فصلنامه مهندسی و مدیریت انرژی
سال دهم شماره 1 (پیاپی 35، بهار 1399)

The basis of the photovoltaic systems is the conversion of solar energy into electrical energy. Therefore, the maximum efficiency of photovoltaic systems is achieved by placing the system at a vertical angle to the sun. To achieve the maximum power and efficiency of the photovoltaic cell, tracking the position of the sun with high precision is important. A new linear-rotational dual axis sun tracker is designed and built to be robust against environmental impacts and to minimize the energy consumption of motors. Meanwhile, controller parameters have been optimized with Imperialism Competitive Algorithm (ICA) in order to track faster and more energy saving. Optimizing control system parameters for two cases--one axis and two axes-- has optimzed power production so much so that in addition to reducing power and time, the energy consumption of motors is also reduced. Meanwhile, in order to demonstrate the efficiency and performance of the system, a comparison was made between the tracking the speed and energy consumption of motors with Genetic Algorithms (GA), Artificial Bee Colony (ABC), Chaotic Particle Swarm Optimization algorithm (CPSO) and Imperialism Competitive Algorithm (ICA). The results indicate that the ICA has a better performance than other algorithms.

In this paper, a novel sensorless commutation method for BLDC motors is presented to eliminate simultaneously phase shifter and low-pass filter. An analytical model of the motor is presented, and the ripples resulted from the current commutation are investigated in details. By detecting the zero crossing points of the unfiltered voltages of the motor terminals with regard to the ground and to the DC link, the commutation signals can be generated using a set of proposed logical equations. The extracted commutation points are phase delay-free, because the low-pass filters have been eliminated. Therefore, the proposed method can be used in a wide range of speeds. Moreover, the method is cost-effective because it does not need any phase shifters. Simulation and real-time implementation results show the effectiveness of the proposed method.

Evaporative coolers, as one of the least efficient and commonly used electrical power consumers, are used in different areas in Iran. Recent government agencies have focused on the improvement of this consumer by modifying motor designs or the replacement of the single-phase induction motors with higher-efficiency motors, such as brushless motors. The control method of brushless motor, used in this application, is often based on the speed control which is constant (for example, two speeds high and low). However, laboratory tests show that due to special characteristics of the cooler’s fan, the amount of air flow rate is not related to the fan speed alone. Commercial evaporative coolers are designed for a certain length of the channel that is able to deliver its nominal flow. Increasing the length of channel by the owner can reduce the airflow rate and practically, despite the paid cost, no good airflow rate can be achieved. To remedy this problem, a new approach is proposed in this paper to stabilize airflow rate. For this purpose, the motor, instead of using the constant speed control approach, is controlled in a constant power approach. The details of the requirement’s design, the application of brushless motor in the evaporative cooler, as well as the results of the test of a 0.5 hp (horse power) brushless motor using the dynamometer are presented.  The results are compared with the results of a typical single-phase induction motor test. Afterwards, a 5000 m3/h evaporative cooler, equipped with brushless motor, is tested in the reference laboratory under airflow test. The test is carried out both in a constant-speed and in constant-power control approaches. The achieved results indicate the absolute superiority of brushless motor over single-phase induction motors;also the constant power control method has a better performance in comparison with a constant speed method.

Population growth and industrial developments lead to an increase in the consumption of fossil fuels as well as air pollution. Since the road transportion is one of the major sources of air pollution, it is necessary to replace diesel fuel with liquified natural gas (LNG). Generally, liquefied natural gas has been transported to the LNG stations using special carriers and is consumed there. In this study, the feasibility of constructing a liquified natural gas unit feeding from the Iranian gas trunk lines was investigated. A modified version of a single mixed refrigerant (SMR) process was chosen for LNG production, and its simulation was done in Aspen HYSYS V8.6. In this simulation, Temperture, pressure, and composition of the produced gas in the South Pars gas Refineries, as well as the standard composition, were used. By comparing the performance of the proposed process with the conventional process, the feasibility of production of LNG from the feeding of gas trunk lines was approved. Simulation results show that it is possible to produce 62.1 to 62.5 tonnes LNG per hour by the consumption of energy in range of 156 to 162 MW, respectively. In these operating conditions, 89.3% of gas feed could be converted to LNG. Moreover, the energy of 310 to 350 kW per tonnes of produced LNG is required in the liquification units. The proposed LNG unit is better to be constructed in the vicinity of the gas trunk lines and close to large cities. By this way, the required fuel for heavy diesel vehicles will be supplied simply.

: The steel industry is energy intensive and water intensive at the same time. The largest Iran’s steel-making plants are mainly placed in the hot climates and arid regions; thus, the study of the integrated water-and-energy systems for this industry is very important. In this paper, the developed watergy concept is presented, and, then, WERS (WatErgy Reference System) for steel industrys is drawn. The research investigates the water-energy nexus in different units of a steel-making plant as the conceptual model for the analysis of the water-energy nexus. Furthermore, the mathematical WatErgy system Model of the Steel industry (WEMS-1) is developed based on the Energy System Model (ESM). The optimal configuration of the system’s technologies is assessed based on the Pareto optimal function and with the objective function of the minimum total cost. For model validation, the results of the model, was presented for BAU scenario in Esfahan Mobarakeh Steel Company (MSC) and compared with the data of Iran steel comprehensive plan. Then, WEMS-1 is run to analyze the optimal technology assessment of the MSC case study concerning water scarcity and the rise of electricity price. As a result, it is shown that the water consumption index decreases from 6.78 m3/ton steel in BAU to unconventional water consumption of 5.5 m3/ton steel in the optimal scenario; this improvement is achieved by technology revolution and a small increase in electricity demand.

In this paper the performance of Ice Thermal Energy Storage (ITES) systems has been modeled for an official building. In the present study, the ice storage tank is considered to be charged for 8-16 hours out of peak- time, and the tank content is supposed to be consumed during peak consumption time. In this paper, the internal Ice-On-Coil technology has been investigated. A four-floor official building of about 3106 m2 area is considered. The effects of different climates in various cities of Iran on energy consumption for charging and discharging storage tanks are considered. A comprehensive comparison between power consumption chiller without ITES system and power consumption chiller with ITES system in various coefficient of performance (COP) of chiller has been studied. It has been found from the obtained results that Bandar Abbas, among the considered cities, has higher energy consumption during peak hours of National Power Grid (NPG), so ITES system has a greater impact on the NPG peak saving in tropical regions. At the same time, COP Chillers with and without ITES systems, by using ITES system, had a reduction of about 26 percent in electricity consumption per day.

City gate stations are installed at gas network entries to decrease pressure along gas transmission pipelines from 1000 psi to roughly 250 psi. Since Joul-Thomson constant of natural gas is positive, the aforementioned decrease in pressure also results in a decrease in the temperature, making the existing water vapor in the gas to condense or even to freeze during cold seasons. Hence, indirect heaters are employed to somewhat raise the gas temperature to eliminate the possibility of freezing. A major portion of the resulting heat from gas combustion is transferred to the environment through a smokestack. In the present study, the purpose is recovering this lost energy by modeling the smokestack and calculating the parameters of its passing smoke parameters. To this end, a thermoelectric generator was designed for installation on the smokestack in these stations. According to the findings, more than 400 kW of electrical power may be generated using 90 high-efficiency modules of type TEG1-241-1.4-1.2 installed on a smokestack of 3 spaces.

The power supply, as the main supplier of electrical energy, is used in many electronic devices and circuits. This research has experimentally investigated the thermal management of a computer power supply which uses phase change materials to increase the lifetime, to improve the performance, and to reduce energy consumption. Two heat sinks have been designed and fabricated in two types of plate-fin and pin-fin. The experiments were carried out in the thermal fluxes range of 2.1 – 4.8  and in the constant volume fraction of the phase change material. The results show that the maximum reduction in steady temperature is 10.4  and 8.6 , in the pin-fin and plate-fin heat sink respectively,. Also, the results indicate a better performance of the plate-fin heat sink in comparison with the pin-fin in the process of reducing temperature and cost.

This study focuses on the flow analysis of alumina nanofluid with volumetric ratios of 2% and 4% into non-porous and porous thermal coils under solar heat flux.. Furthermore, the comprehensive study of the nature of boundary layers, the pressure and velocity distributions, and the thermal effects inside the metal porous coil are discussed. To solve the problem, the equations of continuity, momentum, and energy for nanofluid into non-porous and porous coils are used. The comparison between results of average Nusselt number at the present model and experimental data for a non-porous coil shows an acceptable agreement with maximum error of 10.5%. In porous coil, increasing the volumetric ratio of nanofluid has resulted in an increase in the pressure losses where these largest values occurred at 4% volumetric ratio with a value of 4.4 bar. By increasing the volumetric ratio, the amount of convection heat transfer coefficient and Nusselt number are raised and, consequently, the transferred heat into the porous thermal coil will increase.

The aim of this study is to investigate the performance of a gas turbine cycle equipped with a Stirling engine from the thermodynamic point of view. In this system, a part of the heat loss from the gas turbine is transmitted to a Stirling engine to generate more power. In the analysis of the proposed system, the governing equations of the hybrid cycles are modeled in MATLAB software and Schmidt, and ideal adiabatic models are used to solve the Stirling engine. In the analysis of the hybrid cycle, the compressor pressure ratio and turbine inlet temperature are considered as two Important and effective parameters. The results show that reducing the compressor pressure ratio and increasing the turbine inlet temperature improve the performance of the Stirling engine. The results indicate that the use of the hybrid gas turbine cycle and the Stirling engine will increase the power of the gas turbine from 268 kW to 468/6 kW, based on the Schmidt model, and 457/3 kW, based on the ideal adiabatic model. Also, the electrical efficiency of the system increases by 18/1%, based on the Schmidt model, and about 17/1%, based on the ideal adiabatic model.