in buildings located in high cooling load requiring regions of Iran. In addition, the heat flow through the buildingschr('39') external walls plays a major role in cooling load estimations for the countrychr('39')s hot regions. Therefore, the application of insulation materials in external walls has gained more interest in recent years. In the present research, a systematic approach to optimize the insulation material thickness has been developed and applied to those regions in Iran which require high cooling load, namely Bandar abbas and Bushehr, through deploying life cycle cost analysis. Moreover, a correlation between optimum thickness and thermal conductivity of insulation materials has been recommended for the buildings located in the above-mentioned hot regions of the country. The study has showed that the relationship between optimum insulation thickness and thermal conductivity has a non-linear trend and obeys a polynomial function.

Energy, environment, and economy are three pieces of a chain which are cohesively bound together and always in a correlation with each other. Therefore, offering a suitable substitution for current fuels that satisfies energy requirements and reduces fuel costs with less pollutant gases needs a detailed assessment of available alternative fuels as well as a complete analysis of Strength, Weaknesses, Opportunities, and Threat (SWOT). A comprehensive overview of the environmental and economic aspects of liquefied natural gas (LNG), as an alternative to marine fuel, is presented with a focus on the codes, standards, regulations, restrictions, and guidelines which are vital for maintaining a balance between market and industry. The various characteristics of LNG has been compared with other fuels and depicted that LNG has lower emission and offers major environmental benefits at regional and global levels.

Microgrid control in the isolated mode is a highly important subject area. In the present paper, a new method is used for controlling isolated microgrids. This method was used based on the classification of the microgrids into two groups, namely fast-dynamic (battery and flywheel) and slow-dynamic (diesel generator, electrolyzer, and fuel cell). For the microgrid components with fast dynamics, a separate controller has been used. Also, another separate controller has been deployed for those components of the microgrid that are characterized by slow dynamics. This method was simulated in MATLAB software. A fractional-order proportional-integral-differential (FOPID) controller optimized by the grey wolf optimizer (GWO) algorithm was used as the proposed controller in the new control strategy. The proposed method was compared with the FOPID controller that has been optimized by particle swarm optimization (PSO) algorithm and genetic algorithm (GA). Besides, it was compared with the common Proportional-Integral-Differential (PID) controller, the coefficients of which have been obtained using the Ziegler-Nichols method, and proportional-integral (PI) controller, the coefficients of which have been obtained using the neural network (NN) method. The obtained results indicated the improved response speed, improved transient-state performance, and an improved steady-state performance of the proposed method compared with those mentioned.

A parabolic dish solar collector system is one of the main types of concentrated solar power systems that are based on point focusing and is more beneficial than the other kinds of concentrated solar power systems. Most of the literature concerning concentrated solar power systems focused on thermal losses and their relationship to the receivers with different geometries. A few former researches have investigated the impacts of the real solar flux distribution on the receiverschr('39') absorber surface in parabolic dish solar collector systems. The inaccuracy level appertaining to the isothermal assumption is more than that of a receiver’s walls with constant heat flux, simply due to heat transfer fluid running through the receiver. On the other hand, the constant heat flux approach cannot be so accurate due to the non-uniform distribution of solar heat flux at receiverchr('39')s internal walls. The current paper investigates the usage of a two-phase nanofluid in a baffled parabolic dish solar collector under a non-uniform distribution of solar heat flux. The geometrical parameters of the collector are analyzed in this work; for this purpose, the SIMPLEC algorithm and Finite Volume Method are employed. The heat transfer fluid is based on water/Al2O3 two-phase nanofluid. The most expected average Nusselt number is achieved at Re = 15,000 in June. In the next section, the effects of different Reynolds numbers and months on the predicted average Nusselt numbers will be investigated in detail. Finally, the PDSC with Z = 70 mm and F = 600 mm filled with nanofluid at  = 4% and dnp = 20 nm is introduced as the most efficient model in the present investigation.

The main aim of the present article is to produce a smaller and cheaper heat exchanger with similar performance. The second goal of this investigation is to study the effects of using oil-based nano-fluids in a refinery heat exchanger. The third objective of this paper is to compare the results which are obtained from the singe- and multi-phase approaches. To fulfill this demand, ANSYS-Fluent and Aspen-HYSYS softwares are employed. Also, MgO-SAE10 nanofluid is studied in this paper using two-phase approaches. The THPEC, Thermal-Hydraulic Performance Evaluation Criteria, and specific heat flux, q", have major roles in this paper. In the second step, the authors try to achieve an efficient model which has not only the THPEC > 1 but also the maximum value of q". According to obtained results, the usage of nanofluid and turbulators can enhance thermal-hydraulic performances of the heat exchanger significantly. Furthermore, it is concluded that by employing nanofluid and turbulators, the cost of manufacturing refinery heat exchangers are sharply reduced. A heat exchanger filled with MgO-SAE10 nanofluid and equipped with SOL-shaped turbulators with =0.5mm, =5.8mm and =5.8mm is suggested as the best configuration, which can improve the thermal characteristics of heat exchanger about 62% in this work.